hydraulic retracts
03-22-2013, 11:28 AM
#82
RE: hydraulic retracts
The gears came from a specialist gear manufacturer.
Biddle and Mumford Gears Limited
8-18 Kings Place
Buckhurst Hill
Essex
IG9 5EA
UK
The gears were 1 Brass 4mm wide 2mm bore 9teeth, 9mm O/D, 7.4mm meshing centres.
1 Steel with ditto dimensions.
I would recommend using 4mm Festo NYLON tubing for the retract. I have though used 3mm for the gear doors, they of course consume a far smaller volume of fluid.
m
Biddle and Mumford Gears Limited
8-18 Kings Place
Buckhurst Hill
Essex
IG9 5EA
UK
The gears were 1 Brass 4mm wide 2mm bore 9teeth, 9mm O/D, 7.4mm meshing centres.
1 Steel with ditto dimensions.
I would recommend using 4mm Festo NYLON tubing for the retract. I have though used 3mm for the gear doors, they of course consume a far smaller volume of fluid.
m
03-22-2013, 01:35 PM
#84
RE: hydraulic retracts
Mick....
Been following your adventures with hydraulic gear for a while... You've got a great collection of aircraft, my compliments to you!
I understand most of your system, and like the accumulator made from an air cylinder. I have a couple of questions though if you would be so kind.
How do you estimate the spring value that goes inside the cylinder? In the States there are a few manufacturers of cylinders that will make a cylinder with a spring in it and they list a variety of pressures to overcome that spring. I was hoping to use one of those but don't know how much pressure would be needed. I suppose it would vary some from airplane to airplane due to gear size and design, but was hoping you could give us a ballpark figure. I would assume that if it took 75 lbs of air pressure to move the cylinder to full travel against the spring, then the hydraulic system would be operating at a little under 75 lbs and then shut off when the gear is locked and the accumulator piston travels to its full length and hits the micro switch.
Secondly, you mention that you have the micro switch wired to a relay, and possibly another master "arming" switch. I'm hoping you can explain that a little better or maybe provide a diagram. I assumed that you would turn on a mechanical switch that would energize the pump system, and when the gear valve was operated the pressure would drop, the accumulator rod would retract, and the pump would run. When the gear stopped moving, the pressure would build, the accumulator would extend and press the switch shutting off the pump. From your descrptions it sounds like you have something else in the system that will energize the system via radio command, or possibly work in conjunction with the micro switch.
Help me out if you can!
Thanks!
KennyMac
Been following your adventures with hydraulic gear for a while... You've got a great collection of aircraft, my compliments to you!
I understand most of your system, and like the accumulator made from an air cylinder. I have a couple of questions though if you would be so kind.
How do you estimate the spring value that goes inside the cylinder? In the States there are a few manufacturers of cylinders that will make a cylinder with a spring in it and they list a variety of pressures to overcome that spring. I was hoping to use one of those but don't know how much pressure would be needed. I suppose it would vary some from airplane to airplane due to gear size and design, but was hoping you could give us a ballpark figure. I would assume that if it took 75 lbs of air pressure to move the cylinder to full travel against the spring, then the hydraulic system would be operating at a little under 75 lbs and then shut off when the gear is locked and the accumulator piston travels to its full length and hits the micro switch.
Secondly, you mention that you have the micro switch wired to a relay, and possibly another master "arming" switch. I'm hoping you can explain that a little better or maybe provide a diagram. I assumed that you would turn on a mechanical switch that would energize the pump system, and when the gear valve was operated the pressure would drop, the accumulator rod would retract, and the pump would run. When the gear stopped moving, the pressure would build, the accumulator would extend and press the switch shutting off the pump. From your descrptions it sounds like you have something else in the system that will energize the system via radio command, or possibly work in conjunction with the micro switch.
Help me out if you can!
Thanks!
KennyMac
03-22-2013, 04:12 PM
#85
RE: hydraulic retracts
Hydraulics
The value of the spring in the acc cylinder is arrived at from experiments, as rule of thumb though the piston is fully extended at 150psi. Now from this point several adjustments are possible, you can pack the spring with washers to increase the pressure and vary the distance the micro switch is from the pushrod to raise or lower the pressure switching point. If the pressure is set too low the pump will be switched on and off until the gear is away.
I use a high quality radio controlled 6amp relay which is obviously between the battery and the pump. The micro switch, switches the negative wire between the Rx and the relay. Now if you want to keep it really simple that's all you need, I though utilise a timed radio program to operate the relay. I also have an extra switch so am able to energise the pump at any time, this switch function is essential on my Sea Fury's wing mechanism as it is not possible to have this function timed.
One little wheeze on the A10 through "logic" switching when the gear is down and full flap is deployed and the throttle is shut the pump is energised.
m
The value of the spring in the acc cylinder is arrived at from experiments, as rule of thumb though the piston is fully extended at 150psi. Now from this point several adjustments are possible, you can pack the spring with washers to increase the pressure and vary the distance the micro switch is from the pushrod to raise or lower the pressure switching point. If the pressure is set too low the pump will be switched on and off until the gear is away.
I use a high quality radio controlled 6amp relay which is obviously between the battery and the pump. The micro switch, switches the negative wire between the Rx and the relay. Now if you want to keep it really simple that's all you need, I though utilise a timed radio program to operate the relay. I also have an extra switch so am able to energise the pump at any time, this switch function is essential on my Sea Fury's wing mechanism as it is not possible to have this function timed.
One little wheeze on the A10 through "logic" switching when the gear is down and full flap is deployed and the throttle is shut the pump is energised.
m
03-27-2013, 02:30 PM
#87
RE: hydraulic retracts
The relay is the switch, unless you are refering to the micro switch in which case you certainly cannot run the pump off that, the amperage is far too high particularly at start up.
m
m
03-05-2017, 10:39 AM
#89
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Mick,
what have you been using for fluid in your hydraulic retracts? I recently got a mig-29 that has the eurokit hydraulic system. I need to top off the hydraulic tank and want to make sure I don't use something that's going to ruin the O-rings. I heard sewing machine oil works good. Any suggestions?
what have you been using for fluid in your hydraulic retracts? I recently got a mig-29 that has the eurokit hydraulic system. I need to top off the hydraulic tank and want to make sure I don't use something that's going to ruin the O-rings. I heard sewing machine oil works good. Any suggestions?
03-06-2017, 04:30 AM
#92
