"Galloping Ghost" crashes at Reno Air Races

[Guest jahman]

If you shorten a wing then, yes, with the same total lift here will be a decrease in the root bending stresses. But the root shear stresses will be unchanged, and the stresses on the skin panels and attachments will increase because of the increased wing loading (lb/ft²).

That's incorrect: With a shorter wing span all moments about the root decrease, including shear.

If you then increase the lift there will be an increase in all three stresses. The lift can't necessarily be increased by shortening the span.

Loss of lift from shortening the span is more than compensated for by increasing speed (the primary reason for shortening the span.)

I'm not following how the cropped wings have anything to do with the crash. As we all know, the elevator trim sets the speed for the plane. These planes are trimmed at speeds the NA engineers probably never imagined the plane would be sustainedly trimmed at. That means that tab is set at deflections higher than it was originally designed to be at. That could be simple reason enough for these tabs to keep breaking like this at the races.

You are assuming the elevator trim-tab failure caused the loss of control, but there is no evidence of this: The trim-tab could have failed as a result of elevator failure in another part of the elevator assembly. For example, in this photo of another P-51 with a similar elevator trim-tab failure: it's difficult to imagine the failed trim tab could have caused such a divergence in the position of the two elevator halves (note the other trim-tab is not affected). Without the blueprints we don't know whether the design safety margin built into the trim tab is greater than that of the elevator assembly. Consider if at higher than normal speeds trim-tab forces are greater, elevator forces are much, much, greater easily by more than an order of magnitude (given the ratio of trim-tab vs. elevator surface). Generally speaking, larger assemblies tend to have more aggressive (lower) design safety margins because more weight is saved so it would not be imprudent to assume the design safety margin of the elevator to be smaller than that of the trim-tab.

...On a slightly different point, who in the USA is responsible for maintenance and ensuring airworthiness of such aircraft? In the UK, such aircraft are only granted a Permit to Fly - not a full Certificate of Airworthiness. Also, maintenance, continued airworthiness and Permit-to-Fly renewal of this type ex-military aircraft are to be controlled by a suitable CAA approved BCAR A8–20 Organisation

See:FAA Part 21 - Certification Procedures- Subpart H - Airworthiness certificates- - Section 191, 193 - Experimental Certificates. Cheers, - jahman.

[Raindance 25]

"t's difficult to imagine the failed trim tab could have caused such a divergence in the position of the two elevator halves (note the other trim-tab is not affected)."If the tab failed and began to flutter violently in flight then I guess it could overstress the elevator, causing that in turn to fail.

[Guest jahman]

"t's difficult to imagine the failed trim tab could have caused such a divergence in the position of the two elevator halves (note the other trim-tab is not affected)."If the tab failed and began to flutter violently in flight then I guess it could overstress the elevator, causing that in turn to fail.

Yes that could happen, but the flutter would also somehow have to stop rather quickly before complete failure of the elevator assembly. Cheers, - jahman.

[dmaher 0]

IMO the damage to the elevator above clearly looks to be due to the trim failure.It appears the left side elevator has broken free…its nearly resting balanced minus the tab weight.There would have been a huge asymmetrical force on the elevator with a trim failure on one side.…considering the speed and the size of the tabs. I understand trim tabs and servo tabs have a significant mechanical advantage...Actual forces are deceptively large.Enough to wrench a stick out of a racer’s hand and climb un-commanded at high G's.

Pulling higher Gs requires more lift. How would cropping the wings - reducing wing area - help to achieve this?

A clipped wing gets its req'd lift with a higher speed.Area is reduced but dynamic pressure is higher.The wing spar, being shorter, can carry more weight too.Like G's in turns at speed.

[mgh 89]

That's incorrect: With a shorter wing span all moments about the root decrease, including shear.

It is correct. Shear is not a moment, it's a force which has to be transmitted from the wings to the fuselage. If W is the weight of the fusdelage then the shear force is nW/2 at each wing root when pulling nG. It's independent of wing span.

[scott967 62]

First of all, I'm no expert on the rules and regulations pertaining to air shows and/or air racing, but as is to be expected, we've been getting a lot of information on local television and radio about the crash a week ago at the Reno Air Races. With that in mind, I am only repeating what I have learned from those in charge of the Reno Air Races and from the FAA, as has been discussed over the last few days. ... [snip for brevity]

thanks for the update (this and others!) scott s..

[scott967 62]

I'm not sure I'm folloeing it either. On a slightly different point, who in the USA is responsible for maintenance and ensuring airworthiness of such aircraft? In the UK, such aircraft are only granted a Permit to Fly - not a full Certificate of Airworthiness. Also, maintenance, continued airworthiness and Permit-to-Fly renewal of this type ex-military aircraft are to be controlled by a suitable CAA approved BCAR A8–20 Organisation

F. Aircraft Eligibility. To be eligible to participate in an aviation event, an aircraft must be in an airworthy condition. The waiver or authorization’s named responsible person is responsible for ensuring that the participating aircraft have the required documentation to show the aircraft is in airworthy condition. 1) To ensure that the aircraft participating in an aviation event are airworthy, an IIC or his or her representative should examine the general condition of the aircraft and required aircraft documents, and determine if the aircraft has met the specified inspections. 2) The ASI should use one of the following methods to determine compliance with required inspections: a) Review of the aircraft’s maintenance records (logbooks); or :( Review of a current and valid form supplied by the owner/operator.1. The completed form must be similar to the sample FAA Aircraft Inspection and Status Form (Figure 3-38).2. An appropriately qualified airman who holds a mechanic or repairman certificate or an Inspection Authorization (IA) must sign the form.3. The ASI who inspected the aircraft and determined it was airworthy may sign the form.4. If an ASI has previously signed off on this form, an aircraft inspection is not required. From: FAA Order 8900.1 scott s..

[dmaher 0]

It is correct. Shear is not a moment, it's a force which has to be transmitted from the wings to the fuselage. If W is the weight of the fusdelage then the shear force is nW/2 at each wing root when pulling nG. It's independent of wing span.

jahman didn't actually say shear was a moment either. Length does affect the moment - and shorter is stronger.I don’t know this, but intuitively I’d think the moment is more critical than the shear on a wing.Because of the material...

[BIGSKY 316]

"who in the USA is responsible for maintenance and ensuring airworthiness of such aircraft?" the owner / Operator, per part 43 of the FAR's

[mgh 89]

jahman didn't actually say shear was a moment either. Length does affect the moment - and shorter is stronger.I don’t know this, but intuitively I’d think the moment is more critical than the shear on a wing.Because of the material...

Yes he did.

That's incorrect: With a shorter wing span all moments about the root decrease, including shear.

Aircraft aren't stressed on the basis of intuition. The root fittings will be stressed based on the design loads they have to carry.

[pilotguy03 1]

His health record are up to date. Just because he is "old" doesn't mean he cannot fly. The airplane was having control problems with his trim tab for the elevators.

[mgh 89]

His health record are up to date. Just because he is "old" doesn't mean he cannot fly. The airplane was having control problems with his trim tab for the elevators.

That is true but Google pilot heart attack