Why are the engines on the F-18 so close??

[Broadsword2004]

Okay, this is a small question I suppose, but I remember reading somewhere that the engines on the F-14 Tomcat were placed far apart from each other so that if one got blown to smitherines somehow, the other engine would most likely remain undamaged.

But the F-18 is anewer aircraft, and it has its engines very close together. Just wondering if there is a reason for that at all? Or is it just a tradeoff to allow for two engines, but better maneuverability, etc...?

 

[Penguin]

Remember "we're in a flat spin, headed out to sea"? Two words: adverse yaw. The farther apart the engines, the more adverse yaw if one goes out. The F-14 I believe also generates a significant portion of its lift from the fuselage, so it's wide. To get a real answer you'd need to talk to an experienced aeronautical engineer.

Penguin

 

[Broadsword2004]

I C; yeah, I guess so, I don't really even know right now what yaw is lol.

 

[Fly Navy]

I C; yeah, I guess so, I don't really even know right now what yaw is lol.

You have three axes in the 3D world. X, Y, and Z.

If you look down on the plane, like from the top, X goes lateral, Y goes longitudinal, and Z goes through the center, up and down.

Yaw is rotation on the Z axis, the vertical axis.

 

[Clux4]

There has to be somewhere to put the fuel cells for that gas drinking beast. The size and the fuction of the aircraft played greatly in the design and might have affected the distance between port and stabboard engines.
I think your best answer would come from someone who has studied or worked closely with the F-14.

 

[Clux4]

look at this. This is what Fly Navy is talking about.
http://liftoff.msfc.nasa.gov/academy/rocket_sci/shuttle/attitude/pyr.html

 

[Penguin]

Adverse Yaw: EX. when the big ugly guy in the dawg house bar in Pensacola says "hey yaw, let's git the sissy in the white pants with the little black board thingys on his shoulders."

Also, a flight condition where the nose of the airplane is not lined up with your intended flight path. Stomp too hard on the rudder, or not hard enough, you get adverse yaw. OR flameout the left engine on an F-14, the nose could swing left even though you put in right rudder.

 

[petescheu]

Adverse Yaw: EX. when the big ugly guy in the dawg house bar in Pensacola says "hey yaw, let's git the sissy in the white pants with the little black board thingys on his shoulders."

Also, a flight condition where the nose of the airplane is not lined up with your intended flight path. Stomp too hard on the rudder, or not hard enough, you get adverse yaw. OR flameout the left engine on an F-14, the nose could swing left even though you put in right rudder.

Beta = angle at which longitudinal axis is misaligned with the relative wind. Adverse yaw accurs because of drag due to lift when you input a roll.

http://www.aerospaceweb.org/question/dynamics/q0045.shtml

 

[Penguin]

Beta is the angle of the misalignment, but adverse yaw is the condition. IF you roll with the ailerons and don't use the rudder properly, you experience adverse yaw. The nose is not lined up with the turn you are making due to the aileron input. Am I missing something? Maybe you call it something else if the yawing motion was caused by a situation like an engine failure. Perhaps unwanted yaw, or yaw that might kill you ?
The point was to explain the situation to someone who doesn't even understand the term yaw yet. I doubt "angle at which the longitudinal axis is misaligned with the relative wind" is going to clear up his question, either.

 

[HueyCobra8151]

Remember "we're in a flat spin, headed out to sea"? Two words: adverse yaw. The farther apart the engines, the more adverse yaw if one goes out. The F-14 I believe also generates a significant portion of its lift from the fuselage, so it's wide. To get a real answer you'd need to talk to an experienced aeronautical engineer.

Sir,

I am by no means an expert, but this explanation does not make sense to me. If adverse yaw is such a dire condition that an aircraft's whole design would be predicated upon eliminating it in the case of a catastrophic engine failure, then how does that explanation account for aircraft such as the A-10 Thunderbolt which was specifically engineered to not only have widely spaced engines, but to be able to fly in the event of a single engine failure?

 

[Fly Navy]

Asymmetrical Thrust is the condition that occurs when you have a dead engine in a multi-engine bird.

If your rudder can't counter act the asymmetrical thrust, then you have a potential problem on your hands if the aircraft becomes unstable.

 

[Pitz]

The Tomcat designers made a big mistake when they separated the engines so far apart.

If you’ve ever noticed, Tomcat pilots are the only guys who don’t brace their heads against the headrest during a cat shot. The reason is that they are watching the engine instruments.

If an engine is lost during the cat stroke you had better have full rudder in the good engine side before the end of the cat stroke or else the plane will turn into a Fresbie.

Another big problem which has accounted for about 30 percent of the Tomcat losses is loss of one engine while at slow speed during a dogfight. Prior to the installation of the digital flight control system, it was easy to fly the tomcat into a dangerous regime of the flight envelope where an engine would stall out, resulting in a flat spin because of the large moment arm from the other engine in full blower.

When the Tomcat was new it was advertised as spin proof. They quickly discovered that not to be the case. Only one pilot that I know of has ever got a Tomcat out of a flat spin, and that’s probably because he flew it below the out-of-control mandatory ejection altitude where he was in thicker air.

I believe that aircraft designers learned lessons from the Tomcat so they will never design a fighter with engines so far apart again. The lateral position of the engines doesn’t make any difference on the maneuverability of an aircraft but it does make a huge difference during single-engine operations.

 

[kmac]

First, aircraft with multiple engines have a rudder that corresponds to both the distance aft of the Center of Gravity that the rudder is as well as the distance laterally that the engines are placed. This is to allow enough rudder authority if you have assymetric thrust. Remember, the farther outboard from the center of the aircraft, the bigger moment is placed around the CG. Likewise, the further aft the rudder is of the CG, the bigger moment it can place to counteract that of the engines. For an aircraft like the S-3, which has 2 engines but the rudder is relatively close to the CG, a large rudder is needed to compensate. The E2 and C2 have 3 rudders to be able to directionally control the aircraft in single engine flight.

Adverse Yaw. Shoo had it right, with a nice article linked to his post. Adverse Yaw is very dangerous when getting slow close to the stall speed. Let's say you're turning left coming in to land. If you roll left, the right wing has a higher angle of attack (AOA) than the left wing, causing it to produce more lift. Without rudder input, the increased lift has an increased drag component. Due to the drag, the aircraft yaws to the right. Thanks now to the change in relative wind to that right wing, the AOA increases. If we started this whole evolution already with a high AOA, it's possible to stall the right wing and start either a spiral or spin. Close to the ground, you wouldn't have a chance to recover.

 

[Lonestar155]

Since were talking about aircraft here, what jet puts out the most power out of all Navy and AF?

 

[Flash]

Since were talking about aircraft here, what jet puts out the most power out of all Navy and AF?

Operational, the F-15. The F-22 has a lot more though.

Below is the thrust for each engine

F-14-20,900 lbf

http://en.wikipedia.org/wiki/F-14

F-15-23,930 lbf and 29,000 lbf

http://en.wikipedia.org/wiki/F-15

F/A-18E/F-22,000 lbf

http://en.wikipedia.org/wiki/F/A-18E/F_Super_Hornet

F-16-23,840 lbf

http://en.wikipedia.org/wiki/F-16#F-16_C.2FD

F/A-22-35,000 lbf

http://en.wikipedia.org/wiki/F-22