An upgrade to the PPL. For pilots wishing to extend their skills and qualifications as to allow them to fly safely in poor weather conditions that are often presented by the Great British weather, just like the larger commercial aircraft.
There is basic training on this within your PPL syllabus, but its more appreciation to “trust your instruments”.
Since my last plog I have seen 8 lessons cancelled, this being my Lydd Solo, My cross country qualifier and my PPL skills test. This time away can be disheartening but it can give you the opportunity to do ground work = a better pilot!
Recently I have been reading and practising the “Max Drift” method. This is the method of working out drift needed in flight if you have to divert to other airfields without using a CRP computer in flight. This method is pretty accurate and is used by pilots I know and by the instructors.
To use this you just have to follow a simple way:
Divide 60 by the TAS (your true airspeed and not ground speed ie: Cessna 152 would be 90 aprox)
Multiply the forecast wind speed at the altitude you wish to fly at. This is the maximum drift correction (degrees) you will need to apply when the wind direction is perpendicular to your track.
When the wind is at any other angle to your track, use mental approximation method for crosswind components = ¼ at 15°, ½ at 30°, ¾ at 45°, all of this at 60°, or the clock code method shown below in diagram and apply that to the max drift angle.
For example: TAS = 90kts, Track is 000°, wind/velocity = 030°/18kt
The max drift is 60/90 x 18kt = 12 Degrees.
The drift correction we should apply to maintain our track is ½ at 30° of 12° = 6° used.
Simples!!
You can also use the diagram/method below to work out your G/S from your TAS.
The “Clock Code” method can also be used when working out groundspeed. Like above if say the wind is 30°off heading at 22 knots then like above this is ½ = 11knots.
Once you have worked this out you then need to work out if it’s a tail wind or headwind so then you either add this wind onto the TAS if a tailwind or take it off TAS if a headwind.
This can be worked out my drawing the wind/velocity on your map for quick reference.
Example: Heading is 090°, wind/velocity is 240°/28 knots & TAS is 110knots
You can see it will be a tailwind by either looking at your wind drawn on map or a quick work out on a compass rose.
Directly behind your heading is 270° and the wind is at 240° = 30° off so you then take ½ the wind speed = 14 knots. So you add this number to your TAS to make G/S = 124 knots.
It sounds harder then it is but a few trial attempts on the ground and it will be really easy in the air if and when needed.
Hey,
ReplyDeleteJust want to say your explanation has really helped me learn the clock method and max drifts.
Cheers,
Sam!
This actually isn't quite right! Your method for the drift is correct, using the 6th's. But this relationship of drift is not directly applicable to headwind/tailwind component as you have done it.
ReplyDeleteI'm sure you are aware crosswind is based on the sine rule, which fairly accurately becomes the 6th's relationship most people are familiar with. Sine works out the opposite vector, using the angle and the wind speed (hypotenuse). To work out the groundspeed, using the angle between track and the wind you would need to work use the cosine to find the adjacent vector strength. This is not so easy in the head. But.
As you have correctly drawn, but incorrectly applied. if you subtract 90deg from the angle you have between the wind and the a/c track then you can use the 6ths again, as the opposite angle once again is being calculated, this therefore gives the opposite length value, which tells how much of the wind you need to add/ subtract to get the GS.
From your first example heading 90 240/28. it is 1/2 the crosswind, so half you max drift , but 6/6 of the tailwind ie 90-30, therefore add all the wind as tailwind. therefore gs is more like 138knots, not the 124 you have gone with...