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TFF

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Sex sells and the leading edges are sexy. Reality is coupled leading edge/flap is limited in extension. Flap only gets more deflection and matches stall speed of the other. That’s from Earl Luce’s mouth. He also said he usually lands clean as it’s still very Cub like. It is a great airplane in many iterations.
 

120mm

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I never did understand how you can look at an airplane and think its sexy . To me airplanes are beautiful because of the lines of the airplane, sex would never come in my mind.
I believe that is hyperbole. By "sexy" he means "cool factor".
 

rv7charlie

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I really don't think that what's holding aviation back is money. Been to a boat show lately and priced a bass boat? In most states you can swipe your credit card for that bass boat and be fishing in less than half a day. Contrast that with the literally months of work required to get the most basic pilot's license before you can just go play. For most, that learning process isn't fun; it's most of the cost of admission. (Instant Gratification Generation) Then there's the danger issue; the average person *knows* aviation is *so* much more risky than hitting 45 mph in a river in a bass boat on the way back to the marina to restock after you've finished off that 12 pack. ( obligatory ;-) here )

Having said that, I suspect that Cessna spends roughly the same number of hours building a C-172 today that it spent in 1955. About a decade ago I read that there were <40 hours of labor in a typical car. I'd bet that the number is less than half that, today, and today's cars are *much* more complicated than a C-172. One reason cars are a lot cheaper than a/c. That, and for some reason, people pay the asking price...

Charlie
 
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BrianW

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The caulking gun isn't dealing with hundreds of PSI like the master cylinder is, and I've seen caulking guns wear out soon enough, too.
The flexible brake hose is rated medium pressure - and good for 900 psi or so....
I never had a brake master apart, so I am guessing the piston diameter is about one inch.
Design rules for rudder pedals require 200 lb force on the pedals without failure.
Let's suppose a one side force of 80 lb for a full-blooded brake - wouldn't that be about 63 psi in the brake hose??
 

Dana

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Let's suppose a one side force of 80 lb for a full-blooded brake - wouldn't that be about 63 psi in the brake hose??
200# force against a 1" diameter piston is 63 psi, yes, but is the master cylinder that big? Car cylinders are usually about half that size, which would be 4X the pressure, then there's the mechanical advantage of the pedal against the cylinder, which would make it a lot more.

The "low pressure" Scott diaphragm master cylinders on my plane are 350 psi at 100# pedal force. Standard master cylinders are more like 1200 psi.
 

BrianW

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200# force against a 1" diameter piston is 63 psi, yes, but is the master cylinder that big? Car cylinders are usually about half that size, which would be 4X the pressure, then there's the mechanical advantage of the pedal against the cylinder, which would make it a lot more.

The "low pressure" Scott diaphragm master cylinders on my plane are 350 psi at 100# pedal force. Standard master cylinders are more like 1200 psi.
I looked over this Matco unversal master cylinder
You are right - it features a piston of 0.625 in diameter, leading to a c/s area of 0.307 sq in and a pressure of 261 psi when pressed with 80 psi force. This does indeed ignore the effects of leverage.
 

Dan Thomas

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The flexible brake hose is rated medium pressure - and good for 900 psi or so....
I never had a brake master apart, so I am guessing the piston diameter is about one inch.
Design rules for rudder pedals require 200 lb force on the pedals without failure.
Let's suppose a one side force of 80 lb for a full-blooded brake - wouldn't that be about 63 psi in the brake hose??
The master cylinder diameter in a Cessna and many others is a hair over a half-inch. Nowhere near an inch, not even 5/8". It uses a 9/16" O-ring that gets squeezed some as the piston goes in.

Medium pressure hose used in light aircraft brake systems is rated for 3000 PSI. I have overhauled master cylinders and rebuilt hose assemblies. Those assemblies get tested at 200% of rated pressure. Their burst pressure is four times the rated operating pressure, or 12,000 PSI for that small hose.

The pressure in a light aircraft brake system can easily hit 600 PSI and a really hard brake could easily hit 800 or more. The pedal geometry magnifies the force the pilot applies at the top of the pedal. It takes serious pressure on that caliper to generate the friction to stop several thousand pounds of airplane.

1604768867230.png

Facts, not assumptions, are what matter.
 
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meglin1

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Ukraine
Yup. The interior stuff degrades. Plastic wingtip and tail fairings degrade. But so does the plastic on or in any 50-year-old car that has sat outside most of the time.
We are working on this issue. Any pilot can verify this.
 

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Dan Thomas

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200# force against a 1" diameter piston is 63 psi, yes, but is the master cylinder that big? Car cylinders are usually about half that size, which would be 4X the pressure, then there's the mechanical advantage of the pedal against the cylinder, which would make it a lot more.

The "low pressure" Scott diaphragm master cylinders on my plane are 350 psi at 100# pedal force. Standard master cylinders are more like 1200 psi.
Those Scotts used a diaphragm instead of a piston and had much more area. They were intended for the old low-pressure bladder brakes used on old ragwing Pipers. I once ran into a Supercub that had those Scotts driving Cleveland calipers. Hopeless braking. Couldn't even hold it against the runup. Someone had violated the parts manual or an STC by doing that on a type-certified airplane.
 

BJC

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Those Scotts used a diaphragm instead of a piston and had much more area.
Shameless plug:


BJC
 

BrianW

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The master cylinder diameter in a Cessna and many others is a hair over a half-inch. Nowhere near an inch, not even 5/8". It uses a 9/16" O-ring that gets squeezed some as the piston goes in.

Medium pressure hose used in light aircraft brake systems is rated for 3000 PSI. I have overhauled master cylinders and rebuilt hose assemblies. Those assemblies get tested at 200% of rated pressure. Their burst pressure is four times the rated operating pressure, or 12,000 PSI for that small hose.

The pressure in a light aircraft brake system can easily hit 600 PSI and a really hard brake could easily hit 800 or more. The pedal geometry magnifies the force the pilot applies at the top of the pedal. It takes serious pressure on that caliper to generate the friction to stop several thousand pounds of airplane.

View attachment 103811

Facts, not assumptions, are what matter.
**************************************************************************
Here's a fact that may interest you. Its author is Dan Thomas.

2020-11-07 12_41_43-Window.jpg

Page 9-20 A/B of AC43.13-1B Acceptable methods shows the acceptable test pressure in a brake line after repair or replacement should be 150% of working pressure. If you are still using nylon 1/4 in tubing which bursts at 1200 psi - AC43 seems to indicate your working pressure should be 800 psi or less.

Or have you changed your mind, or am I missing something? Facts matter!
 

Dan Thomas

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**************************************************************************
Here's a fact that may interest you. Its author is Dan Thomas.

View attachment 103819

Page 9-20 A/B of AC43.13-1B Acceptable methods shows the acceptable test pressure in a brake line after repair or replacement should be 150% of working pressure. If you are still using nylon 1/4 in tubing which bursts at 1200 psi - AC43 seems to indicate your working pressure should be 800 psi or less.

Or have you changed your mind, or am I missing something? Facts matter!
The working pressure in my Jodel (1200 pound gross, 65 hp) maxed at 650 psi standing on the brakes and I seldom used even half of that, all well within the tubing's working pressure. Heavier and more powerful airplanes need more. The Jodel is light and has a very light tail so it's easy to nose over with too much brake.

The master cylinders were from 1950s Austin cars and had a 5/8" bore. Leverage from the heel brakes was less than 2:1.

Using medium-pressure hose in that airplane would have been vast overkill, far more expensive, and a lot heavier.

So yes, you're missing stuff.
 
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Dana

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Those Scotts used a diaphragm instead of a piston and had much more area. They were intended for the old low-pressure bladder brakes used on old ragwing Pipers. I once ran into a Supercub that had those Scotts driving Cleveland calipers. Hopeless braking. Couldn't even hold it against the runup. Someone had violated the parts manual or an STC by doing that on a type-certified airplane.
My Hatz has the Scott diaphragms and Cleveland calipers, braking is more than adequate
 

BJC

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The Scotts have lots of leverage, plus heel force is naturally more than toe pressure.


BJC
 

BrianW

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Correct, and ABS is an acronym for Abysmal, Brittle, Stuff.


BJC
Sadly, nylon too grows brittle with age, though some use it for brake lines.
I enjoyed watching a mechanic replacing the hose on the Aeroquip style medium pressure brake fittings like those shown here:
All it took was determination, an arbor, and new hose - and a little lubrication.
Come to think of it, he replaced the rudder pedals too, for ones he had in the shop. He gave me the old ones, with elongated pivot holes. And charged me $400 for the annual - but that was a LONG time ago. More recently, I owned a plane whose brake flexibles could be mistaken for car brake flexibles - except this mechanic mentioned they need to be 37 degree cone terminals - these were crimped in place.
Given my druthers, I would prefer the anodized light alloy fittings which are good when the hose needs replacement.
 

BJC

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I just shortened a 303 hose to an oil cooler with a 491-8. The -8 is about twice as hard to do as a -6.


BJC
 
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