Main Gear Issues
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Hydraulic Brake Mod

Our ship is equipped with a hydraulic disk brake. The hose is routed through a hole in the side of the wheel enclosure, near the bottom, front. The routing of the hose, and the location of the hole in the enclosure results in a very sharp "jog" for the hose, right where it needs to flex to accommodate the wheel retracting up, into the enclosure. The designer of the hydraulic conversion attempted, unsuccessfully, to deal with this with a grommet in the hole in the enclosure; the grommet refuses to stay put. This is causing the outer woven jacketing of the hose to become cut and frayed. Our AI tells us we need to replace the hose by the time the next inspection rolls around. I want to modify the (non-structural) enclosure in order to eliminate, or reduce, the wear and tear on the new hose. Sure would be easier if I could remove the enclosure, but I don't see how this can be done easily. Evidently, RJ's experience confirms this.
Chuck Stoltz

Where did you get the disc brake conversion? Has your ship now in the "experimental" catagory due to this modification? I heard there was a kit for this years ago, but is it available again?
Mike Panek

The Disk Brake conversion was designed and supplied by Jensen Aircraft and installed by Gehrlein in 1977, near as I can tell from the paperwork. It is based on a Gerdes master cylinder & caliper. It was done early in the ships history, for the original owner and the airworthiness certificate was changed to experimental at the time the conversion was done. This was reveresed later, with a 337 and lots of correspondence with the FAA, so it is back to Standard Airworthiness (supplimental) certificate, as of June, 1981, well before we purchased it. I don't know if any other Std Cirrus has been converted to disk brake, using this or any other kit. I wish it were still available. I've been able to track down wheel bearings for it, but not much else. I do not think anyone is currently offering a conversion kit. Even Tost doesn't list one. The brake acutation has been moved from the lever on the control stick to the spoiler -- the last 5% of spoiler handle movement actuates the brake. It is effective, you can put the ship on it's nose, but it takes a lot of force to operate.
Chuck Stoltz

Wheel Box

How difficult is it to remove the fiberglass housing for the main wheel? I know that someone out there has done it. Can it be removed through the fuselage interior? What else has to be removed, first?
Chuck Stoltz

I did it once, certainly not impossible but not easy. It's best to get the plane inverted on saw horses, then remove the entire wheel and then all the landing gear framework; one of the bolts for the rear attachment point has to be accessed by the hole on the side of the fuselage. Then remove the ten or so tiny screws around the housing that hold it in place. The housing came out, with much careful maneuvering, bending and sometimes an extra set of hands, through the landing gear opening. Removing and reinstalling the landing gear frame work was difficult as there is very little clearance to work with some of the nuts and bolts, especially the front pair. I took (but no longer have) digital pictures for reference at each step.
RJ Stutzmann

I removed my wheel enclosure through the fuselage and without taking the wheel or wheel assembly off. It is a tight fit to bring it past the tube members behind the seat but it will fit. I do not have any additional items behind my seat such as hydraulic lines or o2 bottles.


Standard Cirrus Brakes

According to Schempp-Hirth in 2004, three hubs were used for Standard Cirrus gliders. The first was a hub from ZÜNDAPP that quickly became unavailable. The second hub was a 4"-Lilliput from TOST, which is still available. The third was a 4"-Kobold with 5"-brake from TOST, which is also still available. Based on design drawing dates, the switch from Lilliput to Kobold appears to have occurred in 1979. Blueprints for the retract mechanism with these two hubs follow:


4"-Kobold with 5"-brake

Maintenance Suggestions

I have finally gotten around to having my Tost wheel brake rebuilt by that motorcycle shop in California (Michael "Mercury" Morse). Michael turned the inside of the drum, replaced the brake pad material and arc'd the shoes to fit the drum. Yesterday, I was able to test it for the first time and it WORKED!!! In fact, it worked better than the original brake ever did - no matter what I did each season to "tune" it up. I am attaching a photo to show you what was done. I am hopeful that this will be a long term solution - time will tell...

--- Jens Aarnaes, Standard Cirrus #129

To: Standard Cirrus Group
From: Tom Knauff, USA Dealer for Schempp-Hirth Sailplanes

Gregg Foster asks the following questions. I have included my comments after each question.

>Is anyone aware of a "bolt on" hydraulic disk brake replacement for the mechanical Tost brake?

No, but it would be expensive. The Tost brake works fine if it is maintained properly.
I'll do the best I can to answer more questions.

Tom Knauff

I have a TOST drum brake that for all intents and purposes doesn't work. My friends have various ships (Discus, Pegasus, etc.) with TOST drum brakes that don't work. Between us, we have tried all kinds of tricks including the "free-floating" modifications only to result in having TOST wheel brakes that still don't work. If all we need to have "proper maintenance" please define what that is or how we can find out what that is.

Jeffry Stetson

From: Doug Haluza (
Subject: Re: Std Cirrus Group --- TOST wheel brakes
Newsgroups: rec.aviation.soaring
Date: 1996/12/03

Jeffry Stetson wrote

> If all we need to have "proper maintenence" please define what that is
> or how we can find out what that is.

I believe one of the major problems with the Tost drum brake assembly is that the metallic brake shoes have a tendency to "glaze" which reduces their effectiveness. The solution is to remove the glaze from the shoes and hone the drum surface with some sandpaper at regular intervals.

Another problem is that the brake cables have a tendency to stretch which also leads to ineffective braking. One solution I have heard of is to use "Mountain Bike" brake cable which supposedly doesn't stretch as much. I don't know of a source for FAA PMA approved "Mountain Bike" brake cable, however. ;-)

From: Wings and Wheels (
Subject: Re: Std Cirrus Group --- TOST wheel brakes
Newsgroups: rec.aviation.soaring
Date: 1996/12/03

By far the biggest problem with the TOST wheel brake or any drum brake is the smallsh amount of brake shoe that actually contacts the drum due to the pivot end of the shoe being opposite the hinge end...Brake function can easily be improved by sand-blasting the inside of the drum and allowing the brake shoes to wear further where they already contact the drum surface thereby increasing the total amount of brake shoe to actually come in contact with the drum...Obviously this requires the brake cable be re-adjusted after the shoes have worn further but does greatly improve the effectiveness after... I have even converted TOST wheels to a full floating/self energizing brake by removing the pivot pin from the drum completely and using just a bolt in the pivot end to replace the space left by removing the pin. With this simple mod I managed to make a non-exsistent wheel brake on our IS28B2 Lark into a FUNCTIONING brake that actually lifts the tail when fully applied....This does however cause the brake to fade quickly if left applied which is quite understandable when trying to stop the energy of a 1200lb. glider with a 5" wheel... . I'd happily Fax a simple drawing to anyone who would like to see this better...

Wings and Wheels

From: (
Subject: Re: Std Cirrus Group --- TOST wheel brakes
Newsgroups: rec.aviation.soaring
Date: 1996/12/05

Tim hit upon the major problem of the Tost brake: the pad does not contact the drum for much of its area. A long term solution is to take the drum and pads to a high performance motorcross shop (easy to find here in Southern Calif) and have them put high performance shoes on the pads and radius them to the drum. These pads do not glaze are very aggressive and they have nearly 100% contact with the drum.

Several customers have put their ships on the nose despite warnings about their new brakes. More work for me I suppose (jest).

In addition, the cable can be replaced with stainless steel motocycle cables and nylon lined housings. Makes for WAY less stretch and a smooth, easily modulated brake. You can be subtle with your new found braking power as supplied by solution #1 above.

From: Mark (
Subject: A Tost drum brake that works
Newsgroups: rec.aviation.soaring
Date: 2001-06-13 11:23:22 PST

Last fall I posted a message asking for feedback about the Tost wheel brake modification that had been written up in Soaring Magazine by Tillman Steckner (SP?). I got mixed reports about that modification, particularly accounts of brakes that went on but not off after the mod. I did receive encouraging advice about a different approach. Instead of reworking the brake mechanism, have a motorcycle shop install better qualitiy linings and "arc" the shoes to better fit the drum.

I took the motorcycle shop route with very good results. They installed linings typically used on motocross bikes and did the machining to make everything fit as it should. The wheel brake performance on my ASW-20 has gone from dismal to very good. I would recommend keeping the stock mechanism and improving the linings and fit of the parts to make the thing work.