When the DC-8 Went Supersonic (2011)(airspacemag.com)
airspacemag.com
When the DC-8 Went Supersonic (2011)
https://www.airspacemag.com/history-of-flight/i-was-there-when-the-dc-8-went-supersonic-27846699/?all
30 comments
Good story, and a great example of test pilot presence of mind as the crew discovers that the elevators don't work...
Near criminally stupid though. Not only did they have issues with two separate control surfaces, a unplanned stall and a safety violation on takeoff, they did all of these things for a marketing piece establishing the plane was safe. This at a time where metal fatigue and structural load was not well understood, as the Europeans where finding out as their planes decompressed explosively midair.
There was a 747-SP that went supersonic by accident and was only saved by the crew deploying the landing gear to slow the plane down. He amount of damage was non trivial.
Someone will probably jump all over the critics of Douglas and point out Boeing’s Tex Johnson’s barrel row. 1) that was not endorsed by the company and 2) was a neutral G maneuver. 3) the company appropriately freaked and told him never to do that again.
We have occupational safety and standards operating procedures for a reason.
There was a 747-SP that went supersonic by accident and was only saved by the crew deploying the landing gear to slow the plane down. He amount of damage was non trivial.
Someone will probably jump all over the critics of Douglas and point out Boeing’s Tex Johnson’s barrel row. 1) that was not endorsed by the company and 2) was a neutral G maneuver. 3) the company appropriately freaked and told him never to do that again.
We have occupational safety and standards operating procedures for a reason.
Since when is voluntary experimentation on a test rig, under controlled circumstances, criminally stupid? It’s not like this was a passenger flight.
It would warrant criticism if the pilot tried it without informing the crew prior to takeoff. All participants entered into the activity with an understanding that they were risking their lives.
These people did it because they enjoyed the challenge, not to score points with corporate overlords or jockey for a raise and a promotion. The marketing angle was simply to provide cost justification and demonstrate that a perceptible reward would be earned with the risk undertaken.
It would warrant criticism if the pilot tried it without informing the crew prior to takeoff. All participants entered into the activity with an understanding that they were risking their lives.
These people did it because they enjoyed the challenge, not to score points with corporate overlords or jockey for a raise and a promotion. The marketing angle was simply to provide cost justification and demonstrate that a perceptible reward would be earned with the risk undertaken.
That's a optimistic reading of the article. The article states it was for marketing reasons, and also states that they had several plan threating outcomes that were not planned for.
If it where in the context of understanding the plane's behavior at trans-sonic speeds, I can understand it, but that is not really given as a justification.
If it where in the context of understanding the plane's behavior at trans-sonic speeds, I can understand it, but that is not really given as a justification.
> This at a time where metal fatigue and structural load was not well understood
You're mixing up problems that are completely irrelevant to the issue. Fatigue is only an issue in high load cycles (typically over 10^6) which means that it becomes a problem only after years of significant commercial operations.
Running a prototype is, obviously, not the case.
Moreover, structures designed to meet fatigue requirements are designed so that ultimate load is far higher than operational loads (over 5 or 10 times), and ultimate loads are covered by their own design scenario.
Fatigue and ultimate loads only cause problems when aged structures (i.e., planes that were well used and reaching their design life) are subjected to loads close to their ultimate load. That may lead structures to fail when subjected to loads that, although higher than typical operational loads, are far from the expected limit strength.
Here's an example of a retired C130 being used in firefighting missions that gets its wings to break off mid-flight.
https://www.youtube.com/watch?v=PK49QALNj-0
Running a prototype is, obviously, not the case.
You're mixing up problems that are completely irrelevant to the issue. Fatigue is only an issue in high load cycles (typically over 10^6) which means that it becomes a problem only after years of significant commercial operations.
Running a prototype is, obviously, not the case.
Moreover, structures designed to meet fatigue requirements are designed so that ultimate load is far higher than operational loads (over 5 or 10 times), and ultimate loads are covered by their own design scenario.
Fatigue and ultimate loads only cause problems when aged structures (i.e., planes that were well used and reaching their design life) are subjected to loads close to their ultimate load. That may lead structures to fail when subjected to loads that, although higher than typical operational loads, are far from the expected limit strength.
Here's an example of a retired C130 being used in firefighting missions that gets its wings to break off mid-flight.
https://www.youtube.com/watch?v=PK49QALNj-0
Running a prototype is, obviously, not the case.
We know that now. They didn't know that then. Remember, this was well less then 5 years after the de Haviland Comet's started falling out of the air because they used square windows instead of ovals, and metal fatigue at the corners of the windows were resulting in massively more rapid wear cycles then projected.
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What surprised me the most was that they did it on purpose!
Two reasons are pretty clear from the article. It was fun. And it could be sold to management as safety PR.
The engineering data alone from the flight was worth the risk. What they measured and learned during the flight probably gave the aircraft designers at Douglas priceless insights.
Modern aircraft undergo testing near the speed of sound to find issues as well.
https://youtu.be/rpP7hsuVuoE?t=1155
Not only safety but so they could say they beat Boeing.
What does it mean when he says he pushed over into the dive more? Does that mean he went faster down?
Yes. To relieve stress on the stabilizer.
Yes, it means he pitched down even more.
In a dive.
The biggest issue wouldn't have been designing a power system that could bring a jet to mach speeds. The bragging rights for them were that the plane survived the transition to mach 1.
Does something magically happen at Mach 1.0 that would compromise structural integrity significantly more than, say, Mach .99...9?
If you read the parts where they mention “buffeting” that’s the dangerous part, where uneven airflow introduces instability, causing the airframe to rattle.
Buffeting occurs when the soundwaves of the noise of the craft and its motion directly affect the air as it flows across the surface of the plane.
This happens as the plane enters the shockwave of the sound barrier, and ceases when they accelerate beyond the speed of sound.
At and beyond Mach 1 the buffeting is behind the plane, and flight is smoother, with no rattling or shaking from the incidental turbulence.
It also happens when decelerating, although it’s easier to decelerate safely through the buffeting quickly, since less time is spent in the shockwave, and a reduction in speed grants improved control.
Buffeting occurs when the soundwaves of the noise of the craft and its motion directly affect the air as it flows across the surface of the plane.
This happens as the plane enters the shockwave of the sound barrier, and ceases when they accelerate beyond the speed of sound.
At and beyond Mach 1 the buffeting is behind the plane, and flight is smoother, with no rattling or shaking from the incidental turbulence.
It also happens when decelerating, although it’s easier to decelerate safely through the buffeting quickly, since less time is spent in the shockwave, and a reduction in speed grants improved control.
I see, thanks for the explanation
It seems not quite - supersonic airflow would already be having an effect in places if the plane was doing 0.99 see https://www.quora.com/What-happens-if-an-airliner-reaches-Ma...
In a commercial passenger jet designed in the 1950's.
... which subsequently went into commercial service, for 19 years!
If you count freighters, the DC-8 is still in commercial service. Not too many of them, though.
Queue up the Ryan Reynolds "But Why?" gif for this one I think.