Tailwind Takeoff ?

[201er]

I back-taxi the 100ft long displaced threshold at Central Jersey when taking off heavy and turn around on the runway. It's 50ft wide and I just barely make it around staying on the pavement with braking.

 

Tailwind penalty is massive. Just the other day I landed with a negligible tailwind and it still stretched my landing a good way. AWOS was reporting wind calm so I took the preferred runway. Wind sock showed 2-4kt direct tailwind on landing and it made the landing a good bit longer. Wouldn't want to be taking off like that.

[Yetti]

I turn around to back taxi on 50 foot runways without batting an eye.  Part of normal ops.

It may make a difference, but I start left then go right to do a left hand turn so the widest part of the turn is not directly across the narrowest part of the runway.

Edited December 29, 2016 by Yetti

[Oldguy]

The biggest problem I see with a TW takeoff is if you do it once successfully, it may become a consideration at other times.

[Danb]

27 minutes ago, Oldguy said:

The biggest problem I see with a TW takeoff is if you do it once successfully, it may become a consideration at other times.

John unfortunately you may only have one chance if unsuccessful

[joegoersch]

1 hour ago, Oldguy said:

The biggest problem I see with a TW takeoff is if you do it once successfully, it may become a consideration at other times.

I understand the increased take-off distances and (ground) speeds for tailwind take-offs and the need to be aware of them.  Not being aware of the penalties of a tailwind can be fatal.  But the exact same thing can be said for, say, density altitude.  Many people have learned that lesson the hard way.  That does NOT mean 'NEVER take off when it is hot outside".  It means know your POH, performance numbers, leave a good cushion for skill level, aged plane etc.  

It seems like some people here are saying "Never take off with a tailwind" and I'm not sure that's one of the lessons to be learned. 

E.g. when it's IFR at LDJ, Newark won't let you take off to the East.  You pretty much have to depart Runway 27.  Often, it's an east wind with IFR conditions in the east.  I don't think that doesn't mean you can't take off Rwy 27 if you have a 5 kt tailwind.  LDJ has a 4100 ft runway, and takeoff minimums published in the Chart Supplement (formerly AF/D).  If you can easily clear a 86 ft stack 825 feet from DER than I think it's a reasonable option.

Is there anyone who stands by "Never" take off with a tailwind ?  The POH gives performance numbers for (up to a) 10 kt tailwind. 

Edited December 29, 2016 by joegoersch

[Mooneymite]

Downwind takeoffs are a fact of life at some airports for the airlines.  Just the other day, LAX was using the 25 and 24 for departures with the wind 060/8.  The crux of the issue is to have "the numbers" for your weight.  Happily, no one ended up in the Pacific despite all the downwind takeoffs.

[chrisk]

42 minutes ago, Hyett6420 said:

I agree Pete.  My Runway is only 850 metres and is uphill for the first bit, but even fully loaded i am off well before the two thirds mark.  Option 1 was possible, Option 2 was the better of the three, but to me a tailwind is always a no no.  Richard Collins of Flying has drummed that into our skulls for decades.  

What also focusses me is everytime i take off on 26, there is a nice cemetery waiting for me at the end of the runway if i cock it up. Check out google egtr  

Im just a Pilot so what do I know.  

Andrew

There is always an exception.  For example.  KLAM has a one way runway.  The AFD (or what ever it is now called) states  RY 09/27 ALL LNDGS TO THE WEST & ALL TKOFS TO THE EAST.   If there is wind, you are either landing or taking off with a tail wind. And I am not to sure you would want to do a go around there.   There is a sizable obstacle at the end of runway 27.  Know your POH,  know the plane, and leave some margin for the unexpected.

[Vance Harral]

5 hours ago, Bob - S50 said:

Solve for T and I get 14.46 seconds to get to takeoff speed (if your plane and performance is exactly the same as the one used for POH testing).  I can now substitute in either equation to find A.  109.7 = A * 14.46.  This yields a value of A = 7.59 ft/sec²

The math above gives you an average acceleration of 7.59 ft/sec².  That doesn't mean the airplane is accelerating at a constant 7.59 ft/sec² throughout the takeoff roll.

5 hours ago, Bob - S50 said:

Filling in the known values in equation two, we get 119.8 = 7.59 * T.  Solve for T and we get 15.78 seconds.

Again, you're using a constant value for "A" in your V=AT equation, but in reality the value varies with time.

The correct math would integrate A as a function of time rather than treating it as a constant value.  Doing that requires you to know how A varies with time, which is a complex equation.  But as Carusom says, acceleration in cars and piston airplanes generally decreases as velocity increases.  Using a fixed value of 7.59 ft/sec² is giving you an optimistic answer of a 19% increase in ground roll for a 6 knot tailwind, when the reality is closer to 30%.

Edited December 29, 2016 by Vance Harral

[Bob - S50]

11 minutes ago, Vance Harral said:

The math above gives you an average acceleration of 7.59 ft/sec².  That doesn't mean the airplane is accelerating at a constant 7.59 ft/sec² throughout the takeoff roll.

Again, you're using a constant value for "A" in your V=AT equation, but in reality the value varies with time.

The correct math would integrate A as a function of time rather than treating it as a constant value.  Doing that requires you to know how A varies with time, which is a complex equation.  But as Carusom says, acceleration in cars and piston airplanes generally decreases as velocity increases.  Using a fixed value of 7.59 ft/sec² is giving you an optimistic answer of a 19% increase in ground roll for a 6 knot tailwind, when the reality is closer to 30%.

First, as I said in my post:

"Not a physics teacher, and I made some assumptions such as constant acceleration, but hey, it should be pretty close! "

I added bold for emphasis here.

Second:  I asked those with charts that allowed for TW to check my work.  Going back to the chart that someone posted, if I enter the wind correction part of the chart at an assumed 1000' takeoff roll and then move up the dashed line until I get to 6 knots, the new answer is 1200', a 20% increase.

Third:  I know that acceleration won't be constant otherwise we could accelerate forever with no speed limit.  However, I believe prop efficiency changes with airspeed (poor at zero airspeed).  To a certain point, as speed increases, prop efficiency increases at least partially offsets increases in drag.

But hey, it was just a SWAG (scientific wild ass guess) anyway.

Bob

[Bob - S50]

22 minutes ago, Mooneymite said:

Downwind takeoffs are a fact of life at some airports for the airlines.  Just the other day, LAX was using the 25 and 24 for departures with the wind 060/8.  The crux of the issue is to have "the numbers" for your weight.  Happily, no one ended up in the Pacific despite all the downwind takeoffs.

Detroit (DTW) was the same way.  They used 21/22 until there was a 10 knot tailwind and we started refusing the runway.

[laytonl]

For the past few years I've been flying out of 3,000' grass strip with 50' tress at one end and a steep slope for the last 1,500' that makes it a one way runway.  

Because of this I've tracked actual takeoff distances under a variety of conditions (weight, temp, tail wind, headwind, wet grass, tall grass).  I compare each flight to the POH.  I've found my numbers for ground roll match the POH almost exactly for a paved runway and the 50' numbers are 10% longer than book value.  

Landings are a non issue because I'm landing into the slope and almost always need to add power to taxi to mid-field.

lee

[carusoam]

Lee - what are you using to measure your actual T/O performance?

Joe - I don't think your are going to get many responses that include 'never' to describe a wide range of useable topics.  I use 'never' to describe performing a T/O without data.  Either from your plane's POH or data you have collected yourself.  But, even that is up to you as PIC...

I'll also say 'never' to landing without checking you airspeed against your groundspeed.  Subbing a good look at the windsock can do.  But knowing what the windsock was doing a half hour ago can leave you running off the runway after landing.  

'Never' can be used with... Deciding too late to go around.  This has left a Mooney pilot in NJ in the trees off the end of the runway. This was earlier this year...

 

Short runways make the performance of our planes become more critical.  A few degrees more temperature, a few degrees more incline, a few more pounds in the back, a few knots of tail wind, can add up to a conspiracy.

All of these details are hard to have memorized.  Know when to refer to the data.

Just a PP relaying what I have learned.  I learned this stuff Mostly because I don't want to accidently kill myself flying an airplane.

Best regards,

-a-

[Hank]

Yes, a quick glance at the groundspeed page on the Garmin vs ASI is a wonderful confirmation, especially at low use fields with neglected wind socks, that you are indeed landing in the right direction. I generally do this on downwind, and more than once have recalled myself as Upwind for the other runway.

i recollect two tailwind landings, both at light weight. The first I believed what I was told by someone in the ground because I couldn't find the windsock. The landing was long, using most of the 5000' runway, Very squirrelly and hard to hold centerline. Taxiing in I saw the large, faded tetrahedron, a first for me as a low time pilot.

The second was at FXE, coming in to land in 27 when ATC offered me 31 as it was closer to my current position (they vectored me 4nm out to sea in a clear VFR day). I finally touched down several thousand feet down the runway, and stopped just after crossing the other runway. The next plane they brought in on 13! Now the feeling is burned into me, squirrelly directional control, constantly weathervaning and ballooning, that sick feeling of the tail skidding out to the side . . . And runway sliding by with the plane unwilling to go where I am trying to put it. Thousands of feet of pavement passing by . . . Can't imagine trying to depart like that.

[laytonl]

15 hours ago, carusoam said:

Lee - what are you using to measure your actual T/O performance?

Joe - I don't think your are going to get many responses that include 'never' to describe a wide range of useable topics.  I use 'never' to describe performing a T/O without data.  Either from your plane's POH or data you have collected yourself.  But, even that is up to you as PIC...

I'll also say 'never' to landing without checking you airspeed against your groundspeed.  Subbing a good look at the windsock can do.  But knowing what the windsock was doing a half hour ago can leave you running off the runway after landing.  

'Never' can be used with... Deciding too late to go around.  This has left a Mooney pilot in NJ in the trees off the end of the runway. This was earlier this year...

 

Short runways make the performance of our planes become more critical.  A few degrees more temperature, a few degrees more incline, a few more pounds in the back, a few knots of tail wind, can add up to a conspiracy.

All of these details are hard to have memorized.  Know when to refer to the data.

Just a PP relaying what I have learned.  I learned this stuff Mostly because I don't want to accidently kill myself flying an airplane.

Best regards,

-a-

My measurement is seemingly not very precise as my wife calls it.  She says "we broke ground at Wayne's barbecue grill, the left of David's hanger door". What has been amazing is the consistency in the data over a lot of data points so it must be close enough.  Lrr