Servos For A 3D Gas Plane
 

Hi, I'm thinking of flying gas planes and was hoping for some advice on servo choice. I'm posting on this forum because I intend to fly 3D and from my limited nitro experience, I understand that 3D applications tend to be a little more demanding on the servos. The servos are proving to be the most costly part of "going gas" but I don't want to skimp and put a big gasser plane in the ground or worse, onto someone.

I've got a 25CC sized plane for various reasons including cost, ease of transport and local legislation.

First, do I need metal gear servos? Or will, for example, a Hitec HS-6975HB with Karbonite gears or a Futaba 9252 suffice?

How much torque I need off the servo? Will 6 kg/cm suffice? I'm guessing I need less for the ailerons and more for the rudder/elevator?

What should be the minimum transit speed I should consider? I just tried my first all digital setup on my glow plane and really dig the difference but I guess I can live with a little less performance for now. There are some pretty high torque analogue servos available at reasonable prices but the 60 degree times are around .24s or so. Too slow?

Thanks guys.

RE: Servos For A 3D Gas Plane
 

Hey,
First of all i dont think i've ever been the first to respond before...

Here are some guidelines for servos, i think they are the same for 26cc and 50cc

for all surfaces -
- Metal gears are crucial
- Transit time of less than .14, .12 or less is ideal
- At least 111 ounces of torque - (different for rudder)
- Digital for smooth movement, not a MUST but really nice

For Rudder
- Quick transit time - .12 or less
- Loads of torque 140oz +
- I like to use a high quality one here

Elevator
- Quick transit time - .12 or less
- Not TOO much torque, since each elevator has it's own in most cases... ohhh 120oz+
- I like to have digital servos here as well

Ailerons
- Transit time can be a little less, mine are like .15
- A little more torque than elevator, 3d planes generally have HUGE ailerons - 120oz+
- Speed isn't too important, but nice to have .15 or less

Throttle
- important, engine vibrates like mad, get a good servo here HS 81 MG i like

Things to remember
- 3D flying is all about rudder and elevator -- ailerons are used a lot but don't do the kinda of stuff the tail surfaces do
- Use quality servos -- metal gears are really good to have. I've come to find that most JR SPORT servos don't really cut it
- Gas engines vibrate tremendously, so i really really highly recommend metal gears
- Digital servos are really nice because they are really smooth
- Coreless servos are really nice for the same reason

Here is the setup i have on my funtana (comparable to a 26cc plane)

Rudder - Hitec 9525 - $100 / 131 oz torque / .1 transit time (i'm really skating on thin ice with that low torque, but i love the servo... It's a digital coreless, it's friggin smooth, and friggin fast, jesus christ it's nice

Elevator - Hitec 5625 - $55 / 130 oz torque / .12 transit

Ailerons - Hitec 5645 - $55 / 160 oz torque / .16 transit

Throttle - hitec 225

On my 46CC gasser i have JR 2721 coreless servos all the way around, they are so smooth it's sick

for FUTABA, a lot of people at my field use Futaba's 9451 series, good speed, okay torque, not sufficient for rudder though....

If cost is an issue, you can get Hitec's 625 servos, they are about 30 dollars and have good performance for the price, in fact, they meet all of the criteria i mentioned... A lot of people use them... My friend has them in his showtime 90, works great and more!

.2 or more transit time is too slow for 3d i think

That's all i got for now

hope this helps

Have FUN!

RE: Servos For A 3D Gas Plane
 

hitcttd has nailed most of the salient points but I'd add:

Run a 5-cell (6V) flight pack and you'll find that your servos are faster and stronger, you'll *really* notice the differnce. That extra cell makes more difference than going from analog to digital servos and it's a whole lot cheaper too :-)

Don't use Karbonite on a gaser -- overhyping this material was one of Hitec's biggest marketing stuff-ups and they're still unwilling to admit that they got it very wrong when they claimed it was suitable for large models -- it aint!

On larger planes the speed of the servos isn't quite as important as on small nitro models. Big models respond more slowly anyway (due to their greater mass) so, if you're on a budget you might want to consider the HS645 servos which are very strong and acceptably fast on 6V.

If you've got some money to burn, just use HS5955 servos on everything. These servos *rock*. They are digital and have titanium gears. They don't reach the claimed 300+oz/in of torque but they're still way stronger than you'll ever need on anything short of a 40% model.

A mid-priced option would be to use HS5625 servos on elevator and aileron with an HS5645 on rudder.

But, to give you an idea, my 30% Extra 330L has:

4x HS645 servos (analog metal-geared) on aileron (2 per wing)
2x HS5955 servos (digital titanium geared) on elevators (1 per half)
1x HS5955 servo (digital titanium geared) on rudder
1x HS425 (analog nylon-geared) on choke
1x WayPoint 1620 (analog nylon-geared) on throttle

They're all way-fast-enough on 6V.

RE: Servos For A 3D Gas Plane
 

XJet...your spot on with everything you said. Hitech 5955's are "rocketship" certified!

RE: Servos For A 3D Gas Plane
 

these are on my 27% and 33% planes

Hitec 5985's for the ailerons
Hitec 5955's for the elevators/rudder

On the ones with JR servos I have

8411's and 8611's

Stay away from JR sport servos for gas planes. They get sloppy quickly from large glow and a gasser with eat them alive quickly.

I tried the JRsport on the throttle of a 2.3M Comp-Arf Extra which promptly lasted 4 flights.

As far as determining what torque to use I always add 25% to what the plane calls for, I then find the closest match in metal gear and faster response on a 6volt system.

Most 25% planes will do fine on the Hitec 5985's with torque to spare and they are nice and fast.

Now on the opposite side of the Karbonite gear debate. I use the 6975 (I think that's the number) for most of my throttle servos since they are something like .08 or .10msec. They are Karbonite and have held up well

If you want use the Hitec 5955's use them as they are the servo to have, they will never get sloppy since they are titanium, all other metal geared servos eventually get sloppy which leads to all sorts of other problems

RE: Servos For A 3D Gas Plane
 

On my 2 50cc planes I have

5955's for all flight surfaces
5965 and 6965 for throttle..

RE: Servos For A 3D Gas Plane
 

Hey, good point about the thing about gas planes not moving fast... My extra handles considerably slower, than the funtana, it's still an insane thing to fly, but likes to do things at a slightly less "torrets syndrome speed" I was on a serious budget when building the funtana, otherwise i would've opted for the 59xx series as well.

One more thing I will add is this:

Hitec makes high quality, high performance servos, for a fraction of the price compared to Futaba and JR. Now Futaba and JR are great manufacturers, please don't knock on my door, but if you're on a budget and want goooood bang for your buck.. Hitec... The only reason I have the JR on my Extra, is because they were given to me...


Have fun with your 26cc gasser..

BTW i want that aeroworks 90 Yak now... now...

RE: Servos For A 3D Gas Plane
 

Wow, thanks so much the very useful info and the sample setups - its exactly what I was looking for. Guess there's no substitute for experience and it's good to be able to get help from guys who are actually doing it.

HITCTTD and XJET - your posts are going to be a standard reference for me as I go gas; wonder why such info is almost impossible to find on a google search as compared to the vast plethora of info available on nitro setups.

I guess all of you guys just saved me from a crash or three by warning me off about sticking nyon geared servos in a gas plane.

Was advised locally just to stick Hitec 645 MGs on the plane, but the transit times look a suspect to me. Then again, there aren't many 3D fliers I've met, whether on nitro or gas. Someone even *strongly* suggested I put JR DS 821s on the plane.

Anyhow, at the moment, I'm leaning towards the Hitec 925 and/or 945MGs. They do seem to provide the best bang for my servo dollar; I don't really want to skimp or to splurge, just want to put decent money down on a decent setup. I don't think I'm a good enough flier to deserve the titanium geared servos....

Thanks again so much guys for your interest, time and expertise. Its all very much appreciated.

RE: Servos For A 3D Gas Plane
 

titanium!! and why not go with a lipo for your RX with a regulator. a 26cc plane isnt that big you would probably be ok with karbonite gears i have them on a katana, and fast which is good when you get into the larger sizes its worth having good servos, its not worth saving to ultimately lose your plane or not be happy with it.

RE: Servos For A 3D Gas Plane
 

Thanks hobbydude, a lipo/regulator setup was already on the cards for the engine EI.

How many amps would I need for a 6 servo setup? Would 4 suffice? just a little concerned because all the high torque/possibly digital performance must draw mega current!

Was just gonna take the safe route and put in a high drain NiMh or plain vanilla NiCd receiver pack just for the reliability and peace of mind. But I'm open to suggestions..... Recharging every third flight can be a bummer! Actually, running a 4 cell high drain 1200 mAH NiMh and JR Sport digitals on my glow plane now, I recharge every 3rd flight with a field charger. Think things would only get worse on a high end servo setup.....

RE: Servos For A 3D Gas Plane
 

Was gonna put this in a separate post, but since there are a few pros on this thread already.....

How much AUW should a 26cc plane have for reasonable 3D performance? Put some numbers through a calculator and a 17 x 8 Menzs prop spinning at 7000 rpm puts out just under 12lbs of static thrust (with a air density of about 30mmHg). With smaller planes, I've always been told to try to shoot for a 1.5 power to weight ratio. I really don't think I can get my plane to have an AUW of 8lbs for a 1.5 power to weight ratio. Are my numbers off, or is a lower power to weight acceptable for 3ding with a gasser?

Planning to get the gasser up in about a month and half so I'm just starting to work through a long and growing list of queries and check points .....

Thanks.

RE: Servos For A 3D Gas Plane
 

It might have been better to put it in a separate post to get more responses.
See Quique Somenzini's report and flight video of his 73" Yak 54 powered by an Evolution 26cc Engine at
http://www.somenzini.com/html/aircraft/yak73report.html .
His plane weighs 11.75 pounds and does 3D very well even though the pull out from a hover is marginal with the standard Pitts style muffler.

My 76-inch Ultra RC Giles 202 weighs 11.5 pounds but has far better pullout with a piped MVVS 26cc (same engine as Evolution 26cc). The pipe makes a significant difference. My tachometer reads 8740 - 8800 RPM with the engine turning an APC 18x6w prop.

RE: Servos For A 3D Gas Plane
 

If you had money to burn you could go for the new JR DS8711s. :D

RE: Servos For A 3D Gas Plane
 

Hi Rocketman, thanks - the Quique interview was very informative and the flying was exceptional!

I know the first two replies have expressed an opinion on this already, but has anyone used nylon geared servos for the control surfaces? I have a set of brand new Futaba 9252 servos lying around. They are upper mid range digital coreless servos with a decent reputation with heli fliers. Having seen how the 90 sized 3D heli fliers absolutely torture their collective servos, I really can't imagine a gas plane doing worse except perhaps for the vibrations.

Thanks again.

RE: Servos For A 3D Gas Plane
 

Well, I took a second look at the Futaba 9252 specs and re-read the advice in this thread and I guess using them would really be skating on thin ice!

Scratch that idea then! I've just never had to spend so much on servos before, so its still something of a shock....