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Operation Tips

upslope vs tailwind
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From Amy L. Hoover's Mountain & Canyon Flying Tips - 2016.  She is one of the founders of the McCall Mountain and Canyon Flying course.  Use this info at your own risk:

1.  Gradient Vs Wind

In an ideal world, pilots would always be able to land uphill with a headwind and takeoff downhill with a headwind.  But what about the times when gradient and wind are in "opposition"? Which is best, landing uphill with a tailwind, or downhill with a headwind?  Is it better to takeoff downhill with a tailwind, or uphill with a headwind? Let's look at some of these scenarios.

 

Landing uphill with a tailwind

Planning to land with a tailwind should be done with caution. Even a slight tailwind of 2-4 knots can increase ground roll by 10%.  If the runway ends in a drop-off, such as on top of a mesa or along a riverbank, and a landing is made with a tailwind, one should anticipate an updraft over the drop-off on short final. This updraft can cause the airplane to balloon or float further down the runway before touchdown, and could be problematic depending on runway length and gradient. Additionally, when landing with a tailwind the pilot will have to fly a steeper approach to compensate for increased groundspeed, which can cause visual illusions that hinder judgment of height and distance relative to a sloping runway.

 

Landing downhill with a headwind

A strong headwind is required to overcome the increase in landing roll that a downhill landing creates; if the wind is strong enough to cancel the effects of a large downhill slope, expect a lot of turbulence on the approach, particularly if there are obstacles or trees. If the approach is flown at a faster airspeed to compensate for gusts and turbulence, the increase in groundspeed will lengthen the landing roll.  Also, when landing downhill the plane will float, and float, and float.  Pilots may find it hard to touch


 

 

 

down because the ground keeps dropping out from under the airplane. Once on the ground the pilot is counting on brakes to stop (going downhill). Heavier airplanes have more inertia and can be hard to stop.

 

Taking off downhill with a tailwind

Because a 10% increase in groundspeed increases the takeoff roll by 20%, and every 1.0% of runway downslope equals approximately 10% more effective runway, it takes about 1.0% downslope to counter every 2-3 knots of tailwind for most general aviation aircraft. Thus, for an aircraft with a takeoff speek of 60-70 knots, a 6-10 knot tailwind would require at least a 3.0% downslope to neutralize the effects of wind.  If the downsloping runway ends in a drop-off, the plane may become airborne or fly in ground effect, but will encounter a downdraft over the drop-off once it leaves the runway.

Turbulence will often accompany this downdraft, and water will amplify it. This can be a sticky situation, especially when launching off a mesa or a strip in a river canyon. If no turns can be made and the departure must be flown with a tailwind due to terrain, downdrafts and turbulence may continue along the departure path. The only option a pilot has is to lower the nose and maintain airspeed.

 

Taking off uphill with a headwind

Based on the relationships of groundspeed and gradient, an airplane will generally require a significant headwind to counteract more than a slight uphill slope.  If the runway is short, choose a takeoff abort point; if the airplane is not in ground effect and accelerating by that point it may not outclimb the gradient. Aborting a takeoff uphill provides more rapid deceleration and less distance than a runway without slope.

Anticipate wind shear and turbulence over trees or obstacles after departure. Also, when taking off uphill, chances are the terrain beyond the departure end of the airstrip rises, and may exceed the climb capability of the aircraft.

Use caution when mixing wind and runway gradient.  Many times runways with gradient have surrounding obstacles and terrain that can exacerbate the effects of downdrafts, wind shear, and turbulence on approach and departure. On short runways,


 

 

 

especially with obstacles in the approach or departure path, landing and taking off with more than a light wind may not be a good idea.

 
My home airport is sloped approx. 6% and 1450ft long. My rule is if wind is less than 22 mph I always land uphill take off down hill in my 180, if it's gusty you just have to make a decision.
I have landed here many sometimes with a 15-18 mph tailwind, it works fine. Just know your own limits.
 
There's been lots written on this subject by experienced back country pilots and some good rules of thumb.  To boil it down, there needs to be a helluva wind to justify a down slope landing.   For me, as a rule, I land up slope.  If the tail wind is more than 10-15 give or take, I'll go land some where else.
 
Well then, 8-10kts on the tail would be a "breeze" ?? With all that room you could even do that with 20 degrees of flap all day. 



Sent by Lilly and Rylan's Campa

On Mar 10, 2017, at 6:32 PM, Patrick Daniels (inke22@ymail.com) <mailer@mail2.clubexpress.com> wrote:


Quoted Text

Open approach on both ends. Dry grass, hard surface. Clear approach path.  Runway lenght aprox 3000 ft. 

Rgs

patrick



What kind of approach is available? Pretty open? Over trees? Have to slide around a corner to get to final?  How long is the landing area and is there a decent rollout area? How smooth is the ground under the grass? Wet? How is the go-around path? Many questions to answer prior to making that choice.


Sent by Lilly and Rylan's Campa

On Mar 10, 2017, at 11:55 AM, Patrick Daniels (inke22@ymail.com) <mailer@mail2.clubexpress.com> wrote:

Hi all, 

     On the 185, on a upsloping runway (moderate upslope, grass) would you prefer to land up slope with a 8-10 kt tailwind or downslope with the wind in front? 
      This happened to me in another plane, but was wondering about it in a taildragger. 

Rgs,

Patrick. 
 

Quoted Text

Open approach on both ends. Dry grass, hard surface. Clear approach path.  Runway lenght aprox 3000 ft. 

Rgs

patrick



What kind of approach is available? Pretty open? Over trees? Have to slide around a corner to get to final?  How long is the landing area and is there a decent rollout area? How smooth is the ground under the grass? Wet? How is the go-around path? Many questions to answer prior to making that choice.


Sent by Lilly and Rylan's Campa

On Mar 10, 2017, at 11:55 AM, Patrick Daniels (inke22@ymail.com) <mailer@mail2.clubexpress.com> wrote:

Hi all, 

     On the 185, on a upsloping runway (moderate upslope, grass) would you prefer to land up slope with a 8-10 kt tailwind or downslope with the wind in front? 
      This happened to me in another plane, but was wondering about it in a taildragger. 

Rgs,

Patrick. 
 

Generally uphill.

 

 

-----Original Message-----
From: "Patrick Daniels (inke22@ymail.com)" <mailer@mail2.clubexpress.com>
Sent: Friday, March 10, 2017 13:54
To: "Operation Tips" <OperationTips@skywagons.club>
Subject: upslope vs tailwind <<$168043466211$>>

Hi all, 

     On the 185, on a upsloping runway (moderate upslope, grass) would you prefer to land up slope with a 8-10 kt tailwind or downslope with the wind in front? 
      This happened to me in another plane, but was wondering about it in a taildragger. 

Rgs,

Patrick. 
 
What kind of approach is available? Pretty open? Over trees? Have to slide around a corner to get to final?  How long is the landing area and is there a decent rollout area? How smooth is the ground under the grass? Wet? How is the go-around path? Many questions to answer prior to making that choice.


Sent by Lilly and Rylan's Campa

On Mar 10, 2017, at 11:55 AM, Patrick Daniels (inke22@ymail.com) <mailer@mail2.clubexpress.com> wrote:

Hi all, 

     On the 185, on a upsloping runway (moderate upslope, grass) would you prefer to land up slope with a 8-10 kt tailwind or downslope with the wind in front? 
      This happened to me in another plane, but was wondering about it in a taildragger. 

Rgs,

Patrick. 
 
Hi all, 

     On the 185, on a upsloping runway (moderate upslope, grass) would you prefer to land up slope with a 8-10 kt tailwind or downslope with the wind in front? 
      This happened to me in another plane, but was wondering about it in a taildragger. 

Rgs,

Patrick. 
 
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