Prop tip quistion ???

[h34race]

When the prop tip goes supersonic would it stop all the carnage if the tip was blubis like a ship on the ocean and has it ever been tested ???

[bflynt]

Re: Prop tip quistion ???

By “blubis” I assume you mean the bulb shaped object sticking out the front of a large ship slightly under the water line.

Not sure how this would help.

The tip would still form a shock but it would now be detached. Around the side of the bulb a shock would come off at an angle and impinge on the airfoil portion of the blade. I’m guessing that would be worse.

NASA looked into supersonic propellers for a while and published numerous papers. All the designs I’ve seen were essentially swept prop tips. The sweeping of the tip accomplishes the same thing it does for a wing.

As a side note: Helicopter rotors face the same problem. The rotor tip speed is what limits maximum aircraft speed.

Bryan

[AirDOGGe]

Re: Prop tip quistion ???

From Answers.com:

"A bulbous bow is a protruding bulb at the bow (or front) of a ship just below the waterline. The bulb modifies the way the water flows around the hull, reducing drag and thus increasing speed, range, fuel efficiency, and stability. Large ships with bulbous bows generally have a 12 to 15 percent better fuel efficiency than similar vessels without them."


The bulb nose on a ship isn't designed to deal with supersonic shock waves, which are the major drag-producers of faster-than-sound objects traveling through air. It's a whole different can of worms.

Fine technology for a slow ship in an incompressible medium (water) but the increased frontal area would be a hindrance at high speeds.

[h34race]

Re: Prop tip quistion ???

this is why the russian bear with counter rotating and I think gas tubine?? was so noisey ???? prop tips supersonic ??? think I saw in popular mechanics long prop blads mounted to a gasturbine I think 8 of them didn't have sonic issues I think they were on a leer jet looking thing in pusher mode any clues ???

[AirDOGGe]

Re: Prop tip quistion ???

I can't say about the bear (never seen or heard one fly before myself except on TV).

I CAN say that supersonic tip speed is why a T-6 Texan sounds so loud.

[JamesN.]

Re: Prop tip quistion ???

I know the air force expermented with several prop shapes on the XF84H "Thunderscreach". They had several problems with the plane, being heard 25 miles away, knocking people over, loss of thrust due to air compressability. Theoritical top speed was supposed to be 670 MPH, how ever the top speed during testing was claimed at 623 MPH but that speed has been disputed. The National Museum of the United States Air Force claims it only had a top speed of 520 MPH.

[AirDOGGe]

Re: Prop tip quistion ???

There are a lot of expectations on top speed, but I don't think the XF-84H ever even reached 500 mph in testing.

We had a lot of discussion on the "Thunderscreech". You can find much info in this thread: http://www.aafo.com/hangartalk/showt...ighlight=XF84H

[John]

Re: Prop tip quistion ???

Also there's the XF-88B

http://en.wikipedia.org/wiki/McDonnell_XF-88_Voodoo

[AirDOGGe]

Re: Prop tip quistion ???

Funny how it states that the twin-jet plus turboprop XF-88B is the first propeller-equipped aircraft to go supersonic. The article fails to mention that it wasn't the prop that took it to those speeds. The blades were feathered during that dash from what I understand.