200 quid is a normal price to be paid for a motor rewind but you won’t get paperwork with it 
There should be firms out there who can do “certified” motor repairs even if there is no CMM from the motor mfg. After all, there are firms who can do certified exhaust system repairs without a CMM. Whether there are any in Europe I don’t know.
A Briggs & Stratton electric motor is likely to be chinese.
The Briggs & Stratton DC motor on my Falco burnt out last year due to the original builder making a balls up of the circuitry during the build.
It cost me £200 to get it rebuilt. I didn’t like having smoke in the cockpit, but I do like the tiny bills I get when I have to fix something!
I would say that there a worlds between hydraulic systems (i.e., an overall system operating at a certain pressure and with a certain maximum flow) and a light aircraft landing gear. These really are electrical landing gears where the mode of power transmission is hydraulic rather than mechanical. Similar to the difference between a dynamo-driven lightbulb on your bicycle and a dual-alternator, dual battery voltage regulated electrical system. One of the more interesting aspects of all that long-forgotten ATPL theory…
Peter wrote:
Sure; the other way is to have two or more linked gear pumps. These deliver equal volume flow.
Yes I guess, but that’s not how the airliners do it Flow dividers and volumetric flow regulators are the methods used to assure some constant max speed of a piston or a constant speed relative to another piston. Retracting several tons of airliner gears, I would believe doing it at correct speed is much more important than doing it at equal speed. Pumps are typically continuously varying axial piston pumps and connected to accumulators, making the pumps incapable of doing anything else but to maintain a constant pressure independent of flow (which is exactly what you want a hydraulic pump to do).
For smaller applications things can be done simpler, but a simple flow divider (plunger type) is a very simple and compact device.
Some DC motors in aircraft seem to be trouble free – never had a problem with the C172 flap motors. Our flying club in Houston had a C172 that regularly did 100 hours per month, the flap motor had a 100% reliability :-) (In fact the whole aircraft was pretty decent – it looked a bit shagged from the wear on the upholstery etc. of people constantly getting in and out, but it flew well and rarely had problems. Sadly its hangar collapsed on it during a hurricane a few years ago.)
Well, the only problem I have had with DC brush motors in aircraft has been with the hydraulic power pack
Yes – same for me I have not yet had the motor looked at but when it hesitated it drew a high current which suggests a short in some windings. (The much more common problem is a hesitation with drawing zero current; this is caused by a faulty pressure switch).
But the only other DC brush motors in a TB20 are the flap motor and the electric fuel pump, and both of those give regular trouble in the GA (TB or no TB) fleet, way before you would expect even a crappy chinese motor to pack up. For some reason these motors don’t make anywhere near any sort of reasonable running life.
Well, there are the three autopilot servo motors and they have two specific problems: they are of really crap quality (Globe, USA, certified down to -55C so everybody uses them) and the autopilot thrashes them around all the time, so the commutators don’t last.
Car electrics used to be terrible up to the 1970s, but then much improved. I suspect the main reason is better sealing from moisture. This is still poorly addressed in GA, with very little being hermetically sealed and 1970s-style molex connectors used all over the place (even by avionics shops on new installs).
the no brain solution is to use a volumetric flow devider
Sure; the other way is to have two or more linked gear pumps. These deliver equal volume flow.
I think the Socata kit (I have a diagram somewhere) uses spring-loaded valves. So all the time the back pressure due to stiction is less than the pressure required to open these valves, you will get equal gear movements. It is probably OK reliability-wise because while the pump has to work harder during the entire movement, it has to work really hard only at the very end when compressing the rubber bungs and that happens on the normal system (the ~1600psi switch then cuts the current off).
Peter wrote:
I wonder how airliners implement the concurrent retraction
It’s basic hydraulics. I don’t know the exact english terms, but the no brain solution is to use a volumetric flow devider. A very simple device that divides the volumetric flow in two (or any other ratio), independent of the pressure in the two extensions. The other (no brain) method is to use a volumetric flow regulator in each sub system. With this device you have a constant volumetric flow independent of the pressure. The down side is it will steal a bit pressure and adds more components.
Peter wrote:
Does the mustang have symmetrical operation and if so how is it implemented?
It just has hydraulically driven actuators. No mechanism to ensure symmetrical operation that I am aware of but having seen them from the ground it seems pretty symmetrical. But as said below the system remains pressurised at all times although when the gear lever is moved the pump increases pressure in the accumulator.
Shorrick_Mk2 wrote:
DC brush motors that fail don’t seem to be that much of a problem on Mooneys.
Well, the only problem I have had with DC brush motors in aircraft has been with the hydraulic power pack 
It probably helps having a hydraulic system that is always pressurised and gear actuation that starts instantly the moment the check valve opens, vs. waiting on the pump to spin up.
Staggered deployment (by design) can also have advantages as the peak load on the pump is going to be smaller. Incidentally Airbus has filed a patent for staggered landing gear deployment to minimise hydraulic loads and aerodynamic interference between gear and gear door on deployment (i.e. the inboard gear door will swing way past centerline instead of hanging straight down). Coming to an airliner near you in the close future.
