108in Howard DGA-6 Mister Mulligan guide

Introduction

I get calls for servos regarding the old Bud Nosen model of the Howard DGA-6, aka Mister Mulligan phrased something along the lines of, ‘What have you got for servos?’, or words to that effect.

And of course, it’s quite open ended, because folks are actually wanting to know more than what’s available servo-wise, they want my opinion regarding ‘which’ specific servos would be best for them. Thing is, this can be surprisingly tricky to figure out. Why?

Honestly? Because I need more information. For example, like are they refurbishing an existing model, or building from a kit? And importantly, how do they intend to power it? This last is information I need to know because it affects the AUW weight and thus, the speed at which the model will be flown (the heavier, the faster it lands before stalling, the more horsepower, the faster it flies, for which the corollary is it’ll require more servo torque to maneuver).

So I ask about these things right off the bat – and not to put my nose up your butt regarding things that are none of my business, but because I need the information to help select which servos are right for you.

All that glitters isn’t gold

With regard to how they’ve acquired the model, it varies. Sometimes they’ve bought a model at an estate sale, or got it at a swap meet. This usually means it’s ‘experienced’ and has servos they don’t trust and/or they want to update existing servos from analog to digital.

Sometimes they plan to refurbish the model, covering and all. Believe it or not, this also matters to me when it comes to sharing advice because it’ll affect weight (weight is always a concern).

Sometimes they’ve bought a kit off a friend, or via Flying Giants. Added to which, because there are kit cutting services, some have bought kits that are literally brand spankin’ new.

But mostly they’re original kits. In this photo I swiped off the Internet, a Revell plastic model stashed within is actually quite nice. This, because when it comes to detailing the model, since the engineers at these companies go to a ‘lot’ of trouble to document surface features before committing to the expense of the molds it saves you a lot of work documenting the actual aircraft. Nice find!

And allow me to note, from personal experience, the wood in original kits is typical Bud Nosen quality. Saying it’s going to have a very, very nice selection of balsa and aircraft plywood.

This because Mr. Nosen was first, and foremost, a modeler and only second was he a businessman. He put the kit quality first above all. However this won’t be true of every model you may come across. Let me explain, in brief.

There once was an outfit cutting models of Mr. Nosen’s designs called A&A Industries. Anyway, I’m not privy to the how and why, but it doesn’t matter because they’re long gone from the market. Problem is, their kits are sometimes popping up on various marketplaces, and sellers may or may not know the product could be shit for quality. Shit?

Yes, and this is the reason I bring it up. You see, these guys thought replicating a kit was easy. It’s not. So they were cutting corners by using a less than stellar selection of balsa (often hard and heavy). And as regards the lite ply? They either didn’t know themselves (generous interpretation), or possibly, simply figured most modelers were too stupid to realize they’d substituted laun (an Asian wood) for the good stuff which is made of poplar, instead. But it gets worse.

How? Well, instead of replacing die blades with sufficient frequency, they let them get dull to stretch the run of kits. The predictable results were sometimes you’d be all excited to get started, only to open the box and unroll the plans and then, while examining the wood, discovered you’d been snookered.

Learning your kit has die crunched versus cleanly cut ribs and formers sucks. Has happened to me so I know from experience. So maybe the kit gets built, anyway, but I suspect maybe sometimes someone just said quietly, ‘Bummer!’, and sadly closed the box and stashed it for another time. This perhaps being the very model, which is only now being offered for sale.

The upshot? If you come across a ‘deal’ for a kit on eBay, ask about the provenance, e.g. a photo of the box itself. This, as proof the product you’re bidding on is a genuine Bud Nosen Models product because now you know, all that glitters isn’t gold . . . heads up!

In the alternative, some customers will occasionally tell me they’ve printed off a set of plans they’ve downloaded free off the Internet (or copied a set from a friend). I’ll share a link in a moment.

Major point being, they did this with the intent of cutting their own parts (in effect, making their own kit from which to build). But ultimately, the how doesn’t matter because they’re all asking the same thing . . . what do I need in the way of servos?

Built to 1/4-scale, this model has a 9 foot wingspan (108in), so it’s a fairly large aircraft. Problem comes in with how lightly it may be built, meaning there are certain considerations to be made when fitting engines that didn’t even ‘exist’ when Mr. Nosen first put pencil to paper.

And note; models that have been flying ‘may’, before acquisition, have had such modifications incorporated, but not always. So please don’t take offense at the questions (I ask if they seem impertinent), but I need then in order to respond.

Saying it’s all important information, but more about this, later.

Full scale

So if the Mister Mulligan moniker rings a bell, it’s probably because it’s quite a famous aircraft due to its roots in Bendix air racing in the 1930s, meaning it’s entered into the lore of aviation. And not just for the original aircraft because that example has actually been replicated -several times, and once from a crashed aircraft!

Point being a tribute aircraft may be seen at airshows to this day!

So I also found this next photo of the original aircraft online, source unknown so I can’t make proper attribution. Hope I don’t get sued!

Handsome aircraft, isn’t it? But look how dirty it is due to oil and exhaust streaks down the sides! Major point being, if you build this model, while pristine-white is good, so is dirty-white, in my opinion.

FYI, this source of information is Wikipedia, which states in part . . .

The Howard DGA-6 was a pioneer racing plane, nicknamed “Mister Mulligan”. It was the only airplane ever designed for the specific purpose of winning the Bendix Trophy. The plane was designed and developed by Ben Howard and Gordon Israel, who later became an engineer for the Grumman Aircraft Engineering Corporation. Mister Mulligan was designed to fly the entire length of the race nonstop and at high altitude. Neither had ever been done before. Mister Mulligan won the trophy, and thus changed the way in which long distance airplanes were designed.

. . . and while Wikipedia isn’t a charity, they’re on my yearly ‘give’ list in support of their efforts. Maybe consider a small gift as well, and toward that aim, this link goes to their donate page.

Another nice source is the Fiddlers Green Paper Models website with their fine article about the aircraft. Don’t let the fact they’re into paper models fool you, this is a seriously well researched article.

Saying if you’re interested in building the Mister Mulligan, there are many diverse sources of information . . . of which, now our own article has joined the ranks to become a source, so look around!

Switching gears

Considering the Mister Mulligan kit was initially offered to the world by Mr. Nosen in 1977 and has been out of production +30 years, that I hear from folks so often is rather amazing on its face, but here we are. These are the basic specs.

The use of the descriptive term 1/4 size, which I find funny because Mr. Nosen preceded the very term quarter scale! Like the gentleman was waaaay ahead of his time.

Bud Nosen Models these days

And by the way, Bud Nosen Models remain in business, but now only offering wood, no kits. So they are that rare avis, a business that survives the founder’s death and progresses to become a success on the backs of the 2nd generation. Saying they’re still operating as a family run business. One at which I spend money occasionally, so yes, take this as my personal referral and recommendation. The hallmark of the kits, the good quality wood, is still what they’re about.

Meanwhile, the most recent query regarding the appropriate servos, as it always does, brought forth a flood of memories. This, because I’ve built and flown the Nosen Mister Mulligan. Saying me and Bud Nosen Models are no strangers.

Anyway, while I usually I whip off a quick answer to these Nosen Mister Mulligan queries (as I’m forced to due to the press of time in running ProModeler), this most recent one got me to actually put my thoughts down on paper. Why?

In part, it’s because we’re plumping out the caseSTUDY section of the site. This, in an attempt to help folks get quicker answers (versus waiting on me to respond via email). But also in part because I get asked often enough about this particular model to warrant a fuller treatment. And finally, also in part because of what this guy said in terms of his being a beginner when it came to building larger models.

And it’s in this regard, for which I have a few thoughts to share that forced me to put this information together into a concise whole. Thoughts I don’t always share with my more experienced giant scale-builders who already know much of this stuff.

End results are this article, which I hope you’ll find worth your while. And with regard to the fellow’s actual question, the one which got the ball rolling, it went like this . . .

I’m building Bud Nosen’s Mr. Mulligan and this is my first 1/4 scale build. Your servos come highly recommended and I’d like to know what output servos you recommend. I’ll run single servos for rudder and elevators, duals for ailerons and flaps.

To my answer . . . it’s somewhat convoluted. This, because it depends in part on what the modeler wants to use engine-wise. Also, on whether you’ll be reinforcing the airframe (thus adding weight, and which is – as a practical matter – required, in my opinion).

Fiberglass Specialties

Added to which, will the builder use the stock ABS cowl, or opt for fiberglass replacement. I would – reach out to Fiberglass Specialties.

They offer, from left to right BN-3 which is 11-7/8in diameter and BN-3SR, which is the same diameter but extended by 2in from 6-1/8in to 8-1/8in long. Both have the 18 blisters for the 9-cylinder radial engine.

Speaking of which, this is a composite photo I put together of the three photos they sent me. It shows (on the right) a BN-3SR fitted with their 8-1/2 dummy radial of a 9-cylinder.

Plus how does he plan to cover it, e.g. film, or fabric and paint? Since the latter covering weighs more than film, then this brings us back to discussing weight – once again. Especially if the builder has in mind to add a lot of scale detail because, yup, details means yet more added weight!

But to the greatest degree, my recommendation hinges on which engine it to be used ‘and’ how the owner plans to fly it. This because the engine affects two things; the model’s AUW (all up weight), and its performance. Both necessarily means its flight characteristics, so it affects the servos I’ll advise you using.

So are you sensing a pattern with my focus on weight? There’s a world of difference in flying it with an OS or Saito 120 4-stroke, which isn’t horribly heavier than the engine for which it was originally designed (and which would fly it remarkably well in my opinion if built per the original drawings) versus using a compact gasser like a DLE35. This engine is too heavy for the original design in my estimation and thus, will likely overstress this lightly built model sans judicious reinforcement. I know because I once flew mine with a Quadra 35.

Added to which, the market has created many superb engine choices that were nothing but a pipe dream back in the mid-70s. Back then, we knew small radials engines like my Morton M5 existed but they were rare as hens teeth and stupidly expensive (and these old engines today are even more valuable for collectors these days).

Point being, while some tend to think of small radials as a new development, nothing could be further from the truth. Instead, what they are is relatively common (at least in comparison to back in the day). This, because modern day CNC machining has democratized their pricing and thus, made them readily available to ‘we the people’.

So because I know this, I ask about engines because a customer equipping his Mister Mulligan and selecting a radial engine like the gorgeous OS MAX Sirus 5-cylinder engine (burning nitro fuel), or a lovely Saito FG-60R3, a gorgeous 3-cylinder radial burning gasoline, will be adding significant heft to the model. I need to know this before trying to guide this customer to the best servos for him.

We’re all different so there’s no one size fits all, solution!

So as it turns out, small radials can be made to fit, but like the DLE35, because the model was designed for a 2-stroke .61 on glow fuel (nitro), then because it’s so very lightly built, these engines will all soon prove to be too much mass for the airframe. Point being, it’ll need reinforcing, or put another way . . . yet more added weight!

Note; I’m aware it’s your model, so the adage, ‘Not my circus, not my monkey!’ applies, but I’ve good reasons to bring all this up, trust me.

Background

To begin, my bona fides . . . I built one of these back in the day (ca. 1980, or so). And I followed the instructions exactly. Back then, a few sheets of typed instructions were considered plenty good enough.

My recollection was the wood was excellent. And believe it, or not, the instructions were very well thought out. However, there were no photos or drawings beyond the plans themselves.

Somehow, despite the paucity of information, it came together nicely.

And I will note the 14.5lb flying weight listed on the kit box is fairly accurate for the times. I know because when powered with a two-stroke .61 on glow fuel, equipped with a 12oz fuel tank, and using four servos (mine didn’t have flaps), plus a 500mAh 4-cell NiCd, this was really close to reality.

I recall mine came in at a touch over 15lbs. Maybe 15-1/4lbs and almost to a certainty not as much as 15-1/2lbs (but time fades the memory). As for why it was a touch heavier than Mr. Nosen suggested, this – in my opinion – is because I covered it in silk and dope (and because I painted it in white Aerogloss cellulose dope, which to get good opaque coverage required a lot of coats).

This, versus using white Monokote, which was just making a strong push into the marketplace back then. Maybe you don’t know what silk and dope is; no shame in that because the only thing we’re born knowing how to do it poop and cry. Fact is, we even have to be taught to latch onto the nipple!

Point being, review this brief article to learn more if you’re curious:

• Silk and dope – demystifying modeling’s classic finish!

Propulsion

So I’m dating myself with this, but I initially fitted it with a K&B .61 and 13×6 prop. Flew well? No, not really. It was a tad too much prop and basically struggled into the air but a 12×6 was even less effective.

Why if it’s the recommended engine? Maybe because the prop tips only stuck out beyond the cowl (11-3/4in diameter) by about 1-1/4in but I honestly don’t know as he claimed it worked. And FYI, back then a .61 was about as large an engine as was commonly available (other than Duke Fox’s .78 or an exotic for the time, OS MAX .80).

So with the K&B .61 fitted, the model struggled and barely lifted off into ground effect and because in my judgement there was insufficient airspeed (meaning I was afraid to try turning to gain altitude), discretion won out over valor and I chopped the throttle and she settled back in. It never flew any further than the Wright brothers at Kitty Hawk on their first attempt.

Flight? Yes, but not exactly successful. So traumatized by the effort, I pulled the plug and next, I tried a Du-Bro belt-reduction drive. Speaking of which, I’ve not sold it but neither can I find it . . . it’s here ‘somewhere’, I’m certain. Just where? That’s another story!

Anyway, in the meantime, I also swiped this photo off the internet.

This Rube Goldberg-esque contraption used my K&B .61 engine and added weight to the propulsion system in the form of the alloy mount, supporting frame for the shaft and bearing, plus pulleys and the belt drive. More stuff than you’d think but in exchange I got far more torque.

So the engine still screams away at the same 11k rpm as before, but because it’s multiplying the engine torque it swings a larger diameter prop. And FYI, just like the transmission section within a servo, the deal with gear boxes (or belt-reduction drives) is you swap engine-RPM for prop-RPM to let a puny .61 engine swing a considerably larger 16x8in prop, which it otherwise couldn’t. So this, resulted in maybe 5500rpm at the prop (don’t really recall). However, it definitely delivered a mighty whoosh of moving air!

And I remember being so excited after testing it I couldn’t fall asleep!

Anyway, with this setup the model actually flew. Sort of. More like it lumbered into the sky. And when I went to turn, it just sort of rolled so I had to use a fair bit of rudder, also, to bring it around. I quickly got used to it and while I never felt unsafe turning after takeoff due to inadequate airspeed, I definitely found it rather challenging to fly at first.

So after about 10 minutes of just circuits and getting used to it, I set up to land. And no, I never tried to intentionally roll it on that first flight, and the one time I tried to build enough airspeed to loop it by diving, it fell out at the top of the loop and entered a spin. Startled me but it recovered easily so level flight was the order of the day for the rest of the flight.

The basic issue was insufficient pitch speed. But a prop with larger diameter or more pitch wasn’t readily available. Moreover, looking back from a basis of greater experience, I rather doubt the K&B had the stones to turn a larger diameter or higher pitch prop, anyway.

So on that first flight, I don’t recall needing any trim at all and after many circuits, the turn from downwind to base, and then to final approach was uneventful. The aircraft flared beautifully and the touchdown was perfectly smooth.

Look, I’m a decent stick but even by my standards, that was a greaser of a landing. And the roll out was absolutely perfect! And as I taxied the model back, the guys actually applauded my effort.

An hour later, I did it again! And again, and again for months! But it was something of a love hate relationship. Loved the looks, size, and presence of the Mister Mulligan, absolutely hated it being so badly underpowered as it was.

As an aside, OS MAX subsequently produced a geared engine, the C2 (2:1) and available with various other rations (C3 was 3:1 and C4 was 4:1 reduction).

Anyway, maybe six months of this go by with me flying the Mister Mulligan. Basically, I’m delighted but not happy. I experienced a few mishaps (once crunched the tail going through a doorway, learned to always walk it through tail first), but overall, nothing really bad crash-wise.

Nevertheless, the weight inexorably crept up a little with each repair. By now well used to it, the model overall handled nice but flying an aircraft down on power is no fun. Meanwhile, I’d been reading about gasoline engine conversions in RCM (Radio Control Modeler) magazine and am determined to try my hand at it.

So with the aim of making my own, I’d secured a weed whacker, from which I was intent on harvesting the engine. I felt sure with this power source, I would finally be able to fly the model with more authority. Since it was slow going, this meant sooner or later.

Turned out to be later because after installing it, I never could get it to run. I just wasn’t getting enough RPMs on the follow through after flipping the prop as smartly as I could. So, yes, as I still do today, I was trying to hand start the engine.

Thing is, for the magneto to generate enough spark to actually fire, you need a good turn RPM-wise. Obviously, I wasn’t getting it (or at least this is what I suspect looking back with a lot of subsequent engine experience). And FYI, back then, electric starters hefty enough to do the job didn’t yet exist.

Anyway, next I threw money at the problem. I bought and turned my hand to retrofitting the model with a Quadra 35. This propulsion unit was by a Canadian guy who modified a small industrial engine for model airplane use with a cast mount, a prop driver, and a bell-crank linkage to get a better shot at the carburetor. Fellow’s name was Darryl Briseglia and his little engine turned an 18×8 prop with genuine authority.

The engine was all the rage in RCM and became my first store-bought gas powered engine – many have followed. And as I said, my previous ‘gasser’ experience was limited to fooling around with the aforementioned, but ultimately unsuccessful, converted string trimmer engine.

So this is the famous Quadra. Nope, won’t win any beauty contests!

So before the Quadra 35, I’d rate my gasser success as = 0. With it, I immediately experienced success. So did many, many others. I think it’s fair to say Mr. Briseglia launched the entire gas-powered era!

Only fly in the ointment was now my model’s AUW was almost 20lbs (dry), a considerable increase – 33% – from when it first flew at 15lbs (also dry). And yes, some of the added weight came from repairs. And some from post construction reinforcements (e.g. I doubled the thickness of the firewall to add the Quadra). But mostly it came from the Quadra, itself, which is a porker by pretty much ‘any’ definition.

But it worked and at last, the model flew with decent authority. It could even be looped following a modest dive! Then I went too far. That’s right, I fell victim to the hoary old adage; there’s no such thing as too much horsepower, that’s what the throttle is for!

So this is absolutely true . . . up to a point. This, because it also presupposes you have more discipline than your scribe possessed at that time of his life – sigh. So what happened is I glommed onto a Kawasaki 3.15 engine (52cc).

Bigger is better, right? Maybe. At 8-1/2lbs this engine ultimately proved to be too much for the Mister Mulligan airframe. So there I was, flying along fat, dumb, and happy with that heavy monster of an engine roaring away swinging a 20x8in prop. So I’ve got the model rounding imaginary pylons – think Walter Mitty, with me as the modern day incarnation of Roscoe Turner sans Gilmore the lion (click the link, Wikipedia really is your friend).

So I’d flown maybe half a dozen ‘laps’ (we used the vertical extension of the fence line to approximate where pylons would be, they weren’t real) and the way we flew our ‘course’ was turn 1 was represented by a single pylon and then turns 2-3 were two pylons with a short leg.

So the straightaways were maybe 250yds long and around all three for a lap took about a minute plus. I’d quickly settled into a rhythm and after the straightaway, as the model approached turn 1, a quarter roll to put the model on its side I pulled up elevator to come around when I heard a loud crack! Everybody’s head swiveled to see what had happened. Me? I stood helplessly as the engine continue straight about 100 yards downrange (following a lovely ballistic arc).

As for the model? Instantly tail heavy to the tune of +8 pounds of engine and fuel tank (pulled out of the airframe and hanging by the black neoprene line), the model fluttered into a spiral, kind of slowly, resembling nothing so much as a wounded dove downed in a corn field (hunted with my Dad, saw lots of those).

Everything happened like in slow motion, I remember clearly and even swore I could see the motor and fuel tank rotating around each like Earth and Moon but tethered by the fuel line. Like I’m absolutely certain I saw the fuel level (dark) at the extreme of the tank as it rotated, but admittedly, this could be a flight of fancy because nobody else recalled this but me. Of course I was looking at it when it happened, so I remain convinced.

Anyway, the engine, including the firewall, ripped clean off and the mass of the engine proved Newton was onto something with his observation regarding Inertia. So the engine and fuel tank went tumbling off in one direction whilst the model immediately pitched nose up, stalled, and entered a fluttering spiral as the violence of the stall broke the spar outboard of the fuselage and one wing panel flapped upwards. All in all, it wasn’t a pretty sight.

And as a reminder, the 1st Law of Motion states . . .

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

Surprisingly, the engine was totally unhurt because it had rained recently and the ground was soft but the oft repaired and rather plucky Mister Mulligan, had met its untimely fate. This, because as it spiraled, it built up enough momentum that the sudden stop of impact with terra firma crushed the lightly built fuselage structure.

I heard it crunch in the silence, a crunch held together by the covering because silk envelops busted balsa together at least as well as Monokote! Anyway, once I salvaged what I could, (not much, stabs, engine, fuel tank, receiver, servos, battery, switches, tail and main wheels, pushrods, hinges), straight into the burn barrel it went. A few squirts of fuel later, plus a lit match, and as it went poof it became the latest sacrifice to the great god of RC-modelers, Glitch.

Me? We live and learn, don’t we? And if I were to ever build another, I’ll reinforce the crap out of it. Especially if I planned to use stupid amounts of horsepower. Word to the wise.

Anyway, as fate would have it, when one door closes, another opens. For me this meant I bought another Nosen kit. This, his similar vintage 102in wingspan P-51 Mustang.

This aircraft was far better suited to the powerful Kawasaki engine but that’s a story for another day. However, if you can’t wait and have a hankering to try your hand at that one, Outerzone also has the Nosen P-51 Mustang plans available!

And once again, free! Note, since the full scale P-51D spans 37ft, or 444in, then the 102in model scales at 4.35:1, or slightly smaller than 1/4-scale but not as small as 1/5th, but I digress.

So next, let’s circle back around to some engine alternatives.

Engine Selection

These days, if you have a Zenoah G38 in a drawer, or maybe a G45, then with suitable reinforcement, you’d have a great flying model on your hands at 20lbs. A 35cc Quadra 35 or US Engines 41cc will work great, also but the power of the 50cc engine spoiled me.

Single-cylinder gassers

And if you have a DLE35, instead, you’d get good power and easier starting at about the same mass as the Quadra 35. This, because the ignition module and battery pack add weight back to the engine thus roughly equaling the built-in magneto of the old school engines (proving TANSTAAFL remains in effect).

I mention this because I still have a Zenoah G45, as do many modelers. Mine is installed in a 107″ Cessna C-195 Businessliner, a model of their post-war monoplane precursor to the more modern 210. And yes, it’s equipped with the convenient spring start accessory to aid starting. Interestingly, due to the similarly low amount of dihedral, it too requires a butt load of rudder to turn nicely.

So the spring start mechanism is handy because just like the home brew 25cc engine at which I failed to start, unless you get a good bit of RPM moving past the magneto it won’t fire. And even the Quadra lineup got these innovations. Basically, the spring makes it easy; just wind backward about 3/4 turn and let go. Almost like a Cox .049 engine from when we were kids.

Anyway, were you to use the powerful DA60 or DLE55, then you’ll have a racer on your hands. I’m talking about yee-haw horsepower much like I had with my model using the Kawasaki engine! However, unquestionably, with one of these bolted to the firewall your model will need substantial reinforcements versus the as-designed aircraft (or I predict it’ll meet the same fate as mine).

Remember, Mr. Nosen designed this model aircraft ‘before’ gassers were a thing. So where a K&B 61 goes maybe 12oz, a Quadra 35 goes 64oz and a touch more if you opt for a smoke muffler.

Radial gassers

So let’s say you have a hankering for one of those lovely Saito 3-cylinder 60cc radial gasser engines? Might fit. I’d be tempted. Sound good, also. Superb quality.

However, unquestionably, my first choice if I were doing the Mister Mulligan once again would be the lovely 9-cylinder UMS 9-115 radial. Me? I’m thinking at 10-1/4in diameter it would slip perfectly beneath the 11-7/8in Fiberglass Specialties cowl.

Expensive? Yes. But what are you gonna do, take it with you?

Reinforcements

Thing is, engines like these mean making fuselage reinforcements. So let’s touch on some of these, next because I found several excellent ideas on various forums. Some on the RC Canada and others on RC Universe, both excellent sources of modeling camaraderie and ideas.

RC Canada forum

Point being, when I came across a build thread where a fellow made some intelligent fuselage reinforcements, I swiped some of the photos for inspiration.

Like this one where he made two crutches of plywood to tie together the firewall and several formers.

And where this really works nicely is he incorporate the landing gear legs as well. Simple, light, well engineered.

I’m impressed and believe had I had the smarts to do similar, my model wouldn’t have self destructed in the air.

And with these two photos I’m going to stop – despite – there being many, many more on the RC Canada website. This, because I am ‘not’ intent on replicating the entire thread.

Instead, I’ve swiped a few photos with the purpose of encouraging you to join the RC Canada forum! I found it collegial and pleasant as the engagement was Canadian-nice.

Feel free to click this image because it’s a link to their site.

Note; unfortunately, this particular build thread ended before he covered and finished the model. No clue why – but – it doesn’t really matter because what the fellow ‘did’ show was plenty good enough to get you started with regards to intelligently reinforcing the model, believe me.

This, because he delved into reinforcements aft to reinforce the aft fuselage in the area of the stab. Ditto the forward fuselage as he focused on tying together the firewall, several formers, and the landing gear struts. This, plainly, to allow the model to accept more powerful engines and survive.

Anyway, trust me, join the RC Canada forum. I did, it’s free, and you’ll meet a bunch of good northern modeling mates.

RC Universe forum

Another set of photos I found online showed genius level model engineering. For example, this guy (Mike Pirkl who goes by maddog on RCU) features sprung landing gear legs and his method was simplicity itself. I’m sharing these next few photos with his kind permission.

Sprung gear – external springs

His design for sprung gear legs centers on Du-Bro 4-40 steel rod ends (no. 205) and the tension is adjustable with the threaded link (externally accessible near the wheels).

And this closeup shows what’s going on with enough detail to give free reign to your imagination to implement your own interpretation.

And as an aside, Mike Pirkl mentioned, ‘I bought my Mr. Mulligan as a built model that had been hanging in a shed for about 10 years, I totally stripped and rebuilt broken sections. I also mounted the rudder and elevator servos at the rear of the plane close to the their respective flying surfaces.’

Removable propulsion package

So in this next shot of Mike’s model now sitting on the landing gear, his model sits with the characteristic cocky nose high attitude on the workbench – sans removable power package – ready for covering.

So let’s look more closely at this innovation, a removable propulsion package. Basically, Mike elected to use a smooth running and powerful Zenoah GT-80 twin. The beauty of this engine is in relying on magnetos for ignition, there’s no separate module and battery pack. And while the knock against these engines is they’re heavy, if you re-read that last sentence what’s important to take not of is, by the time you add in the weight of the ignition module and separate battery, the weight for other engines goes up, so it’s macht nichts!

And yes, I know some folks swear by an IBEC where the one avionics battery is also used for ignition, but it’s my opinion you’d be wise to treat the two systems like a player. By this meaning the player doesn’t let his girlfriend know he’s married, and his wife never knows he keeps a mistress on the side. Stays alive, hence why he’s a player!

TANSTAAFL

Added to which, because there ain’t no such thing as a free lunch, and since you need at least a ~2000mAh pack for the ignition (my rule of thumb is 1000mAh per cylinder) plus a another 2500-3000mAh pack for the avionics (due to so many servos), then you’re still going to have to use a 5000-6000mAh pack.

Point being, yes there is a benefit of only servicing one battery instead of two, but in my estimation this convenience is vastly overwhelmed by the systemic risk to the model. By this meaning if even one of the many component within an IBEC goes teats up, then there’s a risk of interference . . . but you’re a big boy, do as you please.

And in any case, the Zenoah GT80 makes the whole argument moot due to relying on a magneto, instead of a module requiring battery power. So circling back to propulsion;

Slide out drawer

In an interesting twist, what Mike’s created is an entire propulsion package mounted in a slide-out drawer. This bit of genius means the thing becomes trivial to service because the entire power package, by just removing four screws, sees the whole thing sliding out and into your hands. Sweet!

So take note; he’s even mounted throttle and choke servos to the tray. In honestly, I advised him to reconsider this last because of experience with what happens to servos mounted in close proximity to hot vibrating propulsion sources. Review this to learn more;

Gasser throttle servo problems & solutions

And Mike, to his credit once advised responded with, ‘Thanks for the heads up, I will look into a new location for it.’

Anyway, once secured with the four bolts, the two become a whole!

Sprung gear – internal springs

Next, I’d like to share another sprung landing gear arrangement. This more sturdy version with internally adjusted springs. And what initially caught my attention was this elegantly engineered sketch by Kelly Fountaine of New Zealand.

The gear design? It’s simplicity itself. Simple is always a good thing.

He’s also the builder of the model in the next few photos and has kindly granted permission to use these photos.

Kelly adds, ‘I powered mine with a Supertigre 3250, 20 x 8 prop which has been more than adequate and I used a bit of rudder mixed with the ailerons as it drags its bum a bit in the turns.’

So not only did he do a superb job of executing the design with a piece of alloy channel and some springs with this being the simple yet at the same time, sophisticated, end result, he adds, ‘That landing gear configuration has worked well and the model survives.’

Factory print

Next, and my final enticement for you to join RCU is this print offered up by Bill Diedrich. I present it at 1024x1329px but within the thread I linked above, it’s available at a much high resolution . . . go get it!

Plans – free

So speaking of free, plans for this design, if you’re unaware, are available online for free. The guys responsible are in England and called Outerzone. They have many, including the Mister Mulligan plans.

Click the above link to download them.

Note; as do all links in these articles, clicking opens a new browser tab so you don’t lose your place whilst reading.

Anyway, I advise you download the plans to a memory stick, hustle over to a Staples, or similar office type place with a large format printer, and a few bucks later you’ll have your own set of plans. Scope out the wood required, make a list, and go to town. The build it not especially difficult.

Or poke around and score a kit from someone’s collection gathering dust. This, because believe it or not, they come up for sale nearly 50 years after being released! And as an alternative, you can also reach out to LDS – Laser Design Service – because they offer a short kit.

On single servo elevators

Meanwhile, one thing the fellow mentioned made me a bit uncomfortable. Basically, he plans to use one servo for the elevator.

Honestly? It’s my opinion, under no circumstances would I depend on a single servo elevator setup for a giant scale model – but – we’re all big boys, his (your) decision, not mine.

Since he’s building a kit instead of taking delivery of an ARF, which merely needs a bit of basic assembly to make ready to fly, then doing a two servo control surface setup for the Mister Mulligan is duck soup to my way of thinking. But again, not my circus, not my monkey, so this is the builder’s decision, not mine.

So while I’m sharing my opinion on the matter (and opinions are like belly buttons because everybody has one), mine is backed up with 50 years of experience and many, many giant scale models under my belt. That, and in this article, I am sometimes speaking to folks new to all this.

Point being, if this information is old hat, skim past it but if it’s new, then my best advice is to dedicate one servo per flying surface with giant scale models. Especially elevator!

Like, just think it through . . .

• If the rudder servo craps out, land using aileron and elevators for steering. Not optimal but perfectly doable.
• If an aileron servo craps out, then the other aileron provides enough control to land the model.
• Similarly if a flap servo craps out, you raise them again and proceed to landing without flaps, bit faster but no biggie.
• If the throttle servo dies, then set up for landing, engage the choke servo or flip the backup kill switch, and glide in for a dead stick landing.
• But if a single elevator servo goes tango uniform? Then unlike having ‘some’ elevator control as you would with two aileron servos, for the vast majority of us . . . things end rather badly.

And sure, you can run your mouth about balancing the use of the flaps and throttle to effect a landing sans elevator control. Whatever, I opine it’s far more likely you’re a crash spectator.

So it’s nothing to do with the fact I stand to benefit of your buying two servos vs one (because I sell servos). Instead, I encourage you to use two elevator servos because . . . . shit happens.

While sharing opinions, the Boy Scouts have it right, be prepared. So up next (finally) are the servos . . . what do I recommend?

A few bits of housekeeping before wrapping this up. Selecting 360oz-in seems like overkill unless you realize 360oz-in is both true and a lie, at the same time. Reason is it depends on the input voltage.

Study this chart, it’s divided by 5 voltages for a reason. And every ProModeler servo discloses these details so you may bring your judgement to bear.

• 1st column corresponds to a 4-cell NiCd or NiMH pack. Old school chemistry, so 1.2V/cell X 4 cells = 4.8V, or a nominally 5V.
• 2nd column corresponds to a 5-cell pack; so 1.2V/cell x 5 = 6V
• 3rd column is a 2S pack with 3.3V cells, so 3.3V/cell X 2 = 6.6V
• 4th column is again a 2S pack, but LiIon at 3.7V/cell X 2 = 7.4V
• 5th column is synthetic sources, BECs relying on FETs (fast switches to make the juice). Usually these max out at 8.4V. Added to which, a 2S LiPo coming off charge will see 8.4V, also.

What’s important about columns 1-4 is these are nominal voltages. What this means is when you see this value with the voltmeter, then stop flying and put the pack on charge.

For example, the A123 pack (3rd column) will be around 7.15V coming off charge and drift down as you use it until you get the 6.6V when it’s time to recharge.

So the very first thing to decide when equipping your model with servos is . . . what chemistry do you plan to use? Unless you’re flying 3D and want everything a servo can give, then because they’re easier to live with, we guide our scale customers to A123 type battery packs. These are the middle column voltage-wise.

Learn more with this brief article:

• On the batteries John prefers using

Packs and switches

While we offer battery packs, so do others. What recommends our is we have them built with more than a single lead. So we offer them with dual DuPont connectors (in the hobby trade called JR, Hitec, or Futaba, but all based on the same 0.1in pitch design) as well as dual XT30 and dual EC3 packs.

This example is dual DuPont.

Here’s what’s in it for you having 2 DuPont leads (JR-type) leads.

First, this enables use of DUAL switches for safety. Useful because the odds of both failing on the same flight are astronomical.

And second thing in it for you is now the model can draw 2X as much current from the battery pack as with a single lead. This is because each DuPont connector is rated at 3.5A, continuous.

So with two connectors, this means you can draw 7A without heat build up. And the switches we offer? Rated a lot higher than that!

For example, this illuminated rocker switch is available with DuPont connectors (universal, what’s called a JR-type connector). This, with 20AWG silicone jacketed wire.

We also offer the same switch with 16AWG leads. But instead of JR-type connectors, it has XT30 connectors. Ditto a version with the EC3 connectors.

We also offer you a toggle switch. This is equipped with a condom (not really, but same idea). And it’s considered waterproof as a consequence. So these have the same connectors, XT30 as well as EC3 so depending on your avionics choices, you’re in tall cotton.

These are rated at 15A and are a good solution for some of us.

Note: nominal voltage for our A123 is 6.6V and when you see this with the voltmeter, stop flying and recharge the pack. Anyway, for this model with DS360DLHV all around a matching DS90DLHV for the throttle, the B2S4000 battery setup is good for 8-10 flights, easy!

Servo Selection

We’ll offer servos using the metric of good, better, and best. So let’s get down to it, the main event . . . servo guidance for Mister Mulligan.

Good

Some guys will opt for our DS180DLHV servos, or maybe DS270DLHV. I think either would be a fine selection with a lightweight build (think 17-19lbs. Figure a lightweight engine, perhaps an OS or Saito 120 four stroke. Modest turn of speed. Sport use, nothing crazy.

At this weight the model is an absolute kite that lands at a walking speed. Save money and use a DS90DLHV for the throttle (and choke if you like), plus PDRS101 servo arms everywhere except throttle, where you’ll select a PDRS105, instead.

• 7) DS180DLHV or DS270DLHV
• 1) DS90DLHV
• 7) PDRS101 heavy duty fiber-filled servo arms
• 1) PDRS105 heavy duty fiber-filled servo arms
• 2) EX20AWG48 – 48in extension, ailerons
• 2) EX20AWG24 – 24in extension, flaps
• 4) EX20AWG6 – receiver –> mate up to aileron and flaps
• 2) Y-harness – for aileron extensions
• 2) Capacitors – for aileron extensions

So you see the last two items and wonder, what is Beech up to now? Simple, whenever extensions go beyond 30in you should add capacitance.

True for all servos . . . any and every brand. Learn more here:

• Why and when to add capacitance

Meanwhile, I just threw some servo models numbers at you and operating under the assumption you’re unfamiliar with our parts nomenclature, it’s surprisingly straightforward and easy to suss out;

So a DS180DLHV breaks down as a 180oz-in digital servo with an iron core 3-pole motor, that accepts up to 8.4V.

And if 180oz-in sounds familiar, it’s because many, many, many servos output in a range of 160-180oz-in. And, I also said 270oz-in.

Competing 160-270oz-in servos

Examples includes several very well knows servos from other high end makers like Hitec and Spektrum (plus others). Perhaps the most famous being the Hitec HS-645MG, which begat the digital version at 6V, the equally famous HS-5645MG, and their newer iteration of that servo, the 8.4V D645MW (133, 168, and 180oz-in respectively).

And pitching 160oz-in for the Spektrum lineup is their well regarded A6380. And note; while we can measure 160, 168, and 180oz-in within the lab, when mounted within a model it’s ‘extremely’ unlikely you, or anyone else on this planet can discern a performance difference between these.

Point being, these servos are collectively within the same ballpark. Also, while Hitec still sell it, I really only mention the old analog HS-645MG as a point of familiar reference as pretty much any digital servo bitch slaps that unit in terms of holding torque, which is what really counts.

And note, bit stronger, in the 270oz-in range, the Spektrum A6320 is a near peer of both ProModeler DS270DLHV and DS255BLHV. All three are standard class metal gear servos with ours bookending theirs in terms of speed and killing it in terms of build quality and price (our opinion of course, but if you review the matchUP article the close up photos will help you form your own concurring opinion).

This brings up how these fine quality competitors compare to ProModeler servos. While diving in is beyond the scope of this Mister Mulligan article, to learn more, just review these matchUP articles.

• Hitec D645MW vs DS180DLHV
• Spektrum A6320 vs DS270DLHV
• Spektrum A6320 vs DS255BLHV

Better

Heavier, call it 20-24lbs? Then this is where I’ll guide you to our DS360DLHV, instead. Perhaps DS415BLHV if you appreciate the finer things in life, like brushless motors.

Yes, still using DS90DLHV for throttle. Now I’ll advise you use to use alloy PDRS25-25T servo arms for the flight controls, and still using the heavy duty PDRS105 polymer servo arm for throttle.

• 7) DS360DLHV or DS415BLHV
• 1) DS90DLHV
• 7) PDRS25-25T heavy duty fiber-filled servo arms
• 1) PDRS105 heavy duty fiber-filled servo arms
• 2) EX20AWG48 – 48in extension, ailerons
• 2) EX20AWG24 – 24in extension, flaps
• 4) EX20AWG6 – receiver –> mate up to aileron and flaps
• 2) Y-harness – for aileron extensions
• 2) Capacitors – for aileron extensions

So now maybe you noticed the BL within the parts number and realized one of these alternatives sports a brushless motor. These are better.

Not to insult you, but if you don’t know jack about servo motors, then this motor article will bring you up to speed lickity split and it frees you of friends and fellow club member who may, or may not, actually know what they’re talking about but have strong opinions.

They say knowledge is power so read this article and you will know which side of your bread is buttered when it comes to selecting servos. Or at least you’ll ‘know’ which type of servo motor best suits you, and why.

• About RC servo motors

Best

So let’s say you’re power mad and opt for a lot of ponies, ‘and’ the model goes well north of 25lbs, say 28-30lbs, or even more. Maybe one of those UMS 9-cylinder radial engines has caught your fancy, or the enduring appeal of the Saito quality does it for you.

With lots of power comes lots of responsibility. Saying a fair bit of weight and high performance means you may be better off with an all-alloy case servo like our brushless motor equipped DS505BLHV.

Yes, I’m saying 500oz-in . . . have I gone crazy? Maybe, let’s see. This is the equipment list in terms of best servos and arms.

• 7) DS505DLHV
• 1) DS90DLHV
• 7) PDRS25-25T heavy duty fiber-filled servo arms
• 1) PDRS105 heavy duty fiber-filled servo arms
• 2) EX20AWG48 – 48in extension, ailerons
• 2) EX20AWG24 – 24in extension, flaps
• 4) EX20AWG6 – receiver –> mate up to aileron and flaps
• 2) Y-harness – for aileron extensions
• 2) Capacitors – for aileron extensions

So let me explain my thinking before you decide I’m out in left field.

Rationale

Reason for guiding you to an all-alloy servo is our good and better servos feature hybrid cases. Examples are our DL-series and BLS0 which are, a) quite a lovely set of well made servos, and b) something of a bargain, and at the same time, c) suffer from a malady of all plastic-case servos upon being heavily loaded. Eventually they suffer from the case top stretching at the output shaft bearing.

Key phrase in the above is a lot of load. Fly a Mister Mulligan at 19-20lbs and it may take 20 years to develop. Fly a 1/5 Mustang with DA-85, or this model at 25-28lbs and it may happens in a one to three seasons.

What?!? I’m admitting to a design defect? Nope. Admitting to nothing of the sort. More like explaining what the limits are. Let’s delve a bit deeper so you may better understand what’s going on.

Look, I’m keenly aware I am giving advice – but – it’s on you to do what’s best for you. So because I know more about servos than my customers, I can give you the straight skinny the other servos guys don’t.

What will you decide to do? Dunno, that’s on you. My job is give you enough info to make the best decision for you, not tell you what to do (plenty of folks on Facebook and the forums perfectly willing to tell you what to do, we’re not one of them).

So your decision . . . yours alone! Here’s what you need to know, about which the other guys stay shtum maybe in order to sell servos.

Limits

Basically, servos with plastic cases, when heavily loaded repeatedly, eventually exhibit stretch deformation. And this eventually also leads to slight movement at the output shaft (perceived as slop).

And not just ProModeler, but any and every servo model and brand, when made with a plastic case top, will do it over time. Believe me, plenty will offer up polymer case servos – far – beyond the point at which ProModeler will, in good conscience, stop and switch to alloy.

Here’s is what nobody tells you, which you need to know . . .

• the larger the model,
• the heavier it is,
• the harder it’s flown,
• the longer the servo arms, and
• the larger the control surfaces

. . . then the quicker it happens. Not a matter of opinion, it’s physics!

Remember, plastic comes from the Greek plastikos which means flow. So it stands to reason when it flows, it changes shape. And this changing in shape in engineering is termed stretch deformation.

The servos in this next photo range from 160oz-in to 624oz-in. All have plastic tops. Specifically, an engineering polymer composed of nylon and fiber fill (can’t speak to theirs but ours is glass-filled 6,6 and this is the kind of stuff Glock uses for handgun frames). Theirs will be similar.

It’s used in servos for pretty much the exact same reason Glock and Smith & Wesson use it, because it’s light, tough and impact resistant.

Solving stretch deformation with alloy

So is there a solution to stretch deformation? Well, funny you should ask, because yes, there is. And it’s found in an all-alloy case servo. More money, of course. This is why the DS505BLHV is the servo we’ve ranked ‘best’ for heavy fast Mister Mulligan builds.

Anyway, hybrid servos top out in a DL-series with the DS360DLHV and with our sweet DS415BLHV in a BLS0 series. However, once our servos go much north of 400oz-in, we switch to all-alloy construction. As exemplified in a BLS1 like our DS505BLHV servo.

Why do others offer plastic case servos going +600oz-in? No offense but you need to ask them. Our line in the sand is our DS415BLHV servo outputting 415oz-in. More powerful than that and we only put our reputation on the line with alloy cases.

Remember, this is going to be your call, we’re a) not going to tell you what to do, and b) we operate on the assumption you’re reading this to learn, not for pablum that’ll make you feel good about yourself.

Bottom line? We’re engineers, not salesmen. And if you want someone to hold your hand, ask your wife or boyfriend, not us. We’re telling you what we feel you need to know, but the decision is yours!

Want to know more about the DS505BLHV servo? Best way to get to know that servo – in my opinion – is seeing what happens when they get destroyed and returned to us for R&R service (repair & rebuild).

This article does a nice job of it with the side benefit of showing how to put a servo back together if you ever take one apart!

• On rebuilding damaged DS505s

Back to stretch deformation

Recalling I’ve built and flown the Howard DGA-6 model at 1/4 scale with enough power it flew like a bat out of Hell. And this back in the day with Futaba servos with plastic gears and no bearings in the tops, I feel entitled to share my 2¢.

Like how I’ve actually purchased a set of aftermarket case tops to add bearings to servos delivered without. Yes, once upon a time, upgrading your servos was a thing!

And the very purpose of this was to address case deformation at the output shaft. So I’m not bringing up something new engineering-wise to the world of modeling, we know how to solve this . . . to a point.

Thing is, they soon got sloppy once again. And this time I blamed the gears. And note; this from long before I got into the servo business.

Anyway, I still remember my surprise coming across them a few years back (I don’t throw anything away). There they were packed away and as I handled them, I noticed something (because I know more about servos these days).

Basically, now, with fresh eyes due to years of servo experience under my belt, I was shocked at realizing their sloppiness wasn’t so much the gears as I’d assumed but due to case stretch deformation ‘despite’ the added bearing. And yes, some gear wear but the proximate cause was the case stretching at the output shaft bearing seat.

Added to which, I could feel movement within the gear train. This attributable to deformation at the pocket where the gear shafts seat.

Two different issues. Let me explain.

Gearshaft pocket deformation

In one instance a weakness of the polymer case construction is stretch deformation where the bearing is fitted. The second instance is deformation at the gear shaft pockets.

Unlike near peer competitors (defined as similar torque and pricing), we add bushing reinforcement at the gear shafts within our plastic case servos. How? By doing what’s called an insert mold process.

This is where bronze bushings are placed in the mold before the injection of the molten nylon 6,6 material. That’s what the shiny bronze bits in this next photo are about.

These bushings serve as reinforcements for the gearshaft pockets. The idea is to preclude the stretching that results in gear play and accelerated wear. More cheaply made servos don’t give you this protection.

Note; in the above photo the gear shafts themselves are the same diameter, the near ones looking larger are an artifact of perspective.

Point being, what you get with a ProModeler hybrid case servo (as a result of our reinforcing the case with bushings) is nearly the durability of an alloy case servo for less money. Just as durable at the gear shaft pockets of an alloy-servo – but – because we don’t have the room to also add a bushing for the output shaft bearing pocket in polymer, an alloy case is still better.

The bushings solves the pocket wear issue (stretch deformation at the gear shafts) for all users, while the alloy case solves the stretch deformation issue for heavy load application, also. Like I said, this is engineering tasked with solving for two different issues.

Operative in the above being ‘nearly‘ and ‘heavy load applications‘.

Combining use-cases

Anyway, I think for most folks the DS360 or DS415 will be plenty enough servo torque-wise. But I would be strategic on where I might use them depending no how heavy the model turns out and especially due to how fast it flies.

This, because just as we learned as little kids when we stuck out hand out the wind to fly it up and down whilst changing angle of attack, there’s a lot more force at 45mph than a 25mph. Same holds with our models, compounded by larger control surfaces.

Point being, on rudder, ailerons, and flaps these surfaces would likely be fine with DLS or BLS0 servos. They would likely experience a long service life. And I’d certainly do this if money were tight.

So mixing and matching becomes a use-case of selecting servos from the better-group ‘and’ the best-group. Or put another way, a savvy user combining the better use-case and the best use-case to customize the servo selection to suit your own particular needs.

I’d also sleep fine using hybrid case servos (hybrid being the term we use for servos where there’s an alloy finned center case and plastic is used for the upper and lower servo sections) as long as I were using 1″ long servo arms like PDRS25-25T. Longer than that with a heavy model and I’d reassess what I was thinking. Consider yourself warned.

Please refer back to my list of conditions where case wear is accelerated. Take note that long servo arms is on the list for bad juju when added to hybrid case servos.

Anyway, I’d be totally fine using hybrid case servos with one-inch long servos arms, like below, rather less so with anything longer.

Servo arms in greater detail

If, for example, I felt the need for a longer arm, perhaps PDRS40-25T, (basically 1-1/2in) or longer (we go out to 60mm, or 2-3/8in), then I would definitely switch to all-alloy servo construction. Especially on elevator when the model is fast because of a powerful engine. And in particular when it’s also a ‘heavy’ model (north of 20lbs).

Why? Simple, it’s because of the added leverage of the longer servo arm compounded by greater mass and higher airspeed. Let me explain. I’ll use a little bit of grade school math, nothing too arduous.

Remember, the servo has a torque rating but you can (your model can, actually) feed force back into the servo. How? Well, there you are flying along fat, dumb, and happy.

It enters your mind to perform a loop, maybe a big 200ft diameter loop. And maybe you didn’t cut power soon enough so on the backside, the speed builds up pretty good. Means as the model rounds out, the G-loads begin to build.

True even if you don’t touch elevator to further tighten up the loop. But especially true if you do tighten the loop, like if you miscalculate altitude and as the model nears the ground you pull up more.

Like I once saw the elevator stick of a transmitter literally bent by the application of force as a panicked modeler tried to save his model from the dreaded figure-9. You know, the one where the maneuver ends about 1 foot below grade. I kid you not.

Anyway, pulling so hard didn’t help and the model splattered like a watermelon falling off the bed of a pickup going 60mph. Engine ended up more than 100yds downrange torn to Hell and back because it bounced on the asphalt the whole way before coming to a stop. Dude cried.

And of course, we all ‘know’ to cut power on the backside of the loop to keep speed from building up but raise your hand if you’ve never ever done it, not once. So in the real world (humans, feet of clay, etc.) we sometimes get a bit distracted/careless whatever. So if we forget and don’t close the throttle enough, the airspeed builds.

Then here’s what happens; as the model transitions from straight down (3 o’clock position) to horizontal (6 o’clock) and into a climb, the G-forces get strong. Like a couple of G is normal but when carrying too much speed, the model may see 3 or even 4Gs, briefly.

So do the math, 20lb model, at 2Gs means it’s experiencing gravity at 40lbs of force at the bottom of a loop (20lbs x 2G = 40lbs). Now say you’re using a 40mm servo arm (this is about 1-1/2 inches, major point being it’s longer than the arm for which servos are rated, by definition, a 1 inch long arm).

So using a 1-1/2in arm means output is reduced by 1.5X but being longer, it also means the arm is ‘inputting’ a larger force. By how much? By the exact same ratio, 1.5X (1-1/2 times).

This effect on the servo is akin to adding a cheater bar to a wrench to help loosen a stubborn nut! Check out some numbers . . .

• With a 1-1/2in long servo arm, a servo outputting 360oz-in outputs at the outermost mounting position 350/1.5=240oz-in. Again, not opinion, physics.
• Conversely, inputting a force back to the servo using a 1.5in servo arm vs a 1in servo arm the force is multiplied, it’s increased by 50%, so 20lbs becomes 30lbs.
• And a 20lbs model at 4Gs at the bottom of a loop? That’s akin to 80lbs being fed back into the servo.
• And just FYI . . . 360oz-in is the same 22.5lbs.

Anyway, at the bottom of that loop, it means now the mass of the model, multiplied by gravity (and the faster it goes the more G-forces) are back feeding the forces of the air acting on the control surfaces backward ‘into’ the servo’s mechanical structure (the case).

Where? Focused at the output shaft. And since the bearing is what is supporting the output shaft, then this is why I keep talking to you about stretch deformation. Saying – bluntly – these forces ‘may’ be in excess of those for which the servo’s been rated.

Beginning to understand the issue of stretch deformation?

Faster and heavier

Next, imaging the model’s going a bit faster, now instead of seeing 3Gs, or 60lbs of force for a 20lb model, imagine it’s maybe seeing 4Gs or even 5Gs, call it 80-100lbs. I bring this up because engineers always go the edge case to understand what can happen.

You are responsible for making a decision regarding what servos to use. Whether you select some of ours, or another brand, if you’re reading this it’s because you’re curious and want to do the research resulting in the best decision for you and your circumstances.

Anyway, as I keep repeating, what resists the force feeding through whatever length servo arm you’ve selected? It’s the 25T splined output shaft. And what’s supporting this? The bearing. But what’s supporting the bearing? For some servos it’s seated in plastic and for others it’s aluminum!

And we know plastic deforms and may even crack with repeated loading. Just saying the foundation for your servo’s entire structure is the case. We, like many others offer cases made with plastic components (technically an engineering polymer).

Genius lies in solutions

So knowing this about stretch deformation, we didn’t just sit on our thumbs. Back in 2023 we redesigned the standard class upper polymer case. What for? To reinforce it!

Remember, everything we’re saying about our polymer case servo holds true for Savox, Futaba, Hitec . . . anybody and everybody’s servo made with a transmission section using plastic case, OK?

So to reinforce it meant a new mold. One adding more material. In fact, we spent a fair bit of coin editing the mold for the upper case of our standard class servos.

What did we accomplish? Eyeball the massive ring of material we added to reinforce the design surrounding the output shaft bearing in this next photo . . . this is before and after.

Note above how – now – there’s more material surrounding the 25T splined output shaft where the bearing seats. Our servos have a ‘lot’ more material than competing designs. And it’s there expressly to better anchor the bearing.

This next photo shows competing approaches in the 270oz-in class.

Added to which, beyond the bearing support ring being much beefier, note how we’ve also boxed in the output shaft bearing with 2 added bolts. Basically, six bolts total but four in close proximity and surrounding (or boxing in) the bearing make the case section stiffer than a case assembled with just four screws.

The extra bolts helps the gear mesh stay at design limits. But no matter what, it’s still plastic so there are limits to how well it’ll hold up, which is why we go to alloy cases north of about 400oz-in.

Again, your call regarding what to use servo-wise. However, it’s our opinion a 20-24lb model is approaching the limit for a polymer case. No, this is not hard and fast rule because as usual, it depends.

On what? On how much the model weighs, how fast it is, and on you, also. E.g. how hard you fly it? Like do you horse it around the pylons like what it is, a replica of an air racer, and the way I flew mine? Or are you a Sunday flier who flies around for fun with the engine large parts of the time at part throttle? This makes a significant difference in the stresses on the entire structure and the servos, take my meaning?

We’re all different and even a heavy model with a super powerful engine can be perfectly fine with hybrid case servos if you’re not out tearing up the sky all the time flying it like you stole it. So it’s a continuum and this is why I can’t (nor can anybody else) tell you with absolute certainty which servos are the very best for you.

Recapping, one servo per control surface, overkill is never a bad idea if you can afford it, and if the model is heavy and fast, opt for alloy at least on the elevator servos. Added benefit is you also get a brushless motor. The motor article I linked earlier will help you understand the differences.

Note; ProModeler servos have soft start. They all do. So you get the benefit of the gentle centering to protect airframes upon the application of avionics power even with our $30 entry level models. Ditto finned alloy centers.

Cooling fins

Fins shed heat better. Cost more also. Worth it, else we don’t do it. Note the o-rings on the bolt heads. You don’t care if they are or aren’t there? We don’t either. But if you do care, then you’ll be glad we put them there. All servos don’t have them. So remember the old saw, you get what you pay for. Problem is, consumer grade servos may charge you but not deliver.

Maybe ask, or better still, take a look for yourself.

All-alloy servos

So for our polymer case servo we reinforce where the gear shafts are fitted with bronze bushings. But it’s not practical to do this at the output shaft where the bearing is fitted. So we beefed up the polymer at the opening. Made it better. It’s a LOT stronger.

Does this make it as good as an alloy upper case? Nope. Does, however, make it a country mile better than competing designs.

So in anticipation of higher loads, you may have noticed our servos switch to aircraft aluminum for the case. Still light, but stronger than polymer. Basically, beyond our DS415BLHV servo, we go to all-alloy cases.

Note; we also reinforce gear shafts bore within our alloy cases.

So this conversation regarding stretch deformation is 100% to do with strength of materials. Plastic is great until it’s not and at 20 lbs and a fair bit of power, we’re at an edge-case. Approaching the limit. Where’s the exact limit? We don’t know, exactly because it’s not like the edge of a cliff. We know it’s there, but don’t know where exactly. Thus, cluing you in so you don’t pony up for servos and regret it.

Unfamiliar with your wallet, I don’t know if the thought of $100 a pop for DS505 elevator servos is out of the question, or no big deal. Just as we’re all different as pilots, we’re all different in terms of our wallets, too.

But when asking my opinion, I’m going to try and present the considerations that go into making a judgement. If you can afford them, I’d guide you to the DS505 servos everywhere. Next best is DS505 on elevators and DS360 or DS415 everywhere else. The weight and speed of the model affect this judgement.

For the throttle servo, the DS90DLHV is all you need.

Other considerations

Beyond selecting servos, with giant scale models you have other considerations. For example, how to power the avionics, the ignition, and issues to do with long servo extensions. Bone up with these articles:

• Servo Leads & Extensions
• On the batteries John prefers using
• Why and when to add capacitance
• Regarding ignition and radio switches

Final thoughts

Allow me offer a few final thoughts. The right servo for your model is a reflection of yourself, your goals, your dreams, and your budget. We put a better grade of servos in your hands. But nobody can make you buy them. This, you decide for yourself.

Any questions? Feel free to reach out, we’re readily available;

• Telephone: 407-302-3361
• Email: info@promodeler.com

. . . maybe together we can suss out what’s best for you!

I’ll close with this, one thing’s certain, best is a race that’s never finished. Best right now? ProModeler, but far from David vs Goliath, we’re more akin to a flea on the elephant’s back in this battle.

Means we need your help. Presuming you like our servos, then do us the favor of taking one to a club meeting. Pass it around. Maybe even pull out a 1.5mm Allen driver and open it up – you’ve seen how they go together, there’s nothing to be afraid of. And please, show them to a pal.

But most of all, kindly grace us with a photo sharing your thoughts. What for? To put on the website, and within articles like this one. Basically, for telling the next guy what you like about our servos.

We’re Jones-ing for photos like this one because your favor is priceless and can’t be bought. We know this. So do others.

Last thing

Have you enjoyed this? If you like reading and are interested in learning more, then maybe find time to review more articles like this;

• On the batteries John prefers using
• About pots vs Hall Effect sensors
• On selecting battery packs
• Pro tips for improving your ARF
• Amazon servo vs DS505s
• Why’s my pack got two JR-connectors?
• Rip Van Winkle, on returning to RC
• How to guide a rocket using servos
• Phoenix Models 70in Strega guide
• Advantages of pull-pull via pulley
• Bret Becker: Mr. Top Gun
• Will ProModeler servos work with NiCds?
• How to determine flight time for a 2S850 LiIon
• Hangar 9 60cc Pitts S-2B servos
• Fear of loss, or how to stack the odds in your favor!
• When LiFePO4 is mistakenly charged as LiIon
• Idle thoughts regarding chargers

. . . and hundreds more. Best part? They’re all free!