IMAC trimming question (s)

[orthobird]

went to the club on friday and I took my Dalton 260 and a Extra 330, and I decided to take some advice from one of the friends i met at an IMAC competition.

He gave me plenty of information, and he was awesome in giving me advice like no one else. I was like a sponge absorbing all the information he gave me.

However, it was 3 weeks since then, and i have now had the opportunity to try to do what he told me.

He told me:
1. fly straight up and check thrust. if it veers to left, then i need to add right thrust.

2. CG check.. inverted climb at 45 degrees, hands off and see what happens, are towards canopy = nose heavy

3. then roll to KE, and see what happens, if there is coupling and it arcs towards gear or canopy, then add rudder to elevator mix, if there is also rolling component, then add rudder to aileron mix as well.


Then, i have read peter goldsmith's recommendations, and he seems to say, check CG 1st, then thrust line.??


on both airplanes, i have corrected thrust line, i have gotten cg where i want it, end result, if i fly it inverted, i do have to apply just a touch of down elevator to keep it level, not bad. and i have added a mix, stays on all the time, of rudder to elevator, and with those two birds, i have never done knife edge like that before. i still have to add just a minuscule amount of rudder to aileron mix on it to keep it straight. The knife edge was like never before i have done before, and i felt like i could have flown it 20 feet above the runway, directly over it, and now i know how the "pros" have been able to do that at fly ins!! They have all kinds of mixes!!

well, here is my question:

1. the knife edge mix, will this improve my level flight rudder turns? meaning, when i do KE, left rudder applies up elevator, coincidentally, right rudder also required up elevator. if before the mix, i applied right rudder during level flight, the airplane would dip down. But now, it remains more level. once i add the aileron mix to it, will it keep it from rolling as well? i guess no mix will make it perfect, but sure will make it couple less? would this be the way to think of it?

 

[orthobird]

here is my second question, just remembered:

1. the low rate rudder travel? would you all say it is safe to say, that the amount of low rate full rudder deflection should be such that it can hold the airplane level when in knife edge flight?

 

[yakpilot]

You are on the right track. Some pilots will also set their mixes based on flat rudder turns. Their reason being that if you apply rudder to correct your track ( which is almost constantly during a flight ) it won't try to pitch or roll your plane.
Comparatively in IMAC our planes don't fly in knife edge for long amounts of time. Point rolls are usually just brief pauses. This differences in mixing values between the two methods usually isn't enough to affect your point or slow rolls.
As for rudder throw, yes you should end up with enough throw hold knife edge at maneuvering speed which is usually somewhere around half throttle or so. But I usually set my rudder throw based on how my plane snap rolls. Too little throw and it looks like a fast roll instead of a snap. Too much rudder and the plane will over rotate when you neutralize the sticks. I will start out with about 25 degrees deflection on a new plane and then start reducing the throw until I get my snaps to stop instantly when I neutralize the sticks. I will usually end up in the 18-20 degree range. I know it doesn't sound like much but it works for me. I also use little to no expo on my low rate rudder which sounds weird, but makes point and slow rolls a lot easier. You will have to switch rates for hammer heads though.

 

[Capt.Roll]

Cam, all good questions. I'll be setting up a new ARF over the next several weeks so the answers provide by more experienced IMAC pilots will be helful. I've alway tried to follow the Peter Goldsmith guide.

I have been under the impression that any given mix to correct/help "X" particular flight attitude/path may negatively influence another. Perhaps impossible to do but I would think you'd want to be able to set up every plane with zero mixes and work with CG, lateral balance, thrust line, and incidence to get a plane dialed in.

 

[reyn3545]

Remember, the plane doesn't know whether it's in a flat rudder turn or a knife edge pass... it's just flying through the wind. Gravity and aerodynamics have some effect, but the plane will react just about the same to any rudder movement. I usually make sure the plane will fly straight and level away from me, then test a vertical upline for right/left thrust angle. Then I'll look at an inverted 45, then the rudder/elevator and rudder/aileron mixes. You'll need to go back and tweek previous settings whenever you change another, and pretty quickly you'll be flying a very well trimmed plane.

When you're looking at mixes, be sure to check your plane in both right and left directions. I guess due to prop wash coming over the flying surfaces, you'll generally see slight differences in the mix % between right and left rudder movement.

And yes, for non-IMAC guys like me, getting those basic settings dialed in makes for a very predictable plane to fly. Depending on prevailing winds, etc, you'll always have just a little correcting to do, but now the electronics are managing 90% of that correction for you!

 

[orthobird]

Remember, the plane doesn't know whether it's in a flat rudder turn or a knife edge pass... it's just flying through the wind. Gravity and aerodynamics have some effect, but the plane will react just about the same to any rudder movement. I usually make sure the plane will fly straight and level away from me, then test a vertical upline for right/left thrust angle. Then I'll look at an inverted 45, then the rudder/elevator and rudder/aileron mixes. You'll need to go back and tweek previous settings whenever you change another, and pretty quickly you'll be flying a very well trimmed plane.

When you're looking at mixes, be sure to check your plane in both right and left directions. I guess due to prop wash coming over the flying surfaces, you'll generally see slight differences in the mix % between right and left rudder movement.

And yes, for non-IMAC guys like me, getting those basic settings dialed in makes for a very predictable plane to fly. Depending on prevailing winds, etc, you'll always have just a little correcting to do, but now the electronics are managing 90% of that correction for you!

thank you all for your comments:
i steal from you:


1. I usually make sure the plane will fly straight and level away from me
2. then test a vertical upline for right/left thrust angle.
3. Then I'll look at an inverted 45,
4. then the rudder/elevator and rudder/aileron mixes.



Would you say, if i do this (4 points above), i should be good then?


i can tell you, it definitely flies way better, wish i had done that last year before the competitions!!

 

[reyn3545]

I'm not an IMAC flyer, so my needs pretty much stop with the mixes above. There are many more you'll want to look at eventually, like a down-line elevator mix, but the mixes above will reduce your need to control the plane tendencies down to a point where you can focus more on the maneuver than on trying to correct what the plane is doing to you. What IMAC region is Shreveport in?

 

[orthobird]

I'm not an IMAC flyer, so my needs pretty much stop with the mixes above. There are many more you'll want to look at eventually, like a down-line elevator mix, but the mixes above will reduce your need to control the plane tendencies down to a point where you can focus more on the maneuver than on trying to correct what the plane is doing to you. What IMAC region is Shreveport in?

thank you!
South Central

 

[reyn3545]

Ah.. lots of IMAC flyers at our field, but we're in the Southeast. One of our guys went to the worlds this year, another one our guys is Wayne Mathews... they are a TON of help, great folks to hang out with, and they make this stuff look amazingly easy. I could watch Wayne to slow rolling circles all day, 1/4 turn to each 1/4 of the circle, perfect just about every time.

 

[Stinger]

First off, Peter Goldsmith wrote a trimming process that for many, is the "Gold Standard" for trimming out precision aerobatic planes.
I'm pretty sure it's on the IMAC web site but I'm not sure where. It would be well worth your while to seek it out and use it.
Next, I personally am a staunch believer in using mixes to obtain the flight conditions you want for competition flying.
This assumes that the plane you are working with has the standard motor offset built into the plane as well as zero or one degree
incidence on wings and stabs.
Shimming the motor with up or down thrust actually only works at one speed. Mixes associated to the throttle can be mixed for all speeds. Again, this assumes that the standard offsets and incidences are built into your plane.
You should think about this carefully as I'm sure you will find many different opinions on the subject.