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Proposals for air breathing hypersonic craft. II
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Robert Clark
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Joined: 30 Apr 2005
Posts: 129

PostPosted: Sat Jun 24, 2006 10:57 pm    Post subject: Re: Proposals for air breathing hypersonic craft. II Reply with quote

The method as original proposed uses the thrust from the fuel
accelerated rearward plus the thrust from the combustion of this fuel
with the still air.
However, this creates problems with communicating the thrust due to
combustion with the rocket since the air is flowing freely, actually
still, so is outside the rocket "system".
Question: if the air is made to flow in a circle or for example in a
helical path, does this air now become part of the rocket system? Does
momentum imparted to this air also become transmitted to the rocket? If
so, this may provide a means to impart most or all of the thrust
produced from combustion to the rocket.
A key question though is would this create the same type of heating
problems as when the air is decelerated from hypersonic speed? Though
the air is not decelerated, it is being accelerated in moving in a
curved path.



Bob Clark


Robert Clark wrote:
Quote:
...
(III.) However, the key problem is how to communicate the thrust of the
combustion, which is taking place in still air, to the craft. The
problem is the fuel is being combusted in still air while the rocket is
moving away at up to 8000 m/s. So even if the combustion products are
moving at 4500 m/s they still can not catch up to the craft to impart
momentum to the vehicle.
A couple of proposed solutions. Both of these though require the
combustion to be pulsed.
...
(a.) First method to communicate thrust to rocket: use the accelerated
fuel to propel a plate rearward to be at the same speed of the fuel/air
mixture and at the front of it. When the fuel air is ignited since the
plate is still with regards to the fuel/air it receives the momentum of
the combustion products moving forwards. You see here it can only
receive a portion of the thrust produced since it does not receive the
momentum of the combustion products moving rearward. At best it could
receive 50% of the thrust produced.
For this to work this "pusher plate" if you will needs to be of a
light material, lighter in fact than the mass of the fuel/air
combusted. Then the momentum imparted to it will give it a velocity
higher than that of the exhaust gases to be a speed at least as high as
the speed of the rocket moving forward. Once it has received the
greatest momentum boost from the expanding combustion gases, it is
allowed to catch to the walls of the rocket or to a stop bumper towards
the front thereby transferring its momentum to the rocket.
(b.) Second method to communicate thrust to rocket: use in fact not
only a pusher plate but a full combustion chamber moving rearward at
the same velocity of the fuel/air and containing the fuel/air, with its
nozzle pointing rearward. As with the pusher plate it would need to be
made of a light material to wind up at a higher velocity moving forward
than the exhaust gases. To make it lighter you might only want it to
consist of a front plate and a rear nozzle connected by strong thin
rods to keep the volume of the chamber constant as the combuston gases
expand. The walls of the rocket would then serve as the walls of the
combustion chamber. This method has the advantage that more of the
thrust produced will be transmitted to the rocket.

Bob Clark
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