Exploring Jet Engine Position: Front or Back?

[yrjosmiel73]

Hello.

Do you think the idea of placing the jet engine at the front is plausible?
Why? Why not?

Thanks
Yrjosmiel

 

[phinds]

Hello.

Do you think the idea of placing the jet engine at the front is plausible?
Why? Why not?

Thanks
Yrjosmiel

Well, 60 years ago they thought it would work out just fine:

 

[SteamKing]

Actually, in the F-86 (the aircraft shown in Post #2), the engine sits behind the cockpit, and the tail of the aircraft can be removed for accessing/removing the engine:

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The cockpit sits atop the air inlet to the engine. The long, straight pipe you see above directs the exhaust out of the jet engine, thru the aft fuselage, and out the tail of the aircraft.

​

 

[berkeman]

And in the F-16...

http://www.combatindex.com/hardware/images/air/weft/f-16_e.jpg

 

[SteamKing]

All aircraft must be designed to produce a balanced machine when aloft. The lift produced by the wings and the elevators must balance the weight of the aircraft, and the center of lift should be aligned closely with the center of gravity of the aircraft. If you cram too much stuff at one end of the plane, it's going to be nose heavy or tail heavy, and the aircraft will be tricky to fly, assuming it gets off the ground at all.

 

[AtomRamjet]

As SteamKing said, engines are very heavy and are a major influence on the placement of the CG (center of gravity) of an aircraft. Odd CG placement can and will severely affect the static stability of an aircraft.

 

[yrjosmiel73]

Assume that there is a counterweight behind the aerocraft. How about that?

 

[SteamKing]

Assume that there is a counterweight behind the aerocraft. How about that?

Yeah, no. Aircraft aren't constructed with counterweights sticking out behind the fuselage. Besides engine placement, there are several other factors which govern aircraft design. One of the most important is keeping airframe weight to a minimum so that a realistic payload capability can be obtained. (payload =weight of pilot, passengers, fuel, cargo, etc.)

Again, having heavy weights at either end of the fuselage would affect the flying characteristics of the aircraft adversely.

 

[yrjosmiel73]

It's going to be harder to control, right?

 

[SteamKing]

Yes, assuming it gets off the ground.

 

[yrjosmiel73]

Will there ever be an instance when heavier aerocraft is better?

 

[Bystander]

http://www.telegraph.co.uk/news/pic...ng-machines-from-the-1950s.html?frame=2707722

 

[russ_watters]

Another problem with having the engine all the way in the front is that you then need to channel hot exhaust gases to the back of the plane.

 

[NTW]

Another problem with having the engine all the way in the front is that you then need to channel hot exhaust gases to the back of the plane.

For that reason, the first jet plane prototype, the Heinkel 178, stayed as a prototype, not going into series. The long pipe needed to exhaust the gases robbed too much energy, in the form of heat and friction losses.

The first Spanish-made jet warplane, the HA-200 Saeta, was fitted, for reasons related with its design, with two small turbojets at the nose, and with the exhaust installed below the wing trailing edge roots, again because of the convenience of avoiding a lengthy travel of the gases, and the corresponding losses.

 

[rcgldr]

Will there ever be an instance when heavier aerocraft is better?

Not for a powered aircraft, but for a glider, a heavier glider (within reason) will have the same glide slope but at a higher speed. Both the forward speed and sink rate will be greater, but if the updraft is enough to keep the glider going, then then heavier weight will result in faster forward speed. Full scale gliders use water for "ballast", which is dumped at some point before landing to reduce landing speed. Model contest gliders use metal ballast to increase weight on windy days in order to return back upwind (faster speed needed here) after following a thermal downwind. Model dynamic soaring gliders are more than double the weight of a similar sized thermal type glider, since the shear boundary between two streams of air moving at different speeds provides a large energy source for dynamic soaring. The last dynamic soaring speed record that I've read about is 498 mph. There's a youtube video of a 468 mph run (hard to see, but the 405 mph run in the second half of the video tracks the glider better).

 

[AtomRamjet]

It's going to be harder to control, right?

Its performance would also suffer greatly. More weight equals more lift needed to sustain flight. More lift means more induced drag. More induced drag translates to more thrust required. More thrust means higher fuel burn rates which yield reduced range and endurance. What's worse is that a counter-weight would be dead weight. It contributes very little to the function of the aircraft. Dead weight is the last thing you need in an aircraft or spacecraft .