Which way is forward?

[McColm]

I have to disagree to agree.
For those of you that are professional drivers will know that whilst executing a 'J-turn' your car doesn't stop. The momentum will keep the car/vehicle moving in the direction the driver wants to go. Otherwise you would do a three point turn instead.

secondly
For those of you that have ever tried walking whilst the aircraft is flying at 150ft carrying out M.A.D. maneuvers will know that it is nearly impossible to walk due to the G-forces.

third
If you've ever been in the back of a C-130 landing at Gibraltar, when has the pilot ever considered the comfort of his/her passengers?
At least in the Nimrod there was a running commentary of what was going on!!

So in theory, if your jet engine is sucking in air to turn its' blades and forcing the exhaled gases through nozzles in the direction the pilot wants to travel and you have a wing that can flex/adapt itself to both forward and backwards flight whilst in the air, accompanied with fly-by-wire management system so that you don't fall out of the sky.

[PR19_Kit]

secondly
For those of you that have ever tried walking whilst the aircraft is flying at 150ft carrying out M.A.D. maneuvers will know that it is nearly impossible to walk due to the G-forces.

You didn't have to fly with the 'low level RAF' to experience that. You just had to have booked a flight with Spantax in the late 70s. Their DC9 and Convair 990 pilots were all ex-Spanish Air Force and they never read the bit in the company handbook that mentioned 'passenger comfort'........ 

[Weaver]

I have to disagree to agree.
For those of you that are professional drivers will know that whilst executing a 'J-turn' your car doesn't stop. The momentum will keep the car/vehicle moving in the direction the driver wants to go. Otherwise you would do a three point turn instead.

secondly
For those of you that have ever tried walking whilst the aircraft is flying at 150ft carrying out M.A.D. maneuvers will know that it is nearly impossible to walk due to the G-forces.

third
If you've ever been in the back of a C-130 landing at Gibraltar, when has the pilot ever considered the comfort of his/her passengers?
At least in the Nimrod there was a running commentary of what was going on!!

So in theory, if your jet engine is sucking in air to turn its' blades and forcing the exhaled gases through nozzles in the direction the pilot wants to travel and you have a wing that can flex/adapt itself to both forward and backwards flight whilst in the air, accompanied with fly-by-wire management system so that you don't fall out of the sky.

We seem to be talking at cross-purposes here. As I read it, your proposal is that if your aircraft is flying North, you want it to stop flying North and start flying South, with it's nose still pointing North. Is that correct?

[McColm]

Yes,
Nose pointing north and travelling south.
A bit like pulling an rubber band. Hold onto one end(south) and pull with the other(north). On release (north) the band goes back to (south). You don't see it stop to change direction.
Or a humming bird that doesn't stop to change direction, or fall from the sky.
Helicopters are slightly different as they need to hover first before moving backwards.

What about a wing that could swivel from 270 through to 90 and align at 180 the turbo-prop engines would be fixed to the moving wing? That way the aircraft wouldn't plummet to the ground, and you'd still have your aerofoil. as in the pic (270-90) and 90-180. Haven't found away to doctor the picture to show the wing/propellors turned the other way.

[Hobbes]

Yes,
Nose pointing north and travelling south.
A bit like pulling an rubber band. Hold onto one end(south) and pull with the other(north). On release (north) the band goes back to (south). You don't see it stop to change direction.
Or a humming bird that doesn't stop to change direction, or fall from the sky.

That is physically impossible. You may not see that the hummingbird/rubber band stops, but that's a limitation of the human eye. Record it with a high-speed camera, and you will see that they stop. An instantaneous change of direction would mean an infinite accelleration which defies the laws of physics, as it would require an infinite amount of energy.

[McColm]

Nothing is impossible if it is a whatif,
If you want to build your B-52 with only one engine, that's fine by me. It won't fly but in your mind it will. Or build a submarine with sails and rigging or paint the 'flying scotman' pink go a head.
Its your mind, the impossible the possible. when I build my V-22 I'll show you the transition from 270 through to 180. Even an R/C model could do it.

[Weaver]

If you want to science-fantasy about it then yes, you can do anything you like: have a giant eagle on one wing tip, a magic carpet under the other and a big book of spells in the cockpit and you can do anything you like.

However, the general tone of your original question implied a novel application of real-world physics, and in that case, NARSES is right: if you go straight from flying North to flying South without changing heading, then you DO stop, even if only momentarily. Your forward airspeed drops through stalling speed, through zero, and goes back up to "minus stalling speed", and all that time, your wing isn't lifting.

Yes, you can get around this by having enough engine power to hang on the tilted props in the manner of a helicopter, but the installed power neccessary is FAR greater than you need for the cruise condition, so for most of the flight, the weight of those extra engines is detracting from your payload and if they're running, they're burning excessive fuel to boot.

[McColm]

So I take that as a no then.
Isn't whiffing fantasy?
So back to the Harrier, that doesn't stall. Just need to build something a bit bigger that's all

[Weaver]

So I take that as a no then.
Isn't whiffing fantasy?
So back to the Harrier, that doesn't stall. Just need to build something a bit bigger that's all

Whiffing can be fantasy, science-fiction or fact-based speculation, the difference being that in the first, anything goes, in the second you have to be reasonably internally consistent and logical, and in the last, you have to apply real-world physics and engineering as if it's a real project. Basically, you need to define your terms of reference for the discussion: it seemed to start off with a real-world engineering question so that was the basis of most of the replies.

The Harrier's wing does stop working to any meaningful degree as it slows down, which means that, just like the V-22, it depends entirely on it's engine power to support it at below stalling speed. That means that, just like the V-22, it's VTO weight is severely constrained by the available power:

Harrier GR.9:

Engine thrust = 24,750 lb, Max vertical take-off weight = about 24,000 lb

F-16C:

Engine thrust = 28,600 lb, Max horizontal take-off weight = 42,300 lb

So the F-16 gets 76% more fuel and weapons off the floor with only 16% more thrust, purely because it can use it's wing and bloody long runway to generate extra lift not available to the Harrier.

A  P-3 has a max take-off weight of 142,000 lb. If you want to hover it on jet thrust mid-mission, you're going to need at least 130,000 lb of thrust. To get that level of thrust, you'd need something like two RR Trent 700s, which is the powerplant of an A330 Airbus that's three-a-half times heavier than a P-3 and 150kts faster. Those two engines are more than twice as heavy as the P-3's so that's about 9000 lb of payload gone, before you even start to think about the fuel consumption and the weight penalty of your tilt-wing system.

[McColm]

Thanks Weaver,
I'll try and refine my questions in future.
I've noticed in my research a lot of aircraft stall, and fall backwards, thus giving the impression of backwards flight and other sites that have debated this same question. Too deep for me.
Although there are stories told of Tigermoths traveling backwards due to strong winds and gliders used during WWII during the D-Day Landings.
Just need to buy a plastic model kit of a V-22 and pivot the wing.

[Weaver]

A slow, high-lift aircraft can travel backwards over the ground if the headwind is sufficient to keep it travelling forwards relative to the air it's flying in. For instance, if you're flying at 30kts into a 40kt headwind, your ground speed will be -10 kts. From an aerodynamic point of view though, Your wing is still going forwards at 30 kts.