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How to make a propeller driven aircraft go really fast ?

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Riggerrob

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Red Baron's primary advantage was its Rolls-Royce Griffin engine that - stock - developed twice as much horsepower as a stock Merlin. The counter-rotating propeller was more of an after-bonus because it was stock on later model Spitfires and Shackletons.
I doubt if even a billionaire could afford to develop a race-specific counter-rotating propeller.
 

Wild Bill

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It’s interesting to look at some of the 1940’s era strut braced monoplanes.
They don’t appear to have a whole lot going for them in the aerodynamic department.
What they do have is a 500 +/- HP radial engine and a large propeller.
Some of those planes are scary fast even by today’s standards.
Two of the fastest modern prop planes I know of are the nemesis NXT and a turbine powered lancair legacy.
The NXT set records somewhere just over the 400 mph mark. A impressive speed but still 100-150 mph short of the speeds of the larger unlimited racers.
The modified legacy had, I believe 850 hp yet still in the 440 mph range.
Another hot little homebuilt that comes to mind is the turbine legend. Speeds in the mid 300mph range.
At a glance it seems they should be faster than that with all that HP.
That shows that it takes some serious HP to get GA sized aircraft over 400mph

It seems pretty clear that the small airplanes can’t get anywhere near the speeds of the modified military designs like the mustang and bearcat

The small single seat examples that were built for speed seem to top out around 250 mph or so. The Nick Jones lighting bug comes to mind.
Formula 1 racers are in the same 200+ knot speed range. Which is still impressive given the relatively low HP.
If you look at props, a 500 mph prop regardless of diameter has around 36 degrees of pitch at the tip.
On a small plane that would be say a 48” dia by 110” pitch.
A larger prop at 144” dia.. 330 inches of pitch or 27.5 feet.
If you look at it that way, pulling that much prop and overcoming drag at that speed would take some serious horsepower.
 

Speedboat100

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Yes a man carrying "sledge" has to be beyond 2000 hp to go anywhewre in Reno...preferably 3 000 hp+.

To carry a man or woman the plane has to have certain dimensions and lotsa fuel to be able to compete...and adi etc.

It takes lotsa tweaking....and a new craft takes years to design....and several more to be build.
 

N804RV

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Does anyone know what kind of minimum weight you’d need to achieve those kind of speeds in propeller driven airplane using the engineering and materials we have today? I’d be worried about mass distribution problems and flutter in really light weight aircraft with controllable surfaces and the ability to land like a traditional airplane.
 

Riggerrob

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To avoid flutter, pay careful attention to control surface outer mold lines and install heavy weights in their leading edges. A variety of profiles can reduce the risk of flutter: concave surfaces, blunt trailing edge, control leading edge larger than wing trailing edge, etc.
Preventing the entire wing from fluttering requires similar strategies. Airliners hang wings well forward of their wing leading edges to bias the wings' centre of gravity as far forward as possible.
 

Riggerrob

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... It seems pretty clear that the small airplanes can’t get anywhere near the speeds of the modified military designs like the mustang and bearcat. ...
I disagree. The formula for speed is still to install the most powerful engine in the smallest airframe. Look at how many thousands of pounds of guns, armour, radios, hydraulics, etc. they strip out of Reno Unlimited racers. Less weight allows them to fly at shallower angles of attack to reduce induced drag. Lighter weight also allows them to turn tighter.
Secondly, you can always wrap a smaller airframe around an existing engine. Tsunami had essentially the same external mold lines as a P-51 Mustang, but was only 2/3 the size with the same RR Merlin engine. Tsunami had a gross weight of 7,000 pounds compared with a stock P-51D at 12,300 pounds. Of course Tsunami was way faster than a stock Mustang.
 

rv6ejguy

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Red Baron's primary advantage was its Rolls-Royce Griffin engine that - stock - developed twice as much horsepower as a stock Merlin. The counter-rotating propeller was more of an after-bonus because it was stock on later model Spitfires and Shackletons.
I doubt if even a billionaire could afford to develop a race-specific counter-rotating propeller.
The latter versions of the Merlin used in the Hornet were rated at 2030hp. Most powerful Griffon, about 300hp more if I recall.
 

rv6ejguy

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That shows that it takes some serious HP to get GA sized aircraft over 400mph

It seems pretty clear that the small airplanes can’t get anywhere near the speeds of the modified military designs like the mustang and bearcat


If you look at it that way, pulling that much prop and overcoming drag at that speed would take some serious horsepower.
As I said earlier, nobody has come close to tapping the potential of the current Sport class rules. Take a 900 inch Mountain motor, turbocharge that with only 60 inches and you get well over 2000hp. Install in a carbon GP-5 size plane and you get 550+ mph. Work the math. Taking Andy's Super Legacy and installing 2000 hp and you'd go around 570 mph if you could minimize the compressibility effects on the airframe and prop. Think slightly swept wing. This wouldn't be cheap or easy of course, just a recipe.
 

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Wild Bill

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Getting a practical power plant with 1500-2000 hp in a GP-5 sized airplane just isn’t going to happen.
Don’t get me wrong, I would like to see it. But it’s a bit of a pipe dream.
The reliability, size, weight, cooling issues, fuel consumption, etc of that engine would be extremely problematic.
 

Kyle Boatright

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Getting a practical power plant with 1500-2000 hp in a GP-5 sized airplane just isn’t going to happen.
Don’t get me wrong, I would like to see it. But it’s a bit of a pipe dream.
The reliability, size, weight, cooling issues, fuel consumption, etc of that engine would be extremely problematic.
This would be a racing airplane. The engine would only need to be run "at power" for an hour or two to win races/set records. So with a 10 hour TBO (9 hours at 40% power,1 at 100% power), you could put some points on the board.
 

rv6ejguy

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Getting a practical power plant with 1500-2000 hp in a GP-5 sized airplane just isn’t going to happen.
Don’t get me wrong, I would like to see it. But it’s a bit of a pipe dream.
The reliability, size, weight, cooling issues, fuel consumption, etc of that engine would be extremely problematic.
It would have to be scaled up about 15% for a MM. MMs reliably make over 2500hp in blown trim and have been around for 20+ years. Cooling is well understood, I see no issue with doing that. Add some more tankage for the fuel. The biggest issue would be developing the PSRU IMO.

There are two new racers being developed right now using forced induction LS engines, right along similar lines... It all fits.
 

Steve C

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I dont think it's trivial to get 1000hp and make it survive continuous use. Maybe if you use 2 engines. I believe the Pond Racer would qualify for sport class. It was fast enough it you could get some more reliable power in it.
 

rv6ejguy

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I dont think it's trivial to get 1000hp and make it survive continuous use. Maybe if you use 2 engines. I believe the Pond Racer would qualify for sport class. It was fast enough it you could get some more reliable power in it.
Easy these days. Sonny Leonard has been doing this stuff for years and has 800 inch marine versions making 1500 hp naturally aspirated and 1000 inch versions making 2100 hp- again naturally aspirated. Calm down the valve train stuff, add 60 inches and you can easily and reliably make 2000hp+ at under 5000 rpm. Will live for hours. No problem lasting for 8 minutes at a time for Reno. Sonny is a legend.
 

rv6ejguy

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Still gotta keep it cool enough to run 8 laps. I'm clueless to how much fluid is needed... Ross and others would know.
For lowest drag, you're going to want to spray ADI and the rad face to reduce the rad size down. In Sport Class we spray 2-3 gallons/ min. combined. Would have to make this 4-5 with a 2000hp liquid cooled engine probably- 40 gallons total- over 300 pounds but you get lighter every lap. Run methanol as one guy plans and you can cut rad mass flow about 30% so 30% less cooling drag.
 
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