Forum: Technology

As for supercritical wings, they are primarily for subsonic aircraft to delay drag due to Mach as long as possible...they are not real efficeint at supersonic speeds because they tend to be too thick.

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Quote:

Gums,
Early supersonic jets had a "diamond" airfoil, like the VooDoo that I flew. Think the Zipper also had a diamond. It was really made for supersonic flight to exploit the various pressures behind the oblique shock waves. So we had one at leading edge, then two different ones resulting from the top and bottom facets. We also learned that if you had enough power you could get lift outta a flat plate, heh heh.

Yup, those folks didn't have wind tunnels to test the Zipper so they fired rockets with cameras on them to test different wing configs. So they came up with a Mach 2.5+ config and had to figure out how to make it turn when subsonic and land so they came up with LEF for maneuvering up to 520 kts and blown flaps for landing which also existed on the A-5 and F-4 both running the J79...

Can’t imagine the engineering stretches to do that with no Mach wind tunnels and using only slide rules.

wow, my brain hurts reading this thread. You also have to include the digital flight controls (FLCS) in this discussion. The F-16(which I fly) will not fly without it, the F-22 has a simmilar system. Anyone going to Purdue should know that modern fighters are unstable and cannot fly without computers. Just my two cents.....

Last edited by allenperos on Sep 03, 2005 - 09:26 AM; edited 1 time in total

Just for kicks guys, I'll be test flying the Pitts S-2B on 09/03/05. It is virtually divergent, almost but not quite. I'm going to put it through the ringer so to say and will post the results with pics. It has no FCC's, but a MAC of 1.25" to 3.25" depending on the model.

The airfoils are symetrical, even dual ailerons are. The superior wings have a 5 degree sweepback and the lower wing is slightly dehedralized. I will be testing the aircraft IAW "Aerodynamics for Naval Aviators", MATMACWC - this little plane can perform my friend, it's not going to shoot you to the moon like an F-16, however it will climb in the vertical for a substantial time period. It can do everything an F-16 can do on a smaller scale including going negative. Crazy Pilot

Active Member Joined: Jan 10, 2005 - 07:58 AM Posts: 137

I LOVE this thread and for a very good reason. I've done testing with highly swept designs (think F-16XL cranked arrow) on X-Plane for a few years and found that sweep combined with a very low wing loading (under 25lbs/sq ft) is good in most situations except low level and high speed. For the life of me I cannot get this thing to go supersonic down low (above FL250 it will break mach without afterburner). I've checked different airfoils from NACA 2412 to NACA 0009 and none work. In fact the best performance was achieved with a theoretical laminar flow flat plate. I'd love to hear from someone who can wrangle numbers better than me on what's wrong.

Chris W

Chris, the wing loading in my configuration will be 12.2 lbs/sqft. The NACA airfoil is the 0009, however our EAS is less 0.3 M, of course, just for technical and data gathering reasons, I have decided to do this. It's not a jet.

Down low in high speed your Reynolds #'s will be at high velocites, and large chord surfaces. The exact number will vary from airfoil to airfoil. Laminar flow from a flat plate will yield high RNs because of the low drag at low alpha units and low RNs at high alpha units. The flat plate has a lower profile creating eddies further downstream than an airfoil with ever increasing symetrical/asymetrical curvature.

When RN has increased to 50,000, transition happens on the flat plate and flow becomes partly turbulent. The Cd of the plate increases from laminar curve to the turbulent curve. When RN nears 20 to 50 million the drag curve of the plate approaches and nearly approaches the value for turbulent flow.

Didn't know you were a test pilot! Salute

Active Member Joined: Jan 10, 2005 - 07:58 AM Posts: 137

Oh lordy no I'm not a test pilot. Only on my computer after I get off of work Embarassed

I do however posess an interest in aerodynamics and a rather sick obsession with low aspect ratio aircraft ever since I read an article on the Facetmobile (Flight Journal: November/December 1996).

Turns out the problem was not with the design, it was system power. After a video card upgrade the jet slipped through mach 1.0 at 2000 feet with no trouble and minimal pitch change. The low RN info will really help now that I'm working on improving turn performance at higher altitudes.

Of course, from the comfort of my room Very Happy

Forum: Technology

Military Airfoils