What is the feasability of flying, say Mach 2.5 at very low-levels (100-200ft)?

Question

I'm under the impression that high Mach numbers at low level can lead to catastrophic buffeting. Is that right, and can a good pilot/computer counter that effect?

Answer 1

That speed at low altitude is impossible to control. Only computer systems can react quickly enough to avoid disaster.

Buffeting is a serious problem. The most significant problem is that at that speed once the pilot recognized a hazard and starts to initiate evasive action, it's too late and the aircraft impacts the hazard.

The F-111 fighter/bomber did fly supersonic at low altitude but used an automatic flight control system linked to radar to prevent catastrophe. In the very early days of the F-111's service life, several were lost when the pilot disengaged the flight director system in the mistaken belief that he could do a better job or to smooth out the ride. With the flight director engaged, the ride was VERY rough.

The B-1 bomber also can fly at supersonic speeds at low altitude but the pilot cannot disengage the flight director system below a certain altitude.

Answer 2

It would be sheer idiocy.

At such a low altitude where the air is dense, the resistance would heat the airframe to dangerous levels. You can end up with warping of control surfaces (if the wings remain attached....) and other overheating issues. Excessive buffeting, (and other aerodynamic / aeroelastic phenomena, i.e flutter) will come into play.

A bird strike will put an end to your day, if you dont hit a building on the trip beforehand - because you wont have any time to react.

Even if you survived without killing yourself, or anyone else - you would have some serious explaining to do to the authorities as your low level supersonic flight would result in every window in the vicinity being shattered due to the shockwaves from the resulting Mach cone.

Answer 3

Mach 2.5 at Low Level...oh no...but,
Anything is possible with vast amounts of fuel!

Because the atmospheric pressure at this low altitude, the resultant drag (shock,parasitic,induced,) is so high as to warrant such flight not economically viable.
The aircraft would require ram/scramjet technology and these inherently consume vast quantities of kerosene.
Also don't forget the intrinsic dangers of flight this low and at that speed makes it a bit ridiculous...birds, wires, towers, kites other light aircraft.
Even a sparrow at mach2.5 would be like a .50cal througfh the windscreen
Hope this banishes all thought of this!

WRT to Brian below;
Yes, temperature is the main determinent in the speed of sound. Standard Lapse rate in an ICAO atmosphere is -2C/1000' .
Irrespective of other answers, the difficulties arising from low level flight at high Mach numbers stands.
FYI a quick way of determing the speed of sound in a gas
is 49.1 multiplied by the SqRoot of the O.A.T. in degrees Rankine
ie: for sea level on a ISA day...49.1 x SqRt of (460+59) = 1118fps

Answer 4

Flying that low and that fast, is a serious health risk. You would have to have extreme reflexes to deal with things that are on the ground. A good pilot would never fly that low at that speed. To many dangers are a factor. Trees, power lines, buildings, mountains and hills. The list goes on and on. The higher altitude you go the better. Besides the air speed needed to attain MACH 2.5 is lower, than say at sea level.

Answer 5

As you know the higher you go the thinner the air and the colder it gets. That being said the lower you go the thicker the air and the hotter it gets. I don't think we have anything yet that can take the heat that would be generated by an object moving at that speed through that thick air. The SR-71 could do it at 60 to 80 thousand feet but if it tried it at a lower altitude the wings would rip off if the didn't burn off. So the answer is no.

Answer 6

Mach 1 is 728 mph at sea level, and the speed increases with altitude. I agree with a earlier person that answered this question. The air thins as the altitude increases. Mach speed at low altitudes is very dangerous, and also illegal in the continental U.S. The only aircraft allowed to break the sound barrier in the U.S. is the Space Shuttle, which it is normal operation of the craft and it occurs as it re-enters the earths atmosphere.

Answer 7

The F-111 and the B-1 were designed as supersonic low level penetrators useing terrain following radar they would fly as low as 50 feet at speeds well above Mach 1

Answer 8

Pull the specs on the F-111. It is in moth balls now because it is obsolete and not cost effective to operate but you will be amazed at what the aircraft could do. Its terrain search radar was something else and it operated in the envelope you are asking about.

Friends who flew the Aardvark have told me that a Mach 2 dash at 50 ft AGL was a doable thing.

Answer 9

Ok people, let me help you all again.... You people are really good at being WRONG! Mach speed is directly related to temperature NOT pressure. Mach DECREASES with altitude because of the temperature lapse rate. (2 degrees C per thousand feet)

With that said, it takes a lot of excess thrust to go as fast close to the ground as it does at altitude.....
Good day....

Answer 10

At that speed and altitude,if the pilots finger twitched on the controls he'd be in the ground.And modern jets can only go that fast at high altitudes in thinner air.