Rocket Plane in Level Flight?

[Justin]

Would it be possible to design something like the XCOR Lynx for level
flight, with a rocket but still have a useable range?
Let's say a normal cruise speed, size and passenger capacity competitive
with a Lear Jet 23, or a Cirrus Vision.

[David Spain]

My take on this is that you *could* build one with a longer range, but it
would not be economical to do so because of the added expense of carrying
around all that oxidizer, and certainly not for whatever you are defining as
'normal cruise speed' for a Lear or a Cirrus.

In other words it would be more expensive to fly than the Lear/Cirrus. In fact
it would aways be more expensive to fly that an air breather. So unless there
was some other distinct advantage (like hypersonic speed), there would be no
point to doing it. SABRE technology excluded here....

Dave

[Jeff Findley]

In article <jj4f60$ku9$1...@dont-email.me>,
jus...@nobecauseireallyhatespam.edu says...

Rocket engines are not at all efficient for cruise because they don't
take advantage of the atmosphere in any way. For subsonic cruise, you
can't do much better than a modern high bypass turbofan engine.

Jeff
--
" Ares 1 is a prime example of the fact that NASA just can't get it
up anymore... and when they can, it doesn't stay up long. ;) "
- tinker

[Justin]

I had to look up SABRE. ;)

Let's bring SABRE into the mix. Would it be possible to desich a rocket
to use the atmospheric O2 when available and then switch to an on board
supply?

[Jeff Findley]

In article <jj6uso$bn0$1...@dont-email.me>,
jus...@nobecauseireallyhatespam.edu says...

In theory, but if you're designing a vehicle for hypersonic cruise, you
could leave off the ability to run off of on board O2 (i.e. rocket
mode).

If you're going completely out of the atmosphere, then you're
essentially talking about flying a suborbital trajectory, similar to an
ICBM. In that case, I'd argue that you'd be better off ditching the
air-breathing mode and use a pure rocket to get above the atmosphere as
quickly as possible to reduce gravity and drag losses.

But the devil is in the details. If SABRE is ever fully developed, the
trajectory of the vehicle would need to be optimized for the actual
specs of the operational engine. In other words, I have little
confidence in a paper vehicle designed to use a paper engine.

[cra...@gmail.com]

On Mar 7, 2:26 am, Justin <jus...@nobecauseireallyhatespam.edu> wrote:
> Let's bring SABRE into the mix. Would it be possible to desich a rocke
t
> to use the atmospheric O2 when available and then switch to an on board
> supply?

Yes, it is possible. It won't be competitive with turbofans for
atmospheric cruising, though. Rockets and turbojets waste a lot of
horsepower that turbofans and turboprops capture.

It might help to have some more explanation. I read your initial post
asking for a usable range, normal cruise speed, size, etc. But what do
you want to do with this rocket plane? (Don't hold back - I've posed
some odd thought experiments on usenet, too.)

Is it a suborbital tourist rocket that can self-ferry to the boost
point? Is it trying to be a faster (hypersonic?) Lear jet? Or are you
after a typical business jet with an alternative propulsion system? Or
do you want a ground-to-orbit spaceplane?

Mike Miller, Materials Engineer

[Justin]

On 3/12/12 8:34 AM, Cra...@gmail.com wrote:
> On Mar 7, 2:26 am, Justin<jus...@nobecauseireallyhatespam.edu> wrote:
>> Let's bring SABRE into the mix. Would it be possible to desich a rocke
> t
>> to use the atmospheric O2 when available and then switch to an on board
>> supply?
>
> Yes, it is possible. It won't be competitive with turbofans for
> atmospheric cruising, though. Rockets and turbojets waste a lot of
> horsepower that turbofans and turboprops capture.

Sorry for the delay, been traveling for job interviews!

I think I understand. A rocket wouldn't be cost effective for
atmospheric travel - even those SABRE's that I just wikied!
Why carry your O2 when you can pull it out of the air?

>
> It might help to have some more explanation. I read your initial post
> asking for a usable range, normal cruise speed, size, etc. But what do
> you want to do with this rocket plane? (Don't hold back - I've posed
> some odd thought experiments on usenet, too.)

It's embarrassing... But here goes!
I was at an interview in February and the guy I interviewed with has a
model plane on hie desk. It looked like a mini space shuttle. It turns
out it was a "Farscape" toy! I downloaded a few episodes and I have to
say the show sucked, but that rocket plane mini shuttle thing looked
pretty neat.
From what you, Dave and Jeff said, something that small wouldn't be
able to carry enough fuel and O2. I was just wondering if we were even
remotely capable of a craft that small capable of air and space flight.
There was a scene where the pilot took the craft into an atmosphere and
did a dogfight.

[Robert Heller]

Basically, given current tech and limiting ourselves to basic chemical
engines (air breathers or not), what you see in the movies or on TV
just does not work well in reality (or not as well as the special
effects people make it look like it does), at least not with a
'typical' Earth atomosphere or gravity. The only way around this is
some sort of craft with something like anti-gravity or some sort of
mini fusion power plant or something else current tech cannot do (or
else they violate one or more laws of physics or something). The craft
is either pure rocket and only really works well in a vacuum or a pure
air-breather, like you basic fighter jet (which won't work well without
air). For example, the real space shuttles flew like 'bricks', not
like the X-Wing Luke Skywalker flew or the Colonial Vipers Apolo and
Starbuck flew. :-)


>
>

--
Robert Heller -- 978-544-6933 / hel...@deepsoft.com
Deepwoods Software -- http://www.deepsoft.com/
() ascii ribbon campaign -- against html e-mail
/\ www.asciiribbon.org -- against proprietary attachments

[John Halpenny]

On Mar 21, 7:47 pm, Justin <jus...@nobecauseireallyhatespam.edu>
wrote:

A jet engine gets oxygen from the atmosphere, but much more
importantly, it gets reaction mass. Using rocket fuel at a high
exhaust velocity is much less efficient than using jet exhaust at
lower velocity. In fact, modern engines are fanjets - basically
shrouded propellers - and are twice as efficient as earlier turbojets
which had higher exhaust velocity.

John Halpenny