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Need some advice from the experts please!!!----1/5 scale ROBART Retracts

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Need some advice from the experts please!!!----1/5 scale ROBART Retracts

Old 10-23-2006, 01:01 PM
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willey
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Default Need some advice from the experts please!!!----1/5 scale ROBART Retracts

Well guys, all that's left to do is balance the TF GS P-51 and were good to GO!!, last night we were trying to fine tune the Robart retracts and they do not seem to come down smooth.

They go up OK, little jurky-can't get them to go up smooth either but acceptable, one go's up, then the other, then the other, kinda back n' forth, then at the last second there IN at the same time. I can control the speed but not the smoothness.

Now coming down one leg comes down and locks before the other has exited the wing, and they both kinda just drop, fast and not smooth or slow at all. Cannot control the speed or smoothness coming down? We tried working with the valve screws but with no success.

I also added the robart valve/line restrictors in the lines (up & down). Now I used ONE restrictor per line for BOTH main gear (one for going up and one restrictor for going down) should I use two restrictors per line??

***What can I do to have them come down smoother??? Do I need a better valve? Should I use a little lube/oil in the cylinders?

***To make one go UP before the other do I need a seperate valve on one line or two line restictors??

Tail wheel retract works fine.

Or could you guide me to another thread about this topic??

THANK YOU guys for your help!!!!!!!!!!!!!!!!!!
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Old 10-23-2006, 01:32 PM
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willey
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Default RE: Need some advice from the experts please!!!----1/5 scale ROBART Retracts

Also, I think the wife stole my builders manual for this????

Could someone out there give me the recomended throw measurements (out of the manual) for the rudder, elevator, ail, flaps. I think I have the throttle throw OK!! LOL

any recomendations are welcome!!

Thank You very much!!

Mark Willey

JUST DOWNLOADED THE MANUAL OFF TF WEBSITE,THANKS GUYS!
Old 10-23-2006, 02:20 PM
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Default RE: Need some advice from the experts please!!!----1/5 scale ROBART Retracts

Mark,

First open the bleed screws on the valve all the way and check how the gear works. It sounds like you may need to double check the restrictors. You may have one or more of them in backwards. The other possible option on the restrictors is the relative location to the cylinder. i.e. how far away from the cylinders are they? If I remember correctly the bleed screws on the valve do not control how fast the air goes into the cylinder but rather how fast it exhausts.

Jim
Old 10-23-2006, 03:03 PM
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frisconick
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Default RE: Need some advice from the experts please!!!----1/5 scale ROBART Retracts

Mark,

It sounds like you're about a week ahead of me on the build. I'm just now putting the tail wheel retract in my TF P51. I have not cycled the Robart mains yet, but I have Century Jet Retracts on my Corsair along with a regulator for speed. My guess is that unless you hit the retract system with the full output of the holding tank, the wheel with the least resistance will move until some other component in the system has less resistance; meaning, one wheel may move the full travel before any other wheel starts to move. I would be surprised if all wheels moved at exactly the same pnuematic pressure. One wheel may extend half way where there may be a little drag, then another wheel may begin to move. But, in all cases, all three should eventually lock up or down if there is nothing wrong with the system. How much pressure are you running? It seems to me that once the lock is released on the mains, gravity is strong enough to pull them down (down, but not locked), so it doesn't sound unreasonable that the mains just kind of flop down, but maybe lock a second or two later. Do they behave differently if the plane is right side up or inverted? That may be a good clue as to what's going on. My guess is if it's inverted, they will tend to flop to the UP position.

You can get the manual on line from Top Flite. Let me know if you discover any tricks with the Robarts.....I'm right behind you. If I get them plumbed tonight, I'll report on their behavior.

Nick
Old 10-23-2006, 07:48 PM
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Default RE: Need some advice from the experts please!!!----1/5 scale ROBART Retracts

Awesome looking bird there Mark!


Congrats...
Old 10-23-2006, 09:31 PM
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willey
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Default RE: Need some advice from the experts please!!!----1/5 scale ROBART Retracts

Jim, you mentioned that the restrictors could be backwards?
I thought about that when I installed them but did not think it would matter, so I just
put them in whatever way they were facing at the time, I'll have to check on that to what way they are facing.

so would the small hole face the air cylinder or away?

You also asked how close is the restrictor be to each cylinder? Probly guessing about 12-15" from each cylinder.

That makes sense to me because the closer the restrictor is to the cylinder the less air it has to move before it takes effect, would that be correct thinking or am I way off? I'll move them closer say about an inch or two too see if that changes things, thanks.

mark
Old 10-23-2006, 10:04 PM
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Default RE: Need some advice from the experts please!!!----1/5 scale ROBART Retracts

Nick, would really like to see your project! post some pics here when you have time!

Now - the gear locks in both directions without any problems at all, I'm just trying to smooth out the action inbetween.

I have only tried retracting right-side UP, NOT up-side down, did not think of retracting with the plane up-side down.

I'll put in 90 -100lbs. air pressure and getting 6-7 good cycles, what pressure should this system carry to be safe??

Thanks for the manual download idea! I just did that and have the measurements now!

mark


"HEY GOOSE" thanks for that input!!!
Old 10-23-2006, 11:19 PM
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Default RE: Need some advice from the experts please!!!----1/5 scale ROBART Retracts

Go to TF website and download the manual

http://www.top-flite.com/
Old 10-24-2006, 01:20 AM
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Peter_OZ
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Default RE: Need some advice from the experts please!!!----1/5 scale ROBART Retracts

it may be worth considering a Ultra Precision valve, you can get one specifically for the P51D that will do mains AND the inner doors in the correct sequence, ie switch to down, inner doors open, gear extends down, inner doors close and the opposite for gear up.

Do not put lube oil on your retracts, yes it smooth the operation but it will attract dust and dirt like you will not believe and cause major problems in very short time.

Have you seen the gear on full size warbirds going up? It is normal for one leg to hang down till the other is almost up up.

With the UP valve you can adjust the down travel to almost a crawl and same for up.

good luck
cheers
Peter
Old 10-24-2006, 02:25 AM
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bigtim
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Default RE: Need some advice from the experts please!!!----1/5 scale ROBART Retracts

on my 60 size robarts they go up unevenly and rather slowly then snap down pretty fast without the restrictors I just adjusted them from the valve. they were super sticky and sometimes didn't work until I used some nail gun oil on them just a drop or two they are allot smoother now and so far have worked perfectly since.
Old 10-24-2006, 12:57 PM
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Default RE: Need some advice from the experts please!!!----1/5 scale ROBART Retracts

Mark,

Yes it does matter which way they are facing if you have one with the small hole towards the cylinder and the other the opposite direction they are going to regulate the air unevenly. Also 12"-15" is way too far from the cylinder. They should be in the 1"-2" range you mentioned moving them to. I always install mine with the small hole facing the cylinder. The reason you install them with the small hole towards the cylinder is to regulate the air going into the cylinder. The closer the small hole is to the cylinder the more it is going to regulate the air flow going into the cylinder. You will also be very surprised at how much of a difference the smallest variance in distance can make. I know several guys that before Robart had the adjustable control valve would put as many as three and four restrictors per line to regulate the speed. If you need any further help please don't hesitate to PM me.

Jim
Old 10-24-2006, 01:39 PM
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willey
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Default RE: Need some advice from the experts please!!!----1/5 scale ROBART Retracts

Thanks guys! I will post the results soon after I make the changes in a couple days.

willey
Old 10-24-2006, 03:28 PM
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CarverTripp
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Default RE: Need some advice from the experts please!!!----1/5 scale ROBART Retracts

Hello Willey,
I also own a pair of these Robart struts, and experienced the same problem on my TFGS P-51. I found the reason they "snap down" is because of the pin and groove method of locking the strut in the up position and down position by way of the air pressure. That you know. The weight of the wheel and strut when in the "up" position causes downward pressure on the locking unit and takes more air pressure to release it. By the time the pin does release, there is conciderable pressure built up in the valve, so when it releases down, with the added weight of the strut, it snaps down! That you probably know also. This is the way I solved it. I simply filled the groove so that the pin doesn't lock in the "UP" position. Think about it, it doesn't need to lock un the "up" position anyway, Why? because 100psi. holds the gear up anyway, so to me, the "up" locking position is redundant.
Carver
Old 10-24-2006, 10:29 PM
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Default RE: Need some advice from the experts please!!!----1/5 scale ROBART Retracts

The air bleed adjusters on the Robart valve do not have big enough passages to allow for fine tuning the retract speed to any great extent. You can get more adjustment with a Sierra valve but in all honesty the guys I fly with would rather have gear that goes up and down all the time than mess with scale retract speed. One modification I can recommend is to buy the solid aluminum replacement parts for the Robart gear from Sierra. Makes the gear much stronger. I replaced the parts on my set of Robarts and have been much happier. Also if you take the gear apart you will see that Robart uses a soft steel cylinder that rides up and down to lock the gear up and down. Hard to describe exactly what it is but it is the part that engages in the locking slots at the end of the gear travel. This cylinder rides up and down on a steel pin. Every set of gear I have seen eventually starts sticking because the very end of the steel cylinder gets out of round from the stress of landing. It's easy enough to just drill out the hole to get it freeded up again but it will get out of round again with a hard landing. My solution was to ream the end of the cylinder out a little with a tapered reamer to give it more clearance. Just a little taper is enough. Has worked fine since, without getting out of round.

Larry
Old 10-27-2006, 01:16 AM
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willey
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Default RE: Need some advice from the experts please!!!----1/5 scale ROBART Retracts

OK! first I want to thank you guys for all the Great Info! After really studying these retracts for a while and looking closer on how they actually work, same time thinking of what everyone has said (above), I can see ALL your comments make "complete sense" so thanks again!

Well here's the deal - Originally I only had one restrictor between the "T" and the main valve, one for the feed and one for the return line operating BOTH main gear 12"away from both mains. (total of 2 restrictors) Definitely NO GOOD THIS WAY!!

UPDATE!! - I installed one restrictor 2"away from each cylinder for each line, feed and return. (total of 4 restrictors for main gear)

The gear was a little stiff/dry so I lubed the moving parts with a little air tool oil wiped the excess off.

Turned the valve screws in all the way then backed them off a shy of a quarter turn, snugged the jam nut down, pumped in 100lbs. flipped the switch and WAA-LAAA, SMOOOOTH!!!!! I was like HOLY Shi-MOKY!! it can't get any better then that!! I get 6-7 good cycles per fill. Going up they are as real as you could get, one before the other-and smooth!

coming down - one leg drops completly down and locks then the other leg, but it's very smooth and slow now, not like before!! I'll mess with that issue later, we need to get this in the air before our field is snowed in!! VERY happy with these results. now it's time to balance and were ready for maiden voyage.

Thanks to all that helped us out here!!

Mark Willey




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