Forum: Technology

No purely propellor-driven aircraft so far created has broken the sound barrier in level flight. One possible attempt to do this was with the XF-84H "Thunderscreech" experimental aircraft:

http://en.wikipedia.org/wiki/Thunderscreech

It seems to have a designed top speed of 670 miles per hour, but only reached 520 miles per hour in practice.

This, however, was way back in 1955 and 1956. Surely turboprop and drag-reduction technology has advanced significantly since then. Could a supersonic, propellor-driven aircraft be created with today's technology?

Propellors lose efficiency near the sound barrier, which is probably why supersonic prop planes have not been seriously pursued in a long time. There seems to be no practical use for such a plane, as jet engines are much better for the job. Let's say that we aren't trying to build an aircraft for practical purposes, though. We are just trying to build one just to see if it can be done.

The XF-84H had an engine with between 5,000 and 6,000 horsepower. The most powerful turboprop today generates 15,000 horsepower, which is two-to-three times as powerful. So we can build stronger engines.

Another of the XF-84H's problems was the torque generated by its propellor. This could be offset today by using a counter-rotating propellor system. If visibility or turbulence generated by the propellor is an issue, then it could be mounted on the back of the aircraft as a pusher prop instead of in the nose. If this is not a problem, then an aircraft in the vein of the Dornier Do 335 Pfiel could be constructed (in which one engine pushes the aircraft and another pulls the aircraft). This type of construction would reduce drag relative to other twin-engine designs because both engines are mounted inside the fuselage.

A more highly-swept delta wing could be used to reduce drag relative to the swept wing of XF-84H whilst carrying more fuel. Also, more propellor blades (maybe up to six) could be mounted on the engine(s) in order to increase thrust (at the expense of fuel economy).

If noise would be a problem for the pilot, we could make the aircraft a UAV.

Remember, I'm not going for what's practical, I'm going for what's possible.

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I'd say it's possible....

Would most likely be something like a prop-fan engine like this.

http://en.wikipedia.org/wiki/Propfan.

(EDIT) Attachments working now...

Perform a "Google Image Search" for "PROPFAN"

Keep 'em flyin' Thumb

TEG

www.youtube.com/watch?v=oVT3Go1lr3c

This one (Convair XFY1) could have come close, designed for 610 mph top speed.

Kryptid wrote:

We are just trying to build one just to see if it can be done.

Remember, I'm not going for what's practical, I'm going for what's possible.

I suspect if you put enough engines on anything, you can make it go supersonic.

At least once.

regards, OL

Research by NACA and other organizations during the mid-1940s and German research during WW2 showed that transonic/supersonic propeller driven aircraft were feasible.

The profile of the blade required to sucessfully operate above M=0.9 is significantly different from the designs used to operate below that speed; beyond Mach=0.9, the propeller blades must become significantly shorter and thinner and the blade angle (the angle of attack of the blade) must be decreased compared to blades used on slower aircraft.

Here are a couple of pictures of the transonic test propeller mounted to a turboprop in the XF-88B research aircraft (F101 Voodoo prototype).

For more information on a research program go to Chapter 4 in this link:

http://www.hq.nasa.gov/office/pao/Histo ... ntents.htm

For further reading you could track down a copy of NACA TN-4389 published in 1958 which has extensive information on the propeller sections tested and their results.

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But why?

Seems to me that if you wanna go supersonic in a propeller-driven airplane, you'd have to spin the prop fast enough for the tips to go way supersonic. That's what made the noise on the XF-84H, and makes the noise (never heard it myself, though) on the Soviet Bear bomber.

I'd think it would be totally impractical in today's world to have a supersonic prop plane. But then, if you got enough money, it'd be way cool...

Don't forget that we lost some P-38s and P-47s during WWII when they dove and went supersonic and the pitch forces got so high the pilots couldn't pull out of the dives.

Forum: Technology

Supersonic Propellor-driven Aircraft?