[HN Gopher] I was there when the DC-8 went supersonic
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I was there when the DC-8 went supersonic
Author : areoform
Score : 125 points
Date : 2021-08-22 03:51 UTC (19 hours ago)
(HTM) web link (www.airspacemag.com)
(TXT) w3m dump (www.airspacemag.com)
| dehrmann wrote:
| > Boeing will never try it [with the 707] because they don't want
| to be second
| Syonyk wrote:
| Yeah, but Tex Johnston had already rolled the 707 prototype
| back in 1955 as well. I think both companies had the good sense
| to not keep pushing the limits of showmanship with transport
| category aircraft.
| datameta wrote:
| The only time an airliner intentionally went supersonic besides
| the Concorde and Tu-144. Cool read.
| bombcar wrote:
| I believe there are a few unintentional cases ...
| https://en.wikipedia.org/wiki/China_Airlines_Flight_006 and
| https://en.wikipedia.org/wiki/TWA_Flight_841_(1979)
| Vecr wrote:
| Possibly the 737 MAX 8 aircraft that crashed as well, but I'm
| not sure it was confirmed.
| t0mas88 wrote:
| Those weren't supersonic, but they were above the mach limit
| for the aircraft. Which is dangerous because it could cause
| severe flutter and break control surfaces or worse.
| ohazi wrote:
| 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.
| andi999 wrote:
| 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 wrote:
| 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.
| redis_mlc wrote:
| 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
|
| - 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 wrote:
| You have to correct for the shockwave that sits in front of
| the pitot static probe. Otherwise you get crazy results.
| Gravityloss wrote:
| 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-.
| ..
|
| Of course there was the wider sad story of management
| problems in UK industry and the long decline after the war.
| cameronh90 wrote:
| 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.
| redis_mlc wrote:
| 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
|
| 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.
| jabl wrote:
| 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.
| WalterBright wrote:
| 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.
| bob229 wrote:
| Boring
| BXLE_1-1-BitIs1 wrote:
| With the arrival of jets, airliners required a movable stabiliser
| to accommodate CG changes as fuel was consumed from tanks in
| swept wings (later on fuel was put in the stabiliser in some
| models).
|
| Of course the supersonic program led to the development of the
| movable stabiliser.
|
| Typically an airliner stabiliser is moved with a screwjack. Air
| loads can overpower the screwjack;so, you have to relieve the air
| load enough to allow the screwjack to do its job.
|
| Next to none of this applies to smaller aircraft which have a
| variety of trim systems, mostly single axis.
| mastazi wrote:
| Edit: after re-reading the passage, I think that what happened is
| that the elevator had stalled, not the wing? So it wasn't a
| "normal" stall. Original comment below.
|
| > It stalled, because of the load. What he did, because he was
| smart, is something that no other pilot would do: He pushed over
| into the dive more,
|
| This part made me chuckle. The fact that you need to go nose down
| to recover from a stall is one of the first things new pilots
| learn[1], it's not "something no other pilot would do", but I get
| it, they're trying to make the story interesting for the general
| public.
|
| [1]
| https://www.faa.gov/regulations_policies/handbooks_manuals/a...
| joshvm wrote:
| Also pushing the nose down is the first thing you're taught as
| a glider pilot for engery management: launch failures, stalls,
| spin recovery, etc.
|
| Flight Chops did a video on this - it's drilled into commercial
| pilots (as well as glider pilots), but not GA nearly as much
|
| Think it's this one:
| https://m.youtube.com/watch?reload=9&v=m_tKShlf_gU
| mastazi wrote:
| > is the first thing you're taught as a glider pilot
|
| I love gliders, I grew up near a glider school, near Rome,
| Italy. I live in Australia now and it seems that glider
| culture is not as strong as in Europe.
|
| > it's drilled into commercial pilots
|
| Probably even more after Air France flight 447
|
| > but not GA nearly as much
|
| Really? It was one of the first things I learned as I was
| studying towards the PPL (I haven't finished it yet because
| flying is expensive :-( but I'm done studying the theory).
|
| I'm in Australia BTW, not in USA - maybe things are different
| throckmortra wrote:
| Wouldn't take advice from that guy
| https://www.avweb.com/news/pilot-arrested-after-airport-
| inci...
| Syonyk wrote:
| I would assume they were talking about the stabilizer trim
| motor not being able to run the stabilizer trim because of the
| loads.
|
| > _When he pulled back, the elevator was ineffective; it didn't
| do anything, so he said, "Well, I'll use the stabilizer," and
| the stabilizer wouldn't run. It stalled, because of the load._
|
| Key in there: "Wouldn't run."
|
| Almost all transport class aircraft have the same sort of trim
| setup on the tail - they have the movable elevator at the
| trailing edge, and then the entire horizontal stabilizer can
| tilt up/down for trim. This is a lot lower drag than having the
| elevator deflected, and gives you an extra control surface for
| emergency use as well - usually, the control authority of the
| entire moving stabilizer is more than the control authority of
| the elevator, so you can use that in an emergency for pitch.
|
| That the elevator wouldn't work effectively in the transsonic
| region was known - that's why they planned to use the whole
| moving stabilizer to pull out of the dive. Just, the air loads
| on it were too high with what limited authority the elevator
| still had, so they had to unload it again to run the trim, at
| which point they were able to recover.
|
| The term "stalled" is overloaded an awful lot in aviation, but
| I'm pretty sure in this case, it didn't refer to an aerodynamic
| stall of the tailplane. There's virtually no way it could be
| aerodynamically stalled at ~Mach 1 without ripping pieces off.
| mastazi wrote:
| Yes you are right it was the stabilizer not the elevator. I
| knew that airliners have a stabilizer, but I wasn't familiar
| with how it functions since I've only ever studied in
| relation to small planes, thanks for adding some details.
|
| And yes I think it was a "stall" in quotes, not a stall ;-)
| doctor_eval wrote:
| Well, you're trained to push the nose down in a stall because
| stalls normally happen at a very high AoA, when there is not
| enough airflow over the _wings_ , typically when you're
| pointing up, not when you're in a dive, and certainly not when
| you're in a Mach 1.01 dive. And this was an elevator stall.
|
| You're not taught to pitch down when there is no elevator
| authority - in fact you wouldn't be able to, by definition. But
| the problem here was _too much_ airflow over the horizontal
| stabiliser - from what I can see, it hadn't really stalled.
| Pitching down relieved the load and let them move the
| stabiliser. I suppose the combined deflection of the stabiliser
| and then the elevators was enough to get it under control
| again.
|
| I for one am always pretty impressed with stories like these
| because they show just how well the pilots understand their
| aircraft.
| mastazi wrote:
| > But the problem here was too much airflow over the
| horizontal stabiliser
|
| Yes, after thinking about it, maybe they shouldn't have used
| the word "stall" because in this case it's a bit ambiguous
| WalterBright wrote:
| A 727 once went into a dive due an autopilot malfunction. The
| separation of airflow over the stabilizer meant it was
| ineffective. The pilot recovered by lowering the landing gear. It
| tore the doors off, but slowed the jet down enough that he could
| regain control. I don't know if it went supersonic or not.
|
| If you're not careful with a jetliner, it can go into "mach tuck"
| if you're in a shallow dive, where (again) the separation of flow
| over the stabilizer makes it ineffective. In one incident on a
| 707, the pilots weren't paying attention and it went into a
| shallow dive, and mach tuck. The elevator was ineffective, and
| the stab trim system wasn't functioning (I don't recall why, but
| likely it was overloaded). So the copilot got down on his needs
| and cranked the manual stab trim wheel, and got control back just
| in time.
|
| (The 707 and 737's had a manual stab trim wheel, as does the
| 737MAX.)
|
| Edit: Well, well, another poster linked to a wikipedia article
| about the 727 incident
| https://en.wikipedia.org/wiki/TWA_Flight_841_(1979) so it seems
| my memory was accurate.
| throwthere wrote:
| Autopilot malfunction is too charitable to the pilots. From
| wiki, "Investigators believed that 727 pilots (in general, and
| this flight specifically) were setting the trailing edge flaps
| to two degrees during high altitude cruise, while at the same
| time pulling the circuit breaker for the slats so that they
| would not activate."
|
| The captain denied that, but who can believe him? He erased 21
| minutes out of 30 minutes recorded from the cockpit voice
| recorder.
| WalterBright wrote:
| Airplane accident causes are often complicated. I was told
| the story by my lead in helping me to understand separation.
| The reason for the dive was not germane, he just said
| autopilot malfunction.
|
| Probably the funnest part about working in engineering at
| Boeing was hearing all the war stories from the previous
| generation.
| LeonM wrote:
| > He erased 21 minutes out of 30 minutes recorded from the
| cockpit voice recorder.
|
| The investigation never concluded this.
|
| _In a deposition taken by the Safety Board, the captain
| stated that he usually activates the bulk-erase feature on
| the CVR at the conclusion of each flight to preclude
| inappropriate use of recorded conversations. However, in this
| instance, he could not recall having done so._
| throwthere wrote:
| Are we talking about the same investigation?
|
| The NTSB made the following statement in the accident
| report:
|
| We believe the captain's erasure of the CVR is a factor we
| cannot ignore and cannot sanction.
| yread wrote:
| 727 has a high horizon stab which means that this can also
| happen in a stall - the stab is in the disrupted airflow from
| the wings
| unnouinceput wrote:
| Quote: "And John Londelius, VP of Flight Test, gave us each a
| $1,000 bonus, so that was rather nice. That was back when a
| thousand dollars was worth a thousand dollars."
|
| That got me curious and got that in today's dollars that's
| ~$8750. Indeed back then a thousand dollars was worth a thousand
| dollars :).
| zhte415 wrote:
| 10% of the median price of a house then vs less than 2.5%
| today. Inflation isn't always a great measure for comparison,
| especially as over longer periods of time it starts to get
| decisively apples to oranges.
| gambiting wrote:
| I think it's better to look at certain items to understand
| the value. For instance, a brand new Ford Mustang back then
| was $2300 when it launched. So in that context, getting a
| $1000 bonus is very nice indeed.
| dwighttk wrote:
| Hey we didn't know we wanted oranges back then
| charles_f wrote:
| > But the recovery was a little scary. When he pulled back, the
| elevator was ineffective; it didn't do anything, so he said,
| "Well, I'll use the stabilizer," and the stabilizer wouldn't run.
| It stalled, because of the load. What he did, because he was
| smart, is something that no other pilot would do: He pushed over
| into the dive more, which relieved the load on the stabilizer.
|
| So. Nuts.
|
| Note that they also took off with broken slots, which prevented
| them from extending the flaps, unknowing why these were broken.
| BUT STILL WENT.
|
| For whatever reason I believe this wouldn't fly (ahah) today, too
| much risk.
| WalterBright wrote:
| > something that no other pilot would do
|
| I doubt that. A military fighter pilot would do that. Military
| fighter pilots are not afraid of diving.
|
| My dad (KW fighter pilot) told me his favorite method of
| attacking ack-ack guns was to dive straight down on them. Anti-
| aircraft gunners do _not_ want to fire straight up, for obvious
| reasons. He said he 'd keep one eye on the altimeter, one eye
| on the airspeed, and his third eye (!) on the target. The trick
| was to keep the airspeed below the maximum and leave yourself
| altitude to recover. He also got yelled at once for flying a
| B-17 like a fighter.
|
| The other two methods of attack are diving out of the sun (just
| put your airplane's shadow on the gun emplacement) so they
| can't see or hear you, and hedge-hopping off to the side. This
| makes it a very difficult deflection shot to hit you, and if
| you're close enough the gun cannot swivel fast enough to get a
| bead on you, then turn hard at the last second, line up, and
| blast it.
| GuB-42 wrote:
| In fact, I think most pilots would have done that.
|
| Pilots are trained to recover from stalls over and over,
| until it becomes second nature. And the way to do it is to
| follow into the dive until you regain control authority and
| then pull back slowly. This is not a regular stall but the
| idea is the same: pulling doesn't work? try pushing.
|
| Of course I wasn't in the cockpit, and I would probably be
| panicking if I was, but from my armchair, it looks like the
| kind of reaction a properly trained pilot would naturally
| have.
| t0mas88 wrote:
| Definitly would not fly today, there is a list called the MEL
| which specifies exactly when you can and cannot fly. Something
| like this where an engine failure would be unrecoverable would
| be an absolute "no fly" item.
| sokoloff wrote:
| The MEL (minimum equipment list) applies only to normal
| operations.
|
| Test flight programs are generally done in the experimental
| category, where the MEL would not apply.
|
| Side note: production airplanes are also regularly ferried in
| violation of the MEL or other airworthiness requirement under
| a ferry permit (Special Flight Permit is the official name) -
| https://www.faa.gov/about/office_org/field_offices/fsdo/phl/.
| ..
| xyzzy21 wrote:
| No many people realize that jets have been slowing down since the
| 707/DC-8. And this has been intentional as a trade against fuel
| efficiency. Both the 707 and DC-8 were nearly transonic by
| design.
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(page generated 2021-08-22 23:02 UTC)