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E flight trimming question, motor thrust

Old 02-24-2010, 06:43 PM
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tph1
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Default E flight trimming question, motor thrust

Is there more of an importance on thrust lines in the electric motors than in glow? I have read where some just mix it out and some don't. For flying the lower classes like sportsman and intermediate with relatively no inverted manuvers, what is the best way to get a neutral plane? I know this is pretty vague but I'm trying to get my first electric plane trimmed and want some sort of starting point to work from.
thanks, T
Old 02-24-2010, 07:08 PM
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Walt Thyng
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Default RE: E flight trimming question, motor thrust

The laws of physics don't care what the fuel is; if there's a mass spinning (prop, motor, etc) there will still be gyroscopic and P forces to contend with.
Walt
Old 02-24-2010, 07:18 PM
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Default RE: E flight trimming question, motor thrust

yep, you're right but I guess I was trying to find out since my plane is basicly a 60 size plane and it is swinging a 16" prop instead of a 12" is the torque produced enough to change the recommended thrusts?
thanks
Old 02-24-2010, 07:56 PM
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Hauling-A
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Default RE: E flight trimming question, motor thrust

Go To this website, It should answer your Question.

Jim

http://rcaerobats.net/
Old 02-24-2010, 08:03 PM
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Default RE: E flight trimming question, motor thrust

thanks, I'll give it a read
Old 02-25-2010, 09:22 AM
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Walt Thyng
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Default RE: E flight trimming question, motor thrust

Whether yo can fine tune thrustlines closely enough to ajsut for small torque changes is debatable. All models vary slighty from one to another and suggested thrust lines are just that suggestions.
Walt
Old 02-25-2010, 09:48 AM
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rcpattern
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Default RE: E flight trimming question, motor thrust

One issue is the size of the props now. We are getting to a point where the amount of right thrust needed to counter act torque is so much that it would really screw with other parts of the flight. I have adopted Chip's method of mixing rudder to throttle. It definitely works better than just right thrust in my opinion.

Arch
Old 02-25-2010, 11:38 AM
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Default RE: E flight trimming question, motor thrust

for a mix programming newbie, how do you do that?
Old 02-25-2010, 11:49 AM
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Chris Moon
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Default RE: E flight trimming question, motor thrust

Remember that right thrust is only properly set at one specific power setting too. Every other second of the flight, it is wrong. Check out most people's planes, they have right rudder trim on the ground because it is trimmed for full power loops. In any other situation, you have too much right and the only way to properly fix that is to have the rudder trim (mix) vary with power. Planes with large electric props will need right mix with full power and actually a little left mix with idle.

If you want to get more critical, you also need left aileron with high throttle too and right aileron with low. Not much, maybe 1-2% but it is there.

People that boast they have a plane with no mix don't understand that is not always an optimum situation to have.
Old 02-26-2010, 09:42 AM
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Walt Thyng
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Default RE: E flight trimming question, motor thrust

ual hit the nail on the head, any thrust offset is only correct for a given speed. If you're a competition type then you need to use mixing. If you're a sport flyer you pick a trust angle that works for your typical flying speed. In this case less is generally better.
Walt
Old 02-26-2010, 11:05 AM
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Default RE: E flight trimming question, motor thrust

well, given that, the plane I'm flying is so overpowered with the set up I have on it that I have been flying it about 2/3 to 3/4 throttle,
I am going to fly it in sportsman this spring, untill I get a bigger plane together, should I just try to get the 3/4 setting and the downline settings right?
Old 02-26-2010, 12:17 PM
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Default RE: E flight trimming question, motor thrust


ORIGINAL: tph1

well, given that, the plane I'm flying is so overpowered with the set up I have on it that I have been flying it about 2/3 to 3/4 throttle,
I am going to fly it in sportsman this spring, untill I get a bigger plane together, should I just try to get the 3/4 setting and the downline settings right?
Actually the mix is very simple. You will want to mix the rudder to your throttle. Start with the rudder at neutral at idle, and at full throttle start with about 1/8 right rudder to wide open throttle. Then fly a veritical line at full throttle in calm conditions and see if the plane continues up straight, or moves right or left. Adjust the mix accordingly until it goes up perfectly straight. One key though is starting out level and making sure that you START the line vertical. If you are offline when you start you'll never be able to tell. This is easiest to do with the plane flying straight away from you. It is a very simple mix to setup. Most airplanes are fairly linear with this, so if you are flying at 3/4 throttle mostly, you should still be fine.

Arch
Old 02-26-2010, 01:05 PM
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Default RE: E flight trimming question, motor thrust

No disrespect to those using a thr-rudder mix, but I disagree with the posts that say you can't trim with thrustline only.

I have done it both ways, and I find that a thr-rud mix does not work correctly across all speeds, and if you have it set to work at the top of an upline you will have a model that yaws to the right on high power level flight. I was never able to eliminate this and caused more work for me when flying faster than where the mix was set to work. If I set it to work good across all horizontal speeds, then it was not enough for the vertical.

Spending some time to get the balance between rudder trim, and right thrust you can get a model that goes straight up to the top of the box, and flies straight on high power horizontal flight. It takes some time, but IMO provides a better flying model. I flew with a thr-rud mix for over a year, and went back to not using it as I was never able to get a satisfactory setup from it.

I also don't use the left mix at idle, I have never noticed a tendency in my planes that would require this mix. I have tried and tried to see why its needed, and even put a mix in just to see what it does, but I really don't get it
Old 02-26-2010, 05:53 PM
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Default RE: E flight trimming question, motor thrust

I discovered some or most of the trim problem. I bought the plane from a guy and put back into it the same motor servos etc. I just took for granted that everything was lined up and set.
Now I just went and bought a digital level, blocked everything up nice and level and started taking some measurements. First it had no right thrust according to my measuring and math. Second it had 2.5* of UP thrust. It now has 1.5* down and 2* right. I will start from there and after some flights and observations I will try to mix out what's left.
Old 03-01-2010, 07:14 PM
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Default RE: E flight trimming question, motor thrust

I got in 2 flights this afternoon and the thrust changes seem to have fixed all the "weirdness". I can chop the throttle and it doesn't pitch much in any direction and the down lines are pretty strait. I didn't have time to do much other than that and fly around inverted with slight down elevator but now I have another question. Why can I not do a left stall turn when the turn to the right is fine?
Old 03-02-2010, 11:04 AM
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rcpattern
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Default RE: E flight trimming question, motor thrust

Two things to consider on your stall question. Is there any wind? This should only affect one direction though, and also, are you 100% sure you are totally vertical? Most people tend to lean one way or the other and this would impact that. A quick test is to pull vertical and just touch some left rudder to where it is slightly leaning to the left and see what it does.

Arch
Old 03-02-2010, 12:04 PM
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Default RE: E flight trimming question, motor thrust

wind was pretty much straight down the runway, and I was very close to vertical, I tried it going both directions

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