Takeoff Roll Question...

GreenDayPilot

GreenDayPilot

Well-Known Member
Regarding the takeoff roll for a C172..

The POH has a ground roll and a distance to clear a 50' obstacle.

What exactly does that 50' obstacle distance provide? To my understanding it simply means you're going to clear the obstacle...

My question is, is there a clearance by which you will clear it? 1 foot? 10 feet? 100 feet? 200 feet?

A student asked me and I figured it was a good question. I'm guessing its something the manufacturer provides without publishing the altitude by which you will clear the obstacle for liability reasons...
 
I am pretty sure it is the distance over the ground from the point you begin rolling to the point at which you are 50 feet AGL. I don't think that it gives you any clearance. I will see what I can find.
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jhugz said:
I am pretty sure it is the distance over the ground from the point you begin rolling to the point at which you are 50 feet AGL. I don't think that it gives you any clearance. I will see what I can find.
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Well, many POH's say "Distance to clear 50ft obstacle," so I think it does give some sort of clearance.
 
Assuming the conditions given in the POH, the 50' Takeoff Distance is the length of runway/distance the plane will need to go from a complete stop to reaching an altitude of 50' AGL. Generally it will be calculated with the use of flaps and earlier rotation speed.
 
I think the point is that it will CLEAR the 50' obstacle. If you're 50' feet AGL after the given distance, you'd still strike the obstacle.... so I'm guessing you'd have to be at least 51', but I'm assuming their lil' test made it a more round number like 50', in which case you'd be 100 AGL' (50' obstacle + 50' clearance= 100' AGL)...
 
GreenDayPilot said:
I think the point is that it will CLEAR the 50' obstacle.
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You need to draw a distinction between the interpretation and the actual requirement. Here's what Part 23 states:

§ 23.53 Takeoff performance.

(a) For normal, utility, and acrobatic category airplanes, the takeoff distance must be determined in accordance with paragraph (b) of this section, using speeds determined in accordance with §23.51 (a) and (b).
(b) For normal, utility, and acrobatic category airplanes, the distance required to takeoff and climb to a height of 50 feet above the takeoff surface must be determined for each weight, altitude, and temperature within the operational limits established for takeoff with—
(1) Takeoff power on each engine;
(2) Wing flaps in the takeoff position(s); and
(3) Landing gear extended.
(c) For commuter category airplanes, takeoff performance, as required by §§23.55 through 23.59, must be determined with the operating engine(s) within approved operating limitations.
​
There is nothing in the requirements about clearing any obstacle.
 
tgrayson said:
You need to draw a distinction between the interpretation and the actual requirement. Here's what Part 23 states:

§ 23.53 Takeoff performance.

(a) For normal, utility, and acrobatic category airplanes, the takeoff distance must be determined in accordance with paragraph (b) of this section, using speeds determined in accordance with §23.51 (a) and (b).
(b) For normal, utility, and acrobatic category airplanes, the distance required to takeoff and climb to a height of 50 feet above the takeoff surface must be determined for each weight, altitude, and temperature within the operational limits established for takeoff with—
(1) Takeoff power on each engine;
(2) Wing flaps in the takeoff position(s); and
(3) Landing gear extended.
(c) For commuter category airplanes, takeoff performance, as required by §§23.55 through 23.59, must be determined with the operating engine(s) within approved operating limitations.
​
There is nothing in the requirements about clearing any obstacle.
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So then POH's should be reworded/interpreted as "distance to achieve 50ft above takeoff surface elevation."

Well poop in my pants.
 
tgrayson said:
You need to draw a distinction between the interpretation and the actual requirement. Here's what Part 23 states:

§ 23.53 Takeoff performance.

(a) For normal, utility, and acrobatic category airplanes, the takeoff distance must be determined in accordance with paragraph (b) of this section, using speeds determined in accordance with §23.51 (a) and (b).
(b) For normal, utility, and acrobatic category airplanes, the distance required to takeoff and climb to a height of 50 feet above the takeoff surface must be determined for each weight, altitude, and temperature within the operational limits established for takeoff with—
(1) Takeoff power on each engine;
(2) Wing flaps in the takeoff position(s); and
(3) Landing gear extended.
(c) For commuter category airplanes, takeoff performance, as required by §§23.55 through 23.59, must be determined with the operating engine(s) within approved operating limitations.
​
There is nothing in the requirements about clearing any obstacle.
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AWESOME! Thanks... I thought it might be in section 23... I was just too lazy to check, haha
 
If you don't smack the obstacle, then you cleared it. Of course, your aircraft may now be brown instead of white, but hey, that'll wash right off.
 
May be some day whoever writes these regulations will understand the difference between acrobatic and aerobatic............:rotfl:
 
calcapt said:
Sorry, I completely misunderstood your post. :o

You are 100 percent correct.
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I have NEVER done that. Other people just misunderstand their misunderstanding which is mistakenly misunderstood as my misunderstanding when in fact it is their misunderstanding misconstrued as my misunderstanding- which of course it isn't.:rolleyes:

calcapt said:
You are 100 percent correct.
Click to expand...
calcapt said:
You are 100 percent correct.
Click to expand...
calcapt said:
You are 100 percent correct.
Click to expand...
calcapt said:
You are 100 percent correct.
Click to expand...
calcapt said:
You are 100 percent correct.
Click to expand...
calcapt said:
You are 100 percent correct.
Click to expand...
calcapt said:
You are 100 percent correct.
Click to expand...
calcapt said:
You are 100 percent correct.
Click to expand...
I just like the sound of it.
 
deadstick said:
Is there a difference since only the 1997 and newer 172s were certified under PArt 23?
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Not in any significant way. The only thing that can be measured is the altitude gained over the starting altitude. The actual clearance over any particular obstacle will depend on the terrain elevation where the obstacle is located, which obviously the manufacturer cannot know. A 49.9 foot obstacle located on rising terrain would not be cleared, even if you could get book performance, which is unlikely.

But if you're interested, here's the CAR 3 regulation:

TAKE-OFF
§ 3.84 Take-off.
(a) The distance required to take off and climb over a 50-foot obstacle shall be determined under the following conditions:
(1) Most unfavorable combination of weight and center of gravity location,
(2) Engines operating within the approved limitations,
(3) Cowl flaps in the position normally used for take-off.
(b) Upon obtaining a height of 50 feet above the level take-off surface, the airplane shall have attained a speed of not less than 1.3 Vs1 unless a lower speed of not less than Vx plus 5 can be shown to be safe under all conditions, including turbulence and complete engine failure.
(c) The distance so obtained, the type of surface from which made, and the pertinent information with respect to the cowl flap position, the use of flight-path control devices and landing gear retraction system shall be entered in the Airplane Flight Manual. The take-off shall be made in such a manner that its reproduction shall not require an exceptional degree of skill on the part of the pilot or exceptionally favorable conditions.
 
Blackhawk said:
Other people just misunderstand their misunderstanding which is mistakenly misunderstood as my misunderstanding when in fact it is their misunderstanding misconstrued as my misunderstanding- which of course it isn't.:rolleyes:
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I kno-o-ow...I myself was wrong once when I thought I was wrong but I wasn't.
 
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