I was watching a documentary the other day and there was an interview with Chuck Yeager where he stated that he was pretty sure that during WWII he reached the sound barrier while in a dive in a P-51.

My questions: Is it possible for a prop plane to break the sound barrier in level flight? Is it even possible for a prop plane to break the sound barrier in a dive as Yeager suggested?

I don't know.

Aerospaceweb.org:

This might be the best attempt: XF-84H Thunderscreech

__________________
0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 ...

Do you think a prop-plane that was built with today's technologies could break the barrier in level flight or a dive?

I found this. They are only predicting Mach 0.82 but still pretty fast for a prop plane:

http://www.popsci.com/popsci/aviatio...cbccdrcrd.html

We would be remiss in this discussion not to bring up the venerable Tu-95 (Bear), which has been reaching its top speed of 575 mph (925 km/hr) regularly since somewhat before I was born. Depending on what numbers really apply to the Thunderscreech, it may not have ever been the fastest propeller-driven plane (in level flight, etc.).

I was just reading about it on wiki. I think it is still the fastest propellor plane that went into production. I like the part where it says that is so loud that ocean underwater sound detector buoys can detect it.

This might be viewed as a particularly unfortunate feature for its antisubmarine patrol adaptation.

Now that the museum down the road from you has a B-36, the Tu-95 must be one of the things they would most like to have. One would look so menacing rolled across from one of the three B-52s out there on the caliche.

The prop on the Thundescreech was supersonic. If you can get the prop tip to function at supersonic speed, what is the limiting factor, power?

__________________
Reality: What a concept!……………………..><Ç(((Ç°>

Probably propeller speed. and altitude.

__________________
"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
"The Mayan symbol for "book" looks a lot like a triple hamburger, but I've never seen them claiming it as proof the Mayans had Big Macs." - KaiYeves
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

I haven't been to the Pima museum in about eight years. I really enjoyed the large radial engine that they had cut up to show its inner workings. This is a mammoth engine from a WWII bomber (B29?) - amazing how complex it is.

Are you asking whether there is something fundamental about the nature of moving a plane by twirling a propeller that makes it impossible to move faster than sound?

This is just a gut feeling, but I think that if the motor's air was fed to it in a regulated way, or was some high-tech electric motor, and that the plane itself could withstand the pressures, there is nothing fundamental preventing it. That is, given enough horsepower and torque.

On the other hand newer technologies make the engineering challenge seem not worth while, and probably not energy efficient.

__________________
Forming opinions as we speak

Yes. Since it is pulling (screwing) itself through the air instead of pushing, even if the propellor is in the rear, is there some fundamental reason why it can't break the sound barrier?

My father was in the Army Air Corp during WWII and he told me of discussions with pilots who described weird effects during some dives that he later contributed to being near the sound barrier. Control issues mainly, which seem to match what I remember being the reason the "sound barrier" got named that.

Wikipedia: sound barrier - early problems

The fact that the US did not take the Tu-95 seriously is interesting since the Tu-95 is still in service.

From wiki:

The Beachcraft Starship (designed by Burt Rutan ) used a turboprop engine which had the propeller behind the engine. One of the features of this design is that the air flowing over the engine nacelle is compressed as it approaches the prop. So is the air/exhaust from the turbine engine itself. The prop is biting into higher density air, and therefore should be able to provide more thrust in this configuration.

__________________
Reality: What a concept!……………………..><Ç(((Ç°>

Not sure, but this could indicate why it wasn't tried again - shockwaves from the prop, which was running at supersonic speeds, even on the ground. From the XF-84H Wiki article:

__________________
Sleep? Isn't that that totally inadaquate substitute for caffeine I've heard so much about?

Quantumfoamy.com, my astronomy/astrophotography blog.

From your link - Maximum speed: 335 knots (385 mph, 620 km/h)

Interesting. It is similar in design to Renaissance Research's Dart Racer, which I linked to earlier.

Some WWII era pilots thought they'd broken the speed of sound in a steep dive but those planes simply had too much drag to do so. The pitot/static system (used to measure airspeed) was also found to be inaccurate at very high speeds, making the airspeed indicator read much higher than was actually the case.

Most propellors lose a great deal of efficiency when the tip speed exceeds about Mach 0.9. Specially designed props like the one on the XF-84H and the Tu-95 can operate higher but the sound levels from the shock waves are incredibly loud, causing severe problems. Even for some light planes whose props exceed about Mach 0.9, the noise levels get very high, making them unpopular in populated areas.

In general, the answer to the OP appears to be no, it isn't possible to use a propellor to get a plane past Mach 1 in level flight.

Tucson Tim,
I never said that the Starship was even close flying at Mach 1, it was never designed to fly that fast. I was referring to the pusher-prop design and how it might assist in higher speed thrust.

Larry Jacks,
I have not seen any information here that says it is impossible to get a prop driven plane past Mach 1. The fact that the noise level is almost intolerable is not the point. We aren’t talking practical or production, just possible. The question is, is it possible?

__________________
Reality: What a concept!……………………..><Ç(((Ç°>

A prop at the front of the aircraft bites into undisturbed air, but there will be a boundary between the accelerated air from the prop and the ambient air that the airframe is flying through. I suspect this will the source of significant engineering challenges in dealing with these different supersonic flows and the interactions between them.

A prop at the rear cuts into disturbed air, which, at supersonic speeds, would probably present some design challenges too. The advantage is that the thrust doesn't have to interact with the airframe. I remember reading, when I was a kid, about the intial design of the rear-engine BD-5 having problems with airflow interactions bewteen the propellor and some control surfaces ahead of it.

This got me thinking about my old Cessna 185. It was on floats, and was equipped with an 86" propellor that turned at 2850 rpm for takeoff. That yields a tip speed of 729 mph, or ~Mach 0.96 at sea level standard air pressure. Between the engine and the prop, it was an incredibly loud machine.

I recall reading that the "solution" was tested by taking the plane to 42,000 ft. and putting it into a full power vertical dive! Even with two Allison V12s screaming their hearts out, the plane did not exceed the speed of sound!

__________________
Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

And I appreciate the info you posted. Thanks. I wasn't berating you - I posted the speed from the link for me and the other readers of this thread.

As a propeller tip reaches the speed of sound, more and more energy goes into making more and more noise, and no improvement in thrust. We are, after all,
looking for more thrust. You dp get more thrust from the turbo prop on a
C-130 Hercules , but.....it isn't really practical on a Mustang.
I expect that a prop near mach one is experiencing cavitation ....a vaccuum
forming near the surface of the blades, and we know how an outboard cavitates near the surface and loses thrust. In jets, we go through a lot of trouble to keep the speed of incoming air below the speed of sound, utilizing a lot of fancy little tricks ie. the variable geometry nose cones on the SR -71.
There 's a lot going on with high tech areodynamics. Take your hat off to a few good men.
Best regards, Dan

This got me thinking about my old Cessna 185. It was on floats, and was equipped with an 86" propellor that turned at 2850 rpm for takeoff. That yields a tip speed of 729 mph, or ~Mach 0.96 at sea level standard air pressure. Between the engine and the prop, it was an incredibly loud machine

Planes like the C-185 floatplanes were the ones I was thinking about when I wrote, "Even for some light planes whose props exceed about Mach 0.9, the noise levels get very high, making them unpopular in populated areas." A T-6/SNJ trainer seems to fall into this category as well. As long as we have people building houses next to airports and then complaining about the noise, we have to be aware of just how loud some planes actually are.

Don't helicopter blade tips go supersonic in some cases? With the extra effect/problem that this happens on one side of the helicpoter first when the copter is moving.

__________________
To the regular visitor of internet bulletin boards it is clear that it's an excellent idea your parents get to choose your real name.

Yep. The last time I flew that plane was to deliver it from my home to Edmonton. At 5:30 am I idled it past all the homes along the river until I was downstream of the subdivision, and took off. I am, afterall, a resident of that same subdivision.

Nicholas:
I'm not certain about the numbers for helicopter blades, but I have done lots of low level flying with steep turns in a Bell 206, and that 2 blade system sure makes some loud banging or slapping noises at times.

I have noticed that helicopter blades can make very loud bangs in steep turns indeed, but I don't think that is related to tips going supersonic per se.

__________________
To the regular visitor of internet bulletin boards it is clear that it's an excellent idea your parents get to choose your real name.

I found this page while researching this post:

http://airspacemag.com/issues/1990/d...h_1.php?page=9

From the page:

"Other U.S. and British pilots have claimed to have done it as well, recalling flights in Spitfires, P-38s, P-47s, and P-51s. But there is one basic, irrefutable reason why their claims are, as Fisher might have put it, malarkey. A propeller—even one designed to current state-of-the-art standard for maximum efficiency—continues to create thrust up to a point somewhere short of supersonic. At that instant, it suddenly loses efficiency and begins to create not thrust but enormous drag. “It becomes a flat plant,” Fisher said; “a big brake.” One Spitfire pilot, who attained the highest verified speed, Mach .9, achieved by a World War II propeller-driven aircraft, discovered this in a big way when the sudden braking forces became so powerful during a dive that the entire propeller and most of the engine cowling broke off."

The fact that the WWII planes had to DIVE to reach very high speeds may explain the claim of supersonic speeds:

"So were the P-47 pilots fibbing? Not at all, Fisher (and Johnson) explained. They were tricked by a simple phenomenon: airspeed indicators don’t function reliably in high-speed dives. The airplanes are falling so fast they can’t measure static air pressure quickly enough: while the instruments were down here, they were still measuring air from up there. Had neophyte Hurtienne’s indicator been accurate at an indicated 675 mph at 20,000 feet, for example, his true airspeed would indeed have been at least Mach 1.05 at typical temperatures. But it wasn’t. Because the airspeed calculation would have been based on an artificially high altitude reading, the airspeed indicator would show the airplane to be traveling faster than it really was."

So, while the Jug is my favorite WWII aircraft, it probably is not feasible for it to reach or exceed the sound barrier, no matter what the circumstance.

tbm

__________________
Paddle faster!! I hear banjo music!!

Thanks for the research tbm.

It looks like the answer is "No. No prop plane has ever broken the sound barrier, whether in level flight or a dive."

I have to believe that that there is no physical law preventing it and given enough power and aerodynamics it could be done, but no one is going to spend the money required to do it. Too bad. It would be an interesting record but that's about it. Not worth much else, I guess.

My thanks to all who posted.

Hi, You "do" realize the idea that at supersonic blade tip velocity, you don't get more thrust, just more noise? Weare both telling you this. It's true.
They pushed props as far as they could. Then they used jets. Simple.

I think for absolute WW2 velocity, the Dornier Arrow, a centerline thrust
configuration, provided a minimum frontal area while employing two propellers,
fore and aft. This yieled some scorching speeds.
"The first ten Do 335 A-0s were delivered for testing in May. By late 1944 the Do 335 A-1 was on the production line. This was similar to the A-0 but with the uprated DB 603 E-1 engines and two underwing hard points for additional bombs, drop tanks or guns. Capable of a maximum speed of 474 mph (763 km/h) at 6,500 m (21,300 ft) with MW 50 boost, or 426 mph (686 km/h) without boost, and able to climb to 26,250 ft (8,000 m) in under 15 minutes, the Do 335 A-1 could easily outrun any Allied fighters it encountered. Even with one engine out it could reach about 350 mph (563 km/h).

Delivery commenced in January 1945. When the U.S. Army overran the Oberpfaffenhofen factory in late April 1945, only eleven Do 335 A-1 single seat fighter-bombers and two Do 335 A-12 conversion trainers had been completed.

In his book The Big Show, French ace Pierre Clostermann claims the first Allied combat encounter with a Pfeil in April 1945. Leading a flight of four Hawker Tempests from No. 3 Squadron RAF over northern Germany, he intercepted by chance a lone Do 335 flying at maximum speed at treetop level. Detecting the British aircraft, the German pilot reversed course to evade. In spite of the Tempest's considerable speed, the RAF fighters were not able to catch up or even get into firing position.
Best regards, Dan