3 ms·

Something similar happened on early Bell X-1 flights before they realized they had to modify the tail. Supersonic airflow does weird things, and tends to separ

by ohazi 5y ago

Something similar happened on early Bell X-1 flights before they realized they had to modify the tail. Supersonic airflow does weird things, and tends to separate from the horizontal stabilizer well ahead of the control surfaces on the trailing edge. Early transonic aircraft would go supersonic in a dive, wouldn't have the control authority to get out of it, and would careen into the ground. They eventually figured out that the entire tail needs to be the control surface if they wanted it to remain effective beyond mach 1. I thought this would have been well known by the time the DC-8 flew, but perhaps not, because if it had been, nobody in their right mind would have attempted a stunt like this.

redis_mlc 5y ago
Your comment matches common anecdotes, but I can provide more detail (I study aerodynamics.) The background is: - Britain sent data on the Miles M.52 supersonic jet to the US, so at least some Americans knew about the flying tail before the X-1 (first supersonic flight in 1948), and the Germans did some work on flying tails https://en.wikipedia.org/wiki/Miles_M.52 https://en.wikipedia.org/wiki/Miles_M.52 - most of the pre X-1 planes that crashed didn't reach Mach 1, but they did lose control. Those are called loss of control due to compressibility, not supersonic flights. - as the article says, the DC-8 flew ok up to Mach 0.97 in previous flights, so they thought things were fine. Note that in every Mach 1.0 flight that I've read about, the airspeed indicator jumps from around Mach 0.96 to 1.0, perhaps meaning the indicator is not accurate around Mach 1.0.
- knolan 5y ago
  You have to correct for the shockwave that sits in front of the pitot static probe. Otherwise you get crazy results.
- Gravityloss 5y ago
  It's crazy how advanced some UK technology was back then. Designing afterburners in 1943. And then canceling just before completion of the aircraft. The same happens in many cases. What's a successful breakthrough is usually not only technological. UK was extremely indebted after the second world war, mostly to USA. https://www.exchangerates.org.uk/articles/1325/the-200-year-pound-to-dollar-exchange-rate-history-from-5-in-1800s-to-todays.html https://www.exchangerates.org.uk/articles/1325/the-200-year-... Of course there was the wider sad story of management problems in UK industry and the long decline after the war.
  - redis_mlc 5y ago
    I grudgingly give credit to the British for being very clever (magnetron, battle of the beams, etc.) during and after WW2. Having said that, London had food rationing for 9 years after the war, and really didn't have the money or facilities that the Americans had. (A B-29 was used as the mothership for the X-1!) The W article below mentions "After the rocket plane experienced compressibility problems during 1947, it was modified with a variable-incidence tailplane following technology transfer with the United Kingdom." https://en.wikipedia.org/wiki/Bell_X-1 https://en.wikipedia.org/wiki/Bell_X-1 Additionally, around half the X-plane pilots died, so Britain avoided a lot of test pilot fatalities. The US poured unlimited funding and talent into the program, with everybody being stars/aces (Yeager, Hoover, etc.) Both were injured seriously and almost died in various X-plane tests. One X-plane test pilot set a record, then just quit and started a gun range.
  - cameronh90 5y ago
    The UK is also the only nation to successfully produce an orbital-class spacecraft then cancel their space program. Our inability to follow through in recent decades can be depressing. Hopefully SABRE/Skylon doesn't turn out to just be vaporware.
WalterBright 5y ago
The German Me-262 (jet fighter) had regular elevators, and if flying one you have to be very careful not to overspeed it because of separation.
andi999 5y ago
Precisely. It also makes me wonder if they really reached Mach 1.01. I mean if you can recover with such an airliner, why did everybody before chuck Yeager die?
- Gravityloss 5y ago
  Jetliners differ from old prop planes in that they do have a completely moving stabilizer, like fighter jets. But it's used for trimming, not for fast maneuvers. It has the regular elevators for faster maneuvers too.
jabl 5y ago
As an aside, most modern sailing boats tend to have rudders like this, called "skegless" or "spade" rudders. Though AFAIU this is to simplify construction, and rudders with a skeg are supposedly better.

by ohazi 5y ago

redis_mlc 5y ago

Your comment matches common anecdotes, but I can provide more detail (I study aerodynamics.) The background is: - Britain sent data on the Miles M.52 supersonic jet to the US, so at least some Americans knew about the flying tail before the X-1 (first supersonic flight in 1948), and the Germans did some work on flying tails https://en.wikipedia.org/wiki/Miles_M.52 https://en.wikipedia.org/wiki/Miles_M.52 - most of the pre X-1 planes that crashed didn't reach Mach 1, but they did lose control. Those are called loss of control due to compressibility, not supersonic flights. - as the article says, the DC-8 flew ok up to Mach 0.97 in previous flights, so they thought things were fine. Note that in every Mach 1.0 flight that I've read about, the airspeed indicator jumps from around Mach 0.96 to 1.0, perhaps meaning the indicator is not accurate around Mach 1.0.

knolan 5y ago
You have to correct for the shockwave that sits in front of the pitot static probe. Otherwise you get crazy results.
Gravityloss 5y ago
It's crazy how advanced some UK technology was back then. Designing afterburners in 1943. And then canceling just before completion of the aircraft. The same happens in many cases. What's a successful breakthrough is usually not only technological. UK was extremely indebted after the second world war, mostly to USA. https://www.exchangerates.org.uk/articles/1325/the-200-year-pound-to-dollar-exchange-rate-history-from-5-in-1800s-to-todays.html https://www.exchangerates.org.uk/articles/1325/the-200-year-... Of course there was the wider sad story of management problems in UK industry and the long decline after the war.
- redis_mlc 5y ago
  I grudgingly give credit to the British for being very clever (magnetron, battle of the beams, etc.) during and after WW2. Having said that, London had food rationing for 9 years after the war, and really didn't have the money or facilities that the Americans had. (A B-29 was used as the mothership for the X-1!) The W article below mentions "After the rocket plane experienced compressibility problems during 1947, it was modified with a variable-incidence tailplane following technology transfer with the United Kingdom." https://en.wikipedia.org/wiki/Bell_X-1 https://en.wikipedia.org/wiki/Bell_X-1 Additionally, around half the X-plane pilots died, so Britain avoided a lot of test pilot fatalities. The US poured unlimited funding and talent into the program, with everybody being stars/aces (Yeager, Hoover, etc.) Both were injured seriously and almost died in various X-plane tests. One X-plane test pilot set a record, then just quit and started a gun range.
- cameronh90 5y ago
  The UK is also the only nation to successfully produce an orbital-class spacecraft then cancel their space program. Our inability to follow through in recent decades can be depressing. Hopefully SABRE/Skylon doesn't turn out to just be vaporware.

WalterBright 5y ago

The German Me-262 (jet fighter) had regular elevators, and if flying one you have to be very careful not to overspeed it because of separation.

andi999 5y ago

Precisely. It also makes me wonder if they really reached Mach 1.01. I mean if you can recover with such an airliner, why did everybody before chuck Yeager die?

Gravityloss 5y ago
Jetliners differ from old prop planes in that they do have a completely moving stabilizer, like fighter jets. But it's used for trimming, not for fast maneuvers. It has the regular elevators for faster maneuvers too.

jabl 5y ago

As an aside, most modern sailing boats tend to have rudders like this, called "skegless" or "spade" rudders. Though AFAIU this is to simplify construction, and rudders with a skeg are supposedly better.