3D Joy

I am doing intermediate sequence this year and I have a problem with my new airplane, a CAP 232 25%.

The snap roll in the goldfish goes correctly but as soon as I do my reverse half roll, on the 45 deg upline, the aircraft pitches down to the belly very much . In other words, the aircraft climbs on an inverted 45 deg upline .

The first thing I did is check my CG. When going full throttle on level flight, I chop the throttle instantly, and see what appens. The aircraft instantly pitches up SLIGHTLY and then stays SLIGHTLY nose up for a good moment (5 to 8 seconds). It made me think my CG is a tad on the aft side.

Am I correct saying this

Any help would be greatfull.
Could this also be a thrustline issue ??

Flyfalcons

My plane does the same thing on this maneuver. It doesn't pitch to the belly very hard but if I push at all it will pitch too much. It might be a function of having a little too much down thrust, but the plane feels good during other maneuvers so I'm just living with it for now.

Rcpilot

My Feedback: (78)

If it's climbing when your inverted on a 45 degree upline-- then you might be tail-heavy.

Is your elevator a bit sensitive on landings? It might be hard to tell if your using any exponential.

Try these steps to check your plane out. This is pretty much straight from a handout that I got from the guys at Aeroworks. I edited it for length and clarity.

For balance:

Full throttle flat and level. Pull to a 45 degree upline and roll inverted. Plane should continue up at a 45 degree incline. If it starts to drop the nose, then you are still nose heavy. If the nose goes up and the tail drops, then your tail heavy.

When adjusting the engine thrust, there are a few different methods. I usually try both and come too a happy medium.

For engine thrust:

Come in about half throttle- flat and level
pull straight vertical and wait for it to ALMOST stop
Slam the throttle full open and then close it quickly
Do it again
Slam it full throttle and then close it quickly

If your plane torques too the left more than you'd like, then add right thrust. If it's gonna torque left; then it will happen when you slam it full throttle when vertical.

If it doesn't torque left, then your probably fine.

Checking for proper up or down thrust is a bit more fun.

Come in flat and level- about 1/2 throttle
pull straight vertical
go Full throttle when perfectly vertical
LET GO OF THE ELEVATOR!!!!!!!!

Watch it and see if the nose comes back onto the top or if it goes towards the belly of the plane.

If your nose comes towards the top of the plane and you need to add down elevator to keep it vertical, then you need more DOWN thrust.

If the nose falls towards the belly and you need UP elevator to keep it vertical, then you need more up thrust.

The other way; I usually do the next method after the vertical test

Take it up HIGH.

Start out HIGH-200' or 300'- whatever you consider high
full throttle and flat and level
shut the throttle quickly and let it glide
DO NOT TOUCH THE ELEVATOR
watch it and look to see if it falls quickly

Your plane should glide reasonably well. If it is nose heavy, then it will come down fast and accelerate at an idle.

Keep in mind that aerobatic planes don't really glide very far, but most; if properly built and have reasonable wing loading, will glide for awhile. Any plane that drops like a rock after shutting the throttle is most likely, too nose heavy, has improper engine thrust or has DRASTICALLY high wing loading.

Check your incidence. Incidence meters are great. I use them on every plane I build. But there's no substitute for checking the plane in flight after setting it according to plans.

To check wing incidence:

Take it up REALLY REALLY HIGH- at least 300'
flat and level
1/2 throttle
close the throttle down to a nice idle
put the plane into a VERTICAL dive at idle
TOTALLY VERTICAL
LET GO OF THE ELEVATOR
watch it
pull out and throttle up before you get too close for comfort

What your watching for is to see what the plane does in a totally vertical position at an idle. You must do this Vertical, with the nose pointed DOWN at the ground. Thats why I say- start out HIGH.

If, when vertical, the plane comes down and pulls out to level flight. Then your wing incidence may be positive too much. On a plane that calls for ZERO incidence on all surfaces-(wing, stab and engine), it should come straight down.

Some might just come up towards the top and creep towards level. That might be fine. Depends on the plane.

If, when vertical, your plane tucks towards the belly and starts too pull out and go inverted, then your maybe a little on the negative side of the incidence.

Now for my disclaimer: I'm no genius. I read all this stuff in books and heard it from other more experienced pilots than myself. I do each and every one of these tests on all my planes now. Yes, I spend almost a gallon of fuel doing all these tests again and again. Each time; landing and adjusting. Then going through the test again. Sometimes I spend MORE than a galloon of fuel to get a plane right where I like it, but in the end, its money and time well spent.

I only try and adjust one thing at a time. One day I will take a new plane out and only work on engine thrust. Next time I take that plane out to the field, I will only work on balance or wing incidence. The point is; only adjust one thing at a time. And above all BE PATIENT!! (thats the hardest one for me)

Sometimes, you might think you have the engine down thrust right where it should be, then you go and start checking the incidence, and you wind up going back and changing the thrust again to make up for an adjustment that you made to the wing.

It sounds like your just a bit tail-heavy to me.

3D Joy

I just made some flight testing to see what is wrong. Results of this flight testing goes like this:

-I slightly advanced the CG
-I added some up thrust
-I sealed the elevators

I made all those changes at the same time, as was not recommended above, I don't know what really helped. I may suspect sealing the gaps helped somewhat since gaps were rather large due to 3D movements and big robart hinges.

I have now readjusted all my knife edge mixes since they were off due to those changes.

I still have some down pitching when I roll inverted. It seems to be worse when, just after the snap (still talking about the goldfish) I roll inverted full throttle but with low speed. This leads me to think I should add more up thrust. Is that possible ???

Thanks

v-snap

My Feedback: (18)

To check up or down thrust fly level at 75% or more power, pull power to idle. If plane pitches up (climbs) you need up thrust, if it starts a nice descent then it is o.k., if it pitches abruptly down then it needs down thrust.

Works for my planes every time.

V-Snap