Author Topic: D.H.88 Comet Follow-Ons  (Read 2294 times)

Offline Old Wombat

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Re: D.H.88 Comet Follow-Ons
« Reply #50 on: July 22, 2021, 03:31:26 PM »
 :smiley:
"This is the Captain. We have a little problem with our engine sequence, so we may experience some slight turbulence and, ah, explode."

Offline Robomog

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Re: D.H.88 Comet Follow-Ons
« Reply #51 on: July 22, 2021, 06:27:50 PM »
This thread just keeps on giving !

Love the DH 88F   :-*

(Hmmmm  thinks: DH88f on floats ?)


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Offline jcf

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Re: D.H.88 Comet Follow-Ons
« Reply #52 on: July 23, 2021, 01:28:51 AM »
 :smiley:
“Conspiracy theory’s got to be simple.
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Offline GTX_Admin

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Re: D.H.88 Comet Follow-Ons
« Reply #53 on: July 24, 2021, 02:33:09 AM »
 :smiley:
All hail the God of Frustration!!!

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Offline apophenia

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Re: D.H.88 Comet Follow-Ons
« Reply #54 on: July 24, 2021, 07:22:07 AM »
Thanks folks!

...(Hmmmm  thinks: DH88f on floats ?)...

I know, right? What is it about the Comet that keeps suggesting floats? But it sure does ...  ;D
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Offline ChernayaAkula

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Re: D.H.88 Comet Follow-Ons
« Reply #55 on: July 29, 2021, 08:53:18 AM »
The D.H.128 Meteorite is just lovely!  :-*
Cheers,
Moritz

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Offline apophenia

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Re: D.H.88 Comet Follow-Ons
« Reply #56 on: July 30, 2021, 07:17:07 AM »
Thanks Moritz! I really do wonder how the Gipsy Twelve would have faired had DH offered a variant without reversed-cooling.

Such an engine would have been in the same class as the Renault 12R, Walter Sagitta I-MR, or Isotta Fraschini Gamma. None of those engines excelled as fighter powerplants. But I can imagine the imaginary conventionally-cooled Gipsy Twelves on up-powered Oxfords, for example ...
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Offline jcf

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Re: D.H.88 Comet Follow-Ons
« Reply #57 on: July 31, 2021, 06:40:03 AM »
Thanks Moritz! I really do wonder how the Gipsy Twelve would have faired had DH offered a variant without reversed-cooling.

Such an engine would have been in the same class as the Renault 12R, Walter Sagitta I-MR, or Isotta Fraschini Gamma. None of those engines excelled as fighter powerplants. But I can imagine the imaginary conventionally-cooled Gipsy Twelves on up-powered Oxfords, for example ...

There was nothing in the design of the Gipsy King/XII that required reverse-flow cooling, that
was a matter of the installation design which resulted from De Havilland's desire to minimize
drag.

The main thing that worked against the engine was size and weight, larger than a Kestrel V in all
dimensions, weighed 100lbs more and produced 250+/- fewer horsepower. Truthfully the engine
had a pathetic output for its size with a power to weight ratio of a paltry 0.4 hp/lb.
“Conspiracy theory’s got to be simple.
Sense doesn’t come into it. People are
more scared of how complicated shit
actually is than they ever are about
whatever’s supposed to be behind the
conspiracy.”
-The Peripheral, William Gibson 2014

Offline apophenia

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Re: D.H.88 Comet Follow-Ons
« Reply #58 on: July 31, 2021, 11:12:01 AM »
Sound like DH would have better focusing on reducing weight rather than drag. Although I had fun using the Gipsy Twelve for my whif, none of those air-cooled IV-12s made for much of a combat engine - even the more powerful Isotta Fraschini Delta or Ranger V-770.
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Offline jcf

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Re: D.H.88 Comet Follow-Ons
« Reply #59 on: August 01, 2021, 02:05:51 AM »
Sound like DH would have better focusing on reducing weight rather than drag. Although I had fun using the Gipsy Twelve for my whif, none of those air-cooled IV-12s made for much of a combat engine - even the more powerful Isotta Fraschini Delta or Ranger V-770.

Even if they had reduced the weight of the engine, you'd still want minimum drag for
the airframe design. Even if they'd had a reduced weight version, De Havilland would
have still used the same design for the nacelles of the Albatross and the cowling of the
Don.

“Conspiracy theory’s got to be simple.
Sense doesn’t come into it. People are
more scared of how complicated shit
actually is than they ever are about
whatever’s supposed to be behind the
conspiracy.”
-The Peripheral, William Gibson 2014

Offline GTX_Admin

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Re: D.H.88 Comet Follow-Ons
« Reply #60 on: August 01, 2021, 02:40:37 AM »
What about a version with tricycle landing gear and the engines reversed into a pusher arrangement?
All hail the God of Frustration!!!

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But you can make the Bastard work for it.

Offline apophenia

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Re: D.H.88 Comet Follow-Ons
« Reply #61 on: August 01, 2021, 04:39:32 AM »
Even if they had reduced the weight of the engine, you'd still want minimum drag for the airframe design. Even if they'd had a reduced weight version, De Havilland would have still used the same design for the nacelles of the Albatross and the cowling of the Don.

True. I'd been focusing in on other, more conventional air-cooled IV-12 approaches. Perhaps DH realized that this market was already glutted. So it was either come up with a fresh arrangement with low-drag advantages or just stick with the existing straight inline Gipsy families?

What about a version with tricycle landing gear and the engines reversed into a pusher arrangement?

I like that! And it would certainly change the look  :smiley:
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Offline jcf

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Re: D.H.88 Comet Follow-Ons
« Reply #62 on: August 01, 2021, 10:03:38 AM »
Reverse flow concepts for air-cooled engines were on other peoples minds because the inherent problem
with an inline air-cooled engine is that the rear cylinders are the ones that tend to overheat first, also it
had some promise in cleaner airframe design. But again this a matter of airframe and installation design
rather than engine design, and the best results were when the airframe company worked closely with the
engine manufacturer. Douglas's humongous oversized cowlings on the C-74 for the R-4360 drove the P & W
folks up the wall, Andrew Wilgoos acerbically wondering if Douglas intended to use the extra space for a
luggage compartment.
 ;D

If there had been a commercial, or military, interest in their IV-12 engine DH would have sold it to whoever
wanted one and not worried much about how they wanted to use it. The existing I-6 engines wouldn't have
been powerful enough for the Albatross, and again they were larger and heavier than the I-6 engines from
the competition and had a lower horsepower to weight ratio. DH's engine side in the '30s definitely showed
the effect of not having a good replacement for Frank Halford.

“Conspiracy theory’s got to be simple.
Sense doesn’t come into it. People are
more scared of how complicated shit
actually is than they ever are about
whatever’s supposed to be behind the
conspiracy.”
-The Peripheral, William Gibson 2014

Offline apophenia

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Re: D.H.88 Comet Follow-Ons
« Reply #63 on: August 05, 2021, 10:45:45 AM »
What about a version with tricycle landing gear and the engines reversed into a pusher arrangement?

I had a go at trike-geared pushers but none of them worked visually. So, I've shifted gears and returned to Arthur Hagg at Walton-on-Thames ...

High in the Sky - a Comet-Influenced Photo-Recce Aircraft

With the rejection of their 'High-Speed Hagg' concepts, the Walton Yacht Works team had returned to small craft design. However, as war-clouds darkened, the Air Ministry made inquiries about the development of a dedicated high-speed photo-reconnaissance aircraft derived from the basic de Havilland D.H.88 structural techniques. Like the second of the 'High-Speed Hagg' concepts, this was to be a single-engined aircraft. The actual design would be constrained by the Air Ministry's required use of existing, in-service components - specifically the engine installation and main undercarriage from the Supermarine Spitfire fighter.

The requirement for a Spitfire landing gear dictated a low-set wing but also presented a major design challenge - since there was no way that such an undercarriage could be accommodated by the very thin profile of the D.H.88 Comet wing. While many of the original construction techniques of that Comet wing were kept, Hagg completely revised his actual wing design for the new 'Recce Comet'. The birch-ply and spruce rib concept was retained and so too was the RAF 34 airfoil. However, that airfoil section was deepened to increase the thickness/chord ratio. The latter to allow stowage space for a retracted main undercarriage within these thicker wings. The presence of that landing gear dictated changes to the D.H.88's triple-spar arrangement.

For what became the Walton-designed de Havilland D.H.188W, a beefier arrangement of two full-span spars was adopted - these spars being positioned at about 20% and 65% chord. A third stub-spar - positioned at 40% chord - supported and absorbed the loads of the main undercarriage legs. Outboard of that stub-spar, stiffness was ensured by spruce stringers. The Comet wing had been skinned with a combination of spruce planking (inboard) and birch veneers (outboard) attached to the ribs and stringers. For the D.H.188W, Hagg adopted a new technique whereby the entire wing skin was formed by pre-moulded plywood panels - in upper, lower, and leading edge sections. The entire structure was then covered with a filling compound - to smooth over joints and wood grains - before painting.

Hagg's High-Flyer - the de Havilland D.H.188W Danby

By an agreement arranged through the Air Ministry, prototype airframe components would be prepared at Walton Bridge and shipped the 40 miles to Hatfield Aerodrome in Hertfordshire for completion by DH. As assembled, the prototype D.H.188W was powered by a standard Spitfire Mk.I engine. But, in place of the Spitfire's two-bladed Watts propeller, the D.H.188W's 1,030 hp Merlin I drove a 3-bladed de Havilland two-pitch metal propeller. The main undercarriage was unchanged from the Spitfire but a fully-retractable tail skid was employed. For its photo-recce role, the prototype D.H.188W was fitted with two, government-supplied F.24 5-inch cameras in its rear fuselage. This camera type was an odd choice since the new aircraft was best-suited to a high-altitude role.

Bottom Prototype D.H.188W Danby still showing its de Havilland Class B registration E.15. (despite the application of RAF Type A roundels). Note the pointed spinner for the two-pitch DH prop and retractable tail skid.

Despite having provided the photographic equipment, the Air Ministry insisted that a vertically-placed F.24 camera with an 8-inch lens be installed. The tail skid was also a source of complaint. Although a drag penalty invariably resulted, a fixed Spitfire tail wheel was substituted for the skid. Other minor changes were also made - eg: to improved heating ducts both to the camera bay and for windscreen demisting. A slight tail-heaviness was addressed but switching from the two-pitch propeller to a slightly heavier constant-speed DH prop. All of these changes were quickly introduced on production D.H.188W airframes then being prepared at Walton Bridge. When completed at Hatfield, these production D.H.188Ws were delivered to Sidney Cotton's newe PR Unit at Heston with the name Danby Mk.I assigned. [1]

Top Production de Havilland D.H.188W Danby finished in the RAF's new 'Camotint' finish. Note the change to ID Blue (from Roundel Blue) on the fuselage Type A roundel and complete elimination of underwing roundels.

The first operational flight by an RAF D.H.188W Danby took place on 06 September 1939 when the PR Unit's Shorty Longbottom overflew the neutral Dutch port of Ijmuiden. The first truly long-range mission followed on 29 September when the German island of Sylt was photographed from almost 32,000 feet. Unfortunately, in the absense of cabin pressurization, higher flights were not practical. As a result, the longspan wings of the Danby were not fully taken advantage of. [2] By October 1939, two loaned Spitfires had been 'Cottonized' at Heston and were ready for action. By comparison, the Danby Mk.I had a slight altitude advantage and greater range but the gunless Spitfire PR Type A was faster.

With PR Spitfire range improving, in early 1940, the new Ministry of Aircraft Production chose to eliminate D.H.188W Danby production. Counter-arguments that the Danby used fewer 'strategic' materials in its construction could not outweight MAP's desire to eliminate duplication by reducing the number of aircraft types in  production. With never more than a half dozen Danbys in service at any time, the D.H.188W quickly became a half-forgotten aviation history footnote.

________________________________________

[1] The name Danby honoured World War I Royal Flying Corps aerial photographer, Major C.S. Danby.

[2] The D.H.188W Danby had a wing span of 44 feet with an area of 212.5 sq ft. By comparison, the Spitfire PR Type A had a wing span of 36 feet 10 inches and an area of 242 sq ft.
« Last Edit: August 06, 2021, 04:11:01 AM by apophenia »
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