Scramjet, Pulse Detonation Engines

Allen Meece wrote:
http://www.pr.afrl.af.mil/divisions/...Q/pde_faq.html

PDE's can take off under their own power and attain mach four with great
efficiency. They are light and simple to make.
As airbreathing flyback launchers with very good Isp, what's not to like,
unless you're a misanthrope wishing us all the worst luck?

noise and vibration?

^
//^\\
~~~ near space elevator ~~~~
~~~members.aol.com/beanstalkr/~~~

--
Sander

+++ Out of cheese error +++

"Allen Meece" wrote in message
...
http://www.pr.afrl.af.mil/divisions/...Q/pde_faq.html

PDE's can take off under their own power and attain mach four with great
efficiency. They are light and simple to make.

I have to disagree with you there.. Have you seen the picture of their
prototype on their home page?!?
http://www.pr.afrl.af.mil/divisions/prt/pde/index.html

Sorry, but I would not call that simple - not in the same way that a
hydrogen peroxide rocket engine is simple, anyway - and as for *light*..
well, see for yourself.

Let's see how good it is when they fly it. As for me, I'm betting that
XCOR's Ez-Rocket could fly rings around them.

Cameron:-)

Heh. You can bring the t-shirt to Space Access. I'm told they've
been flying a small PDE in a Long-EZ out at Mojave. Loud! For about
200 pounds thrust, the thing sounds like a "jake brake" (engine
compression brake) on a truck the size of the Queen Mary.

On all other points, no argument - but they have now flown one.

(the other) Henry

Henry Spencer wrote:

In article ,
Allen Meece wrote:
http://www.pr.afrl.af.mil/divisions/...Q/pde_faq.html
PDE's can take off under their own power and attain mach four with great
efficiency. They are light and simple to make.

And not one has ever flown. All those nice properties are "projected" or
"predicted" or "estimated"... and the impact of nasty little problems like
noise and vibration is still uncertain. (Notice that the pretty graph on
that web page also shows scramjets, another largely-vaporware technology.)

As airbreathing flyback launchers with very good Isp, what's not to like...

Noise, vibration, uncertain lifetime, unverified performance, poorly
developed technology, lack of commercial availability.

And of course, the fact that not everybody thinks an airbreathing flyback
launcher is worth the trouble.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

In article ,
Henry Vanderbilt wrote:
Heh. You can bring the t-shirt to Space Access. I'm told they've
been flying a small PDE in a Long-EZ out at Mojave. Loud!

For something as important as a T-shirt, we clearly can't take the word of
random rumor-mongers from Mojave. :-)

(Of course, that's going to get me in trouble with the RRMFMs when I see
them at Space Access in a couple of weeks!)
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

Well, as I understand it, the t-shirts are virtual anyway,
and the schtick must be getting a little old by now. But
for what it's worth, I was on the phone with a RRMfM when
a test was underway, and it sounded like a truck was on a
loooong downslope right there in the room with them. I was
told no, it's a very small airplane a half-mile away...

Which brings out one aspect of PDEs: A big high-power one
is likely to be just about as lethal to be near as, what
was that mach 3 nuclear ramjet cruise missile project?..
Even a small one seems to be about as sonically noxious
as that supersonic turboprop F-84 they tested back in the
fifties. If it sounded like that a half-mile off, I'd
hate to be pilot or ground crew on those tests - there's
only so much hearing protection can do; beyond a certain
point your ears get damaged by conduction through flesh.

PDEs and scramjets both might make sense for military
missiles, but not for much else that I can see.

Henry

Henry Spencer wrote:

In article ,
Henry Vanderbilt wrote:
Heh. You can bring the t-shirt to Space Access. I'm told they've
been flying a small PDE in a Long-EZ out at Mojave. Loud!

For something as important as a T-shirt, we clearly can't take the word of
random rumor-mongers from Mojave. :-)

(Of course, that's going to get me in trouble with the RRMFMs when I see
them at Space Access in a couple of weeks!)
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

Henry Vanderbilt wrote in message ...
Heh. You can bring the t-shirt to Space Access. I'm told they've
been flying a small PDE in a Long-EZ out at Mojave. Loud! For about
200 pounds thrust, the thing sounds like a "jake brake" (engine
compression brake) on a truck the size of the Queen Mary.

I wonder what this does for the rumors of a secret PDE-powered
aircraft flying out of Groom Lake? If you need ten times more thrust
for such a hypothetical vehicle, it seems like you wouldn't be hearing
intermittent reports of low-frequency noise as much as the phones
ringing off the hook with neighbor's complaints.

-jake

Actually, if it sounds like a truck engine-braking in the distance
when operating at altitude, chances are nobody'd ever notice it most
places in the southwest... I sure wouldn't want to be under the
takeoff path, though.

Jake McGuire wrote:

Henry Vanderbilt wrote in message ...
Heh. You can bring the t-shirt to Space Access. I'm told they've
been flying a small PDE in a Long-EZ out at Mojave. Loud! For about
200 pounds thrust, the thing sounds like a "jake brake" (engine
compression brake) on a truck the size of the Queen Mary.

I wonder what this does for the rumors of a secret PDE-powered
aircraft flying out of Groom Lake? If you need ten times more thrust
for such a hypothetical vehicle, it seems like you wouldn't be hearing
intermittent reports of low-frequency noise as much as the phones
ringing off the hook with neighbor's complaints.

-jake