I am going to be starting my second year in IMAC in 2005. I had a blast last year and learned a great deal. One thing I learned is that I need to go through the trim chart carefully. One thing that got me interested in this is that I had to compensate on my down lines all last season for my planes tendency to pull up (to the canopy) on down lines. When I look at the trim-chart it tells me to adjust my incidence for this. Although it is possible to do this, it will take some care.
My question is should I be adjust the incidence first or go through the trim chart in full before I decide to go back and adjust my incidence? If I fail to adjust the incedence and go through the trim chart am I doing it all for nothing or could I possibly find that incidence adjustment was not required?

Here are my specs for reference

Aeroworks 31% Edge 530T
3W 75US
21.75lbs AUW

Pulling to the canopy on downlines is NORMAL. However, you can address this by creating a mix that allows for a certain percentage of down elevator at idle. I've got this in my Comp-Arf 2.6. I used 6% down at idle. This gives me straight down lines when the throttle is pulled ALL the way back to idle. When at least one click of throttle is given, the the program is nullified and I'm back to regular flight mode. The only thing is I've got to remember during hammerheads and spins, right at the stall point, that I've got to at least leave on click of throttle or things turn really ugly. I've just got it on a switch and after I take off, I flip the switch. Then I flip it when I'm ready to land. BTW, I've forgotten to switch it when I did land, and it wasn't all that bad. In fact, it was really quite easy, but I'd rather remember the switch. Try it.. It really works great.

i flew intermediate with a 29% edge a few years back, and i left the down elevator mix on the all the time....it was i think about 3 to 4 %...it never bothered me during landing and i liked it for stall turns as it would tuck the nose following the stall.

I concur. Use the radio to mix in some down elevator at low throttle. I leave mine on all the time as I do not see any problems in Hammerheads, etc. The amount you need will vary depending on your airplane. 6% for one plane may be 3% for another, or 10% for another. Simple trial and error will get you fixed in about 1 flight.

And it can also be trimmed out by adding up thrust to the engine. Adding up thrust will require some down elevator trim under full power. Then when you drop the throttle to idle for the down lines, the engine is not pulling up so that the plane heads straight down. If your plane flies straight up lines and downlines and 45 degree lines upright and inverted ascending and descending, then you've got it licked.

Adding the upthrust in the engine wil probably change the upline trim though. I'd try the mix first.

Ryan

Jack,

trimming using the wing incidence is a very powerful tool. Many of the guys flying the Giant Scale models don't trim their models this way but it can help things a bunch. Just like many of us do on our pattern models. The one thing that you can notice is that the pattern models have devices that can be built into the model to adjust the wing incidence. These devices are too small to be used on big model so most guys don't bother.

A good test to see if it will help...raise or lower both ailerons slightly. Like a Flapperon type thing...Both ailerons up or both down. If you drop both ailerons say 1/16-1/8th inch...then go fly it and see what happens. If the result helps the model performance then give the model more positive in the wing and put the ailerons back to neutral.

If you need less incidence the same thing works with raising the ailerons up...

Just a word of advice. I tend to fly my model much more nose heavy than most. They track better this way. When you have a good properly trimmed setup it is very common to have the a slight pull on the down lines. When you have good uplines but the model pulls on the downlines I add positive to the wing...Too much positive in the wing and the model will pitch to the belly in up lines..meaning too much down thrust type of thing. The reason you just added more down thrust in relation to the wing by moving the wing positive. I have also seen situations where up lines hands off are fine but if you touch the rudder it will pitch to the belly on the upline. When you are flying knife edge the mixing is already setup and perfect...yet on uplines with just a breath of rudder it pitches belly this is too much positive in the wing.

The angle the wing flies at really sets the fuse angle in the air. If the model looks like its flying along tail high then decrease wing incidence, Tail low like the model looks tail heavy when flying then increase positive in the wing.

All these things interact and there are lots of ways to trim the model to accomplish the goals. But Incidence adjustment is a very powerful tool to make the airplane fly better. The guys that fly pattern planes learned this and now 90% or more of the plug in wing models built today get gator wing adjusters. It makes the trim process so much easier.

A mix can help this but I would dial a little + int he wing first and see what happens. Like I said the aileron droop will tell you if it will help or not. Be aware positive in the wing means needs down elevator trim. SO be prepared to give a little 3-4-5 clicks of down trim....Trim the model for hands off level flight..Then do a long downline to see what happens.


Good Luck

Troy Newman
-Team JR, Central Hobbies, ZN Line, YS Performance, Cool Power Fuels
-AMA 163080
-NSRCA 2239

Mixing works. Changing incidence is a real pain on large planes, works nice on the smaller pattern ships. Also, changing incidence effects other flight modes. Why fool with it when a simple mix does the trick??

Thanks for all the tips guys.
Lots of good info there Troy, I need a guy like you in my pit crew.
I think I am going to go through the whole trim chart minus the incidence and see how it reacts. I think the the thrustline may do the trick but who knows, this is all experimental for me, learning a lot in the process though. If It is still exhibiting this characteristic then I am going to take a poke at the incidence. I figure It shouldn't be to tough to move the rings that retain the wing pins.

Wish me luck

you might check your engine /wing incidence. being a mid wing airplane, the edges like to fly at 0-0. as was said, the pulling to the canopy is normal on downlines. you didn't mention what it did going straight up, and that's where a lot of people start playing with incidence. you should be able to transition from horizontal to vertical flight without elevator corrections. it's probably worth mentioning that one of the locals buried a 39% 540T when he tried to apply pattern know how and changed the wing incidence. the first time he tried to land it, it wouldn't settle, and it stopped flying about 10' in the air. no more edge.