Me and my dad had set out to Make a plane from scratch. We have come up with a design with one major flaw. It death spirals uncontrollably when we launch it. The CG is all good. We originally thought we needed to add better vertical stabilizer, but this had no effect on the death spiral. I need someone who can help fix this issue and get our little foamy in the air. I’ll attach photos below.
Having trouble with my original design scratch build!
- Thread starter lukem66
- Start date
Yes, the deflections are alright. The control surfaces also are moving the right way. But any input cause it to do a barrel roll I can’t control.
quorneng
Master member
Where exactly is the CG?
In a delta the CG has to be far enough forward so the elevons need to be set slightly up to give a reflex trailing edge. This gives a delta some longitudinal stability. Even so a delta is very sensitive to roll inputs whether from the controls, motor torque or unwanted wing flexing.
The conventional delta layout is a big central fin or two not too far from the centre line. Fins further out can upset the formation of wing vortices which form an essential part of a delta's stability.
Just my understanding from the several RC delta I have built.
This EDF flies very nicely once I got the CG right.
In a delta the CG has to be far enough forward so the elevons need to be set slightly up to give a reflex trailing edge. This gives a delta some longitudinal stability. Even so a delta is very sensitive to roll inputs whether from the controls, motor torque or unwanted wing flexing.
The conventional delta layout is a big central fin or two not too far from the centre line. Fins further out can upset the formation of wing vortices which form an essential part of a delta's stability.
Just my understanding from the several RC delta I have built.
This EDF flies very nicely once I got the CG right.
Do you think if we got a big vertical stabilizer on the center of the plane it would allow to remain level? Also would we have to remove the outer vertical stabilizers?
badpilot27
New member
You should probably move the vertical stabilizers rearward, right now they look really close to where the center of lift is so they don't really contribute enough to maintaining lateral stability.
I agree with @quorneng, CG is absolutely critical.
On my Versa wing, a 1/4 inch change in the CG will turn it into a flying squirrel.
Try moving the CG forward 1/2 inch or so.
Also the wings look like a single layer of fb, that is very difficult to get flat. If the wing has any warping or twist, it could be the source of the problem.
On my Versa wing, a 1/4 inch change in the CG will turn it into a flying squirrel.
Try moving the CG forward 1/2 inch or so.
Also the wings look like a single layer of fb, that is very difficult to get flat. If the wing has any warping or twist, it could be the source of the problem.
We put spars on the bottom where you cant see. Thank you though, ill try and pack that battery forward!
badpilot27
New member
you might also want to move the vertical stabilizers rearward because they look like they don't provide enough lateral stability as they look like they are too close to where the center of lift is. Not having enough lateral stability can make your plane slip or skid very easily which could make it easier for your plane to enter a aggravated stall and enter a spin similar to what you described.
quorneng
Master member
I would certainly recommend moving the fin(s) back to get there effectiveness as far behind the GF as possible.
You also have to consider the side area of the fuselage ahead of the CG. If counters the stabilising effect of the fin. Your delta has a pretty big flat sided fuselage well ahead of the delta wing.
As you have a pusher prop I would suggest a fin either side of the prop disc with as much area as possible aft of the delta trailing edge.
Note the fin on this Skyray sweeps backward well aft of the wing trailing edge. The red line is its CG position.
It flies very nicely and can also fly remarkably slowly.
You also have to consider the side area of the fuselage ahead of the CG. If counters the stabilising effect of the fin. Your delta has a pretty big flat sided fuselage well ahead of the delta wing.
As you have a pusher prop I would suggest a fin either side of the prop disc with as much area as possible aft of the delta trailing edge.
Note the fin on this Skyray sweeps backward well aft of the wing trailing edge. The red line is its CG position.
It flies very nicely and can also fly remarkably slowly.
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