h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

If ramjets are so amazingly efficient and reliable, but they need to be moving at high speed before they can be activated, why not accelerate an aircraft with small takeoff rockets, then activate the ramjets?
I realise that rockets have an inherent danger of explosion, but surely in this age it would be possible to design one that is safe enough?

Would your average aircraft passenger - possibly with a heart condition appreciate a 5g take off do you think

I'm *gutted* I forgot to mention this, and a big thanks to Scumbag (crazy name, crazy guy...) for reminding me!

There IS a "rocket, then jet" solution commonly used by the military. If you have a big place (say a C-130 transport) that normally needs a big, long runway, but the best runway you can manage is something short you've hacked out of the jungle, a good pilot can plonk a plane down on it. The problem then is how to take off again.

The solution is the JATO - Jet Assist Take Off unit. This is a solid-fuel rocket which is strapped to the plane to give it a boost up to take off speed much faster than it would be capable of on its engines alone, and can reduce the take-off distance considerably. Since everyone on the plane is by definition military trained (i.e. fit enough) or in serious trouble, the fact of the high acceleration isn't too much of a problem, especially as these things are normally applied, as I say, to large planes, rather than, say, pickup trucks. Normally.

If you type "Darwin Award" into a search engine you will eventually find the tale of some schmuck who got hold of one of these things and strapped it to his truck out in the desert in the USA. The police found the flattened remains of the truck embedded in a cliff, and estimated he was doing over 400 mph when he applied the brakes. The brakes melted and the tires exploded, which was when he took off...

Anyway, rockets, then jets DOES work, you need to be fit to stand the acceleration, and it's only used in circumstances of dire need. In most cases a normal turbine jet is a more controllable and safer method of reaching a speed where a ramjet starts to work.

H.
Thanks for asking!

I thought that thing about a guy fitting JATO rockets to his truck was an urban myth...

You've just reminded me of something.
If you think that Jet Assisted TakeOff is interesting, how about Jet Assisted Landing? This was actually tested by the US military.
Imagine that C-130 transport trying to land on that short runway. Wouldn't it be handy if as soon as the wheels touched the ground, you could activate a massive reverse-thrust to stop you immediately? So somebody came up with the bright idea of some rocket engines that pop out from the side of the aircraft, facing backwards, that could be activated by the pilot.
The idea was abandoned because one of the test-pilots was a bit too eager, and activated the rockets a few seconds early. The plane was still off the ground, and smashed straight down onto the runway.

This is not an urban myth - I have seen the film footage, and it is hilarious!

The Official Darwin Award website has the JATO-on-a-truck story in as a verified occurence - and they have a separate section for urban myths and things they haven't been able to check out, so I *think* it's reasonable to take it that it's true.

Is that video available on the net anywhere???

H.

Huh? They've changed their minds then. I discovered that was urban myth *from* the Darwin Awards website.
Ho hum - somone must have found verification of it. That's how the Darwin Awards work after all

I'm glad that's true - it's a quality story

I must say I though B52s always used jet assisted take off.

Oh no! I checked the Darwin website, and it's all lies, lies I tell you! I'm seriously disappointed. Anyone wishing to check this out can go to my space at http://www.bbc.co.uk/h2g2/guide/U114627 and check the link. It's a myth! Gutted!

Ah well. At least the one about the guy cutting his own head off with a chainsaw was true...

H.

Rockets then jets was most commonly used on guided missiles: the old Bloodhound was the classic example; four strap-on booster rockets got it into the air, then two ramjets took it to the target.

The idea for using rocket engines to stop a plane on a short strip is even older. It was actually used on german DFS 230 assault gliders in the second world war. They were used for example in the raid to rescue Mussolini.