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P51 Mustang, what if?


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I have an idea to re-engine a 1/48 P51 with a  RR Griffon. What an aircraft that would have been! Don’t know why they didn’t do it?! Has anyone attempted this? Any ideas on which kits to use? I guess the engine donor would have to be a Spitfire? Not looking to count rivets, just provide a reasonable example.

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What's noteworthy about both is that they chose the late contra-rotating Griffons, but despite that the extra length on the nose resulted in them increasing the surface area of the fin and rudder and this will be because the vertical surface area in front of the CofG got larger thanks to the bigger, longer engine. Had a production variant been produced of the Mustang using a Griffon, it's highly likely that they'd have had to do the same thing. Making aeroplanes' noses longer usually results in the fin area getting larger - one certainly wouldn't want to make an aeroplane faster whilst destabilising it directionally. That way, bad things lie.

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1 hour ago, Aerofix said:

Don’t know why they didn’t do it?!

Packard were not making Griffon engines,  so where would you get the Griffons?

 

And the P-51D was then in full mass production.  the 8th AF had 20 Fighter groups alone at the end of WW2, so you have a very successful type with a established supply chain,  the American's efficient logistics was a major part in their success.

 

The replacement for the D, the P-51H, was pretty much a new plane, but was too late.  AFAIK, some engine problems aside the H model was an improvement on the D.

 

It should be noted that the A model was (despite what is often written), a very successful type in it's altitude envelope,  the lack of supercharger being the problem. The D was apparently a bit of a 'dump truck' in comparison. 

 

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1 hour ago, Aerofix said:

I guess the engine donor would have to be a Spitfire?

Probably not, not how the racers approached the solution, note the lack of cylinder head bulges.    

There are conversion kits for racers.

https://www.hpmhobbies.com/high-planes-na-griffon-mustang-racer-world-jet-kit-1-48/

 

HPR048001_BX_revB__16274.1359429169.1280

 

 

this is Precious Metal with a Griffon

P-51-Griffon-startup-website-735x413.jpg

 

and this is D for comparison

3267601452_c637573b90_o.jpgP51 Mustang. by Aerofossile2012, on Flickr

 

the engine is not as tightly cowled as on a Spitfire. 

 

HTH

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4 hours ago, Troy Smith said:

Packard were not making Griffon engines,  so where would you get the Griffons?

 

And the P-51D was then in full mass production.  the 8th AF had 20 Fighter groups alone at the end of WW2, so you have a very successful type with a established supply chain,  the American's efficient logistics was a major part in their success.

 

The replacement for the D, the P-51H, was pretty much a new plane, but was too late.  AFAIK, some engine problems aside the H model was an improvement on the D.

 

It should be noted that the A model was (despite what is often written), a very successful type in it's altitude envelope,  the lack of supercharger being the problem. The D was apparently a bit of a 'dump truck' in comparison. 

 

All of this is true, and there is an additional factor:

 

It's all very well putting putting a Griffon on a P-51 when all you need it to do is run as fast as possible for over a very short distance, like an Unlimited class racer at Reno. But to do so in WW2 would have rendered it significantly worse at its actual job, as a long range fighter. And in late 1944 and 1945, long range was the whole point of it. It would have lost significant useful load due to the additional engine and cooling system weight, so would have been able to carry less fuel or less in the way of guns, ammo and external weaponry.  The reduction in fuel load and the deterioration in fuel economy in terms of MPG would have combined to put it back behind the range of the P-47D.  A Griffon P-51 would also have been significantly more expensive to build per unit than the legion of Merlin P-51s due to lack of economies of scale. 

 

By reducing range and increasing cost you would undermine both the advantages that the P-51D had over the Thunderbolt.  If you want to make a long range Griffon-powered fighter that makes sense, it would have to be a significantly bigger aeroplane. Compare the CAC CA-15 with the P-51D and you will see how much longer and deeper the fuselage is.  

Edited by Work In Progress
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1 hour ago, Work In Progress said:

Compare the CAC CA-15 with the P-51D and you will see how much longer and deeper the fuselage is.  

 

for ease of referencecac-ca-15-side1.jpg

 

https://en.wikipedia.org/wiki/CAC_CA-15

Quote

Although the CA-15 bore a superficial resemblance to the North American P-51 Mustang,[3] the CAC design was not based directly on the American aircraft and had quite different performance objectives and dimensions.[3] For instance, David had been impressed by assessments of captured Focke-Wulf Fw 190s[4] and intended using a radial engine rather than the inline engines used in fighters like the Mustang. In fact, development of the CA-15 was slowed by a recommendation from CAC head Lawrence Wackett, that the company build Mustangs under licence, rather than bear the cost of developing a unique design. By the later stages of its development, it was believed that the CA-15 would have capabilities enabling it to replace the P-51.[5]

At first, the CAC designers planned to use the 2,300 hp (1,715 kW) radial Pratt & Whitney R-2800, with a turbocharger. However, that engine became unavailable,[6] causing further delays in development, and it was decided to fit an in-line Rolls-Royce Griffon Mk 61 (2,035 hp/1,517 kW). Engines for a prototype were leased from Rolls-Royce.[5] It was intended that any production engines would have a three-stage supercharger.

 

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      Oddly enough been wanting to do a racer like this for years. Biggest hurdle is the cylinder head bulges on the upper cowling. Ive never come across anything in aftermarket for 1/48th or 1/72nd. If anyone knows a way to do this PLEASE PLEASE let me know ? Milliput is one option but the only place that carries it locally wants $21 for a small tube. If i could find someone that has the ability to cast resin and has the Airfix seafire 47 i know they come as separate in that kit. Maybe they come that way in the Spitfire 22/24 kit as well ?  

 

Dennis

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5 hours ago, Corsairfoxfouruncle said:

      Oddly enough been wanting to do a racer like this for years. Biggest hurdle is the cylinder head bulges on the upper cowling. Ive never come across anything in aftermarket for 1/48th or 1/72nd. If anyone knows a way to do this PLEASE PLEASE let me know ? Milliput is one option but the only place that carries it locally wants $21 for a small tube. If i could find someone that has the ability to cast resin and has the Airfix seafire 47 i know they come as separate in that kit. Maybe they come that way in the Spitfire 22/24 kit as well ?  

 

Dennis

High Planes had a range of racer mustangs. Don't know if they still are available, though.

 

Crude kits, but accurate outline.

 

/Finn

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5 hours ago, Corsairfoxfouruncle said:

      If i could find someone that has the ability to cast resin and has the Airfix seafire 47 i know they come as separate in that kit. Maybe they come that way in the Spitfire 22/24 kit as well ? 

 

In 1/48, Barracuda/ Roy Sutherland makes a more accurate set of bulges for the Seafire/Spit 22 kit (same basic kit with relevant changes as different parts).  Or someone who has used these would have the kit ones spare.  Someone like me, come to think of it...

 

As for Griffon in the Mustang, North American was interested in the Griffon, and either got or tried to get an example to poke at, but concluded that the developing Merlin was the better choice for Mustang developments, which is probably correct.  Hmm, a Griffon-powered F-82... 🤔

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13 hours ago, Jamie @ Sovereign Hobbies said:

What's noteworthy about both is that they chose the late contra-rotating Griffons, but despite that the extra length on the nose resulted in them increasing the surface area of the fin and rudder and this will be because the vertical surface area in front of the CofG got larger thanks to the bigger, longer engine. Had a production variant been produced of the Mustang using a Griffon, it's highly likely that they'd have had to do the same thing. Making aeroplanes' noses longer usually results in the fin area getting larger - one certainly wouldn't want to make an aeroplane faster whilst destabilising it directionally. That way, bad things lie.

In fact the noses of the Griffon Mustangs were not much longer than the Merlin Mustang. On both Griffon conversions the firewall was moved back, allowing the engine to be mounted a bit further aft, to help maintain the CG position, (as well as relocating other equipment to aft of the cockpit, and also moving the cockpit aft on Red Baron. The destabilising effect was due to the contra-rotating props used on the Griffon 58, (ex Shackleton). Increasing the size of the prop, or an increase in the number of blades, has a destabilising effect. In the case of the Griffon Mustangs this was a reduction in directional stability of some 40%, requiring a comensurate increase in fin area, (not to mention also having to set the fin back to zero degrees as there is no rotating slipstream effect form the prop). Without a contra prop, the job would have been a little easier, but one has only to look at the Griffon Spitfires to see that handling would have became a major problem to be sorted.

 

So, as pointed out by others, while the mod could be done to meet a specific requirement, i.e. racing, to do it on an operational aircraft would have required considerable time and effort. Better to keep producing the beast you know in considerable numbers, rather than disrupt production for a fairly minor gain.

 

Peter M

 

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10 hours ago, Work In Progress said:

Compare the CAC CA-15 with the P-51D and you will see how much longer and deeper the fuselage is.  

The CAC CA-15 was designed around the R-2800. When the Griffon was installed, (so flight tests could be conducted, never considered for production), as it was a lighter engine, with radiator and oil cooler mounted aft, it had to be slung well forward to maintain the CG. Little relevance to the Mustang.

Peter M

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11 hours ago, Work In Progress said:

Compare the CAC CA-15 with the P-51D and you will see how much longer and deeper the fuselage is.  

Likewise the Griffin powered Martin Baker MB5, although looking somewhat like a P-51, it is somewhat bigger, its wings are close to Hellcat size, & it is tempting to suggest that an attempt to re-engineer the P-51 for the Griffon might have ended up with a similar sized machine for those reasons enumerated above.

Steve.

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I may be wrong but I think that the Griffon 58s used in the Mustang conversions, coming originally from Shackletons, do not have the 2-stage superchargers that came in with the 60-series Griffons. So the engines might be slighly shorter at the back end, which would also help with the overall nose length and CoG issue. I think that the Battle of Britain Memorial Flight Spitfire XIXs use Griffon 58s too, whereas the Rolls-Royce's PS853 has a pukka Griffon 65/66.

 

Justin

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1 hour ago, Welkin said:

Obvious comment, but - Martin-Baker MB.5 lookalike?

They are actually very different structurally. The underbelly radiator producing the Meredict trust effect was probably taken from the P-51 and very much in vogue at the time

 

Both looks like thoroughbreds and a pity nothing more came out of it.

 

/Finn

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One thing I often wonder is how actually useful could a Griffon be on the Mustang. The V-1650 variant used on the P-51H was very close to the Griffon in terms of power, why introduce a new larger engine when the one already in production can be brought to a similar power output ? Really the P-51H would have had little benefit from a Griffon.

As to redesigning the P-51D to use the Griffon, the H was already in development and it would have made little sense to stop this and focus on a new variant.

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