Airdrome Airplanes Sopwith Pup Project

[Machinbird]

SNJ5, Take a look at rudder bar | sponge rubber | lb | 1932 | 0627 | Flight Archive "A New Dunlop Brake". This seems to be the origin of the pneumatic braking systems for aircraft.
I personally like this system because I believe it can be inobtrusively installed in a replica without visible brake lines and with a simple thumb button or a paddle valve as the only visible control.
The rudder valve is relatively simple in that it can be linked below the floor board to the rudder bar and can be manufactured if you have rudimentary machining skills. As described in the article, the air goes to both brakes at the same time when activated and when the rudder moves in one direction, the opposite brake is released (vented to atmosphere).
Mustang didn't mention it, but the Hurricane had this type of brake.
I'd really like feedback from one who has used this type of system as to the unique operational characteristics.
Sid

[mustang]

Mustang didn't mention it, but the Hurricane had this type of brake.
I'd really like feedback from one who has used this type of system as to the unique operational characteristics.
Sid[/QUOTE]

I haven't flown the Hurricane so I can't comment on it. Howvwer it had the same system as the Spitfire, the Fairey Battle, the early Vampires, the various marks of Meteors and the Bristol Freighter, all pneumatic. The Canberra was hydraulic. I have probably, without scanning through log books, two or three thousand hours using this system,.

The operation is entirely instinctive, you want to turn left you apply left rudder, up to full travel if required. If that is not enough a squeeze of the brake lever applies left brake to assist the turn. Similarly with a right turn.
If you want to stop, or slow down while travelling straight ahead, just squeeze the brake lever.

However, the installation of this system will require the use of a compressor, a pressure reservoir and a pressure guage plus a suitable actuating mechanism in the wheel hub. The aircraft I have experience with used drum brakes and an airbag to expand the brake shoes onto the drum.

The best system for a replica, in my judgement, would be the Chipmunk type, a differential valve on the rudder bar fed from a hydraulic master cylinder operated by a hand lever. Whether the lever was mounted on the stick or easily reached somewhere else in the cockpit would be a matter of choice.

Mustang

[hank jarrett]

If you are going to think about a pneumatic brake system make sure you keep it SIMPLE! There is a Hawker Hurricane that is maintained out of the airport where I fly from and (tries to) fly regularly from the WW-II museum in Virginia Beach. They have a great talk from a WW-II pilot speaker every month and fly one of the war birds. Really a great way to spend a Saturday. If you are ever in Virginia Beach get out to the Virginia Beach airport and look around (they are even building a WW-I replica section and have several WW-I planes).
All that said brings me to how this relates to this thread. Even with all the fantastic maintenance help they have, and how they keep dozens of rare war birds flying, the BIGGEST problem I have seen in the years I have been going out there is the brakes on the Hurricane. The pneumatic system is a real nightmare. The hydraulic brake systems are dead on reliable. Mechanical systems can be made to work well if maintained and kept "tuned up". Pneumatic systems hiss like a snake for a reason. They always seem to rise up and bite you at the worst time.
One of my jobs in the navy was to do the pneumatic engineering for the A-6 and I was glad there wasn't much in it. Recently I did a lot of the engineering on the airbag inflation system for the Orion (CEV replacement for the Space Shuttle). It was an incredible PITA and if you haven't noticed, the Orion airbag system is gone and it is now going to land in water, like Apollo. Getting that system reliable and light was nearly impossible. We did it, but overall vehicle weight caused it to be removed anyway. It can be done, but why?
Hank

[snj5]

Originally Posted by mustang

The best system for a replica, in my judgement, would be the Chipmunk type, a differential valve on the rudder bar fed from a hydraulic master cylinder operated by a hand lever. Whether the lever was mounted on the stick or easily reached somewhere else in the cockpit would be a matter of choice.

Mustang

I have scouered the internet from aardvark to zwart and find neither the name or source for said hydraulic valve, nor even a schematic. Anyone?

[Machinbird]

Originally Posted by snj5

I have scouered the internet from aardvark to zwart and find neither the name or source for said hydraulic valve, nor even a schematic. Anyone?

SNJ5, There are two design approaches that have been used over the years. Hydraulic/pneumatic system activated and pilot activated.
For a system activated brake, take two spring loaded 3-way valves and activate with two interconnected cams. One valve-cam set for right brake, one for left brake. The valves port the wheel cylinder to pressure or to return. You will need a source of controlled pneumatic or hydraulic pressure.

For pilot energized brakes the above won't work since the pressure line is also the return line. The Chipmunk hydraulic braking system could be used, but take a look at this accident report to get a better understanding of its operation/limitations:http://www.aaib.gov.uk/cms_resources...pdf_027250.pdf
The Chipmunk brake system is very different from anything else out there. It appears that the individual wheel master cylinders are brought up against a rudder activated cam by the lever in the side of the chipmunk cockpit and this can limit available rudder throw if activated.
For Hank,
I've operated pneumatic system equipped aircraft (F-4) and they weren't that tough to maintain (mostly compressor and dryer work). I can imagine why an almost 70 year old Hurricane might have brake maintenance problems. The brake bladder spares must be at least 65 years old. Rubber is definitely a life-limited item. I'm thinking about a slightly different approach to the brake bladder thing. See:Dynamic Rubber, Inc. - Fabric Reinforced Inflatable Seals and Rubber Products
Mustang, thank you for the pilot viewpoint. You cant ask for anything better than intuitive operation.
Sid

[mustang]

The Chipmunk brake system is very different from anything else out there. It appears that the individual wheel master cylinders are brought up against a rudder activated cam by the lever in the side of the chipmunk cockpit and this can limit available rudder throw if activated.

Sid[/QUOTE]

This is correct. It is a taxying technique only and it is, or should be, part of the pre-takeoff checks to ensure that the catch is released and the lever is fully forward at brakes release. This not only ensures that full rudder travel is available during the takeoff run but also ensures that FULL rudder travel is available during any subsequent spin recovery, whether intentional or otherwise.

Mustang

[snj5]

Thanks everyone for the discussion. I believe we have hit the unneccesarily complicated for a WW 1 replica wall.

I had hoped it was rather a stick lever operated master cylinder providing pressure to a proportioning valve tied to the rudder bar, then out to the calipers.

Back to the more mundane heel vs toe activation conundrum...

Thanks again all!

[Brad]

Originally Posted by snj5

Thanks everyone for the discussion. I believe we have hit the unneccesarily complicated for a WW 1 replica wall.

I had hoped it was rather a stick lever operated master cylinder providing pressure to a proportioning valve tied to the rudder bar, then out to the calipers.

Back to the more mundane heel vs toe activation conundrum...

Thanks again all!

Putting mechanical (cable) toe brakes on a WWI replica with a rudder BAR would be extremely simple. You simply have a brake pedal that pivots on the bar to either pull the cable or push the cable housing. (I'm referring of course to the type of brake cables used on bicycles, motorcycles, etc.)

[RAF56_Ball]

Originally Posted by drrivah

Chip:
Inspirational photo-documentation on your build.

What are dimensions of the Chen Shin wheel hubs (width of hub and ID)?

Thanks.

-pete

The kit's wire wheels use 100 or 110 X 19 tires (or should I say tyres? <G>). The American size is 2.50 to 2.75 X 19" IIRC.

Hank,
These use small cables (3/32" galvanized) becaue air loads are so light. the aluminum tube structures more than adequate for the loads of even both pedals being depressed. If you were to "stomp" on the brakes in one of these, unless you slid, you would be on your nose ASAP.

Fro all, Tracy O'Brien just sent me a message that Robert Baslee is working with him on the small discs like on his site for the C-90. You could set these up (or any brake) with individual or joint controls. Several small planes activate both brakes with a single lever without differential braking.
I am not saying that is what I want, just that it does work. The Baslee planes really only need brakes for run-up and to slow on pavement, as they (and the GL Nieuport's I hear) land so slow, they stop ASAP on grass. 300' is a long landing roll, if the guys are to be believed, at least on grass. On pavment/bitumen you almost have to have brakes to get the final stop, as just the thrust of the engine will allow it to taxi, even at idle. Or so the story goes.

[Maxim08]

This is an interesting discussion re brake activation.
The D VII that I'm building uses a rudder bar and not pedals. Like another member in this thread, I was very interested in utilising the British pneumatic sytem until I did some work with a Hurricane.
This is a complex system which ties two functions together in the pneumatic circuit: brakes and flaps. There are two valves involved one to direct presure between the two services, the Dowty Pneumatic Control Valve and the Pneumatic Relay Valve which proportions pressure between the right and left brake. Ultimate pressure is from the control column control lever that looks like a bicycle brake handle. I thought that if you could have a hydraulic discriminator of some type linked to the rudder bar that would define the percentage of left vs right and the braking force from the control lever as used by some ultralight brake systems, you would have a simple and low visibility braking system. To date I have been unable to find the important part, the discriminator valve. I have talked with: Battle of Britain Memorial Flight; Hawker Restorations and 2 private collectors. This appears to be a universally difficult piece to find.
BTW, some of the Yak/Nanchang trainers uses a similar system but nothing that works with Hydraulics. FYI the Yak system uses about 700 psi and the Hurricane is tested at 1800 psi. More equipment, weight and complication than I want.
Some early Cherokees used a hand operated brake but this gave equal braking to both sides and was designed to slow the aircraft down not control it directionaly on the ground. To me, the reason for having brakes at all on a WW1 replica is for directional control on the ground primarily to assist in weaving for vision ahead, while taxiing.
The best solution that I have found to date is the Ron Sands system designed for the full size Dr1 replicas which uses toe brakes with seperate masters mounted to the rudder bar.
Interested to see where this tread goes and whether someone can create a more elegant solution.
Regards,
John