Oh, the stupid, it burns

[pecunium]

There's a show on, about stunts.

This guy is diving out of one plane, to catch up to, and then enter another, which is below him.

The bottom plane is nose down, with the motor off, and a drogue out.

The explanations...

1: It's in a vertical stall. It's not, it's in a nose-down dive.

2: It's travelling faster than he is, because it's heavier than he is. No, it needs the drogue because the powered plane was accellerating down, and; even if it weren't, he, and it, accellerate at the same speed, and so he can't catch up.

Sigh.

Comments

[enname.livejournal.com]

*facepalm*

You are right, the stupid does burn. These are not tricky concepts either.

[antonia-tiger.livejournal.com]

Point 2 is certainly more complicated than they seem to describe, because acceleration is the combined effect of weight and drag. So they use the drogue to increase drag, a lot.

Checking dim memory and the back of the nearest envelope, when Rolls Royce got into the jet engine business, a Merlin engine could give around 1000lb of thrust. roughly one-sixth of the aircraft weight. So I doubt running the engine would make much difference.

[pecunium.livejournal.com]

Well, the same motor which has the power to keep the plane climbing against the force of drag and gravity is going to add to the downward speed. It may not be much (even with a Cessna 172, which is what he was trying to get into), but it's going to be enough that there's no way he gets in.

1,000 lbs of thrust, added to one G accleration (which is, runnng a different back of the envelope) is, roughly 150 lbs of thrust, isn't inconsiderable as a factor.

In an ideal world constant friction, and no ground to hit at the bottom, the two bodies will come to a different terminal velocity, but in the time frame of the event (jumping at roughtly 8,000 ft) it's a factor, (because I think the Cessna has a TV of greater than the 120 mph which is the, rough, TV of a human body), but that's not what they said.

They said the plane fell faster because it was heavier, which, irrespective of the complex nature of the equation, is simply false.

The Rolls Royce isn't the best example, because the engines, in question, put out 3,500 lbs thrust, which means the two of them were a but less than half the loaded weight of the plane (a but under 16,000 lbs) with a thrust/weight ratio of .45.

Which doesn't really matter, because acceleration is acceleration.

TK

[antonia-tiger.livejournal.com]

A Spitfire masses about 6600lbs, depending on fuel load.

No way is 150lbs thrust, or 1000lbs, going to get 1G of acceleration out of that. That's basic physics. The thrust you get from gravity, engines off, is your weight, no more and no less.

And it's that extra force from the weight that got Spitfires to speeds where the test pilots started talking about the sound barrier.

Oh, and the figures you're quoting sound like a Meteor F Mk 8, with two Derwent jet engines, not a Spitfire with a Merlin piston engine.

[pecunium.livejournal.com]

Yes, those are derwents, in a Meteor, because you said jet engine. What spitfire had a jet engine?

Checking the tables, i see I did make a mistake, I misrememberd 1 poundal as 1g which would be 150lbs thrust, but 1 poundal = .249g, so the actual downward thrust of a 1g field is = 600 lbs.

But weight has nothing to do with that thrust.

Put me outside the immediate pull of the earth and I can use a ridiculously small thrust (something like 15 lbs) as a constant acceleration and be at Mars in 3 months, and Pluto in 6.

When a plane is nose down, and not fighting gravity, the thurst of the motor (be it prop, or jet, or rocket) is gravy, because the free-fall of the object (which is only affected by density/surface area) means everything else is already applying 1G of downward acceleration.

The place where the 1,000 lbs of thrust are inadequate is when it's fighting gravity, not when it's added to it.

TK

[pecunium.livejournal.com]

As a small bit of amusement, the energy in a sneeze generates a bit less than 3g acceleration, while a cought (which seems less violent) can get to 3.5.


Popular Mechanics has a list of various accelerations.

TK