IFlyVeryLittle
Topic Author
Posts: 53
Joined: Mon Jan 29, 2018 7:31 pm

Too far?

Fri Mar 15, 2019 7:38 pm

Have we gone so far off the track that we're designing airframe/engine combinations that simply don't fly right without complicated sensors and avionics designed to counteract what aerodynamics insists on doing? I recall the F-117 was built so unstable it required a sophisticated fly-by-wire interface to keep it from tumbling out of the sky. But that's a different kettle of fish. What do we really gain by building jets that cost billions to develop, save marginal percentages in fuel consumption and still require HAL to keep flying? Or did I miss the point entirely?
 
unimproved
Posts: 70
Joined: Sun Jun 22, 2014 7:14 pm

Re: Too far?

Fri Mar 15, 2019 8:22 pm

Military aircraft are designed to be unstable since a plane that only wants to fly straight ahead would be at a huge disadvantage in aerial fights.


Nobody designs a passenger aircraft that way, but certification costs for a new design can drive them to keep on stretching. The basic 737 fuselage has grown more than 10m from the -100 to the -max8.
 
stratclub
Posts: 1156
Joined: Fri Jan 05, 2018 10:38 pm

Re: Too far?

Fri Mar 15, 2019 8:29 pm

Same reason modern cars have gone digital. Just engineers taking advantage of newer technologies. Is digital integration a good thing? Mostly yes and occasionally no.

With the 787 as one example, it gets aerodynamic efficiencies that were imposable with old analog control systems.
 
WIederling
Posts: 8359
Joined: Sun Sep 13, 2015 2:15 pm

Re: Too far?

Fri Mar 15, 2019 10:30 pm

unimproved wrote:
Military aircraft are designed to be unstable since a plane that only wants to fly straight ahead would be at a huge disadvantage in aerial fights.
Nobody designs a passenger aircraft that way, but certification costs for a new design can drive them to keep on stretching. The basic 737 fuselage has grown more than 10m from the -100 to the -max8.


The solution for military craft is an ejection seat.

Transport class aircraft don't have ejection seats.
Neither for crew nor for selfloading payload.
Murphy is an optimist
 
stratclub
Posts: 1156
Joined: Fri Jan 05, 2018 10:38 pm

Re: Too far?

Fri Mar 15, 2019 10:54 pm

An ejection seat has nothing to do with an aircrafts stability. Fighters are inherently unstable because it makes them more maneuverable. If a pilot were to always fly within the aircrafts flight envelope, never botched a take off or landing and was never shot down, a fighter would not need an ejection seat.

Civilian air craft except for possibly aerobatic aircraft are designed to be inherently stable because they don't need to be as maneuverable as a fighter. The design intent with civilian aircraft is that if it is trimmed correctly, when you let go off the controls it will return to straight and level flight.
 
747Whale
Posts: 726
Joined: Fri Dec 07, 2018 7:41 pm

Re: Too far?

Sat Mar 16, 2019 3:51 am

IFlyVeryLittle wrote:
Have we gone so far off the track that we're designing airframe/engine combinations that simply don't fly right without complicated sensors and avionics designed to counteract what aerodynamics insists on doing?


No, because that's not remotely the case.

IFlyVeryLittle wrote:
But that's a different kettle of fish.


It is, which makes it irrelevant.

IFlyVeryLittle wrote:
What do we really gain by building jets that cost billions to develop, save marginal percentages in fuel consumption and still require HAL to keep flying? Or did I miss the point entirely?


We could go back to hang gliders, but we can do better.
 
WIederling
Posts: 8359
Joined: Sun Sep 13, 2015 2:15 pm

Re: Too far?

Sat Mar 16, 2019 8:25 am

stratclub wrote:
An ejection seat has nothing to do with an aircrafts stability. Fighters are inherently unstable because it makes them more maneuverable. If a pilot were to always fly within the aircrafts flight envelope, never botched a take off or landing and was never shot down, a fighter would not need an ejection seat.


You are pointing to the wrong shell.
Murphy is an optimist
 
stratclub
Posts: 1156
Joined: Fri Jan 05, 2018 10:38 pm

Re: Too far?

Sat Mar 16, 2019 5:40 pm

WIederling wrote:
The solution for military craft is an ejection seat.

Transport class aircraft don't have ejection seats.
Neither for crew nor for selfloading payload.
I was commenting on your misunderstanding in this post of yours.

stratclub wrote:
An ejection seat has nothing to do with an aircrafts stability. Fighters are inherently unstable because it makes them more maneuverable. If a pilot were to always fly within the aircrafts flight envelope, never botched a take off or landing and was never shot down, a fighter would not need an ejection seat.

Civilian air craft except for possibly aerobatic aircraft are designed to be inherently stable because they don't need to be as maneuverable as a fighter. The design intent with civilian aircraft is that if it is trimmed correctly, when you let go off the controls it will return to straight and level flight.
My unedited post that contains my complete thoughts.

WIederling wrote:
You are pointing to the wrong shell.
I have no clue what that means.
 
WPvsMW
Posts: 1972
Joined: Thu Mar 23, 2017 7:30 pm

Re: Too far?

Sat Mar 16, 2019 7:07 pm

The shell game... under which of 3 shells is the marble?
 
WIederling
Posts: 8359
Joined: Sun Sep 13, 2015 2:15 pm

Re: Too far?

Sat Mar 16, 2019 9:31 pm

stratclub wrote:
WIederling wrote:
You are pointing to the wrong shell.
I have no clue what that means.


In the case of the astable FBW wrapper stability added military craft your safety fall back ( on loosing the stability augmentation or some other indispensable functionality ) is the ejection seat: Saves the ( assumed to be ) most valuable part of the vehicle.

On a transport class airplane you don't have that option fall back from losing stability augmentation must a basically stable craft.
engines out? the plane must provide for basic operability. you must be able to land ( if you find some place suitable.)
Murphy is an optimist
 
stratclub
Posts: 1156
Joined: Fri Jan 05, 2018 10:38 pm

Re: Too far?

Sun Mar 17, 2019 4:06 am

Oh O.K. I guess were not going to get you to post anything that makes any sense.
 
WIederling
Posts: 8359
Joined: Sun Sep 13, 2015 2:15 pm

Re: Too far?

Sun Mar 17, 2019 8:46 am

stratclub wrote:
Oh O.K. I guess were not going to get you to post anything that makes any sense.


I try to fit in. :-)))))))))
Murphy is an optimist

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