Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
Landing (Stopping) Distance Of Small Aircraft  
User currently offlineFlexo From St. Helena, joined Mar 2007, 406 posts, RR: 0
Posted (7 years 2 weeks 6 days 21 hours ago) and read 10629 times:

The other day I was reading a car magazine and noticed that most modern automobiles can come to a full stop within a distance of about 40m (~120 feet) when going 100 km/h (60 mph).

Now since that is about the landing speed of small aircraft (C172, C150, etc.) I was wondering why those need almost ten times the distance to come to a stop (~300m / 1000 feet)?
Since they have wheel brakes like cars and weigh about the same should it not be possible to stop within a similar distance, or are the official minimum runway lengths always stated for the worst case scenario (i.e. wet / slippery runway) and therefore in optimal conditions you can stop way faster?

36 replies: All unread, showing first 25:
 
User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2556 posts, RR: 24
Reply 1, posted (7 years 2 weeks 6 days 21 hours ago) and read 10621 times:

The wheel diameter of a car is larger and so the brake discs are larger and more powerful. Tyre contact area of a car is correspondingly larger too. Cars have four wheel braking, light aircraft two wheels only.

I suppose the aircraft brakes could be made more powerful than they are, but that would add weight for no real gain as there aren't many 100 m tarmac runways about.  Smile



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineJamesbuk From United Kingdom, joined May 2005, 3968 posts, RR: 4
Reply 2, posted (7 years 2 weeks 6 days 21 hours ago) and read 10617 times:

Also could it be because the aircraft brakes aren't as effective straight away? Because the aircraft is still generating lift so not all the weight is on the wheels.

Just an idea I'm throwing out, not sure if its right.

Rgds --James--



You cant have your cake and eat it... What the hells the point in having it then!!!
User currently offlineBok269 From United States of America, joined May 2007, 2104 posts, RR: 0
Reply 3, posted (7 years 2 weeks 6 days 21 hours ago) and read 10612 times:

An educated guess...

Remember that cars propel themselves forward by pushing against the ground with the wheels. Airplanes propel themselves through the air by pulling/pushing against the air. As a result, when on the ground, the aircraft moves as a result of the plane pulling itself through the air. The tires move while taxiing or while landing because the airplane is pulling itself through the air, but the weight is on the tires. Now, when you brake a car, you are slowing it's direct source of forward movement-the wheels. Automobile brakes work by putting pressure on a disc or a drum that rotates with the wheel. Pressure is put against that and it works against the wheel turning. Now in an airplane, braking is done against the wheel (I am not familiar with the exact setup). However, the plane isn't moving as a result of the wheel turning. Its moving due to the propeller's pulling the plane forward against the air. When you hit the brakes, you are putting pressure against the wheel. This doesn't stop the plane's forward momentum because the plane's forward momentum was the result of the entire flight's worth of propulsion. While the propellor is at idle, the plane still has a lot of forward momentum. Stopping the wheels just makes it harder for that forward momentum to pull the plane forward. Eventually, it becomes too much, and the momentum can not pull the plane any further.



"Reality is wrong, dreams are for real." -Tupac
User currently offlineFlexo From St. Helena, joined Mar 2007, 406 posts, RR: 0
Reply 4, posted (7 years 2 weeks 6 days 21 hours ago) and read 10606 times:

Thanks for the replies!

So I guess there are several reasons why planes take longer to stop than cars:
- Continuous forward momentum applied by prop at idle
- Continuous lift generation by the wings resulting in less weight on the ground
- Shorter stopping distances are just not needed therefore the extra weight of bigger wheels / brakes is avoided

So as an extra question: What would be the absolute minumum distance (at optimal conditions) a C172 could stop? Anyone tried it?


User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2556 posts, RR: 24
Reply 5, posted (7 years 2 weeks 6 days 21 hours ago) and read 10602 times:

Quoting Bok269 (Reply 3):
An educated guess...

A few problems with your theory. Car brakes and aircraft brakes work the same way. Both put a torque on the wheel, via discs or drums, which slows the vehicle down. It makes no difference whether the wheel is driven or not. Also an idling propeller is providing quite a lot of drag, especially if it has a constant speed unit. Finally momentum is nothing to do with thrust. It is simply mass times velocity.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineSEPilot From United States of America, joined Dec 2006, 6907 posts, RR: 46
Reply 6, posted (7 years 2 weeks 6 days 21 hours ago) and read 10602 times:

Aircraft brakes are not designed for panic stops; the above posts explain why they wouldn't be able to in any case. At the time an aircraft touches down little weight is on the wheels; and consequently little braking power is available. What would be the point in any case? The runway has to be at least that long for the plane to take off anyway. In fact, most small planes are capable of landing in a shorter distance than they can take off in in any case.


The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
User currently offlineBok269 From United States of America, joined May 2007, 2104 posts, RR: 0
Reply 7, posted (7 years 2 weeks 6 days 20 hours ago) and read 10596 times:

Quoting Flexo (Reply 4):
Continuous forward momentum applied by prop at idle

Not quite what I was getting at...let me give you an analogy [looks over at dog sleeping on the couch]. When you walk a dog, you act like their brakes. You stop them from running away, slobbering over small children, etc. For argument's sake, let's say you can stop a dog one of two ways: you can hold the leash firm, or you can physically hold their legs so they can't move (not that you would, but bare with me). When you physically hold their legs back, you stop their means of using the object that delivers their energy to the ground: their legs. Thats how automotive brakes work. They stop the wheels, which use the energy to push against the ground. When you pull on the leash, you are acting like aircraft brakes; you aren't stopping the actual propulsion system, but you are giving it more resistance that it will have to overcome.



"Reality is wrong, dreams are for real." -Tupac
User currently offlineIFACN From Italy, joined Nov 2005, 153 posts, RR: 0
Reply 8, posted (7 years 2 weeks 6 days 20 hours ago) and read 10595 times:

Landing roll, on a plane, is influenced by many factors:
- weight
- air temperature/runway elevation (density altitude)
- speed at touchdown (is influenced by the preceding factors plus crosswind/gust component)
- flap setting (influences touchdown speed)
- runway slope

The C172M (1043kg max landing weight) at 15 Celsius at sea level stops in 155 meters (landing distance is 381 meters).
For temperatures above 15C, add 10% to those distances for each +15 tranche (+10% at 30C, +20% at 45C, etc.).

A.


User currently offlineKELPkid From United States of America, joined Nov 2005, 6381 posts, RR: 3
Reply 9, posted (7 years 2 weeks 6 days 20 hours ago) and read 10589 times:

I used to rent a Cessna 172 with the Horton STOL Craft kit on it. One day, I asked an instructor to show me how to take advantage of the STOL (Short Takeoff and Landing) features. On my first STOL landing, he told me to aim for the piano keys (the runway end markers). We made the first taxiway turnoff that time  bigthumbsup , the one that you'd normally use to enter the runway for takeoff.


Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineKELPkid From United States of America, joined Nov 2005, 6381 posts, RR: 3
Reply 10, posted (7 years 2 weeks 6 days 20 hours ago) and read 10583 times:

Quoting Flexo (Thread starter):
The other day I was reading a car magazine and noticed that most modern automobiles can come to a full stop within a distance of about 40m (~120 feet) when going 100 km/h (60 mph).

A Cessna 172 is indicating about 65 knots or so on a typical landing...a knot is approx. 1.2 mph, so figure on about 78 mph groundspeed (assuming no wind).

Quoting Flexo (Thread starter):
Now since that is about the landing speed of small aircraft (C172, C150, etc.) I was wondering why those need almost ten times the distance to come to a stop (~300m / 1000 feet)?

Negative-see the computation above on the speed.

Also, notice how in a car, the minimum acceptable rim diameter seems to be about 14" or so (much larger for performance models, or even a little smaller for some Korean imports)? Well, a Cessna 172 has 6.00x6" mains (the 6.00 means the rim diameter is 6", so you can imagine what the brake disk size is compared to car...TINY!). Much much less braking area, and the tire has a tiny contact patch to boot.

Hey, at least in the plane, we can do one cool thing that cars can't: control the left and right brakes independently Big grin (perfect for taxiing the plane into a tight parking spot).



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2556 posts, RR: 24
Reply 11, posted (7 years 2 weeks 6 days 20 hours ago) and read 10577 times:

Quoting Flexo (Reply 4):
Continuous forward momentum applied by prop at idle

Propellers do not apply momentum.

Quoting Bok269 (Reply 7):
Thats how automotive brakes work. They stop the wheels, which use the energy to push against the ground. When you pull on the leash, you are acting like aircraft brakes; you aren't stopping the actual propulsion system, but you are giving it more resistance that it will have to overcome.

That analogy only makes sense if you imagine the engine is providing forward thrust during the rollout. But it's at idle so with any significant forward speed is creating drag. Wheel brakes are the same, whether fitted to cars or aircraft, working in exactly the same way, via friction.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineSilverComet From Mauritius, joined Apr 2007, 85 posts, RR: 0
Reply 12, posted (7 years 2 weeks 6 days 20 hours ago) and read 10573 times:

Quoting KELPkid (Reply 9):

How does a STOL Craft Kit work? Is it some sort of feature you 'activate' whenever you want (like extra flap settings?) or is it some sort of permanent modification to the airframe/engine/wheels to alter the aerodynamic/mechanical properties?


User currently offlineKELPkid From United States of America, joined Nov 2005, 6381 posts, RR: 3
Reply 13, posted (7 years 2 weeks 6 days 20 hours ago) and read 10567 times:

Quoting SilverComet (Reply 12):
is it some sort of permanent modification to the airframe/engine/wheels to alter the aerodynamic/mechanical properties?

 checkmark 

The Horton STOL craft kit consists of: (on the 172 at least):

- A cuffed leading edge that droops "lower" than the original leading edge of the 172.

- Flap gap seals

- An aerodynamic fence between the ailerons and flaps on the top of the wing

- "Drooping" wingtips

Quoting SilverComet (Reply 12):
How does a STOL Craft Kit work?

It basically improves the low speed aerodyamics of the aircraft so that it's safely controllable at lower indicated airpeeds than it would otherwise be...when you're on the back side of the power curve with the STOL kit, the aircraft isn't mushing along and is more controllable at those speeds.

Here's a picture of the Horton STOL Craft kit (on a Cessna 150):


View Large View Medium
Click here for bigger photo!

Photo © Adam Wright




Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 14, posted (7 years 2 weeks 6 days 20 hours ago) and read 10564 times:

Many published "landing distance" figures are from over a 50' obstacle. So even with a very steep approach a good deal of this distance is flown over, not rolled upon.

If we are talking actual landing roll - touchdown to full stop we have a more valid comparison.

Most published stopping distances for cars refer to "panic stops" where the driver is trying for the smallest possible number. Rarely is an airplane landed with such a purpose.

Believe me I have done a lot of STOL operations. Here are a few figures from memory:

DeHavilland Beaver - I routinely used a grass strip 333 feet long (101.5m) at a fairly high density altitude.

Helio Courier - I once landed in a sky diving target, a shallow pit filled with wood chips about 40 feet (10m) across. For regular ops, I like a thousand feet but never used more than 200-250 (61 to 76m) The rest is for clearing the trees.  Smile

Cessna 206 with STOL mod - I routinely took myself and five passengers in and out of 1000' (305m) dirt strips at elevations up around 7000 feet (2134m) I carried just enough fuel for the round trip and VFR reserves.

I've landed a stock Cessna 402B many, many times in a measured 500' (152m) but it does heat the brakes up pretty good.

As a student pilot I got a Cessna 150 stopped in 140 feet. (43m)

Non-STOL?

How about watching McDonnell-Douglas DC-10 test pilots do a "maximum energy stop" at maximum landing gross weight at KYUM. It rolled about 1000 feet (305m) at 363,500 pounds (164881kg)

Now how much distance do you think would be needed to stop a Mercedes sedan from something like 240 km per hour and at 164881kg using Mercedes sedan brakes? I'm guessing Europe might be too small for such a test.  Wow!



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineRalgha From United States of America, joined Nov 1999, 1614 posts, RR: 6
Reply 15, posted (7 years 2 weeks 6 days 19 hours ago) and read 10547 times:

I've stopped a C152 in about 100 feet.  bigthumbsup 


09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
User currently offlineBok269 From United States of America, joined May 2007, 2104 posts, RR: 0
Reply 16, posted (7 years 2 weeks 6 days 17 hours ago) and read 10512 times:

Quoting Jetlagged (Reply 11):

That analogy only makes sense if you imagine the engine is providing forward thrust during the rollout. But it's at idle so with any significant forward speed is creating drag. Wheel brakes are the same, whether fitted to cars or aircraft, working in exactly the same way, via friction.

I was thinking that would be the kink in my explaination. Thanks for clearing it up.



"Reality is wrong, dreams are for real." -Tupac
User currently offlineN231YE From , joined Dec 1969, posts, RR:
Reply 17, posted (7 years 2 weeks 6 days 16 hours ago) and read 10498 times:

This should help, from my PIM. Also note the the various items that must be factored in when computing the distances:

Disclaimer: this is from a Cessna 172R Pilot's Information Manual (PIM). This is also an internet site, therefore, this IS NOT to be used for realistic navigation or flying purposes



Quoting KELPkid (Reply 13):
- Flap gap seals

Don't you mean, aileron gap seals?


User currently offlineEjapilot From United States of America, joined Aug 2007, 7 posts, RR: 0
Reply 18, posted (7 years 2 weeks 6 days 15 hours ago) and read 10488 times:

One other thing to consider, most single engine piston planes do not have antiskid, that will have an effect on the distance compared to a similar weight car with an ABS system,

User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 19, posted (7 years 2 weeks 6 days 13 hours ago) and read 10464 times:
AIRLINERS.NET CREW
DATABASE EDITOR

I'm surprised nobody has brought up the issue of weight distribution.

When a car stops, the weight shifts to the front wheels, and a great deal of force can be applied to those wheels before lockup becomes a factor.

When aircraft brakes are applied, the weight also shifts to the front wheel(s). Because the braking power is restricted to the rear wheels, however, lockup occurs much sooner, and the maximum braking force is much lower.

Think of it this way....grab a handful of rear brake on a bicycle, and the rear wheel will lock up and start skidding. Grab a handful of front brake, and your ride will quickly become very interesting.

In short, if you only have rear brakes, weight distribution (under braking) will greatly reduce their effectiveness.


2H4




Intentionally Left Blank
User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 20, posted (7 years 2 weeks 6 days 12 hours ago) and read 10454 times:

Quoting 2H4 (Reply 19):
In short, if you only have rear brakes, weight distribution (under braking) will greatly reduce their effectiveness.

True, but an airplane still has some elevator authority well below flying speed. This can be, and is used to keep weight on the mains.



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineSilverComet From Mauritius, joined Apr 2007, 85 posts, RR: 0
Reply 21, posted (7 years 2 weeks 6 days 11 hours ago) and read 10443 times:

Quoting KELPkid (Reply 13):

Thanks for that explanation. Much appreciated.

Quoting SlamClick (Reply 14):
Many published "landing distance" figures are from over a 50' obstacle. So even with a very steep approach a good deal of this distance is flown over, not rolled upon.

 yes  I should think that this is the most contributing factor to the discrepancy in the figures.


User currently offlineKELPkid From United States of America, joined Nov 2005, 6381 posts, RR: 3
Reply 22, posted (7 years 2 weeks 6 days 11 hours ago) and read 10442 times:

Quoting SEPilot (Reply 6):
Aircraft brakes are not designed for panic stops

Most definitely not. Any pilot doing a panic stop in a light aircraft will be in the market for new tires in a hurry, as GA aircraft tires flat spot (sometimes down to the chord!) rather easily  Smile

Quoting N231YE (Reply 17):
Don't you mean, aileron gap seals?

Nope, on the Horton kit it's flap gap seals. Besides, the ailierons on the 172 don't really have much of a gap between themselves and the wings when they're in trail. Heck, the piano hinge on the top of the wing between the ailieron and the wing practically is a gap seal  Wink Maybe the other guy's STOL kit (Robertson I believe?) has ailieron gap seals...



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineN231YE From , joined Dec 1969, posts, RR:
Reply 23, posted (7 years 2 weeks 6 days 7 hours ago) and read 10416 times:

Quoting KELPkid (Reply 22):
Maybe the other guy's STOL kit (Robertson I believe?) has ailieron gap seals...

That's the kit I must be thinking of.  smile 

Quoting 2H4 (Reply 19):
Grab a handful of front brake, and your ride will quickly become very interesting.

Been there, done that  headache 

Quoting 2H4 (Reply 19):

To shorten one's landing distance in a 172, one must pull back on the yoke and reduce the flaps, in addition to maximum braking. By doing so, at least one can control some of the weight distribution to the main gear wheels.


User currently offlineVzlet From United States of America, joined Mar 2004, 835 posts, RR: 0
Reply 24, posted (7 years 2 weeks 6 days 5 hours ago) and read 10395 times:

If one were to land a plane on a conveyor belt whose upper surface was in motion at a speed matching the plane's, but in the opposite direction, the plane would come to an instant halt with no ground run. (  Wink Well, at least according to numerous posts in this infamous thread.)


"That's so stupid! If they're so secret, why are they out where everyone can see them?" - my kid
25 BAe146QT : I assume you're joking, but inertia would carry the aircraft forward until the point where the tyres could get sufficient grip, and the brakes became
26 Post contains images Starlionblue : This is not right. The physics of stopping an aircraft with wheel brakes and a car with wheel brakes are the same. Pray tell us more about this incid
27 SEPilot : That's why I have studiously avoided that thread. I'm afraid that such ignorance might be contagious.
28 Lowrider : With a little headwind, I was easily able to achieve a stopping distance of 200 feet. Part of a reason for the discrepincy between cars and light pla
29 Bok269 : So I've been made aware. I stand corrected.
30 Post contains images Bok269 : So I've been made aware. I stand corrected.
31 Post contains images BAe146QT : Bok269 - I hope I didn't come across as snippy. I should have put in a smiley.
32 Post contains images Starlionblue : I have stood corrected many times on these boards. It's always a learning experience.
33 Ralgha : They don't need boosted brakes, it's quite easy to lock up the wheels on a light airplane already. One thing that does make a difference is the lack
34 SlamClick : Another (as has been mentioned above) is the incredibly thin tires on those itty-bitty airplanes. They are incredibly easy to scalp. (Maybe from bein
35 Lowrider : I wasn't arguing that they did, I was merely pointing out some of the differences between the two, particularly in level of applied technology. Those
36 Bok269 : Amen! Not at all!
Top Of Page
Forum Index

Reply To This Topic Landing (Stopping) Distance Of Small Aircraft
Username:
No username? Sign up now!
Password: 


Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
  • DETAILED RULES
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)


Similar topics:More similar topics...
C130 Stopping Distance posted Fri Oct 21 2005 18:38:52 by Gary2880
Passive Stability Of An Aircraft? posted Fri Oct 21 2005 15:55:08 by GLAGAZ
? For Pilots Of 4 Engined Aircraft posted Sat Feb 26 2005 12:03:35 by Undies737
Airlines' Detailed Records Of Individual Aircraft posted Sat Feb 19 2005 23:57:20 by Argonaut
Shortest Stopping Distance On An Airliner posted Sat Jan 1 2005 14:54:17 by Soaringadi
Distance Of Approach Lights Alsf posted Mon Aug 9 2004 12:34:01 by Lh526
Does A Wet Runway Increase Stopping Distance? posted Tue Mar 2 2004 22:04:09 by Cory6188
Xwind, How Much Can You Push A Small Aircraft? posted Fri Oct 31 2003 01:29:46 by SSTjumbo
Where ´s The CG Of This Aircraft? posted Thu May 15 2003 21:35:17 by MASB747
V1 Vs. Weight And Stopping Distance posted Sun Apr 28 2002 17:16:56 by Timbotch

Sponsor Message:
Printer friendly format