Cranked Delta Flat Plate Aerofoil

[rich_hodgetts]

I have designed and flown a small depron flat plate model powered by an internally mounted 64mm ducted fan. In its original incarnation it had a pure delta wing section and whilst it flew well it lost a lot of speed when in a turn and during other high alpha manouvers.

I have redesigned the model with a cranked delta wing in an effort to gain some of the qualities of both delta and traditional planforms.

I am wondering however how this might affect the flight charachteristics of the model. I studied aeronautical engineering at university buy none of my old textbooks have any information on this somewhat unusual planform. I believe that is suffers from a pitch up problem as the angle of attack increases due to the sudden increase in vortex stregth from the highly swept inboard section. I was also wondering how far back the centre of pressure can be expected to be compared to its pure delta cousin.

Any info from those in the know would be appreciated. As its a simple model I ought to just make it and try it but I kind of want to understand the aerodynamics first!

Thanks

Rich

[Sparky Paul]

It will pitch up.
All my attempts at such things have been miserable failures at lower model speeds.
Once the power cuts off and it glides, unless you can get the glide speed close to the minimum speed when powered, it will pitch up and depart, most often when turning.
It's the nature of the beast with the vortex generating surface ahead of the c.g. at the higher angles of attack gliding needs.

[nmasters]

You're having superstall. Move the crank forward untill the strake is less than 20% of the total wing area.

http://users.acsol.net/~nmasters/vortex-lift/delta.html
http://users.acsol.net/~nmasters/vortex-lift/lettertoTWITT.html

[Troy]

Do you guys think the F-16 XL would suffer from this as well? Or does the XL wing act more like a delta? I ask because I have one in partial stages of building.
http://www.nasa.gov/centers/dryden/images/content/108492main_F-16XL-1_firstflight.jpg

[Sparky Paul]

Keep the speed up. Drag goes UP seriously with angle of attack.

[Troy]

Yah, that is what I'm figuring... as is standard with most deltas. The wing loading should be reasonably conservative for a belly landing DF but I won't be floating it in too slow.