Ok, this is where it gets a tad bit complicated, so bear with me here. The propeller is spinning in the air right, thats ALOT of force on the blades, trying to pull them out, called centrifigal force. A propellor can only turn so fast. This is where the jet engine comes in. It has rows upon rows of blades, pushing the air back, so not as much strain on the blades compared to a prop. By doing this the jet blades can turn at much higher revs. Also accounting to the fact that you add fuel to the air and you ignite it, you get more added thrust by the heat. This is why a jet can go faster. But there are limits also, you can't go mach 6 with a jet engine, it reaches a limit also, so here comes the ram jet and scram jet. These two engines are similar but the scram jet has more power. Basically if you want to go really fast you use these. The ram jet is based on a deisel engine, there are no spark plugs. If you look straight through a ram jet engine, you dont see anything, it gets small in the middle, and then it gets bigger in the rear, there are no fan blades. What happens is that at high speed air is rammed, hence the name, down the intake, where it is compressed. As it is compressed, fuel is being added to the mixture as well. The intense amount of pressure causes the air to explode, and ignite the fuel, which propells the aircraft. If you remember the movie red october, with the catapiller drive, almost no moving parts, well this engine is the same thing but for the air, no moving parts. By using a ram jet, you can go infinite amounts of speed, BUT that all depends how long before the fuel runs out, or the plane rips apart around you. Below are some examples.

Jet Engines
http://inventors.about.com/library/inventors/bljetenginetypes.htm

trying to overcome the drag induced by a propellor which has its root travelling sub-sonic and its tip travelling supersonic is the main limiting factor in why there is a limit to the airspeed obtainable for a propellor driven aircraft........drag is the biggest factor in Jet aircraft also.....drag climbs by a huge factor as airspeed increases......until we find a way to reduce this drag and raise the power level of our motive force, we will be still travelling around the same speeds as we do now in the air......in the vacuum of space, its a whole 'nother ball game !

Brett - you're wring, of course, haven't you seen the Star Wars movies?  That's how its done...




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Yes, another ball game.

Airplane engines are called "breathing engines" because the fuel combust with the surrounding oxygen (in general fire needs oxygen) In space, chemical rockets need an oxidizer to complete the combustion with fuel.

Let me take you through a general process of the rocket engine.

*ranger sings in the tune of that bone song. (you know, "the hip bone is connected to the.....')*

The fuel and oxidizer is pumped into the injectors, the injectors causes vaporization. Then the vaporization causes mix-ing. The mixing is ignited by the igniters. The igniters causes combustion. The combustion produces hot ga-ses. The hot gases go trough the nozzle. And then hotthrustprducinggasses comes out.  

*note* Igniters and nozzle are not in the diagram.



Thats just a liquid fueled rocket in the chemical category.

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and exactly how do you decelerate in an enviorment with no air if u have one little rocket engine pushing the plane forward?(first person to explain this gets a shiny new quater and a shiny new learjet;)

I cant think much of a better analogy right now, because of my son. . .


Think of a skateboard. Push it on a flat level surface. Its moving, so how is it going to stop? Either it will hit something, or a constant opposite reaction (gravity) will slow it down. In space, a small can of oxygen could easily stop the shuttle in space. It has a constant equal and opposite reaction.

Newton's Law applies here - For every action, there is an equal and opposite reaction.

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I said, "Turn around" , or turn the engine around (thrust pointing in opposite direction),,geez  


Can I have the quarter ?

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Hmmm, thought I "kinda" said that :

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I still want my quarter.

Anyone in my age bracket (40+) surely played Asteriods in the arcades.

That game was a perfect example of how vector math applies to a rocket. Remember when you would run from the little saucer as fast as the ship would fly ? And then when it was safe, you'd have to turn the ship around and apply the thrust just to slow down and gain control.

And that was only on 2 dimensions, imagine trying it in a "3-D" environment 

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ok,ok*gives brett his damn quater*

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Any of the brighter designers would have "retro" (meaning reverse or backwards) rockets or engines already facing the other way!!   

Yes, it's more efficient to use smaller maneouvering thrusters than another "equal and opposite" rocket.

As to mechanical means - an internal "flywheel" type arrangement could be considered, using the torque of a spinning mass to rotate the overall ship.   I think, however, that given the masses involved, thrusters are more efficient.

(Where Andy Libby when we need him?)



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That's the point,,  you don't want 2 at all. You want to use 100% of your engine mass accelerating/decelerating,, any deviation from that adds time to the trip (geometrically I might add).. the shortest possible trip would be accelerating full speed to the 1/2 way point, and then decelerating to a stop.

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I believe you're confusing "mass" with "density"...

Weight is a function of  Mass X Gravity .. on Earth that gravity equals  (32'/sec^2)

Kilograms and Pounds can only be linearally converted on Earth..  

'Kilograms' are units of Mass,, the English-system equivelant is the 'Slug'...

Pounds are units of force (Mass X Gravity),, the Metric-system equivelant is the 'Newton'...

Ever notice that rocket thrust is always given in either 'pounds' or 'newtons',  never 'kilograms' ?

I believe the moon's gravity is 1/6 that of Earth, so here goes the comparison:

An object weighing 6 pounds on Earth weighs 1 pound on the moon.... An object with 6 kilograms of mass on Earth STILL has 6 kilograms of mass on the moon .


Or,,  carried to the extreme.. in zero gravity nothing "weighs" anything,, everything still hass "mass"   

I did say that I could be confused !.....it does explain one thing, though.....it takes less time to get home from the moon than it does to go there......its all downhill(relatively speaking), with only one sixth of the escape velocity required to break free of the moons influence and allow the earths to take over.....5/6ths of the trip back is accelerating.....without further motive force being applied internally at the vehicle........I guess thats why long distance space travel so far, has made use of other celestial bodies and their imparted gravitational influence to the traveller............Americans call it the singshot effect.....in England a slingshot is a catapult .

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We were talking about a Jumbo being moved through space by "the tiniest rocket". This is what I based my comment on. Another "tiny one" would not make that much difference. In fact, depending on the definition of "tiny", it may even have less mass than the thrusters you speak of.

As once a rocket propelled object reaches it's required velocity and remains at that velocity until acted upon by some opposite force (inertia), the extra weight (little as it is) I don't feel would make a difference in this particular scenario. 

Which would cool the air enough that it couldnt cause thrust right? I should know this, but I don't.

-Brad

Yeah, I agree with   and and and ! Thanks for info. I am going back to the garage and make a few adjustments to the jet engine I am building! Now, if only I could find where I put those directions! LOL

Because the air speed indicator says so!!! Jeez Loweez.
Save your brain cells for the HARD questions like why is the grass green or why is the sky blue.

   Hi All,
 
  The only stupid question,  is the question you don't ask.