Allison engines vs Merlins for racing

[Curt_B]

Re: Allison engines vs Merlins for racing

Curt,
Would you mind doing a quick pic/illustration (don't fret quaity,just convey idea) my weak mind just can't quite assemble it all.

Thnx !

My drawing skills are bad, even on the computer. Always had someone I could guide a drawing with. Lol. For trim, the tail lifts down. The slight upward force from the exhaust stacks pointing down, ahead of the cg/cp, means that the tail has to lift down a little less, so trim drag is reduced. If you'd like anything more, I'd suggest we move over to the aero mod section so as not to distract this one. Thanks.

[Samuel]

Re: Allison engines vs Merlins for racing

What about remote mounting one of these?



They do about 100 inches boost and can supposedly support 3000hp+
ProCharger F-4 Supercharger
And of course the competition
V-28 123 Supercharger

[MIKE NIXON]

Re: Allison engines vs Merlins for racing

Re exhaust stacks:
I used the NACA test data and formula for the exhaust stack opening. It takes rpm, boost pressure, altitude, cylinder displacement and gives the outlet size in inches to give max thrust.
no you can't have a copy.
Also, the Merlin heads were tested with turbos and the back pressure and temp increases destroyed the exhust port. The Allison head with the twin ports has more cooling in the middle and survived the turbos.
M

[IcePaq]

Re: Allison engines vs Merlins for racing

There are locomotives making 6000 horsepower on a single turbo. So what does that prove? (and few if any cars really produce 3000 horsepower for more than 3 seconds at a time.)

An unlimited powerplant system has to be able to make the needed power in a limited size/weight package, across the needed RPM range, with suitable mass flow, at the Reno density altitude with range for variation due to weather, tolerant of several positive and some negative G, lateral G, high vibration, with reliability to last the race week and protect the pilot, and a litany of other constraints. Its not easy, or it would have been done already. Automotive tech applied to air racing has had very limited success in the sport class (and "unlimited" failure - pun intended) because of the radically different operating environment than what it was created and evolved for over the decades.

You've missed my point that turbochargers have advanced to the point of supplying enough air to support 4000hp.........regardless of the powerplant they are supplying.

The engine below makes enough horsepower to have beaten the turbine unlimited hydroplanes in 3 races during the 2003 season and turbos have improved greatly since 2003.

Turbos have come a long way and are plenty durable but heat within the cowling would be a big problem.

Very good points are made about the exhaust stacks because you are not simply tossing energy overboard but rather converting it to thrust with the added benefit of not heating the exhaust ports as much as turbocharging does but it's possible that a more efficient conversion of gasoline to thrust can be had if the added heat to the cylinder head can be managed.

That said, I feel the ultimate expression of the aero piston engine in unlimited racing will eventually be electronically managed and turbocharged with ADI fluid being run between turbo outlet and cylinder head and fuel being injected a bit further downstream close to the head which will reduce intake explosions for the simple fact that most of the pressurized column of intake charge doesn't contain fuel in a mixture that supports combustion until just before the cylinder head.

You still get the benefit of cooling by evaporation by the ADI fluid through the entire pressurized column but without the risk of blowing your intake tract off the plane.

[MRE]

Re: Allison engines vs Merlins for racing

Now all you have to do is come up with an airframe to fit that in to. It ain't going to be no Mustang.

[Big_Jim]

Re: Allison engines vs Merlins for racing

Now all you have to do is come up with an airframe to fit that in to. It ain't going to be no Mustang.

I agree.

A few years ago I was working with Frank Taylor after he bought Dago from the Costo's. He had talked with Ed Cooper Jr. (the guy who owns the hydroplane in the photo above) about putting a turbo Allison in Dago. I was talking with Kerch about the probability of doing that, since he had helped put a turbo-Allison in Tipsy Miss when he was working with Sandberg. Kerch's feeling was that to truly take advantage of the turbos on an Allison (to put it on par with the power a Mouse Merlin can make) you'd need THREE turbo's per bank...one for every two pistons, for a total of six. And he agreed with Mike's comment above....where you going to put it?

[IcePaq]

Re: Allison engines vs Merlins for racing

Actually......what it needs is to be packaged specific to the mustang since the one pictured isn't designed with the dimensions restrictions of a mustang airframe.

So the pictured Allison which makes near 4000hp with two turbos would require 4 more turbos to make the horsepower it already does?

That's ridiculous and you don't have to fabricate turbo systems for a living like I do to understand that.

Two of the turbos linked below would have no problem supplying an Allison and fit into the space formerly occupied by the supercharger and the carburetor........ but again, the problem is managing the heat generated between the exhaust valve and the hot side of the turbo.

A turbocharged engine will put the same horsepower to the propeller at a much lower manifold pressure since you no longer have to make up for the supercharger consuming upwards of 1000hp.

What you get is the benefit of an engine less stressed that puts the same horsepower to the propeller.

http://www.precisionturbo.net/Street-and-Race/ss/2-000--HP/details/Street-and-Race-Turbocharger---PT118-CEA®/329

[wyhdah]

Re: Allison engines vs Merlins for racing

Actually......what it needs is to be packaged specific to the mustang since the one pictured isn't designed with the dimensions restrictions of a mustang airframe.

So the pictured Allison which makes near 4000hp with two turbos would require 4 more turbos to make the horsepower it already does?

That's ridiculous and you don't have to fabricate turbo systems for a living like I do to understand that.

Two of the turbos linked below would have no problem supplying an Allison and fit into the space formerly occupied by the supercharger and the carburetor........ but again, the problem is managing the heat generated between the exhaust valve and the hot side of the turbo.

A turbocharged engine will put the same horsepower to the propeller at a much lower manifold pressure since you no longer have to make up for the supercharger consuming upwards of 1000hp.

What you get is the benefit of an engine less stressed that puts the same horsepower to the propeller.

http://www.precisionturbo.net/Street...PT118-CEA®/329

I don't even think the 112s are necessary since we are making about what the Merlins make with just the billet wheel Pro Mod 96mm. However, I will say that the hot side plumbing and the turbos behind the motor would be a problem. There are other systems on the back side of the motor that wouldn't react well to uncooled turbos. Maybe a water cooled turbo like the ones used in some boats could be possible but they ramp up complexity.

I would say that with the Griffon the two stage supercharger is probably our best bet and that's coming from a true blue turbo guy. Several things are run off the SC drive that would be hard to work out with the whistles.

[omalley1537]

Re: Allison engines vs Merlins for racing

I seem to recall someone on here talking about the fact that above a certain manifold pressure, the boost isn't doing as much for the power level as it is for the thrust from the stacks. Would a large amount of this be lost due to the turbo? I will readily admit that my knowledge of turbos is limited to a Dodge diesel pickup that I owned, always been more of a supercharger guy with cars, etc...It just seems like the exhaust spent driving the turbo would lessen the amount of thrust from the stacks.

I'll also throw out my standard disclaimer here-I am not an expert, nor did I stay at a Holiday Inn Express last night...

[1:1 Scale]

Re: Allison engines vs Merlins for racing

Well, the exhaust gasses still have to leave the turbos, so you can still have some of the exhaust energy turned into thrust, but it would certainly have less energy after passing through the turbine. I would guess that the extra/more efficient hp gained with the turbos would more than offset the loss of exhaust thrust as long as it could be put to good use through the prop.

I wonder what the blade angle on the props are while running in the 500-550mph range

[Samuel]

Re: Allison engines vs Merlins for racing

Personally I think the Turbo system from the P-47 would probably be the best in the long run.

[gp70442]

Re: Allison engines vs Merlins for racing

Personally I think the Turbo system from the P-47 would probably be the best in the long run.

Are you suggesting to put all that plumbing inside a mustang airframe?

GP

[440_Magnum]

Re: Allison engines vs Merlins for racing

Also, the Merlin heads were tested with turbos and the back pressure and temp increases destroyed the exhust port. The Allison head with the twin ports has more cooling in the middle and survived the turbos.
M

And THAT is the piece of clarification that I've never seen stated clearly in the past.

Thanks!

[440_Magnum]

Re: Allison engines vs Merlins for racing

Actually......what it needs is to be packaged specific to the mustang since the one pictured isn't designed with the dimensions restrictions of a mustang airframe.

So the pictured Allison which makes near 4000hp with two turbos would require 4 more turbos to make the horsepower it already does?

That's ridiculous and you don't have to fabricate turbo systems for a living like I do to understand that.

So Kerch (who we know has knowledge of the Tipsy Miss engine as well as the engine that YOU posted a link to) scratched his noggin and came up with a quick answer... you scratched your noggin and called his quick answer 'ridiculous.'

'Scuse me if I lean toward Kerch's noggin. I don't claim to be an expert, but Kerch certainly is. Neither of you may have actually run detailed calculations, either.

A turbocharged engine will put the same horsepower to the propeller at a much lower manifold pressure since you no longer have to make up for the supercharger consuming upwards of 1000hp.

But you have backpressure in the exhaust plumbing that has to produce more or less that same "1000hp" (to use your number which I think is wrong for a Merlin, but its an OK working number) to run the turbocharger compressor, so you're changing the nature of the stress to generate boost rather than eliminating it. Backpressure in the exhaust translates to higher pressure in the intake for the same power, so it still all comes back around to some degree. And if you're talking backfitting an Allison or Merlin, you have to have some load on the gearcase end of the crank because those engines use the supercharger drive as a torsional damper to protect the crankshaft. It can be done (eg, the Meteor version of the Merlin), but its a consideration.

I'm not totally naysaying you here, but I think you're locked into a car-engine mindset, and aircraft are more different than you think.

[IcePaq]

Re: Allison engines vs Merlins for racing

I earned my airframe and powerplant cert. back when we had warbird engines on which to work and it was long before I started on high performance cars so your "car mindset" is incorrect.

You have to also consider when "kerch" worked on it and that his dabbling could very well have been his first exposure to turbocharging and also consider that turbocharger technology has experienced a geometric growth in sophistication and efficiency since that time.

I stand by what I said and I believe the future will be far more kind to my posts than it will be to the naysayers who forcefully object to new technology without having any experience in said new technology.

We'll just have to wait until someone is able to see the benefits and is in a position to build it.

When it happens, engines will last longer and crew chiefs and engine builders will be forced to embrace it once owners see "the other guys" running just as fast without grenading engines and intake tracts as often as they do.