De Havilland 108 "Swallow"...

[TheGreenGoblin]

I recently reread "Wings On My Sleeve" by Eric 'Winkle' Brown and was interested in his comments on the DH 108 which he flew as part of the investigation into the accident that killed Geoffrey de Havilland...

“In 1946, he also led the crash investigation into the mid-air disintegration of a De Havilland DH108 jet as it attempted to break the sound barrier. The accident shocked the aviation community to such an extent that some people questioned the future of jet power. ‘Winkle’ Brown recreated the fatal flight, coming within seconds of death.”

In 1949 he test flew a modified (strengthened and control-boosted) de Havilland DH.108, after a crash in a similar aircraft while diving at speeds approaching the sound barrier had killed Geoffrey de Havilland, Jr. Brown initially started his tests from a height of 35,000 ft, rising to 45,000 ft and during a dive from the latter he achieved a Mach number of 0.985. It was only when attempting the tests from the same height as de Havilland, 4,000 ft, that he discovered that in a Mach 0.88 dive from that altitude the aircraft suffered from a high-g pitch oscillation at several hertz (Hz). "The ride was smooth, then suddenly it all went to pieces ... as the plane porpoised wildly my chin hit my chest, jerked hard back, slammed forward again, repeated it over and over, flogged by the awful whipping of the plane ...". Remembering the drill he had often practised, Brown managed to pull back gently on both stick and throttle and the motion; "... ceased as quickly as it had started". He believed that he survived the test flight partly because he was a shorter man, de Havilland having suffered a broken neck possibly due to the violent oscillation.

Test instrumentation on Brown's flight recorded during the oscillations accelerations of +4 and −3g's at 3 Hz.

Brown described the DH 108 as; "A killer. Nasty stall. Vicious undamped longitudinal oscillation at speed in bumps". All three DH.108 aircraft were lost in fatal accidents.

One can only salute John Derry for becoming the first pilot to take off and land an aircraft (the DH 108) that had gone supersonic.

On 12th April 1948, the aircraft gained a world-speed record for a 100 km closed circuit flight at 605.23 mph. De Havilland Chief Test Pilot John Derry then went on to exceed Mach 1 in the aircraft on 6th September 1948, this being the first British-designed aircraft to ‘break the sound barrier’.

He manage this in a dive and close to the edge of control.

[Pontius Navigator]

Reminds me of a high speed run in a Vulcan with automach trim out. I don't know exactly what the aircraft was doing.

I was in the back and whole Nav crate in front of me appeared to be going up and down. Now I know the crate wasn't moving and neither was I. The aircraft oscillation was causing my eyeballs to move but my brain interpretated it as the crate moving. We were near 0.93 but I don't know which way.

[TheGreenGoblin]

Reminds me of a high speed run in a Vulcan with automach trim out. I don't know exactly what the aircraft was doing.

I was in the back and whole Nav crate in front of me appeared to be going up and down. Now I know the crate wasn't moving and neither was I. The aircraft oscillation was causing my eyeballs to move but my brain interpretated it as the crate moving. We were near 0.93 but I don't know which way.

I remember reading that the auto-mach trim (up elevon) was designed to trim up as the Mach number went up to prevent the aircraft from diving as the centre of pressure moved backward on the delta wing. Could the pitch deviations you encountered have been down to pilot induced oscillation due to the absence of the auto-mach trim?

It seems that things could get very hairy indeed close to Mach 1...

In 1957, a Vulcan B.1 XA892 attached to the Aeroplane and Armament Experimental Establishment (A&AEE) at Boscombe Down for acceptance testing was unintentionally flown to an Indicated Mach Number (IMN) above 1.04, alarming the crew that it had reached supersonic speed. XA892's commander, Flt Lt Milt Cottee (RAAF), and co-pilot, Flt Lt Ray Bray (RAF), were tasked to fly at 478 mph (769 km/h) and 0.98 IMN, taking the aircraft to a load factor of 3 g. It climbed to 35,000 ft (11,000 m) and then dived, intending to reach the target speed at 27,000 ft (8,200 m). Approaching the target altitude, the throttles were closed and full up-elevator applied, but XA892 continued to pitch nose-down. Cottee contemplated pushing forward to go inverted and then rolling upright; instead, he opened the speed brakes. Although the airspeed was above their maximum operating speed, the speed brakes were undamaged and did slow the aircraft, which came back past the vertical at about 18,000 ft (5,500 m) and leveled off at 8,000 ft (2,400 m). There were no reports of a sonic boom, it is unlikely a true Mach Number of 1.0 was reached.[N 10] Afterwards, a rear bulkhead was found to be deformed.

In 1957, a Vulcan B.1 XA892 attached to the Aeroplane and Armament Experimental Establishment (A&AEE) at Boscombe Down for acceptance testing was unintentionally flown to an Indicated Mach Number (IMN) above 1.04, alarming the crew that it had reached supersonic speed.

Both quotes from Wikipedia...

I post a gratuitous photo of the most amazing looking aircraft. Hard to believe it flew just 7 years after the end of WW2 and its basic design dated back to the war...

[Pontius Navigator]

In Cyprus, early 70s, and I think Pete Armstrong had similar problem. I don't recall speeds or why but they were In a very high speed dive with aircraft diving at high speed. Both pilots pulled hard on the controls.

I am no pilot but the Vulcan was effectively FBW with control column movement sent powered control units PFCUs. As there was direct control there was no feedback. To give feedback there was Artificial Feel.

As the aircraft descended they began to regain control in thicker air below 30k. I think they pulled high G and may have overstretched the aircraft. They recovered.

In the subsequent inquiry the Brain Box determined that they should have let the aircraft descend and it would have recovered. Wasn't hindsight wonderful.

[boing]

I recall PN, I was in the right seat. It wasn't Pete.

Airtest with automach trim inop. Captain flying the test, we flew to maximum mach number whatever that was and then closed the throttles to decelerate. Instead of flying gently along and slowing down as we expected the nose pitched down and the mach number began to increase. An attempt was made to fly level but almost immediately the elevons lost effectiveness (the control column was moving back but it had no effect on pitch). The air brakes were deployed which seemed to cause a further pitch down and we began the wild ride. Control column hard back from the high forties to around 30,000 then the elevons, which were still held fully up, suddenly bit the thicker air and the nose pitched up rapidly followed by the obvious pilot action of pushing the control column forward which caused a rapid pitch down. It took a while to damp the phugoid. I imagine the mach shockwave suddenly repositioned as the air got thicker and the controls suddenly became effective.

RTB with no problems other than breaking the plotter's stop-watch but then came the interviews. The manufacturer's rep. examined the aircraft opining that it was less bent than a lot of the other aircraft on the line and that the RAF was plain stupid to deliberately fly the aircraft at maximum mach number without automach trim.

Strangely no one had thought to mention this pitch problem to either the Captain or myself during training so we were inadvertent test-pilots. Fortunately the aircraft was well rigged because the wings stayed level throughout the event, rolling upside down without control is not a pleasant thought. There were no thoughts of abandoning the aircraft, the high altitude gave us plenty of time to think and, as you know, getting the rear crew out would have been problematic.

I think I saw mach 0.98 in the dive. The Captain and the co-pilot had different styles of airspeed indicators, his was electrical with a digital display mine was the old analogue type. In the dive my airspeed was heading around the dial for the second time and I saw 110 knots on the indicator in the later parts of the dive.

Isn't flying fun.

.

[boing]

Stupid mistake in the above story.
The Captain's airspeed indicator was not digital, that was the altimeter. The Captain's ASI had two pointers as in a clock, the inner pointer marked the large increments, perhaps 100 knots per division, the outer pointer measured perhaps 100 knots per revolution. This was the more accurate instrument of the two. The co-pilots ASI had one pointer but it could make something like one and a half revolutions of the display which, in this case, was very confusing.

..

[TheGreenGoblin]

Airtest with automach trim inop.

"So ignorierten Sie die Experten wieder boing!..."

Interesting to have the input of one of the pilots at the pointy end in that case.

I was watching a documentary on the development of the Victor, also not designed as a supersonic aircraft, at 03:00 hrs this morning (as one does) and notice that the Victor's wing, while also a radical design based on German know how, was designed to ensure that the critical Mach number was the same over the whole wing and came very close to meeting the requirements of the area rule, the rule not known at design time, thereby minimizing drag at Mach 1. Test pilot Johnny Allam who "inadvertently" went supersonic in the Victor noted that the aircraft showed none of the critical Mach number and tuck issues associated with the Vulcan.

On 1 June 1956, a production Victor XA917 flown by test pilot Johnny Allam inadvertently exceeded the speed of sound after Allam let the nose drop slightly at a high power setting. Allam noticed a cockpit indication of Mach 1.1 and ground observers from Watford to Banbury reported hearing a sonic boom. The Victor maintained stability throughout the event. Aviation author Andrew Brookes has claimed that Allam broke the sound barrier knowingly to demonstrate the Victor's superiority to the earlier V-bombers. The Victor was the largest aircraft to have broken the sound barrier at that time.

https://en.wikipedia.org/wiki/Handley_Page_Victor

This was not the case for these gentlemen though...

Supersonic Victor Incident

https://jsaxon.org/index.htm

[Pontius Navigator]

Boing, thank you. Not sure where I got Pete from, either my false memory or some otherwise false post.

Can you PM me the captains name and the date. I think it was after I left in May 73.

Wherw you there when wee willy Wilkins (IIRC) OC Ops bent one seriously doing a flashy departure from Tehran. He never reported it and it was only discovered when one of the ground crew tripped on the wing. He thought at first it waz the airbrake that hadn't fully retracted.

[G-CPTN]

There was a significant amount of Nazi technology that was adopted/investigated following WWII.

[TheGreenGoblin]

There was a significant amount of Nazi technology that was adopted/investigated following WWII.

Indeed and the RAE employed German aerodynamicists to continue their work with them after the war vide. Johana Weber and Dietrich Küchemann (of Victor and Concorde fame).

[ian16th]

There was a former Nav on Victors, on the Boy Entrants forum, who indicated that it was pretty much SOP for Victors to be 'tested' for their ability to better Mach 1.0, on their delivery flight from Handley Page.

He is sadly no longer with us.

[TheGreenGoblin]

There was a former Nav on Victors, on the Boy Entrants forum, who indicated that it was pretty much SOP for Victors to be 'tested' for their ability to better Mach 1.0, on their delivery flight from Handley Page.

He is sadly no longer with us.

I do remember reading that Handley Page considered an optimised supersonic Victor, that involved a redesigned forward fuselage, an "area-ruled" rear fuselage, shorter wings, and redeveloped engines. Like many ideas it remained on the drawing board.

[G-CPTN]

Victor was retired from the nuclear mission in 1968, following the discovery of fatigue cracks.

[Pontius Navigator]

Victor was retired from the nuclear mission in 1968, following the discovery of fatigue cracks.

The two sqns of Mk 2 were both in the Blue Steel role. Blue Steel was vulnerable to SAM and was being replaced with the free fall lay down bomb. Unlike the Vulcan which did low level cruise at 240 kts with a 350 kts dash (in training) the Victor was limited to 220 kts.

The Victor 2 had a larger wing span (like the Mk2 Vulcan) to enable it to fly higher. Coincidentally the Victor 1 as a tanker was really only a stop gap as its fuel giveaway was much less than the Valiant. As the deterrent was to be assumed by the RN it was deemed better to convert the Victor 2 to the tanker role with BAE fitting new shorter wings. That is another story.

[boing]

PN Wilco, give me a chance to look at my logbook and I will have the date. Pete Armstrong was famous for a couple of things including being the Captain on the crew that stole the Tirpitz bulkhead from Cottesmore and smuggled it to Cyprus. Not bad for something that probably weighed a ton.

GG, the difference between the Victor and the Vulcan (and this would apply to the 108 also) was that the transonic shockwave on the Vulcan completely blanked off the elevons which provided pitch control. The Victor tail was mounted high up in clean air so it maintained pitch control.

To clarify further both the Captain and myself were aware the aircraft would enter an uncontrolled dive if the maximum mach number was exceeded. Neither of us had been briefed on recovery technique (obviously not a thing to do on a training flight). We had both flown the aircraft at maximum mach number previously with automach trim operative. Dispatch for a normal flight with the automach trim inoperative was permitted. What was probably unwise was to dispatch the aircraft for a post-maintenance test flight with the system inop.

.

[Undried Plum]

[boing]

Despite my loyalty to the Vulcan I suspect the Victor, at least the later Mk.2s, was a better aircraft than the Vulcan. Unfortunately the pounding of low level flight wore out the structure faster than the relatively more sturdy Vulcan design.

.

[TheGreenGoblin]

PN Wilco, give me a chance to look at my logbook and I will have the date. Pete Armstrong was famous for a couple of things including being the Captain on the crew that stole the Tirpitz bulkhead from Cottesmore and smuggled it to Cyprus. Not bad for something that probably weighed a ton.

GG, the difference between the Victor and the Vulcan (and this would apply to the 108 also) was that the transonic shockwave on the Vulcan completely blanked off the elevons which provided pitch control. The Victor tail was mounted high up in clean air so it maintained pitch control.

To clarify further both the Captain and myself were aware the aircraft would enter an uncontrolled dive if the maximum mach number was exceeded. Neither of us had been briefed on recovery technique (obviously not a thing to do on a training flight). We had both flown the aircraft at maximum mach number previously with automach trim operative. Dispatch for a normal flight with the automach trim inoperative was permitted. What was probably unwise was to dispatch the aircraft for a post-maintenance test flight with the system inop.

.

Thanks for that gen. boing. With the high tail I wonder whether the Victor was subject to deep/stable stall issues?

Although a cursory glance at this reveals a possible answer to my question...

https://aviation-safety.net/wikibase/wiki.php?id=55307

[boing]

GG

Don't really know but probably not. The deep stall issue tends to be a characteristic of passenger aircraft with rear mounted motors. When you create a long bodied passenger aircraft with engines at the back you have to put the wings a long way back to balance the forces (VC10, B727, BAC111). This puts the turbulent air from the wing roots in a stall right into the air intakes initially which is not good for recovery. The long forward body at a high angle to the airflow produces lift which rotates the nose up tending to resist recovery. If the pitch up gets high enough the turbulent air will blank the tail plane as you know and then you are in trouble. A stalled aircraft and no way to get the nose down. I am guessing the Victor, with wing root engine intakes, a shorter fore body and a better weight distribution did not suffer deep stall problems.

The Vulcan had no true stall you just got to a position where a very high nose angle caused so much drag that it stopped flying. The wing sweepback/camber controlled the airflow by something called a "Ram's horn vortex" to a very high AOA and I believe this effect was deliberately utilized on Concord.
.

[Pontius Navigator]

Regarding a Vulcan stall, there was a crash at Boscombe where I think it pancaked from altitude.

Pete Armstrong, the bulkhead is where my brain mist got the name.

IIRC the Vulcan 1 was capable of 0.98 IMN. Tbe Mk 2/201 was 0.93 (I think) and Mk 2/301 0.92. These were all Indicated and I have no idea on the TMN.

Probably at the time of the Transatlantic Air Race my Boss, Dad Stanley, reckoned that a Vulcan could go much faster than 0.93 with automach trim out. He had been on the GSU. I only recall flying with him on the Lancaster and doing 250 kts.