I recently received a query from a fellow regarding selecting the appropriate servos for a Hangar 9 Ultra Stick - the 30cc instead of the original 10cc version (the small one has a 60" wingspan while the 30cc version sports a two-piece wing spanning 81" that's nearly the size of a closet door). His question offered a lot of subtlety, so I post it in its entirety.
Q. What would be the appropriate servos to use in a Hangar 9 Ultra Stick 30cc. Which will most likely be fitted with a DA-35 engine. Mostly flown for sport flying some 3d maneuvers. Just by comparing torque and size I think I may be able to use your DS90DLHV. Any recommendations you have for the build would be greatly appreciated.
A. There was a time I'd have said, yes, use the DS90DLHV in the 30cc Ultra Stick and moved on to other things. Especially because they themselves (Hangar 9) recommend their Spektrum A6180 standard size servo, which on 6V is rated at 94oz-in - but - over time we have revised our opinion. These days we now recommend the DS90DLHV principally for the 10cc version, instead and the DS180DLHV for those who intend to fly the smaller version really hard.
Specifically to John's question; would the DS90DLHV work? Sure it would. Especially if your flying style leans more toward the relaxed end of the scale (read this as instructing, plus light sport flying, and most especially when you love spending nearly a whole tank doing nothing but lazy circuits with lots and lots of touch-and-goes).
Some caveats before I continue
If the above paragraph strikes you as an example of me covering my ass, you're right. This is because over time we have built up a fair base of actual user opinion/experience. Naturally, this feedback from folks using our servos when outfitting their 30cc-size Ultra Stick sticks in my mind. On top of this, and I admit I'm reading between the lines, but I'm taking note of two things; he's planning on using a DA-35 and he mentions 3D. More later - but - remember, I don't actually fly with this guy. The point is; I don't really know much of anything about him beyond what he said - and - what he means by 3D and what I mean are probably two different things . . . but I digress.
Bottom line? This kind of question always poses a tricky situation because I have incomplete information so please allow me some dancing room. Nevertheless, below is what we've learned and maybe you can use the information to make a better decision servo-wise if you're thinking of building one of these outstanding models for your fleet!
So to recap before proceeding: first; I have learned folks are generally flying this 30cc version rather aggressively - and some are flying it really, really hard. Second; this guy mentioned a DA-35, said engine generally being considered the wild mustang in the paddock amongst horses, e.g. the standard bearer for high performance engines in this class. Third, he also mentioned the magic words, '3D maneuvers'.
The use case for various torque values:
About half of our customers opted to use the DS180DLHV. This servo is rated at nearly twice the torque as the recommended servo. It's my opinion they opt for the DS180 because they planned to fly the model pretty hard, and in general, the harder you're going to fly a model (any model) the more powerful a servo you should use. Thing is, flying styles are really subjective and what 'I' think is a hard maneuver, another guy looks at me performing, smirks, and thinks, 'pansy' (and some actually say it out loud). The other thing has to do with the large size of the Ultra Stick control surfaces.
Anyway, about 1/2 of those folks from whom I subsequently heard back (those using the DS180), mentioned being perfectly happy. However, the other 1/2 mentioned that due to the large control surfaces they would have been happier with a more powerful servo. Note; with due regard to their opinion, I actually suspect speed would be a more important attribute because the torque of the 180oz-in should, in theory, be ample. That said, remember these wise words regarding theory . . .
Honestly, opinions regarding the the DS180 being less than suitable surprised us - but - it's what we've learned. Facts 'can' be inconvenient and hiding from them doesn't help anybody. I asked, they shared their opinions and I am sharing what I've learned. In short, half the pilots who got DS180 wish they had gotten something more powerful. And note; we don't interpret this information as a knock against the DS180. Instead, we view it more as a reflection of how guys are actually flying the 30cc Ultra Stick, e.g. they're flogging it pretty darned hard.
And this brings us to the other half of our Ultra Stick 30cc customers, those whom almost to a man opted for the
DS360DLHV - although one customer, noting he had more money than God,
outfitted his with one of our top-of-the-range all-alloy brushless servos - yikes! Plus there are a small handful of folks who selected our DS385CLHV (the similar torque but tremendously faster model equipped with an all-steel gear train). Anyway, these were folks who had in mind pretty aggressive flying if not real-3D from the get go, and they report being satisfied with the the DS360DLHV as well as the DS385CLHV (or at least, nobody complained). Moreover, virtually all of them (I actually believe 'all' but I'm hedging), said this the DS360 servo is what they would recommend to a friend. Note, I only heard back from one DS385CLHV owner, and while obviously pleased, we went off on a tangent regarding an Extreme Flight 85" Extra before we could discuss his Stick. For the curious, he was trying to decide between the DS385CLHV and the pricier DS555BLHV (both with all-steel gear trains) and he opted for the DS385CLHV, once again. Note, however, you pay a pretty good price for all-steel gears and more speed.
Furthermore, it's my suspicion the folks praising the DS360 were perhaps enjoying not just the 2X torque advantage over the DS180 but probably more so, the added speed this servo offers. Regarding the DS385CLHV, it's my opinion selecting it has more to do with speed being as that's the very first thing hard flying pilots comment on regarding similar torque servos (the DS385 is quite a bit bit faster than the DS360) so it's conceivable I'm all wet about this and it's all down to more torque.
Also, it's worth noting we offer the DS270DLHV, which is faster than the DS360 by a little bit but also less powerful. One or two outfitted their models with this servo and reported being quite pleased although one of them said if he had to do it again he'd pony up the extra dough for the DS360 leading me again to suspect this large model loves torquey servos.
To summarize, the harder you're going to fly, the more torque you should plan on throwing at the problem. We've learned half those using the DS180 wish they'd gotten something more powerful. And pilots who got the DS360 instead, were to a man, happy. So in closing (and yes, I know this isn't the hard and fast answer some may have been hoping I'd have), but the answer to which servo is most appropriate for the 30cc Ultra stick when equipped with the more powerful 35cc engine is . . . it depends. And bear in mind, a lot of guys use an even more powerful engine than called for, often a 50cc (and the DA-35 may well be as powerful as some 50cc engines). Thus, just like you can't have too much horsepower, sometimes overkill is called for in the servo department, also!
John Beech - GM (and janitor)
PS, please note an important consideration is the voltage delivered to the servo after the extensions because this hugely affects actual torque at the control surface. Basically, all servos (all brands, 'not' just ours) deliver less torque on less voltage. That, and extensions can knock 1/2 volt off, easily. Also, you must account for the starting voltage, e.g. the battery chemistry, because a 2S LiPo delivers 7.4V nominal, a 2S LiIon gives you a bit less at 7.2V nominal, while a 2S LiFe is rated nominally at 6.6V, and thus, all things being equal, results in the least amount of servo-torque of the three pack chemistries. Anyway, there are askJohn articles delving into both of these topics for those curious to know more.