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crosswind

"Galloping Ghost" crashes at Reno Air Races

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"..is each elevator actuated by it's own bellcrank for redundancy?" Of course it would only be redundant if you had two cranks on a single shaft, otherwise there would be two potential failure points rather than one. It would be easier to just make everything stronger. On a different subject -- danger to spectators, I can't imagine that moving them further away would reduce the potential hazard to spectators from an out of control plane in the least, unless they were so far away that they'd need binoculars to see anything meaningful, unlike F1 where a strong enough barrier will stop a speeding car. The only hope is that it would give a (conscious) pilot more time to avoid the crowd if control was lost for some reason.

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I assume you mean with the modifications made to these aircraft. Stock these planes were never designed to fly at the speeds in this race. Also remember they are over 60 years or more old!!
Yes. Though we don't know how much of the original aircraft was still present. I would think the original design was based on a designed power output, wing design etc, not at all what these unlimited class configurations have. And I suppose in WWII they maybe were willing to allow for some possibility of failure that wouldn't be acceptable in peacetime. But when another racer has what looks to be a similar failure mode, well that's something I think an engineer would want to look at. scott s..

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On a different subject -- danger to spectators, I can't imagine that moving them further away would reduce the potential hazard to spectators from an out of control plane in the least, unless they were so far away that they'd need binoculars to see anything meaningful, unlike F1 where a strong enough barrier will stop a speeding car. The only hope is that it would give a (conscious) pilot more time to avoid the crowd if control was lost for some reason.
I saw some data suggesting that the facility met the requirements of FAA order 8900.1 3-151. In particular the section of the race course along the primary spectator area is designated the "show line" and 500' separation is required. In addition, a "scatter distance" is required to be computed for each class of aircraft and that distance must be applied for the "critical turn". In Reno's case the distance from the critical turn to the primary spectator area was 5000'. It seems like the criteria were developed based on the possibility of things falling off the race aircraft, and not on loss of control of the aircraft itself. scott s..

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"..I suppose in WWII they maybe were willing to allow for some possibility of failure that wouldn't be acceptable in peacetime." Quite likely I should think, at least in the sense that the planes would not be designed to have the long life expected in civil aviation. I'd have thought, though, that they would have been designed to cope with the sort of maneouvres that aerial battles would necessitate. So strong, but maybe not built to last. Just speculation though ;)

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Sounds like they might recover some data, hopefully useful in the investigation. scott s..

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I saw some data suggesting that the facility met the requirements of FAA order 8900.1 3-151. In particular the section of the race course along the primary spectator area is designated the "show line" and 500' separation is required. In addition, a "scatter distance" is required to be computed for each class of aircraft and that distance must be applied for the "critical turn". In Reno's case the distance from the critical turn to the primary spectator area was 5000'. It seems like the criteria were developed based on the possibility of things falling off the race aircraft, and not on loss of control of the aircraft itself. scott s. .
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. They explained that in the specific case of the Unlimited and Jet course layout, the critical turn is mid-way threw pylon 7, with the distance to the most western grandstands is 5,200'. The minimum distance for the "show line" is 500', but Reno maintains a minimum 1,200' separation distance. There are two considerations for their determination of scatter, one is "scatter distance" (based on the average known aircraft race speed and average race altitude at the critical turn) and the presumed "scatter cone" in the event of a crash (relating to an expanding debris field from the point of impact). The Jets run a rather short course to keep their average speeds below 475 mph, while the Unlimited "Gold" classification aircraft run a longer course, where they average 475 - 505 mph. (in 2009, an Air Force F-16 completed a lap on the Unlimited course at an average speed of 612 mph) In all, there are 3 courses for the 5 classes (sport plane, sport biplane, formula one, jets, unlimited, and AT-6), with the sport biplanes & formula one on course 1. Jets, AT-6, and the sports planes run on course 2, with the Unlimiteds running on course 3. Pylon 7 and 8 being the only common pylons listed as being the critical turn for all 3 courses. The accident involving Jimmy Leeward's "Galloping Ghost", a highly modified P-51, was outside any of their prior computer modeling, as this accident scenerio had never been considered or anticipated. They are considering future regulation modifications, including a redesigning of the trim-tab system on those aircraft exceeding 300 mph (or some speed to be determined later) and the application of a dead-man throttle switch or control on "all" race aircraft. Steve (Bear) CartwrightReno, NV

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Guest jahman
...They are considering future regulation modifications, including a redesigning of the trim-tab system...
Assuming the trim-tab caused an elevator assembly malfunction and not the other way around, as it could very well be elevator forces exceeed design forces when the aircraft wings ae shortened. Cheers, - jahman.

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Why would pulling the same g with cropped wings necessarily increase the elevator forces?

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Why would pulling the same g with cropped wings necessarily increase the elevator forces?
Perhaps because with cropped wings the plane would have to fly faster to maintain the same lift, consequently pulling higher G forces in tight turns. Just guessing though.. Scratch that. Jahman's point (previous post) was that shortening the wings was done so that the aircraft could pull higher Gs -- important in a race -- but maybe the elevator was not correspondingly strengthened.

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

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Guest jahman

As I said in my original post, the wing is a cantilever wing, so if you make the wing shorter the wing spar is also shorter, and given the same internal structure the shorter the wing spar the more weight it can bear. With a shorter wing you can also fly faster because flutter-inducing aeroelastic effects will also be reduced because, given the same internal structure, a shorter wing is also stiffer. Cheers, - jahman.

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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). 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.

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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.

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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

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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: dsc066.jpg 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.

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"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.

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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.

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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.

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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.

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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..

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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..

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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...

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

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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.

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