goboeing
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SR-71 Picture -- Question

Thu Sep 08, 2005 2:37 am

http://artur54.no.sapo.pt/images/sr71.jpg

Anyone know what the stuff on the wings is? It looks wet.

Nick
 
Arniepie
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RE: SR-71 Picture -- Question

Thu Sep 08, 2005 2:43 am

Sprayed on fuel after in flight refueling??
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drewfly
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RE: SR-71 Picture -- Question

Thu Sep 08, 2005 3:29 am

That is fuel leaking out of the fuel tanks. Because the aircraft is designed to go Mach 3+, the skin is built to expand as it heats up (like the Concorde). Thus, when the aircraft expands length-wise, the skin and tanks contract. But, when the aircraft is sitting on the ground or flying at 'average' speed, the skin and tanks have not contracted into a seamless fit. That is why the SR-71 had to be refueled right after takeoff, because it leaked so much on the ground.
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curlyheadboy
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RE: SR-71 Picture -- Question

Thu Sep 08, 2005 5:07 am

Quoting Drewfly (Reply 2):
That is why the SR-71 had to be refueled right after takeoff, because it leaked so much on the ground.

From latest informations released on the SR-71 this appears to be not completely true. Infact, it seems that even with the thermal expansion of the fuselage panels the tanks still leaked during the whole flight. The amount of fuel lost was considered acceptable (moreover if compared to the quantity consumed by those monster engines).
If God had wanted men to fly he would have given them more money...
 
Arniepie
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RE: SR-71 Picture -- Question

Thu Sep 08, 2005 5:42 am

If you take a good look at the picture you can clearly see where the wetspots originate from, namely the refueling point.
Besides I highly doubt the leakage would be so intense and certainly not upwards.

Quoting Drewfly (Reply 2):
That is fuel leaking out of the fuel tanks. Because the aircraft is designed to go Mach 3+, the skin is built to expand as it heats up (like the Concorde). Thus, when the aircraft expands length-wise, the skin and tanks contract. But, when the aircraft is sitting on the ground or flying at 'average' speed, the skin and tanks have not contracted into a seamless fit. That is why the SR-71 had to be refueled right after takeoff, because it leaked so much on the ground.

Which was ,according to kelley Johnson ,not deliberately so but the result of an engineering fault.
They first noticed it when the first plane was ready to go and they saw it leaking after fuel up.
ISO redesigning and reengineering everything they decided not to change a thing because the seals would close enough quickly into flight.
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Duce50Boom
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RE: SR-71 Picture -- Question

Thu Sep 08, 2005 7:59 am

Quoting ArniePie (Reply 4):
If you take a good look at the picture you can clearly see where the wetspots originate from, namely the refueling point.
Besides I highly doubt the leakage would be so intense and certainly not upwards.

Not quite, most of the fuel leaking from the receptacle to the upper rotating beacon is from the receptacle, indicating it refueled from a KC-135. But the fuel behind that on the spine is leaking out of the 715 split line (A/C station 715). The fuel spray on the wings doesn't match the spray patterns of the receptacle (fuel won't spray 15 or 20 feet to the side and not hit anything else on the way). But it certainly does leak upwards, look at the cover of the book "Sled Driver" by former SR-71 pilot Brian Shul. And the fuel leak is alot more intense than you think: look at a picture of the bottom of one. Fuel EVERYWHERE as shown here if you look close:

http://theaviationzone.com/images/other/various/recon/sr71_03.jpg

And here's some words of a former SR-71 pro-sup who was involved in the reactivation of how they made their choice of which aircraft to reactivate based on the condition of their fuel tank sealant:

"The first order of business was to perform fuel leak evaluations on the four SR-71's, and to select the best two. This was accomplished at Site 2 at Palmdale, by completely filling all aircraft fuel tanks, pressurizing the system with Liquid Nitrogen (LN2), and allowing it to sit for about two hours. A hand full of previous SR-71 mechanics were borrowed from the LM U-2 operation to perform the tests. At completion, we would defuel the aircraft, and head to the next one. Fuel and LN2 was trucked in from NASA, and the first evaluation was performed on January 5th on 967. It had significant leaks in the nose wheel well, forward mission bays, forward bottom wing areas, top wing areas, with a severe leak (a real gusher folks) coming from tank 3 at the fuselage split line. We checked out 968 five days later. It showed significant leaks from the right main wheel well, the entire bottom fuselage, right upper fillet areas, drag chute compartment, mixer area, and two extremely severe gushers coming from the tank 3 splitline and the left aft wing beam areas. On January 12th, 971 was flown in from EAFB by NASA's Ed Schneider. The flight lasted about 10 minutes, afterburners were used for takeoff, with only 20,000 pounds of fuel onboard, and with the landing gear locked in the down position. On the 13th, we performed the evaluation of 962. This proved to be disastrous, with severe leaks just about everywhere. It leaked so bad, LN2 pressure would not build up, and we had to obtain more fuel from NASA to perform the leak test on 971, which was done three days later. 971 was in great shaped compared to the first three, with no gushers, and only five areas of concern. So the aircraft were ordered 971, 967, 968, and lastly 962. Of course, we still wouldn't have a feel for the repairs needed until the fuel cells could be opened and evaluated. Let's just say, 962 was parked and forgotten again. That was kind of sad, as it was my favorite aircraft, and Terry and I used to crew it together at BAFB."

Quoting Drewfly (Reply 2):
Thus, when the aircraft expands length-wise, the skin and tanks contract.

True, spirit wise. But the SR doesn't have actual fuel tanks; the skin of the aircraft is what seals the fuel inwards. I don't know if Arniepie is right about the leaking being completely unintentional. I think Kelly Johnson and company were too smart to not know what would happen given the prep work to make the fuselage stretchable and along the same lines knowing the fuselage/aircraft skin would be the fuel tank.

Quoting Drewfly (Reply 2):
That is why the SR-71 had to be refueled right after takeoff, because it leaked so much on the ground.

No, that's just an urban myth. In actuality, the mx limits of fuel leakage per tank (6 fuel tanks IIRC) was 2 gallons per hour. Here's the real scoop, from one of the maintainers on an SR website:

"The SR takes off with almost dry tanks

Well not exactly empty, the SRs tanks hold 80,000 lbs. of fuel, the SR-71 usually takes off with 45,000 lbs. of fuel on board. Not what I call almost dry! The SR takes off with either 45,000 lbs., 55,000 lbs., or 65,000 lbs. of fuel. Almost all flights are refueled by KC-135Q's (now "T"), there are a few exceptions though... one was called the "Rocket Ride", which were flown from Kadena AB, Okinawa and then on to Northern Korea, on 65,000 lbs of fuel. The only SRs that launched with a full fuel load were the test flights from Palmdale, CA."
 
AR1300
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RE: SR-71 Picture -- Question

Thu Sep 08, 2005 3:27 pm

Quoting Duce50boom (Reply 5):
knowing the fuselage/aircraft skin would be the fuel tank.

So the whole plane is full of fuel???Sounds weird....

Mike
You are now free to move about the cabin
 
Duce50Boom
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RE: SR-71 Picture -- Question

Fri Sep 09, 2005 12:21 am

Not the whole plane....But a large percentage of it. Instead of how a normal plane would have an actual fuel tank inside the fuselage, with the A/C skin covering the structure, the SR-71's fuel was kept in "tanks" that were really just the aircraft's support structure, ie, a/c ribs, spars, etc. And the skin was what kept the fuel in those areas. Kinda hard to describe, but hopefully it makes sense. Here's a diagram showing the tanks:

http://www.sr-71.org/blackbird/manual/1/1-48.htm

BTW, I was wrong. The SR has 7 fuel tanks not 6. 5 fuselage tanks and two wing-fuselage tanks.
 
HaveBlue
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RE: SR-71 Picture -- Question

Fri Sep 09, 2005 12:30 am

Quoting AR1300 (Reply 6):
Quoting Duce50boom (Reply 5):
knowing the fuselage/aircraft skin would be the fuel tank.

So the whole plane is full of fuel???Sounds weird....

Mike

I'm glad Duce said it, because that's the first thing I had on my mind when reading the first few posts. Yes it is true the Blackbird had no fuel 'tanks' per se. The skin was the tank. Of course there were areas cordoned off for camera bays, drag chute compartment, etc. But as normal bladders couldn't withstand the extreme temperatures that the SR would be subjected to they decided to do it that way.

And I also agree that Kelly and company were way to smart not to have known that the fuel would leak beforehand. Like everything in engineering it was a compromise, but one I am sure they were aware of.
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Arniepie
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RE: SR-71 Picture -- Question

Fri Sep 09, 2005 5:44 am

Quoting HaveBlue (Reply 8):
And I also agree that Kelly and company were way to smart not to have known that the fuel would leak beforehand. Like everything in engineering it was a compromise, but one I am sure they were aware of.

I am however pretty sure that I read somewhere in a book that Johnson explained about the leaking fuel that it was unexpected and something they couldn't rectify with the existing technology at those days.
Remember that we are talking the very early sixties here and that everything was new unexplored territory and there were no real possibility's to test everything before they actually build it.
The quote actually came indirectly from Kelly trough the mouth of some SR71 pilot (Gilliand or Gilland,.. not sure about his correct name) after they delivered the 2nd plane which was excessively leaking from the beginning.
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HaveBlue
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RE: SR-71 Picture -- Question

Fri Sep 09, 2005 5:50 am

Well perhaps you are right then ArniePie, I just never heard that before and it would surprise me if that were true.

It's one of my favorite birds and I've read a lot about it over the years, but you learn something new every day.  Smile
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Arniepie
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RE: SR-71 Picture -- Question

Fri Sep 09, 2005 6:19 am

This does not mean it wasn't a truly engineering marvel.
The best prove for this doesn't come from the USAF or some Lockheed employee but comes from a direct quote from a Russian Foxbat pilot stationed in Siberia.
One day in the beginning of the Foxbat program they tried to shadow a Blackbird flying next to the border from Siberia, they where amazed that a design that was already 10 years old by then still could outperform them and do this over and over again for several hours while they had to rebuild the engines every time they went into the MACH3+ zone.

You see respect from the enemy is the highest form of respect you can get.


P.S.
The Foxbat was also a true marvel of engineering , certainly if you consider that it was build not with exotic materials but plain steel.
What was truly remarkable where the welding techniques they used.
Also it was a good performer up until a very high FL (turn rates, general maneuvrability).
Also the electronics where very EMP resistant and the Radar was much more capable than initially expected.
[edit post]
 
Duce50Boom
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RE: SR-71 Picture -- Question

Fri Sep 09, 2005 7:25 am

Quoting ArniePie (Reply 9):
I am however pretty sure that I read somewhere in a book that Johnson explained about the leaking fuel that it was unexpected and something they couldn't rectify with the existing technology at those days.......The quote actually came indirectly from Kelly trough the mouth of some SR71 pilot (Gilliand or Gilland,.. not sure about his correct name) after they delivered the 2nd plane which was excessively leaking from the beginning.

I think I know what you're talking about. The first flight of the SR-71 (22 Dec, 1964) had a bunch of AF brass in attendance. During a low fly-by one of the generals said something to the point of "what the hell is that?" Reffering to the fuel coming out of the bottom of the airplane. He explained it to the general how it was designed to be like that because of A/C stretching and how there are no fuel "tanks", but the general still had that bewildered look to him. After that Kelly Johnson said something to the effect of "I always regretted that fly-by"

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