Brake load in cockpit
Brake load in cockpit
(OP)
I am trying to size a brake cable for a footbrake on an experimental sailplane. Single seat, single landing wheel.
I am tring to figure out what load a pilot CAN exert, arching his back and shoving as hard as he/she can. Since the aircraft is a tail dragger design, if the pilot over does it he/she is likely to put the aircraft up on its nose. The other scenario which bother me more, is wet grass, where the pilot locks the wheel which then skids, and the pilot not realizing this, just shoves harder and harder.
FAR 23 is not very helpful on this: it says: ""Sec. 23.405 Secondary control system.
Secondary controls, such as wheel brakes, spoilers, and tab controls, must be designed for the maximum forces that a pilot is likely to apply to those controls.""
All I can find is rearward stick loads of 167lbs in " 23.397 , and I am thinking that a pilot hauling back on the stick must be producing similar loads to a guy shoving on the brakes. If I double that number to 334lbs would this be adequate?
I am not considering G loads such as the 9g forward loading here, I am considering if it gets that high , the pilot has already hit something.
B.E.
I am tring to figure out what load a pilot CAN exert, arching his back and shoving as hard as he/she can. Since the aircraft is a tail dragger design, if the pilot over does it he/she is likely to put the aircraft up on its nose. The other scenario which bother me more, is wet grass, where the pilot locks the wheel which then skids, and the pilot not realizing this, just shoves harder and harder.
FAR 23 is not very helpful on this: it says: ""Sec. 23.405 Secondary control system.
Secondary controls, such as wheel brakes, spoilers, and tab controls, must be designed for the maximum forces that a pilot is likely to apply to those controls.""
All I can find is rearward stick loads of 167lbs in " 23.397 , and I am thinking that a pilot hauling back on the stick must be producing similar loads to a guy shoving on the brakes. If I double that number to 334lbs would this be adequate?
I am not considering G loads such as the 9g forward loading here, I am considering if it gets that high , the pilot has already hit something.
B.E.
The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor





RE: Brake load in cockpit
FAA seems happy with 375 pounds for light sports planes.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Brake load in cockpit
RE: Brake load in cockpit
Either the last portion of stroke, or a squeeze handle.
RE: Brake load in cockpit
That was the old school thinking,the newer sailplanes now have heel brakes operated by a slide bar on the rudder adjusting pedals.
B.E.
Mac
I had looked at the rudder loads, and had missed the point that the pilot can push on both at the same time.
B.E.
Based on this I will use a 3/32" size cable rather than 1/16".
Thanks for you help gentlemen.
The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor
RE: Brake load in cockpit
how about setting up a test rig, what can you push in a semi-reclined posture in a cramped cockpit ?
RE: Brake load in cockpit
It is a recreational glider, with of course a semi reclining cockpit. I guess I can set up a load cell on the rudder pedals when we get that far, Right now I was looking for a first cut ( so to speak ) on that brake cable.
3/32" cable has a breaking strain of between 930 and 1100 lbs depending on the type, so I will try that first and see if anybody can break it. If they do I will be surprised, but strange things have a way of happening around aircraft.
B.E.
The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor
RE: Brake load in cockpit
A strong male can bench press what 150% ? of their own weight, you'll probably find the limit is the seat strength.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Brake load in cockpit
RE: Brake load in cockpit
RE: Brake load in cockpit
So what did you get with both feet?
B.E.
The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor
RE: Brake load in cockpit
http://en.wikipedia.org/wiki/Leg_press
Apparently "Former US Secretary of State and septuagenarian Madeleine Albright claims she is able to leg press in excess of 400 pounds." If I were you, I would not let Madeleine Albright fly my sail plane :)
I do not work with controls, but we size for 250 lb limit, 375 ultimate on "steppable" surfaces for part 25 interiors per our company standard.
RE: Brake load in cockpit
Well now you have me worried about the brake cable, the brake pedal assembly, the seat back and half of the cockpit.
B.E.
The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor
RE: Brake load in cockpit
Reference Diffrient, Niles, et al. Humanscale 4/5/6, October, 1981