eFlite Grasshopper Servo Question

[pesmarker]

Hi all,

I am new to fixed wing aircraft. I ordered this model because a slow flyer seemed like a reasonable place to start learning to fly outside with limited space. Plus I already had most of the electronic hardware to complete the build.

However, I have a question about the servos. The manual specifies four SPMDSP60J servos. I already have two of the SP60's and a pair of SPMDSP75 servos. The SP75 servos are a little more powerful/faster. The sizes are identical. The weight on the 75's are a a few ounces more, so rather than buying more partrs, I plan to use thes 75's as one set and the 60's as the other.

My question is what makes more sense, assign the stronger faster servos to the wings on the ailerons or to the tail for the elevators and rudder? I don't know which area would benefit from more headroom.

Does anyone know if either the wings (ailerons), or tail (elevators and rudder) receive greater load (read stress) than the other? If surface area is the deciding factor, then the ailerons would get the SP75 servos

I'd like to starts assembling this plane over the next few nights.

Thanks

pesmarker

[max2112]

pesmaker,

I've always thought of it like this:
The elevator is the most important control surface and should have the strongest and most reliable servo. If one aeleron goes out, the other will still provide some roll control. If the rudder goes out, you can still fly and land. If the elevator goes out there is not much you can do.

For left/right balance the aeleron servos should be the same.

I'd put the 75's on the tail.

[pesmarker]

Thanks seems like a reasonable solution. Besides I realized on my third work tired read through the manual, that all four servos mount in roughly the same location in the cockpit so weight distribution for Ctr of gravity is mute. I'll try the 75's in the tail.

pesmarker

[quorneng]

The elevator is undoubtedly the most critical control but the eflight Grasshopper is not exactly large or heavy so even the original servos are unlikely to be be needed for the aerodynamic loads although the friction of the linkage and hinges may be significant. I am sure a more powerful servo will make no difference apart from its extra weight.

With very free running servo links and hinges I fly planes very successfully that are twice the weight, size and power of the Grasshopper but using even smaller 3.7g servos.

[Wrongway-Feldman]

I just finished building this ARF myself. I also had two different sizes of servos available for the build.
Unless you want to do some alterations to the servo mounts in the fuselage I would recommend putting the larger two servos in the wings.
There is much more room to mount them in the wing and you won't have to do any alterations to make them fit.

[pesmarker]

The servos are identical in size and only a few grams heavier in weight. The set of 75's is a little faster and delivers a bit more torque.

So my real question is: Woul either the ailerons as a pair, or, the elevators and rudder in the tail be a more advantageous position to assign the more powerful servos.

I'm starting to think since the aileron servos are running in parallel off one channel on the receiver, that position electronically makes the most sense for the factory spec servos and use the above spec 75's in the tail where each would be on its own channel

[HobbyJumper]

I have that plane and it is so light and small that I can't see it making the slightest difference. The servo load is miniscule.

I agree with Feldman about space being an issue -- there isn't much room in the cockpit, so that might be a factor. Not sure what you mean by, "all four servos mount in roughly the same location in the cockpit"

By the way, that plane is not a slow-flyer. With a flat wing it requires a bit of speed to maneuver -- and in a breeze it's a handful. The faster you fly it, the less it wobbles. Even HH calls it an intermediate plane. Maybe because it breaks very easily, so be careful.

[pesmarker]

Thanks,

The dealer's tech support said put the hotter servos in the tail because the elevators and rudder are the two most critical controls.

So based on what max2112 said, which matched th e dealer, my gut sense of what loading issues may exist in a parallel circuit (read the ailerons Y connector), and not wanting to show the receiver something it may not expect. After all Spektrum and eFlite are both Horizon products. I won't test fate.

The 75's go to the tail and the stock servos go to the ailerons.

PS: I know that aircraft is feather weight and low power. It is a no breeze at all or fly in a gymnasium plane. It is for all intents and purposes a 250 class single rotor Heli ins the sense it has the capability of going fast and doing all the moves.... But it can't tolerate much in terms of outside interference. And when it crashes becase it is far from robust.... Expect significant damage.

This is why I went to 50 and 90 size Helis. They are large enough to resist a bit of mother nature, while being strong enough to survive minor unscheduled landings with only marginal casualties

pesmarker

[HobbyJumper]

One last note: My L4 flies a lot better now that I have removed the Eflite outrunner 250 and replaced it with a HURC 2712-15 Outrunner from Headsup.

ps: Might be a HURC 2712-17. I would need to check.

[Big Johnny]

I agree with Quorneng. Smooth bindfree controls are the ticket. I spend extra time to make sure I don't have any binding linkages. One thing I also do is make sure that the control wire is up to the job. I have seen many ARF Balsa and Foam with to wimpy of wire. All is good when tension is applied, but thingsget flakey when the wire is subjected to compression. It bends when trying to overcome wind resistance. Even on my small foamys I use 2-56 size hardware and anything over 4 pounds gets 4-40 hardware. I am willing to accept the weight penalty for piece of mind, knowing the linkages will do their job properly. On a typical 480 side plane we are only talking at most a ounce difference.

[pesmarker]

Most interesting.

The more I read the more it starts to read like what I know from single rotor .50 and .90 class Helis.

Thanks

pesmarker