orthobird

My Feedback: (1)

hi, i have a GP revolver 70 with a saito 4 stroke 125 a. i have a question for you all: iflew the revolver again today, did much better than last week. when i fly upright, i have trimmed plane so that it flies level. this required some down elevator, this trim was done on maiden flight, yet i still remember this. today, plane was flying level, however, when i get plane inverted flight, it requires significant "down elevator" to prevent planes nose from pitching down. any suggestions?

fun2fly24

when flying inverted you always need down elevator...thts just how it is. if you look at any pilot he uses down elevator when inverted. the only thing i can thing of to make it "EASY" would be to make a mix into your transmitter so that when your inverted and flick a switch it gives it down elevator by itself but everyone mostly just uses there down elevator.

BMatthews

Just because the elevator has a little down trim it does not mean that the overall stabilizer and elevator together have a positive angle of attack when flying upright.

What you describe is exactly how a model with some positive pitch stability should behave. It indicates that the stabilizer and elevator as a whole is slightly negative with respect to the wing. And the model is happy with that setup in upright flight because of where your balance point is located.

As you move the balance back and then re-trim for level flight you'll find that the model becomes less pitch stable and closer to being neutrally stable. As it approaches neutral stability you'll need less and less "down" to hold the model in level inverted flight. But as you approach that state of trim you'll find you need to fly the model more for elevator inputs than currently where it seeks its level flight trim speed on its own.

orthobird

My Feedback: (1)

thanks, that is what i thought, the cg does have something to do with it. on this date of flying, i flew this revolver, my gp 1/3 scale cap, and the yak by gp. the GP matt chapman eagle cap, would require minimal "down" elevator with inverted flight, and thus, i would fly plane by at low altitude and then roll it inverted with minimal drop in altitude, and still keeping it straight, however, with the revolver, no way that was going to happen. i tried it 1st at 3 mistakes high, and thank god for that, since the plane dropped down to about 1 mistake high, ouch, lol

karolh

When rolling into an inverted position and wanting to maintain level flight one should always be on the ready to input some down elevator just in case.

Karol

da Rock

Have you had a chance to move the CG since that revealing test?

The Revolver can be a very steady airplane. The ones I've maidened for friends have all been rock solid and went where they were pointed. I usually do a dive test to get an idea how much pitch stability they have. They all recover slowly, suggesting they are closer to neutral than nose heavy. None of them so far has required excessive elevator to fly inverted.

The real reason I'm posting however, is to ask about your Revolver's landings. The ones I've flown all have a strong tendency to bounce as soon as the wheels hit. They had to be greased in to keep from porpoising. My opinion is that eventhough they swept the gear legs back, it wasn't enough for the CG location that works best in the air. Your CG sounds like it's pretty far forward, which should suit the wheel positioning better. How does she act when the tires touch?

AA5BY

You might verify that both ailerons are trimmed properly, that both are not down a little or up a little.

orthobird

My Feedback: (1)

well, unfortunately, i fly in a farm field, and there is a cropduster there, and his runway is about 8 feet wide, so tough to practice landing there. i will take off from paved area, but always land on the cut grass area. i have not seen this plane bounce. i have an electric extra 300, small plane, goes very fast, and i have been able to do touch and gos on the paved runway, but i have not tried doing this yet with the revolver.

orthobird

My Feedback: (1)

thank you for comment. yes, i do this, but i am not used to her "attitude" just yet. just got to keep flying her. i will move the cg back, as you all have mentioned, i really believe this has something to do with it as well.

wingster

My Feedback: (26)

If your holding significant down elevator for level flight, move the cg back until your comfortable. This will require more down elevator in order to trim for level flight. Since the elevator already has down elevator you are left with changing the stab or wing incidence. If people are complaining the airplane wants to lift off on landing(as in post#6) I would suspect the wing incidence is too positive.

If you can, try raising the wing trailing edge.

eroc144

My Feedback: (1)

Rock - My Lanier Extra lands that way. I have to fly every landing all the way in and can't relax until until the tail drops. I've contemplated moving the wheels further forward from the CG, but if I understand your post correctly you're saying that moving them closer together would solve this. Why?

EG

da Rock

For the same reason the Original Thread Poster experiences a significant difference in elevator position from upright flight to inverted, the CG position. EXCEPT the bouncing I've seen every Revolver do is caused by the CG being too far back instead of too far forward. I asked him about the bouncing to see if it was not present for a reason. If his didn't bounce, it would suggest it really was forward and was actually curing one problem while causing another. anyway.........

Conventionally geared aircraft designers over the years have proven again and again it's best to have the tires contact the ground at an angle forward of the CG. (we could stop right there and say.... duh) Everyone knows that, but in fact, designers also have figured out how far forward that should be.

Designers have worked it out that an angle of 15-20 degrees works best. The angle is measured with the CL of the plane parallel to the ground. It's very close to the attitude of the plane as it touches down on the mains when flying the plane into a landing on the mains. On that type of landing, when the wheels touch if the plane has a fair angle of descent, what happens? The wheels run into an immovable object (the world). However, the mass of the plane that's on that angle of descent keeps going. If the mass of the plane exerts it's forces from the CG and it's behind where the wheels have hit the ground, the wheels will only stop the front of the plane from continuing down. The CG is going to continue on down because it's not directly over the wheels. The rear of the plane is one end of a see-saw. The wheels are the middle of the see-saw. The see-saw does what when only one kid is on one end of it? The end with the kid (or the CG) bangs into the ground. Unfortunately, our plane isn't a see-saw, firmly planted in the ground. It's actually still flying down the runway and the wing often hasn't stopped flying. Tail goes down, wing's still flying. Wing suddenly is driven into a climb AOA, and boing....

Designers found that when the CG is at 15-20 degrees to the tires' footprints, it'll also be where it should be for flying balance. They have to design the gear to be in the right place, and usually do it after they figure out where the CG is going to be for good flying characteristics. With models, it doesn't always happen that way.

AA5BY

Adding slightly to what da Rock says about the mains position... in my experience, the more lift the wing has, the more critical the gear position.

I designed and built a plane last winter having 96 inches of span on a 35cc size plane. It porpoised on landings and lifted off before the tail would come up. Adjusting the gear position aft solved both issues.

Ben Lanterman

I haven't ventured to this forum too often in the last few years - too much disinformation and stubbornness gives me migraines. But the inverted switch gave me pause.

When the very first proportional radios came out - 4 channel, nothing else - I thought an inverted switch (button in my case) might be a good idea. So I installed one and it worked beautifully. Once the appropriate trimmer was set a person could just push it when the airplane was in the 90 degree position and when he was inverted the airplane would stay perfectly level. All maneuvers could be done from an inverted standpoint and you never noticed it. Only when finally rolling upright would I release the button.

As I got more exotic radios I didn't want to cut into them and then later on my skills got to the point that I didn't notice holding the small amount of down.

I might try it again!

Ben