How fast is Fast enough?

[mtnmnstr]

With the Dynamic Soaring reaching faster and faster speeds at what point will the current designs need to change do to aerodynamic forces. May-be bumping a scaled down version of air compression?

Gene

[Z06kal]

I think we are already at that point. Very few planes have proven to be stable flyers in the 200's.

[Ollie]

http://www.charlesriverrc.org/articles/flying/markdrela_ds.htm
"An unbreakable full-size sailplane with L/D=50 could probably reach 500 mph in 50 mph DS conditions. Not for the faint of heart.-- - Mark"
http://members.tripod.com/douglasturner/id27.htm
" An interesting note is that the maximum potential final velocity is linearly dependent on the velocity delta across the shear boundary. So if the shear delta goes from 30 to 60 mph, the final velocity potential goes from 224 mph to 448 mph!"
http://www.sloperacing.com/results/ds-speeds.htm
http://www.rcgroups.com/forums/showthread.php?t=101242

"Straight wings of high aspect ratio maintain these properties at speeds up to 70%, sometimes even 80%, of the speed of sound."
"Wing Theory" by Robert T. Jones, Chapter Five, page 74.

[Z06kal]

Having DS'd in 30mph conditions and 60mph conditions I can attest to the energy difference. Huge is not even the word for it. On a 60mph day you can be doing 200mph in 3 circuits. It's just unreal how much more energy there is.

[Ollie]

Again:
"Not for the faint of heart.-- - Mark"
http://www.shredair.com/album/dsfest5.html

"Crinkle, crinkle, little spar,
strained beyond the yield-point far.
Up above the world so high,
bits and pieces in the sky..."
-Darrol Stinton

[mtnmnstr]

Thanks Ollie.

Gene

[raptor22]

"Crinkle, crinkle, little spar,
strained beyond the yield-point far.
Up above the world so high,
bits and pieces in the sky..."
-Darrol Stinton

LOL.

Gene, like ollie said, its not a matter of compressibility. it's simply that the planes are warping like hell from the stresses.

[jay flay tway]

I know very little about DS but...
Why do they still make these DS planes light. Does weight matter much at such high speeds? I know they have to be launched though at lower speeds...
Why not more use of aluminum and other stronger materials? Or twin booms or biplanes to avoid the flex.

[raptor22]

Aluminum is not nearly as strong as carbon.

Anyways, have you ever seen a double or triple carbon opus? Its one fo the few real purpose-ds layups and is heavy as hell.

--Alex

[ElectroLawndart]

Having only seeing a video that was posted, I would think the G's build up fast. That being said, weight would be very critical. An extra once equals an extra pound at 16 G's.

Dart

[Ollie]

At 250 MPH and a lap time of 1.7 seconds, the plane has about 32G's (Cl = 0.2). If the weight of the plane is about 15 pounds at 250 MPH, the kinetic energy is about 57,000 foot-pounds. The same plane with maximum lift (Cl = 1.6) in a maximum gust has about 250G's. Awesome!!!