Allison engines vs Merlins for racing

[440_Magnum]

Re: Allison engines vs Merlins for racing

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.

Again, I'm not naysaying everything you're saying. But I don't think its as simple as "throw a turbo on it." And I do not unquestioningly believe that turbocharging is a better path than supercharging for warbirds as air racers. Re-read what Sparrow was talking about earlier in this thread: fixed gear ratios and the limited number of available "stock" ratios. That includes the gearing ratios between the crank and the blower, as well as between the crank and the propeller. An argument could easily be made that engines have won (repeatedly) with less-than-ideal ratios. Customize those, tweak the prop, and optimize all of that to the airframe, and I personally think there are still gains to be made, and internal engine stresses that can be lowered in the process... and still fit in the exact same envelope as a Merlin in a Mustang.

The turbocharging you're talking about is best suited (just IMO, again) to another clean-slate racer ala Tsunami or Pond. If for no other reason than simple packaging, particularly in a Mustang or Bearcat. And who knows, you may well be right that such a hypothetical combination can ultimately beat the Merlin/Mustang or radial/Sea Fury and radial/Bearcat combinations that have been winning this thing for 50 years.

[IcePaq]

Re: Allison engines vs Merlins for racing

I'm just giving the Indians advance warning that the white man is coming.

[Mluvara]

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.

One of the things that always comes back in the debate about any form of racing is "horsepower". Throughout history, there is a macho-ism of horsepower. More is better, they say. (Cue the 'Tool Time Grunt - http://www.youtube.com/watch?v=YQwYNca4iog). The problem is that there are diminishing returns in air racing at the speeds the gold unlimiteds are going and more horsepower is not necessarily better. It would be more beneficial to put one's effort into aerodynamics, propellers, etc. Drag increases with the square of the speed, whereas the horsepower to overcome that drag increases with the cube of the speed.

Where would you put your effort?

Turbos are a wonderful thing. However, irregardless of their stated reliability, they are another item in the chain to maintain and fail.

No matter whether a motor is turbo'd, supercharged, there is a load on the engine when it is making horsepower. Merlins were never designed to put out the horsepower they are doing. The engines often fail because they are way beyond their limits. The amount of structure bolted onto the engine to keep it from twisting apart is pretty substantial.

Michael

[IcePaq]

Re: Allison engines vs Merlins for racing

I'm proposing something that requires a lot less horsepower to be sent to the crankshaft, block, and rods.

I also feel that many failures were caused by non-exacting engine management in spark control and mixture balance cylinder to cylinder in addition to having a pressurized intake tract full of combustible mixture.

Sure, there are other things that will be more stressed with a turbo motor but it's mostly heat management that needs to be addressed and you will extract more crankshaft horsepower at lower boost levels if you aren't spending nearly 1/3 of the horsepower your engine is making to spin that big supercharger wheel...........which was designed in the 1940s.

This car below came with a supercharger and we've even experimented with both turbos and supercharger together on one car and found the engine was more stressed while outputting less usable horsepower with the mechanical supercharger so it's two turbos for now.

We can actually drive this car around on the street with 87 octane fuel just by changing a macro in the boost management system and I just don't see that happening with a supercharged engine because of the lack of ability to easily change boost level or curve.

We've actually gone to improved turbos since the picture was taken so it isn't giving away anything our competitors didn't already know.

[440_Magnum]

Re: Allison engines vs Merlins for racing

I'm just giving the Indians advance warning that the white man is coming.

Talk is cheap, General Custer.

[IcePaq]

Re: Allison engines vs Merlins for racing

It's probably a good chance member morerevsm3's employer has the ability to custom make a gearset with a more favorable ratio but I'm sure he's less than motivated considering the reception he received here.

The very guys with the thinking who can take engine reliability and power levels to the next level are here at this forum or are working with guys who manufacture billet engine blocks and heads, pistons in new super alloys such as pandalloy, and can make most anything out of a chunk of metal or better yet, out of a pile of sintered metal using a laser.

If we can run billet blocks in a car, I don't see why the airplane guys have the budget to pop engines with relative regularity but won't consider working with something other than the same old stuff.

There is a lot of improvement that can be done and I'll bet it doesn't cost a whole lot more than the old technology that is currently being used.

[440_Magnum]

Re: Allison engines vs Merlins for racing

If we can run billet blocks in a car, I don't see why the airplane guys have the budget to pop engines with relative regularity but won't consider working with something other than the same old stuff.

The nice thing about unlimited racing is that anyone can come try pretty much any idea. Go for it!

[Matt Jackson]

Re: Allison engines vs Merlins for racing

It's probably a good chance member morerevsm3's employer has the ability to custom make a gearset with a more favorable ratio but I'm sure he's less than motivated considering the reception he received here.

The very guys with the thinking who can take engine reliability and power levels to the next level are here at this forum or are working with guys who manufacture billet engine blocks and heads, pistons in new super alloys such as pandalloy, and can make most anything out of a chunk of metal or better yet, out of a pile of sintered metal using a laser.

If we can run billet blocks in a car, I don't see why the airplane guys have the budget to pop engines with relative regularity but won't consider working with something other than the same old stuff.

There is a lot of improvement that can be done and I'll bet it doesn't cost a whole lot more than the old technology that is currently being used.

I have heard claims for 50 years in air racing on how the car guys were going to build an engine that would out perform the engines now running in these old airplanes. The fact is talk is cheap and the proof is in the pudding so to speak. Rolls Royce and Pratt & Whitney were no dummies as engine builders. Tough then and tough now. Room for improvement, you bet. People out there willing to bet their lives on it? Not so much!!! Show me a big block that will put out 3800 HP and live for 30 minutes at race power and then fly it home. Ill take two. Oh, it also has to fit under the cowling and have a nose case that will stay on the engine under high g loads with a 600 pound prop trying to rip its self off the front of the engine. This race isn't for 3-5 seconds its for 8 minutes and thats after 20 plus minutes before the final race even starts. There is always someone out there with a better mouse trap if you ask them. The real issue becomes producing one that will stand the test of time.

[IcePaq]

Re: Allison engines vs Merlins for racing

I'm not suggesting running an automotive engine.

You also have to address that RARA's rule change has "limited" the "unlimiteds" and effectively sanctioned the thunder mustangs and other smaller machines out of the "unlimited.....well....kinda" class.

[MIKE NIXON]

Re: Allison engines vs Merlins for racing

Nothing like a night at the old Holiday Inn Express.
Lots of new posts on old issues.
Boats: The Hydro's usually run at low altitude, sea level to 1,000'.
Reno is over 5,000' on a cool day and close to 10,000' on a hot day.
One of the best comments about turbos said that 4,000 hp turbos were made.
Back to basics: The engine is an air pump with fuel added. Add fuel to 1,000 cubic feet of air per min and you get:
a lot of HP. (and a lot of BS) How much depends on engine design. All a blower of any kind does is push more air into the engine per cycle. The boost pressure also reflects the design of the valve train. Take your engine and open the valves more and longer, you can get more HP until the curve falls off.
The blower needs HP to drive it and that can come from the end of the crank or from the crankpins. If the crankpins, the HP comes from the exhaust stroke fighting the increased back pressure.
Any way, it all comes down to plotting the curve which is going to resemble a cross between a sine and a bell.
Without taking a huge amount of time lets use the sine curve for now.
The propeller curve for the P-51's peaks at about 85% of mach. It changes for temp but not altitude.
That number is based on the tip speed vector of rotation and forward speeds.
While the engine can produce more HP with increase in RPM the net curve will flatten and then fall off.
Thats why you can go faster at 3500RPM than 3600 RPM.
To quote Yoda " more is not always more".
Now take into account all the variables: RPM, Boost, Compression ratio,valve timming and lift, ignition timing, number of spark plugs and location, fuel octane and mixture, ADI, Ram air, exhaust systems and the "k" factor.
Using a dyno, start with a baseline setting and play with one of the above to generate a HP curve for the changes.
You want the top half of the sine curve.
Leave the engine setting at the top of the curve.
Step back from the engine and smile. It will be your last time to experience this feeling.
Now pick another variable and get a new curve. With the engine set to the top of that curve, re-run your first test and then the second.
You now have the best settings for two variables.
Continue through all the variables untill you have the perfect engine settings.
Now go back and check the weather reports and find some variation on different days of testing.
Remember the "k" above, all the tests have to have the same air temp, pressure and moisture to be valid.
Or a correction curve for each of those variables.
We see all this when testing a carb. All the outside variables have to be accounted for or corrected first before testing.
Once we have the perfect engine we then test in the aircraft and with the prop.
And now we start over with the testing for the A/C and prop. Then armed with the numbers for A/C ram pressure and best prop speeds. We go back and re-do the engine testing for the new operating numbers.
Then we add the pilot and adjust for that set of variables.

Much of what has been posted above only looks at a few of the variables and is for the most part, a rabbit trail. All the great additions to aircraft engines over the years were to solve specific problems. What works at 40,000 feet is a problem at 40. When we raced at Miami, Mojave and Reno we had three different settings for the engines.
Last to all this is the "L" factor. Luck of the draw. I requested the L formula from NACA but nothing so far.
MN

[FlyKidChris]

Re: Allison engines vs Merlins for racing

I requested the L formula from NACA but nothing so far.
MN

L = $

So, 10L = $10. You want bigger L? Bring bigger $. Of course, I know MN knew that already.



Thanks for the great post, Mr. Nixon.

[IcePaq]

Re: Allison engines vs Merlins for racing

I was expecting something a bit more exacting and specific to engine running conditions.

Now we have an entire thread running over rich to compensate for one lean cylinder.

Modern engine management automatically adjusts to variables and you don't have to play with springs and weights and articulation of timing advance or a linkage with cams in order to get the perfect timing curve for all conditions.

If the cylinder head design is lacking cooling on one cylinder, you can compensate that cylinder individually whether fattening up it's mixture independent of the other cylinders as well as change the ignition advance.

If the density altitude changes 2000 feet in 3 hours, advanced engine management has no trouble compensating.

I'm yelling it and eventually someone will listen enough to get curious and the rest will play catch up once it arrives in force.

Best to be prepared and open to the new ideas or those same ideas will be what the competition uses to beat you.

I hope this thread is archived and readable in 10 years when the same people fighting it end up being credited for the revolution in engine management that will surely come to reno air racing.

[1:1 Scale]

Re: Allison engines vs Merlins for racing

Maybe this will speed things up: efi101.com

There are some sport class racers using EFI on Continentals and having good luck with it. If nothing else, it should help the longevity of the engines (assuming proper tuning) if it doesn't make any more power.

[MIKE NIXON]

Re: Allison engines vs Merlins for racing

Re the last response on electronic engine management, ie a fulltime computer running the engine.
The only real way to manage valve timing is using electric control on the valves which works great on my wife's fiat 500. The performance is only matched by the milage.
However, the presure on the exhaust valve face at full boost will require a coil thats 10 times or more the size of one that will work at stock power. Part of the challenge is reversing the valve to close and not damage the seat. I know the modern engines work well here but for the most part smaller is better. The merlin/allison engines are 130 to 140 CID per cylinder with a lot of mass in each valve.
With some funding I am sure we can get the ideal to work but one little hiccup and you have destroyed an engine.
Fuel injection can be done also but automotive systems use a low pressure nozzle in the intake. The Germans got it right when they used a high pressure nozzle in the head. With electronic control and sensing for knock and temps it would work great.
So do we do this on old engines or modern ones.
What is the biggest modern engine out there? What are the endurance numbers at 4,000HP?
A 600CID v-8 at 3,000 HP is making 375 Hp per cylinder.
A Merlin making 375 HP per cylinder is making 4500 HP.
When you look at the lack of failures in the Merlins for the last 6 years and the win record/speeds for the little money we win, you are going to have a hard time finding experimental funding for this sport.
I think what we are going to see is a steady increase in the numbers from the sport class. At the rate they are going, I would expect to see a 500MPH lap in the next 4 or 5 years. Sadly, I would expect to see a number of major failures along the way. Just look at all the A/C and pilots lost in the Mustang's development in the war and racing.
It is easy to sit at a keyboard and push for more speed etc.
Its not so easy to watch a friend pay the ultimate price.
MN

[IcePaq]

Re: Allison engines vs Merlins for racing

I'm still amazed rara guaranteed that further depletion of rare hardware will continue by instituting a weight limit.

Maybe they think people wont watch the races if the unlimited class sees irreplaceable warbirds gradually giving way to scratch built racers?

I'm there to see the fastest planes in the world race regardless of it's origin or configuration.