Takeoff Ground Roll

Sport Pilot

Sport Pilot

Pre-takeoff checklist
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I am using the Airplane Takeoff Distance graph in my book to find out my takeoff ground roll over 50ft obstacle with full fuel, 29C, 5kt headwind, altimeter 29.64.

My approximate calculations are 29.64 is 280 pressure altitude conversion. The airport elevation is 480, so I have 760 pressure altitude.

The graph I am looking at does not allow for my weight of 1320lb or my low pressure altitude. (Picture attached)

Would someone KINDLY give me guidance? Is there another chart I should be looking at?
 

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Too much math for pressure altitude.
Put 29.92 in the kollsman to get pressure alt. The chart has a temp correction built in to get density altitude.
Work across from there.
 
It looks like the airplane used for the example is much heavier. It’s probably more than 1320 empty.

If you’re studying for the written, stick with what’s in the book.
 
lexpilot said:
Too much math for pressure altitude.
Put 29.92 in the kollsman to get pressure alt.
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Easy to say if you’re in the airplane already, but what about if you need to know it before the flight? What will you do then?
 
Also see the line SL below 2000? That means sea level.
You're not in Death Valley are you.
Second, what weight are you using? The load you have? Supposed to use total, basic empty, fuel, pax, cargo etc..
 
Ryanb said:
Easy to say if you’re in the airplane already, but what about if you need to know it before the flight? What will you do then?
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Doesn't everyone have an altimeter on their desk?
Seriously, I'd check the current metar for the density altitude and back up from temp.
In reality, unless you're in Denver at 30C or flying an Aero Commander (lead sled), or in hurricane low pressure, field elevation is close enough for planning if you're not actually ready to go at the airport.
 
lexpilot said:
Doesn't everyone have an altimeter on their desk?
Seriously, I'd check the current metar for the density altitude and back up from temp.
In reality, unless you're in Denver at 30C or flying an Aero Commander (lead sled), or in hurricane low pressure, field elevation is close enough for planning if you're not actually ready to go at the airport.
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Agree. I was mostly just asking that as a rhetorical question to get you thinking. PA isn’t something we really use in a practical sense all that often like we do density altitude. Still good to know how to calculate it manually.
 
Yep, I get it if it's for a written test. However if it's real life and half an inch of mercury makes or breaks clearing a 50 footer in a 172, I'd wait for a head wind or cooler morning!
 
This is not for the written. That was completed in January 2018.

1320 lb is max weight for light sport aircraft. Need to use weight of fuel fuel (222 lbs), Jabiru (816 lbs), me (160 lbs), and 20 lbs of luggage.

Total 1218 lbs. the chart I attached goes to 2000 lbs.
 
Sport Pilot said:
This is not for the written. That was completed in January 2018.

1320 lb is max weight for light sport aircraft. Need to use weight of fuel fuel (222 lbs), Jabiru (816 lbs), me (160 lbs), and 20 lbs of luggage.

Total 1218 lbs. the chart I attached goes to 2000 lbs.
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You need to use the chart for your airplane. That chart is for some mystery aircraft on the FAA exam.
 
You need to use the chart for your airplane.
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Exactly right. This was my issue. I am looking at a generic plane and numbers. I found the POH for Jabiru. With all my calculations, looks like I need a 360 foot runway. That is calculating for the headwind, obstacle, weight, altimeter setting, and my girlfriend screaming for me to stop the plane.
 
if it so close that interpolation and a TABR reading of the chart doesnt give you a nice margin, use a different airport. planning on the edge leads to falling off the edge.......
 
unsafervguy said:
planning on the edge leads to falling off the edge.......
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But the more accurately you plan, the more accurately you can apply the desired margins.

And part of planning accurately is knowing how your performance compares to the book...if there are runway lights I can gauge my performance to +/- 100 feet. If my chart operations are +/- 300 feet, I'm limiting myself.
 
On the topic of Pressure Altitude:
In the absence of having an altimeter handy, there is a chart in the FAA Knowledge Test Supplement that allows you to convert field elevation or indicated altitude to pressure altitude based on the altimeter setting.

A slightly less accurate, but "good enough" way to calculate PA is to simply use the 1"Hg/1,000' rule of thumb. In other words, PA = IA + (29.92 - AltimeterSetting)*1,000.
 
Sport Pilot said:
I am using the Airplane Takeoff Distance graph in my book to find out my takeoff ground roll over 50ft obstacle with full fuel, 29C, 5kt headwind, altimeter 29.64.

My approximate calculations are 29.64 is 280 pressure altitude conversion. The airport elevation is 480, so I have 760 pressure altitude.

The graph I am looking at does not allow for my weight of 1320lb or my low pressure altitude. (Picture attached)

Would someone KINDLY give me guidance? Is there another chart I should be looking at?
Click to expand...

The chart for your airplane. If you have 1320 lb airplane and that chart only goes as low as 2200 it can't be for your airplane.
 
If you are flying "the book" numbers in a real world, make it or break it situation, save yourself the time and pain.
Just shoot yourself.
Look at the date on the POH and figure in all those years of additional dirt (weight) hidden in the airplane, subtle, or not so subtle misalignment in the airframe, slop in the rigging, (probably) less than optimum horse power from a many years old engine.
The aviation landscape is dotted with guys who "did the numbers" and calculated that they could probably make it.
If you own the plane, go out with a friend and a ruler, find a nice long, wet, grass strip, and figure out exactly what your plane can do. Take copious notes.
Now you have your worst case scenario, in writing. And you probably had a hell of a lot of fun doing it.

I've been making the people at NY1 scratch their heads with my antics in the Cubs. I'm trying to get real performance numbers. It's a perfect set up. A long grass runway, and telephone poles evenly space and evenly high the entire length of the runway. I know exactly how far it takes to get over the pole in each plane now. It was a real eye opener.
 
Shepherd said:
If you are flying "the book" numbers in a real world, make it or break it situation, save yourself the time and pain.
Just shoot yourself.
Look at the date on the POH and figure in all those years of additional dirt (weight) hidden in the airplane, subtle, or not so subtle misalignment in the airframe, slop in the rigging, (probably) less than optimum horse power from a many years old engine.
The aviation landscape is dotted with guys who "did the numbers" and calculated that they could probably make it.
If you own the plane, go out with a friend and a ruler, find a nice long, wet, grass strip, and figure out exactly what your plane can do. Take copious notes.
Now you have your worst case scenario, in writing. And you probably had a hell of a lot of fun doing it.

I've been making the people at NY1 scratch their heads with my antics in the Cubs. I'm trying to get real performance numbers. It's a perfect set up. A long grass runway, and telephone poles evenly space and evenly high the entire length of the runway. I know exactly how far it takes to get over the pole in each plane now. It was a real eye opener.
Click to expand...
With no performance charts, the T.O.P. Computer has been my recommendation for a lot of years...even with charts, it gives you data for conditions that your charts don't. https://sportys.com/pilotshop/takeoff-performance-computer.html

But if you have book data, you can do the same thing get a good gouge to apply pretty much across the board to book numbers and get your actual performance.
 
Making this too complicated. If the table says you can clear a 50 foot obstacle in x feet, that means with zero margin, brand new plane and engine, and test pilot technique. Real world with adequate margins will be 1.5 - 2.0 times that depending on aircraft condition and pilot skill.

My POH says I can clear the mythical obstacle in 1600 feet under standard conditions fully loaded. That's laughable in real life. For me 3000 feet is comfy and 2500 feet is cutting it close, especially as you get away from standard conditions. Determined by noting real world performance on a longer runway with margins I can live with, as in clearing the trees by more than a few feet.
 
chemgeek said:
If the table says you can clear a 50 foot obstacle in x feet, that means with zero margin, brand new plane and engine, and test pilot technique. Real world with adequate margins will be 1.5 - 2.0 times that depending on aircraft condition and pilot skill.
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Honestly, in my experience technique is a bigger driver I determining the multiplier than condition and/or skill.

Granted, skill has a lot to do with technique, but very skillful, precise pilots very often use techniques like "a couple extra knots for the wife and kids" or soft field technique on grass, or just the good "normal" technique of setting a pitch attitude and letting the airplane fly when it's ready that have a huge impact on field length performance.
 
The question is from pre-solo exam. I was not at the end of the runway wondering if I could clear this 50 foot tree. I couldnt answer question, as I do not have the POH for my specific airplane. I was using a generic chart from pilot handbook study book.
 
Also you know the 50/70 rule?

Find a point half down the runway, if you’re not at 70% takeoff speed ABORT.
Stay in ground effect full power, like DOWN in ground effect, build energy and then pull up, better to pull right before the trees then mush along into them, I see many a CFI not teach that properly.


Sport Pilot said:
... looks like I need a 360 foot runway. That is calculating for the headwind, obstacle, weight, altimeter setting, and my girlfriend screaming for me to stop the plane.
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I don’t know much about that light sport, but that sounds too good to be true for a LSA with a 160lb Pilot a ton of fuel and a 120lb pax.


Also your other issue is you’re taking off on land, that’s rookie stuff ;)
 
I'm a little confused here, what I see is "airplnae landing distance graph" but you are talking about takeoff over a 50' obstacle. What am I missing? What type of airplane is this?
Takeoff and landing are two different things.
 
Sport Pilot said:
The question is from pre-solo exam. I was not at the end of the runway wondering if I could clear this 50 foot tree. I couldnt answer question, as I do not have the POH for my specific airplane. I was using a generic chart from pilot handbook study book.
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If you don't have the proper POH then you can't really answer your question in a meaningful way.
 
Exactly right. I am flying today after work and purchasing one at the airport.
 
Merlin GT rag and tube LSA taildragger
Wind 160 at 5
Temperature 22, dew point 15
Altimeter 30.35
Runway 17 at ONZ - 590' MSL

1050 pounds takeoff weight (my lard ass, and an empty seat)

Stop with the tail right on the end of the runway - Apply brakes, run up the mighty Rotax 912 to the full screaming max! and go. Ground run 196 feet.

Roll in from the taxiway at a moderate speed (110ish degree turn), start pushing power in as I turn - as much as I felt comfortable with. Ground run (measured from the end of the runway) about 165 feet.
 
James331 said:
I don’t know much about that light sport, but that sounds too good to be true for a LSA with a 160lb Pilot a ton of fuel and a 120lb pax.
;)
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He doesn't say what he's flying but in the Skycatcher to get over a 50' obstacle you need (per the POH) between 1000' and 2800' (sea level at 0C vs 8000' at 40C). Ground roll at sea level/0C is 570'.
 
Doug F said:
He doesn't say what he's flying but in the Skycatcher to get over a 50' obstacle you need (per the POH) between 1000' and 2800' (sea level at 0C vs 8000' at 40C). Ground roll at sea level/0C is 570'.
Click to expand...

At full gross?
 
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