Propeller Secondary Effects and Asymmetric Flight Flashcards
what is the P-factor?
If the prop axis is not in line with the direction of flight then the length of the path of the individual blades through the air will be different and the prop will generate more thrust on one side of the disc than the other
For a right-hand propeller, the longer path is on the right-hand side of the disc, giving this blade both a higher alpha and a higher relative airflow speed
Thrust on the right-hand side is increased and the aircraft yaws left
Direction of yaw of course depends on the direction of blade rotation and is referred to as the P-factor
propeller power absorption is determined by three factors, which are …
Prop diameter - increased diameter can absorb more power, but diameter is limited by tip speed because when tips speeds reach transonic values, all the expected problems associated with shockwaves appear
Disc solidity – a measure of how much of the prop disc is filled with blade – the ratio of the frontal area of all the blades to the surface area of the prop disc
Max lift coefficient – affects the ability of the prop to absorb power. Can be improved by increasing camber of the blade section, but while increasing power absorption this increases drag and makes the lift/drag ratio worse, thus reducing efficiency
on a MEP aircraft with right handed propellers, what engine is the critical engine and why?
left engine is the critical engine
what is the effect of having counter rotating props with regards to the critical engine?
The situation can be improved with counter rotating props as the thrust line can be moved inboard
By doing so we can arrange to have both offset thrust lines inboard of the engine and the yawing moments created after engine failure will be the same for either engine, therefore will have no critical engine
what happens to the size and position of the drag vector in the event MEP engine failure?
When an engine fails it will windmill and cause massively increased drag on the failed engine side
The drag on each side of the aircraft will become very unequal and not only will the vector sum of the drag move rapidly away from the centre line of the aircraft towards the failed engine, but the total drag will also increase dramatically
After an engine failure and the pilot has regained control of the aircraft, he will feel in control and the wings will be level. Equilibrium has returned but the aircraft will be in a steady sideslip
which direction will the aircraft sideslip and what will be the position of the slip ball?
the aircraft will sideslip toward the failed engine, and despite this the slip ball will be centralised
how can the resulting sideslip after engine failure be eliminated and what will be the position of the slip ball after this?
by applying about 5 degrees of bank towards the live engine – five to the live
This creates a lateral component of weight that is acting parallel to the rudder side force but is opposing it and if it is large enough to cancel out the rudder side force altogether, the cause of the side slip will be eliminated
the slip ball will be displaced about half a width towards the live engine, due to the bank angle – although there is no sideslip and no turning
what is the assumed gear position and prop condition for Vmca?
Gear retracted, but otherwise in the most critical take-off config
prop windmilling (highest drag)
what is the effect of increased mass on Vmca?
Although an increased mass will reduce climb gradient, the effect of the lateral component of weight in the 5-degree bank will be increased at higher mass. So, because we can fly slower and still retain control, Vmca will be reduced (this assumes we have the bank angle applied. If wings are level there is no lateral component of weight and Vmca will be higher)
Vmcl must be a speed high enough so that after engine failure with the remaining engine at max GA power, lateral control can be maintained and roll the aircraft away from the … engine through … degrees in … seconds
Also a requirement that, with power reduced to that sufficient to maintain 5% descent slope, the roll test is carried out in … seconds
failed
20
5
3.5
