Nose pitch's up

[Chris Puckett]

I should have said that I only experienced this during landing. Not something I ever noticed in flight with throttle changes.

[jack01]

This may be a little repetitive, but here's how I trim out a new airplane:

First off, you have to remember that in aerodynamics everything is a balancing act. There is no free lunch. Weight balances lift, thrust balances drag, and so forth. When you change one, you directly affect another and indirectly affect something else. One apparent problem can actually be something else all together. When trimming an airplane, you've got to remember that it will likely take several flights and some trial and error to get it dialed in. Even after that, you'll probably be tweaking it for a while. Remember, if you make a change in any of the below steps, start over from #2.

1. Set all of the incidences per the manual. On most monowing giant scale airplanes, this will mean everything is set to zero. Typically, the top of the motor box is leveled, and then everything else is leveled based on that. Right thrust is typically 2.5 degrees.

2. Take off, and trim the airplane for straight and level at 50% throttle. Wind makes this tricky, so if it's windy/bumpy, try to pull an average.

3. Roll the airplane inverted with the throttle still at 50%. It should dive slightly. By slightly, I mean you shouldn't be able to fly an entire upwind/downwind leg without a noticeable pitch change, but it shouldn't try to do a loop either... 2-3 clicks of down elevator trim should make it fly level. If it stays level or climbs, you're tailheavy and vice versa.

4. Roll upright. Then pull the throttle to idle, and watch what happens. If it dives immediately, you probably have too much upthrust. If it climbs, you probably have too much downthrust. Just make sure to quickly figure out what it's doing, because after the speed changes much, you're looking at a CG issue rather than a thrust one. That's why noseheavy airplanes dive on landing, and tailheavy airplanes balloon.

5. If you've trimmed the airplane properly so far, you should be very close to where you need to be. Everything else is fine tuning. Try some downlines and see what it does. 90 and 45 degree downlines are pretty good at showing CG issues. If it pitches up, you've got some uptrim to compensate for being noseheavy. If it pitches down, you've got downtrim because it's tailheavy.

6. Now try some uplines. You should try these from a full throttle pass and a smooth, but firm, pull. Make sure you are truly wings level when you pull. Watch what the airplane does after pitching up to 90 degrees. From here, you should be able to fine tune your thrust line. If you find yourself doing a lot of IMAC style flying with multiple vertical snaps, your speed will probably try to bleed off during the upline. In that case, you may need more right thrust than normal. Just remember, as your speed builds again, the plane will now try to go right.


If you need to change your thrustline just a little bit, I usually use washers made out of Coke cans. For example, if you need downthrust and rightthrust, add two washers behind the mounting lug on the top left, and one washer each on the top right and bottom left. That will make sure the engine is making even contact all the way around.


Remember, a properly designed, built, and trimmed airplane requires very few if any mixes. It's like a computer radio. If you took the time to properly setup your servos mechanically, your subtrims and travel adjustments should all be pretty darn close to even. IMHO, all the mixes in the world are no substitute for learning how to fly the airplane.

[cjcyclesrc]

Good Info Jack.



On the CG topic, I have found a Yak to fly straight and level inverted with a neutral CG. I'm guessing it's due to the symmetry to the airframe. Other airframes require a slight push inverted.

[Tired Old Man]

Pitching up on landing is when most will immediately notice a down thrust issue. A little bit too much either way can be hard to see higher up. Cut the throttle, pitch up, add throttle and pitch down. Makes for some interesting landings. Good way to have a prop strike or two. Balance is exibited more with changes in elevator deflections. Tail heavy and each change is more than the last. Nose heavy and you can't hold the nose up for the flair as well as you think it could. Also makes for long low level flight just above the runway trying to bleed off speed for the touchdown.

[Edgeman 540]

Thanks guys for taking the time to share all of this info. We still have 15mph winds here so the next day that it's more calm I'll be taking it out.
I'll post here what fixes the problem.

[scott m lyons]

	Quote: Originally Posted by Tired Old Man
	Pitching up on landing is when most will immediately notice a down thrust issue. A little bit too much either way can be hard to see higher up. Cut the throttle, pitch up, add throttle and pitch down. Makes for some interesting landings. Good way to have a prop strike or two. Balance is exibited more with changes in elevator deflections. Tail heavy and each change is more than the last. Nose heavy and you can't hold the nose up for the falir as well as you think it could. Also makes for long low level flight just above the runway trying to bleed off speed for the touchdown.

See the last sentance that is the 40%.Hows the hatch does it fit?

[Edgeman 540]

	Quote: Originally Posted by scott m lyons
	See the last sentance that is the 40%.Hows the hatch does it fit?

The hatch fits good just like the original.

[Edgeman 540]

Gentleman the weather was permitting do do some accurate testing today and I found out like many of you said it needed more up thrust.Along with that I also found that it was a touch too tail heavy.I also fine tuned the throttle curve and now it fly's like a totally different airplane.These changes also dramatically helped finding the sweet spot for torque rolling.
Thanks for all the pointers.
Chris

[Oilsands]

Thanks for letting us know. Glad you got it working for you and are very happy with it. I have the 36% PAU Edge and I really enjoy flying it around. Also had their Ultimate, which was fun to fly as well (till it met the trees).

[rc4flying]

	Quote: Originally Posted by Edgeman 540
	Gentleman the weather was permitting do do some accurate testing today and I found out like many of you said it needed more up thrust.Along with that I also found that it was a touch too tail heavy.I also fine tuned the throttle curve and now it fly's like a totally different airplane.These changes also dramatically helped finding the sweet spot for torque rolling. Thanks for all the pointers. Chris

Glad to see you have solved your problem. Nothing like flying a plane that does not fight the pilot.

[littlecrankshaft]

Some very good info in this thread.

I would just like to add a few things to I have learned for consideration as well.

First off, most of the time when we talk about CG it is usually in relation to some specified fore or aft distance from the wings leading edge or some other similar point of reference. The actual CG is a point within the aircraft that would allow the airframe to balance similarly as a propeller would balance on prop balancer…i.e. in any position from which suspended, it would stay put…

Secondly, thrust line can have its own effects during power applications. A high thrust line designed plane, such as the PAU Edge will tend to act more nose heavy under pull and more tail heavy under the brake of the prop.

With all that in mind, consider that airplanes with a lower (as opposed to fore and aft) center of gravity and a high thrust line will have a greater tendency to pitch up under the prop braking when the throttle is reduced…especially if power is suddenly reduced.

Now, two things can be done to reduce this undesirable effect. Put more of the mass higher (to raise the CG) in the airframe and/or use a prop with less braking action and of course, reduce power slower.

Of course, moving the CG forward will also help reduce or cover up the symptom but an overall CG (fore, aft, high, low) along with best prop choice and power application will pay the biggest dividends.

BTW I have found a small amount of up thrust in high thrust line airframes is also a benefit but anything over 1 degree is probably to much for this Edge.

Anyway, good luck and blue skies to you.

[Edgeman 540]

That was some great additional info.It sounds like you've had some experience with the Edge.As of right now I'm very happy with the flight characteristics but I may try to tweak it a little more.

[notorious_benny]

I am just a 'no name' unlimited flier but heres the technique I use to set up my models for precision flight.
The order you do things is very important, you need to follow the sequence logically........

Just chucking mixes in is masking a problem not fixing it. I have never had to use a downline mix..........

Anyway heres how I do it.

http://www.flyinggiants.com/forums/f...tml#post172774