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How to make a propeller driven aircraft go really fast ?

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Jimstix

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Let's assume that 500 KCAS is "really fast". First you will need gobs of shaft horsepower - 10k to 15k shp. Second you need a propeller and gearbox that can absorb and transmit that power to the air. Third you will need a very low transonic drag airframe, likely a pusher configuration. Several pallets of $100 bills from the US Treasury and a hugely talented engineering team will also be needed. Easy!
 

Vigilant1

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Minimal drag with extreme power to weight ratio with suitable propeller for the system.
Power to weight doesn't matter much at all.
If we just want to go as fast as possible in a straight line at 1G, then we sacrifice everything else to improve thrust to drag ratio. Weight is not an important factor in itself (if we have enough runway). Reduced weight does reduce induced drag by reducing the lift required, but at high speed this induced drag is trivial anyway.
 
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Speedboat100

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Power to weight doesn't matter much at all.
If we just want to go as fast as possible in a straight line at 1G, then we sacrifice everything else to improve thrust to drag ratio. Weight is not an important factor in itself (if we have enough runway). Reduced weight does reduce induced drag by reducing the lift required, but at high speed this induced drag is trivial anyway.

Are you kidding me ?
 

rv6ejguy

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Rare Bear reportedly developed about 4500hp from its R3350, Strega, Dago Red and Voodoo around 4000. All have well exceeded 500 mph at around 5000-8000 ft. density altitude. These are big aircraft though and something much smaller with less hp can achieve similar speeds. Andrew Finday's Super Legacy and other Sport Class entries have exceeded 430 mph on telemetry with something less than 850hp.

A purpose built racer with narrow fuselage (most fast Sport Class planes are side by side designs) with a forced induction V8 would certainly be able to trounce the current crop of Sport Class planes. Think something along the lines of a carbon GP-5.
 
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Speedboat100

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Spruce Goose has power to weight ratio about 0.12 shp/kg....and Rare Bear at around 1.0-1.2.

Rare Bear went 528 mph and Spruce Goose around 200 mph.

Convince me with a better example how weight has little or nothing to go with the speed !
 

rv6ejguy

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Spruce Goose has power to weight ratio about 0.12 shp/kg....and Rare Bear at around 1.0-1.2.

Rare Bear went 528 mph and Spruce Goose around 200 mph.

Convince me with a better example how weight has little or nothing to go with the speed !
Think maybe the Spruce Goose has a bit more wetted area...
 

Vigilant1

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Spruce Goose has power to weight ratio about 0.12 shp/kg....and Rare Bear at around 1.0-1.2.

Rare Bear went 528 mph and Spruce Goose around 200 mph.

Convince me with a better example how weight has little or nothing to go with the speed !
Sorry, but that's a ridiculous example because it doesn't address drag. which is the issue.

Speedboat/Topspeed, enough.
 

Speedboat100

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Sorry, but that's a ridiculous example because it doesn't address drag. which is the issue.

Speedboat/Topspeed, enough.

HK-4 was vely clean plane.

Stemme 12 motorglider has very similar specs with it.

It has 0.127 hp/kg and 161 mph topspeed.


Having bigger re-number the HK-4 is slightly on top.

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Europa XS Monowheel ( very low drag ) reaches the Spruce Goose speed at 0.185 hp/kg.


 

WonderousMountain

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The De havilland Hornet is a good example of Speed/power ratio.
Add a pusher engine, and mount an inverted V tail off the outboard
engine Nacelles. You'll need a kinda big tail gear leg, deal with it.
 
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