De Havilland 108 "Swallow"...

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Re: De Havilland 108 "Swallow"...

#21 Post by boing » Thu Nov 19, 2020 6:27 pm

One thing you need to watch on a swept wing aircraft is the movement of CofG as fuel is used. Not so much applicable to relatively small aircraft like the 108 but certainly on larger aircraft. Because of the wing sweep the forward wing fuel tanks will be forward of the CofG and the aft wing tanks to the rear of it. The fuselage tanks may also be involved.

Usually there is some sort of crude fuel balancing on older designs but over time a trim and control load problem can occur. CofG forward will give you a more stable aircraft in pitch and vice versa, a more aft CofG can improve fuel burn depending on design. Military aircraft tend to use more of the CofG envelope than civilian ones. If a fuel balancing malfunction occurs or if the pilot deliberately moves the CofG to an extreme position the aircraft can respond noticeable differently in pitch.

Problem with the stall is that the inboard section of the wing is usually designed to stall first because this is a more stable situation. Of course, the engine intakes and tail plane are going to be directly in the path of the turbulence.

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Re: De Havilland 108 "Swallow"...

#22 Post by Pontius Navigator » Thu Nov 19, 2020 6:32 pm

Here is the report of the Boscombe stall crash

https://www.google.com/url?sa=t&source= ... 5810671407

And a slightly different story:
On 11 May 1964, Vulcan B.2 XH535 crashed during a demonstration. The aircraft entered a spin while a very low speed and high rate of descent was being demonstrated. The landing parachute was deployed, stopping the spin briefly before it began to spin again. At around 2,500 ft (760 m) the aircraft commander instructed the crew to abandon the aircraft. The commander and co-pilot ejected successfully, but none of the rear compartment crew did so, presumably due to the g forces in the spin.[230]

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Re: De Havilland 108 "Swallow"...

#23 Post by ian16th » Thu Nov 19, 2020 6:45 pm

boing wrote:
Thu Nov 19, 2020 6:27 pm
One thing you need to watch on a swept wing aircraft is the movement of CofG as fuel is used. Not so much applicable to relatively small aircraft like the 108 but certainly on larger aircraft. Because of the wing sweep the forward wing fuel tanks will be forward of the CofG and the aft wing tanks to the rear of it. The fuselage tanks may also be involved.

Usually there is some sort of crude fuel balancing on older designs but over time a trim and control load problem can occur. CofG forward will give you a more stable aircraft in pitch and vice versa, a more aft CofG can improve fuel burn depending on design. Military aircraft tend to use more of the CofG envelope than civilian ones. If a fuel balancing malfunction occurs or if the pilot deliberately moves the CofG to an extreme position the aircraft can respond noticeable differently in pitch.

Problem with the stall is that the inboard section of the wing is usually designed to stall first because this is a more stable situation. Of course, the engine intakes and tail plane are going to be directly in the path of the turbulence.

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I installed an IBM 1800 process control computer on the Concorde Fuel Test Rig at BAC In Bristol, its sole function was to do calculations WRT fuel use and a/c stability.

I suppose that Concorde was the only civilian a/c to approach the fuel consumption of a military one.
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Re: De Havilland 108 "Swallow"...

#24 Post by boing » Thu Nov 19, 2020 6:58 pm

PN

I'd like to see a technical report of that incident since both, there appear to be two stories reported, seem incomplete.

Certainly you could not truly "stall" a Vulcan and I am sure that anyone from Boscombe knew better than to try. They may have been doing some sort of high AoA trial. If you landed and decided to do "aerodynamic braking", which meant put the wheels on and continue to hold the nose up until a very low speed, you still had elevator control (which does not prove there is no stall but a stalled wing would provide less lift and the nose would probably drop on its own).

Look at this landing, you can see that the pilot can barely see over the nose but the wing still has not stalled and the elevators are effective. If you look carefully you can see the little lever dangling below the tail cone that is supposed to tell the pilot he has the nose too high and he risks a tail strike. It illuminated two blue lights on the coaming. One was a warning and the other told you you had probably screwed up.



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Re: De Havilland 108 "Swallow"...

#25 Post by boing » Thu Nov 19, 2020 7:05 pm

Ian,

As you know you could control the Vulcan fuel distribution (to a limited extent) manually but the fuel pumps that moved the fuel between 1 and 7 tanks were pretty darned powerful. Once you started to transfer to even things up, if you got distracted, you would almost certainly screw things up and need to start moving fuel in the opposite direction again.

Thank Heaven they computerised Concord.

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Re: De Havilland 108 "Swallow"...

#26 Post by Pontius Navigator » Thu Nov 19, 2020 7:11 pm

Boing, you got in before I could add the source for the second case :

Wikiwand/en/avro_vulcan

I think the falling leaf description was the more accurate. Whether it span or effectively stalled I don't know.

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Re: De Havilland 108 "Swallow"...

#27 Post by Pontius Navigator » Thu Nov 19, 2020 7:18 pm

An incident with CofG and distraction occurred at Butterworth when we did a pilot swap for night continuity. Our copilot, RW, decided to balance the fuel as we taxied to dispersal but forgot to check. He then..... (could not remember when I ribbed him many years later). Ricky Crowder then jumped in and off we went. Already light our rotation was spirited and he bunted at 2,500 ft. Our boss, Bob Tanner commented and Ricky checked the Cof G which was well aft. We did a circuit just sorting it out.

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Re: De Havilland 108 "Swallow"...

#28 Post by boing » Thu Nov 19, 2020 8:26 pm

Was that Rob?

It was a trap. Since the fuel control panel slid in and out under the instrument panel it was very easy to set the switches, get distracted, and stow the panel out of sight with the pumps still on. Since the fuel panel must be stowed to change pilots I can see the events.

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Re: De Havilland 108 "Swallow"...

#29 Post by Pontius Navigator » Thu Nov 19, 2020 8:56 pm

Correct😊
I know one practise was to put a glove on the switches

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Re: De Havilland 108 "Swallow"...

#30 Post by boing » Thu Nov 19, 2020 9:06 pm

I just trained myself, it only took the usual 3000 repetitions.
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Re: De Havilland 108 "Swallow"...

#31 Post by TheGreenGoblin » Fri Nov 20, 2020 6:32 pm

While we discuss the British aerial speed merchants of the 1950's one might make a call out to the preposterous The Bristol 188 which first flew in 1961.

https://www.rafmuseum.org.uk/documents/ ... script.pdf



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Re: De Havilland 108 "Swallow"...

#32 Post by Pontius Navigator » Fri Nov 20, 2020 8:52 pm

TGG, in fuel burn?

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Re: De Havilland 108 "Swallow"...

#33 Post by TheGreenGoblin » Fri Nov 20, 2020 9:06 pm

Pontius Navigator wrote:
Fri Nov 20, 2020 8:52 pm
TGG, in fuel burn?
Both aircraft (I await Boac's righteous wrath) were both supersonic joke's when it came to endurance, although the Lightning by dint of operational development was eventually turned into an aircraft equal to its mission. The Bristol sadly, although a lot faster than the Lightning, was never much use, not even as a prototype but I love the fact that it was developed, when Britain was still a vibrant engineering powerhouse!
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Re: De Havilland 108 "Swallow"...

#34 Post by G-CPTN » Fri Nov 20, 2020 9:09 pm

The late 1940s / 1950s were a wealth of aircraft types from many manufacturers - mostly gone by being absorbed or bankrupted.

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Re: De Havilland 108 "Swallow"...

#35 Post by boing » Fri Nov 20, 2020 9:50 pm

I've always been amused by Fairey. Small company, Swordfish to FD2.

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Re: De Havilland 108 "Swallow"...

#36 Post by G-CPTN » Fri Nov 20, 2020 9:55 pm

boing wrote:
Fri Nov 20, 2020 9:50 pm
I've always been amused by Fairey. Small company, Swordfish to FD2.
Gannet and Rotodyne too . . .

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Re: De Havilland 108 "Swallow"...

#37 Post by Pontius Navigator » Fri Nov 20, 2020 10:10 pm

Bristol from Freighter to 188
Saunders Roe, boats to SR177
Shorts Sterling to Belslow
Blackburn
Gloucester Javelin to Meteor (I reversed that deliberately)

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