I've got an idea I am going to try, and I really don't see why it won't work. On my Tams F-16 I am going to tee an airline into the down air line for the gear, with a check valve into the brake line. If I get an air leak in flight and can't extend the gear, I can hit the brakes on the other air system and gear will go down. If all is normal, the down air pressure will not be able to get into the brake system, so all will be as it should. All the full scale aircraft I have flown or been associated with always had an alternate gear extension, and this is so simple I am surprised I never tried it before. Any opinions or ideas? Thanks for the input. Bob

Could you post a diagram of the layout you are describing? What type of retracts are you installing in this configuration?
Thanks.

I guess I could draw something up, but it is so simple. Any gear system that uses air up and air down would be ok. Just a simple tee into the downline from the brakes, and a one way check valve so down pressure would not apply the brakes. Bob

It sounds like a good idea. As long as you have the space in the plane and the rx. If it's a small leak, it should work. If you blow a line, probably not. Just sol.

Great idea. Your gear sytem would not have to have a major leak for this to work but it is better then nothing. Too bad we could not just free fall the gear like a lot of full scale large aircraft do as a back up. This is why I like Springair for it's fail down design. Bob

A large leak on the upline would not matter. The up side is shut off when you put the valve to down. You just cant go back to up and then hit the brakes, because it would port air out the exhaust side of the gear valve. Just leave the switch down, and hit the brakes. No extra channel needed on the receiver either, as all is mechanical. i will try to get time to give it a try tomorrow. It will work. It has too. Just simple physics. Bob

Great idea! Do they make check valves in 1/6" id or would you have to make an adapter?

Mike

Bob

Thats a great idea!

http://www.specialtymfg.com/check_va...es/default.asp

I found this on the web for small check valves.

That actually sounds like a great idea.

Some obvious observations are the brakes cannot be actuated with down elevator(if you intend on blowing the gear close to the ground. If there was a leak, I would want to blow the gear down at the last possible moment since air up/down gear can possibly collapse without air pressure holding the trunnion and pin in the locked position. I would think you would need a little larger air cylinder for back up than you would normally use for brakes only.

You have a point on the down elev! I never use that so didn't even consider it. Most of the gear now lock overcenter when up or down, but you could wait until final to drop the gear. Again, if you have a leak in the upside in flight, as long as you leave the valve in down it should not port air back out the same leak. Anyway, I will give it a try. Don't know why I didn't think of it a long time ago. On the B-52 we had a shuttle valve that would switch hyd pressure from another system if you lost primary hyd to lower gear. Same idea, just using the brake system. Not perfect, but very simple. Bob

Sounds like that should work fine and is a great idea.
Mark

You could fill the extra tank with liquid propane or CO2 then the tank could be very small and have tons of volume
or just use those small CO2 containers and a servo to pop the top and refill the whole system then you will have
the breaks too.. for a short time.

Eddie Weeks

Bob:

I have never seen one hooked up with just a check valve, but Pro Builder Paul Hopkins down in Florida has built a couple of planes where he had tapped the brake air for emergency gear extension......he used a small button valve and a mini servo to control it....worked perfectly.....but did take up an extra channel....

Tom

A differential pressure check valve would be better, in other words a check valve that would not allow pressure through unless the delta P was whatever you set it to be. Then no channel required.

Any other way, a radio funtion would be neccessary as best I can tell.

Sean depends on the leak rate. If it was too rapid then your emergency supply would also bleed down.

Although not a gear backup system, I have seen one of BV's ARF Bobcats that he had rigged up with a single system for brakes and retracts, not just using a common air tank......as I recall, it was set up so that if you lose air with the gear up, you lost brakes, but then don't need brakes if you are landing gear up.......if you lost air with the gear down, you still had brakes as he tapped off the down line.....if you lost air before the split into up/down lines, you of course were screwed, i.e....the airline came off the tank....he used a modified eccentric circular output wheel on the servo that controlled a button valve and slow servo speeds to control the whole thing....this was on the P-60/BC that he was trying to keep as light and as uncluttered as possible.....this system dispensed with a separate brake valve, it's servo, and a second air tank....

I have used his old Bandit system of controlling the full nosegear door on my Kingcat, tapping off the retract lines to the nosegear and using a button switch that is activated by the N/G strut when it comes up (BV used to use an overcenter rotation of the output arm of the gear servo for control of the button switch)....either way, foolproof with only one retract servo, HiFlow retract valve, and button valve for the whole system.....

I think Paul Hopkins went with the servo so that he had control of the air flow from brakes to retracts.....it only took a brief moment to blow down the gear.....you could then switch back to standard lines and get your proportional brakes back.....important as buzzing thru an overrun without brakes often can do more damage than a gear up.....

Point of gear not locking down with the overcenter without air on it is a good one.....I know that Robart 630 will not lock down and stay locked down without at least 30 lbs air if there is any bumping around during the landing roll.....I found this out as I fly off grass most of the time......other gear like AirMagic, Tom Cook, Century Jet and BVM stay locked quite tight once locked down...

Interested to hear how Bob's trials went.......


Tom

Not really. If the down line air pressure is higher that the brake line pressure, the check valve will prevent flow. If the brake pressure is higher, it will just add a bit more pressure to the down line. Could be a problem if you put the brakes on in flight. Your gear would come out. Don't know why you would do that? I put the brakes on the right hand slider on my 10X. Oh well, I am doing it on this jet, and we will see how it goes. I would hate to skin up that nice belly paint if I blew an airline. The prior thread about leaky fittings made me start thinking. Bob

what you really need is pressure tap on every engine... The AMT 450 puts out about 40 psi and most
engines put out around 30 psi... put a check valve and pipe bleed air right to the retract valve and
I bet they will come down.. No servo or chanel required.

I guess it really depends on where the air leak in the retract system is. If it is leaking at the retract unit and it is a big enough leak, you would just lose all the brake air too. but if the leak was small it should work.

Well, works fine on the ground. Maybe find out in the air this weekend, since it is a 3 day one for some of us. Bob

SpringAir.

Bob,
I have been working on a fail safe system for some time now, and I have been flying it in one of my demo Super Hornets. This system is all electronic programable, and T's into the air system. The unit is pre-set to your desired minimum air pressure level, and hooked into your retract servo line. When the air pressure drops to the level that you have pre-set, the gear switch is triggered and your gear come down before its too late. Here is a picture of the prototype unit, look for an announcememt on my website soon.
The only problem with the testing so far is that my Super Hornet holds great air pressure..........but when testing on the ground and slowly bleeding out the air, it works flawless! Another feature of this unit is that it prevents your gear from colapsing if you turn your radio on with the gear switch in the "UP" position.......a feature that I found to be much in need around my demo team![:'(]

I saw one type here:

http://www.hangtimes.com/chargers.html -scroll down to the retract accessories. Saw a couple cool air line products there, too...

B58 what a great idea![8D] And like all good ideas, simple too. I had been considering carrying a small CO2 cylinder used by cyclists for inflating tyres, but this is better as we all mostly carry a brake tank full of air.
Nice one,

John