RickP

My Feedback: (2)

Hello All,
I'm getting close on trimming this 2.6M Extra out. Now I'm to the point where I start up high and push the nose straight down. She pulls to the canopy pretty hard all by itself when it reaches the bottom.
Also, If I do a 1/8 cuban eight and omit the roll to right side up it will pull to almost straight down all by itself.
Motor thrust line looks good, straight and level full power and cut, she will climb ever so slightly. (I think I want the up thrust for 3D and not sure how much of a factor it really is at idle in the downline). Elevator was set to zero and I added only one click of down trim.
So what do you I should go after? Move the CG back a little?
RickP

cruzmissile

Hello RickP, you stated that the elevators are at zero but need down trim to stay level, but you state that it dives while inverted? hmm.... I would try and move the GC back a little at a time. A technique I use when testing the CG, I would trim the plane for straight and level flight. Then I would put it iverted and if it dives I would need to move the CG aft. Not too much aft because it makes it very unstable. You probably already know this technique but that's what I would do. I'm not familiar with your plane but does it have any dihedral, that might cause it to canopy up on a down-line. Also I read in your post that it elevates upward when on full power. You could check it again but it might be that the thrust line is at an upward angle. A combination of up thrust and forward CG could cause your plane to behave the way it does. Hope this helps.

BPKlein

My Feedback: (1)

You have too muuch DOWN thrust in the engine. While carrying power, the engine dominates the elevator/stab. As soon as you cut the power the elevator will dominate. You said when you do the full power trimmed level flight and cut to idle test that the plane climbs.......right? The plane should start to descend almost immediately. The fix is to put some up thrust in the engine. The up thrust will then have you carry the elevators slighty more down in level flight. Then they will be slightly more down in your POVD, (power off vertical downline) helping to correct the pull to the canopy. Most IMAC style planes need some up thrust in the engine. I build all of my IMAC birds with 1 deg up in the engine.

Now you will probably never get the plane to track a perfect up line and a perfect POVD. You can move the CG back, and this will able you to carry more down elevator to continue to fix the down lines, but at the expense of the plane pulling to the belly in the up lines, and pulling to the belly harder in knife edge.

Set the cg first by flying and trimming the plane in up right straight and level flight and then roll the plane inverted. You should have to hold just a touch of down elevator while inverted. After the CG is set then move to the engine cut test and adjust your up/down thrust. After the CG and the thrust line is set then move to trimming the POVD. The plane will still pull to the canopy slightly. Just mix some down elevator with idle throttle and the problem will be fixed. Now you might be asking yourself about the vertical upline. If it is not straight try adjusting the ailerons. Both up or down. If the plane pulls to the canopy while on an upline, adjust both ailerons up some, and vise versa. This will affect the trim on your POVD. Just adjust the amount of mix as neccesary.

Hope this helps,
Bryan

Don Szczur

My Feedback: (1)

Suggest the following:

First trim for straight and level, whatever your cruise speed is (normally half to 3/4 throttle). This includes aileron and elevator trim.

Next, thrust should be checked by pulling up to vertical from a left to right pass, then from a right to left pass. If the plane goes out the first time then in the second (after climbing verically) you need (more) right thrust. Let go of the sticks when you do this- if it pulls to the canopy both times you need down thrust. My extra, and cap pull to the Landing gear slightly, so I add up thrust.

Finally point the nose down, if its still pulling out as you describe, add mixing- down elevator with low throttle... its easy on JR, just three steps- Throt- Elec (1), page to next screen and hit "orig" (2) and finally, give 3 clicks of throttle stick, hit "offset" and then bump up the % to give you some down elevator.

This will help your down lines, and also the half cuban 8.

Normally don't need to change wing/elevator incidence or CG if its set to the plans/ or factory settings if its an ARF.

Let me know if it gets you set.

Cheers,

Don

RickP

My Feedback: (2)

Hey Guys,
Thanks for the responses. I think Bryan might be on to something with the up thrust (now it is close to zero), that may be. But I would still like the POVD to be straight with nutral trim.
I lined up the elevators as dead close to zero as humanly possible and with that it needed only one click of down wich is negligable IMO.
I know I need some upthrust, but also some tail weight too. I will do the following. I will strap some wight to the tailwheel and try it out. Then after that I will try adding a washer up up thrust. Thanks guys.
RickP

3D_CAP232

Hi,
Check thrust line on vertical uplines as the model slows down which will tell you left/right and up/down thrust...CoG position will determine if the model pulls out in a dive.
This is the way I do it and it works for me!.

Regards
Rich

RickP

My Feedback: (2)

Rich,
Thanks - I'll have to double check. I don't reacall any pulling on the upline at all. I have to wait for my new canopy before I can try it again.
RickP