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Unregistered
11-08-2003, 06:13 PM
In the Air Classics Reno '03 edition it was suggested that the Rare Bear Team is considering installing a leading edge extension on the wing -to help with the critical mach number (I think). I find this extremely interesting as it was discussed on this site several years back with Matt Jackson -after he had flown the Bear.

Does anyone know what the current critical mach is on the Bear wing?

I believe (from reading) that the critical mach for the Mustang wing is about .8 (point 8) ...or rather that it is getting sonic flow over the airfoil at that speed.

Thanks,
John

Randy Haskin
11-09-2003, 02:42 AM
Perhaps the world's first Learjet-winged Bearcat is just around the corner?
:D

Ron101502
11-09-2003, 04:34 PM
I know Levitz died due to rudder or elevator flutter, but the day he chrashed I was looking at how thin the wing was from a head on view and wondered how that wing could sustain 6 gs. Although the wing didn't fail and a Lear is obviously heavier than the LearStang, every large airplane I have flown has a limit on how much fuel can be in the wings while there is still fuel in the belly, and since the Lear has tip tanks, I wonder if the Lear needed fuel in the tip tanks to reduce the bending moment of the wing. I know a few former Lear pilots at work and I will ask them next time I see them, but I wonder if the bending force on the wings at 6gs without fuel in the tip tanks (which have been removed) would cause a Lear wing failure under racing conditions.

I have heard that there is just no money to do the Bear wing mod, but I know from experience that A. in the F-4 (hard wing) the critical Mach number was about .93 and you could hold that at about 90% N1. If you went to military power the speed would stay at Mach .93 and the only difference was an increase in fuel flow, and B. The DC- 9 has a red line of .84Mach but the Mach trim compensatorer starts back pressure at about .82. If you turn of the MTC and hand fly the airplane you can definitely feel it start to Mach tuck although it is easy to trim out and control. But if the speed was varying (as going around pylons at high G and rolling out at at lower G) I can imagine that it would be a VERY busy cockpit just trying to keep the pitch attitude where you want it with constantly changeing pitch force (for example, an F-4 pulling a given G load supersonic and decelerating to subsonic, with no change in stick position/load, would result in an increase of 2-3 Gs just due to the forward movement of the center of pressure on the wing that occurs when decelerating from super to subsonic flight.

Ron Henning

stuntflyr
11-09-2003, 11:28 PM
Ron,
Very interesting stuff. I would add to the comment on the Lear wing that, I was told, the Learstang was always operating at an IAS over the Lear redline at race speeds. I don't have a rating in a Lear nor have I flown one so I don't know this from personal experience.

I would imagine that the airplane was flown with forces exceeding 6 G on a regular basis on the course and during it's initial test period.

In general I figured the Lear wing had a good airfoil but the wing area was too large to benefit the airplane in a pylon race at the speeds they go today. When G'ed up hard in a corner my impression was it really would change direction well, so maybe on a small course it would've had some advantage.

Your picture of the CP moving from airspeed changes sounds like some unlimited pilots descriptions of their experiences. Attitude changes without stick movement or control pressure changes seem to have been part and parcel of aft loaded and oversped pylon racers going back to the forties.

Add to that the GP activity of the Bearcat and you have a nasty little racing plane that has it's tongue hanging out (as I would imagine does it's intrepid pilot) trying to keep up at the speeds that are competitive today.

Just my opinion, what the hell do I know?

Chris...

hattend
11-10-2003, 10:38 AM
Chris, Randy, John, Ron,

I remember reading somewhere these guys are only pulling 3 g's on the turns at Reno. Much more than that scrubs off too much speed.

I could be talking out of my ...er hat.

John Penney, do you have time to enlighten me (us) on the g's you're pulling in the Bear on the turns?

Thanks
Don

speeddemon
11-10-2003, 10:56 AM
If I remember correctly, the Lear wing was a virtually exact copy of a Swedish fighter plane...so I wouldn't worry too much about the wing/stress loading of the design.

And the wing was not the speed-limiting factor on that aircraft. Both in Vendetta and MAII, the wing was one of the most efficient out on the course.

That wing (since it was the same on both planes) never came close to the design speeds within the Lear's envelope.

stuntflyr
11-10-2003, 11:06 AM
Perhaps the Learstang never exceeded the design speed of the fighter's wing from which the Lear sprung. I wonder what the IAS limit on the Lear 23/24 is, and what determined that speed. As you say, it may not have been the wing at all, but some other factor.
Chris...