Delta flight characteristics ?

[dvint]

I have plans for 29 " span delta with reflex airfoil. Plan to use
Mega 16-15-8 on 10 cells direct. Any unusual flight characteristics
for deltas?
Thanks

[vintage1]

loads.

Not usre of the theory, biut the 'dutch roll' is one, where it waggles its nose about as it flies..and the ability to fly extremely nose up and extremely slowly is another one.

[Ollie]

A low aspect ratio delta's wing operates entirely within the tip vortex. This produces a large down wash on the wing and a very large induced angle of attack. The induced angle of attack is additive and the high pitch attitude can give the impression that the delta is almost stall proof.

Landing a delta with the power off can be exciting. Be prepared to yell, "DEADSTICK," in a hysterical tone of voice. Low aspect ratio deltas glide only a little better than bricks. A very hard landing (crash) can be avoided by flairing just before touchdown. That's the way the Space Shuttle does it. As the glide is slowed, the coefficient of lift increases and the induced drag goes up as the square of the coefficient of lift. It's the huge induced drag that steepens the landing approach. Induced drag is also inversely proportional to aspect ratio. If very low wing loading is employed, a low aspect ratio delta can be landed at a reasonable speed without power by not having to resort to operating at such a high lift coefficient with the associated high drag. To get a reasonable glide slope a delta needs to be flown much faster than higher aspect ratio wings of similar wing loadings.

Since an electric powered delta will have a high wing loading, you should land it well before the battery charge runs out. You should also take care to use an adequate sized ESC that has little chance of cutting off due to thermal overload. Also, don't over prop it so as to induce thermal cut off.

[Bill Glover]

Typically, fast roll rate (as for any low aspect ratio wing), not so responsive in pitch. And as Ollie said, drag increases dramatically as you raise the nose at low (landing) speed. If you offset this by adding power then you can potentially fly very slowly, if not it will sink rapidly!

I had a Mirage 2000 with a piped .61 IC in the nose (prop driven), as you slowed down & increased power you had to hold more and more right aileron to offset the torque. Eventually you were at full right stick, any slower and the plane slowly rolled left :D

IIRC the full-size Vulcan bomber was capable of getting into a situation (nose high) where the drag exceeded the maximum thrust of the engines and there was insufficient control authority left to lower the nose - not good! At least one crashed on approach that way.

[max z]

IIRC the full-size Vulcan bomber was capable of getting into a situation (nose high) where the drag exceeded the maximum thrust of the engines and there was insufficient control authority left to lower the nose - not good!

That reminds me of the footage I saw of a Vulcan landing at Wellington (NZ) airport as part of an airshow in the 60's (?).
It landed short of the runway, damaged the landing gear but was able to power away from it and litterally staggered back into he sky. Awesome sight! IIRW it later crashed during landing somewhere else when the gear collapsed.

Max.

[John Boren]

I have designed and flown a lot of Delta winged craft in my day and if you have a decent airfoil they can be real floaters. Since they have a ton of wing area for their span they usually have a low wing loading, so I must disagree with a previous post.
The hardest part you will have in flying your delta is in the fact that it looks different in the air from what you are used to flying. As for the Dutch roll problem, just make sure you have enough vertical tail area and you won't have a problem.


John Boren

[dvint]

Thanks everyone-great information.

[Thomas B]

If you add a conical camber leading edge (sometimes referred to as a vortex flap), it does wonders in getting rid of the dutch roll effect some delts wings see. It also helps wth energy loss in tight turns.

This was a prominent feature in the B-58 delta winged bomber. This feature works VERY well in models and has been included in a number of published delta designs.

One way to create one is to simply cut away part of the leading edge of your plain delta. You start with nothing at the root edge and end up with a an inch or so cut away at the wingtip. glue this part back on canted down a few degrees and experiment a little.

[heli frapper]

Using a typical glider 1 kilo with high aspect ratio 5 to 1 long thin wing with surface of 25dm^2 you can expect a sink rate engine off of 1 metre per second

Using a trainer high wing type with same weight same surface area but lower aspect ratio 3 to 1 you can expect engine off sink rate of 2.5 metres per second

Using a square wing with 1 to 1 aspect ratio same surface- weight you can expect a sink ratio of 4.5 metres per second engine off

As the force of gravity is 9.8 or 10 for easy numbers the square wing requires a glide angle close to 45 degrees to glide and glider requires some 10 degrees or so to glide.


From the wing dezine the air treats a delta as a square wing in that it will be the same as the average cord of wing multiplied out so it resembles often a near 1 to 1 aspect ratio square wing to the atmoshere passing over wing

Basicaly this means delta engine off are near total bricks and for models if they have high wing loading are very dificult to fly unless a lot of power is used

The delta requires a huge proportion of its power just to stop the sink rate and the rest can be used for climbing
or speed

The lowwer aspect ratio return less induced drag that is induced drag goes up by the square not by the cubic
(ordinary drag goes up by the cubic) so this
feature helps large military planes get an extra return as they accelerate over the horizon

In models this dosnt really apply as we need to put deltas into turns to keep it in sight
and in turns deltas lose speed like no bodies buisness

In electric and ic the power to weight of models do not suit the delta shapes until you get BIG and realy fast
and go into kero jets
or except you decide to live with its limitations
short flights
easy rolling
and cool looks
and extra STOL type landing

Basicaly no plane is perfect and deltas got thier problems advantages too

Stephen