Beerlight 0 #1 February 11, 2003 Ok, today someone asked me, "What would have been the Columbia's indicated airspeed (if any) @ 200,000 feet?" Ok, you pilot/physics/meterologist people, I know one of you shall render the answer...... Quote Share this post Link to post Share on other sites
quade 4 #2 February 11, 2003 Damn! Great question. Ya stumped me! I'm almost certain it would have been an indicated airspeed in reference to a Mach number, but I sure as hell don't know what that would have been. You -might- be able to find something HERE. I'll take a look at some stuff I have at home later tonight as see if I can find any references in a typical decent profile that I think I have a copy of.quade - The World's Most Boring Skydiver Quote Share this post Link to post Share on other sites
PhreeZone 20 #3 February 11, 2003 I heard Mach 18 ish being tossed around.Yesterday is history And tomorrow is a mystery Parachutemanuals.com Quote Share this post Link to post Share on other sites
mouth 0 #4 February 11, 2003 When you find it compute it for those of us who are not mach speed literate, please. -- Hot Mama At least you know where you stand even if it is in a pile of shit. Quote Share this post Link to post Share on other sites
n2skdvn 0 #5 February 11, 2003 mach 18 or 12,500 mph .......if my calculations are correct SLINKY + ESCULATOR = EVERLASTING FUN my site Quote Share this post Link to post Share on other sites
quade 4 #6 February 11, 2003 Oh, one last thing . . . Are you sure you want to know "indicated" airspeed or do you really want to know what the true airspeed was supposed to be? The difference? Indicated Airspeed is a function of dynamic pressure and changes with pressure. In this case, at 200,000 feet, there's not a lot of pressure, but obviously a poop-load of speed. Is your friend trying to figure out the forces involved or is he just curious about the overall speed?quade - The World's Most Boring Skydiver Quote Share this post Link to post Share on other sites
quade 4 #7 February 11, 2003 QuoteWhen you find it compute it for those of us who are not mach speed literate, please. Ok, I'll have to admit something, I'm not going to be able to compute jack from the information I find, my E-6B just doesn't go up that high. It's not just a simple matter of making the numbers "bigger", a whole lot of this stuff changes drastically when you get up in those numbers & pressures as it just doesn't scale.quade - The World's Most Boring Skydiver Quote Share this post Link to post Share on other sites
n2skdvn 0 #8 February 11, 2003 mach 1= 675 mph * 18 = 12150mphif my calculations are correct SLINKY + ESCULATOR = EVERLASTING FUN my site Quote Share this post Link to post Share on other sites
pilotdave 0 #9 February 11, 2003 I havent done the calculation but the day of the disaster my aircraft design prof mentioned he calculated it around 300 knots. Dave Quote Share this post Link to post Share on other sites
pilotdave 0 #10 February 11, 2003 Ok, I just did a calculation. I might have messed up somewhere because my answer came out to about half of what I expected, but here's my work: First you need to look up the density of the atmosphere at 200,000 feet (found in a standard atmosphere table). density = .6061e-6 slugs/ft^3. Then we need to figure out how fast they were going. The speed of sound at that altitude is 1047.9 ft/s, so at mach 16 they were doing 16,766 ft/s. dynamic pressure is (1/2)(density)(velocity^2) which comes out to 85.2 lb/ft^2. Now we look at the sea level equivalent speed. Put in the sea level density (.23769e-2 slugs/ft^3) into the dynamic pressure equation, and we solve back for a velocity of 267.73 ft/s, or 182.55 miles per hour. Ok, someone smart find my mistake if I have one. Dave Quote Share this post Link to post Share on other sites
pilotdave 0 #11 February 11, 2003 One thing to add. Their indicated airspeed wouldn't really be what I solved for. Assuming they use a pitot tube (which i doubt to be true but i have no idea), the shockwave changes the airspeed reading. To solve for that we need to use shock tables (or REALLY ugly equations). At Mach 16, the mach number of the air on the back side of a normal (perpendicular) shockwave is only 0.382. At 200,000 feet, thats equialent to 400 ft/s or 273 mph. But that calculation really doesnt say much. That's just the speed a pitot tube with a shockwave in front of it would see. It really has little to do with actual aerodynamic forces and all that. Dave Quote Share this post Link to post Share on other sites
billvon 3,120 #12 February 11, 2003 True airspeed was around 13,000 MPH. Indicated airspeed has little meaning at that altitude; there is effectively no air pressure (it's under .1 PSI) and indicated airspeed is the difference between pressure in a pitot tube and ambient pressure. Zero minus zero is still zero. You also have the issue that the energy of the air molecules ramming into the pitot tube (and then stopping suddenly) at that speed is pretty considerable. That heats up the air in the tube and the air expands, throwing any pitot based measurements off. Someone else said: > (IAS is) 182.55 miles per hour and that's probably pretty close if you neglect stagnation heating effects. It's slow because there's just not much air up there to effect a pressure change in a pitot tube. It's such an exotic environment that many of the normal considerations don't apply. For example, in a real sense the shuttle flies much of the reentry completely stalled; flow is completely separated from the top of the wing. It has so much energy, though, that the abysmal L/D you get in a stall doesn't matter. Quote Share this post Link to post Share on other sites
Beerlight 0 #13 February 11, 2003 Wow, yes indicated versus true or calibrated...etc..etc... Quote Share this post Link to post Share on other sites
mouth 0 #14 February 11, 2003 Thanks anyway...not that I truely understand it. Unlike Wendy, I am NOT a rocket scientist. -- Hot Mama At least you know where you stand even if it is in a pile of shit. Quote Share this post Link to post Share on other sites
Hooknswoop 19 #15 February 11, 2003 Quotemach 1= 675 mph "A less familiar measure of speed is the use of a Mach number. This is a ratio and has NO units. It is a measure of how many times faster an object is moving than sound does in the SAME medium and under the SAME conditions of pressure and temperature. Usually the medium is air - but it does not have to be - it could be water. Thus Mach 1 is the same as the speed of sound, Mach 2 is twice as fast and so on. The problem is that the speed of sound is not constant in any given medium. It does vary quite considerably with the pressure and the temperature. In the case of aeroplanes, as they go higher, both the air pressure and temperature become less. So Mach numbers do not give an exact speed unless all the surrounding conditions are known. To get some idea of the size of a Mach number, the conversion done in the calculator is based on the speed of sound being 331.5 metres/second, which it is at sea-level at 0°C.' 331.5 m/s = 644 kts = 742 mph http://www.januranusjaymartin.de/air/aircraftspeedsatmachspeeds.html Hook Quote Share this post Link to post Share on other sites
billvon 3,120 #16 February 11, 2003 >The problem is that the speed of sound is not constant in any given > medium. It does vary quite considerably with the pressure and the > temperature. Strictly speaking, it only varies with temperature and atmospheric composition. Since temperature changes with altitude (composition does too, at very high altitudes) altitude is a factor when calculating mach numbers. Quote Share this post Link to post Share on other sites
Hooknswoop 19 #17 February 11, 2003 I copied that off a web site. I understood that Mach speed varies w/ the viscosity of the medium, faster through water than air at sea level, slowing down as the air got thinner with altitude, eventually reaching 0 mph in space. Is this correct? Hook Quote Share this post Link to post Share on other sites
quade 4 #18 February 11, 2003 Ok, looking through some lit I have at home . . .Orbit is approx 17,100 mph400,000 ft is approx entry interface312,000 ft & 16,700 mph communication is blacked out due to ionizationWhen flight instruments detect 10 psi roll RCS is turned off and elevons control roll.By the time the shuttle has slowed to 15,000 mph the shuttle should be at about 20 psi and pitch RCS is turned off -- elevons then control pitch.At about 230,000 ft and 15,000 mph the shuttle is experiencing maximum heatingBy about 180,000 ft the shuttle has slowed down to about 8,300 mph.I do not have figures for intermediate altitudes.quade - The World's Most Boring Skydiver Quote Share this post Link to post Share on other sites
kallend 2,150 #19 February 11, 2003 I posted this stuff a week ago, here. www.dropzone.com/cgi-bin/forum/gforum.cgi?post=372037;search_string=dynamic%20pressure;#372037 Don't you guys ever remember anything? (Edited for spelling, which I can't remember)... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
billvon 3,120 #20 February 11, 2003 >By the time the shuttle has slowed to 15,000 mph the shuttle should be > at about 20 psi and pitch RCS is turned off -- elevons then control pitch. I think you mean psf. You'd have to be about a mile below sea level to get 20psi. Quote Share this post Link to post Share on other sites
AggieDave 6 #21 February 11, 2003 QuoteYou'd have to be about a mile below sea level to get 20psi And that would suck...--"When I die, may I be surrounded by scattered chrome and burning gasoline." Quote Share this post Link to post Share on other sites
quade 4 #22 February 11, 2003 I'm telling ya, that's exactly the notation that was used!-I'm- assuming that's the pressure on the control surface and not the ambient atmospheric pressure.quade - The World's Most Boring Skydiver Quote Share this post Link to post Share on other sites
Craig 0 #23 February 11, 2003 Pretty sure this is how it should read.... At 400,000 feet, a pre-entry phase begins in which the orbiter is maneuvered to zero degrees roll and yaw (wings level) and a predetermined angle of attack for entry. The flight control system issues the commands to the roll, yaw and pitch RCS jets for rate damping in attitude hold for entry into the Earth's atmosphere until 0.176 g is sensed, which corresponds to a dynamic pressure of 10 pounds per square foot, approximately the point at which the aerosurfaces become active. The aft RCS jets maneuver the spacecraft until a dynamic pressure of 10 pounds per square foot is sensed; at this point, the orbiter's ailerons become effective, and the aft RCS roll jets are deactivated. At a dynamic pressure of 20 pounds per square foot, the orbiter's elevators become effective, and the aft RCS pitch jets are deactivated. The orbiter's speed brake is used below Mach 10 to induce a more positive downward elevator trim deflection. At Mach 3.5, the rudder become activated, and the aft RCS yaw jets are deactivated (approximately 45,000 feet). Quote Share this post Link to post Share on other sites
Beerlight 0 #24 February 12, 2003 A lively discussion......so..uh... you're in a J-3 inverted at 200 feet agl, zero airspeed, can you recover........?? Nah, just kidding, hell I never want to compete in a pissin contest on anything aviation related with U guys.!!!!!!!!!! Ya'll rock........! Buck Quote Share this post Link to post Share on other sites
phatcat 0 #25 February 12, 2003 Quote you're in a J-3 inverted at 200 feet agl, zero airspeed, can you recover No prob, just hold my beer... Quote Share this post Link to post Share on other sites
