747 Tries to escape Graveyard - Page 2 - PeachParts Mercedes-Benz Forum

Dudesky · #16 05-31-2012, 12:33 PM

Quote:

Originally Posted by Brian Carlton

Without engines, the CG of the aircraft moves aft to a significant degree and, apparently, is just slightly forward of the main gear.

It wouldn't take much lift to bring the nose off the ground as was evidenced in the video.

Whether the wings would generate any lift at 70 kts. is the real question.

Typically, such an aircraft would never generate any lift until it rotates and it needs 120 kts. for sufficient downforce on the tail to effect rotation.

So, I'm a bit skeptical of the result.

It should generate lift, the thing is it hasn't created enough to cause buoyancy on the whole airframe.
Its getting lift off the fuselage too.
The interior could be missing in the front cabin, you never know.

Aquaticedge · #17 05-31-2012, 12:36 PM

Quote:

Originally Posted by tbomachines

Neat! Looks like the rear tail wings (I don't know the term) are in the lift position, pushing down on the tail and using the wheels as the fulcrum, and of course the wings giving lift helps too.

Too bad it's been done already
Soul plane - YouTube

You'd think doing that it'd punch holes through the tarmac O_o

Can't Know · #18 05-31-2012, 12:59 PM

Actually they just fit some low-rider hydraulics to it and started it bouncing, then slowed the video way down to make it look like the wind did it.

Aquaticedge · #19 05-31-2012, 01:21 PM

I just posted the video out of interest. Kinda poetic in a way :/ an airplane trying to fly free from being in a airliner graveyard

kinda sad

Air&Road · #20 05-31-2012, 01:25 PM

Quote:

Originally Posted by Aquaticedge

I just posted the video out of interest. Kinda poetic in a way :/ an airplane trying to fly free from being in a airliner graveyard

kinda sad

Yes, I understand what you saw in it and that's why I thanked you for posting it. I enjoyed it.

The Clk Man · #21 05-31-2012, 04:49 PM

Quote:

Originally Posted by Brian Carlton

Without engines, the CG of the aircraft moves aft to a significant degree and, apparently, is just slightly forward of the main gear.

It wouldn't take much lift to bring the nose off the ground as was evidenced in the video.

Whether the wings would generate any lift at 70 kts. is the real question.

Typically, such an aircraft would never generate any lift until it rotates and it needs 120 kts. for sufficient downforce on the tail to effect rotation.

So, I'm a bit skeptical of the result.

I'm a bit skeptical about you.

tonkovich · #22 05-31-2012, 08:08 PM

Quote:

Originally Posted by Aquaticedge

I just posted the video out of interest. Kinda poetic in a way :/ an airplane trying to fly free from being in a airliner graveyard

kinda sad

well, being that i am almost as old as dirt, i remember when the 747 first started flying. and, yes, it's kind of sad to see one stuck in the boneyard.

also - off topic - sad to know that there are very probably no extant, unmodified, airworthy 377/stratocruisers remaining. time marches on.

Fulcrum525 · #23 05-31-2012, 08:27 PM

Quote:

Originally Posted by LarryBible

I'm also skeptical, but if the plane is as stripped down as some folks indicate, the wing loading would be so light, it wouldn't take a whole lot of wind.

The flaps were also deployed which would help matters even further. Also for all we know they decided to gut in interior and store everything in the tail section

Brian Carlton · #24 05-31-2012, 08:42 PM

Quote:

Originally Posted by LarryBible

I'm also skeptical, but if the plane is as stripped down as some folks indicate, the wing loading would be so light, it wouldn't take a whole lot of wind.

In reality, the wings cannot generate any lift with the airplane lacking rotation.

The real issue is the position of the elevators and the CG. If the CG is very close to the main gear, it only takes a bit of downforce on the tail to raise the nose.

If, as was suggested, the horizontal stabilizer was trimmed for nose up, a relatively low level wind (70 mph) could provide sufficient force to lift the nose.

The wings still generate no lift. They are essentially irrelevant in the equation.

Air&Road · #25 05-31-2012, 08:58 PM

Quote:

Originally Posted by Brian Carlton

In reality, the wings cannot generate any lift with the airplane lacking rotation.

The real issue is the position of the elevators and the CG. If the CG is very close to the main gear, it only takes a bit of downforce on the tail to raise the nose.

If, as was suggested, the horizontal stabilizer was trimmed for nose up, a relatively low level wind (70 mph) could provide sufficient force to lift the nose.

The wings still generate no lift. They are essentially irrelevant in the equation.

Hmm... okay, then what generates lift in straight and level flight? Sure, it will generate more lift at a higher angle of attack, but it still generates lift with wings level. Acelerate down the runway and if you build enough speed with the fuselage level, it willl fly off the ground seemingly by itself.

It's just a matter of, is it ENOUGH lift? Also as the weight goes down the stall speed goes down because the wings don't have to overcome as much weight. They are much more lightly loaded.

You know, the old "lift = weight & thrust = drag" in straight and level steady speed flight thing.

Cheers

Brian Carlton · #26 05-31-2012, 09:09 PM

Quote:

Originally Posted by LarryBible

Hmm... okay, then what generates lift in straight and level flight? Sure, it will generate more lift at a higher angle of attack, but it still generates lift with wings level. Acelerate down the runway and if you build enough speed with the fuselage level, it willl fly off the ground seemingly by itself.

It's just a matter of, is it ENOUGH lift? Also as the weight goes down the stall speed goes down because the wings don't have to overcome as much weight. They are much more lightly loaded.

You know, the old "lift = weight & thrust = drag" in straight and level steady speed flight thing.

Cheers

If you want to generate sufficient lift with the airplane with a perfectly zero pitch attitude, you'd need to have 250 kt. of speed or so.

I suppose the airplane can generate sufficient lift to offset its weight without any rotation. It might be possible at 250 kt. airspeed, but, effectively, that's not likely to happen.

In this situation, you don't need to lift the wings at all. If you simply push down on the tailplane with sufficient force, the nose will lift. The only question that begs is the amount of the force and whether a 70 mph wind can generate it.

Air&Road · #27 05-31-2012, 09:19 PM

Quote:

Originally Posted by Brian Carlton

If you want to generate sufficient lift with the airplane with a perfectly zero pitch attitude, you'd need to have 250 kt. of speed or so.

I suppose the airplane can generate sufficient lift to offset its weight without any rotation. It might be possible at 250 kt. airspeed, but, effectively, that's not likely to happen.

In this situation, you don't need to lift the wings at all. If you simply push down on the tailplane with sufficient force, the nose will lift. The only question that begs is the amount of the force and whether a 70 mph wind can generate it.

Yes, indeed in a 747 it would take LOTS of speed to come off the runway in a level attitude. It ain't no Cessna for sure! Remember though, this is a plane at a fraction of Max Gross weight. The Vso and Vfe speeds will be Way lower than a complete plane.

Also remember that the tail section is an airfoil as well. Air flow both under and over the tail section will cause lift. Air pressure on the top of the elevator would create down force.

Anyway, regardless of whether it is for real or not, which I think it is, it's fun to watch.

Brian Carlton · #28 05-31-2012, 09:24 PM

Quote:

Originally Posted by LarryBible

Also remember that the tail section is an airfoil as well. Air flow both under and over the tail section will cause lift. Air pressure on the top of the elevator would create down force.

Negative.

On these airliners, the tail section always generates downforce. It's the only thing that keeps the equilibrium in pitch.

The CG of any airliner must be forward of the center of lift. That's why the CG calculation is critical for every flight. The further forward the CG, the more downforce is required on the tailplane (and the more fuel is consumed due to drag).

Air&Road · #29 05-31-2012, 09:31 PM

Quote:

Originally Posted by Brian Carlton

Negative.

On these airliners, the tail section always generates downforce. It's the only thing that keeps the equilibrium in pitch.

The CG of any airliner must be forward of the center of lift. That's why the CG calculation is critical for every flight. The further forward the CG, the more downforce is required on the tailplane (and the more fuel is consumed due to drag).

Well I think I will politely withdraw from this discussion. As a licensed pilot I totally understand the forces involved with flight and calculate weight and balance before every flight, but I don't want this to turn into any sort of pissing match.

Very best regards,