Question for the engine guys: Merlin/Griffon Boost Engine??

[AAFO_WSagar]

I've heard that back in the thunder boat days that Harrahs tried to run the supercharger on either a Merlin or a Griffon using a V6 GM engine... apparently, for whatever reason, it didn't work out (fairly spectacularly if memory serves correct) but it strikes me as a pretty neat idea... if, it would work..

Wondering just how much of the total engine output goes into creating the squeeze? Could something like a second "boost engine" be something that would answer the low boost issues with the plentiful small blower Griffs? Would it be legal?

Laid in bed trying to get to sleep last night thinking of how the power controls would have to be set up, pilot workload.. etc.. Wild Bill, you got your finger on the pulse..

Is this a hair brained idea , or... could it work?

Speedy, you remember anything about the Harrahs project where they tried this?

[ChrisMX105]

Re: Question for the engine guys: Merlin/Griffon Boost Engine??

If memory serves me correctly at 1 time I heard that the supercharger on a Merlin took well over 1000 HP to produce race level boost. Would think that the extra weight would be detrimental to having a second engine to run the supercharger as well as the question of what removing that would do to harmonics and loads within the engine. If one could get away with no Supercharger I would think that a Turbocharger would be the way to go but again what effects the G loads would have on that size turbo would be interesting.

Hopefully one of the V engine Guru's will chime in and tell me how much Crack I am smoking..............

[morss]

Re: Question for the engine guys: Merlin/Griffon Boost Engine??

in sport class we had a white lightning that had a small eng driving a supercharger
sounded really odd taxiing out of the pits

[Wild Bill Kelso]

Re: Question for the engine guys: Merlin/Griffon Boost Engine??

I think most attempts at reinventing the blower wheel have not fared so well. If I was to go and try and do something different I would use a more modern impeller design. The "guru's" that I know and listen to told me that it would be the smartest thing to do, and so far they have been right about many other things. Who am I to argue?

[J.A.W.]

Re: Question for the engine guys: Merlin/Griffon Boost Engine??

I guess there must be a feasible [tight-rope] balance between those pressures
that may be reliably/efficiently developed by mechanical pumping
& those made by chemical [fuel] means..

[Big_Jim]

Re: Question for the engine guys: Merlin/Griffon Boost Engine??

Yes, I talked with Dixon about this setup a few years ago, since he was actually working on the crew in 1966 for part of the season. It was Harry Volpe's idea to put the Buick engine up front to run the supercharger on the Allison. There apparently was a direct linkage from the throttle of the Allison to the Buick...so as one accelerated, the other did too...but they had a hard time syncing the rpm's up. Not sure if they didn't think of that aspect, or they tried, or something, but Dixon said that the Buick would bog down at times and couldn't turn the supercharger fast enough to give it enough boost. Not sure if it was a torque or RPM issue. They tried that setup experimentally in 1966, as well as all of 1967...when it replaced the big Aux-stage Allison.

They gave up and went to a Griffon engine in 1968.

PIcture is from the Newton Marine website.

[ChrisMX105]

Re: Question for the engine guys: Merlin/Griffon Boost Engine??

Who am I to argue?

Wild Bill of Course!!!

And just for purely theoretical gibberish

1200 HP to drive a Merlin blower at race power, Stuffing an engine that could come even close to that HP into an airframe, cool it, carry fuel for it........
So lets say a race Merlin runs at 120 inches to develop 3000?HP at the prop shaft and 1200 HP to drive the supercharger for a gross of 4200HP. If one were to remove the supercharger it would take around 84 inches of MP produce the 3000HP at the prop (if it was all linear). Assuming the same efficiency blower one would need an 8-900 HP engine to drive the external supercharger. If one could make a much more efficient blower and get it down to 500 hp to drive the supercharger it would still require a very stout small block V-8 sitting where the pilot does........
Then you would have the weirdness of changing all the internal stresses in the engine.

All in theory and good fun as I left my slide rule at work..... so have fun with the blowtorches.........

[Race5]

Re: Question for the engine guys: Merlin/Griffon Boost Engine??

Yes, I talked with Dixon about this setup a few years ago, since he was actually working on the crew in 1966 for part of the season. It was Harry Volpe's idea to put the Buick engine up front to run the supercharger on the Allison. There apparently was a direct linkage from the throttle of the Allison to the Buick...so as one accelerated, the other did too...but they had a hard time syncing the rpm's up. Not sure if they didn't think of that aspect, or they tried, or something, but Dixon said that the Buick would bog down at times and couldn't turn the supercharger fast enough to give it enough boost. Not sure if it was a torque or RPM issue. They tried that setup experimentally in 1966, as well as all of 1967...when it replaced the big Aux-stage Allison.

They gave up and went to a Griffon engine in 1968.

PIcture is from the Newton Marine website.

Even if they could get the rpm to sync up it seems like the Allison would be loading and unloading all the time, especially in rough water. I could see that being an issue if the blower stayed at a more constant RPM compared to what the big motor was doing.

[J.A.W.]

Re: Question for the engine guys: Merlin/Griffon Boost Engine??

Jim Hall ran a snowmobile mill on his Chaparral sport-racing car to pump the air out from under it
for down-force reasons..

There was an experimental Do 217 that ran a 3rd [big]engine in the fuselage to provide hi-alt boost..

What about a light & compact turbo-shaft mill to drive an aux' charger?

Or 'piggy-back' it via a fluid drive/ torque converter?

Kind of a reverse turbo-compound type deal..

[Snidely]

Re: Question for the engine guys: Merlin/Griffon Boost Engine??

That was my thought, does the 'boost' drive have to be reciprocating?

Snidely

[Sparrow]

Re: Question for the engine guys: Merlin/Griffon Boost Engine??

It does indeed require 1250 HP, with -9 blower gears, to drive the Merlin blower at race power. I have seen, and have the video, of Merlins running 3450 with the MAP gauge going between 140" & 150". In actually, anything past about 135 is really cool, but your just making noise.

With -7 blower gears, you run out of boost somewhere around 115" on a really good day, with a good intake trunk and pretty close to 3600 RPM with the .420 nosecase gears. Going past 3600 with those gears and a prop that is close to full length is not good and the prop is really going to **** due to tip speeds amongst other things. With those gears, the blower consumes about 500 HP to drive it. The -7 gears are all done when the -9 gears are really just starting to overcome the losses and make it worth while.

This is why several years ago we built and developed the custom blower drive gears and reduction gear set. Some folks seemed to find that quite amusing. However, the combination seemed to prove itself in RR III since a "stock" canopied Mustang went over 490 in a race on the clock.

But wait, I guess I'm wrong about that---- the telemtry apparently was in error

[J.A.W.]

Re: Question for the engine guys: Merlin/Griffon Boost Engine??

I 'm guessing that thermodynamic entropy notwithstanding..

the benefit of exhaust jet thrust..

..still beats the turbo, back-pressure-wise - at Reno race altitudes?

& here's a Griffon article from `45..

http://www.flightglobal.com/pdfarchive/view/1945/1945%20-%201855.html

[J.A.W.]

Re: Question for the engine guys: Merlin/Griffon Boost Engine??

This graph shows what a wartime Mustang & Griffon Spitfire did on +25lbs boost..

& at Reno-type heights..

What would the Mustang do with the Griffon up-front?

[Or a Fury with a Sabre running 4,200rpm & +25lbs..]

http://www.wwiiaircraftperformance.org/spit14+25lbs.jpg

[MIKE NIXON]

Re: Question for the engine guys: Merlin/Griffon Boost Engine??

Well lets start with the Griffon. Due to its bore and overall rotating mass, it peaks out early. It would take a third spark plug in the center of the head to get a big increase in HP. The time it takes to light and burn the charge is the issue here. Yes you can increase the boost and try to balance the timing and octane. Nitrous works also but the net HP to the prop (which is bigger) just never equals the Merlin. Small pistons, lots of them and RPM is where the speed is.

The supercharger has 2 fans in series and generates about 5 times the inlet pressure at max effect. Beyond that boost, the heat generated and the HP consumed slow you down. It also take a lot of ADI to keep the induction temp in a safe range.

A turbine in the exhaust is not effective as that was tried years ago. The heat in the exhaust port caused major problems. It works with the Allison because the exhaust port is split into two ports with extra cooling in the middle.

Think about all the variables in the engine/propeller. Bore, Stroke, compression ratio, combustion chamber shape, spark plug location and number, fuel system(carb or injected), supercharger design and speed, intercooling, prop gear ratio, prop design, cam timing, valve lift, ignition timing, fuel mixture and enhancers, fuel burn rate at full power, spark plug gap and heat range, oil pumps ( pressure vs flow), and a few other things I won't share. Then add the aircraft and of course the pilot. It is a huge number of things to get to the opitimal point for the best results. Every varible generates a bell curve in its effect on performance. Changing the fuel mix changes the curve for the ignition timing. The effectivness of the prop at higher speeds will offset any increase in engine HP at higher RPM's. The question is always where is the peak of the net curve? The net curve is the sum of all the variables listed above overlayed on top of each other. The one who gets close is the one who gets the prize. And of course "keep it simple" still rules.
Later

[Reever]

Re: Question for the engine guys: Merlin/Griffon Boost Engine??

Threads like this are the reason I come on these sites!!!!!!!!!!!!