The Brute Force Solution / Power Pack

Jonathan Baron

Jonathan Baron

New member
Although we all have to endure the vagaries of life, sometimes there is point beyond which you cannot compromise.

I'd waited for my 'Master a long time. My particular friend had to put in a lot of work to make it so. Thus, now that it is here, no force in the known universe can keep me from flying it...even when the temps are hitting 100+ with Virginia humidity. Only one problem remained though. The hydraulic fluid reservoir tank on the firewall was just a little too small to handle the increased volume of the new system. If you've seen one, you know its size: roughly that of one of those small cans of tomato juice with the pull-off openings. Although my mechanic has been an utter jerk, taking nine months and counting to finish the clean-up work after hanging the freshly overhauled engine on my Luscombe, he's great with short-cycle fabrication jobs. I made it CLEAR that I wanted this last problem to end FOR ALL TIME. There could be NO QUESTION about the solution. He took his measurements, fabricated a new tank, installed it, and - yes - the problem went away.

Those of you with these systems will appreciate the solution.

Jonathan
 
You were right, as usual, Russell...and it really, really solved it too :) It visually makes the statement, "Fluid? You say you want FLUID? Well HERE'S YOUR DAMNED FLUID, and I hope you drown in it!" Yep, that tank has made me sooooo happy :p
 
I wonder if that was my problem with my "Power Pack".
If you have the time, and for the sake of clutter in this forum look up my postings.
Then please reply.
 
Sorry....don't have the time to run a search on all of your posts, I am not a technical person who could not provide an informed answer, plus any answer I could give would be out of context in the forum topic flow.
 
I think you have a 14-19 - does it have a -2 Electrol valve pack or the 750B original equipment pack? What hydraulic pump do you have, the eastern industries pump?
 
Well I did find the modal number and serial number on the power pack. I am not sure I like what I found but here it is. The label said Warner Division and modal 750 P-W. Serial number 9. The only other thing I could read was the wards Kingston NY.

The tag on the pump is on the bottom down between the mags. Can’t read it. My log books don’t show an change of power packs. I hope to be wrong about that “P”.
 
I know ther have been posts on this subject before, but I don't recall this issue. My search function won't work either so I can't look up the old posts. First this is the old type system, that is pure hydraulic, no electrics. This is among the last of these, on a 1968 17-30 Viking, but I believe this to be identical to the 14-19-3 & 3A. Problem is the gear goes up fine, but about half or maybe a third of the time the right main sneaks down. First the red indicator goes out, then if ignored long enough the right green will come on. The micro-switches are correct, the right main actually comes down. If I cycle the gear 2 times in short cycles (not fully down, fully up) it will then stay up. It is always only the right main, never any other.

Corrective measures taken so far: 1. remove res from firewall & thoroughly flush-clean. It was very dirty & had chunks of debris. 2. remove res on the pack itself, clean all the black off the accessible plates and reassemble with new big O ring. 3. Flush the whole system, draining at at all 3 cylinders, went through 3 quarts of fluid. Also put her up on jacks & with the hand pump the gear remains locked & welded up...won't budge.

Prior to corrective measures got so as I could hardly keep the right retracted. Now, while much better, it still needs something. As with all intermittent problems there is lots of guessing. Anyone have similar experience?

Thanks
 
Hmmm...wonder of that's a B with the bottom of the letter missing.

Only through PAINFUL experience do I know squat about this subject. Technical information...well...if this were high school, and tech knowledge were a key subject, I'd be in the "special class."

1950-1951 14-19s used the Electrol 750B pack. 14-19-2s used the 750N. Unfortunately nobody is overhauling the 750Bs any longer. Dick Pifer of Pifer Airmotive will say he can overhaul them, but it depends on his mood when you phone, and I had terrible luck with his shop when he did mine. It took lots of time, it never worked well, and you're looking at a 1400-1500 dollar job. Going to he later pack in not trivial. First of all, the mounting hardware is different. Russell performed this retrofit on mine and he can go into detail about this.

Actually knowing whether the pack is the problem is not trivial either. In some cases - gear won't stay up, hydraulic pressure is low when you push the lever, and other snafus - can be caused by other problems. This is a zero pressure system, meaning that the hydraulic pressure goes to zero when the lever is in neutral. Thus, a leaky actuator cylinder could be to blame with the former, and a worn out pump could be the problem with the latter. Takes some troublshooting prior to coming to conclusions.

Jonathan
 
Jonathan's right about the valve pack part numbers. Although a 750P (assuming the P is real and not a poor stamping of a "B") could be a base unit from an Apache, they look the same as a 750N but have a shorter reservoir.

The -2 750N packs have a cylindrical reservior about 2.5 inches tall and about 8" that sits on top of the unit. As I recall the 750B packs don't have that round reservoir but it has been a while since I looked at one.

The conversion of a 14-19 to a 14-19-2 750N pack isn't that hard. The hardest part is building a mounting adapter plate for the pack that adapts the 750N bolt pattern onto the welded-on tabs on the airframe of a 14-19 which are set up for the quite differently shaped 750B pack. The rest is plumbing, although I would advise getting rid of a lot of the cruft that tends to accumulate in plumbing systems where different mechanics repair and add unions into the hydraulic lines. In Jonathan's plane, for example, there previously were 4 unions in one line that ran for about 2 feet, and a mixture of hardware store compression fittings and AN flare fittings in the same line. That's just sloppy.

Jonathan's not quite right about a "zero pressure" system that releases pressure when the selector levers are in neutral. The engine driven hydraulic pump runs continously. When the levers are in neutral the pump output is bypassed into the reservoir on the valve pack and returns back to the pump reservoir. There is very little pressure on this line but quite a bit of flow in this state.

When you select a position for gear or flaps then the pump output is routed through the pressure regulator in the valve pack and to the actuator. The lines to the actuators are restricted enough so that a working pressure of between 500 to 800 psi is applied, depending on whether the actuator is in motion. Upon reaching the end of motion then the pressure goes to maximum and will stay there as long as the pack levers are still out of the neutral position. At full travel the overpressure is supposed to kick the selector lever of a 750N pack back to neutral, but it doesn't always do this depending on the condition of the system. When the selector lever is moved back to neutral the line is hydraulically locked, and there's the trapped static pressure in the line as well.
 
Now, just imagine how sloppy it would have been had I worked on it <shudder>.

By zero pressure I meant that fluid is not being pumped into the actuating cylinders when the levers are in neutral...not that everything was taking a nap. I've often heard of it referred to as a zero pressure system, and this puzzled me - not because I could not understand the concept, which sounds much like holding your finger on the top of a soda straw, but it made me wonder how other systems worked. No matter. This is the first and ONLY aircraft I will ever own with retractable landing gear. One more snafu with the hydraulics and I won't own even it.

Jonathan
 
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