Stick Force and High Speed Flight Questions

[ask26]

Hi there, I am studying for my ATPL's and in looking at feedback I have 4 that I was wondering if people could help with, I think they are quite hard and so this is a more appropriate place than in the Wannabees forum:

1) An aircraft with a high Design Limit Load Factor allows a manufacturer to design for a smaller stick force/g
=== True or False

I think true as for example in an aerobatic aircraft you don't want to over stress the pilot so the sf/g would be less but the max stick force would be the same

2) The stick force/g is a limit in use of an aircraft; the pilot can check this out in the flight manual.
=== True or False

3) Where is the discontinuity plane in a normal shockwave?
=== Normal to the surface
=== Normal to the relative airflow

Different websites suggest both but I was wondering if there is a subtle difference between one normal to the surface as a shock wave and normal to the relative airflow as in a bow wave.

4) Does a bow wave form at M=1.0 or just above Mach 1

Again different results, Googling gave me Selkirk Aviation College that suggests at M=1.0 but Nasa seems to imply at above M=1.0

===========

Any help that people can give would be much appreciated

[Genghis the Engineer]

Originally Posted by ask26

Hi there, I am studying for my ATPL's and in looking at feedback I have 4 that I was wondering if people could help with, I think they are quite hard and so this is a more appropriate place than in the Wannabees forum:
1) An aircraft with a high Design Limit Load Factor allows a manufacturer to design for a smaller stick force/g
=== True or False
I think true as for example in an aerobatic aircraft you don't want to over stress the pilot so the sf/g would be less but the max stick force would be the same

True, the airworthiness standards for civil aeroplanes requires a minimum back stickforce of 15lbf to reach the maximum positive g limit. If the g-limit is higher, then Fs/g can be smaller for the same outcome.

2) The stick force/g is a limit in use of an aircraft; the pilot can check this out in the flight manual.
=== True or False

Untrue, it's a design factor - important in certification work, but largely transparent to operators.

3) Where is the discontinuity plane in a normal shockwave?
=== Normal to the surface
=== Normal to the relative airflow
Different websites suggest both but I was wondering if there is a subtle difference between one normal to the surface as a shock wave and normal to the relative airflow as in a bow wave.

Hmmm, a terminology question. I hate them - in my case I'm afraid that I'm not familiar with this particular form of words.

4) Does a bow wave form at M=1.0 or just above Mach 1
Again different results, Googling gave me Selkirk Aviation College that suggests at M=1.0 but Nasa seems to imply at above M=1.0
===========
Any help that people can give would be much appreciated

Generally a bit below in reality because of local flow variations, but for the purposes of a simplistic question it would form at M=1+a_little_bit, because that's the point when air ceases to be able to get properly out of the way. At M=1 the air is *only just* getting out of the way of the aeroplane without a shockwave forming.

G

[Mad (Flt) Scientist]

Originally Posted by ask26

1) An aircraft with a high Design Limit Load Factor allows a manufacturer to design for a smaller stick force/g
=== True or False
I think true as for example in an aerobatic aircraft you don't want to over stress the pilot so the sf/g would be less but the max stick force would be the same

As with so many design questions, the real answer is "it depends". Stick force/'g' is dependent on more than just the minimum stick force at limit load. IF your critical design condition is the limit load condition, then increase in the limit load will allow some alleviation. But if other considerations - say pitch feel characteristics - dominate, then the limit load factor is irrelevant.