chrisk

Up Hill take off

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I've been flying for years, but this last weekend was my first experience with a runway with a substantial slope.  I landed at KGUR in Wyoming this last weekend.  Plenty long enough, at 5000 feet long, but with a 1.25% slope, a field elevation of 4400 feet, near by hills, and 90 degrees (DA around 7500).  Fortunately the wind was reasonably high at 10+ kts and I was 100 under gross.   

Time to pull out the POH and look carefully.  Unfortunately, the POH only lists the distance to clear a 50 foot obstacle.    But the end of the departure end of the runway is more than 50 feet above the start of the take off run.   Finally I picked an abort point where I knew I could  stop.  If I wasn't in the air, it was going to be an abort.  

What a slow take off roll heading up hill!  The plane however lifted off well before my abort point and was climbing well at Vx.    I easily cleared the near by hills. 

 I'm curious what rules you apply for an up hill take off.  And I'm curious if anyone here has experience with KGUR.   KGUR felt a bit surreal.  Its a dual use airport, but it was deserted.  The tower was closed and there was only a single aircraft on the field (Not military).  There were no people at the airport.  The FBO was a very small building with an unlocked door.   And in the back ground you could hear machine gun fire, which is presumably why there is a restricted area just north of the field.

 

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28 minutes ago, chrisk said:

I've been flying for years, but this last weekend was my first experience with a runway with a substantial slope.  I landed at KGUR in Wyoming this last weekend.  Plenty long enough, at 5000 feet long, but with a 1.25% slope, a field elevation of 4400 feet, near by hills, and 90 degrees (DA around 7500).  Fortunately the wind was reasonably high at 10+ kts and I was 100 under gross.   

Time to pull out the POH and look carefully.  Unfortunately, the POH only lists the distance to clear a 50 foot obstacle.    But the end of the departure end of the runway is more than 50 feet above the start of the take off run.   Finally I picked an abort point where I knew I could  stop.  If I wasn't in the air, it was going to be an abort.  

What a slow take off roll heading up hill!  The plane however lifted off well before my abort point and was climbing well at Vx.    I easily cleared the near by hills. 

 I'm curious what rules you apply for an up hill take off.  And I'm curious if anyone here has experience with KGUR.   KGUR felt a bit surreal.  Its a dual use airport, but it was deserted.  The tower was closed and there was only a single aircraft on the field (Not military).  There were no people at the airport.  The FBO was a very small building with an unlocked door.   And in the back ground you could hear machine gun fire, which is presumably why there is a restricted area just north of the field.

 

Depends on how steep. I operate out of an 1800’ strip that is 40 ft higher at one end. Most of the slope is before mid-field. It drops about 30 ft before the first 1000’ of runway. I typically land up hill (in spite of the 330ft displaced threshold) and take off downhill unless the winds are well above 15kts.

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Check the T/O performance charts for notes at the bottom...

I have seen some notes... but don’t recall all of the details...

All of my charts are noted with level, dry, hard surface... or level dry grass.

 

Grab a physics book, and start working out the mechanics...  compare how much energy needs to be added to the system to raise the plane the extra 20’... example... 2% grade of 1,000’ T/O length... is 20’...

or worst case 1.25% of 5k’.... 62.5’  how much you would need to climb if you use the whole runway...

Everything counts including DA, and RH...

 

While collecting experience...

A great time to have CloudAhoy measure your actual T/O distances... to compare to what your expectations were...

You will probably find it adds a few seconds to the T/O roll, that could add about 200’ additional feet....? Many variable to consider including weight of the plane...

PP thoughts only not a CFI...

Best regards,

-a-

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35 minutes ago, chrisk said:

 I'm curious what rules you apply for an up hill take off.  And I'm curious if anyone here has experience with KGUR.   KGUR felt a bit surreal.  Its a dual use airport, but it was deserted.  The tower was closed and there was only a single aircraft on the field (Not military).  There were no people at the airport.  The FBO was a very small building with an unlocked door.   And in the back ground you could hear machine gun fire, which is presumably why there is a restricted area just north of the field.

 

Sounds like a lot of the little airports in the western half of the country.

We looked at going to KGUR during the eclipse but wound up just NW of there at Converse County airport by Douglas.

Every time I've done an "uphill" takeoff it was a non-event, but maybe I've been lucky.   I do still try to pay attention to surrounding terrain and have some sort of plan, but other than that I don't do much special.

 

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Good for you for getting out the POH and thinking this through. An abort point is an excellent idea for any takeoff, but especially in critical situations. 

A useful rule of thumb is that a 1% gradient is about equal to a 10% addition (down hill) or reduction (uphill) in runway length. Using this and the POH takeoff charts for headwind or tailwind will help you decide what to do. 

Some mountain airports are one way in and out due to obstacles/terrain.

Skip

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You might try the 70/50 rule for each departure.

Sent from my Pixel 2 XL using Tapatalk

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The 70/50 rule of thumb (70% of takeoff speed by 50% of runway) turns out to not be very conservative. Theoretically, it gets you to takeoff speed at 100% of the runway and doesn’t allow for any obstacles. But, it’s a good start. Maybe 80/50 would be better. 

Skip

50-70_20190704_0002.pdf

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Something else worth mentioning is that the published slope calculations are sloppy.  Often just rise over run from threshold to threshold.  We have the technology with google maps to check the slope in sections for a more accurate picture. An airport with a 50’ drop over 4000’ has a 1.25% grade but if 40’ of the drop occurs in the first 1200’ that’s 3.33% and will have a profound affect on initial ground roll.

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33 minutes ago, Shadrach said:

Something else worth mentioning is that the published slope calculations are sloppy.  Often just rise over run from threshold to threshold.  We have the technology with google maps to check the slope in sections for a more accurate picture. An airport with a 50’ drop over 4000’ has a 1.25% grade but if 40’ of the drop occurs in the first 1200’ that’s 3.33% and will have a profound affect on initial ground roll.

This should not be the case.  The slope is in the first half or first 3000' of the runway (which ever is shorter).  So unless an equal slope is listed for both ends of the runways it is not threshold to threshold.  Many runways only list a slope for one end and not the other.

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Any particular reason you did not takeoff downhill? What was the tailwheel component? The general rules of thumb, absent POH guidance is:

Runway gradient:  each degree of slope means a 10% change in takeoff (or landing) distance.

Tailwind: 10% increase in takeoff distance for every 2 kts tailwind (there's actually a formula for this one but this rule of thumb is reflected in a number of aircraft performance tables and is fairly conservative)

Tailwind takeoffs on sloped runways are a staple of mountain airports. Slope and as surrounding terrain are the two main reasons for one-way-in/one-way-out airports)

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10 hours ago, PT20J said:

Good for you for getting out the POH and thinking this through. An abort point is an excellent idea for any takeoff, but especially in critical situations. 

A useful rule of thumb is that a 1% gradient is about equal to a 10% addition (down hill) or reduction (uphill) in runway length. Using this and the POH takeoff charts for headwind or tailwind will help you decide what to do. 

Some mountain airports are one way in and out due to obstacles/terrain.

Skip

Skip has it right.  There is a reason why they do runway slopes as a %.    They help you calculate your ground roll distance.     I always calculate it (and airlines do it this way)  was 1% conversion is,  1%  x 10 =   10,  then double it for uphill.   So add 20% to your takeoff distance.     Downhill is.  1% x 10 =  10, the take half.  So a downhill slope would be about 5% decrease of your takeoff roll.  

 

So your calculation should be,  1.25x10=  12.5.  Then 12.5x2=  25% increase to your distance.    So if your takeoff distance was calculated at 1000'  your slope correction would be 1250'  takeoff roll.  

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2 hours ago, midlifeflyer said:

Any particular reason you did not takeoff downhill? What was the tailwheel component? The general rules of thumb, absent POH guidance is:

Runway gradient:  each degree of slope means a 10% change in takeoff (or landing) distance.

Tailwind: 10% increase in takeoff distance for every 2 kts tailwind (there's actually a formula for this one but this rule of thumb is reflected in a number of aircraft performance tables and is fairly conservative)

Tailwind takeoffs on sloped runways are a staple of mountain airports. Slope and as surrounding terrain are the two main reasons for one-way-in/one-way-out airports)

In short, I could take off up hill with a headwind and climb over some hills(1200 feet).  Or I could take off down hill with a strong tail wind and climb over a smaller hill (200 to 300 feet tall).    

For a down wind take off,  the tailwind would add 50+% increase for take off roll, and an  aborted takeoff down hill with a tail wind is going to be a serious challenge.   And  I really wanted to be able to abort if things were not going well.    Taking off down hill (per DP)  requires a climb of 363 feet per mile, until 500 above the runway end.  With a 10+ knot tail wind, the climb rate per minute needs to be higher (around 600 fpm)

An up hill take off requires approximately the same rate of climb until about  2000 ft above the runway end, but the climb rate per minute is much closer to 400 fpm.    For me, the option to abort and better climb rate per nm made the decision.

 

I've put the DP data below to help give an idea.

Elevation for Rwy 14 is 4401, for Rwy 32 its 4337

TAKEOFF MINIMUMS: Rwy 14,300-2½ or std. w/min.
climb of 363’ per NM to 4800. Rwy 32, std. w/min. climb
of 360’ per NM to 6500 or 2400-3 for climb in visual
conditions.
DEPARTURE PROCEDURE: Rwy 14, climb heading 141°
to 5800 before proceeding on course. Rwy 32, climbing
right turn heading 070° to 6500 before proceeding on
course or for climb in visual conditions cross Camp
Guernsey Airport at or above 6700 before proceeding on
course.
TAKEOFF OBSTACLE NOTES: Rwy 14, vehicles on road
42' from DER, 209' right of centerline, up to 15'
AGL/4334' MSL. Trees beginning 731' from DER, 336'
right of centerline, up to 45' AGL/4564' MSL. Rwy 32,
trees beginning 181' from DER, 155' left of centerline, up
to 45' AGL/4424' MSL. Trees beginning 999' from DER,
192' right of centerline, up to 45' AGL/4504' MSL.

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43 minutes ago, chrisk said:

In short, I could take off up hill with a headwind and climb over some hills(1200 feet).  Or I could take off down hill with a strong tail wind and climb over a smaller hill (200 to 300 feet tall).    

For a down wind take off,  the tailwind would add 50+% increase for take off roll, and an  aborted takeoff down hill with a tail wind is going to be a serious challenge.   And  I really wanted to be able to abort if things were not going well.    Taking off down hill (per DP)  requires a climb of 363 feet per mile, until 500 above the runway end.  With a 10+ knot tail wind, the climb rate per minute needs to be higher (around 600 fpm)

An up hill take off requires approximately the same rate of climb until about  2000 ft above the runway end, but the climb rate per minute is much closer to 400 fpm.    For me, the option to abort and better climb rate per nm made the decision.

 

I've put the DP data below to help give an idea.

Elevation for Rwy 14 is 4401, for Rwy 32 its 4337

TAKEOFF MINIMUMS: Rwy 14,300-2½ or std. w/min.
climb of 363’ per NM to 4800. Rwy 32, std. w/min. climb
of 360’ per NM to 6500 or 2400-3 for climb in visual
conditions.
DEPARTURE PROCEDURE: Rwy 14, climb heading 141°
to 5800 before proceeding on course. Rwy 32, climbing
right turn heading 070° to 6500 before proceeding on
course or for climb in visual conditions cross Camp
Guernsey Airport at or above 6700 before proceeding on
course.
TAKEOFF OBSTACLE NOTES: Rwy 14, vehicles on road
42' from DER, 209' right of centerline, up to 15'
AGL/4334' MSL. Trees beginning 731' from DER, 336'
right of centerline, up to 45' AGL/4564' MSL. Rwy 32,
trees beginning 181' from DER, 155' left of centerline, up
to 45' AGL/4424' MSL. Trees beginning 999' from DER,
192' right of centerline, up to 45' AGL/4504' MSL.

Just like you did,  there is more to this than takeoff distance and obstacles.    Handling on the ground,  aborted takeoff distance, wind speed are all other factors to consider.  You have to run the numbers with each,  gradient, windspeed, and DP's. And see what makes sence.  

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The effects of runway slope cannot be easily canned because the net effect is dependent upon acceleration and that is a factor of thrust. The number is somewhere between 2 and 4 per 1 %  of slope.Thus thrust to weight ratio becomes relevant. Very high thrust aircraft will be less affected than low thrust aircraft. Obviously this means, turbo vs non-turbo etc. and even an inch off the prop blade can have an effect. In order to get a really accurate number you really have to flight test to get an acceleration factor unless you can get a net thrust number of the particular power plant and propeller combination. My source is Aerodynamics for Naval Aviators. If you don't have a copy I suggest it, which is in print and Axioms of Flight, which is out of print but often available on Amazon. All that said, PT20J's suggestion of the 70/50 rule is very sound advice.  

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3 minutes ago, GeeBee said:

The effects of runway slope cannot be easily canned because the net effect is dependent upon acceleration and that is a factor of thrust. The number is somewhere between 2 and 4 per 1 %  of slope.Thus thrust to weight ratio becomes relevant. Very high thrust aircraft will be less affected than low thrust aircraft. Obviously this means, turbo vs non-turbo etc. and even an inch off the prop blade can have an effect. In order to get a really accurate number you really have to flight test to get an acceleration factor unless you can get a net thrust number of the particular power plant and propeller combination. My source is Aerodynamics for Naval Aviators. If you don't have a copy I suggest it, which is in print and Axioms of Flight, which is out of print but often available on Amazon. All that said, PT20J's suggestion of the 70/50 rule is very sound advice.  

Takeoff distance charts account for "thrust' to weight ratio.  For piston props it's actually power to weight ratio.  

That book was written in the 60s.  Still good and used for college courses

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Power to weight merely expresses the delivered horsepower but not the thrust. We got into this with PA18's and different propeller STC's. The amount of hp converted into thrust can vary markedly with a given propeller.

All these examples have the same power, 180hp on the same airplane. Yet they have markedly different thrust ratings.

https://www.propilotsinc.com/questions-answers/#faq-2

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3 hours ago, ExpressJetter said:

Just like you did,  there is more to this than takeoff distance and obstacles.    Handling on the ground,  aborted takeoff distance, wind speed are all other factors to consider.  You have to run the numbers with each,  gradient, windspeed, and DP's. And see what makes sence.  

Exactly the reason I asked the question. Was it a knee-jerk "never take off with a tailwind" I generally hear from flatlanders, or was it an analysis of the options to choose the best course.

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3 hours ago, midlifeflyer said:

Exactly the reason I asked the question. Was it a knee-jerk "never take off with a tailwind" I generally hear from flatlanders, or was it an analysis of the options to choose the best course.

I don't have a problem with a tail wind takeoff, since the POH lists the take off distances up to 10 kts.   Beyond that, I'd be cautious.  And for some airports (Like KLAM), you need to either land or take off with a tail wind since its one way.  But of course if you take off with a tailwind at KLAM, there is no obstacle to clear, just a valley to fall into.  I was really looking for the runway slope calculations, since the POH seems silent on the topic (or I missed it). 

Thanks for all who replied.  I'll have to add the +20% for each 1% of slope to my list of rough calculations.

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32 minutes ago, chrisk said:

I don't have a problem with a tail wind takeoff, since the POH lists the take off distances up to 10 kts.   Beyond that, I'd be cautious.  And for some airports (Like KLAM), you need to either land or take off with a tail wind since its one way.  But of course if you take off with a tailwind at KLAM, there is no obstacle to clear, just a valley to fall into.  I was really looking for the runway slope calculations, since the POH seems silent on the topic (or I missed it). 

Thanks for all who replied.  I'll have to add the +20% for each 1% of slope to my list of rough calculations.

While it's not exact, it will get you a good number.  Rules of thumb get you close enough. Sometimes we as pilots love to get technical and everything flying. Imo if you need to figure out the difference between a few feet of runway, you are too close to an accident.  

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AKA, measure with a micrometer, cut with an axe. That is true of most General Aviation because CAR 3 and FAR 23 numbers are not that good.

 

 

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39 minutes ago, GeeBee said:

AKA, measure with a micrometer, cut with an axe. That is true of most General Aviation because CAR 3 and FAR 23 numbers are not that good.

 

 

Its funny,  after flying with many many people you learn there are a million ways to fly a plane.  Sometimes people think there is only 1 way and everything else is wrong. It always seems the best pilots are the ones that can adapt, overcome,  and work with rules of thumb vs concrete #'s.  Just my opinion. 

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1 hour ago, GeeBee said:

AKA, measure with a micrometer, cut with an axe. That is true of most General Aviation because CAR 3 and FAR 23 numbers are not that good.

 

 

Measure with a micrometer.

Mark with chalk.

Cut with an axe.

I've heard this in many contexts, but today is the first time for aviating . . . . But the concept still applies.

I don't recall doing very much special when visiting non-flat airports, although significant downhill landings can be strange, floating along with the runway falling away just about the same rate that I'm descending . . . Makes for longer landings. Taking off uphill can also take longer. Just don't go anywhere that makes you worry about getting in or out.

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3 hours ago, ExpressJetter said:

While it's not exact, it will get you a good number.  Rules of thumb get you close enough. Sometimes we as pilots love to get technical and everything flying. Imo if you need to figure out the difference between a few feet of runway, you are too close to an accident.  

Rules of thumb are great if they’re derived from personal experience, practice and calculations. Driven by pilot lounge chatter and internet posts? Not so much... They don’t help much in explaining one’s sins if one is fortunate enough to be around to be questioned.  I wonder if the crew that deposited Dale Jr’s Lattitude in the dirt of the end of 24 at Elizabethon we’re up on the appropriate rules of the correct thumbs?... there are indeed many ways to fly an airplane and many ways to crash an airplane as well. It takes someone very special to do either in a truly new way.

Edited by Shadrach

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It all happens really fast in a jet. There is a point where one can’t fix it in the jet as you could a single. That’s why planning is so important. Nice hearing the gouge from some of you Gents. Just ordered the Navy book. Another good book is “Everything explained for the professional pilot”

Learned a little bit about winds and sloped runways with my dads 75hp T-Craft. Taking off with a tail down hill slope is almost a requirement. There is not enough HP as mentioned to out climb the trees. Landing is just as bad, unless it’s really windy, gravity always wins. Landing down hill in a t-craft (aka glider) doesn’t work either.  

-Matt

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