# Tail & Slope - Expert advice required

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Guys,

I use my 700m strip mainly as a one-way, as there are tall gum trees at one end.. It also has a slope - downhill away from the trees.

This means that I often land with a tailwind, and sometimes take-off with a tailwind. So I have some Qs for the more learned of you out there:

1. How do I calculate the affect of tailwind on take-off? i.e. the increased TO roll with say a 10kt tailwind? (I have a wind-speed meter)

2. Likewise the increase in landing roll when landing tail?

3. Is there a limit on ground speed at the point of touch-down? i.e. If I land a Jabiru at IAS 60kts, with 10kts of tail, then ground speed is 70kts; are there any issues with wheels, etc. in contacting the ground at higher than 'normal' speed?

4. How do a I calculate the affect of the slope on roll - I know the slope % - on TO down the slope and landing up it?

Thanks,

Chris

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G'day Chris,

the charts in your POH will give you this information

Others may know if you can calculate this from scratch but certainly many a/c have this info in the POH.

Regards

Mike

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Guys,I use my 700m strip mainly as a one-way, as there are tall gum trees at one end.. It also has a slope - downhill away from the trees.

This means that I often land with a tailwind, and sometimes take-off with a tailwind. So I have some Qs for the more learned of you out there:

1. How do I calculate the affect of tailwind on take-off? i.e. the increased TO roll with say a 10kt tailwind? (I have a wind-speed meter)

2. Likewise the increase in landing roll when landing tail?

3. Is there a limit on ground speed at the point of touch-down? i.e. If I land a Jabiru at IAS 60kts, with 10kts of tail, then ground speed is 70kts; are there any issues with wheels, etc. in contacting the ground at higher than 'normal' speed?

4. How do a I calculate the affect of the slope on roll - I know the slope % - on TO down the slope and landing up it?

I concur that this information should be in the POH.

Point 3 - I'm not aware of a limitation on ground speed for the running of the undercarriage on any aircraft, but that is a good question. You'd have to assume that the wheel and tyre combination should be able to handle the maximum speed of the aircraft, whilst on the ground.

Your limitation would be the brakes. Slowing down from 100 knots might overheat your brakes versus 50 knots so you might not be able to stop.

Landing roll can be dramatically affected by a tailwind, especially with the wind pushing you along from behind after landing, plus you have the increased surface area of the flaps acting as a sail.

Landing uphill even with a tailwind is usually the preferred option.

I was once at Grovedale (Geelong) and witnessed 2 aircraft come in to land. They were both Piper Cheyenne III's from Essendon. One had passegers and the other had their golf clubs. One landed downhill with a 15 knot head wind and the other landed up hill with a 15 knot tail wind.

The one that landed up hill with the 15 knot tail wind pulled up much shorter than the other which did surprise me at the time, but I guess it all depends on your slope.

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I concur that this information should be in the POH.

Point 3 - I'm not aware of a limitation on ground speed for the running of the undercarriage on any aircraft, but that is a good question. You'd have to assume that the wheel and tyre combination should be able to handle the maximum speed of the aircraft, whilst on the ground.

Your limitation would be the brakes. Slowing down from 100 knots might overheat your brakes versus 50 knots so you might not be able to stop.

Landing roll can be dramatically affected by a tailwind, especially with the wind pushing you along from behind after landing, plus you have the increased surface area of the flaps acting as a sail.

Landing uphill even with a tailwind is usually the preferred option.

I was once at Grovedale (Geelong) and witnessed 2 aircraft come in to land. They were both Piper Cheyenne III's from Essendon. One had passegers and the other had their golf clubs. One landed downhill with a 15 knot head wind and the other landed up hill with a 15 knot tail wind.

The one that landed up hill with the 15 knot tail wind pulled up much shorter than the other which did surprise me at the time, but I guess it all depends on your slope.

Thanks Brent,

Will go dig through the POH.

I should have said - with my tail wind landings they are ALWAYS uphill. The slope is about 1 in 20 (5%).

Your observation on the 2 Cheyennes landing is consistent with my experience. That is - if the wind is blowing up the strip (and up the hill) at 10kts, and I approach over the trees (down the hill and into the wind) and dive it in, I am chasing the slope all the way and getting ground affect. Yet if I go around and then land downwind and up the slope, I come in heaps fast (ground speed) but it cuts through the ground affect quickly and pulls up relatively quickly, due to the uphill roll. So I guess that would also ease the punishment of the brakes.

Cheers,

Chris

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SOme of the info in this link might help :

Cheers

John

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Get the chainsaw out mate... get rid of them there gumtrees...hehe...problem solved...But the council would have to approve it first so if you put the paperwork in now, mabye your great grandchildren will bennefit from it..;)

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You might consider larger dia tyres for the Jab. Better for t/o, and also for heavy braking.

Some pilots retract full flap immediate on touchdown with a tailwind, but it seems to work best if you are heavier.

I've used 5 kts t/w as likely to add 10-15% to my run, and 1% slope to do the same,ie, + or - 5% to the run distance.

Aggressive 'forward' slipping over trees might allow you to touchdown shorter too - but with a t/w you'll have some turbulence on the lee side of the trees - just where you are slipping. It can cause some excitement if you are really low on IAS.

Nothing beats more HP of course for the t/o phase

cheers,

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Q1. TW affect on TODR

TW= 10% of TOSS = 21% increase in TODR

TW= 20% of TOSS = 48% increase in TODR

TW= 30% of TOSS = 68% increase in TODR

Q2. Relationship is the same as above just use your Vref approach speed instead.

Q3. Doubt very much you'd have any issues, BUT ask Mr Jabiru.

Q4. At 5% slope your outside all charts I know of when used in a adverse direction. However based on extrapolation probably in the order of 20% to 30% adverse affect. However I wouldn't bank on those numbers, it could be significantly more depending on your actual L/D ratio in the ldg config. From reference material this is not any easy calculation or one that I have ever seen, as thrust to weight ratios come into play for T/O as well as an exponential factor with the slope, requiring some trigonometry. And thats where I bail out!

Regards

Mick

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Cheers

John

Hey John - Very helpful article! Thanks.

Cheers

Chris

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One of the big problems with downwind takeoff and landings is the flatter flight path. it can be very seriously "off putting" to be taking off and it looks as if you are not climbing, making it easy to pull the nose up too high and get even poorer climb. For landing the approach if done properly will appear to be very flat.

Here at Rodds Bay we have quite an upslope at the start of runway 13, but there are trees behind you, so I use 13 unless there is more than about 10kts of tailwind. As I always do power off approaches I have to be very aware of wind strength to pick base turn and heading on base leg. On those days when I take off on 31 I hate to see all those big eucalypts, with very limited options if the engine fails.

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A good rule of thumb is to land uphill unless you have a downwind component of three times the slope or more. So in your case you would want at least 15kts of downwind before its worth landing down hill and into wind. I use this most days as the strip I fly out of has a small slope and it works very well.