Fwd: Reno Air Race - Probable conclusion to fatal crash

Yes Lloyd, I read it.

If we are going to be huffy maybe I could reply that you don't know much about aerodynamics and didn't bother to find out before you posted.

But I generally don't go into that kind of reply. IT just leads to a pissing match and a lot of hard feelings.

So, instead, let me offer the following... Understand that this is very simplified approach to calculations of aerodynamic forces, but it valid in subsonic flight.

Equation: Lift = .001188 * (Coefficient of Lift) * (Velocity Squared) * (Wing Area)

.001188 constant allows: Sea level density altitude Velocity in MPH Wing Area in Square feet

And, of course, the equation can be rearranged to solve for any of the included terms.

So...

Take off performance: (given) Stall Speed = 100 MPH Wing Area = 235 SqFt

CL calculates to 1.66

Max Speed performance: (given) Velocity = 500 mph Wing Area 235 sq ft

CL calculates to .0066 (!)

If, at high speed, the nose pitched up to the take-off angle of attack (thus providing the take-off Coefficient of Lift) (given) Velocity = 500 mph Wing Area = 235 sq ft

Lift calculates to 249,340 pounds. For the 10,000 pound weight that means 24 Gs possible load factor.

Like I said earlier, the forces are tremendous! The thing that modulates the wing's lift is the tail. The long arm from wing to tail allows smaller forces to control the pitch of the wing.

The trim tab in question is located at the very aft edge of the control surface (elevator, aileron, whatever). The distance between the hinge points (elevator hinge and trim tab hinge) define the trim arm. That's how the small trim tab can deflect the much larger elevator, and the elevator control the pitch of the much larger wing.

Now, yes, there are other approaches that can be taken. Tailless (flying wing), tandem wing, and canards. But they all have to face the same issues.

Tailless types have very short tail arms and are thus very limited in their pitch authority. That usually means higher take off speeds.

Canards are kind of in the same category. The forward control surface (the canard?) is designed to stall before the wing stalls. Has to be this way to avoid the serious problems of a deep stall - where the wing stalls before the canard - with an uncontrollable pitch up resulting. Again that usually means higher take off speeds.

So the design of modern aircraft has evolved to the aft-tail arrangement because it offers the widest range of performance.

Conclusion: Directly related to the question at hand, this configuration also offers higher speed potential since it can provide higher pitch down forces at high speed.

I hope that perhaps this helps illustrate the "why" behind "this is how it's done".

The pitching moment of the main wing airfoil itself is the source of the pitch-up force. Not the tail.

You know your stuff alright.

But, for a moment, imagine what it would be like to fly any airplane without a trim system.

The aircraft will be naturally trimmed to fly hands-off at ONE GIVEN SPEED.

So at any other speed, the pilot has to provide the control force to maintain attitude (and thus airspeed)

Assuming we are trimmed for cruise - approach and landing are going to be "interesting"...

I don't think this P-51 pilot had time to be a hero, but I'm imagining what he might have accomplished given a few seconds to think it through. The knife edge idea was along the lines of steering away from the crowd, and cartwheeling elsewhere.

I once read about a quick-thinking pilot making an inverted approach, then rolling it over just in time for touchdown.

Also, a test pilot unable to break a stall crawled out of the cockpit out onto the nose to force it down.

Richard fired this volley in news:MaadnRinScHtmePTnZ2dnUVZ snipped-for-privacy@earthlink.com:

I guess I can only answer, "No, duh!". You don't get a _high_ positive angle of attack on the wing with a loosely trailing elevator. The elevator will more-or-less follow a neutral angle of attack with the wings. It's the elementary aerodynamics of an empenage-equipped aircraft.

LLoyd

Beryl fired this volley in news:j5l6q1$qg$1 @speranza.aioe.org:

Then there's the aerobatic pilot who landed on one wing. Anything (almost) is possible if you have large enough control surfaces, and enough power. For the one-wing guy, if it had been the _other_ wing, he'd have died, because P-torque was part of what he used to save himself.

LLoyd

Then there was this guy .

A document named "Flight test of P-51H Airplane", dated 14 October

Elevator trim for take off is 1 degree Nose Heavy, i.e., nose down.

It goes on to state that "at high manifold pressures approaching 90 Hg, where water injection is required, the elevator trim is inadequate and excessive forward pressure on the control stick is necessary to maintain level flight."

So, it appears that even at low (take off) speed the P-51H required some nose down trim and at high power settings the elevator trim was inadequate to maintain level flight and the pilot had to hold forward pressure on the stick.

When operating at high power settings it is obvious that full nose down trim plus additional stick force will be required. If while flying in this condition the elevator trim tab were to separate from the aircraft it is logical to assume that extremely violent nose up forces would occur.

Cheers,

John B.

"J. Clarke" fired this volley in news: snipped-for-privacy@hamster.jcbsbsdomain.local:

I've had two in-flight emergencies, and neither compromised the flight controls.

It takes one more thing, besides what we'd mentioned, to bring in a plane with a missing wing --- BALLS!

LLoyd

Sorry, sir, but balls have -much- less lift than an airfoil profile. Hanging your balls out will not replace a missing wing, and your legs will create considerable drag. The Bernoulli principle ensures that you'll have blue balls from the effort, though, with all that cool air flowing over 'em so quickly.

-- If you're trying to take a roomful of people by surprise, it's a lot easier to hit your targets if you don't yell going through the door. -- Lois McMaster Bujold

Larry Jaques fired this volley in news: snipped-for-privacy@4ax.com:

Larry, just landing that successfully, and then seeing the wing missing would have given me blue balls!

I've had one cockpit electrical fire in the air, and one high-speed malfunction deployment of my landing gear at about 60 knots over the maximum allowable speed at which to deploy the gear. Neither caused me any injury -- only a few very tense moments. (Well, in the case of the gear emergency, it took a half-hour, and three low passes over the tower in Sarasota to ensure I had everything down and locked. I only had two lights!)

Both were simple, non-fatal, not-control-surface, not-engine-failure emergencies that scared the Sh*T out of me. I handled them, sure -- that's only training. But I can't even imagine how scary it must be to survive a mid-air, and still retain control!

LLoyd

Maybe that "Flight test... " document was about a particular airplane that needed some re-rigging. The words "inadequate" and "excessive" say unsatisfactory.

The stock P-51 was made to be handled by twenty-something-year-old pilots with little experience. The vertical fin on the stocker is turned to offset P-Factor, relieving some of the need for the pilot to hold rudder at high power and low speed. The Reno racers are rigged differently. They have their fins set straight, they want to minimize trim drag.

And that would be draggy at 400+ mph.

All depends on the horizontal stab incidence. I think the trim tab should be doing very little at high speed.

I see no reason why it wouldn't.

Yeah, tense. Too bad it couldn't have been a few high-speed buzz runs past the tower, with all parts in working order, eh?

Dad and I were on an Aero Mexico flight from LaPaz to TJ (our boys-only vacation one year) and they were out of beer. The way the pilot flew, I was certain that he alone had drank it all. In TJ, he nearly overshot the runway, put her down on one wheel, and I could have sworn he was going to take us into the sand at the end of the runway. I swear the nose of the plane was hanging over the end when he pirouetted it in place far enough to get us rolling. That nose wheel was at 90 degrees from normal all that time. Dad was Air Force and he disagreed with my estimation of the landing. I gave it 1 point out of

Oh, no kidding!

-- If you're trying to take a roomful of people by surprise, it's a lot easier to hit your targets if you don't yell going through the door. -- Lois McMaster Bujold

Beryl fired this volley in news:j5mafu$okn$1 @speranza.aioe.org:

Yep, and the stabilizer is going to have its incidence angle set to produce _minimumum_ drag at the desired racing speed.

Therefore, one can almost completely rule out the possibility that losing the trim tab would have immediately resulted in full-up elevator.

LLoyd

Lloyd,

Speaking on behalf of college students adjoining the Sarasota Airport, I'd like to express my appreciation for your not overshooting the runway and taking out (say) the Circus Hall of Fame or the NatSci Lab.

Frank McKenney

LOL, the air force must instill that type of humor. One time my dad and I took a commercial flight and when the lady said we can use our seat cushion as a flotation device my dad turned to me and said ' When the water comes in I'm going to scoop it up in my hands and inhale, cause I'm not going back in the sea."

One time I was flying back to Vegas and the pilot must have had to wait and then get in line, like they missed the first opportunity. Anyhow, while meandering around lake mead the plane was banking and pulling up and up and up till I started to worry, then the plane slipped a bit to the left and then it was corrected like someone wasn't paying attention. I looked around like someone else might have noticed that, while I was thinking "Better not stall this thing over the lake or anywhere else !" As I got off I noticed the pilot was a short chick at about 30 and shook my head.

You are wrong Sir. The P-51 was designed to meet the specifications set out by the British Purchasing Commission and the prototype was rolled out 102 days after contract sighing and was first flown on 26 October 1940. They were first used by the Royal Air Force and from late 1943, were used by the USAAF's Eighth Air Force to escort bombers in raids over Germany,

I can find no evidence that the Vertical fin was offset in any manner and I do know that the late model fuselages and canopies required addition of a dorsal fin to increase lateral stability.

The report I quoted was prepared by the AAF Flight Test Division at the request of the Production Section, Procurement division, to verify the supplier's figures.

The stated conclusion was that "control and handling characteristics of the P-51H are good under conditions tested with the exception of a tendency to hunt directionally at indicated speeds above 400 MPH.

(this by the way is typical of a plane with a marginal amount of vertical stabilizer)

As for 20 year olds, I know of no military airplane that performance was dummied down to meet the abilities of inexperienced pilots. Quite the opposite in fact, they are designed to meet a need specified by the Military and in quite a few cases that results in aircraft that are distinctly "Twitchy". The F-100A, for example, officially entered USAF service on 27 September 1954 with 479th Fighter Wing at George AFB, CA. By 10 November 1954, the F-100As suffered six major accidents due to flight instability, structural failures, and hydraulic system failures, prompting the Air Force to ground the entire fleet until February 1955. Does that sound like an airplane designed to be flown by novices?

The F-51 did not have a movable horizontal stab. A trim tab will generate more force as air speed increases.

Cheers,

John B.

I saw a video of that, and there were six or eight things that were different in the video, and video of the plane on the ground. An obvious photoshop job. Not to say that planes have never landed with one wing, just that one of them was a hoax, and not too good a hoax at that.

Steve

A good landing is any landing you can walk away from. A great landing is any landing in which you can still use the airplane.

(quoted as best I can recall from a cartoon I saw)

Jon