New legs for the Avid

43 posts in this topic

Posted (edited)

Heel brakes anyone?
Has anyone tried heel brakes on an Avid? I didn't know the concept before but it appears to have some advantages over toe brakes like not breaking against moving pedals, way easier to the geometry right - in addition to it probably being easier to apply required force with the heels than with the toes.
Anyone with experience and eventual photos to share? 
This is an example of an off the shelf product to a ridiculous price but rather easy to make yourself:

heelbrakes.thumb.jpg.1d8f4f17932a9a07733

Or like this for a deported cylinder installation:

from-the-pilot-seat.thumb.jpg.a212603431

from-the-firewall.thumb.jpg.b01e3118cd00

Edited by FredStork

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Posted

See the source image

I did most of my primary flight training in a Super Cub with heal brakes. They work ok but I am not a fan of them.  I prefer toe brakes because they are easier to use.

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Posted

I prefer heel brakes for really aggressive off airport work.  You can get full rudder deflection and use the brakes at the same time very easily.  A lot of the old cub drivers were not crazy about them as the brakes were marginal at best but that was not due to them being "heel" actuated brakes, its because the masters and calipers sucked 50+ yrs ago.  The certified world sucks as changing the brakes out of course takes an STC or the all but extinct 337.  Using modern masters and double puck brakes I think going to heel brakes in the avid would have definite advantages.

I don't think I am too crazy about the cable actuated set up your showing.  Way too much opportunity for flex and stretch.  You could take a page from the cub play book and put the masters under the seat and run a rod to them to actuate them and keep the masters tucked out of the way or put them under the floor boards.

 

The more I think about this the more I am liking the idea.  It would also solve the issue of toes getting caught up under the cross tubes on the firewall etc.

:BC:

 

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Posted

I redid my old Avid brakes using new thin master cylinders that allow me to get much more leverage between my pedal and the cylinder - see the picture below, the old master cylinder hole is clearly shown, the new hole gives about 21/2 times more pedal force and 2 1/2 times more brake pressure. The only work was to drill the new holes, fit the cylinders to them, and hang the small external reservoir. I did have to shorten the cylinder threaded ends a little to fit the cylinder into the old space.

I now can hold my Avid Mk IV on the ground against 5500 engine rpm (with a 670 engine, probably about 60 HP) and the brakes feel rock hard when I press.

 

new brakes.jpg

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Posted (edited)

I don't think I am too crazy about the cable actuated set up your showing.  Way too much opportunity for flex and stretch.  You could take a page from the cub play book and put the masters under the seat and run a rod to them to actuate them and keep the masters tucked out of the way or put them under the floor boards.

That is very close to what I have in mind, a deported system with the brake cylinders under the seat actionned by (pull) rods. It should be fairly easy to incorporate a parking brake once I have the cylinders and lever mechanism under the seat. 

With your heel brake experience, what is the best postioning of the pedals? On most photos I find the brake pedals are not in line with the rudder pedals, they are lightly more in thge center and you have to twist the foot to reach the brake pedal with the heel. Is there a rational reason for this, and if this is your expoerience, it good or should they better be alligned? 

Edited by FredStork

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Posted (edited)

A radically different approach to brakes..

After multiple attempts to modify the toe brakes, thinking about heel brakes and reading endless posts I locked myself in my workshop and came up with this:

image.thumb.jpeg.c8e9b953debc858c122877aIt is 2 valves operated with a common lever. In the middle position they are both open (half open to be exact), push to one end and one close and the other goes to full open, push the lever the other way and it is the other way around. This way the braking power can be directed to either one of the wheels or to both.  The electric switch is flashing an alarm when not in "neutral".
The lever is manipulated with a little handle placed on the throttle quadrant that I have on the left had side of the seat.
image.thumb.jpeg.c01ddc5dbeb219482f1f52bAnd while at it I made a parking brake. A small handle is placed under the seat. 
image.thumb.jpeg.fe88f61f54c3856c3154c10So nothing on the pedals, I have a motor cycle brake handle with master cylinder on the stick (ergonomically turned 45 degrees to the left as I fly and brake with my right hand). The master cyliner goes directly to the parking brake, followed by a "T" that goes to each of the switch valves and from there to the wheel brake calipers.
And it works. By directing the brake power to both wheels I can brake evenly without problems. When directing the brake power to only on wheel I can turn as sharp as I want, all the way down to around the blocked wheel. With my 92hp, new prop and 22 inch wheels I have some difficulties holding still on full throttle... 

 Sorry about the really low quality of the video...

 

 

Edited by FredStork
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Posted

Well I've been fighting with bad brakes on the Avid for a while, and thought I had fixed the problem with the new brake pedals.  They were super sensitive though, and it was hard to stay off the brakes.  Also, I thought the leverage could be better.  I bought a set of the shortest master cylinders Matco sells.  # MC4GH  www.matcomfg.com/catalog.html?Tp=6&adv_search%5B1%5D%5B37%5D=0&adv_search%5B4%5D=5&adv_search%5B1%5D%5B56%5D=0&adv_search%5B1%5D%5B38%5D=0&adv_search%5B1%5D%5B39%5D=114&adv_search%5B1%5D%5B41%5D=0&adv_search%5B1%5D%5B42%5D=346&adv_search%5B1%5D%5B43%5D=0&adv_search%5Bkeywords%5D=&sbT=Go   They are only 5" long, the next length Matco sells is 6 1/2" long.  If there was a 5 3/4" length, it would be just right.  I was going to use some brake pedals from a Kitfox 1, cause they have way better leverage then the Avid brake pedals.  I did end up using them and it seems like they will work fine.  Couldn't really test out the brakes, cause I have snow on my runway, but I think they will work out.  I'm not riding the brakes, and it doesn't take much push to lock the wheels.  Course it's in snow, but still I feel it's going to work out.  If I remember right, with the Avid brakes, the master cylinder hooked on about 2 1/4" from the pivot, on the Kitfox pedal, it's about 1 1/4" to the pivot.  The new cylinders are 5/8" bore, the old ones were 1/2" bore.  All in all, an improvement in pressure I believe.   I had to make up a bracket on the one side to mount the cylinder in the right place, what I did would not involve pulling the rudder pedals out and welding tabs on them, although, that may be a better way to do it.  I think the nice thing about this is you could use your existing Avid pedals, if you weld new arms on them to mount the master cylinder to.  The left pedal would get turned around 180 degrees and the existing arm would be cut off.  I did make some extensions for the bottoms of the cylinders to make them longer, but you could also weld the new arms lower to make up the difference, and that would probably give you even better leverage.  Well I'll quit typing, and try to find the pictures now.  Don't laugh at the crappy welding.  It should hold.  JImChuk

20181029_153907.jpg

20181029_153916.jpg

avid brakes 1.jpg

avid brakes 2.jpg

avid brakes 3.jpg

avid brakes 4.jpg

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Posted

Looks a lot like what I did, except I changed to an external reservoir and the shortest cylinders matco makes (4g or 4h), and made the cylinder connection right above the pivot point.  It gave me the 2.5x mechanical advantage Matco recommends, and went from barely able to hold the plane at idle (with the 'intensifier' kit in the old 5 cylinders), to holding it at full throtttle.  Avid Model C, 582, original Peery prop

Mark

 

Matco makes nice stuff but it's way over priced just because it's going in an airplane. The master cylinder in my Austin Healey has the same bore and almost the same stroke and overall length as some of those Matco cylinders for a lot less money. Someone would have to get creative to mount them but at $19.47 each you won't be out much money. There are after market versions with different bore sizes for $53.00 each. Here's a link if you want to see what they look like: https://www.bpnorthwest.com/brake-master-cylinder-bn7-bt7-bj7.html 

Another cheap option would be to adapt a clutch slave cylinder as a master cylinder such as the one on the Austin Healey Sprites and MG Midgets as seen here: https://www.bpnorthwest.com/clutch-slave-cylinder-1275-sprite-and-midget.html  I've never seen a slave cylinder used as a master but it has a spring return and about the right amount of travel. It is way smaller and lighter than anything I've seen in most airplanes. I've got one or two of them laying around somewhere. They are a piece of cake to rebuild too.

I'm just thinking outside the box for the creative minds trying to save a buck.

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Posted

If you think Matco is expensive, try pricing out Clevelands….  It would be nice if they gave the dimentions of the cylinders you linked to.  As in length.  JImChuk

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Here is a link to an after market cylinder that's a replacement for one used in one of the Austin Healey cars: https://www.wilwood.com/MasterCylinders/MasterCylinderProd?itemno=260-6087  You could always call or email the other supplier and ask for length. My current Austin Healey now has a rebuilt original master in it and it's a completely different animal as the clutch and brake cylinders are built into the same casting. The replacement I had taken out of it was from a newer model and had the separate master cylinders.

I was tempted to look up the replacement master cylinders for the Honda Goldwing I sold a few months ago as that weighs even more than our airplanes and it's braking is also applied to just two wheels. Those cylinders are also small in size and effective.

The slave cylinder I mentioned is shorter than my hand, I'd guess about 4 or 5 inches long but I'd have to crawl under the car to measure it or hunt through boxes to find the  spares.

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Posted (edited)

4130 for landing gear?

All is in the first line... I assume 4130 / 25CrMo4 is the correct steel for the landing gear - in the appropriate thickness 0.049 or 0.058, any advice?

Edited by FredStork
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Posted

I designed mine using .058" .  I also upsized the tubes a bit to take more abuse in the field.  Yes sir, 4130 is "the right stuff!" for aircraft.

:BC:

 

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Posted

Well I've been fighting with bad brakes on the Avid for a while, and thought I had fixed the problem with the new brake pedals.  They were super sensitive though, and it was hard to stay off the brakes.  Also, I thought the leverage could be better.  I bought a set of the shortest master cylinders Matco sells.  # MC4GH  www.matcomfg.com/catalog.html?Tp=6&adv_search%5B1%5D%5B37%5D=0&adv_search%5B4%5D=5&adv_search%5B1%5D%5B56%5D=0&adv_search%5B1%5D%5B38%5D=0&adv_search%5B1%5D%5B39%5D=114&adv_search%5B1%5D%5B41%5D=0&adv_search%5B1%5D%5B42%5D=346&adv_search%5B1%5D%5B43%5D=0&adv_search%5Bkeywords%5D=&sbT=Go   They are only 5" long, the next length Matco sells is 6 1/2" long.  If there was a 5 3/4" length, it would be just right.  I was going to use some brake pedals from a Kitfox 1, cause they have way better leverage then the Avid brake pedals.  I did end up using them and it seems like they will work fine.  Couldn't really test out the brakes, cause I have snow on my runway, but I think they will work out.  I'm not riding the brakes, and it doesn't take much push to lock the wheels.  Course it's in snow, but still I feel it's going to work out.  If I remember right, with the Avid brakes, the master cylinder hooked on about 2 1/4" from the pivot, on the Kitfox pedal, it's about 1 1/4" to the pivot.  The new cylinders are 5/8" bore, the old ones were 1/2" bore.  All in all, an improvement in pressure I believe.   I had to make up a bracket on the one side to mount the cylinder in the right place, what I did would not involve pulling the rudder pedals out and welding tabs on them, although, that may be a better way to do it.  I think the nice thing about this is you could use your existing Avid pedals, if you weld new arms on them to mount the master cylinder to.  The left pedal would get turned around 180 degrees and the existing arm would be cut off.  I did make some extensions for the bottoms of the cylinders to make them longer, but you could also weld the new arms lower to make up the difference, and that would probably give you even better leverage.  Well I'll quit typing, and try to find the pictures now.  Don't laugh at the crappy welding.  It should hold.  JImChuk

 

I used the same brake cylinders, and although I total redid my pedals, the basic end result is the same.  Much better braking.  With the old stock setup, I couldn't hold 3,000 rpm, now I can hold to about 5,500 rpm.

Mark

 

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Posted (edited)

Someone have a diagram or photo of how to plumb in a parking brake? I assume the brake lines for both wheels would pass through a shutoff of some sort.

Never mind. I went and looked on Spruce. It's all there.

Edited by Shipl14

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Posted

I put a parking brake on my Avid.  I talk about it and have pictures on page four of this thread.  I like it and will do it on all my future projects.  JImChuk

www.avidfoxflyers.com/index.php?/topic/3415-ive-got-it-covered/&page=4#comment-45612
 

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Posted

Let's see if I can attach the photo of my bush gear fairings.

20180922_075017.jpg

it looks like you've got a hose support clamp holding the fairing over the springs? Any brands that are better than others? How did you mount that spinner over the cabane? I'm trying to come up with ideas how to fair my gear. 

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Posted

Good to keep in mind when fairing out aircraft parts is..the fairings also add "wetted surface" which adds a bit of drag. However, if done correctly, the added wet surface drag is less than the drag reduced by fairing.

 

John M

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Posted

Good to keep in mind when fairing out aircraft parts is..the fairings also add "wetted surface" which adds a bit of drag. However, if done correctly, the added wet surface drag is less than the drag reduced by fairing.

 

John M

Much less!  A forward-facing flat, at AR=1 has a drag coefficient of 1.1.  At high AR it asymptotes to 2.0.  Either of these can be cut in half by placing a rounded fairing on the windward side, such that the air flowing around it is able to leave the leeward edge in the outer-flow direction.  Forward-facing flats are an aerodynamic sin!

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