A few questions

[multi_engined]

I have my PPL exam coming up and just have a few unanswered questions that I was hoping I could get some answers to...


1. What is the effect of mixture on airspeed? also if this is affected by altitude can you please explain what and why the effect of this is also.

2. Does glide range increase with an increase in weight or decrease? I have seen answers to both so am confused.

3. If you are flying from airport A to airport B, meanwhile 20 minutes after takeoff you establish that you are 8 degrees right of track so you alter your heading 16 degrees to the left, when you are back on track what HDG alteration should you make to maintain orginal flight plan track.

4. What is the difference between "Arm" and "Station" in terms of loading and balance?

5. Is it possible to get icing on the propellor blade in-flight? If so what icing is used to prevent this from happening? What would be the effect of flight if this happens?

All replies greatly appreciated.

ME

[Capt Claret]

A few answers.

1. What is the effect of mixture on airspeed? also if this is affected by altitude can you please explain what and why the effect of this is also.

If the mixture is not at the optimum, then the power output will not be optimum, therefore IAS will be degraded. As a contrast one needs to consider whether the engine manufacturer recommends running the engine lean of peak (egt) or rish of peak.

2. Does glide range increase with an increase in weight or decrease? I have seen answers to both so am confused.

Weight should not effect glide range if one knows the speed that correlates to the best AoA for the weight when gliding.

If one doesn't know the best AoA speed, then one will glide at less than the optimum AoA, therefore glide range will be reduced.

The heavier the aircraft then the higher the pitch attitude to gain the recommended glide speed, conversely, the lighter the aircraft, the lower the pitch attitude to achied the best glide speed.

3. If you are flying from airport A to airport B, meanwhile 20 minutes after takeoff you establish that you are 8 degrees right of track so you alter your heading 16 degrees to the left, when you are back on track what HDG alteration should you make to maintain orginal flight plan track.

If you altered heading 8 degrees left, after determining that you were off track, then, assuming the wind is constant, you will parallel track.

Therefore, in your scenario, at 40 minutes after takeoff, you should be back on track and a turn, 8 degrees to the right should maintain track.

4. What is the difference between "Arm" and "Station" in terms of loading and balance?

I have always thought of ARM and STATION as synonymous.

5. Is it possible to get icing on the propellor blade in-flight? If so what icing is used to prevent this from happening? What would be the effect of flight if this happens?

Prop blade icing is not uncommon. In my experience, Anti-icing of prop blades is predominately electric boots fitted to the leading edge of the prop blade, from near the blade root to almost the tip. I believe some anti-icing systems include a chemical anti-freeze/ant stick being fed to the prop blade and then flowing along the blade as the prop spins.

Additionally, aeroplanes such as the DH8 have reinforced synthetic panels on the fuselage to take the impact of ice shedding from the prop in flight. The ice makes a hell of a din and often causes alarm for pax/cabin crew.

Warning: It's been a long time since I've thought of this stuff. Use answers with caution!

[multi_engined]

Thank you so much.

Still don't get the off track question though.

My thought was if you turn 16 degrees to the right then that would half the distance it would take to get back on track than it did to get off track.

Also as opposite angles are equal I thought you would require a turn 16 degrees to the right to maintain original flight plan track.

Everything else is great though!

[GearOff]

If you are 8 degrees right of track and turn left by 8 degrees, you will parallel your planned track, but never regain it. So to regain your flight planned track, you need to turn further left. In this case, you are turning a futher 8 degrees left to regain your flight planned track.

Once you get back on track, you don't need the closing angle anymore, so you can turn right by 8 degrees.

[andrew495]

2. Does glide range increase with an increase in weight or decrease? I have seen answers to both so am confused.

Captain Clarent answered correctly.
So if you keep best AoA by increasing the best glide speed when heavier, the distance will remain the same.

Not sure if you've seen this question or not but it sums it up i think:

Q: Which of the following describes the effect of increased weight on the maximum gliding performance in nil wind?

A: The speed for best glide increases and the gliding distance remains the same.

Hope this helps :ok:

[Chimbu chuckles]

There is only one fuel/air ratio (mixture) that will give you maximum power...anything leaner or richer than stoichiometric will give less power therefore less IAS.

Two identical jets gliding side by side..one is 10000lbs heavier than the other. Think about the vector diagrams for these two aircraft...for unaccelerated flight lift=weight and thrust=drag

The heavier jet has a weight vector which is longer than the light aircraft acting straight down toward the ground (gravity). The lift vector MUST be increased to balance the weight vector otherwise the aircraft will ACCELERATE downwards...and ever increasing VS. To achieve UNACCELERATED gliding flight you lower the nose and this angles the lift vector forward and the resultant of those two vectors gives a horizontal vector which is effectively 'thrust'. The aircraft accelerates until at some higher IAS the total drag=thrust and the aircraft stabilises at that new IAS.

The distance in still air will be the same but the heavier aircraft will arrive sooner.

Think about the drift question...you have had a TE (track error) of 8 degrees for 20 odd minutes. If you turn left 8 deg you only stop further drift without regaining planned track. By doubling the drift you not only stop the right drift but induce 8 deg left drift that must regain original track in the same time as you took to get off track. At that time turning 8 degrees back to the right will maintain track because you will be holding a heading 8 degrees left of the original heading. Say you were heading 090 when you discovered this TE...you turn left to 074 and 20 minutes later you turn back to 082 magnetic to maintain planned track.

Get it?

Arm= the distance from the datum to the point being considered.

Station= is the point being considered.

In many light aircraft the 'Datum' is the firewall. The 'station' is a physical point where you may put something in an aircraft. For arguments sake lets call the front two seats in my Bonanza Station 1, the middle row Station 2, third row Station 3.

If I put 100kg of bags in station 3 it will move the CofG further aft than that same 100kg placed on the seats in station 2. Think about holding a ruler between your finger tips and moving a weight out along that ruler in 1CM increments. Your fingers are the datum, the ruler is the arm and each 1cm is a station. By multiplying the weight at each station by the length of the arm (the amount of leverage that weight can exert) we can calculate how far the CofG moves forward or aft.

Icing is very possible on a spinning prop. Over the years many forms of anti/de icing have been used. An example of anti icing would be props electrically heated which stops ice forming and an example of de icing is pneumatic boots which are activated once a certain amount of ice forms abd crack it off.

N1 fan blades on a jet are heated because the result of ice cascading through the engine after being cracked off would be disastrous as would ice forming assymetrically on the N1 bades causing it to be unbalanced...not so with an external prop.

From memory anyway.:ok:

[M.25]

2. Does glide range increase with an increase in weight or decrease? I have seen answers to both so am confused.


The reason that you may have seen both answers is probably due to the effect of wind. In nil wind the glide range will be the same (assuming the best glide speed (AoA) for the given weight is held).

If you are gliding into a headwind, a faster best glide speed (due to a heavier weight) will mean that the aircraft is exposed to the headwind for a shorter period of time. This means that the heavier aircraft will glide further than the lighter one into a headwind.

Similarly if you are gliding with a tailwind, a slower best glide speed (due to a lighter weight) will expose you to the tailwind for a longer period of time. This means that the lighter aircraft will glide further than the heavier one in a tailwind.

[Chimbu chuckles]

Yup...which is why gliders carry dumpable water ballast.:ok:

[witwiw]

for #3 (the off track scenario)


imagine drawing a line vertically on a peice of paper (your planned track), and a line heading out 8 degrees to the right (your actual track)- you could make this 2nd line 20cm and each cm is equal to one minute if you really wanted to draw it.

this 8 degrees is called Track Error.

now, if you turn left by 8 degrees and projected a line, you would be going straight back up the page. turning left by more than 8 degrees will mean you will eventually get back on your planned track.

if you altered your original heading by 16 degrees to the left, you go past paralleling your track by 8 degrees. the angle that the planned track makes with the new track intercepting it is called the closing angle, which in this case is 8 degrees.
(if however you altered by 24 degrees left, your closing angle turns out at 24-track error = 16 degrees).

note that your track error and closing angle are both the same, so for the sake of simplicity (nil wind), you will get back on track in the same time from your present position as it has taken you to get from point A to your present position.
a closing angle greater than your track error results in you getting back on the planned track quicker than the time it has taken from your previous fix to present position; consequently the reverse is true- a closing angle lesser than your track error results in you getting back on the planned track longer than the time it has taken from your previous fix to present position.

once back on track, if you turn 8 degrees right you will then go straight back up the page and stay on track.

the heading to fly after intercepting the planned track is your original heading plus your track error.


i hope that clarifies it.

[Ratshit]

1. What is the effect of mixture on airspeed? also if this is affected by altitude can you please explain what and why the effect of this is also.

If you pull the mixture control all the way out - airspeed will eventually decrease !!

Sometimes quite abruptly !!

R:cool:

[Ratshit]

3. If you are flying from airport A to airport B, meanwhile 20 minutes after takeoff you establish that you are 8 degrees right of track so you ............

hit the "direct to" button on your GPS and adjust your heading accordlingly !!

R:cool:

[Andy_RR]

all else being equal, mixture has no effect on airspeed, unless you are running at full throttle or have a CS prop.

Then you will need to be around lambda=0.92 for best power (around 13.5:1, or 5% CO). Running at stoichiometry gives you nothing optimal, unless you happened to have a three-way catalyst, in which case it will give you minimum exhaust emissions (nearly). This last point is obviously irrelevant for aircraft! ;)

Anything either side of 13.5:1 will obviously give less power, hence lower IAS.

A

[multi_engined]

Just thought I would give you guys an update,

I passed my PPL exam with 75%, I was hoping for 80 but I guess this will have to do.

Thanks for your help.

ME