What if Vickers had built the Venom powered by the Bristol Mercury armed with 6 LMG.

[Kevin J]

and the trouble when you start with "Small, cheap," is it seldom works out to be "adequate, ideal"

312mph may have been plausible for an unarmed prototype. there is argument about that. You still, for plane to be used after the summer of 1940, need to add armor and self sealing tanks for a western nation.

We do have this quote from "The British Fighter Since 1912" by Francis Mason.

"Constant trouble with the Aquila engine and its ancillary systems prevented it from undergoing full service trial, although Fg Off Jefferey Kindersley Quill, who had recently joined Vickers, continued to perform manufacturers trials for some months."

The plane is supposed to have weighed 4165lb all up.

AS Tomo has pointed out and supplied an engine chart for for, the rated altitude for the engine is nowhere near the altitude at which the 312mph is claimed. Now perhaps the Venom had a different engine than the chart is for? But getting anywhere near 600hp at 14-16000ft is going to be impossible for such an engine. The Aquila was a 15.6liter engine, the French 14 cylinder engine used in the two planes pictured above was 19 liter engine and it ran at 3030rpm, So engine that is almost 22% bigger in displacement running at the same rpm has trouble doing what is claimed or implied for the Aquila?
You could try sticking the Mercury in it, it is only 200lbs heavier, 5.5in bigger in diameter (3 more square feet of frontal area) and will need a bigger prop.

I would also note that the Ki 27 prototypes used two different engines while the production aircraft got a 3rd. This is where we have to be really careful in comparing engine powers.
This is an old book and could be wrong so here it goes,

Nakajima PE had a Nakajima Ha-1-Ko engine rated at 710hp for take-off and 650hp at 6,560ft (2000 meters) it also had a 176.5 sq ft wing.
The 1st Nakajima Ki 27 prototype had a slightly bigger wing of 189.4 sq ft and the 2nd prototype got a 199.8sq ft wing. The bigger wing knocked 4mph of the top speed.
After some 10 or so pre-production examples were built they went for the production Ki 27-Ko which was fitted with the Ha-1-Otsu engine which was rated at 710hp for take-off but 780hp at 9,515 ft (2900 meters). so the 290mph is being done with 780hp. 25% more than the Aquila if the Aquila, by some miracle actually made 625hp at

Same take off power and perhaps the cruise wasn't far off but the difference between this engine and Mercury at 3-5000 meters is not going to be that great. At least not anywhere near what the original engine was.

I've been looking at similar lightweight interceptors. The Demon with 850 hp, 314 mph: Shoki I, 1250 hp, 363 mph; Shoki II, 1440 hp, 378 mph; FFVS J22, 1050 hp, 357 mph. So maybe the Venom would have 20 mph knocked off its top speed fully armed and would need a Bristol Mercury just to recover that lost speed. However, we do need a fighter in the Far East, preferably of local construction, 2 HMG, 4 LMG.

 

[Dinger]

Been doing a bit of digging, first stop is Eric Morgans article on the Venom in Aeroplane Monthly September 1982. The Aquila engine obtained on loan from Bristol is an "AE3S" model (in another short piece on the Venom in his "Spitfire -The History masterwork he calls it the "AE35" engine) - On arrival at Vickers it was rated as follows - " 620 / 645 bhp at 3,450 rpm at 13,500 ft at +5lb boost " - Note that very important 3,450 rpm. - Now when they came to fit it in the Venom and complete the initial tests they got 620 bhp at 14,000 ft. These figures are completely at odds with the figures in Lumsden and a bit out on the figures in the "Flight" table posted by Tomo. - One particular extra bit of information is that the "fade-outs" in power of the Aquila under test in the Venom always occurred when the engine was doing 3,100 - 3,200 rpm. Now in Lumsden the Aquila is listed as having an rpm of only 2,250 !!!!!

This suggests to me that this "AE3S" Aquila was a more highly rated version, running at a higher speed. You have to remember that from Bristol's point of view, when designed, the Aquila would have been an unlikely engine to be used in military projects, being so small. They probably saw it as their rival to the AW Cheetah, Napier Rapier and Gypsy Queen and King engines in the civil marketplace. In the 1930s we British had this strange preoccupation for airliners with smaller engines ( AW Atlanta, DH 86, Short Scion, Airspeed Envoy, DH Albatross etc, etc). I imagine the figures in Lumsden are for their initial civil-rated Aquila as used in the Bristol Type 143 small airliner prototype. The AE3S model supplied for the Venom would have been made to run at much higher speeds If you look at other Bristol engines you find a striking difference in power between their "civil" versions and the "military" versions. - For example, the Civil Perseus Mk XVIC is rated at 745 bhp while the military MkXII is 910 bhp.

The Venom certainly had a remarkable performance on the Aquila when it was working okay - that top speed of 310 mph is not an estimate but reflects the actual speeds recorded. (Jeffrey Quill goes a bit further saying "around 325 mph at 15,000 feet" ). This was with the Aquila using 87 octane petrol. Vickers ordered some 100 octane fuel for use with testing the Venom but never used it, later inquiring if the supplier would take it back!

The original AE3S engine suffered a catastrophic failure on Jan 7th 1937 but Jefferey Quill managed to pull-off a dead-stick landing at Gosport aerodrome. The Venom did not fly for six months after that and it was during this time that Vickers considered re-engining the Venom with either an Alvis or American Pratt and Whitney engine. Also considered during this time was putting some 600 lb of armour plate into the Venom - but calculations showed this to be impossible without a complete redesign of the structure.

Vickers seemed to have lost interest in the Venom, but it was the Air Ministry that showed a renewed interest in it. After the prototype had laid dormant for 6 months it was re-engined with another AE3S engine from Bristol, this one was rated as giving 600 bhp at 3,325 rpm at 14,000 ft using 100 octane petrol. - This difference from the original AE3S engine suggests they were very much "one-offs", hand-made. This new engine seemed not to suffer from the "fade-outs" encountered with the first engine but it did suffer a complete cut-out just after take-off on what was to be its last flight. Thankfully the engine started again.

The subject of those machine guns is very mysterious. Certainly, none of the available pictures ever show any hint of gun ports, or ammunition reload panels, or even ejection ports for spent cartridges. - Yet the test-pilot Jeffrey Quill in his book "A test pilot's story" makes a particular point of stressing that the Venom flew with a full complement of machine-guns, as does Eric Morgan in his article. Interestingly, later in the article when detailing the all-up weight of the Venom Eric Morgans article lists it like so... " .... whilst loaded (with 50 gal fuel and 4 1/4 gal oil) was 4,171 lb. This figure included the eight machine guns (not fitted) 2,400 rounds of ammunition and TR9 radio". - That "not fitted" does raise an eyebrow! - One other piece to the puzzle, after being fitted with its second engine the aircraft was re-evaluated by A&AEE, during which some wrinkles developed on the starboard wing, when it returned to Vickers "Fore-and-aft grooves were made on each wing above each gun position to accommodate wing flexing". It should perhaps be noted that the 3-view drawing that illustrates Morgan's article does show the position of machine-guns in the leading edge of each wing.

Does anyone know if any record exists of the Venom's testing at A &AEE? - There was that "Probe Probare" series by Alec Lumsden and Terry Heffernan in the Aeroplane magazine in the 1990s about the testing of various types at A&AEE - Anyone know if that ever covered the Venom?

 

[Shortround6]

As a comment I would note that the Gloster F9/37 got a very strange set of Taurus radials that allowed to go 360mph at 15,000ft which seem to have disappeared after a landing accident
and it took years (if ever) for a Taurus to develop that kind of power at that altitude again. A Taurus III was supposed to have been used in Australian Beauforts that made 1060hp at 14,500ft at 3300rpm. How many got this engine I don't know as the Taurus VI was also used in Australian Beauforts before they switched to P&Ws. The VI was low altitude engine that maxed out at 3100rpm.

The Taurus used the same bore as the Aquila but used another 6mm (1/4in) of stroke. How close the cylinder barrel finning and heads were to each other I don't know.

A few comments on fuel. Higher octane fuel will not usually increase the FTH of the engine. That should be the height at which the throttle is fully open and the supercharger is delivering all the air it can at the full rated speed (rpm) of the engine. If you over speed the engine the supercharger of course turns faster and can deliver more air/higher boost.

If the engine is having cooling problems and running into temperature limits causing detonation with low octane fuel switching to higher octane may allow higher boost and/or higher rpm, at least for short periods of time. In general high octane fuel allows for substantial increases in power at lower altitudes where this is excess supercharger capacity (throttle not fully open). At Altitude if you over rev the engine by 10% you will get a lot more air through the supercharger. But we seem to be at odds with flights using somewhat experimental or development engines vs service engines, Taurus engines in service were known for overheating at low altitudes running at lower rpm/power settings than we are taking about here.

as the guns and weights. It was not uncommon to ballast a plane to represent the weight of the guns and ammo and often they tried to place the weights close to where they would be. that is weights are placed in the wings in an appropriate location to simulate the weight of guns/ammo when rolling the plane or maneuvering vs just sticking a bunch of lead right on the CG in the fuselage.

I am guessing the plane was ballasted for the guns/ammo but was not suffering from the drag of access hatches or ejection slots. Muzzles were usually taped over in tests anyway and in normal flight.

 

[Dinger]

As a comment I would note that the Gloster F9/37 got a very strange set of Taurus radials that allowed to go 360mph at 15,000ft which seem to have disappeared after a landing accident
and it took years (if ever) for a Taurus to develop that kind of power at that altitude again. A Taurus III was supposed to have been used in Australian Beauforts that made 1060hp at 14,500ft at 3300rpm. How many go this engine I don't know as the Taurus VI was also used in Australian Beauforts before they switched to P&Ws. The VI was low altitude engine that maxed out at 3100rpm.

The Taurus used the same bore as the Aquila but used another 6mm (1/4in) of stroke. How close the cylinder barrel finning and heads were to each other I don't know.

A few comments on fuel. Higher octane fuel will not usually increase the FTH of the engine. That should be the height at which the throttle is fully open and the supercharger is delivering all the air it can at the full rated speed (rpm) of the engine. If you over speed the engine the supercharger of course turns faster and can deliver more air/higher boost.

If the engine is having cooling problems and running into temperature limits causing detonation with low octane fuel switching to higher octane may allow higher boost and/or higher rpm, at least for short periods of time. In general high octane fuel allows for substantial increases in power at lower altitudes where this is excess supercharger capacity (throttle not fully open). At Altitude if you over rev the engine by 10% you will get a lot more air through the supercharger. But we seem to be at odds with flights using somewhat experimental or development engines vs service engines, Taurus engines in service were known for overheating at low altitudes running at lower rpm/power settings than we are taking about here.

as the guns and weights. It was no uncommon to ballast a plane to represent the weight of the guns and ammo and often they tried to place the weights close to where they would be. that is weights are placed in the wings in an appropriate location to simulate the weight of guns/ammo when rolling the plane or maneuvering vs just sticking a bunch of lead right on the CG in the fuselage.

I am guessing the plane was ballasted for the guns/ammo but was not suffering from the drag of access hatches or ejection slots. Muzzles were usually taped over in tests anyway and in normal flight.

Cheers, I assumed Morgan was talking about ballast. But both Quill and Morgan both stress the point that the Venom was fitted with both its guns and their associated electrical heating system from the start of the flight trials. But none of the pictures available (and there are quite a few in remarkable good quality) show even the slightest hint of an access panel or blanked-off gun port. Those Vickers boys must have done an extraordinary job with the filler! Thanks for the info on fuel octane, very helpful. A re-read of Morgan's article shows they were hoping the higher octane fuel would somehow help with the "fade-out" problem rather than boost performance.

BTW, if anyone interested there is a great little video on youtube of the Venom - showing the unique way the engine could be swung to the side. The fact that it's only Vickers and Supermarine aircraft on display suggests its some sort of factory "open day" at either Brooklands or Eastleigh.

 

[Graeme]

Does anyone know if any record exists of the Venom's testing at A &AEE? -

According to Tim Mason (British Flight Testing) no report was written because it was returned to Vickers early in the testing - when the wing skin started "wrinkling".
Which doesn't sound good....

 

[Shortround6]

Hey, what's a little skin wrinkling (impending structural failure?) between friends?

P-36s had wing skins wrinkle. P-40E wing was 200-250lbs (?) heavier than a P-36 wing.

 

[Graeme]

Hey, what's a little skin wrinkling

You're right - I've been wrinkling for years.

 

[Shortround6]

The Demon with 850 hp

I would be a little careful comparing to the Curtiss CW-21 Demon. the 850HP is the max continuous rating.
Take-off was either 950hp or 1000hp. This was a commercial engine and never got a "military" rating.
It did have two speed supercharger.

 

[Dinger]

According to Tim Mason (British Flight Testing) no report was written because it was returned to Vickers early in the testing - when the wing skin started "wrinkling".
Which doesn't sound good....

Strange, because they had the Venom at A&AEE for over two months (Oct 4th - Dec 14th 1937) and the skin wrinkling on the top of the starboard wing was fixed very quickly at the end of that time by Vickers (this was with its 2nd Engine). The Venom had been to A&AEE the previous year with its first engine ( July 7th 1936) for handling trials by one Flt Lt Edward Jones. Hard to believe all that time did not produce any documentation at all? - That Tim Mason book sounds a good reference. Would you recommend it? I've got his Hikoki title "The Secret Years" and that is excellent.

 

[nuuumannn]

Hard to believe all that time did not produce any documentation at all?

A lot of A&AEE documentation was destroyed during the war in bombing raids etc.

Getting back to the Venom, as it was, it was built as a private venture by Vickers and was not up to military specs, just to prove the design, so it was never fitted with armament or military stuff. Remember that it was built to a 1934 specification F.5/34 and didn't fly for the first time until 1936, three months after the Spitfire prototype. This is because there was no intent by the government to put it into production and Vickers funded it privately. As an aside, Martin Baker, latterly known for its line of emergency escape systems built the MB.2 to the same spec.

Martin-Baker MB2 Fighter

 

[Graeme]

Would you recommend it? I've got his Hikoki title "The Secret Years" and that is excellent.

Hi Dinger. I think "Secret Years" is a better and more detailed book - but of course the era is different.
Cheers.

 

[yulzari]

There are iffy issues with the Aquila engines but one does have to ask why Vickers chose to use it. Just to publicise it but expecting to fit a Perseus/Mercury later on? Or they had some reason to expect the Aquila to get better and be a viable choice? One might note that their Perseus was in the 900ish bhp power range as expected so a developed Aquila presumably would be less. Were Vickers looking more at a less daunting fighter to sell to less developed countries perhaps. Building to F/34 would be a marketing decision rather than a sales one.