Jake Ruddy

My Feedback: (40)

Hey guys,

This is being discussed in another thread in the WHhhhh support forum... but I wanted to open it to a broader audience to get some input.

I have a new Cap that flys level with about 1/16" down if I measure at the counterbalances. Obviously this issue effects KE and every other move. The nice thing is if I mix rudder to el. back to neutral for KE it flys pretty well.. so I know when I get this issue fixed I will be a happy camper.

I have moved around the CG and I am now right in the middle of the range. Even with this much down needed to fly level right side up when I go inverted it requires more down then I expected to maintain level flight. Infact it requires more than I am used to for more planes. It also doesnt like to flatten out well in flat spins or waterfalls.. so it is def. nose heavy.

As it sits right thrust is off a bit but up thrust seems to be good... if I fly at half throttle and chop the throttle it flys straight for a bit and slowly starts to curve down like it should. If I jump on the throttle from half it goes forward and not up or down. First flight it ballooned up quiet a bit when I chopped the throttle so I believe I am pretty good right now.

The one thing to note is that because of the up / right thrust needed the engine is now 1/8" up and over to the right off center in the cowl. I need to move the engine down and over a bit o center it back in the cowl.

I have checked the incidence and it appears to be 0 - 0.5 and it should be 0 - 0. I was under the impression 0 - 0 to 0 -1 is acceptable?


Anyhow.. I am looking for suggestions on what is causing my issues.. I havent had a plane that needed this much work to get it to fly well. Don't get me wrong it's a sweet flying plane... but I want it flying sweeter

Rcpilot

My Feedback: (78)

Your stab and wing should be at zero.

Your engine thrust will have to be adjusted. It sounds like you have it okay for right now, but that will change if you end up adjusting the stab or wing incidence.

Is the stab glued on? Can you move the stab?

If the stab is solidly mounted or glued on--then your going to have to adjust the wing to match the stab. Only other way to adjust it is to rip the stab out and rework the stab saddle. With plug in wings and a tube, all you need to do is slot out the holes for the alignment dowels to allow movement in the wing incidence. Then get a piece of ply about 1" square and drill a hole in it for the dowel. Slap it on the dowel and set the wing incidence while the epoxy dries. I'll do that 10 times before I rip out a stab or cut open the tail just to adjust the stab incidence on an ARF. Hopefully, your stabs are at least matched to each other. If you got one stab higher or lower than the other, it really stinks.

Once the wings and stabs are matched to each other--your going to have to adjust that engine thrust again.

Good luck.

Jake Ruddy

My Feedback: (40)

thanks for the response...

I just had a chance to double check it and they are 0-0.. I thought they were off half of a degree but I just checked 3 times and def good on the incidence.

So that leaves CF and thrust... and CF is saying it's nose heavy. I did have it slightly tail heavy with a CF spinner on it for it's madain last month. Yesterday I went to an AL. spinner and made sure I was right in the middle of the range. Def. flys nose heavy.

SO I guess the real question is.. if my engine is slightly off center and a bit higher than it should be will that cause a plane to fly needing down EL?

Tired Old Man

My Feedback: (1)

Thrust line will effect the way the plane flys, absolutely. You want a plane that "falls" the same, or very close to it, inverted and right side up. I find that a zero engine thrust line works best for this.

Each trim function you change will have an effect on all the others. That's why I find the proper c/g for my type of flying before I try tweaking any mixes. Most planes have the c/g range set pretty conservatively by the manufacturer to make the planes as easy for anyone to fly as possible. A Cap is one that requires quite a bit of dialing in, regardless of the manufacturer. Try moving your c/g to the aft most suggested and go from there. Keep the control throws conservative for now.

Essentially move the C/G until the plane flys level without any trim input. That should be pretty close for the starting mix and trim point. If the controls are much too sensitive, then either dial the range of motion down or move the c/g forward again until the sensitivity becomes what you like. From level flight, both right side up and inverted, pull th power back to idle and see what the "fall" of the plane looks like as level flight speed bleeds off. How close are they to the same? If the inverted is substantially different for the upright, then you may need to adjust the thrust line. It's quite possible for a manufacturer to have built in an up or down condition by accident. Most all of them have right thrust built in. No big deal to correct.

Up, down, and side thrust effects the plane in different ways in different flight attitudes and speeds. That's why I prefer to use a zero thrust line in most cases and simply use my thumb for take off and landing to keep the plane straight. It's a lot easier to set trims and mixes if the engine is always a constant with the exception of torque and P factor from the propeller.

Jake Ruddy

My Feedback: (40)

Thanks for the input Silver... will get the engine back to center again for the 2nd time haha

mike gruenwald

the first thing to do before you do anything else, fing the mean aerodynamic chord. Then find out where your current balance point is based on the mean aerodynamic chord (from this point on I'll refer to the mean aerodynamic chord as mac) a good base point to start with is 28% back from the leading edge at the mac. If you cg is forward or behind this spot then change it and start over with the trimming process. The recomended cg on alot of airplanes is no where near the spot they need to be. as an example, a friend has a new 100cc krill katana which was balanced right on the spot on the plans. It flew very tail heavy, after doing the math I found it was balanced at 35.5% back at the mac. now the 28% number is not gospel, just a good starting point. for precision flight you probably won't have to move it very far, if you prefer 3-d you may end up moving it back to as far as 34%. As far as incidence goes I prefer to have the wing set at +.5 degrees. at that number I feel that the airplane has a better "locked in" feel and it usually helps with knife edge flight in decreasing the required elevator mixing. Sorry for the long post but I'm from the old days of radios with no mixing so to have a winning pattern airplane you had to figure out how to make it work without a computer radio, tiny changes in c.g.
tiny changes in wing incidence, sawing you foam wing in half at the field to change the dihedral for perfect knife edge etc. etc. Let me know if I can help out any further.

Jake Ruddy

My Feedback: (40)

Cool.. thanks for the input... I will get that figured out and go from there.

Tired Old Man

My Feedback: (1)

Mike,

You forgot raising and lowering the horizontal stabs. Then again, that prolly was included in the etc, etc. part.

I came from the same school. Nothing like the good ol' days, right

Geistware

My Feedback: (16)

From what you have stated, I don't see anything wrong with your engine thrust.
Try to fly at a climbing 45 degree line then roll inverted. It should hold that course.
Adjust your CG to hold that track. Up elevator with applied rudder is expected.
Mike McConville has written about using a throttle rudder mix to adjust for imperfections in right thrust.
He is best to talk on that subject. Get the plane to fly true with no mixes.
Once you have that, any bad tendencies can be mixed out. Pitch and roll with applied rudder is natural for most models and is easily mixed out.

mike gruenwald

I disagree, thrust is trimmed for a straight vertical line