Downwind Takeoffs

[Ed Cesnalis]

Both 09 and 27 had 15kt+ tailwinds this morning. I chose niner because it is downhill, the Bonanza behind me chose 09 because he thought the mid-field sock favored 09.

 

I went first and it took me 4-5,000' of runway to establish a positive rate of climb. Directional control was challenging and the climb when I finally hit the headwind was intimidating.

 

What is the best practice or thinking when the socks oppose each other? Which are worse tailwinds or headwinds?

[CT4ME]

IMHO a 15kt+ tailwind is a serious thing, perhaps worse than a stiff crosswind, especially at your DA. I'd wait until one direction or the other becomes dominant. Why would headwinds be a problem?

Tim

[Ed Cesnalis]

Why would headwinds be a problem?

 

When the socks at either end oppose each other then there will be wind sheer somewhere in between.

 

Today's tailwind first meant high speed take off roll into wind sheer but at least I had a headwind at the departure end.

 

If both ends present a headwind then the departure end will have the tailwind and if the wind sheer in the middle is encountered without enough margin then the transition to tailwind might mean descending with a high ground speed.

[Jim]

It's the pilot's call, but I'd stay on the ground if it were an elective flight.

[Jim Meade]

You're going to have to give me the slow learner version of this. When you are on the ground with a tailwind, you will have to achieve take off speed per the ASI, just as you would into a headwind. Ground speed is quite different, of course. Once you are airborne, it would seem to me you are in the fluid medium and what your ASI shows is how your plane acts.

I didn't get the part about taking distance for the climb. Do you mean on the ground? Total? I hope we don't end up in a downwind turn discussion.

[josjonkers]

Both 09 and 27 had 15kt+ tailwinds this morning. I chose niner because it is downhill, the Bonanza behind me chose 09 because he thought the mid-field sock favored 09.

 

I went first and it took me 4-5,000' of runway to establish a positive rate of climb. Directional control was challenging and the climb when I finally hit the headwind was intimidating.

 

What is the best practice or thinking when the socks oppose each other? Which are worse tailwinds or headwinds?

 

You have some weird local wind conditions there in California. Good thing you have a long rwy. I also assume 09 take off would ultimatly bring you to lower terrain? Does 27 t/o force you to climb soon after getting off the ground?

[Roger Lee]

Hi Ed,

 

My field at Ryan is pretty flat in all directions and the Mnts. are at least 8-10 miles away. We have rwy 06-24 and 33-15. The winds here can be 90 degrees once in a while, but not very often.I always pick either the crosswind or the closest to a headwind. A 15 knt tail wind can cause an issue if you all of a sudden hit a differential wind part way down the runway and I would make my takeoff speed a little higher at lift off and all the way through for a little altitude. Too slow here with a severe wind shift could make a marginal situation worse real quick. We all know you can takeoff with a cross wind (certainly not preferable), but speeds need to be much higher with a 15 knt tail wind and it could bite you in the rear so to speak if things change faster than you can. 15 knt tailwind is a little stiff to say the least.

[Ed Cesnalis]

You're going to have to give me the slow learner version of this. When you are on the ground with a tailwind, you will have to achieve take off speed per the ASI, just as you would into a headwind. Ground speed is quite different, of course. Once you are airborne, it would seem to me you are in the fluid medium and what your ASI shows is how your plane acts.

I didn't get the part about taking distance for the climb. Do you mean on the ground? Total? I hope we don't end up in a downwind turn discussion.

 

Today there were 2 reasons it took me 5,000' of runway to establish climb. First it took a lot of runway to get flying speed with a gusty tailwind, 2nd once off of the runway and encountering the 180 degree change in wind direction at the same time, i personally required some speed before I was willing to get away from the ground and it wasn't until the 6,000' mark when I had the wind on my nose and Vx, that I could really climb, then my climb went to 1,500'/min.

 

In a laminar flow wind, once airborne everything is relative and no problem but here is a collision of a turbulent wind exiting a very big canyon and hitting the prevailing wind mid-runway. To complicate things there is a very big glacial terminal moraine at the canyon exit as well as a 600' high ridge in the pattern. You can realize sink above this runway that can overcome a CT.

[Ed Cesnalis]

It's the pilot's call, but I'd stay on the ground if it were an elective flight.

 

Certainly the right call, lately I have been using the spring winds as an opportunity to refine my skills. I have had some nightmare flights in the CT in the mountains and it was good that I have explored the plane's limitations.

[Ed Cesnalis]

... Does 27 t/o force you to climb soon after getting off the ground?

 

It does, and the sight picture just don't seem right, people do stall/spins right into the end of the runway cause they are fooled, and heavy, and not leaned for a 7,200' take off, ... etc.

 

This Cessna went in just across from my hangar for those reasons.

 

[Ed Cesnalis]

...speeds need to be much higher with a 15 knt tail wind and it could bite you in the rear so to speak if things change faster than you can. 15 knt tailwind is a little stiff to say the least.

 

Take-offs with high ground speeds feel even worse than landings with high ground speeds. I hate them both.

 

The deer migration is just ending, meaning turkey vultures are plentiful, 3 of them and a bald eagle decided to join the fun on my landing. I had eye to eye visual with the buzzards climbing as I was descending, a few thousand feet of wind sheer over the runway to avoid with the eagle being my last obstacle.

 

I'm going to get a leather helmet

[mocfly]

I'm curious why you would take off in conditions which indicate that wind shear may be present?

 

[N89WD]

Certainly the right call, lately I have been using the spring winds as an opportunity to refine my skills. I have had some nightmare flights in the CT in the mountains and it was good that I have explored the plane's limitations.

"Ed the CT stunt pilot".....15kt tailwind takeoff in a CT....no way

[Ed Cesnalis]

I'm curious why you would take off in conditions which indicate that wind shear may be present?

 

Such conditions can be common.

[mocfly]

Next time you fly in conditions like that please take a video and post it. I would be interested in what flying in those conditions in our plane would look like.

 

What is it about the airport location that lends itself to those conditions being common?

[Roger Lee]

Nothing changes for a 15 knot tail wind take off except you need 15 knots more speed. I've been there a time or 2 for a take off and a landing, but the extra ground speed doesn't bother me, just the slow full stall guys.

 

That ought to start a discussion.

[Jim Meade]

Here are some possible issues with taking off and landing with a strong tailwind

1. We are not used to it so our habits and visual cues may desert or confuse us.

2. The idea that the wind will be gusty with a tailwind but not a headwind is dubious on the face of it. We add a few knots (there are various rules of thumb for this) for a gusty head or crosswind so one would assume the same solution would work for a gusty tailwind.

3. There is more momentum at touchdown because there is more velocity. That translates into a need for more room to slow and stop. Obviously short field operations with a tailwind are problematic. However, so is the old habit of turning off at a certain taxiway which one might now over run.

4. If the runway is wet, especially if there is any standing water, the chances of hydroplaning increase. Per AFH 8-34, dynamic hydroplaning starts with at least 1/10" of water and the speed in knots is 8.6 times the square root of the main tire pressure in pounds/inch, so if you are running 36 lbs of tire pressure the dynamic hydroplaning threshold speed is 51.6 knots. Once dynamic hydroplaning starts it can persist at a lower speed. Nearly all of us would land at more than 52 knots ground speed with a 15 knot tailwind. Some would land at 65 or 70 knots with a 15 knot tailwind.

5. It may take more braking when landing at higher speeds if you want to stop in the same distance as you do with no or a headwind. Hopefully the brakes can handle it.

6. An accident just at or soon after a tailwind touchdown means you are going faster when you hit the

[Ed Cesnalis]

Next time you fly in conditions like that please take a video and post it. I would be interested in what flying in those conditions in our plane would look like.

 

What is it about the airport location that lends itself to those conditions being common?

 

 

I am saving for a Hero 3 but don't have a video camera yet.

 

The photo below is shot from downwind looking over the runway. The peak off of my wingtip is less than 1 mile and over 13,000' with higher peaks behind. The lake is in a giant canyon that produces a turbulent 90 degree crosswind that hits high terrain on the other side of the runway and returns in a horizontal rotor. The prevailing west wind mixes in mid field.

 

The airports on the east side of the sierra are all leased from Los Angeles DWP and they are located at different bodies of water that got diverted to Los Angeles by Molholland. The location of this airport is like a bad joke.

 

 

[Adam]

The following is a paid political announcement...

 

CharlieTango flies out of a place that has some of the most beautiful scenery on earth. The winds on a good day are unpredictable and the mountain flying conditions cause those from an LSA through King Air to be a little white nuckled at times. Now me, I'd be chicken shit to take an LSA up to Mammoth without a whole lot more experience in mountain flying and a highly competent CFI sitting next to me, but hey, I'm a fair weather joy riding burger chaser and am happy to admit it. If I'm at runup and I'm seeing two wind socks pointing in different directions on the same runway, I'm taxing back to my hangar and sitting in a lawn chair to see how it affects others who are venturing out or coming in. I'd imagine that after several years of flying in and out of Mammoth in an LSA that CharlieTango has to be one of the best stick and rudder paper airplane flyers out there! I have flown through here many times (as a passenger in a King Air 350), the Sierra Nevada range is no place for unskilled pilots.

 

(Ed, you can drop $20 bucks out the window next time you fly over for the endorsement)

 

haha!

[Jim Meade]

I suppose I'm going to get flamed, but I am one of a fairly large group of people that really believe we can converse without vulgarity. For us, the vulgarity doesn't strengthen the message, it distracts and detracts from it.

[Ed Cesnalis]

...

 

(Ed, you can drop $20 bucks out the window next time you fly over for the endorsement)

 

haha!

 

I would have to bust the Class Bravo, how about I buy you a buffalo burger at Catalina?

[Ed Cesnalis]

What is it about the airport location that lends itself to those conditions being common?

 

There was a convergence of a typical morning east wind and a more general west wind.

 

There was also a south wind coming out of convict canyon and it hits the big moraine and rotors across the highway and runway.

 

Next this south rotor wind hits doe ridge and splits and rotors back horizontally.

• West - Prevailing
  
• East - Colliding with west
  
• South - Colliding with terrain and rotoring
  
• North - Horizontal rotor off of east and west side of Doe Ridge
  

The red lines are supposed to show the various winds.

 

First photo is abeam 09 numbers looking south

 

Second photo is short final for niner and shows the moraine and Doe Ridge.

 

 

 

The end result is wind sheer in the runway environment.

 

[Doug G.]

I agree completely Jim.

[Mick]

God bless you son

I'm an 82 year old 900 hr pilot who has spent his whole life as a "flat lander" (Long Island, NY and Fort Pierce Fla.).

I got my ticket and Instrument rating about at my 70 th birthday.

If I saw conditions like that I would be loath to even sit in a plastic chair in front of the hanger.

We each have our own.

[mocfly]

Great place for an airport.......

 

I would probably join the others in a chair and watch.