As usual, one of these servo articles begins with a question - this time, several questions from one fellow over the course of several messages.
Summarizing, he asked, ‘What servos would you recommend for my new Hangar 9 Pitts S-2B ARF? What will I need in the way of servo arms and extensions. What about a battery? What are your thoughts about using an IBEC?'
To begin, while I've never owned this particular S-2S model, I've seen it, flown it, and have one a lot like it (Great Planes 33% S-1 spanning 68."5 instead of 71.6" for the Hangar 9 S-2S). Major point being, I have a pretty good idea which of our servos will work well based on personal experience. Thing is, I don't know you, or whether you can afford what I may recommend. So I need more information!
This is why we went back and forth until I knew how he flew, and also a bit about his budget. Then I laid out his alternative. This, because how you fly matters in servo selection as does the depth of your wallet. Ultimately, there's no one size fits all.
So if you're reading along and wondering how all this affects you? Let me hasten to add, we'll get to the answer to which are the best servos for you because I'll make three recommendations. Then you can decide for yourself.
First, and circling back around to the ARF I own and the one he owns. Spanning 68-1/2”, my Great Planes S-1 model is within a hair of being a 33% model of the 17’4” wingspan full-scale aircraft. Doing the math works out to (68.5/208)*100=32.93%. If I do the same math for the H9 S-2B that spans slightly larger than mine at 71.6" (but for a full scale aircraft spanning 220" instead of 208"), then (71.6/220)*100=32.54%, so once again, about 33%.
Propulsion - powering the model
Did you know how you power the model may make a difference in how it flies? It's true so let's briefly touch on this aspect of ownership before delving further into servos because if you don't have a sufficiently capable motive source, then equipping it with servos to perform the most aggressive XA maneuvers is pointless if there isn't enough grunt to pull out of a hover. Take my meaning?
As usual, our usual choices are a nitro engine, a gasoline engine, or an electric set up.
Mine is powered by an OS Max 300T (four stroke twin), and is a delight to fly. Being a nitro fuel engine means there's no ignition, so shutting it off involves closing off the fuel supply with the throttle servo.
Hangar 9 positions their S-2B for the same engine-market and thus, recommends 50-60cc engines. If glow engines float your boat, a Saito 300T is the functional equivalent of my big OS. So if the gorgeous Pegasus FF-320 four-cylinder engine by OS Max.
And for context, my OS Gemini turns a 20x10 at 7200 and is reliable as an anvil. But it barely has enough power for XA-maneuvers. It's great for IMAC and sportsman maneuvers but you can pretty much forget about torque rolls with powerful vertical climb outs and such because there's just not enough power to pull out with authority. It'll start upward but then you're going to have to transition to horizontal fairly quickly
Another engine I own, which I think would be lovely in this model is a DA-70. It too is a twin, but it's two-stroke gas burner. Makes more ponies than my Gemini, but it also has an ignition. You'll need some way to shut it off remotely, and from the outside of the model without using the radio (per the rules). More later.
Note; my DA-70 isn't quite stock and has Bad Dog nozzles for the smoke system. It's a wonderfully performing engine but there are other alternatives, less costly ones like an EME-70, when it comes to small twin gassers. And if you want to fly XA-maneuvers, then much like the big OS Gemini, these small twin-cylinder gassers don't really have enough grunt in my opinion unless you're an expert pilot, which I'm not. Yes, you can fly a lot of XA maneuvers, but the vertical will be somewhat limited.
And as it just so happens, while I really like this baby DA, engine maker DLE (also offered by Horizon) offer their DLE-60 60cc twin. It'll fit quite nicely but like the DA-70, it won't have the grunt for serious XA, either. Ditto if you have a Zenoh G-62 lurking in a drawer. Great engine, but again, not enough oomph for XA-maneuvers.
If, however, you're planning on using something like a DA-85 (a big thumper of a single), then in my opinion, this engine *does* have the grunt for unlimited vertical XA-class maneuvers in the S-2B - easily. So it's horses for courses when it comes to internal combustion engines in this S-2B. Heads up!
Note; when it comes to gas burners, vibration is a concern so I'd advise you to review this article that goes into vibration mitigation and trying to ensure your throttle servo lives a long life.
If electrons floats your boat, and while there are tons of 60cc class outrunners on the market that on 12S will allow you to perform XA-class maneuvers, my pal Jim Kitt in Tampa offers something unique. It's called a StinGR85. It's a belt-reduction drive based on a 700-class helicopter motor.
This setup swings through a 26.5x13" prop with authority and makes close to 50lbs of thrust and would be my first choice for XA-class performance.
Anyway, believe me when I say, powerwise, it's a whole new world out there from when I built my old S-1S in 2003!
Moving on; it’s my experience flying both my Great Plane's S-1 and the Hangar 9 S-2B back-to-back . . . theirs is the better flying model. Both are 33%, and the mere 4" great wingspan shouldn't amount to much difference, but it does. So come the day I crash my model, the Hangar 9 Pitts S-2B is what I'll buy to replace it. And it's my further view the crew at Hangar 9 are to be congratulated for this fantastic achievement (and you too for recognizing what this model bring to the game).
So how did the Pitts come about in the first place?
Background
In 1943 Curtis Pitts began developing what would become the Pitts Special. Taking wing in 1944 as WWII drew to a close, it became famous a few years later when Betty Skelton used hers (the 2nd one ever built and nicknamed Little Stinker), to become the US Female Aerobatic Champion in both 1949 and 1950. Do you like trivia? Did you know she often flew around the country with her dog, a chihuahua named, Little Tinker? She did and the pooch even had a custom-made parachute for if the worst happened!
Anyway, flooded by demand, by 1962 Curtis had set up Pitts Enterprises to sell plans for the S-1C to homebuilders. And as it came to pass, the little biplane that could dominated world aerobatic competition throughout the 1960s and 1970s.
These days, homebuilders can buy plans and kits from Steen Aero Lab (S-1C and S-1SS), while S-1S plans are available from Aviat Aircraft. Aviat also offer factory built aircraft (certificated) of both S-1 and S-2 versions. FYI, the S-1 is a single-seat and two-place models are denominated S-2. And all are derivatives of Curtis' original. Note; he passed away at 89 y/o in 2005.
As for the S-2B the Hangar 9 model is based on, the S-2B was actually modified from an Aerotek-built S-2A (260 hp Lycoming). Now out of production (but they built 196 of them), Aviat continues to offer service. Another bit of trivia is the S-2B was actually designed by Herb Anderson, chief engineer for Pitts Aerobatics (after Curtis sold his business in 1977).
Anyway, a more well known bit of Pitts trivia is the full scale has a roll rate of 240°/sec, call it 1-1/2 seconds per roll. This model by Hangar 9 is faithful to the full scale model and is a delightful flying model aircraft that will roll every bit as fast, if not faster. And as compared to my own 33% Pitts, this Hangar 9 version is arguably better beyond flying better. Why?
Well, for example, the GP-version parks the stab-servos (rudder and dual elevator) beneath the horizontal stab. Thus, rudder and elevator servos are exposed to view (and in the case of mine with the fuel-thirsty glow-powered big twin, they get covered in oil). While the servos beneath the stab offer a very short direct pushrod link to the surfaces, they're not a very attractive setup.
Conversely, Hangar 9’s Pitts S-2B places the rudder and elevator servos within the fuselage and near the CG on plywood trays with hardwood bearers (all designed for standard class servos).
In the above photo, the two elevator servos are on the top level and the rudder servos is mounted below. All three on a plywood tray. And yes, these servos require the use of longer pushrods but this makes no functional difference whatsoever in terms of control precision or authority because they also create a very precise setup.
However, being mounted within the fuselage is important for two reasons. First, the servos are protected from exhaust-yuck and beyond being more protective of your servo investment, this results in a *much* cleaner appearance due to being tucked away.
And second, because the mass of these three servos (~6oz) is closer to the CG, then the aircraft tumbles better due to the reduced moment (dumbbell effect).
- Move the weights in closer to the CG and the mass spins more easily
Another thing that’s nice is instead of a one-piece wing, the upper wing of the Hangar 9 model joins a fixed center with an alloy tube. That, and the model is covered in Ultracoat versus Monokote like my older aircraft. Monokote is becoming more difficult to source if repairs are necessary.
Anyway, both are attractive and the S-2B is trimmed in the handsome Rich Goodwin airshow scheme. That, and both the Great Planes and the Hangar 9 mount aileron servos the same way, to mounting plates that are then screwed to the wing. This is my favorite method!
Finally, the Hangar 9 model has other nice touches like an included instrument panel (I had to buy my own when GP offered their model). And you also get a carbon fiber landing gear versus the duralum mine has.
- On the flightline, Jeff Skowron's Hangar 9 Pitts S-2B at the ready
So ultimately, it’s my opinion this Hangar 9 version is the better design for a host of reasons. And all this is useful to know for if anybody bends your ear regarding how great the model, which Great Planes once offered, was (and it truly was), but this one is better!
Servo recommendation
So I’m going to offer up 3 different servo recommendations instead of one.
First, there’s the recommendation for the average pilot, a sportsman or duffer like me. E.g. a club pilot who just loves how these models look and fly but couldn't perform a harrier roll if his soul depended on it.
The second recommendation is for the pretty capable pilot; the guy good enough to be asked to fly noon-time demos for his club events and who flies light 3D and IMAC maneuvers. This is the guy other pilots frequently ask to perform the maiden for their models . . . a good stick.
And finally, the third servo recommendation is for those who can challenge the best pilots in the world. If you fly and try to wring the model out so hard it's like trying to rip the wings off, if rolling Harriers are within your wheelhouse, and if everybody stops to watch you, and if you can afford them, then these will be the servos for you.
But before I get to servos, let's first answer the other question he asked; what else will you need for to complete your 33% Hangar 9 Pitts S-2B? This, because regardless of the servos you decide on, you're gonna need these bits and bobs to make the install.
Extensions:
Note; these are 20AWG wire, the thickest you can buy to handle the most current with less voltage loss. Speaking of which, review this material to learn more about extensions and their mechanical and electrical characteristics.
Another nice thing about the extensions we offer you is they are twisted to resist stray RF (for if your ignition module ever begins to take a crap on you). Plus, they have that soft and super supple silicone jacketing, which resist abrasion and flexes nicely. Next up, we'll touch on servo arms.
Servo arms for the sport pilot
Servo arms for the 3D and IMAC pilot
Servo arms for God’s gift when using BLS2 servo with 8mm splines
Battery pack
Battery pack wise, it depends if you buy into the school of using two packs, for the receiver, or not. We don't engage in the fear trade and believe one pack with dual leads is all you need.
What's more, with a single pack equipped with two leads you get 10A of current into the receiver without heat buildup and in our experience, this is enough. Read this to learn more:
Why is 10A into the receiver important? Because it's enough!
You see, what everybody obsesses over is voltage but with regard to servos within our models, what really matters is current flow. Eyeball the specs for a bog standard servo like the ProModeler DS270DLHV.
Every servo in our line up includes a comprehensive set of specs.
While everybody obsesses with voltage (abbreviated with symbol V), what really matters is current (denoted in amperage, or shortened to amps, and abbreviated (A).
So we present specs determined by voltage in five columns. These range from a low of 5V, through 6V, 6.6V, 7.4V, and 8.4V. Why? Principally to show what you can expect in the way of performance.
Moreover, like all manufacturers, we put lipstick on the pig in order to sell product, so we present the specifications within our propaganda to depict the highest rated performance, e.g. at 8.4V. Thing is, our servos work just fine at many different pack voltages - like 5V (for a 4-cell NiCd) and the 6V of a 5-cell NiCd. We tell you this because many old school modelers prefer the nickle-cadmium (NiCd) chemistry they know best. However, we also share the data for the 6.6V of a 2S LiFePO4 pack, as well as the 7.4V nominal voltage of a 2S LiIon pack, and the 8.4V of a regulated synthetic source (or 2S LiPo coming off hot from a charge).
Major point in all this being, take note at 8.4V a DS270 is a +3A servo and if you have a butt load of servos in your model, a battery pack equipped with a single connector (rated at 5A intermittent) may get overheated. Our packs have two leads (so 5A+5A=10A) and 10A this is enough - in our opinion. Heck, we make it easy to get even 20A out of the pack without resorting to toting the dead weight of a 2nd battery pack.
Heads up, batteries aren't rocket science - you don't need to spend a ton of money!
They say parts are parts but we feel if you use better parts (meaning better components) then you get a better servo. AKA, more bang for your buck. In what follows, keep in mind all the goodies you get when you opt for ProModeler versus the alternatives clamoring for your money. What do we expect you to do? Simple, what's best for you!
Servos for the sport pilot
This model uses one servo per aileron, total four. And one each on the two elevator surfaces, so two more. Plus one each for rudder and throttle, so eight standard size servos in all (unless you want a ninth for choke use).
For the Hangar 9 60cc Pitts S-2B the manufacturer, Horizon, recommend their A6380, a standard class servo making 160oz-in and transiting in 0.13sec/60°. This metal gear servo is actually a pretty decent servo especially for the money, but it's my opinion, it's a bit light duty for such a model. Your money, your decision, I'm sharing my experience and opinion.
First up, servos for a sport pilot who likes the looks of these things *but* is a realist about his skills *and* doesn't want to torch his wallet. This fellow can - in my opinion - easily be very happy with . . .
- DS270DLHV times 7 (4X for ailerons, 2X for elevators, plus one for rudder)
- DS90DLHV on throttle
More powerful and quicker than the factory recommended servos, these are great for taking your 33% Pitts S-2B around the patch. You know, to do a spot of inverted flight, perform a few loops, string together three rolls whilst flying downwind, and perform stall turns or humpty-bumps turnarounds. It’s also adept at graceful combat maneuvers like the Immelmann and split-S. And it looks terrific flying Cuban 8s, performing Lomcovák, and both snap rolls and especially if your skills are up to it, slow rolls. You know, just basically farting around the sky having a blast.
If you're unfamiliar with our servo designation, we try hard for the model numbers to actually mean something in plain English. You don't even need a decoder ring because we'll just tell you the secret code . . .
- DS = Digital Servo
- xxx = rated torque in oz-in
- DL = Iron pole motor (BL means brushless)
- HV = High Voltage (to 8.4VDC)
So how can we possibly recommend a servo that goes for a mere $45 each for such a large and heavy high performance model aircraft? Simple, it's because these maneuvers don't require a ton of speed so the 0.12sec/60° you get from this servo is plenty fast enough. And at 270oz-in, we're handily offering you significantly more than a 50% bump in torque over what they recommend.
Add to it, the DL-series servos feature very rugged construction with all-steel gears so they hold up really well over time. Believe me, these servos are the best bang for the buck in our lineup, and probably on the planet! Just eyeball the lovely all-steel gear train.
- DL-series servos have all-steel gear trains for long lasting performance
Part of what makes the ProModeler DS270DLHV such a solid alternative is that unlike hobby-grade servos, they're built to meet military standards (and subjected to these tests).
MIL-STD-810G-Part 16
- Shock - Test Method 516.6
- Vibration - Test Method 514.6
- Rain - Test Method 514.5
So with DL-series servos you get the super reliable iron-pole motor. Plus these servos even have soft-start! Moreover, you save money by selecting servos built with our hybrid case construction (glass filled nylon) but you're getting an aluminum center compared to more cheaply built all-plastic construction servos. Plus in ours you also get bronze inserts and alloy center.
Regarding the polymer components, we reinforce them with these tiny bits of bronze. These are insert molded and reinforce where the steel gears shafts are fitted. In the alternative, gear shafts bedded directly in plastic, it won't take long for the loads and vibration of a gasser, especially, to result in round bores that are more egg-shaped. And once this happens, it's time for a new case because the gear mesh is shot. And you'd better do it quick before you need new gears, also.
So it's our opinion - spending good money on servos without bronze reinforcements - is a bad idea. Ours have this feature, which means you benefit with greater precision and durability. Cast your eyes on this beauty!
- Bronze hardpoints insert molded in the case are great reinforcements
By the way, servos are available (all servos, all brands and models) with three types of motors. These are iron pole, coreless, and brushless. Don't know diddly about servo motor? Learn more about motors with this article where we cut some apart using a lathe and then photograph the inside to show you what's what.
Moreover, we don't short change you in any regard with DL-series servos (five in the line up, ranging from 90-360oz-in, and priced between $30-50) because the internals for all of them include hardpoints.
But beyond the hard points and super reliable motor, we also give you the best center case in the business. We call it the porcupine alloy case. Can you figure out why?
- CNC-machined from a solid billet of 6061-T6 to cool better than plastic
So beyond the bronze hardpoints, you get an alloy center machined with with cooling fins for the best cooling (and far superior to plastic case servos). You also get 13 o-rings for sealing your servo from the hazards of the environment. Plus we button it up with Allen head machine-thread cap screws instead of the typical el cheapo Phillips head screws.
This render off the workstation CAD shows you more about the guts.
- Yellow are the o-rings, and the bronze bits are hardpoints
Servos for the IMAC and mid-range 3D pilot
The IMAC pilot is typically more concerned with smoothness than trying to rip the wings off the model. That, and when he performs 3D maneuvers, they have a certain element of élan and panache.
For a perfect example, take maneuvers mentioned above, and add to those the elegant rolling Harrier, rolling circles, plus Blenders (rolls whilst going straight down vertically, into a snap, release and exit). The maneuver looks great but because it's a variation on a snap roll it isn't especially difficult, it's more a matter of timing.
If these maneuvers, plus torque rolls are in your wheelhouse, e.g. aggressive XA-type where forward airspeed isn't off the charts, then for this pilot, our recommendation is a bit more nuanced;
These servos are more powerful, and faster than our DL-series. These also feature an alloy center case. However, what else changes is the motor goes from iron core to brushless. These last 5X longer than iron pole or coreless motors, and are considered the best money can buy.
These have all-steel gears as well, and while steel is metal, when compared to what's advertised with all-metal gears (where they're including gears made of brass, and aluminum as well as steel), ours are all-steel gears. All-steel is top of the range in the world of all-metal gears.
So doing the math and you'll see outfitting your model with these significantly quicker DS415 servos plus a DS505 servo means spending close to $850, or about twice what a sport pilot would need to spend. And for this, the competitive pilot gets servos with uncompromising performance and build quality. How good are they?
To show you, I'll refer you to an article titled, On rebuilding damaged DS505s where the photos show a coupe of badly damaged servos. The customer returned them for repair following an 'incident' and we took photos.
So why on Earth would I show you the repair process of a broken servo? Simply because this way you get insight into what our servo competitors don't show you - what inside. Instead, they make like life will be all honey and unicorn farts if you just buy their servos because they're pretty on the outside.
Instead, we contend it doesn't matter what the servo looks like on the outside, the only thing that matters is what's inside because beauty *is* more than skin deep. Anyway, if you agree what's inside the servo is what really counts, then you'll be pleased we show you!
Please make a few minutes in your schedule to see how the DS505BLHV are made before deciding on your next set of servos. And note; these 415 servos on the ailerons and elevators are significantly faster at 0.052sec/60° so high caliber pilots will feel a substantive difference in performance in this class of model.
Servos for the 2nd coming of Jase Dussia
The serious XA pilot could care less about smooth. Instead, he flies the aircraft like he stole it, and looks to be trying to break the airplane in the air. Maneuvers he'll perform include all the above plus rifle rolls, and HARD type 3D maneuvers like hitting The Wall. Also, he'll fly Rifle Rolls, which involve high speed (as fast as it'll go) *and* then shoving humongous ailerons out in the breeze.
This last does two things. First, it causes a huge spike in current draw - like through the roof, and second, makes the model roll until it's almost a blur. This is a level of violence that can destroy models - I'm not shitting you.
But here's the thing, what a customer says and actually does are two different things. Some guys call and want our fastest servos *but* if they're anything like me, couldn't tell the difference if their soul depended on it.
So my best advice is to listen to the bard, Shakespeare himself when he wrote . . .
--- To thine own self be true ---
. . . from which I take this to mean, don't fool yourself. Look, you can spend a butt load on servos capable of performing rifle rolls (because they take both immense torque and speed, and cost it), or you can be more reasonable in your expectations. But only *you* know what you really need. My best advice? Don't buy to impress the peanut gallery, buy to satisfy your needs.
Remember, I don't know the customer, or you. Not really. He's a voice on the phone or an email telling me what he wants. So I have to take him at face value - but - I'm always mindful of one thing above all, he also could just be a bullshitter with a fat wallet. Like who am I to say?
Servos for this top level pilot are our series-2 (BL2) and a series-0 (BLS0) so we have another mixed lot;
Why series-2 instead of series-1 on the flight controls? Simple, they're far more rugged and they're fast as a raped ape!
That, and the pilot performing rolling Harrier rolls and Walls wants both high torque and speed in one servo. This costs money. So how much will this pilot spend? A cool $1200 on his servos, or roughly 3X as much as a sport pilot.
Then again, as well all know, hot rodders have a saying . . . speed costs, how fast do you wanna go? Same holds true with servos that offer blistering speed, excellent centering, and loads of torque. If you can afford it, these are our very best.
All of the servos we've discussed use the same 1 million cycle Noble pot for superb centering. There's nothing better at any price.
But series-2 servos (BLS2 technically), are built to a more rugged standard. Gears are bigger, bigger bearing, shafts are larger in diameter, output shaft is larger, etc.
So like the coach needing one lousy yard for a 1st down to cinch the game will send his fullback to carry the rock instead of the lighter halfback, the series-2 servos are what's called for if you're the 2nd coming XA pilot-wise.
BLS2 servos are just more beefy in order to take the abuse being imposed on them by maneuvers of such violence as top level pilots can demand. If you're really one of those, then these are the servos you want. Heck, just eyeball how one of these compares to a well regarded competitor like the Savox 2290SG Monster.
- An uncompromising level of build quality is what it takes to be our top-of-the range
And it goes beyond this as the servo's alloy case is reinforced expressly to better withstand what happens when pilots call on all the servo can deliver flight, after flight, after flight. This, as the old saying goes, is when the bullshit walks!
Miscellaneous
Thoughts on dual batteries. Poke around and you'll find plenty of anonymous folks online telling you you need two battery packs for your avionics. And always armed with apocryphal stories of losing a model to pack failure or knowing someone that did.
Us? If models were crashing left and right due to battery pack failure, then we'd have been using two battery packs since the early 1970s when I got into the sport. We didn't then, and we don't need to, now. That's *my* opinion (but opinions are like bellybuttons in that we all have one).
Beyond that, take notice how many manufacturers promote this concept versus how many don't (most?). But heck, you wanna buy two avionics packs, then KYO, because we'll take your money. Anyway, this is what we recommend for you.
- Receiver: if you're a pro, then get the B2S5000 higher voltage - enough for 4-5 flights
- Receiver: if you're a lover not a fighter, B2S6000 (LFP cells are easier to live with)
- Engine: BS2500 (we figure 1000mAh per cylinder, so this gives you a small cushion)
Wrapping it up
I love this model airplane and want one, bad. I know there will come a time I do something stupid with my 33% Great Planes Pitts S-1 and when it happens, I won’t shed a tear and I’ll hustle to go buy one of these S-2S from Hangar 9.
Anyway, unless you have money to burn, I really do think you’ll be perfectly happy with the DS270 servos (I am), and maybe the PDRS32-25T servo arms instead of the PDRS101.
For my Pitts, I opted for the B2S2500 pack for the avionics and a B2S1500 for ignition. And this, in a tangential manner, answers his question of an IBEC. Fact is, no, I’m not a fan of these devices. Yes, I know how folks feel about the Tech-Aero Ultra, ditto the PowerBox Spark Switch, and Booma's IBEC Telemetry switch.
I really am sorry, but I just don’t care what folks say about how great those things are. I am very old school and thus, I don't want these two systems (control and ignition) to even know the other exists. Much less am I willing to make a connection between them. Optical isolation be darned.
So in practice, exactly as a player doesn’t let his girlfriend know he has a wife, and for darn sure keeps his wife in the dark about his girlfriend, I prefer to keep the ignition module, battery, and external on/off switch forward of the firewall with as much physical distance between it and the receiver as I can.
Moreover, I also use a non-metallic pushrod from the carb to the servos (I like using both throttle and choke servos - especially as either will shut down the engine remotely). That, and I mount the receiver as far back in the model as I can (usually in the turtledeck area behind the pilot's head). This to physically separate the receiver from the ignition module for if the module begins to broadcast RFI.
Any further questions, suggestion for this article, etc. then just reach out to me at 407-302-3361, or via email: info@promodeler.com
- My pal Jeff Skowron shared this photo of his S-2B model nicely stored