A lot of gas/balsa designs are older and that was standard back in the day.
Lots goes into consideration of size, more than I fully understand but while a 50 might not be necessary I'd sure never use a 9 on anything with an engine other than 1/2a.
I'm sure vibration factors in but with speed comes back pressure on control surfaces.
My go-to throttle servo is the venerable plastic geared Flite Test 9-gram servo. No reason to use anything fancy or heavy to open a nitro carb. The vibration doesn't harm them one iota.
Big planes need big servos.
Smaller planes need smaller servos.
Tiny planes need tiny servos.
Different parts of the airplane require different servo specs. A nitro carb barrel is fine on a 9-gram servo whether you're opening the carb of an Enya 09 IV or a Super Tiger G3250. You'd want different servos on the flight controls between the airplanes carrying those two engines, but as far as opening the carb is concerned, a standard little 8 dollar plastic geared Flite Test 9-gram is more than enough. Hell you could use a FT 5-gram if you wanted to really pinch grams.
My big servos from the 1970s were made from discrete transistors instead of chips like today. My servos from the '60s had just a motor, switches, gears and a couple wires, were 4 times bigger and heavier. Planes were sized accordingly which isn't needed today. My 9 gram servos have more speed and power than a "steering" servo from that era and will pull the hinges out if the throws aren't set correct.
is right, heed his advise, BUT YMMV
I've seen that with my VK Cherokee 60. That thing was designed so far back in the past that RC itself was in its infancy and is set up for reed radios. I'm putting a handful of modern servos in it instead...three Futaba S3004s for flight controls and an FT 9-gram for throttling the Super Tiger G60-16 up front...and it's astonishing how much empty space there is in the cabin of that thing! And of course the servos I'm putting in it outperform what was available in the early 1960s by orders of magnitude...
I don`t think I would want to put in a 9 gram servo featuring 16.6 ounces of torque into a .40 size glow plane. When you consider weight and size of the control surface and the very small drive train, nope nada ain`t going to happen..
When the rudder on my bashed 17 NGH gasser 3D Ugly Stick in knife edge would stall my HT-475HB servo in a high speed knife edge at 76 oz of torque bigger to a point is better. I know it was not linkage as it would stall in both directions if I slowed down it was fine.
I do it all the time, but I don't do it on flight surfaces. I use the right size servo for the right job; on my 40-size ships I use something like a Futaba 3004 or U-400 for flight surfaces but if the task is simply opening the carb of a Magnum 52 4-stroke or an OS 46ax or something? Yeah a FT 9-gram is perfectly fine for that and is what I use. Don't need to throw 50 grams of servo in to do the job 8 grams of servo will do.
Hell, I ever get an airframe for my Super Tiger G3250, I'll have a humble Flite Test 9-gram plastic-gear servo on the throttle of a 32cc giant-scale bird!
That may be a huge engine, but it's still a nitro engine, and the perry carb on it requires little more than a gnat's fart to open and close. So again, no reason to use 50 grams of servo for an 8 gram job.
Thanks guys. I should be more specific. Im more curious about the vibration than the torque. The throttle for example needs almost no torque at all but on the used planes I bought it has the same servos. I get that its not worth taking a risk with a tiny servo on a throttle, but Im just curious if small ones from electric planes would fail immediatly from the vibration of a glow engine.
It works fine. It's what I do on ALL of my planes. I fly exclusively nitro and I've never had any issues with using plastic gear FT 9-grams as throttle servos. I even had one survive a crash that destroyed everything forward of the rear headrest except the engine itself! Bent the 2-56 pushrod into a prezel, ripped the servo off the fuse wall, but that little trooper still works without flaw.
I don't take any steps to vibe damp them, either. I usually just remove the stickers, sand the side of the servo rough, then CA it right to the balsa somewhere close to the carb.
Those little servos are absolute tanks and are ideal for opening and closing nitro carbs. No need to spend money and weight on a 50 gram standard servo to do a job an 8 gram servo can do just fine.
Of course, I also only use known to be reliable servos. FT/EMax, Futaba, etc. You get those 2.99 Wish.com specials, buy one of those unknown Amazon brands, whatever? You're on your own. I wouldn't trust those things to run the needles on a gauge in an FPV model's scale cockpit, nevermind anything important. When a genuine Emax/Flite Test 9-gram servo is only 8 bucks, when a genuine Futaba S3004 is only 14 bucks, I really don't see any reason what-so-ever to cheap out on servos. I still fly S3003s/4s that are older than I am!