Fairey aero engines - any good info?

[wuzak]

You're very welcome.

The P.24 has been of interest to me, and others, for some time in aviation forums around the web, Usually the stats given in books such as Lumsden (2240hp) give a rosy picture of the state of development of the P.24, but these documents show that by late 1940/early 1941 the engine's development was nowhere near the standard required for a production contract and the stated doubt that the engine would achieve sufficient performance and state of development to be of any use during the war. Considering that at the time there was no way of knowing how long the war was to go that is a damning call.

Reality check. One of the engines the P.24 was compared to is the Vulture. At the time of these discussions the Vulture program was either suspended or cancelled. The Vulture II had a rated (type tested) cruise power setting of 1,480hp compared to the P.24's maximum all-out (type tested) power of 1,490hp. The Vulture II's rated maximum (combat) power was 1,845hp.

The Vulture V's take-off power was 1,955hp.

Fairey claimed 2,200hp based on short duration power readings. RRHT confirmed the Vulture ran at 2,500hp, the period for which is unknown but is likely to be longer than the 2 minutes stated for the Fairey engine.

I'd also hate to think what "spot" readings the Sabre was able to make on the bench.

 

[wuzak]

Further development of the Prince was abandoned in 1943 while Sir Richard Fairey was in the USA. The P-24, had it been adopted as Fairey originally intended, would have given the Battle twice the power and a rather more adequate performance. What eventually happened to the H-24 is, as Sir Peter Masefield has recorded is, unfortunately 'still lost in the mists of wartime affairs'. It is a sad reflection on wartime finances and politics that, with a limited amount of money to go round and the existence of a number of established aero-engine manufacturers, a very senior government official was heard to express the view that 'Fairey would have to go it alone, or fold up'. This was a pity because with real support, Fairey and Forsyth might well have achieved useful results.

Just quoting the last passage that nuuumannn quoted from Lumsden regarding the Fairey engines and, particularly, the P.24.

It is pretty clear from the archives I have been able to obtain and the details I have related above that the MAP had no illusion that there was no place for the P.24 in their production program for the forseeable future. As far as the MAP was concerned the engine had no future in the UK from late 1940/early 1941.

Production facilities were spoken for by engines already in production or ready for production. Development facilities, other than money, were those of the manufacturers themselves. Rolls-Royce had considerable development facilities and monetary support from the MAP yet it was decided to, at its own behest, cancel all programs save the Merlin and Griffon (and to a minor extent, the Crecy) so that its resources weren't spread too thin.

Given that Fairey had little or no engine development facilities, certainly not in Rolls-Royce's league, or even Napier's, its prospects can't ever have been bright.

Mention is made of the £100,000of his own money that Fairey spent on this project. Surely that pales next to the money Feddon poured into sleeve valve development through the 1930s for Bristol?

 

[wuzak]

On 12 April 1941 H.C.H.Townend (not sure of the initials) of the Admiralty Research Laboratory writes to Sir Henry Tizard of the MAP:

Dear Sir Henry,

D.S.R. has asked me to send you some notes on the value of the Fairey P.24 Engine from the point of view of its use in Naval Aircraft.

From these notes it seems that on technical grounds this engine is most attractive to the F.A.A. in view of the new types of aircraft now being considered. I understand it could be fitted into machines designed for teh Sabre with very little alteration, if means can be found for producing the P.24.

The notes to which he refers make the following arguments in favour of the P.24:

1. Value of the Contra Screw to the F.A.A.
(a) Rreduced height of the aircraft - the claim is that the smaller diameter of the contra-rotating propellers allows for more compact stowage on an aircraft carrier. The example given is for the Supermarine S 12/40 (replacement for Sea Otter and Walrus) with a Merlin engine requiring a single propeller of 11.5' (3 blades), whereas a contra-rotating propeller would only need a diameter of 8.5'.

The overall height with the single prop was given as 16' 3" vs 14' 4" for the contra prop. It is also noted that a single 4 blade prop would give a maximum height of 15' 1".

(b) Elimination of Torque Reaction - surprised this would not be the first point, as it is very important for carrier borne aircraft, though most survived without contra-props.

(c) Take-off thrust.

It was claimed that flight tests of the Battle test hack showed that "the thrust at low values of J is much improved, and teh take-off distance reduced".

(d) More accuracy in manoeuvring, particularly in the dive. It was claimed that test pilots had commented on this aspect.


2. Value of the P.24 Engine against other engines
It is claimed that the P.24 did not suffer from vibration issues found in geared contra-prop setups.

Another claim is that "As regards to take-off it has also been suggested that the P.24 is particularly good, since there is independent throttle control on the two screws. This enables the rear screw to be unstalled by lowering its speed below that of the front screw [?] (the relative pitches being mechanically linked together)".

Advantages of the engine were listed as:
(e) Twin engine reliability - noted that the engine will not be reliable as two separate engines, but most faults would only affect one half of the engine. The reasoning is that most emergency landings in the FAA were not caused by enemy actions.

(f) Economical cruising - a 10% increase in range is claimed for running one half of the engine at 2/3 power compared to running both halves at 1/3 power.

The performance comparison made is as follows:

Engine              Weight     extra wt for     hp   rpm      alt      weight/power
                       lbs     contra screw                    ft   normal   with contra-screw
Sabre NS 2SM          2340          200 (?)   1985  3700   14,250     1.18       1.29
P.24 (Oct 1939)       2190            -       1760  2600   15,000     1.24       1.24
Merlin RM 4S          1420          100 (?)   1180  2850   15,250     1.22       1.29

The altitude of 15,000ft was chosen as that was available data for the P.24, the other engine data from the MAP was matched, as near as possible, to that altitude.

[I can't find what the Merlin RM 4S was]

The report finishes:
"On March 6th 1941 Prof. Bairstow, Mr Relf and others witnessed a demonstration at Faireys of teh Battle - P.24, which was described as follows.

"The machine was loaded to 11500 lbs., and the power available for take-off was between 1600 and 1700 H.P. The aerodrome was in a semi-water-logged condition, and there was no wind, yet the machine left the ground after a run of 100 yards.

"A member of the R.A.E. who flew as passenger, and who has considerable experience of the kind, reported that he had not hitherto experienced such a high acceleration which he estimated at not less than .35 g.

"It was also stated that the machine was very steady in teh dive, no force on teh rudder being required to hold it straight, whilist its manoeuvrability was compared favourable with that of teh Spitfire [seriously?]. The ability to hold a straight course in the dive is obviously a matter of much importance both for dive bombing and for diving attacks by fighters. In the latter case some difficulty is already being experienced with present single engined fighters."

 

[wuzak]

A note from the DDRDE (?) was forwarded to Sir Henry Tizard on 19.12.1940 is similar to an earlier document I quoted. In part it says:

Capt, Forsyth in his letter attached, compares the Sabre rating already established by full type test and cleared for production with the P.24 ratings hoped for, but not obtainable, in our view, without prolonged development for which Fairey Co. have inadequate facilities and which cannot be augmented without dispersal of effort from elsewhere.

In his comparison with the Sabre fitted with a four bladed airscrew he has made assumptions of which we have no knowledge (nor has Major Halford) of thrust; such thrust is only now being worked out by the De Havilland and Rotol Companies in conjunction with the Napier Co.

At the same time we have no evidence to substantiate his claim that two counter rotating three blader 12'6" airscrews with 1560 b.h.p. will produce the same take off thrust as a single four bladed airscrew of 13'6" with 2030 b.h.p. or the same top speed respectively with 1760 b.h.p. compared with 1850 b.h.p.

The note mentions that the decision to not proceed with the P.24 came in October of 1940.

It would seem that although Mr Wright, who was in charge of Fairey while Mr Fairey was in the US, had agreed with that decision much agitation was undertaken from Fairey to try to get governmental support either in direct funding or in efforts to get a US manufacturer on board.

Beyond 1940 it seems the MAP and Air Ministry's only interest in the engine was in the contra-rotating prop feature, and the same seems to be generally true of the USAAC/F.

As an aside, in Lyndon Jones' book of cutaways there appears an H-24 twin Merlin of the same concept as the P.24, based on two complete Merlin 61s. So it had two sets of two speed two stage superchargers and intercoolers and blocks and heads common with standard 60-series Merlins. One has to wonder if that project really existed other than in Mr Jones' imagination. I don't have my book with me, but IIRC it would weigh around 3400lb and produce around 3400-3500hp.

 

[wuzak]

I would mention that during my searches through the National Archives web site I have yet to find any reference to the Fairey P.12 or Fairey H.16 (P.16?). I have seem some reference to the Fairey Felix (D12), but they were all like Performance of Fairey Fox with Fairey Felix Engines.

Lumsden mentions some info came from the Bristol archives, which should now be with the RRHT.

 

[Zipper730]

As Shortround says, it is unlikely that the P.24 had a 4 speed two stage supercharger. As it was basically two engines on a single crankcase it is most likely that each half had a single stage two speed supercharger.

Correct, the four-speed thing came up later to give it the ability to fly higher.

There also seems to be some dispute about the engine weight. Some suggest that the P.24 weighed around 2100-2200lb.

I heard around 2300

I did at one stage have a USAAF report on the P.24, which evidently didn't like some of the features of the engine - like the cranks not having counterweights.

Why is that bad?

The report states that the hours run at power levels over 2000hp do not support the ratings (the ratings were supplied to the USAAF by Fairey).

What supercharger arrangement was used for this?

4 inlet ports are fed by each of the inlet manifolds. The inlet manifolds are integral with the barrels (see picture), the air path requiring many tight turns. It was also considered that this would be difficult to change/develop.

Why was this designed into the engine that way?

The inlet valves did not have sodium cooling. The exhaust valves may have, but the valve actuation design precluded the use of fully cooled stems.

Why did they design this way?

The camshafts were supported by 4 bearings only. These were two at each end and two in the centre, leaving long spans between support bearings.

What was the norm?

The reduction gear pinions were directly mounted on the ends of the crankshafts (not normal practice).

What was normal, and why did they make this choice?

The heads were connected to the barrels by studs fitted to the barrels. Normal practice was to use studs fitted to the crankcase.

Why the difference?

 

[wuzak]

Correct, the four-speed thing came up later to give it the ability to fly higher.

There was never a "four-speed thing". It was a misinterpretation of the system.

I did at one stage have a USAAF report on the P.24, which evidently didn't like some of the features of the engine - like the cranks not having counterweights.

Why is that bad?

Vibrations.

The report states that the hours run at power levels over 2000hp do not support the ratings (the ratings were supplied to the USAAF by Fairey).

What supercharger arrangement was used for this?

The one and only supercharger arrangement used for the engine.

4 inlet ports are fed by each of the inlet manifolds. The inlet manifolds are integral with the barrels (see picture), the air path requiring many tight turns. It was also considered that this would be difficult to change/develop.

Why was this designed into the engine that way?

Not a clue. Just trying to be clever, I guess.

The inlet valves did not have sodium cooling. The exhaust valves may have, but the valve actuation design precluded the use of fully cooled stems.

Why did they design this way?

Not a clue. But I suspect a lack of experience, knowledge or resources.

The camshafts were supported by 4 bearings only. These were two at each end and two in the centre, leaving long spans between support bearings.

What was the norm?

7.

The reduction gear pinions were directly mounted on the ends of the crankshafts (not normal practice).

What was normal, and why did they make this choice?

Normal was to use a quill shaft. Removes some of the torsional vibrations from the engine, and protects the reduction gear.

Don't know why Forsyth chose to put them directly on the crankshaft.

The heads were connected to the barrels by studs fitted to the barrels. Normal practice was to use studs fitted to the crankcase.

Why the difference?

Not a clue.

You'd have to ask Captain Forsyth.

 

[kmccutcheon]

Vibrations.

Not exactly. P.24s featured two 180 degree V-12s, which means opposite pistons were connected to the same crankshaft throw. While this arrangement has perfect primary and secondary balance, internal inertial forces have to be resolved somewhere else on the crankshaft, which only works with completely stiff crankshafts. Since there is no such thing as completely stiff crankshafts, this leads to main bearing distress. A number of V-12s began life with no counterweights, but added them later in development as power increased.

I am attaching a copy of the USAAC's P.24 engineering evaluation, which comes from the Aircraft Engine Historical Society archives.

 

[Shortround6]

A lot of times counterweights were added or changed as RPM increased.
Hispano V-12s at 2400rpm had no counterweights. to go to 2500rpm small ones were added.
On the the Allison the majority of the engines built used small counter weights and ran at 3000rpm. The last ones built added 27lb worth of counter weights to the crankshaft and were rated at 3200rpm or higher, 3200rpm was the service rating.
the effects of the vibration can go up with the square of the speed and the higher the speed of the crankshaft the more chances of hitting harmonic vibrations (two or more vibration patterns overlapping) as you have more possible combinations. I am wording that badly.

 

[Zipper730]

There was never a "four-speed thing". It was a misinterpretation of the system.

Oh, so the idea was for to be two speed one stage? Were there any proposals to add a second stage to the supercharger system?

Vibrations.

That's a legitimate concern, strange that the designer would not add that feature. According to kmccutcheon , the idea had to do with the opposing cylinders were connected to the same crankshaft throw, with the idea that they'd balance each other out. The problem's that it only works with a perfectly stiff crankshaft, which doesn't exist.

I'm surprised they didn't make provision for such additions as the design continued through testing.

Not a clue. Just trying to be clever, I guess.

I might be misunderstanding you, but that doesn't seem to be a clever feature. I guess if everything is formed out of the smallest number of parts it might serve to make the engine simpler, but it eliminates provision for modifications.

Not a clue. But I suspect a lack of experience, knowledge or resources.

I thought this technology was common knowledge by the late 1930's or early 1940's...

7

A little less than half...

Normal was to use a quill shaft. Removes some of the torsional vibrations from the engine, and protects the reduction gear.

So the design would not be able to take these vibrations? The only guess I can remotely think of is that, he might have had the view that the opposing cylinders and a sufficiently stiff shaft would have taken care of vibrations.

It seems that he might have overestimated some things (and possibly underestimated others): The fact that you'd design two blocks that can run independent of each other, in hindsight, seems unnecessary. You can run a contra-rotating shaft without needing two engines, though you might have more throttling ability by shutting one engine down in flight, but I'm not really sure how important it'd be.

 

[special ed]

Fairey P.24 Prince Battle at Wright Field 1942, with 24 cylinder engine and two 3 blade counter rotating props. A National Archives photo

 

[fubar57]

How to turn a semi-ugly aircraft into an ugly aircraft

 

[wuzak]

I might be misunderstanding you, but that doesn't seem to be a clever feature. I guess if everything is formed out of the smallest number of parts it might serve to make the engine simpler, but it eliminates provision for modifications.

When one tries to be clever the result isn't always that clever.

 

[Zipper730]

When one tries to be clever the result isn't always that clever.

I usually ask people I trust if the idea is clever. You have to consider that there's lots of ideas that sounded terribly clever, but turned out to be a disaster waiting to blow up in your face.

 

[wuzak]

It seems that he might have overestimated some things (and possibly underestimated others): The fact that you'd design two blocks that can run independent of each other, in hindsight, seems unnecessary. You can run a contra-rotating shaft without needing two engines, though you might have more throttling ability by shutting one engine down in flight, but I'm not really sure how important it'd be.

That they could run both halves independently was seen as a plus, getting twin engine reliability with the lower frontal area of a single.

The downside is the duplication of systems such as the supercharger, ignition and engine controls
.

 

[wuzak]

Oh, so the idea was for to be two speed one stage?

Well yes!. That is how it was designed.

Were there any proposals to add a second stage to the supercharger system?

I can't recall, but such a proposal would be on the never never unless they got the engine into production and were able to sort out any reliability issues.

 

[Zipper730]

That they could run both halves independently was seen as a plus, getting twin engine reliability with the lower frontal area of a single.

And you could shut down one half in flight and improve endurance and stuff. I'm not sure how much of a benefit this is.

I'm not sure what the odds are of catastrophic engine failure where one engine bank could effectively knock out the other either based on the knowledge of the time? As for combat, it seems quite plausible that gunfire could damage both engines since they are right next to each other. I could be wrong, of course.

The downside is the duplication of systems such as the supercharger, ignition and engine controls

The V-3420 was basically one engine based on two?

 

[wuzak]

I thought this technology was common knowledge by the late 1930's or early 1940's...

Sodium cooled exhaust valves were developed in the late 1920s by Sam Heron (same guy that developed the "hyper" cylinder).

The P.24 design was based on the P.12 which predated the Rolls-Royce PV.12 in the design stage.

You also have to remember that Fairey were not an engine manufacturer, and may not have been up to speed

Forsyth had been a member of the Air Minstry engine section, and may have been aware of the latest designs from Rolls-Royce and Napier. That is the Kestrel, Buzzard and Lion. So he may have been aware of the sodium cooled exhaust valve. That doesn't mean that Fairey could produce them, or had access to those that could.

Because of Forsyth's role at the Air Ministry there may have been a political impediments to Fairey's engine development.

[Earlier I may have suggested Forsyth lacked experience, but I have since read more on the Fairey engines and have found that Forsyth's engine experience stretched back to WWI.]

So the design would not be able to take these vibrations? The only guess I can remotely think of is that, he might have had the view that the opposing cylinders and a sufficiently stiff shaft would have taken care of vibrations.

The engine was probably not run at high power long enough for major issues to reveal themselves.

The problem with not isolating the reduction gear from torsional vibrations of the crankshaft is that it introduces shock loading into the contacting faces of the gear teeth, increasing wear or causing other damage to the teeth.

 

[Shortround6]

You have to remember that in 1930 the internal combustion engine was, for practical purposes, only about 30 years old, the pre 1900 engines being pretty crude. even the ignition system that is familiar today dates to about 1902 (high voltage) and for a while some engines still used make and break (a moveable set of points in the cylinder moved apart and the spark jumped the widening gap). Many of the early engine designers were self taught. It took a while for higher education to come with a curriculum for engine designers

there were some rules of thumb and some designers were conservative and others, not so much.

A lot was learned by breaking things. Harry Miller of Miller-Offenhauser fame built his first engine in 1915, by the early 20s he had a number of successful race car engines under his belt. He designed a 6 cylinder engine for a passenger car company (which he was a partner in) to replace the engine being supplied by Continental. He didn't understand torsional vibration in a 6 cylinder engine (all his previous engines were fours or eghts) and when the cars were sold none of the crankshafts lasted more than few months, the company went bankrupt replacing the crankshafts. This was in 1922 or 23. Hispano aircraft engines didn't use counterweights, NONE, not even small ones.

It took quite a while for engine designers to be properly educated and much of the "design work" was intuition (guess work), or depended on the legacy of someone who was no longer there. Armstrong SIddeley two row radials never got a center bearing and eventually ran into a wall in development because of it. Strangely enough the two row AS engines can be traced back to the Royal AIrcraft Factory in 1916-17 and the R.A.F. 8 engine which had as one of it's primary designers one S.D. Heron. After getting into a disagreement with John Siddeley S.D. Heron left for America and by the late 20s had reworked the cylinder/s on the Wright J5 radial, developed the sodium filled valve and few other things and by the early 30s had gone to work for the Ethyl Corporation, makers of the lead compound used to raise the octane rating of gasoline.

good designers who could work on cutting edge engines were rare.

 

[Zipper730]

Sodium cooled exhaust valves were developed in the late 1920s by Sam Heron (same guy that developed the "hyper" cylinder).

The P.24 design was based on the P.12 which predated the Rolls-Royce PV.12 in the design stage.

You also have to remember that Fairey were not an engine manufacturer, and may not have been up to speed

Forsyth had been a member of the Air Minstry engine section, and may have been aware of the latest designs from Rolls-Royce and Napier. That is the Kestrel, Buzzard and Lion. So he may have been aware of the sodium cooled exhaust valve. That doesn't mean that Fairey could produce them, or had access to those that could.

So it's possible that the company might have lagged behind in engine development, and even if Forsyth knew about it, they might not have had the resources to do it...

Because of Forsyth's role at the Air Ministry there may have been a political impediments to Fairey's engine development.

Such as?