WWI Replica Safety

Machinbird · 13 June 2009, 03:06 PM

There is a condition you do not want to encounter during the test flying build up on your new aircraft. Flutter. Few living people have any experience with the subject. The subject aircraft in the following sequence was flown by Fred Haise of Apollo 13 fame. The sequence ends just as the flutter is beginning to dampen as the chase pilot wisely backs away from an incipient catastrophic failure.
http://www.nasa.gov/centers/dryden/m...r_test_320.mov
From the relatively low frequency of the oscillation, I think the mode being excited was the spanwise bending mode of the stabilator, but I certainly wouldn't mind someone with more knowledge of the subject providing better information.
There is quite a bit more basic information available on the subject of flutter which is a part of the general subject of Aeroelastic phenomena.
The purpose of this topic is not to put fear into prospective test pilots, but to arm them with the information necessary to recognize that they might be approaching an aeroelastic limit on their flying machine.
Let me know if you would like to see more along this topic and of course, feel free to contribute.
Sid

hank jarrett · 14 June 2009, 06:11 AM

Experts on flutter are far and few between. In over 30 years in the aerospace industry I have only had one flutter specialist working for me (not that I understood a lot of what he did). What I DO know about flutter is I have seen it tear major components off an airframe is as little as two cycles! It looks like a simple overload failure until you look at the high speed films and see that there actually WAS flutter. The more commonly seen flutter (because the guys that experienced it actually had a chance to survive) is lower amplitude and doesn't diverge as fast. This is the "buzz" you feel in a surface or strut. You DON'T want to feel it more than once! If you EVER feel anything that feels like flutter the best thing to do (if you have time) is slow down and get on the ground. There are a lot of dead pilots from the study of flutter.
If anyone on this group is a flutter expert I would love to talk to them. There is a real need for some instructions to help the homebuilder understand and avoid flutter. I had planned to address flutter in the series of short articles on test flying I want to do, but all I can personally do is write about the standard design techniques used to avoid it. I am not up on the latest math and theory on flutter.
Hank

Blue Max Aviation DR1 · 14 June 2009, 08:31 AM

Quote:

Originally Posted by hank jarrett

Experts on flutter are far and few between. In over 30 years in the aerospace industry I have only had one flutter specialist working for me (not that I understood a lot of what he did). What I DO know about flutter is I have seen it tear major components off an airframe is as little as two cycles! It looks like a simple overload failure until you look at the high speed films and see that there actually WAS flutter. The more commonly seen flutter (because the guys that experienced it actually had a chance to survive) is lower amplitude and doesn't diverge as fast. This is the "buzz" you feel in a surface or strut. You DON'T want to feel it more than once! If you EVER feel anything that feels like flutter the best thing to do (if you have time) is slow down and get on the ground. There are a lot of dead pilots from the study of flutter.
If anyone on this group is a flutter expert I would love to talk to them. There is a real need for some instructions to help the homebuilder understand and avoid flutter. I had planned to address flutter in the series of short articles on test flying I want to do, but all I can personally do is write about the standard design techniques used to avoid it. I am not up on the latest math and theory on flutter.
Hank

One of my friends was a test pilot on the F-16, A7 and a few other types. He also flies small aircraft. He is in constant contact with most of the major test pilots, past and present and I will ask him for some suggestions. As a matter of interest, he is heavily into large-scale radio control model aircraft. We just have to scale up, or scale down his thinking.

Lynn

Machinbird · 14 June 2009, 09:13 AM

Here is a sailplane with a spanwise higher order oscillation (most likely driven by the aileron system).

YouTube - How to break a gliderÂ´s wing

I see two nodes in the right wing's motion (places where the wing is not moving) and I suspect the opposite wing is not moving in the same direction at the same time (out of phase). They were real lucky on this one because it appears to have reached equilibrium.

Here is a wind tunnel model of a well known airliner behaving in a interesting way. Not dead sure on this, but I think the yaw oscillation is driving the wing twisting as the weight of the engine pods twists the wing. Then the wing twisting causes yaw forces which further drive the oscillation.

YouTube - B747 flutter

Here is a classic flutter of a control surface. It appears to me that the port side surface is the one primarily driving the oscillation and that there is also some wagging of the rather slender tail cone. (Just learned that this is actually a RC sailplane) Obviously they knew they had a problem in the tail of this plane and the camera was put there to document it. If this had been a manned aircraft, this would be considered a high risk test and a parachute would be mandatory.

YouTube - V tail flutter (cam: Flycamone2)

Here is an RC model aircraft experiencing catastrophic failure. As Lynn was suggesting, what happens with RC models has some relevance to real aircraft.
This model had a flying wing design and thus could pitch rapidly enough to encounter flutter even at a relatively low speed.

YouTube - SAE Aero Design 2007 - Flutter

The last example for now is a wing in a wind tunnel with a long slender armament model bolted to a wing pylon. Here oscillations in the wing couple up with oscillations in the pylon mounted store and build with great rapidity.
The wing fails under overload in the negative g direction which is its weakest direction.

YouTube - A6 flutter

These examples are posted for use as discussion pieces.
This can be a highly technical subject, but all I'm hoping to pass on is that you will know Flutter if you see it and that you understand how serious it is.
Sid

TexasGR · 14 June 2009, 01:08 PM

Quote:

Originally Posted by Blue Max Aviation DR1

...snip...

– with a leg broken the night before. I got a cast five days later.

...snip...

I have one hour and ten minutes Captain time on the Lancaster – and one hour and ten minutes total time.

A few months back I was reading the memoirs of a WWII RN pilot who was assigned to Avro for acceptance testing. On his first day, the chief test pilot took him up and did a slow roll in the Lanc. He was amazed. Not really germane, but interesting.

Right now I am reading Jimmy Doolittle's autobiography "I could never be so lucky again." He was in Chile demonstrating the Curtiss P-1 (IIRC) in the early 20's, when a late night party with Chilean flyers had him demonstrating a handstand on a windowsill, 15' above ground. He kept his balance, but the windowsill crumbled and he landed on both ankles, one crack in one, many cracks in the other.

They rushed him to the hospital and the doctors put casts on both ankles, but the wrong cast on each one.

He still had to demonstrate the P-1, so escaped from the hospital and tried to fly the aircraft with the casts. That didn't work so well, so he cut the casts off and flew with busted ankles. When he tried to go back to the doctors for another cast, they refused to admit him. So, he went to a prosthetic salesman who fashioned some cast like things. To fly, he clipped his feet to the rudder pedals (which later on precluded his bailing out during an emergency later).

He traveled around South America for a couple of months like that. When he returned to the US, the doctors were horrified and his mangled ankles and how the set...he was confined to bed for months recovering.

Again, not germane, but interesting...at least to me.

Blue Max Aviation DR1 · 14 June 2009, 01:52 PM

Quote:

Originally Posted by TexasGR

A few months back I was reading the memoirs of a WWII RN pilot who was assigned to Avro for acceptance testing. On his first day, the chief test pilot took him up and did a slow roll in the Lanc. He was amazed. Not really germane, but interesting.

Right now I am reading Jimmy Doolittle's autobiography "I could never be so lucky again." He was in Chile demonstrating the Curtiss P-1 (IIRC) in the early 20's, when a late night party with Chilean flyers had him demonstrating a handstand on a windowsill, 15' above ground. He kept his balance, but the windowsill crumbled and he landed on both ankles, one crack in one, many cracks in the other.

They rushed him to the hospital and the doctors put casts on both ankles, but the wrong cast on each one.

He still had to demonstrate the P-1, so escaped from the hospital and tried to fly the aircraft with the casts. That didn't work so well, so he cut the casts off and flew with busted ankles. When he tried to go back to the doctors for another cast, they refused to admit him. So, he went to a prosthetic salesman who fashioned some cast like things. To fly, he clipped his feet to the rudder pedals (which later on precluded his bailing out during an emergency later).

He traveled around South America for a couple of months like that. When he returned to the US, the doctors were horrified and his mangled ankles and how the set...he was confined to bed for months recovering.

Again, not germane, but interesting...at least to me.

Me too.

Like Chuck Yeager partying the night before the sonic flight and breaking his shoulder on the way home. He fashioned a stick to activate the hatch lock and flew into history.
Jimmy Doolitle helped me with my Breedlove Land Speed record projects. He still had a lot of zip and determination.
I didn't think there was anything unusual about being carried out to the Lancaster, by the guys who were going with me. The only thing I found strange was the fact that three otherwise sane people were willing to go along with someone who had just broken his leg and had never flown a Lancaster.

Lynn

TexasGR · 14 June 2009, 02:03 PM

Quote:

Originally Posted by hank jarrett

There was a discussion started on the Pilots Reports thread that started to get pretty technical and we are going to move over here to continue it. ...

Hank:

OK, I finally caught up. I was confusing this with another thread, but now I've read past the BRS discussion.

Machinbird posted some links. I read the article/transcript on bd5, but it will take me a while longer to finish wading through the advisory circular/testing handbook. In the meantime, I will hold off on my earlier question about how to develop a test program and where to find the right "Boffins."

I've probably read 5-6 first hand accounts by test pilots, but never from the point of view of needing their services or needing to test an aircraft. There are a few more on my bookshelf, so when I read those I'll be looking at them from a new angle.

So, I'd like to ask about using WW I replicas for aerobatics instead.

I read many firsthand pilot accounts. Of all the WW I first hand accounts (and even a number from WW II), aircraft were rendered unsuitable for frontline service very quickly. I think I recall, by 1943, the Brits would pull an aircraft once it hit 100 hours operational flying.

During WW I (based on my anecdotal reading), if a patrol of 6 launched, 1 was almost guaranteed to turn back for various reasons. Within the AEF 3rd Pursuit Group (213th in Summer 1918) in France, their aircraft were in such bad shape, they always scheduled two standby pilots/planes because most of the time two of the designated planes had to abandon the operation before take-off. Another 2-3 would develop issues in the first 15 minutes of the patrol.

A high percentage of these issues were mechanical directly related to unreliable engines. Many more were 'buses' cobbled together from pranged ships, or they suffered battle damage resulting in a patchwork of repairs.

Still, many of the issues were pilot complaints about one "wing heavy", lack of response to control input, poor rigging, and other airframe & control surface matters not related to the early engines.

So, for aircraft using original construction methods that are all wood (e.g. Nick's Snipe) or aircraft with wooden spars (e.g. Jeff Brooks' DVII projects and the various DR I projects), would the repeated stresses eventually lead to weakening of the spars or other critical structural parts?

How would an owner/builder determine an acceptable lifetime for use in aerobatics?

Or is it just a matter over never over-stressing and routine inspections?

Can inspections reveal the most likely issues and/or incremental damage?

...and then what about metal fatigue, particularly on welds?

I read about replicas involved in aerobatic displays, so I know it can be done.

I've also read accounts (in Rickenbacker's book for example) where a virtually new aircraft's wing could fail and fold back in an otherwise normal power dive (Spad VII I think).

...sounds dangerous...not my choice for a faithful to original replica...

I should add: I don't know any of the builders and have no idea about their intentions or goals. I am just following their projects with keen interest and their aircraft seem to be good examples of the construction methods.

I do know their projects really sparked my interest, and I think it would an incredible natural high to do loops, barrel rolls, and spins in a Sopwith Pup or Triplane built by myself.

That is a rather muddled question (or open ended comment?), but I look forward to your response.

Thanks,
Brian

TexasGR · 14 June 2009, 02:28 PM

Quote:

Originally Posted by Blue Max Aviation DR1

...snip...
Jimmy Doolitle helped me with my Breedlove Land Speed record projects. He still had a lot of zip and determination.
...snip...

Lynn:

You knew Jimmy Doolittle?!?!?! Wow!!!

Still not germane, but I have to tell you I am finding his autobiography amazing.

First, I was amazed to learn he lived to be 95!

Second, I always imagined him (looking like Spencer Tracy) being more like a crusty, hard as nails, Greg Boyington type, who learned everything by trial and error (which is probably not fair to Boyington either).

Certainly he was a daredevil (master of the calculated risk is what they called him), but he was a true intellectual and a great aviation pioneer.

He earned the first (IIRC) doctorate in aeronautics. His testing on blind flying (just finished that part) was like a 500 year leap in terms of knowledge gained. He worked with Sperry, Kollsman, and numerous other famous name instrument makers to create the first attitude indicator, the first precision altimeter, and other instruments we rely on to this day.

Third, even in his book, he comes across with a degree of humility and modesty completely the opposite from the likes of Patton (another great American, albeit very arrogant). It is so rare to find that among major figures - at least the the handful I've had the displeasure of meeting (Gov. Pete DuPont being a surprise exception - very down to earth and friendly despite being born to extreme wealth and power).

I am learning so much about Jimmy Doolittle. In a sense, it is a shame his spetacular and courageous raid on Tokyo over-shadowed all his other accomplishments. Of couse, in the government run schools, they don't even teach about the raid, much less all the testing (and dying) that led to safe air transport...sorry, a tangent.

When I was 7 I guess, living in Orange County California, my best friend found a newspaper clipping that Col. Boyington was living in Bakersfield. It was 1975 (IIRC) and so I convinced my friend we should call directory assistance, get his number, and call him long distance.

He answered the phone and was extremely nice to two punk 7 year olds running up their parents' phone bill. Of course I said something stupid and embarassing...but he seemed genuinely amused. We only talked to him for 3 minutes or so, but to this day I recall every second

I tried calling Jimmy Thach (USN, developed Thach Weave) at his home in Coronado in late '79. There was no answer, and unfortunately he died the next year.

Wow...I am really in awe, to actually work with somebody like Jimmy Doolittle...wow!

Machinbird · 14 June 2009, 03:31 PM

Quote:

Originally Posted by TexasGR

.................................................. ...
So, for aircraft using original construction methods that are all wood (e.g. Nick's Snipe) or aircraft with wooden spars (e.g. Jeff Brooks' DVII projects and the various DR I projects), would the repeated stresses eventually lead to weakening of the spars or other critical structural parts?

How would an owner/builder determine an acceptable lifetime for use in aerobatics?

Or is it just a matter over never over-stressing and routine inspections?

Can inspections reveal the most likely issues and/or incremental damage?

...and then what about metal fatigue, particularly on welds?

I read about replicas involved in aerobatic displays, so I know it can be done.
.................................................. ............................................

Thanks,
Brian

Brian, you have written quite a bit, so I think I'll try to answer some of your easier questions.

As far as wood structure goes, my understanding is that wood does not fatigue but it can deteriorate and it can be overstressed. Inspections of wood structures would then be oriented to detecting these latter two conditions.
Metal fatigue of the welds themselves should not be a problem since properly executed welds are stronger than the adjacent tube. You do have to worry about the heat affected zone next to the welds because this can become embrittled if the weld is not done properly. Once the area around a weld is cleaned and painted, about the best you can hope for is to detect cracks in the structure using non destructive test methods.
The whole subject of strength of experimental aircraft and particularly replica aircraft is something to approach cautiously. Historically, aircraft load limits have been set at 2/3 of ultimate strength of the structure.
If you can test enough of your structure to determine it's ultimate load capability then you have a starting point. If you can't test enough of your structure to make an ultimate load determination. Pick an operating g load limit that seems reasonable but cautious and then monitor for damage while operating at that limit. Look at Achim Engels thread. He has done a lot of structural proof testing of sub-components.
I've seen an F-4 come back after pulling 12.5 g or so, but there was some damage. Most planes aren't quite that tough.
Sid

Blue Max Aviation DR1 · 14 June 2009, 04:23 PM

Quote:

Originally Posted by TexasGR

Lynn:

You knew Jimmy Doolittle?!?!?! Wow!!!

Still not germane, but I have to tell you I am finding his autobiography amazing.

First, I was amazed to learn he lived to be 95!

Second, I always imagined him (looking like Spencer Tracy) being more like a crusty, hard as nails, Greg Boyington type, who learned everything by trial and error (which is probably not fair to Boyington either).

Certainly he was a daredevil (master of the calculated risk is what they called him), but he was a true intellectual and a great aviation pioneer.

He earned the first (IIRC) doctorate in aeronautics. His testing on blind flying (just finished that part) was like a 500 year leap in terms of knowledge gained. He worked with Sperry, Kollsman, and numerous other famous name instrument makers to create the first attitude indicator, the first precision altimeter, and other instruments we rely on to this day.

Third, even in his book, he comes across with a degree of humility and modesty completely the opposite from the likes of Patton (another great American, albeit very arrogant). It is so rare to find that among major figures - at least the the handful I've had the displeasure of meeting (Gov. Pete DuPont being a surprise exception - very down to earth and friendly despite being born to extreme wealth and power).

I am learning so much about Jimmy Doolittle. In a sense, it is a shame his spetacular and courageous raid on Tokyo over-shadowed all his other accomplishments. Of couse, in the government run schools, they don't even teach about the raid, much less all the testing (and dying) that led to safe air transport...sorry, a tangent.

When I was 7 I guess, living in Orange County California, my best friend found a newspaper clipping that Col. Boyington was living in Bakersfield. It was 1975 (IIRC) and so I convinced my friend we should call directory assistance, get his number, and call him long distance.

He answered the phone and was extremely nice to two punk 7 year olds running up their parents' phone bill. Of course I said something stupid and embarassing...but he seemed genuinely amused. We only talked to him for 3 minutes or so, but to this day I recall every second

I tried calling Jimmy Thach (USN, developed Thach Weave) at his home in Coronado in late '79. There was no answer, and unfortunately he died the next year.

Wow...I am really in awe, to actually work with somebody like Jimmy Doolittle...wow!

I knew Greg Boyington very well, as a result of our original meeting at the Reno Air Races with my F4U-7 Corsair 133693. He was a true gentleman who always had time for people, as did Doolittle unlike some other aviation people (I won't say personalities) like Greenamyer. Unfortunately, Gre's last years were depleted by a fight with emphysema brought on by end-to-end smoking.
Lynn