Transonic Drag

[rsterne]

I found an interesting graph on Transonic Drag that I thought was worth sharing with you....



Note that the drag starts to rapidly increase between Mach 0.80-0.85 (900-950 fps) and has doubled by Mach 0.9 (1000 fps) and tripled by Mach 0.95 (1050 fps).... This means that the extra energy it takes to get a pellet above 950 fps will quickly be shed in the first few yards anyway.... That ties in exactly with the work I have been doing on how the Ballistics Coefficient changes as you push the velocity close to the speed of sound....

Since 950 fps gives you an energy of 2 FPE per grain of pellet weight (an easy number to remember).... this is just one more reason not to push the velocity past that....

Bob

[SeanMP]

Are you listening to your own advice?

...LOL

That's a nice graphic of what can be so difficult for a new person who is fixated on (1500fps) to understand.

Also shows why Benchrest and sniper rifles have moved past Mach 3

[DocGadget]

That is SO interesting. You gotta love science.

[rsterne]

Are you listening to your own advice?

The new project we have embarked on may be a real test for this.... It will be interesting to test the BC at several velocities such as 900, 950, 1000, and 1050 (assuming we can get that) and see if the 41.5 gr. bullets follow what happens to our waisted pellets.... It may very well be that using 900 fps and accepting the drop but having to deal with less wind drift (from a higher effective BC) may (or may not) be a real possibility....

Bob

[SeanMP]

Those fellows in the Netherlands are pushing those pellets hard. I think Maurice said they were around 1025. I would imagine we can expect the same results, identical results, as you would from RWS Match data. Our speeds will be comparable and the bullet is identical.

I'll see if I can dig that data up for a comparison

Edit...found this

Muzzle 1035
50yd 945
100yd 860

[rsterne]

Actually not as good as I thought.... From the muzzle to 50 yards the BC is 0.070.... From 50 to 100 yards, it is 0.067.... Average over 100 yards is 0.068.... I was expecting nearly twice that BC....

Bob

[SeanMP]

That was for the subsonic.

Oddly enough. Those are manufacturers numbers. But over at rimfire central the have a table of real world test data and they are reporting .125 to .130

Do we have a manufacturer under reporting their product for the first time in history?

[Poor-man Plinker]

OK Guys, Now, remembering that you got an idiot Yank living in the third world asking about this... I did not think the drag itself was the problem. From reading other work, I thought it was the change in drag that brought about tumbling that was the problem. If that were correct it would seem that just getting up to Mach 2 would not stop the tumble, but, it would reduce the drag coefficient mathamatically.

If this is only a mathamatical construct, then the increased drag caused by the tumble would not really reduce the drag at all. Seems it would require a redesigned pellet to beat the phantom. If enginering got Chuck Yager there in a jet; then enginering should be able to get a simple pellet to crack the barrier and not tumble wildly.

Please, Somebody set me straight!

[rsterne]

I guess the ACTUAL BC of the new 41.5 gr. RWS bullets will have to wait until we test them ourselves....

RE: instability at Mach 1, this is a real phenomenon, but bullets and aircraft act quite differently, as bullets are spinning, aircraft (fortunately for Mr Yeager) aren't, at least not a 100,000 plus RPM.... When they first got close to Mach 1 in aircraft (originally unintentionally) they had aircraft crashing, but no reports of what was happening (pilot deceased).... Then a British pilot in a Spitfire in a near vertical dive survived and reported what he called "control reversal" which they eventually found out was the wings and tail twistng from the forces on the ailerons and elevators and generating a force opposite to the intended control input.... The pilot survived by pushing forward on the stick (with both hands) to get out of the dive instead of pulling back.... Once the speed dropped, control returned to normal.... This was a strength/stiffness problem, more than a stability one....

As aircraft got ever closer (intentionally) to Mach 1, pilots reported severe "buffeting" and vibrations, which in some cases tore the aircraft apart.... It is now known that this was locallized shock waves forming and collapsing on various parts of the aircraft, and redesign in those areas (inlcuding using a swept wing) helped.... Yeager's Bell X-1 fuselage was modelled after a 50 cal. machinegun bullet, which was the best shape then known for flight well over Mach 1.... Other than flying with a broken arm (from a drunken horseback ride with Bob Hoover the night before), his flight was pretty uneventful....

Bullets are stabilized by twist, and in addition, our diablo (waisted) pellets are also stabilized by their "shuttlecock" shape like a badminton bird.... They have the center of gravity well forward of the center of drag, which keeps them pointed in the direction of flight like an arrow or dart.... I don't think much is really known about how they act at Mach 1, because that was never their intent.... Logic would say that locallized shockwaves around the sided of the nose would induce instabilities near Mach 1.... The ballistics of "normal" bullets are much better understood, and the twist required (which creates the spin) is faster just as the bullet drops back through Mach 1 than at any other time.... Here is an example....



I don't remember the length of the bullet I chose to generate that chart, but a stability factor of greater than 1.0 is required to prevent the bullet from yawing and eventually tumbling.... You will note that is not the case just as the bullet falls back below the speed of sound, even though the bullet is stable at both higher and lower speeds.... If the bullet was shorter, or the twist rate faster, then stability would be maintained even at that critical speed.... Pellets have certainly been shot at well over Mach 1, and dropped back through it, without tumbling.... providing the twist rate was high enough.... Keeping the bullet flying straight, however, doesn't get away from the very high drag involved in transonic flight....

Bob

[Poor-man Plinker]

Bob, I am more inclined to believe your research than the mirad of "opinions" offered on the internet. The most commonly seen belief, on-line, is that transonic tumble is the problem. You, have obviously done your homework! G.J. (good job)

Thanks for the history and ballistics lesson. Unlikely I will ever have to worry about Mach-One from any of my toy (air)guns or my air-bus rides he he he. I appreciate your taking the time to "bring me up to speed."