What just happened at Reno?

[51fixer]

A thrust line offset is often lateral, a cant left or right but can be up or down as well. The cant is fixed but the forces on the airplane change with thrust; the resulting changes in torque/gyroscopic effect, spiral slipstream, and p-factor. Randy explained the effect of speed on pitch trim. Another reason for change in pitch trim is change of center of gravity. Wartime Mustangs had different pitch characteristics when the fuselage tank contained fuel; that's the large example. A more subtle example would be any tandem airplane pilot noting different trim settings, stick forces, or simply turning around and visually noting a slight change in elevator position when there is a rear seat passenger or change in load as compared to an empty airplane. Another reason is configuration change; extending flaps. Either way, the pilot finds a "new neutral" given the speed, configuration, and CG that day. For that reason I don't think any thrust line cant (fixed) could cause a greater effect than already provided for such as a common CG or configuration shift (dynamic).

Designers take all this into account when establishing the pitch trim range and pitch trim neutral. In general, wings provide lift and horizontal tails provide down force. The tails "negative" lift generates induced drag of its own - made greater when out of streamline. So,for efficiency, designers ideally install the horizontal tail with an angle of incidence to allow for streamlined elevators and trim in the heart of the operating envelope. Seems like this was one reason the handling of the F-86 improved so greatly when the flying horizontal tail was introduced; the tail could be positioned optimally for varying speed regimes. When we talk about the large forces involved with trimming a Reno racer nose down, that illustrates how the course speed differs greatly with the normal envelope of a stock Mustang. Without a flying tail, neutral trim will only be ideal in one speed/CG band; it will take unwanted deflection to go either really slow or really fast.

I'm on the record as being against speculation but a technical discussion is certainly fine with me whether it's on aerodynamics or paint. This thread has become too large to focus on just one thing, but I do hope that our top concern remains keeping this particularly respectful given the trauma that so many people are still going through.

Ken

P-51 doesn't have a L or R offset to the engine. The prop shaft is canted down 1 degree 45 sec on a stock P-51B,C,D or K when if left the factory.
Horizontal has 2 versions, early has a 2 degree positive angle and the late has a 1/2 degree positive angle.
I don't know how GG was set up so I'm not speculating on their setup.
If flying with a 2 degree horizontal then the down thrust line combined with an upward angle of the horizontal (lifting the tail) would be designed to lower the nose to fight the rising nose of an accelerating aircraft, at least to some degree. Because this relationship is fixed then the influence of the tail lifting force will vary as the speed varies I would guess.
One method of determining how these different racers were set up would be to examine the photos of them flying the straightaways on the course and look to see what trim position they have.
Racers have been known to run more toward the rear of the CG range as the weight the tail carries is on a smaller surface and induces less drag.

[ZRX61]

Just seen a post on the Furias FB page that claims someone clocked GG at 497mph when it passed RareBear, but on previous passes had been 480mph.

[51fixer]

A thrust line offset is often lateral, a cant left or right but can be up or down as well. The cant is fixed but the forces on the airplane change with thrust; the resulting changes in torque/gyroscopic effect, spiral slipstream, and p-factor. Randy explained the effect of speed on pitch trim. Another reason for change in pitch trim is change of center of gravity. Wartime Mustangs had different pitch characteristics when the fuselage tank contained fuel; that's the large example. A more subtle example would be any tandem airplane pilot noting different trim settings, stick forces, or simply turning around and visually noting a slight change in elevator position when there is a rear seat passenger or change in load as compared to an empty airplane. Another reason is configuration change; extending flaps. Either way, the pilot finds a "new neutral" given the speed, configuration, and CG that day. For that reason I don't think any thrust line cant (fixed) could cause a greater effect than already provided for such as a common CG or configuration shift (dynamic).

Designers take all this into account when establishing the pitch trim range and pitch trim neutral. In general, wings provide lift and horizontal tails provide down force. The tails "negative" lift generates induced drag of its own - made greater when out of streamline. So,for efficiency, designers ideally install the horizontal tail with an angle of incidence to allow for streamlined elevators and trim in the heart of the operating envelope. Seems like this was one reason the handling of the F-86 improved so greatly when the flying horizontal tail was introduced; the tail could be positioned optimally for varying speed regimes. When we talk about the large forces involved with trimming a Reno racer nose down, that illustrates how the course speed differs greatly with the normal envelope of a stock Mustang. Without a flying tail, neutral trim will only be ideal in one speed/CG band; it will take unwanted deflection to go either really slow or really fast.

I'm on the record as being against speculation but a technical discussion is certainly fine with me whether it's on aerodynamics or paint. This thread has become too large to focus on just one thing, but I do hope that our top concern remains keeping this particularly respectful given the trauma that so many people are still going through.

Ken

P-51 doesn't have a L or R offset to the engine. The prop shaft is canted down 1 degree 45 sec on a stock P-51B,C,D or K when if left the factory.
Horizontal has 2 versions, early has a 2 degree positive angle and the late has a 1/2 degree positive angle.
I don't know how GG was set up so I'm not speculating on their setup.
If flying with a 2 degree horizontal then the down thrust line combined with an upward angle of the horizontal (lifting the tail) would be designed to lower the nose to fight the rising nose of an accelerating aircraft, at least to some degree. Because this relationship is fixed then the influence of the tail lifting force will vary as the speed varies I would guess.
One method of determining how these different racers were set up would be to examine the photos of them flying the straightaways on the course and look to see what trim position they have.
Racers have been known to run more toward the rear of the CG range as the weight the tail carries is on a smaller surface and induces less drag.

From a print section-

[N3Njeff]

Just seen a post on the Furias FB page that claims someone clocked GG at 497mph when it passed RareBear, but on previous passes had been 480mph.

Sounds like Jimmy was doing what he said he would do and "Play another Card"

[Speedy]

Just seen a post on the Furias FB page that claims someone clocked GG at 497mph when it passed RareBear, but on previous passes had been 480mph.

He was already ahead of the Rare Bear on lap 2 when he flew in the 480 range. And while he had put a little distance between himself and Dawson during the course of the third lap, it's not like he was running off and leaving him...nor was he catching up to the first two aircraft.

Just for whatever my observation from pylon 8 is worth.

[mivey]

Since a growling stomach half an hour earlier was the only reason I wasn't in a position to get footage like that, I have asked myself what I think I'd have done. I'd like to think I'd have kept shooting. What's the point in running when you only have time for half a step?

August

You are right in how fast it happened. If I typed out the words that went through my head when he went upside down it would probably take me 30 seconds to say them and only 5 seconds went by before impact. After reflecting back on those thoughts I remember thinking I can try and run one of two directions. But each one could be the wrong one. There was no right decision. I was just lucky it was on a course that wasn't for me...even though I thought it was. This video shows how fast everything happened.

http://www.cnn.com/video/#/video/us/201 ... ?hpt=hp_t2

[CAPFlyer]

To you guys that were thrust into this horror take care of yourselves and your buddies. And remember there is NO harm in seeking help to cope if you need it!

I can only say this is too true Russ. I've consider myself to have been fortunate in the one loss of life I have seen directly and the one that I was on the other end of the phone immediately after. I did not seek professional help, but I did get help from those around me (friend and coworkers), many of whom had been through it before. I'd like to think had I needed the professional help I would have gotten it, but I can't be for sure (no one can until they need to make that decision). I have several relatives whom spent a lot of time in very dark places after witnessing traumatic events as railroad employees. One came out of it, one is still struggling. I'm sure most of us know people in the same situation in one way or another. I think this kind of event is the best time to remind everyone not just to ask for help and not be afraid to if they need it, but to remind people to do the right thing when they see someone who needs help and offer it, whether just being there for them, or helping them find the right professional help to deal with these things because I doubt there's many people who won't have at least one or two very traumatic events during their lives, and we all deal with them differently.

[Flat 12x2]

The racers are all trimmed prior to entering the course with a large nose up trim bias, the idea being as they approach the race speeds they can relax the push, as the trim will be correct for the speeds, 400 plus, so one less item to think about, in what would be a pretty intense environment.

The problem with that, James, is that at speed an aircraft has nose DOWN trim, not nose UP. Speed increases, nose down trim increases.

If the racers were set up for "race speed trim" as they were entering the course, that would require putting back pressure on the stick to keep it in level flight, with the back pressure decreasing as speed increased...not the other way around, as indicated in this passage.

I understand the idea of a little back pressure trim to assist with the control forces while making the turns, but this, too, would be a comparatively nose down trim condition while they were forming up for the start.

For the airplane to be somewhat manageable in the straight stretches when not in a bank, it would still require a significant amount of nose down trim when compared to "neutral".

I can remember reading an interview with Kevin Eldridge (SP?) who had to bail out of the Super Corsair, IIRC he said that the Super Corsair had its non adjustable trim set to run level at 450 mph, letting go of the stick when trying to get out at 200mph the Corsair just wanted to nose down, after he got out, the Corsair went into a dive and as the speed increased it started to 'pull up' by its self.

[oscardeuce]

I am going to change the topic for a minute.

It is clear that several posting here were witness to this event and the carnage that followed. I have been a paramedic for more than 20 years and while I am trained to deal with emergencies and even mass casualty events I can think of few things I have faced that would have come to this level. We are trained and we expect to see what we see. In this case it was not expected and people were not prepared.

That being said I am sure many who were involved and might not have been injured are finding it may be difficult to cope with what they experienced. I would suggest if you are having these issues to read up on post traumatic stress disorder or PTSD. If you have access to a employee assistance program take advantage of it. If not ask around to see if Fire/EMS or even the race organizers are offering any critical incident stress management. If so take advantage of that.

I know in EMS we all like to think of ourselves as impervious to what we see and what we deal with day to day but the reality is that we are all human and there are just somethings we are faced with that go well beyond our coping mechanisms. There is nothing wrong with seeking help to cope with this event. Sometimes just sitting down and talking it out does worlds of good and sometimes you just need more than that.

To you guys that were thrust into this horror take care of yourselves and your buddies. And remember there is NO harm in seeking help to cope if you need it!

Good insight, but as a 15 year Emergency Medicine physician, I would have to say something like this SHOULD have been expected and PREPARED for by the EMS system and local hospitals. I helped with EMS for the Akron show for many years, and we brief this exact scenario. We worked with 3 local hospitals to be sure they were aware the airshow was up and running, and that they were prepared for a mass casualty event. These events are rare, but we need to be ready to face what fate gives us. The best way to do that is preparation. I would assume their preparation and training was orders of magnitude above my 10,000-15,000 attendance airshow. I was very happy with my people when a cardiac event occured, everyone did exactly as briefed. That saves lives.
I spent the whole weekend running what ifs in my mind. My what ifs are stubbed toes to events like this. I even had Emergency Residents involved with the show to prepare them for similar issues.

One time had a mechaninc fall off the wing of an A-10. He dislocated his shoulder. We reduced it and had him back on the aircraft in 15 minutes.

[51fixer]

The racers are all trimmed prior to entering the course with a large nose up trim bias, the idea being as they approach the race speeds they can relax the push, as the trim will be correct for the speeds, 400 plus, so one less item to think about, in what would be a pretty intense environment.

The problem with that, James, is that at speed an aircraft has nose DOWN trim, not nose UP. Speed increases, nose down trim increases.

If the racers were set up for "race speed trim" as they were entering the course, that would require putting back pressure on the stick to keep it in level flight, with the back pressure decreasing as speed increased...not the other way around, as indicated in this passage.

I understand the idea of a little back pressure trim to assist with the control forces while making the turns, but this, too, would be a comparatively nose down trim condition while they were forming up for the start.

For the airplane to be somewhat manageable in the straight stretches when not in a bank, it would still require a significant amount of nose down trim when compared to "neutral".

I can remember reading an interview with Kevin Eldridge (SP?) who had to bail out of the Super Corsair, IIRC he said that the Super Corsair had its non adjustable trim set to run level at 450 mph, letting go of the stick when trying to get out at 200mph the Corsair just wanted to nose down, after he got out, the Corsair went into a dive and as the speed increased it started to 'pull up' by its self.

The Super Corsair had a fixed trim tab on the aileron (wing) but stock adjustable elevator trim system (tail). It was the aileron tab that was set for racing speed wings level.
The issue he had was the beast would want to roll on him as he released the grip on the stick and go nose down as a result.

[lmritger]

A thrust line offset is often lateral, a cant left or right but can be up or down as well. The cant is fixed but the forces on the airplane change with thrust; the resulting changes in torque/gyroscopic effect, spiral slipstream, and p-factor. Randy explained the effect of speed on pitch trim. Another reason for change in pitch trim is change of center of gravity. Wartime Mustangs had different pitch characteristics when the fuselage tank contained fuel; that's the large example. A more subtle example would be any tandem airplane pilot noting different trim settings, stick forces, or simply turning around and visually noting a slight change in elevator position when there is a rear seat passenger or change in load as compared to an empty airplane. Another reason is configuration change; extending flaps. Either way, the pilot finds a "new neutral" given the speed, configuration, and CG that day. For that reason I don't think any thrust line cant (fixed) could cause a greater effect than already provided for such as a common CG or configuration shift (dynamic).

Designers take all this into account when establishing the pitch trim range and pitch trim neutral. In general, wings provide lift and horizontal tails provide down force. The tails "negative" lift generates induced drag of its own - made greater when out of streamline. So,for efficiency, designers ideally install the horizontal tail with an angle of incidence to allow for streamlined elevators and trim in the heart of the operating envelope. Seems like this was one reason the handling of the F-86 improved so greatly when the flying horizontal tail was introduced; the tail could be positioned optimally for varying speed regimes. When we talk about the large forces involved with trimming a Reno racer nose down, that illustrates how the course speed differs greatly with the normal envelope of a stock Mustang. Without a flying tail, neutral trim will only be ideal in one speed/CG band; it will take unwanted deflection to go either really slow or really fast.

I'm on the record as being against speculation but a technical discussion is certainly fine with me whether it's on aerodynamics or paint. This thread has become too large to focus on just one thing, but I do hope that our top concern remains keeping this particularly respectful given the trauma that so many people are still going through.

Ken

P-51 doesn't have a L or R offset to the engine. The prop shaft is canted down 1 degree 45 sec on a stock P-51B,C,D or K when if left the factory.
Horizontal has 2 versions, early has a 2 degree positive angle and the late has a 1/2 degree positive angle.
I don't know how GG was set up so I'm not speculating on their setup.
If flying with a 2 degree horizontal then the down thrust line combined with an upward angle of the horizontal (lifting the tail) would be designed to lower the nose to fight the rising nose of an accelerating aircraft, at least to some degree. Because this relationship is fixed then the influence of the tail lifting force will vary as the speed varies I would guess.
One method of determining how these different racers were set up would be to examine the photos of them flying the straightaways on the course and look to see what trim position they have.
Racers have been known to run more toward the rear of the CG range as the weight the tail carries is on a smaller surface and induces less drag.

From a print section-

Rich, you are an absolute STAR. This (and the response from Ken posted earlier) were exactly the sorts of things I was hoping to learn here... I now have a better understanding of why designers change the thrust lines in their designs. And I will admit to being pleased as punch that I remembered the Mustang had a slight downward incline.

All things considered, it would be better for everyone if this horrible accident had not occurred, but I have certainly gained a lot of knowledge from the technical explanations that have been posted here about G-LOC, CG and trim, etc. My heartfelt thanks go to those who've taken the time to share that info.

Lynn

[ZRX61]

News just announced another fatality, but said it didn't occur at a local hospital?

[Randy Haskin]

But after the abrupt pitch up, the plane went ballistic... and inverted

The term 'ballistic' implies that the airplane was simply moving through the air acted on only by the forces of inertia and gravity. Ergo, the same path through the air that a bowling ball would make if it were hurled at the same velocity and angle. When used in the aviation context, it implies that there were no flight control inputs or forces that were affecting the flight path of the airplane.

I don't see that as being the case at all. In fact, quite the opposite appears to be true, in that the non-trimmed condition of the elevator (and some type of aileron input) was making the airplane execute a relatively high G loop/roll.

[sdennison]

Such a sad event. The speed of fate is so rapid. I have seen it time and time again in auto racing. I feel terrible for all affected and think that Hacker (Randy Haskins) has hit the aerodynamic portion dead nuts.

Auto racing is two dimensional and has more control over safety in that regard. Add the third dimension of air racing and no matter where you place the crowd line, it is truly in the hands of the "Master Plan". We, everyone involved, regulatory, participatory, and spectators need to realize what is involved and hopefully understand when fate steps in to a very controlled environment.

My condolences go to all who have suffered, the living and those lost. We must focus on why all were at the event and the love and joy they all shared for aviation and especially, ultimate high performance aviation.

Thank you for the opportunity to share my thoughts.

[mlenoch]

When we raced at Reno, we put several flat washers under the forward attach points on the horizontal stab. This would reduce the amount of forward trim we need to dial in when at high speed.
One other Mustang had the wing incidence reduced by adding washers at the forward attach points.
FYI. - VL