Jet-Teng L39 for P20
03-08-2014, 08:08 AM
#76
Join Date: Jul 2010
Location: Dallas TX
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Mike,
Thanks for the quick reply,
For the flaps setting first stage 40 degs second stage 85 degs, are you still using these setting, or should I lower down the second stage to 75 degrees??
Al
Am away from home now but I will check tomorrow and lat you know what Model.
Thanks for the quick reply,
For the flaps setting first stage 40 degs second stage 85 degs, are you still using these setting, or should I lower down the second stage to 75 degrees??
Al
Am away from home now but I will check tomorrow and lat you know what Model.
Last edited by ravewithmein; 03-08-2014 at 08:13 AM.
03-08-2014, 09:40 AM
#77
Dry weight of my one is just under 4Kg and it fly's fine once it up and running, bit slow on grass to take off and I have to get the gear away for it to accelerate up to speed, but it is viceless once flying, I have crow set up and it slows right down for landing without any tendency to tip stall.
Power to weight ratio is a bit difficult as the drag from the airframe has a much higher impact on flying performance, a sleek airframe with only have thrust to weight will fly well, but a draggy airframe with the same thrust to weight ratio may not even get off the ground, personally I would prefer at least a 75% thrust to weight ratio or even more to make it a bit exciting, but I have flown some high lift wing airframes with less than 25% thrust to weight, you have to assess what it is you want, sorry I could not be more specific, but there is a lot to take into account on jets.
Have you flown any EDF's this will give you a good idea of what is required.
Mike
Power to weight ratio is a bit difficult as the drag from the airframe has a much higher impact on flying performance, a sleek airframe with only have thrust to weight will fly well, but a draggy airframe with the same thrust to weight ratio may not even get off the ground, personally I would prefer at least a 75% thrust to weight ratio or even more to make it a bit exciting, but I have flown some high lift wing airframes with less than 25% thrust to weight, you have to assess what it is you want, sorry I could not be more specific, but there is a lot to take into account on jets.
Have you flown any EDF's this will give you a good idea of what is required.
Mike
The better the pilot the less oumpf you need - while airborne. I often compare EDF to turbine saying a turbine only needs half the thrust of the EDF as the EDF looses in efflux. But when static thrust is thrust. Jets often have a low thrust to weight ratio, still flies way better "then they should" due to the high efflux, keeping the thrust even at speed. So if flying from tarmac everything will fly under turbine power, so will this one. A Concorde only have a thrust to weight ratio of 0.36:1 with afterburners lit, and did pretty well flying Mach 2 without burners(!)
Last edited by Henke Torphammar; 03-08-2014 at 09:45 AM.
03-08-2014, 10:19 AM
#78
Thread Starter
Thanks Henk, that's a great compliment coming from someone whose opinion I respect.
Al
On flap settings you use the degree that will give you the desired effect, anything up to about 45degs will give increase lift with a smallish amount of drag, anything over 45degs and you are getting more drag than lift, because the wing is not producing so much lift it will come down quicker without a dramatic change in its attitude as long as you have fed in a small amount of required elevator with your flap setting, once you are into that drag curve you have to play power against drag to reach the threshold of the runway, I always have about 5/8mm of up aileron with any flap setting over 45deg to help prevent tip stalling and to increase the rate of decent, seems to work with everything I fly whether it has flaps or not, I also have the whole thing on a mix to throttle to put the ailerons level and flaps back to about 25deg is I open the throttle to go around again, the ailerons level and flap reduction are slowed to allow the turbine to spool up to full power before they are fully away.
Mike
Al
On flap settings you use the degree that will give you the desired effect, anything up to about 45degs will give increase lift with a smallish amount of drag, anything over 45degs and you are getting more drag than lift, because the wing is not producing so much lift it will come down quicker without a dramatic change in its attitude as long as you have fed in a small amount of required elevator with your flap setting, once you are into that drag curve you have to play power against drag to reach the threshold of the runway, I always have about 5/8mm of up aileron with any flap setting over 45deg to help prevent tip stalling and to increase the rate of decent, seems to work with everything I fly whether it has flaps or not, I also have the whole thing on a mix to throttle to put the ailerons level and flaps back to about 25deg is I open the throttle to go around again, the ailerons level and flap reduction are slowed to allow the turbine to spool up to full power before they are fully away.
Mike
03-09-2014, 07:07 AM
#79
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Thanks to Mike and Henk for the great info, it starts to make senses.
Mike, The model that I have is SX.
Ok here is my setting:
4.2 KG Dry Weight,
CG: 80mm
Low Rate: Aileron +/- 8mm 30% Expo, Elevator +/- 10mm 10% Expo, Rudder +/- 10mm 10%expo.
High Rate: Aileron +/- 15mm 30% Expo, Elevator +/- 15mm 10% Expo, Rudder +/- 15mm 10%expo
Take off flaps: 40 degs with 1mm down Elevator.
Landing Flaps: 85 degs with 2mm down Elevator.
Same switch (landing Flaps) with 2 mixes:
Aileron: (Throttle all the way down Aileron up 6mm
, Throttle all the way opens aileron level).
Flaps: (Throttle all the way down Flaps are 85 degs, Throttle all the way opens flaps 25 degs).
Mike I really need to get this right if there is anything that I need to adjust??
Thank you
Al
Mike, The model that I have is SX.
Ok here is my setting:
4.2 KG Dry Weight,
CG: 80mm
Low Rate: Aileron +/- 8mm 30% Expo, Elevator +/- 10mm 10% Expo, Rudder +/- 10mm 10%expo.
High Rate: Aileron +/- 15mm 30% Expo, Elevator +/- 15mm 10% Expo, Rudder +/- 15mm 10%expo
Take off flaps: 40 degs with 1mm down Elevator.
Landing Flaps: 85 degs with 2mm down Elevator.
Same switch (landing Flaps) with 2 mixes:
Aileron: (Throttle all the way down Aileron up 6mm
, Throttle all the way opens aileron level).Flaps: (Throttle all the way down Flaps are 85 degs, Throttle all the way opens flaps 25 degs).
Mike I really need to get this right if there is anything that I need to adjust??
Thank you
Al
03-09-2014, 08:28 AM
#80
Thread Starter
I think you have it nailed, a personal preference is a 30% expo on the elevator, but then I have more movement, but as I said that's a personal thing, but more expo can't hurt.
The change over point on the throttle to ailerons up needs to be at about 50% so you can play with the throttle on decent without putting the ailerons away, when I say 50% I mean 50% power not throttle position, until you get the P20 dialled in you will find that about 75% throttle open is about 50% power output, take a little time and a throttle curve to get the throttle to be linear, bottom 40% does very little if you fly off grass and not a lot in the air either.
One other thing I have the aileron to throttle mix switched from the gear, so no gear down the ailerons stay where they are for flying around.
Mike
The change over point on the throttle to ailerons up needs to be at about 50% so you can play with the throttle on decent without putting the ailerons away, when I say 50% I mean 50% power not throttle position, until you get the P20 dialled in you will find that about 75% throttle open is about 50% power output, take a little time and a throttle curve to get the throttle to be linear, bottom 40% does very little if you fly off grass and not a lot in the air either.
One other thing I have the aileron to throttle mix switched from the gear, so no gear down the ailerons stay where they are for flying around.
Mike
03-09-2014, 08:55 AM
#81
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Mike,
So are you saying when landing that ailerons will not go down to level in less I reach 50% power which is 75% throttle?, so that means after I reach 75% throttle the ailerons should level back and flaps should move up to 25 degs!! Am right ??
Al
So are you saying when landing that ailerons will not go down to level in less I reach 50% power which is 75% throttle?, so that means after I reach 75% throttle the ailerons should level back and flaps should move up to 25 degs!! Am right ??
Al
03-10-2014, 01:22 AM
#82
Thread Starter
Correct, if you think about it when aborting a landing the first thing you do it push the throttle stick all the way up, but when landing you want to play with the throttle to stretch the glide to the patch, hopefully not above 75% throttle.
Mike
Mike
