How To Make Air Retracts Reliable?
10-01-2013, 01:53 PM
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How To Make Air Retracts Reliable?
Guys
Fairly new to the jet scene and the mandatory use of retracts in such aircraft, I was pondering which way to go with my latest build (FB T33) wrt having a reliable retract system, considered electric but would appear that having a system that is totally reliable may still be a little way off, also looked at hydraulics but not keen on all of the ancillary equipment required. That just leaves the pneumatic systems that have been in use since I started building and flying some 40 years ago, my experience with air is very limited so I thought that I would try to tap into the knowledge base that frequents this forum in an effort to find out what is the consensus in making such systems as reliable as they can be.
I am aware that there are still failures with air systems but I am sure that there are things that can be done to lower the incidence of such failures, I also know that there are many pneumatic devices available but what are the things that you always include when assembling an air system, ie do you add a gear fail safe (which one or ones), use any special airline retainers/fittings, what about connectors, how important is the size of the air tanks used in relation to the type of retracts and the associated struts and wheels that they are expected to lift, (my T33 has very large and heavy retract assemblies)? As you can gather I am looking for points that would see me (and others) benefit from the experience that is the norm from the more successful amongst jet fliers, any advice would be gratefully appreciated not only by me but to the general modelling community?
Thanks and Regards
Peter
Fairly new to the jet scene and the mandatory use of retracts in such aircraft, I was pondering which way to go with my latest build (FB T33) wrt having a reliable retract system, considered electric but would appear that having a system that is totally reliable may still be a little way off, also looked at hydraulics but not keen on all of the ancillary equipment required. That just leaves the pneumatic systems that have been in use since I started building and flying some 40 years ago, my experience with air is very limited so I thought that I would try to tap into the knowledge base that frequents this forum in an effort to find out what is the consensus in making such systems as reliable as they can be.
I am aware that there are still failures with air systems but I am sure that there are things that can be done to lower the incidence of such failures, I also know that there are many pneumatic devices available but what are the things that you always include when assembling an air system, ie do you add a gear fail safe (which one or ones), use any special airline retainers/fittings, what about connectors, how important is the size of the air tanks used in relation to the type of retracts and the associated struts and wheels that they are expected to lift, (my T33 has very large and heavy retract assemblies)? As you can gather I am looking for points that would see me (and others) benefit from the experience that is the norm from the more successful amongst jet fliers, any advice would be gratefully appreciated not only by me but to the general modelling community?
Thanks and Regards
Peter
10-01-2013, 04:36 PM
#3
Hmm, the best advice is to get retracts from reliable sources. Robart actually does a pretty good job on their gear. DreamworksRC also will likely have a few different sources of good retracts that may fit, albeit even with some "fitting" needed.
Needless to say, BVM makes some of the most reliable systems on the market. I've actually fit quite a few different BVM retracts in other airplanes because I wanted gear that worked, EVERY time.
Don't forget to NOT use cheap air accessories like retract valves, tee's, brake controllers (BVM actually makes a finicky one I'm not crazy about and can leak) and fill valves.
I do a gear check before EVERY flight. EVERY time. I'm the only one I know that does this and I have had the least amount of gear failures of other people I've seen.
I test my that my gear go up and down, at least twice, EVERY time I fly. If they don't, the jet is grounded.
Let me iterate on all the air accessories that usually come with the chinese jets, your feibao included: THROW THEM ALL AWAY!
Needless to say, BVM makes some of the most reliable systems on the market. I've actually fit quite a few different BVM retracts in other airplanes because I wanted gear that worked, EVERY time.
Don't forget to NOT use cheap air accessories like retract valves, tee's, brake controllers (BVM actually makes a finicky one I'm not crazy about and can leak) and fill valves.
I do a gear check before EVERY flight. EVERY time. I'm the only one I know that does this and I have had the least amount of gear failures of other people I've seen.
I test my that my gear go up and down, at least twice, EVERY time I fly. If they don't, the jet is grounded.
Let me iterate on all the air accessories that usually come with the chinese jets, your feibao included: THROW THEM ALL AWAY!
Last edited by ravill; 10-01-2013 at 04:39 PM.
10-01-2013, 04:59 PM
#4
Hi,
Good advice. Adding to what Rav said, don't assume an item is good because it's metal or assume an item isn't good because it's not from BVM. I've seen people build our airplanes and think they're 'upgrading' by adding more expensive items (like BVM air cylinders) which sometimes are not as reliable as the 'cheaper' item. Whenever I build for others, I NEVER use the metal tees that are glued together. Those seem to come standard with a lot of Chinese arfs. Once your system is together, there's no reason why it shouldn't be able to hold pressure for a long time. The Y/A pneumatic equipment I use can hold pressure for weeks. After that, install a failsafe and enjoy years of trouble-free pneumatic retraction.
Good advice. Adding to what Rav said, don't assume an item is good because it's metal or assume an item isn't good because it's not from BVM. I've seen people build our airplanes and think they're 'upgrading' by adding more expensive items (like BVM air cylinders) which sometimes are not as reliable as the 'cheaper' item. Whenever I build for others, I NEVER use the metal tees that are glued together. Those seem to come standard with a lot of Chinese arfs. Once your system is together, there's no reason why it shouldn't be able to hold pressure for a long time. The Y/A pneumatic equipment I use can hold pressure for weeks. After that, install a failsafe and enjoy years of trouble-free pneumatic retraction.
10-01-2013, 05:00 PM
#5
Invest in good quality airlines and tees. The up charge for using all Festo type connectors odour air system is less than the up charge to go electric. Use a proper cutter for airline and watch for pinholes.
My personal experience is I have seen most leaks at the fill valve and also the retract valve itself.
I like to use servos operating old school valves such as UP series from Ultra Precision. They work and the system is very simple and reliable.
PaulD
My personal experience is I have seen most leaks at the fill valve and also the retract valve itself.
I like to use servos operating old school valves such as UP series from Ultra Precision. They work and the system is very simple and reliable.
PaulD
10-01-2013, 08:15 PM
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Make sure its the easiest system to work on with everything has easy access. We all know any trouble will be with anything that's buried and you have to take half the jet apart to fix.
10-02-2013, 12:16 AM
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Peter
I would second what you have already been told. I would throw away all the pipes, joiners and valves you get and replace them with Robart or BVM gear and pipe. The retract units will have to be removed from the plane and tested one at a time with soapy water to make sure that are no leaks either at the connections or the inner and outer o rings. Most modern planes come with retract cylinders that are really too small. This means having to use lots of psi and higher pressures mean more leaks. I had a Fei Bao Su27 which had nice looking retracts that were very marginal and needed 120 psi to retract in the air. If the retracts are screwed together all screws should be taken out and assembled with Loctite. Mine came apart on the flying field after 2 flights on grass.
I prefer to use electronic valves but they too need checking for leaks. The larger the amount of air in the tanks you carry the more retract cycles you will get. You should aim for at least 4 cycles and that may need 3 large cylinders. You should not need to worry about safety devices if the gear holds air and is well checked out. It always takes a lot less pressure to drop the gear than raise it. Dont forget if there are gear doors attached to the legs they will catch the wind and act to stop the gear going up. I always use a BVM filler valve but even these have been known to leak, so check everything. The gear should hold air for several hours.
The doors I always make a separate system for as they do not need as much air pressure as the gear. My FB door rams worked except for 2 that were a pain to reach and I replaced with UP rams. The doors need to operate faultlessly as they can hang a wheel up.
I use RCBee sequencers which has a system that makes it impossible to switch on the Tx and retract the gear by mistake I have had several and never had a problem with them.
John
I would second what you have already been told. I would throw away all the pipes, joiners and valves you get and replace them with Robart or BVM gear and pipe. The retract units will have to be removed from the plane and tested one at a time with soapy water to make sure that are no leaks either at the connections or the inner and outer o rings. Most modern planes come with retract cylinders that are really too small. This means having to use lots of psi and higher pressures mean more leaks. I had a Fei Bao Su27 which had nice looking retracts that were very marginal and needed 120 psi to retract in the air. If the retracts are screwed together all screws should be taken out and assembled with Loctite. Mine came apart on the flying field after 2 flights on grass.
I prefer to use electronic valves but they too need checking for leaks. The larger the amount of air in the tanks you carry the more retract cycles you will get. You should aim for at least 4 cycles and that may need 3 large cylinders. You should not need to worry about safety devices if the gear holds air and is well checked out. It always takes a lot less pressure to drop the gear than raise it. Dont forget if there are gear doors attached to the legs they will catch the wind and act to stop the gear going up. I always use a BVM filler valve but even these have been known to leak, so check everything. The gear should hold air for several hours.
The doors I always make a separate system for as they do not need as much air pressure as the gear. My FB door rams worked except for 2 that were a pain to reach and I replaced with UP rams. The doors need to operate faultlessly as they can hang a wheel up.
I use RCBee sequencers which has a system that makes it impossible to switch on the Tx and retract the gear by mistake I have had several and never had a problem with them.
John
10-02-2013, 12:35 AM
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After following basically Johns procedure when I am re assembling the setup, I always put it together out of the plane and do the leak checks, I then put a dab of thin cyano on the joints which seems to help.
I have just become aware of an air failsafe unit.Does any one have experience of these and which type gives good performance?.
I have just become aware of an air failsafe unit.Does any one have experience of these and which type gives good performance?.
10-02-2013, 01:32 AM
#9
Hi Peter, I have been flying the FB T33 for three and a half years and can assure you the equipment supplied (all of it) works perfectly.
It of course doesn't hurt to check it all before use ie as John suggests pressure test in soapy water. I run two of the tanks for gear and a separate system for everything else.
m
It of course doesn't hurt to check it all before use ie as John suggests pressure test in soapy water. I run two of the tanks for gear and a separate system for everything else.
m
10-02-2013, 03:34 AM
#11
To save yourself lots of cash, buy your tubing (Fre-Thane 95A Polyurethane) from Freelin' Wade.
http://www.freelin-wade.com/fre-than...1462-l-en.html
McMaster-Carr also carries the same tubing at similar prices.
This place also sells 9462 Impact Resistant Epoxy (V-Poxy, & AeroPoxy) as well as the applicator gun.
http://www.mcmaster.com/#catalog/119/3416/=ord1b8
part# 74695A71
http://www.mcmaster.com/#6430a33/=orcut2
http://www.freelin-wade.com/fre-than...1462-l-en.html
McMaster-Carr also carries the same tubing at similar prices.
This place also sells 9462 Impact Resistant Epoxy (V-Poxy, & AeroPoxy) as well as the applicator gun.
http://www.mcmaster.com/#catalog/119/3416/=ord1b8
part# 74695A71
http://www.mcmaster.com/#6430a33/=orcut2
Last edited by Airplanes400; 10-02-2013 at 03:50 AM.
10-02-2013, 04:13 AM
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Hmm, the best advice is to get retracts from reliable sources. Robart actually does a pretty good job on their gear. DreamworksRC also will likely have a few different sources of good retracts that may fit, albeit even with some "fitting" needed.
Needless to say, BVM makes some of the most reliable systems on the market. I've actually fit quite a few different BVM retracts in other airplanes because I wanted gear that worked, EVERY time.
Don't forget to NOT use cheap air accessories like retract valves, tee's, brake controllers (BVM actually makes a finicky one I'm not crazy about and can leak) and fill valves.
I do a gear check before EVERY flight. EVERY time. I'm the only one I know that does this and I have had the least amount of gear failures of other people I've seen.
I test my that my gear go up and down, at least twice, EVERY time I fly. If they don't, the jet is grounded.
Let me iterate on all the air accessories that usually come with the chinese jets, your feibao included: THROW THEM ALL AWAY!
Needless to say, BVM makes some of the most reliable systems on the market. I've actually fit quite a few different BVM retracts in other airplanes because I wanted gear that worked, EVERY time.
Don't forget to NOT use cheap air accessories like retract valves, tee's, brake controllers (BVM actually makes a finicky one I'm not crazy about and can leak) and fill valves.
I do a gear check before EVERY flight. EVERY time. I'm the only one I know that does this and I have had the least amount of gear failures of other people I've seen.
I test my that my gear go up and down, at least twice, EVERY time I fly. If they don't, the jet is grounded.
Let me iterate on all the air accessories that usually come with the chinese jets, your feibao included: THROW THEM ALL AWAY!
Thanks, V.
10-02-2013, 04:39 AM
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I do all of the supplied tips, ie disassemble thank rebuild with loctite, leak check line etc, but I have used many different brands of air retracts, and accessories and just because it's brand "x" does mean it will always be perfect.... I've had some good Robert gear and some really crap Robert gear. I've had some good air power gear, and some not so good gear, etc etc. I look at everything that included in a kit and make an assessment( which means I sometime carry out testing of my own) as to whether I will use it or not for that build.
something i do for a living and also do on my models is actually maintain them!! It's the only way to maintain them working reliably. I don't fly my jet all that much but every dozen or so flights I go through all the systems and make sure that everything is still properly connected and working as it should, which amongst other things is to check and make sure the retracts are holding pressure.
everyone always tells you you should buy brand "x" or "y", but no one seems to actually suggest maintaining your model?? This is the key to heading off any major problems when you arrive at the field, and goes a long way to ensuring trouble free service from your equipment. If it's good enough for the fullsized aircraft, it's good enough for my models.
thanks
dave
something i do for a living and also do on my models is actually maintain them!! It's the only way to maintain them working reliably. I don't fly my jet all that much but every dozen or so flights I go through all the systems and make sure that everything is still properly connected and working as it should, which amongst other things is to check and make sure the retracts are holding pressure.
everyone always tells you you should buy brand "x" or "y", but no one seems to actually suggest maintaining your model?? This is the key to heading off any major problems when you arrive at the field, and goes a long way to ensuring trouble free service from your equipment. If it's good enough for the fullsized aircraft, it's good enough for my models.
thanks
dave
Last edited by ticketec; 10-02-2013 at 04:45 AM.
10-02-2013, 06:27 AM
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Also use a low pressure safety device. I use Tams. But there are a few different brands out there. You preset it so it will lower the gear if you have a slow leak and pressure reaches the preset point. I had a plane develope a leak with gear up and this lowered the gear in flight. Slight trim change. But better than a gear up landing!
10-02-2013, 07:48 AM
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Use a good O ring lube, Keep the orings from getting dry. Their can be moisture from your pump. JMP's Firebird has been sitting in his shop abetter part of a decade, and it still has air from the last flight 3 years ago.
10-02-2013, 08:46 AM
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I use three separate systems. Gear up, gear down, and brakes. When I have had problems it's always been in the cylinders. Believe or not, mostly with BVM gear. I discovered that if you don't have a big pressure difference across the cylinder, like when you try to slow the gear by restricting the exhaust side, the o-ring would not seat and you would just lose all your air through the cylinder while trying to move the gear. I sequence the valves now such that I dump all the air on one side of the cylinder before I apply air to the other. I have not had any issues at all since I started doing this. With three separate air tanks (systems) I know that I am going to have air to get the gear down even if the up system decides to leak while I am in the air, and brakes when I get down. Important since I fly off of fairly short runways around here. Yes, it's a little heavier and costs a little more, but well worth it in my opinion. I also use heavy wall tubing (Dreamworks, etc.) Thanks for the heads up on tubing Airplane400.
Bryan
Bryan
10-02-2013, 10:16 AM
#18
Bryan what kind of valves do you use to do what you are doing? I kind of picture what you are saying but the only valve I have that (I THINK) would do what you are describing is a Spring Air UP valve, a one way so to speak.
In other work I have done I have seen what you are describing. The oring will not seat in the groove correctly unless there is a lot of differential pressure on it.
In other work I have done I have seen what you are describing. The oring will not seat in the groove correctly unless there is a lot of differential pressure on it.
10-02-2013, 10:25 AM
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This is the latest thing in simple solution to the valve issue. Check it out... From Jet Model Products
I saw these at the dream works Site. also in person they are First Class.
I saw these at the dream works Site. also in person they are First Class.
10-02-2013, 11:02 AM
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mr_matt
I am using Jet-tronic single acting valves. One for up, one for down. I sequence them with a Weatronic receiver. I like them because they do not leak, but I think they are a little fragile. I was using a UP6 brake valve but was not getting good proportional braking from it so I went back to BVM smooth stop. drdoom...Nice, but it costs more than my first house!
Bryan
I am using Jet-tronic single acting valves. One for up, one for down. I sequence them with a Weatronic receiver. I like them because they do not leak, but I think they are a little fragile. I was using a UP6 brake valve but was not getting good proportional braking from it so I went back to BVM smooth stop. drdoom...Nice, but it costs more than my first house!
Bryan
10-02-2013, 11:15 AM
#21
And I don't believe in failsafes. As I check that my gear go up and down, twice before EVERY flight, EVERY time. But that EV-5 valve looks so good and has performed SOOOO flawlessly for me for so long now. If you get an EV-5, get a moisture trap you put inline your air compressor to catch any moisture that might enter your system.
The EV-5 can be found here:
http://www.dreamworksrc.com/catalog/...ulti-Valve-Pro
My first Jet instructor, Ehab, taught me to have METICULOUS retract attention. Its like the only thing I really don't mess with. I hate it when gear don't work. Its my biggest pet peave.
Last edited by ravill; 10-02-2013 at 11:18 AM.
10-02-2013, 01:16 PM
#22
A reliable pneumatic retract system is truly an example of a chain being only as strong as it's weakest link; a failure of any individual component leads to a system failure. You can improve the reliability of your system by buying high quality components and testing each component individually to ensure that it doesn't leak. If it leaks on the workbench, it will definitely leak when the plane is in the air.
Minimize the number of components and design a reliable system - Fewer components means fewer potential leak sites. The BVM F-86 that Andy Andrews and I brought to the JWM had FIVE air systems (retracts, doors, brakes, canopy, speed-brakes). Wow! That was five fill valves, five air gauges, five sets of tanks, five control valves, etc, etc, etc. All systems were pumped up to 120psi (except brakes which was 100 psi). First of all, this set up is expensive ($150 in fill valves alone), but by having 5 X as many components, there was a far greater likelihood of a leak. A lot of folks use a separate gear and brake system for "redundancy". There is nothing redundant about it; a backup system provides redundancy and one system for gear and another for brakes means there is no backup.
Here's the system I use (and this will get retrofitted to the F-86, BTW).....Connect together all the air tanks you were planning on using for retracts, brakes, and doors and connect them to a single fill valve and gauge. This minimizes the number of fill valves/gauges and associated leak sites (each fill valve/gauge/T connector set has seven potential leak sites). Connect the brake valve to one of the gear lines that is pressurized when the gear is down. This way, even if you have a leak in your brake system, system can only leak when the gear is down (so you aren't bleeding off air when you are flying around with the gear up). Install a Tam's (or other failsafe) with the set point high enough (I use 80-90 psi) to drive the gear down and lock it (nose gear units that retract the gear up/rearwards need more pressure to extend the gear down/forward against the slipstream and lock).
This grouped tank system has several advantages over the separate tank system.
1) You are minimizing the number of components and therefore reducing the potential failures/leak sites.
2) If you have a separate tank system and a leak in gear system, any air in the brake system tank is not accessible. If you can't get your gear down, it really doesn't matter if your brake system works perfectly....the bottom of the fuselage and wings are gonna be your brakes on the landing. Having all the tanks hooked together gives you a greater volume of air that has to leak before the system pressure drops to below a useful value.
3) The separate tank system gives you no information on the status of your brake system during a flight. If you have a leak in your brake system and you've bled down the system, you don't know about it until you attempt to use the brakes. Let's say that you are coming in for a landing and you are carrying a bit too much speed so you figure you'll touch down and use the brakes to stop in time. It's too late when you engage the brakes and find out you don't have any air. The grouped system is less likely to leak down because the brake system is completely isolated when the gear is up. Should the tanks leak down, you'll know it because the failsafe will lower the gear. At that point you'll know you have a problem and you are loosing air. So you do a careful approach and touch down as slowly as possible knowing that you may or may not have brakes (depending on how fast is the leak).
Perform system tests to ensure you don't have any leaks after everything is installed. I like to use a digital pressure gauge since the presence of a leak can be quickly detected and isolated. If you tested everything individually, you are less likely to have problems but, if you do have one, find it and fix it. When working on a new plane, I allow a maximum system leakage rate of 5 psi in 8 hours.
Perform Daily Tests - Test your system at least at the start of each day of flying though, like Ravi does, testing it before each flight is best. Just because your gear worked the last time doesn't mean that it will work the next time. There may be damage from the last flight.
Inspect/Maintain your system - Try to plan your pneumatic layout and make it simple, neat, and accessible which will make it easier to maintain and find any existing problems. Don't bury your components and air lines under big component boards. Those big boards may look nice, but they block access to the components underneath. If you can see your components, you may find a problem before it occurs.
Regards,
Jim
Minimize the number of components and design a reliable system - Fewer components means fewer potential leak sites. The BVM F-86 that Andy Andrews and I brought to the JWM had FIVE air systems (retracts, doors, brakes, canopy, speed-brakes). Wow! That was five fill valves, five air gauges, five sets of tanks, five control valves, etc, etc, etc. All systems were pumped up to 120psi (except brakes which was 100 psi). First of all, this set up is expensive ($150 in fill valves alone), but by having 5 X as many components, there was a far greater likelihood of a leak. A lot of folks use a separate gear and brake system for "redundancy". There is nothing redundant about it; a backup system provides redundancy and one system for gear and another for brakes means there is no backup.
Here's the system I use (and this will get retrofitted to the F-86, BTW).....Connect together all the air tanks you were planning on using for retracts, brakes, and doors and connect them to a single fill valve and gauge. This minimizes the number of fill valves/gauges and associated leak sites (each fill valve/gauge/T connector set has seven potential leak sites). Connect the brake valve to one of the gear lines that is pressurized when the gear is down. This way, even if you have a leak in your brake system, system can only leak when the gear is down (so you aren't bleeding off air when you are flying around with the gear up). Install a Tam's (or other failsafe) with the set point high enough (I use 80-90 psi) to drive the gear down and lock it (nose gear units that retract the gear up/rearwards need more pressure to extend the gear down/forward against the slipstream and lock).
This grouped tank system has several advantages over the separate tank system.
1) You are minimizing the number of components and therefore reducing the potential failures/leak sites.
2) If you have a separate tank system and a leak in gear system, any air in the brake system tank is not accessible. If you can't get your gear down, it really doesn't matter if your brake system works perfectly....the bottom of the fuselage and wings are gonna be your brakes on the landing. Having all the tanks hooked together gives you a greater volume of air that has to leak before the system pressure drops to below a useful value.
3) The separate tank system gives you no information on the status of your brake system during a flight. If you have a leak in your brake system and you've bled down the system, you don't know about it until you attempt to use the brakes. Let's say that you are coming in for a landing and you are carrying a bit too much speed so you figure you'll touch down and use the brakes to stop in time. It's too late when you engage the brakes and find out you don't have any air. The grouped system is less likely to leak down because the brake system is completely isolated when the gear is up. Should the tanks leak down, you'll know it because the failsafe will lower the gear. At that point you'll know you have a problem and you are loosing air. So you do a careful approach and touch down as slowly as possible knowing that you may or may not have brakes (depending on how fast is the leak).
Perform system tests to ensure you don't have any leaks after everything is installed. I like to use a digital pressure gauge since the presence of a leak can be quickly detected and isolated. If you tested everything individually, you are less likely to have problems but, if you do have one, find it and fix it. When working on a new plane, I allow a maximum system leakage rate of 5 psi in 8 hours.
Perform Daily Tests - Test your system at least at the start of each day of flying though, like Ravi does, testing it before each flight is best. Just because your gear worked the last time doesn't mean that it will work the next time. There may be damage from the last flight.
Inspect/Maintain your system - Try to plan your pneumatic layout and make it simple, neat, and accessible which will make it easier to maintain and find any existing problems. Don't bury your components and air lines under big component boards. Those big boards may look nice, but they block access to the components underneath. If you can see your components, you may find a problem before it occurs.
Regards,
Jim
Last edited by rcjets_63; 10-02-2013 at 01:18 PM.
10-02-2013, 02:27 PM
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Hi Jim,
Thanks for the info on your preferred air retract system and I'll be re-plumbing my Gripen this winter. I'm currently using separate systems for brakes and retracts but will re-plumb them and add a Tam's failsafe unit. The retract valve is a UP-? to actuate both the gear and doors with a BVM Smooth Stop for the brakes. I originally had a Mini-Hobbies brake valve but it was too unreliable. My Boomer sport jet uses Spring Air retacts, with a UP-5 valve (made for Spring Airs) and a UP-6 brake valve for the BVM brakes. The most unreliable part of the system is the HiTec (LoTec) HS-225 servos that don't care for my A123 receiver batteries. After burning out several serovos I installed a Spektrum voltage regulator to handle the retract and brake servos and all is fine now.
BTW, did you ever find the leak in Jason's F-15 at the JWM? I recall he had a failsafe gear down on one of his flights and Scott was investigating the source afterwards. Many thanks again for the tips.
Art ARRO
Thanks for the info on your preferred air retract system and I'll be re-plumbing my Gripen this winter. I'm currently using separate systems for brakes and retracts but will re-plumb them and add a Tam's failsafe unit. The retract valve is a UP-? to actuate both the gear and doors with a BVM Smooth Stop for the brakes. I originally had a Mini-Hobbies brake valve but it was too unreliable. My Boomer sport jet uses Spring Air retacts, with a UP-5 valve (made for Spring Airs) and a UP-6 brake valve for the BVM brakes. The most unreliable part of the system is the HiTec (LoTec) HS-225 servos that don't care for my A123 receiver batteries. After burning out several serovos I installed a Spektrum voltage regulator to handle the retract and brake servos and all is fine now.
BTW, did you ever find the leak in Jason's F-15 at the JWM? I recall he had a failsafe gear down on one of his flights and Scott was investigating the source afterwards. Many thanks again for the tips.
Art ARRO
10-02-2013, 04:13 PM
#25
My Feedback: (10)
Jim. I subscribe to the same theory as you. More air tanks are cheap insurance. Most of my planes will hold 100 psi for 2-3 days.
I safety wire each connection, generally use sierra or robart valves, use the Mcmaster Carr lines, and on new retracts I usually dissasemble the cylinders and check for burs and lube the orings with air tool oil. It is amazing how many "highly regarded" brand retracts have crapola in them left over from machinig or have damaged orings from being assembled dry.
For a pump, I have a $50 campbell hausefield self contained rechargable flashlight/ compressor combo from wal mart. I made up a pigtail with a robart fill valve, a short piece of air tubing, and a fill chuck. Nice thing to have as you can fill up the tires on your car or bicycle during the off season.
I safety wire each connection, generally use sierra or robart valves, use the Mcmaster Carr lines, and on new retracts I usually dissasemble the cylinders and check for burs and lube the orings with air tool oil. It is amazing how many "highly regarded" brand retracts have crapola in them left over from machinig or have damaged orings from being assembled dry.
For a pump, I have a $50 campbell hausefield self contained rechargable flashlight/ compressor combo from wal mart. I made up a pigtail with a robart fill valve, a short piece of air tubing, and a fill chuck. Nice thing to have as you can fill up the tires on your car or bicycle during the off season.