P-40 with Griffon engine

[Elvis]

It's not just the airscoop. It's also the extended tail. The stab and elevators are in the standard placement, but the fin and rudder are 20 inches farther aft with respect to a P-40E.

Yeah, whatever.
I was just saying that sometimes, a subtle change can make something look totally different...once you notice the change.

 

[wuzak]

Most of the issues you raise are valid and some had already been raised. My specific point was that just because you could shoehorn a racing version of a Griffon into a purpose built airframe conversion, that did not validate the engine swap during wartime.

If you had to have the two stage supercharger, Aftercooler and associated plumbing behind the engine, could you just swap the Griffon for the Merlin? I'm suggesting that the Griffon might have to be placed further forward from the firewall than was necessary on "Precious Metal".

Why would it need to go forward, other than the supercharger section was longer for the 65 than the 57?

I can't recall off the top of my head whether the Griffon on the Spitfire was moved forward relative to the Merlin. I'm not sure that it was, and if it was it may have been for increased oil and fuel tanks.

The XIV had its Griffon angled down for improved pilot visibility.

We are hoping to swap the engine and end up with a better weapon of war, without a major re-design or disruption to production. After all, there is a war on....

That is why it didn't go any further than a suggestion by Rolls-Royce in correspondence to the Air Ministry, USAAF and NAA.

NAA said that a major redesign would definitely be required.

 

[Dash119]

Why would it need to go forward, other than the supercharger section was longer for the 65 than the 57?

Given than the engine is larger, I am assuming that the Aftercooler is larger too...

In the case of "Precious Metal" I assumed they did not use an Aftercooler, so that example doesn't tell us as much as we need to know.

Given how tight the full Merlin package is inside the cowling on the P-51, I am suggesting that a full Griffon package may not fit in the same place forward of the firewall. It was just a thought.

 

[wuzak]

Given than the engine is larger, I am assuming that the Aftercooler is larger too...

In the case of "Precious Metal" I assumed they did not use an Aftercooler, so that example doesn't tell us as much as we need to know.

Given how tight the full Merlin package is inside the cowling on the P-51, I am suggesting that a full Griffon package may not fit in the same place forward of the firewall. It was just a thought.

The aftercooler is larger.

But it sits above the supercharger, supercharger drive and accessories. It doesn't add to the length.

There is more room in the P-51 than there is in the Spitfire. And yet the Griffon fitted in the Spitfire - probably because the goal of fitting the Griffon to a Spitfire was in the requirement not long into the development of the engine.

I would guess you are saying the engine block itself would need to be further forward?

I was thinking from the rear of the engine, which wouldn't need to change much, if at all.

The mounting points would need to change, as they would move forward, and the engine lowered a few inches (the Griffon is 6" taller than the Merlin), but the P-51 has space under the engine (as did the Spitfire). Which would mean the cowling would change.

 

[wuzak]

The Spitfire IX was just over 300mm (12 inches) longer than the I. The Spitfire XII was about 150mm (6 inches) longer than the IX, and the XIV was about 500mm (20 inches) longer than the IX.

Some of those length changes were due to the wider chord rudders used on the IX and, particularly, the XIV.

 

[wuzak]

Given how tight the full Merlin package is inside the cowling on the P-51, I am suggesting that a full Griffon package may not fit in the same place forward of the firewall. It was just a thought.

Sorry, I should be more clear.

Yes, a Griffon P-51 was possible.

Yes, a lot of airframe work would be required - as you point out, probably more than I have previously suggested. Which is one of the reasons why it did not go ahead.

Another problem is engine supply. Where are they getting Griffons?

The best chance I see is that the P-51B is modified to fit the Griffon from the start and that Griffons were being made by either Packard or at the factory built for the IV-1430.

But since the Griffon 65 wasn't in production in the UK at the time the Mustang X and XP-51B were being developed, that scenario is highly unlikely.

 

[Dash119]

All of this was an exercise in what if...

It just seemed to me some posters we're making this out to be a relatively easy swap, based on "Precious Metal".

Also, I haven't seen one up close in a couple of months, but I believe the Aftercooler in the P-51D extends further back in the cowling than the Supercharger casing. In other words, the back end of the Aftercooler is closer to the firewall than the Supercharger itself. If that is the case, than I am suggesting that the block of the Griffon may have to be located further forward of the firewall than the Merlin.

As for the Griffons, aren't there warehouses full of them just waiting for a practical application...

Almost anything is possible, but as you point out that doesn't make it practical.

(Edited to change Supercharger to Aftercooler)

 

[Dash119]

I don't know nearly as much about the Spitfire as I do about the Mustang, but even so...

The XIV had its Griffon angled down for improved pilot visibility.

They may have angled it down, but they had to incorporate 'bulges' in the cowling to accommodate the cylinder banks which were wider and taller. I would be willing to bet that they did not just redesign the motor mount and some of the sheet metal on the cowling when they swapped engines in the Spit. I am guessing there were quite a few design changes to the airframe to compensate for the increased size, weight and power of the Griffon.

 

[wuzak]

They may have angled it down, but they had to incorporate 'bulges' in the cowling to accommodate the cylinder banks which were wider and taller. I would be willing to bet that they did not just redesign the motor mount and some of the sheet metal on the cowling when they swapped engines in the Spit. I am guessing there were quite a few design changes to the airframe to compensate for the increased size, weight and power of the Griffon.

The Spitfire XII had the singe stage Griffon IIB, IV or VI, which was not mounted at an angle. There is a blister in the middle of the front of the XII's cowling to clear the magneto, which was relocated on the two stage engines.

The XII also had to have blisters over the valve covers. The angle of the engine did not make any difference to the cowl blisters, since the cowling was tightly wrapped around the engine.

The Griffon wasn't much wider than the Merlin, if at all. It was, however, taller.

Merlin Spitfires also had blisters over the rocker covers, though not as pronounced.

I posted some pictures on another thread to show this What are those big humps on the cowling above the exhaust stacks of the MK 14 (and as I've seen all Griffon spits)?

The P-51 had even less of a bump, if it was there at all.

One of the main changes to the Spitfire airframe was the use of steel stringers in place of aluminium, at least on the XIV. I'm not sure about the XII. They also added balance weights in the tail.

Other than that, the Spitfire fuselage was the same from the firewall to the fin (not ncluding the rudder) - as the Merlin version it was based on (the XIV on the VIII, the XII on the V and IX).

The wings remained the same as the base variant, except for larger radiators and oil coolers.

The prop was smaller because of the lower propeller shaft (XII, XIV) and the angling of the engine (XIV).

 

[wuzak]

Hard to tell if Precious Metal needs the bulges as well, since the engine is lower and the upper part of the cowling forms an air duct to feed the down draught carburettor - the 2 stage Griffons had up draught carbies.

https://upload.wikimedia.org/wikipe...no_Air_Race_2014_pits_photo_D_Ramey_Logan.jpg

 

[GregP]

Hi Wayne,

Once they made a long-tail version of the P-40, I don't believe they went back to a standard short-tail version. The P-40K tried to add some stability with a decidedly ugly enlarged fin. Here's a P-40E.

Note the fin's fuselage placement is just about even with the stab. Below is a P-40F. Note the fin fuselage joint is now aft of the stab joint.

A little extra power meant some destabilization, and the next iteration was the P-40K. They tried to use the old standard tooling and added extra fin and rudder area. It doesn't look very aesthetic to me.

Then, they went with the long-tail version. Below is a P-40M. The rudder seems a tad farther aft than in the E model, maybe not. making it more effective and the fin area is also multiplied, both due to extra moment-arm. It also just looks better.

.

My thoughts are that they could have added a 2-stage Merlin and moved the entire tail back another 10 -15 inches and would have had a much better airplane. Adding a general cleanup as they did in the P-40Q wouldn't have hurt, either, as well as a concerted effort to lighten the airframe combined with a possible 4-blade propeller. But, that is a "what if" seeing as how they never actually DID that.

I'm not suggesting it would have been a world-beater at all. I'm stating it should have been better than the P-40s that were actually built and deployed. Since the war was going well, perhaps the effort to improve the old dog simply wasn't worth the expense of the effort. I wasn't there and really don't know, but Curtiss had problems around then and had already lost Don Berlin to the lack of action in the design department a couple of years previously. Their aircraft department would last only another 3 years before lack of innovation and the ill-fated XF-87 put them out of the airframe business.

 

[Shortround6]

I believe the Ks over lapped the F production. The modified fin leading edge fairing/extension may have been the first attempt at fixing the problem. Allison and Merlin powered planes were built concurrently.

The early Ns were an attempt to lighten the plane, However you can't lighten the airframe too much without giving up some of the capabilities they were looking for. The N didn't do much of anything to the structure but used magnesium wheels and aluminium instead of copper radiators and oil coolers.

If you want large underwing loads and/or heavy armament in the wings you need a stronger/heavier wing. If you make the engine 200lbs heavier and use a heavier propeller and make the rear fuselage longer/heavier (and use lager radiator and intercooler) you either accept a lower ultimate G rating or increase the weight of the airframe or find ways to lighten the plane (like four guns instead of six).

The P-51H in some ways was not as strong as the D, they used a different load limit or way of calculating the load limit.

 

[Reluctant Poster]

According to a Flight article on the Griffon 65 from September 1945.

 

[wuzak]

Merlin 66:

Merlin 130:

http://www.wwiiaircraftperformance.org/Aircraft_Engines_of_the_World_Rolls-Royce_Merlin.pdf

Griffon 65

Griffon 37 (single stage, downdraught carburettor)

http://www.wwiiaircraftperformance.org/Aircraft_Engines_of_the_World_Rolls-Royce_Griffon.pdf

Maybe the height measurements aren't measuring the same thing? Or maybe the carburettor sits further out from the bottom of the engine than on the Griffon.

 

[Elvis]

You know, I never fully understood the term "H.P. / Hr.".
I can understand "lbs./hr.", in the fuel consumption rating, but ".../H.P. / Hr."?
Can someone please explain?

 

[Dash119]

Pounds per Hour would be the total fuel burn per hour.

Pounds per Horsepower per Hour would be a measure of engine efficiency over the same period.

So at cruise speed the Merlin 130 does a slightly better job converting fuel to Horsepower than the Merlin 66(0.50 vs. 0.53).

 

[Dash119]

Maybe the height measurements aren't measuring the same thing? Or maybe the carburettor sits further out from the bottom of the engine than on the Griffon.

These numbers seem suspicious considering the Griffon has 30% more displacement than the Merlin...

 

[Elvis]

...but isn't the total fuel burn an indication of engine fuel efficiency?
See, this is where I'm confused.
It reads like a fuel economy stat, but what "efficiency" are we measuring? The amount of fuel the engine uses while in operation or the engine's ability to create a certain amount of power for a given amount of fuel?
To me, those are two different things.

 

[Dash119]

Also the frontal area on both Merlins is greater than the Griffon 65...

 

[Dash119]

...but isn't the total fuel burn an indication of engine fuel efficiency?

I am not an Engineer...

A B-17 would have a higher hourly fuel burn than than any single engine fighter, so total fuel burn just tells us how much fuel was burned in a given amount of time.

See, this is where I'm confused.
It reads like a fuel economy state, but what "efficiency" are we measuring? Fuel Economy or the engine's ability to create power with a given amount of fuel?

Fuel Economy would likely be measured in miles per gallon which is different than how much horsepower we produce per gallon. How far we travel per each gallon of fuel we burn is a function of both engine and aerodynamic efficiency. How much Horsepower we generate for each gallon of fuel we burn is strictly a matter of engine efficiency.

The you go, clear as mud...