Video of 747 taking off (cued to 1:53). This is pretty representative of commercial airliners in general: the nose of the plane pitches up 10-15 degrees before the plane lifts off of the runway.
Why the difference? Are these B-52’s carrying no payload (and 30 minutes of fuel)? Are they using way more runway (and reaching a far higher takeoff speed) than they really need? The B-52’s takeoff behavior is more in line with that of the U-2. I’m not surprised that the U-2 does this, since it’s designed for slow flight in extremely thin air. But why would the B-52 behave like this?
I think it’s because of the way the landing gear is set up. It’s spread out for and aft and is pretty far apart. Rotating on the rear gear may be a problem with it being so far back.
It is because of the tandem gear and the fact that the wing is attached at a high angle of attack which aids in takeoff. Being that the wing is already at a high angle of attack, a strong rotation could pitch it past the point where the wing stalls.
The wikipedia entry on MITO is actually detailing this very same B52 MITO technique, since the risk is taken only for the rapid launch of WoMD … eg nuclear.
The B52 makes use of ground effect.
At the point of no return, S1, 120 Kt, it lifts the weight off its wheels.
So its now flying , somewhat stable because of ground effect, and so it steers away from the turbulence of the plane in front, which was only 15 seconds ago, and with less drag, the engine thrust is now able to accelerate it to 150 Kts.
Its still not able to rotate, rotate would cause drag, and its got no spare engine thrust for that. They are already injecting water just to get this far.
At 150 kts, and some left/right separation from the plane(s) in front, they can then leave the ground effect … But only very slowly without any defined rotate. They are slowly increasing lift as they burn fuel … they are burning fuel AND water fast ! look at the smoke left behind… Its not blowing away… its ideal conditions and controlled conditions… The weather check was far more than looking at a wind sock ?
I would have guessed what Isilder said: Operating at the absolute limit of how heavy it can be, the B-52 is staying in ground effect until it can build up some airspeed.
There are a lot of videos of large planes (usually commercial airliners) “crabbing”, but while they come in for a landing at an angle they usually straighten out just before the wheels hit.
In that video, it looks like the BUFF actually lands at an angle with its wheels angled in the direction of travel and not facing straight. That’s impressive, especially in a plane that heavy. I can’t imagine the engineering that went into the landing gear to make them able to do that while still being strong enough to hold that much weight and light enough that they don’t detract much from the plane’s payload weight.
For comparison, here are commercial jets crabbing. They always straighten out either just before or just after the wheels hit the runway. They don’t go down the runway at an angle the way that B-52 did.
The principle works on piston engines, too. Water injection holds down the combustion chamber temperatures, allowing you to stuff more fuel in them and get more power.
BTW, the B-52 can indeed rotate its gear to align with the runway, so it can land in a crab. An airliner pilot will straighten it (“kick out the crab”) just before touchdown, to limit the stress on the gear and prevent tire blowouts. An airplane that doesn’t have a risk of dragging an engine pod on the ground can be landed while banked into the wind, one wheel at a time. That’s how student pilots are taught, so they only have to do one thing at a time.
Yep, the B-52’s main gears are able to pivot 20 degrees in either direction for crosswind landings and takeoffs. I believe this feature is currently unique to the B-52. Some heavy aircraft (A380, AN225), can swivel their main gears but only during taxiing to reduce stress on the gears. They are centered and locked for takeoff/landing. Interestingly enough, the original models of the C-5 Galaxy had this capability but it was removed in later versions.
Very similar actually. B-52H is 136000 lbf and the B747-400 has approx 240000 lbf.
If that’s the case though then it shouldn’t be wallowing around in ground effect as mentioned earlier, it should be able to climb out fairly well. Maybe the wing isn’t as good?
You can question a B-52 all you want but they are the subject of one of my favorite sets of facts:
The original B-52 design was conceived in the 1940’s
The original fleet was built in the 1950’s
The current fleet was built in the early 1960’s
B-52’s are still the best long-range strategic bombers in the world and can fly from the U.S. mainland to any target in the world and back non-stop. During the Iraq wars, crews could go to work in Missouri or Louisiana, fly to Iraq, drop their bombs and then fly back home so that the crew could be home for a late dinner.
The Air Force attempted to replace them with better alternatives several times and no one could could up with a more effective design.
The current fleet of B-52’s isn’t scheduled to be retired until at least 2040 when the planes are almost 80 years old.
They may have some unusual characteristics but there have been few engineering designs in history as successful as the B-52. It predated and will vastly outlast whole generations of other air and spacecraft.
I know that my answer didn’t directly address your question but it should provide some context. B-52’s are just remarkable planes and perfect examples of outstanding engineering in general.
