OT: Wing loading at the speed of sound

If you think about for a moment, if the aircraft is supersonic, then the propeller, no matter how it is designed, swept, etc. must be in a higher supersonic flow -- the sum of the forward velocity vector and the flow past the propellers airfoil due to its rotation. The sum of two vectors at any angle less than 180 degrees must be greater than either one. In this case, the angle is about 90 degrees. The only way to get a subsonic flow in supersonic flight is by means of an appropropriately shaped inlet. In which case, it is no longer a propeller-driven aircraft, but a turbo-fan driven aircraft.

Boris

As I understand it, the XF-84H was originally a Navy program to get a swept-wing turbine that was carrier-capable. The turbojets of the day had such slow throttle response that they could not safely waveoff; the turboprop powerplant cound provide thrust with less lag time.

David

TINS

At one of the Chino airshows in the late 80's, I spoke to a '47 pilot who dove after a 109 from high altitude.

He got going so fast, and the buffetting got so bad, that he lost the 109 and really struggled to pull out of the dive. Said he had both feet on the panel and was pulling back on the stick with all his strength, using both arms. He popped a lot of rivets and limped back home - they scrapped the airplane.

I asked him how fast he had gone in the dive, and his answer was, "My asshole was puckered up so tight I didn't have a chance to look at the airspeed!"

David OD

correction:

just barely supersonic --

Very Good!

Bill Shuey

Hello all,

I was very curious about what kind of plane an XF84H was and did a google on it and found this Japanese site

a wonderful looking ship! Could this be made from an old Monogram Thunderstreak I have somewhere stashed away (or a Thunderflash) I am not that into "modern" jets

-- Dennis Loep The Glueing Dutchman

"The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka!' but 'That's funny ...'" Isaac Asimov

Yes, but as I mentioned you can do things with the tips and the blade design to reduce the effects. And - just because the tip velocties are supersonic doesn't mean that the prop stops working; it just becomes less efficient. Therefore, as the saying goes - you just need to add more horsepower. Hence my "not practical" statement.

I had another item come across my desk this morning - an article on Col. Kittenger. Col. Kittenger (whom just turned 74, if I recall from the article) holds the world record for the longest, highest, fastest freefall by a human being. During this freefall (made from a balloon), he reached or exceeded 714 mph, and broke the sound barrier...with his body. If a human body can reach or exceed Mach 1 in freefall, I'm that much more convinced that one can design a propeller powered aircraft that can do the same, within the parameters I previously ascribed.

wtach that first step!

I seem to remember an old Fine Scale Modeler or possibly Scale Models doing an article on this conversion. They used an Italaeri RF-84 Thunderflash with the props scratchbuilt.

-- John ___ __[xxx]__ (o - ) --------o00o--(_)--o00o-------

The history of things that didn't happen has never been written - Henry Kissinger

Thanks John,

I take it the Heller Thunderflash is about the same kit as the Italeri thing?

-- Dennis Loep The Glueing Dutchman

"The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka!' but 'That's funny ...'" Isaac Asimov

According to "The Chronicle of Aviation" he made it to 614 mph, but I'm not sure if I'd trust it; the important thing is that according to the book Kittenger jumped from 102,800 feet. Up there air density is a lot less, so less drag, and therefore a greater speed is reached before the forces even out and the plummeter stops accelerating; giving a comparatively high terminal speed. If memory serves, as air density drops, so does the speed of sound; if I've remembered that correctly, then Kittenger wouldn't have had to go as fast to go supersonic as he would at lower altitudes. So it wouldn't surprise me that, if a P-47 could get to 102,800 feet, that it could go supersonic on the way down due to gravity. Getting a P-47 up that high is a whole different question.

Jon.

I don't know, I've never looked at the Heller, but if its accurate, it should work. If you have a copy available latch on to Lloyd Jones' U.S. Fighters for a very good 3-view of the 'screech; it might make your project a little easier.

-- John ___ __[xxx]__ (o - ) --------o00o--(_)--o00o-------

The history of things that didn't happen has never been written - Henry Kissinger

To the best of my knowledge the Italeri is 1/72 but the Heller is 1/48. Even so the conversion requires much the same work. I'm fairly certain I have a copy of the article that John was talking about in my files. I figured there was a good case that I'd want to try something that weird someday.

Bill Banaszak, MFE

As they say, the high you go, the faster you fall - nobody said WHERE the aircraft had to break the sound barrier, just that is had to exceed Mach 1. I still firmly belive you could design a prop drive aircraft that could do that in a dive.

Back in my R/C days there came a point where an R/C sailplane exceeded the speed record held by the powered community. It left everyone scratching their heads and pecking at their calculators. Theory went that if you really wanted to break the speed record with a sailplane that one of the things you needed to do was to design a glider with the highest terminal velocity that you could...I would postulate that the same would hold for my theoretical prop-driven sonic diver.

Why not just stick a rocket or jet engine on it and get that prop job supersonic.For that matter why hasn't that been done since the days of the Fireball? Or is this cheating for our purposes?

All's fair as far as I'm concerned...but a pure prop / piston or turbine engined configuration would be more "sporting".

I could see using a rocket to boost it to altitude, though. And I recall reading somewhere that the Me 163 was in theory aerodynamically capable of breaking the sound barrier...but not structurally up to the task.

Rufus wrote in news:kyhWb.274503$xy6.1398222@attbi_s02:

From what I recall, it isn't a good design for approaching Mach 1. As the X-4 and dH108 programmes postwar found there are severe stability problems at high speed with this design.

The design is actually better suited to a glider - which the Me163 was for most of its flight :-)

As for whether it was structurally up to it... who knows. I do know I wouldn't want to have piloted one with the fuel they were using.

ISTR the air racer which broke the old & set a new speed record, a modified Bearcat, 'Conquest 1', I think, did so around a closed circuit atop a plateau out west several thousand feet ASL, where, even a few feet above the ground the a/c is actually several thousand feet ASL where the air is already thin. I always thought that was cheating a bit.