A Trilogy of Twinfires

[Wardukw]

Oh you nailed it mate..contra props will make this look like a real beast..ive gotta get some after market contra props..one build i have on mind would benefit from them to no end.

[Pepsi Concorde]

Oh you nailed it mate..contra props will make this look like a real beast..ive gotta get some after market contra props..one build i have on mind would benefit from them to no end.

Making me think about contraprops for my twin spit now!

[PR19_Kit]

Contra-props would make a lot of sense for a type with two torqued-up Griffons.

Either that or have one engine rotate the other way, but that would be a REAL pain to model as you'd have to scratch up a prop with the blades the other way round.

[Wardukw]

Pepsi mate go for it ..if you can.

Steel ya thats the annoying part..either you go full contra or engines but either way you still have to have one blade going in reverse so ya no better off and with the Griffon ya basicly have to have contra because they look mean as hell.

[steelpillow]

Either that or have one engine rotate the other way, but that would be a REAL pain to model as you'd have to scratch up a prop with the blades the other way round.

H'mm... don't get me thinking again!
The Griffon was deliberately made to rotate in the opposite sense to the Merlin, so as to make it more obviously a different engine and reduce confusion among the erks. With engines stretched to the limits like these ones, redesigning the reduction gear to spin the prop the other way from the crankshaft was not possible. Early-model Griffons had similar horsepower ranges to late-model Merlins.
So a Twinfire with a late Merlin on one side and an early Griffon on the other would balance out nicely!
A five-blader would be more accurate for these engines than a contra-prop; they did try a 3+3 on the Merlin but it was not a great success (though perseverance might have paid off in Whiffland). It would look a little odd, as the Griffon prop sits lower and so has to have shorter blades, made a tad thicker to compensate. And no doubt the superchargers would do their things at slightly different points in the RPM/flight profile, which could give the pilot something useful to do for a change.
Would have to have been done either by Supermarine ca. late 1944/5 (especially the contra-prop version), or in a theatre where Griffon and Merlin Spits were both deployed, which puts it out of my tale. One for some other friendly whiffer to make happen - please....

[perttime]

deHavilland Hornet had Merlins with props turning in opposite directions.

edit: and  the Allisons on P-38 had opposite rotation.

[steelpillow]

deHavilland Hornet had Merlins with props turning in opposite directions.

edit: and  the Allisons on P-38 had opposite rotation.

So they did, thanks for the correction*. An altogether more practical and likely option. Not quite such a striking whiff, though.

* A correction of fact, on a what-if forum? Dear me! Still, if we do not get our facts right, how can we be sure that we have got out what-ifs fictional? 

[NARSES2]

I do like the Mk VV 

[kitnut617]

Oh you nailed it mate..contra props will make this look like a real beast..ive gotta get some after market contra props..one build i have on mind would benefit from them to no end.

Making me think about contraprops for my twin spit now!

For my Twinfire build, I used two of Colin's (Freightdog) Seafire Griffin contra-props sets. Sorry I can't show you photos of it though, the 3rd party host I was using has gone t!ts up.

[PR19_Kit]

The Hornet's Merlins were actually different lengths, so as to gain enough room for the extra chain of gears at the front. It's almost so small a difference as to be not worth modelling, maybe 1 mm in 1/72, and I keep on meaning to check the lengths of the AZ kit, but I've not managed it so far.

[kitnut617]

Oh you nailed it mate..contra props will make this look like a real beast..ive gotta get some after market contra props..one build i have on mind would benefit from them to no end.

Making me think about contraprops for my twin spit now!

For my Twinfire build, I used two of Colin's (Freightdog) Seafire Griffin contra-props sets. Sorry I can't show you photos of it though, the 3rd party host I was using has gone t!ts up.

I think I've fixed my problem

[Wardukw]

Im not sure you could mount a Merlin and a Griffin on the same plane.
The Giffin was twice the litres of a Merlin and a bigger engine in all aspects ..the weight difference would be something to deal with but could be sorted with extra weight added for balance.
I think the Griffin used a bigger prop too and of course the power difference was quite large too.
Good luck to the pilot who test flew that thing 

[PR19_Kit]

Not quite, a Merlin was 27 litres and a Griffon was 37.

The Griffon's bore, stroke and capacity was identical to the Type R engine of Schneider Trophy fame

[Wardukw]

Ture Kit ..bore and stroke and the internals might have been pretty much the same but im pointing more towards to the outside of the engine..i had 2 400cid V8s ..both are the same inside but one engine was 32kgs heavier than the other..one was a alloy block and the other iron..power was pretty much the same..for a little while anyway 
If you take a 1200hp engine one side of a plane and a 2000hp engine on the other your gonna have problems
The Griffin 65 was a 2240cid engine where as the Merlin was 1649cid..that alone is a issue..the weight of the Griffon and larger size would make balance a right pain in the backside and balance is super important to any plane..even RC ..a booboo ive made a couple of times   
And this i know for a absolute fact because once apon a time i took my Great Planes single engined Trainer 60 ( 60inch wingspan) and made it twin engined..I thought both engines were the same ..both .60s .nope..one was a large .40..no markings..cheap nasty engines..made for some quite intresting flying when one side tryed to over take the other side 
With the balance being so out of wack one side of the plane would always lean and would require a heap of trim to try and stay level and landing would be a nightmare.
Id just regear the engines drive to make it go backwards or ..now please correct me if im wrong but didnt the Mosquitos engines run the same direction? I dont remember .
If it did then bingo bango your sorted and we know how brilliant a plane that was.

[steelpillow]

Ture Kit ..bore and stroke and the internals might have been pretty much the same but im pointing more towards to the outside of the engine..i had 2 400cid V8s ..both are the same inside but one engine was 32kgs heavier than the other..one was a alloy block and the other iron..power was pretty much the same..for a little while anyway 
If you take a 1200hp engine one side of a plane and a 2000hp engine on the other your gonna have problems
The Griffin 65 was a 2240cid engine where as the Merlin was 1649cid..that alone is a issue..the weight of the Griffon and larger size would make balance a right pain in the backside and balance is super important to any plane..even RC ..a booboo ive made a couple of times   
And this i know for a absolute fact because once apon a time i took my Great Planes single engined Trainer 60 ( 60inch wingspan) and made it twin engined..I thought both engines were the same ..both .60s .nope..one was a large .40..no markings..cheap nasty engines..made for some quite intresting flying when one side tryed to over take the other side 
With the balance being so out of wack one side of the plane would always lean and would require a heap of trim to try and stay level and landing would be a nightmare.
Id just regear the engines drive to make it go backwards or ..now please correct me if im wrong but didnt the Mosquitos engines run the same direction? I dont remember .
If it did then bingo bango your sorted and we know how brilliant a plane that was.

Im not sure you could mount a Merlin and a Griffin on the same plane.
The Giffin was twice the litres of a Merlin and a bigger engine in all aspects ..the weight difference would be something to deal with but could be sorted with extra weight added for balance.
I think the Griffin used a bigger prop too and of course the power difference was quite large too.
Good luck to the pilot who test flew that thing 

Sorry, I think that bears a response, it is far from accurate. The differences, and lack thereof, between Merlin and Griffon often surprise the unwary.

Yes the Griffon had significantly greater cylinder capacity but it famously packed that into no more overall space than the Merlin; any extra fuselage length was down to the bigger spinner and tail fin. It weighed around 10-20% more, largely balanced out by the bigger tail. And anyway the Merlin Spits were often a bit tail-heavy, so the Griffon actually improved pitch stability.

Later Merlins such as the Spitfire VIII's Merlin 63 delivered around 1,700 hp at 8,000 ft. The Griffon IIB, one of the first in service, gave pretty much the same at that altitude. The 63 was better at higher altitudes, the IIB at lower. So there was very much a crossover period when the two were comparable, and both maintained almost parallel development paths for some time. The last Merlins, for the DH Hornet, were rated over 2,000 hp. The Griffon eventually made it to 2,400 hp, but only with the help of a three-speed supercharger and fuel injection. The Griffon never did deliver the specific power (horsepower per pound) of the Merlin.

A major reason for the lack of differentiation was that a big cylinder may deliver a bigger bang, but the clumsy great thing cannot spin as fast, so the smaller cylinder gives you more bangs per minute. The Merlin typically revved at 2,300 rpm and above, while the Griffon was lucky to hit 2,700. (The ultimate expression of this was the Napier Sabre, which had twice as many small cylinders and hit 3,800 rpm, enabling it to leave both R-R offerings in the dust).

On prop size; it does not correlate well with power. The density of the prop is also important. The density is basically the amount of the swept disc area that the blades cover, and is determined by both the number of blades and their chord length. For a low-slung plane like the Spitfire, prop diameter was limited by the drive shaft position and undercarriage length. The Griffon's shaft was lower, meaning its prop was actually a smaller diameter than the Merlin's. It compensated, as I did akshully mention above, by having a broader chord.

As I also mentioned, provided the two examples are broadly matched in power, pairing them would only throw up wobblies where the power curves differed as the two rather different superchargers cut in and out at different points in the flight envelope.