"Blair Maynard" wrote in message
...
On Wed, 2 Jul 2003 09:16:51 +1000, "The Raven"
wrote:

"Blair Maynard" wrote in message
.. .
I haven't looked much into the future design of the quad tiltrotor, if
anybody else has, please post any info you can.

A variant of the Osprey has been proposed with two sets of rotors.
Consider
it a CH-46 Osprey.......

But a quadtiltrotor
seems to be a promising project. I presume the engines in front and
rear would be standard forward-facing props and I guess they would be
offset so that the rear props would be pulling "fresh" air (as opposed
to air which was already pulled by the front props).

My question is why not configure the rear engines as pusher engines?

Because you'd potentially be swinging the prop arc towards the loading
ramp.
Yes, a good design would minimise the possibility of resultant danger but
it
would be easier to avoid it in the first place by sticking with the same
method as the Osprey. Of course, you then simplify design and support by
utilising interchangeable assemblies etc rather than having "pusher" and
"puller" variants of the engine/pivot/prop assemblies.

Did the German Arrow aircraft not show that this was an effective
combination?

Not really, it wasn't a tilt rotor and didn't have to contend with a
loading
ramp at the rear.


Wouldn't that somewhat alleviate the need to offset the engines/props?
It would certainly space the props further apart.

Disadvantages:

I would guess the main obstacle would be the ground configuration of
the aircraft. Since the rear props would be pushers, they would have
to be pointing down for VTOL.

Why? You could have them pivot upwards.

I am assuming the rear pusher engines are mounted on the tips of a
second wing positioned behind the first, probably slightly heigher
than the first wing. Basically a biplane, but with the top wing set a
significant distance behind the bottom wing.

The rear engines are pushers, so if they rotated up they would be
pushing up. This might help the Quad Tiltrotor to arrive at the
ground, but not in one piece.

Oops, I realised my gaff regarding pusher props and rotating up after
posting it. I see no real benefit in using pushers, the engine is there so
why not stick on the front as a traditional "puller".


Picture an Osprey with pusher props on it (I am not saying that is the
way it should be, it is just to help visualize it), instead of the
current puller ones. The engine would be pointing backwards and
pushing air behind it. Try imagining what would happen if you rotated
those engines upward. They would push the plane downwards.

Yup, agreed.

Anyway, I will work on a drawing in a month. Thanks for everybody's
input.

You should see if you can hunt up pics of the Osprey four rotor concept.
Perhaps that will help.


And yes the rear props would come close to the cargo ramp. That is one
of the disadvantages.

One wonders if jets could be used, thus eliminating the prop...........Of
course, you'd need a lot of thrust to lift it.

But I am sure there are a few disadvantages in the current design
which, i believe, would put rear puller engines partially in the wake
of the front puller engines. They must lose a lot of power if much of
the air that is running thru them has just been pulled by the front
engines.

Stick a normal rotor on the back of an tilt rotor? Give you a hybrid setup.
Hmmmm, sounds more like a Rotodyne every minute.

The Raven