Mighty Mini-Mule

The downside to confessing one's sins on a blog is that there are so many helpful "friends" around the world that are only too happy to assist you in fully understanding the full scope and detail of how you've screwed up. How not only the specific thing you've done is wrong, but macroscopically, how your whole approach is less than bright.

My friend Bernd made this placard for me... with "best regards from Germany". The worst of it is, as safety officer for the museum, I have to agree that it's probably a pretty good idea!

He points out that a large mule is not necessary and that this 24 volt mule meant for the Mi-24 will work just fine on the L-39 (and probably not make a hydraulic lake on the hangar floor).

I like it, but I worry that if this thing ever went through an x-ray machine, we'd be detained by the TSA for having a nuclear suitcase bomb.


With friends like this... :-) Still, over the weekend of May 2^nd we're meeting up with Bernd at the music festival in Bautzen near his home town. If someone has a Russian nuclear radiation sticker I can slip on his mule while he's not looking, please contact me!

Hydrau-Lake

In the movies, Indiana Jones has a common theme that runs through his adventures. "Snakes!" he says with a mix of angst and disgust, "Why does it always have to be snakes?!"

While adventures at the museum are infinitely² more mundane, I seem to have developed a similar lament. "Hydraulic Fluid!" I seem to be constantly saying, "Why does it always have to be hydraulic fluid?!" Whether it's sumping struts, messing with the mule, or showering in it when changing filters, it seems like this slippery, red, sweet-smelling juice is always the rain on my parade.

Getting an L-39 ready for its annual inspection requires getting it up on jacks. I could have predicted that wasn't going to go as planned. I pumped one of the jacks right and it went up a little... then I pumped it left and it went back down. Do what? What's to go wrong with a jack? Well, it turns out not much... but just enough to get me and the hangar floor covered in hydraulic fluid.

The valves on the jack are a typical Eastern Bloc design. Simple, ingenious, rugged, and made with as much off-the shelf components as possible. In this case, a small bearing (i.e. a readily available, precisely-made component) sits on top of a valve seat, a little cap sits on top of that, and it's all held down with a spring.


Except in this case, rough handling of the jack had gotten the cap/bearing/spring mechanism all cattywhompus. Fixing it meant draining the jack, fishing out the parts, dropping them back into place carefully and filling the jack back up. With hydraulic fluid, of course.

The best part is bleeding the air out of the jack. For that the 135lb+ jack has to be balanced on its head and a small needle valve backed off until air and hydraulic fluid, of course, goes spraying all over the place. I've gotten myself covered in the stuff often enough that I now have an allergic reaction to it. I make a special point of trying to avoid touching my face when my hands have been soaking in it, although I always manage to do that anyway.

I've found that if I clean up with Goop hand cream before I've marinated too long and then wash up with soap and water eventually, I can avoid most of the ill effects. Except on my face — I'm doomed to getting a rash there no matter what I do.

It could be worse, I guess... at least it's just 5606 and not Skydrol, which is what the airlines use... that stuff starts to slowly eat your skin on contact.

All pumped up

After we received the replacement pump, Jon installed it and placed an order for massive quantities of hydraulic fluid so we could proceed with ground checks for the various aircraft in waiting.

This pump has two impeller sections and each section is connected to a separate filter and pressure control. This gives the mule two separate systems that can be simultaneously connected to an aircraft. Our larger aircraft (MiG-21, MiG-23 and Mi-24s) typically have two isolated hydraulic systems, primary and secondary.

In its first two days of operation, the mule was used for tests on the Mi-24s, Bord 118 and Bord 120.

The mule is shown here outside the maintenance hanger where it was just connected to Bord 120 to test hydraulic integrity after the transmission was re-installed. The service loop for the mule reaches all of the service bays inside the 14,000+ ft² hanger as well as the adjacent taxiway.

Baby Mule

The new pump for the mule will be leaving the factory in England tomorrow morning for the long journey to Texas.

Hydraulic Pumps (UK) Ltd. were kind enough to provide us with some "baby pictures":

Mule Update

Why do Englishmen drink warm beer? A: Because their refrigerators have Dowty pumps!

The mule has a dual pump made some time in 1979. One imagines that it gave faithful service for many years, but — alas — no more. A cracked housing left us showering in Aeroshell Fluid 4 (aka "good ol' MIL 5606G"). Soviet aircraft use AMG-10, which is so similar to 5606 that the two can be mixed with no ill effects.


When the end casting (which should have been a plate) busted into three pieces, shards of the casting went into the gears and the pump summarily ate itself.


Dowty was bought by Parker some years back and they were able to supply an exact replacement pump. Particularly important was matching the keyed drive shaft and mounting holes.


Parker is shipping us a new pump from South Yorkshire, a transaction greatly simplified by our snazzy new Skype Phone that was bought specifically for locating parts in Europe. The new pump should arrive some time next week.

Woe is Mule

About a year ago, the museum received a hydraulic mule as a donation. It has everything you'd want in a mule: dual systems, high pressure and flow with control over each, and filters so that contamination in one aircraft doesn't migrate to others.


The mule, aka "Smurfette", needed quite a bit of work... new electrical cable, new filters, and new hoses and fittings. Sometimes when things are donated you wonder what might be wrong with them. Well, today we found out what's wrong with Smurfette: Cracked pump housing. Really sprayed fluid like crazy when we turned it on.


Cracked isn't the half of it... the end cap on the housing is completely busted into three pieces. No worries, tho', looks like there are plenty of places to get Dowty pump replacement parts on the net.

Mule is Kicking

The hydraulic mule that was donated a year ago was finally tested on 3-phase power and seems to work quite well. The museum is looking for 100' of 6 AWG or 8 AWG four-wire extension cable (flexible) or three-wire + ground. This will allow us to use the mule in almost any location in hangar three.

This mule has a 10 hp motor which drives two independent systems serving up to 3000 psi. Several of the aircraft require a high-volume, high-pressure mule to fully test their hydraulic systems.