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Delta wing question

Captain Jay

Well-known member
#1
So, I recently built a Mirage 2000 and flew it a bunch. I have never had a Delta wing before and don't know what or if I can do anything about my nosedive issue.
I have perfect C of G and the edf is at the back of the plane. (See pics) thrust tube is dead straight or at least 99% perfect. I have made a flew edf jets and never experienced this before.
My cad partner informed me he finished his prototype and flew it with the exact same results I am having. (80% up trim for level flight) We know the wing is level and c of g is perfect.
Here is the question:
Should the thrust tube be directed upwards a few degrees or should the edf be placed in the middle of the fuselage to correct the nosedive issue? Or is there a question/answer I'm missing to resolve this. We want to release the plans but we need a resolve first...
Thx everyone
 

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leaded50

Well-known member
#2
a EDF dont have the same "rotation" force similar as a typical prop plane would have. I would belive its other thing who does it. I done a few EDF planes, and never could put the EDf so far back, i also like best approx 2.5 - 3 times the edf diameter in thrust tube length for best effect. Yours is very short..
 

Captain Jay

Well-known member
#3
a EDF dont have the same "rotation" force similar as a typical prop plane would have. I would belive its other thing who does it. I done a few EDF planes, and never could put the EDf so far back, i also like best approx 2.5 - 3 times the edf diameter in thrust tube length for best effect. Yours is very short..
I see. So, would that mean the edf should move forward about 6 inches to correct this? It makes sense... thx, let's see what others say as well.
 

Namactual

Well-known member
#4
Deltas can have weird center of lift shifts depending on AoA.

How does it glide vs high speed?
If it is a thrust angle issue, it would only nose dive under WOT but level off it idle.
Does the nose really drop at slow speed without elevator input?
How about slow speed high alpha at high throttle?

It should not matter where the EDF is along the length of the fuse. The thrust is still pushing from the tail either way. The height above the wing will push the nose down though.
 
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Captain Jay

Well-known member
#6
Deltas can have weird center of lift shifts depending on AoA.

How does it glide vs high speed?
If it is a thrust angle issue, it would only nose dive under WOT but level off it idle.
Does the nose really drop at slow speed without elevator input?
How about slow speed high alpha at high throttle?

It should not matter where the EDF is along the length of the fuse. The thrust is still pushing from the tail either way. The height above the wing will push the nose down though.
You pose a good question... I've only glided the plane on landing and that's after I trimmed it. Once I've trimmed it, the plane flys perfectly level at all speeds... Weight of Thrust makes sense. Here is a short video of the hand toss before trim. This is Under full thrust.
https://photos.app.goo.gl/rU2sPKd8qfL9E43Z8

What do you mean "the height above the wing will push the nose down" ? How does that work?
I think I've got learning to do about Delta wings...
Could the answer be to "not have a flat bottom wing"?
Should the wing have an angle of incidenceor would that matter. For this I put 2 click of up elevator and it usually good so I wouldn't think thats the issue...
 
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Namactual

Well-known member
#7
I can't see much on the vid, it seems to end before the plane leaves your hand?

The center of drag is typically in line with the wing. If your center of thrust is not in line with the center of drag, it will pivot the airframe on the center of drag.

So in your case, your wing is low on the plane while the thrust in in the center of the plane. The thrust push is higher than the drag push back. Without airflow flowing over the control surfaces to counter act that force, your plane will pitch down.

Your thrust is higher than the wing, but it does not really look that extreme to need a lot of thrust angle to counter act. If you are not having the pitch down after you trimmed the aircraft even under WOT it probably is not thrust angle.

There really is not such thing as incidence on a delta. There is in relation to the fuse, but not to a second set of control surfaces. It really boils down to the Angle of Attack.
 

Hai-Lee

Old and Bold RC PILOT
#8
A delta, as shown, is a tailless design and therefore it requires reflex for stable flight.
Unfortunately the balance point chosen can be way off and the bird will still fly with enough reflex, (up elevator).
You need to determine the bast balance point or how close you are to perfect by doing a stall test with full up elevator and no throttle.

If the plane wanders or drops a wing at stall rather than just starting to sink then the balance point used is too far aft. If on the other hand the bird wants to bounce its nose up and down then the bird is setup too nose heavy.

After you have the balance correct then you can set the reflex of the elevons for level flight and the bird will be as good as it will get.

Just what works for me!

Have fun!
 

Captain Jay

Well-known member
#9
I can't see much on the vid, it seems to end before the plane leaves your hand?

The center of drag is typically in line with the wing. If your center of thrust is not in line with the center of drag, it will pivot the airframe on the center of drag.

So in your case, your wing is low on the plane while the thrust in in the center of the plane. The thrust push is higher than the drag push back. Without airflow flowing over the control surfaces to counter act that force, your plane will pitch down.

Your thrust is higher than the wing, but it does not really look that extreme to need a lot of thrust angle to counter act. If you are not having the pitch down after you trimmed the aircraft even under WOT it probably is not thrust angle.

There really is not such thing as incidence on a delta. There is in relation to the fuse, but not to a second set of control surfaces. It really boils down to the Angle of Attack.
Thank you for that insight very much!!
Tests may happen in June. Depending on Covid-19...
 

Captain Jay

Well-known member
#10
A delta, as shown, is a tailless design and therefore it requires reflex for stable flight.
Unfortunately the balance point chosen can be way off and the bird will still fly with enough reflex, (up elevator).
You need to determine the bast balance point or how close you are to perfect by doing a stall test with full up elevator and no throttle.

If the plane wanders or drops a wing at stall rather than just starting to sink then the balance point used is too far aft. If on the other hand the bird wants to bounce its nose up and down then the bird is setup too nose heavy.

After you have the balance correct then you can set the reflex of the elevons for level flight and the bird will be as good as it will get.

Just what works for me!

Have fun!
And thank you for your insight.
Again tests will happen after Covid-19 is gone...
 

Vimana89

Well-known member
#11
Looks like you already got the answers you need. I've played with a lot of deltas, and while they are pretty forgiving with CG, slop, and trim, getting them to fly perfectly straight can really take some tweaking. It's all CG and subtrim/reflex(granted your thrust angle is good). Basically, I would just fly it(when you get the opportunity) and make small adjustments in these areas as you go until you have it flying how you like it, focusing on the CG first and foremost and then the reflex after the CG is more or less where you want it, as @Hai-Lee recommended.
 

CustomRCMods

Well-known member
#13
In terms of thrust tubes, as previously mentioned yours seems short. Remember that the longer it is = the more speed you have, but the shorter it is = the more static thrust you have at your disposal. Finding that sweet spot between speed and static thrust is crucial to having a good edf experience.

also, i wouldn’t mess around with thrust tube angles, as that redirects air and loses efficiency, but also could create more problems down the road. Elevon reflex should get the job done, at least to the point where you can make finer observations about your EDF’s performance. Hope this helps!

Happy flying!
 

Captain Jay

Well-known member
#15
What I did learn from all of you guys and Wikipedia is that:
1) a Delta wing needs an upwards angle of attack to create a vortex on top and on the back half of the wing to provide correct stabilization and also provide the appropriate lift. If not the plane will nose dive at all speeds due to no angle of attack. Up elevons until level flight is achieved.
2) there is nothing wrong with my plane or @Flitedesign 3d's plane. They fly as they should
3) a lesson of delta wings was needed.
And here it is:

https://en.m.wikipedia.org/wiki/Delta_wing

Thanks everybody the lesson was as fun as the build/flights...
And,
Stay the f%±& home!!! Hahaha
 

L Edge

Well-known member
#17
So, I recently built a Mirage 2000 and flew it a bunch. I have never had a Delta wing before and don't know what or if I can do anything about my nosedive issue.
I have perfect C of G and the edf is at the back of the plane. (See pics) thrust tube is dead straight or at least 99% perfect. I have made a flew edf jets and never experienced this before.
My cad partner informed me he finished his prototype and flew it with the exact same results I am having. (80% up trim for level flight) We know the wing is level and c of g is perfect.
Here is the question:
Should the thrust tube be directed upwards a few degrees or should the edf be placed in the middle of the fuselage to correct the nosedive issue? Or is there a question/answer I'm missing to resolve this. We want to release the plans but we need a resolve first...
Thx everyone
Before you release your plans, I noticed one problem that you must be aware of. Your thrust tube is sticking way to far out in the open. If a pilot flares too steeply, it will flop down and destroy your tube. You need to protect it or cut a large segment off.

How do I know? I have been using 2D TV gymbols for about 10 years and I totally destroyed the setup due to it being out in the open. Best to have it exit just past the elevons.
Another good way to check your CG is to roll it inverted and if you need just need a tad of nose down, your on. Reason why, if thrust tube is off axis of EDF, it will show up. It doesn't take much, when you add all that thrust to produce a up/down vector.
In the Viggen group build, was able to put my 2d TV gymbol on, reduce the canards to zero(orginally + 10 degrees) and add servos to the canards to tighten the pitch axis. CG did changed by adding all the additional weight fore and aft.
 
#18
Before you release your plans, I noticed one problem that you must be aware of. Your thrust tube is sticking way to far out in the open. If a pilot flares too steeply, it will flop down and destroy your tube. You need to protect it or cut a large segment off.

How do I know? I have been using 2D TV gymbols for about 10 years and I totally destroyed the setup due to it being out in the open. Best to have it exit just past the elevons.
Another good way to check your CG is to roll it inverted and if you need just need a tad of nose down, your on. Reason why, if thrust tube is off axis of EDF, it will show up. It doesn't take much, when you add all that thrust to produce a up/down vector.
In the Viggen group build, was able to put my 2d TV gymbol on, reduce the canards to zero(orginally + 10 degrees) and add servos to the canards to tighten the pitch axis. CG did changed by adding all the additional weight fore and aft.
Before you release your plans, I noticed one problem that you must be aware of. Your thrust tube is sticking way to far out in the open. If a pilot flares too steeply, it will flop down and destroy your tube. You need to protect it or cut a large segment off.

How do I know? I have been using 2D TV gymbols for about 10 years and I totally destroyed the setup due to it being out in the open. Best to have it exit just past the elevons.
Another good way to check your CG is to roll it inverted and if you need just need a tad of nose down, your on. Reason why, if thrust tube is off axis of EDF, it will show up. It doesn't take much, when you add all that thrust to produce a up/down vector.
In the Viggen group build, was able to put my 2d TV gymbol on, reduce the canards to zero(orginally + 10 degrees) and add servos to the canards to tighten the pitch axis. CG did changed by adding all the additional weight fore and aft.
 
#19
So, I recently built a Mirage 2000 and flew it a bunch. I have never had a Delta wing before and don't know what or if I can do anything about my nosedive issue.
I have perfect C of G and the edf is at the back of the plane. (See pics) thrust tube is dead straight or at least 99% perfect. I have made a flew edf jets and never experienced this before.
My cad partner informed me he finished his prototype and flew it with the exact same results I am having. (80% up trim for level flight) We know the wing is level and c of g is perfect.
Here is the question:
Should the thrust tube be directed upwards a few degrees or should the edf be placed in the middle of the fuselage to correct the nosedive issue? Or is there a question/answer I'm missing to resolve this. We want to release the plans but we need a resolve first...
Thx everyone
I would not tilt up or down the thrust exhaust tube. I always prefer to have the exhausts parallel to the cord line of the wing. I think it is convenient just for the control surfaces to do the pitch because it would be very unstable otherwise for loops; landings and take off. :)
 

quorneng

Well-known member
#20
Captain Jay
I am a bit surprised that you said the CofG was spot on. There are many variables in a delta so the CofG is simply where it needs to be as a result of flight testing. ;)

I fly a Delta with the EDF right at the back with no problem except the battery has to go well forward to compensate. This does have the benefit it is well forward of the bifurcated inlet duct.
If your delta needs some up elevator to fly then it is at least stable. You can move the CofG back so it needs less up elevator but do so very gradually thoroughly testing each time but beware don't go too far. An unstable delta is virtually uncontrollable without some very clever electronics.

Just as an aside.
Work out what the area of the duct actually is around the motor body. I bet it is close to 90% of the FSA. This means an EDF truly right at the back (i.e. the end of the motor flush with the end of the duct) actually has a reduced area thrust tube without having to do anything! ;)
EDFrear.JPG

It works for me.