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How to make a propeller driven aircraft go really fast ?

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Steve C

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IF1 prop tip speed are right at mach 1. For them, the extra hp they get with rpm is worth the trade. It's not ideal, but also not a total deal breaker.

Tsunami was actually supposed to be fast with a less powerful engine than the Mustangs use. Holm said it really hauled the mail at flight levels.
 

Riggerrob

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The formula includes the most horsepower you can afford, the smallest, smoothest and lightest airframe you can afford, a comparatively slow turning propeller with lots of disc density and steeply-pitched blades.
Disc density can be improved with wide blades or more blades. Eight blades seems to be the maximum for a single propeller disc. Contra-rotating propellers can sport even more blades.
Contra-rotating propellers are most valuable in tractor configuration because they reduce torque swing on take-off by reducing the amount of airframe exposed to prop-wash.
While pusher propellers may reduce the amount of airframe awash in prop-wash, they present other balance and streamlining problems. Many designers have tried to solve streamlining problems with extended prop shafts, but few have succeeded when combining shafts and pistons because the combination can produce weird torsional resonance problems.
 

Dan Thomas

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Contra-rotating propellers are most valuable in tractor configuration because they reduce torque swing on take-off by reducing the amount of airframe exposed to prop-wash.
That's not torque. It's caused by the spiralling slipstream striking one side of the fin. Torque swing is the airframe's reaction to the propeller's being driven and it places more weight on the wheel opposite the downgoing blade and increases the rolling friction on it.
Left-Turning Tendencies Explained: Why Your Plane Pulls Left During Takeoff

The contrarotating props would indeed reduce torque swing a lot by pretty much eliminating the torque reaction transmitted to the airframe.
 

davidjgall

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Ambient temperature is the limiting parameter; transonic drag rise is a limiting factor on prop tip speed — how much of the prop one can push into the drag rise is a function of available power (and tolerance for noise). Little increment in TAS comes at great cost....
 

cblink.007

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What is the definition of a propeller for these purposes? When does a ducted propeller become a jet...?
One of my former colleagues, years ago, contemplated a speed demon based on the German RFB Fantrainer:

Rhein-Flugzeugbau_Fantrainer_600,_Private_JP6233226.jpg

However, it would have a much more streamlined shape, a powerful turboshaft engine driving a ducted fan in a specially shaped duct to reduce intake flow speed. If we had a ton of money, it would have been fun to try!

I have had a book on ducted fan design for years, but have yet to read it!
 

Mad MAC

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Yes curious thing it is actually flying 950 km/h ( 590 mph ) at same power to weight ratio as Dh Mosquito does 415 mph. So the ( relative ) reduced drag is enermous with swept wings and adequate huge propellers ( and flying very high in the thin air ).
But how much jet thrust is each making?
The Hornet might have been 10% to 20% of its total thrust from exhaust gases, the Bear a lot more.
 

Speedboat100

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Add solar panels and pedals.
Don't uderestimate the FORCE !


Pedalling has taken man at 144 km/h ( 89 mph ) and solar power high nearly 300 km/h....and put them together and you get 144+300= 444.

aerovelo.jpg

Then again minimum power to weight ratio for flight is at around 0.005 hp/kg ( wing loading 4 kg/m2 ).


In comparison Wright Flyer power to weight ratio was 0.0355 ( wing loading 7.1 kg/m2 ): Wright Flyer - Wikipedia

Then the Wright model R " Baby Grand" was a beast already with 34 kg/m2 wingloading and 0.11 power to weight ratio: 1910 Wright Model R

Earlies motorgliders had 0.08 hp/kg loading with 23 kg/m2 wingloading: Raab Krähe - Wikipedia

That could be a good reference for electric flying with a good range.
 
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henryk

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Contra-rotating propellers are most valuable in tractor configuration because they reduce torque swing on take-off by reducing the amount of airframe exposed to prop-wash.
=not exactly=torque (reaction momentum) is equal to engine or reductor momentum...

-iff reductor is Differential=engine momentum only...

-iff CRFLIGT patent= ZERO reaction and gyro momentum!
 

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AdrianS

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It would be interesting, if unlikely, to see something radical in propeller design.

For a long time, cavitation was the major limit for water propellers. The workaround was more blades, bigger slower props, multiple props, etc. Sound familiar?

Then someone worked out how to make a super-cavitating prop, which changed everything. Now it's surface drives, when earlier wisdom said to bury the props as deep in the water as possible.

I don't expect a similar breakthrough with aircraft props, but that's partly because we have jets as an alternative for high speed flight, so no-one is pouring in the R&D funding.
 

rv6ejguy

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The fast Sport Class guys like Andy Findlay have custom made props (his with factory McCauley engineering support). They were strain gauged and specially profiled for the race application. Very limited life. Based on their recommendations a couple years back, Andy used less RPM and more MAP to improve prop efficiency and keep the same power. Some of the other guys were turning them up to 3200 rpm. All the fast aircraft engined planes since about 2008 have used special, thin section, scimitar blades.
 

Speedboat100

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This flew in 1973 with just 11 KW and weighed some 440 kg.

That yields less power to weight ratio as Wright FLYER at 0.0295 hp/kg.

militka.jpg

Fastest electric AC in 1973...and the only one ever before it.

Flew 70 years after Wright brothers did.

 
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Aerowerx

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Many many years ago I read about an attempt to set a prop plane speed record, but putting dual counter-rotating props on a hot-rodded P-51D. But I never saw anything more about it.

Anyone ever hear about that?
 
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