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Brake Boosters Required for Bushwheels?

FullThrottle

FullThrottle

FRIEND
Kenai AK & Houston TX
I saw some threads about brake boosters, but nothing that discusses whether or not brake boosters are required for all types of bushwheels. Although pretty much anyone with over size 26 tires likely uses them (the original Scott brakes aren't amazing), is there anything required in the STC for 31 inch bushwheels (or bigger) that would require either the boosters or double puck brakes?
 
Brake effectiveness with 8.50s will be reduced by about a third with 31s. (diameter ratio, small/large)
 
From a practical standpoint, I think your brakes are going to be lacking with the original Scott masters and single puck calipers. Although I typically don't use much brake other than run-up and close quarters steering, it's nice to have good braking power when you really need it.
 
Thanks Steve. This brings up another question. What is the FAA's definition of "heavy duty brakes"?
 
s-l1600.jpg

Heavy duty Cub brakes Two required.
 

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skywagon8a said:
Thanks Steve. This brings up another question. What is the FAA's definition of "heavy duty brakes"?
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I would think in the case of a cub it would indicate double puck disk brakes.

The word “heavy duty “ is too subjective and is used by most manufacturers to indicate some type of “upgrade “
 
Soooooooo, Most will say a set of double puck brakes for a cub is a Heavy Duty brake. BUT, I do not see a Heavy Duty description listed in the type certificate. I also do not see Heavy Duty description listed on the Cleveland or Bushwheel double puck brakes. Could not find a FAA description of "Heavy Duty Brake" for a CAR 3 aircraft. The bottom line is whatever your IA will sign off is what you need. I see nothing that says brake boosters are required (I am sure more than one cub has been on its back without them). I would go back to CAR 3 and see what the requirement for brake performance is and go from that. For my mission I think brake boosters and double puck caliper on 31 inch bushwheels is a must have. I would be happy to fly a cub without boosters, I would just pay a bit more attention on how long my landing area is.

03.365 Brakes shall be installed which are adequate to prevent the airplane from rolling on a paved runway while applying take-off power to the critical engine, and of sufficient capacity to provide adequate speed control during taxing without the use of excessive pedal or hand forces.

Still dark and cold out here we could stir this pot for a while
DENNY
 
On a Pacer I would consider double puck Clevelands as HD and in a Super Cub I guess I could consider the same over the original expander tubes which are a 4" wheel so I guess you do need heavy duty brakes so you have the correct wheel size. You won't like your stock diaphragm brakes with Bushwheels I can pretty much guarantee.
 
Steve Pierce said:
On a Pacer I would consider double puck Clevelands as HD and in a Super Cub I guess I could consider the same over the original expander tubes which are a 4" wheel so I guess you do need heavy duty brakes so you have the correct wheel size. You won't like your stock diaphragm brakes with Bushwheels I can pretty much guarantee.
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I have stock Scott diaphrams and Bodell wheels/brakes on my PA-12. The combination is "good" with 8.50's, "adequate" with 26" Bushwheels, and a bit marginal with 31's.
 
It should be noted that when the large diameter tires first came into use on the Cubs that 4" expander tube brakes were in use. These did not have enough braking power to keep the wheels from rotating. As a result someone changed the expanders to double puck 6" disc brakes. These didn't hold either but were a lot better than the expander tubes. As a result high pressure boosters were developed to activate the double pucks. Now they worked. The double puck with booster is strong enough to cause you to buy a new prop. Definitely a heavy duty brake.

Did anyone ever try single puck wheel brakes with high pressure master boosters? If so how well do they work? Seems that since the gross weight of a Cub is quite low, the single puck brake ought to be sufficient when coupled with a booster master cylinder.
 
Back when, our Cubs with expander brakes and 25 inch Goodyear Airwheels had marginal braking.....as in they wouldn’t hold the plane during an 1800 rpm run up.

Personally, I like effective brakes most of the time.

MTV
 
It’s not just your stopping distance that’s the issue without boosters. I tried 31 inch Bushwheels with my double puck brakes and standard Scott masters. Crosswind landings on pavement were scary, I quickly went out and bought the boosters.
 
I'll be danged. I have single puck brakes and stock diaphragms on my Exp Cub and my brakes work fine with 31s.

They got a lot better when I went with good high pressure brake lines instead of the old POS lines.
 
Carey Gray said:
I'll be danged. I have single puck brakes and stock diaphragms on my Exp Cub and my brakes work fine with 31s.

They got a lot better when I went with good high pressure brake lines instead of the old POS lines.
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Did you learn from Jerry Burr how to get pressure in the system and lock the parking brake valve, then add more fluid? 8)
 
I do know how to do the parking brake thing, but I don't have parking brakes.
If you don't have it, you never have to fix it.
 
So you just top off the stock master cylinders w/diaphragms, no pressurizing the system and you have good brakes on 31s?
 
I have no problems with 31’s and stock master cylinders. I suggest fresh diaghrams and seasonal fluid level correction.
 
Steve Pierce said:
So you just top off the stock master cylinders w/diaphragms, no pressurizing the system and you have good brakes on 31s?
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Speaking only for myself - I fill through the bleeder valve at the wheel with a piece of plastic tubing on an oil can. A little bit redneck I guess, but it works much better than just filling at the master plug. That gives me so-so brakes with 31's and decent brakes with 26's. On 26's I can hold pretty easily for 1800 RPM mag check.

I suspect the Bodell piston might be bigger cross section than double clevelands, but I've never checked.
 
Steve Pierce said:
So you just top off the stock master cylinders w/diaphragms, no pressurizing the system and you have good brakes on 31s?
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I don't know any other tricks. My brakes aren't as sensitive as with the boosters. I wouldn't want sensitive brakes on something with a really light tail. Everyone has a different story.
Like cruiser said, having good diaphragms is pretty important and the fluid level is obviously important.

Filling from the bottom works great for bleeding, but after the brakes are bled I just fill them from the top. It's easier and not as messy.
 
You can just loosen the 1/4” bolts holding the backplates a couple turns, pump the brake, fill the master, tighten the bolts back up, and have the same effect as adding fluid after locking the parking brake- what I do when there’s no parking brakes and I need to preload them a bit... This has worked well on a customer’s J-5 with stock diaphragms and double pucks with 31’s- enough to hold at full power with the o-290d without mashing the pedals too hard...
 
Rumor has it if you change out the thin copper washers under the cap for some say 1/8” thick and top off the fluid that little bit extra fluid makes for a worthy improvement in braking.
 
OLDCROWE said:
Rumor has it if you change out the thin copper washers under the cap for some say 1/8” thick and top off the fluid that little bit extra fluid makes for a worthy improvement in braking.
Click to expand...
That thin copper washer is someones substituted part by because they didn't have the correct parts. The correct washer is a thick, black, fiber type washer.

Glad my Super Cub had Dakota Cub brakes when I bought it. They stop very well and are trouble free. I only check the fluid level annually, no more fluctuating brake pressures depending on OAT.
 
Steve Pierce said:
That thin copper washer is someones substituted part by because they didn't have the correct parts. The correct washer is a thick, black, fiber type washer.

Glad my Super Cub had Dakota Cub brakes when I bought it. They stop very well and are trouble free. I only check the fluid level annually, no more fluctuating brake pressures depending on OAT.
Click to expand...
Interesting, never trust a rumor to stop ya.
 
Last edited:
FullThrottle said:
is there anything required in the STC for 31 inch bushwheels (or bigger) that would require either the boosters or double puck brakes?
Click to expand...

Yes. Common sense.

I want my brakes to hold the plane in a full power run-up. I want brakes to reliably stop the plane at gross weight. I want to maximize the performance potential that Bushwheels offer in places that Bushwheels allow me to go.
 
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