Rudder reactions

[JimC-MD]

I have a new plane that I am working on trimming out and would like to ask for some advice. I have a GP Cap 232 with a DA50 that I have been putting some time into trimming out. Most times this plane only sees 50% throttle or less as it came out at 13 pounds 9 ounces. I have not had many oportunities at calm day flights to be 100% sure of all the trims and thrust angles, but I have started to make some adjustments. The plane appears to be drawing nice verticle lines, flies inverted with nothing but a thought of down elevator and holds great 45's even with a half roll. I know Caps will have more reaction to rudder input than most Extra designs (this is my first Cap in 22 years of flying). What I have noticed is that I have mixed in 20% up elevator to the rudder in both directions to start to correct for a serious belly pitch in knife edge. This number is close as I can "fly through" the rest of the corrections for now.

What I am wondering is if I may have missed another issue to this point that I should go back and correct before moving forward with program changes.

I am an automotive technician that specializes in diagnostics and I like to use sound methods to approach problems. I have been able to trim out most planes with little trouble. Please understand that this plane flies very well. I just want to be sure I am taking the correct steps to optimize this airframe. I plan on flying some basic with it next year to get a taste and see if I get hooked again. I am more used to the Extra platforms. Any thoughts are appreciated and thanks in advance.

[crazyextra]

I've never flown a Cap but I do hear that they have some coupling issues with the high horizontal stab and low wing, nothing you can do about that, just try your best to mix it out. Also make sure to check your centre of gravity.

How about all you other Cap flyers out there, any thoughts?

[BDSBob]

Here is the trim chart off the NSRCA web site. There is a section on Knife Edge flight. I have a 40% CAP and I can tell you that moving the CG even just a little will affect the amount of mixing needed.

[AHP]

Check your thrustline; you may have too much downthrust. For what it's worth, my H9 33% Cap only required 5% rudder to elevator mix one way and 7% the other (I can't recall which side was which off hand). The coupling was minimal enough to fly through it but it's absolutely dialed in now. My 40% Carden Cap only needed 1% and 2%.

I thought GP moved the stab down from the scale location to prevent potential coupling?

[JimC-MD]

Thanks for the responses so far.

Crazyextra, the CG could be an issue. I will go back and start the trim procedure over again.

BDSBob, thanks for that trim chart. It is a little simpler than some that I have seen. I have used tips from others that worked well but always like to test out other methods. I appreciate the feedback on how sensative your cap was to CG changes.

AHP, I will run the thrustline checks again. I have had a real fun time getting flight time with this bird in calm air. I think every day I have been out has been gusty and variable. I am not good enough to convince myself it is not me instead of the air yet. I know I have the CG on the back half of the range (not the aft extreme but just aft of center) and that may be why I have a little more coupling than the reviews of the bird I have read. I tend to set up a little aft, I may need to rethink this or make it easily adjustable depending on my flight plan. The stab does appear to be lowered.

Again, like I said. I am in no way complaining about the plane. Everyone that has seen it fly is very impressed by the presentation and the flight envelope. It will all but stop in a light headwind, rock solid, walking speed landings. It does not fly heavy at all. It is not even close to being unpredictably snappy. In fact, I have yet to have it snap without my wanting to do so. I will make an effort to write up a little review when I have completed my setup.

[JoeAirPort]

I have the Kangke CAP232 74 inch and it required about 16% in the mix to fly perfectly straight without any elevator stick input.. CG is set for 3D.

It was also pulling to the belly.

[youngflyer]

jim do you fly at dc-rc?

[Pro1Foam]

Often refered to a SNAP 232's. I found out why and I am agreeing with that statment.

[Shawn Berkheimer]

Moving the CG forward will help reduce the amount of mixing required. This is an inherant trait of a Cap and has to do with the wing being down below the center of thrust. Othe manufactureres have figured out that most of these tendancies can be sorted out by lowering the engine and stab and then bringing up the wing slightly. Dihedral will also play a part in making the airplane more nuetral. Most of the GP airplanes I see look as if the designer felt it more nesesary to preserve the scale outline. Truth be known I would have to think that 1 out of 50 guys that buy that airplane is going to even notice the pitch coupling.

Shawn

[Jaybird]

thaflyer,

My cap was anything but snappy.(H9 33%) Anything will snap if it's a nose heavy overweight pig. Are you speaking from experience? I dont believe he was complaining about a snap.
And yes mine pulled a to the belly. My mixes were close to what AHP uses, 6 and 7% and I was on the tailheavy side. My cap had the stab in the scale position(high).
Brian

[JimC-MD]

	Quote: Originally Posted by youngflyer
	jim do you fly at dc-rc?

No, I have been thinking about a visit though. I fly at FMAC and have started to visit Pegasus in Hagerstown. I will probable join that club as well. I used to fly with Reston RC years ago. I do not think that club exists any more. Lost fields due to development. I was a store manager for Doug's Hobby Shop near Dulles airport in another age.

[JimC-MD]

	Quote: Originally Posted by Shawn Berkheimer
	Moving the CG forward will help reduce the amount of mixing required. This is an inherant trait of a Cap and has to do with the wing being down below the center of thrust. Othe manufactureres have figured out that most of these tendancies can be sorted out by lowering the engine and stab and then bringing up the wing slightly. Dihedral will also play a part in making the airplane more nuetral. Most of the GP airplanes I see look as if the designer felt it more nesesary to preserve the scale outline. Truth be known I would have to think that 1 out of 50 guys that buy that airplane is going to even notice the pitch coupling. Shawn

Hi Shawn,

I guess I am on of those 50. I think the CG is going to be a large factor in the issue. the thrust line is high, there is a touch of dihedral built in. The stab is a little lower. The plane flies like a kitten but has some coupling. The only thing that caught me a little (with altitude thankfully) was that you can get an inverted spin flat enough that is can hang on a little longer than you expect. Very workable and shifting the CG a little may take care of that. Most guys I fly with make planes nose heavy out of fear (IMO) and do not make efforts to put tanks on the CG etc. Then they fuss about the down elevator required inverted and cannot slow them up for a small field. Our runway is only about 75 by 150 useable. I usually onle need about a third of it. I purchased this plane as a compromise and a way to build my first gasser. I did not compromise on components though. 8411's and 8611's, 9303 radio, the DA50, airwild MLPs and pull pull and lots of other trick stuff. I did that with the idea of moving it all over to another bird in the future.

Jim

ps again, thank you all for the ideas and suggestions. I have really enjoyed finding and joining this site. I hope to be able to contribute more as time moves forward.