CAPFlyer wrote:
Gunny,
The 8000' normal minimum (which AFAIK is a USMC and USN thing too) is a brake saving thing more than anything. Below 8000 feet, they have to use the brakes a lot which wears them out quickly. Since none of the US's inventory uses drag chutes anymore, this further complicates the matter. Soviet designs are quite different. They are capable of operating from dirt strips, all have drag chutes, and the brakes are quite a bit beefier than most US designs of similar size (although not necessarily more effective).
I'm not saying that 6500' is short enough for the MiG-23, but I am saying that it's difficult to apply US procedures to Soviet aircraft because the design philosophy is much different.
CapFlyer-
I agree with Hacker... it ain't about the saving the brakes.
Here's the skinny... it's about the takeoff and a possible abort. It doesn't matter who made the airplane... physics is physics. The Strike Eagle can get off in less than 3000' fully loaded... but it sure can't abort in that length. The takeoff data is computed to allow acceleration to a refusal speed... where you continue the takeoff or stop in the remaining runway... if you have two engines refusal speed becomes the speed at which you can loose an engine and continue the takeoff... or stop in the available runway. Brake heating has a direct impact on performance.... both in the aborted takeoff, and the landing. But max brake heating doesn't happen until approximately 30 min to an hour after the application. Steel brakes heat up to a fade point faster than modern carbon-carbon systems. Other than the airlines I've never had any official word, procedure or directive that spelled out "saving the brakes."
So, if you want to allow for the possibility that things can go horribly wrong during the takeoff and you might need to abort you have to take into account your weight, the speed when you start the braking and the distance required to stop. Note there is nothing in that equation about how much distance you have available to accel/stop. The pilot has to have the brains here and make that calculation.... if there isn't enough distance... you have to decide how important the takeoff is. And it just doesn't matter if it's Russian, Chinese, British or American manufacture.
Now the landing side of the coin. In the fighter business the USAF min runway length for non-barrier equipped runways is 8,000'. All USAF fighter runways use a Bak-12 or better barrier (read cable, much like the Navy Carrier system, but with different friction equipment). I've had 4 brake failures in the Eagle.... three of them on landing and I used the cable to stop... the 4th one happened when I taxied off the runway and the left brake disintegrated (5 carbon rotors and interleaved carbon pucks)... the right brake worked and the airplane just swerved a bit on stopping. The aerobrake is an effective means to slow down from landing speed (approximately 120 kts). The F-4 used a drag chute.... which was effective from landing ~140ish to 100ish kts.... then it was worthless... steel brakes.... long runways were good for rollout... to prevent overheating the brakes and the possibility of fade... which would mean you loose the ability to actually use the brakes for anything worthwhile. There is nothing about saving the brakes... other than preserving the ability to use them when it is important... note that carbon-carbon brakes are effective to outrageous temperatures (a good working temp is around 1000 degF).... the issue then becomes the heat transferred to the tires and possible fire.
Runway distance is important.... the interesting thing to note is how much the Mig-23 weighs and what kind of brakes it has. I'd bet they are plain steel brakes, with minimal anti-skid and the weight is close to 40k lb.... with the thrust in the .7 range.... it is very much like an F-4... but that swing wing tells you that it is a bit of a pig slow.... takeoff speed in the 140ish range.
My nickel is... Put all those together and 6500' is a bit on the short side to operate from... especially first flight. Let the Russians risk their necks for no good reason... in Russia. If these guys have a problem it reflects poorly on all warbird operators.... whether they live or not. How's that for design philosophy?
gunny
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