Interview Questions

[MTB Autopilot]

I need as detailed an answer as possible for this question as my answer did not seem to hold water!

I was asked to describe with Diagrams the forces acting on an aircraft in a 45 degree bank. I provided the basics but was required to give significantly more detail which I am sorry to say I could not. I have searched the web for an answer to this but have struggled to find the detail which I am looking for.

I appreciate that this may seem like an easy question, in fact it is an easy question, but somehow I could not give a satisfactory answer!

There are also a couple of other questions
1.What happens to your stall speed at very high altitudes and why?
2.Explain Dutch roll and how to prevent it?
3.What is and how does an accumulator work?

Thanks in advace for any answers!

[Genghis the Engineer]

(1) TAS stalling speed goes up, IAS and CAS stalling speed should stay about the same. If you look at the basic equations, W=½.Rho.V².CL.max at the stall, CL.max stays the same as does weight. So, the player is ½.Rho.V² (known in the trade as q, or dynamic pressure), and the aircraft will always stall at the same value of that. So, as density (Rho) goes down, TAS (V) must go up. But an ASI is actually a pressure gauge, measuring q, so it always happens at the same IAS for the same weight,

(2) DR is a combined yawing rolling oscillatory mode. Most aircraft will do it, and you can generate it by rapid aileron or rudder inputs. In a well adjusted aircraft it'll damp out, in badly adjusted one it won't - usually because of poor damping in one or both of the two axes. DR is identifiable by the nose weaving a horizontal figure of 8, or the wingtip describing an oval. The ratio of horizontal to vertical dimensions of that oval are roughly the ratio of directional to lateral stability - normally if not fixable by other means a yaw damper (SAS) will be introducer into the axis with the greatest static stability. Rarely a problem on GA types or airliners, a real embu99eranceance in fighters since any but the best damped Dutch Roll stops you getting a guns lock on the aircraft in front. You can induce DR deliberately by going "left-centre-right-centre-release" on the rudder pedals at a period of about 2 seconds for a light aircraft or 5-6 seconds in an airliner (observing of-course the rule of not-more than 1/3 rudder above Va).

(3) Ask a systems engineer.


Hope that wasn't too simplistic, if you want me to expand just say.

G

[mono]

Did you give figures?

45 degs was chosen because the maths is a little easier with 0.707 and 1.414 being the values needed to work out most of the load and lift values.

The following site may provide enough detail for what you need to get you through the re-sit.

forces in a turn (http://142.26.194.131/aerodynamics1/Lift/Page10.html)

This one (http://www.av8n.com/how/htm/aoastab.html#fig-spiral-start) might help a little too.

Hope these help.