RE: Jetlegend Mig 29 Fulcrum
 

Bart,

Any real reason why not to run clear lines all through the system ?

RE: Jetlegend Mig 29 Fulcrum
 

No, other than easy line identification</p>

RE: Jetlegend Mig 29 Fulcrum
 

Hey Bart, below is a video of my gear operating. Wonder if I could get you take on it. You can see that the mains are not staying in the plane and sagging out and I am wondering what could be causing this. It could be that the nose is sagging to but its just stiff enough to not be moving. The 4mm tubing is much better and I am thinking that either I am getting "blow by" in the pistons or perhaps the valve is not functioning as it should. I don't see any air in the lines and the down is fine, nice and solid, just the up is causing issues.

[youtube]http://www.youtube.com/watch?v=_mVdezMiwRg[/youtube]

RE: Jetlegend Mig 29 Fulcrum
 

Hi Ian,
What you have looks like what mine was like before I got the new solid pistons machined up. It is fluid getting past the pistons. It may be only one, as they are inter connected it is hard to tell so what you need to do is pinch off one side at a time to confirm this. If you don't want to pinch the lines then disconnect them and fit non return valves on the end of the up and down lines. Best of luck, I've been there!



John

RE: Jetlegend Mig 29 Fulcrum
 

Ian

Nice job on the conversion. You are 100% right in that you are losing oil, but there are a couple of areas that this can happen.

First thing that I notice is the decompression of the oil,afterthe gear retracts up and pressurizes, it takes a few seconds before the gear moves, this shows that the oil is actually decompressing and as the pressure dops off the gear starts to drop, this means that there is only a small bypass somewhere.

The first one I would look at is the check valve between the pump and 5 port valve. This check valve (I hope you have one fitted) is imperative in locking the oil in the cylinders. When the gear is retracted, the extend side of the cylinder is ported directly to the pressure port of the pumpvia the 5 port valve, if the check valve is not sealing (or missing) the oil just pushes back through the pump into the reservoir.

The next item to look at is the 5 port valve, if the spool is not moving all the way to the end stops, you have the potential to have the pressure side bleed back through a tank gallery in the valve with the same result, the oil goes back into the reservoir.

Lastly would be the piston seals.

I find the best way to track these things down is with a pair of long nose pliers. The reason for using long nose pliers is that you are only crushing a small area of line that cuts the flow off effectively.

Starting with the line between the 5 port valve and the pressure port of the pump, cycle the gear up and when the pump stops squeeze the line with the pliers to close it off - not so hard that you damage the line though. Anyway, if the gear does NOT drop, then you have bypass through the check valve back into the pump. Remove the check valve give it a blast of air in the free flow direction to clean it and then put some air on the check side to see if it seals. If air gets pass so will oil eventually.

If not the check, then using the same pliers you can also repeat the experiment but this time on the line (after the tee) from the 5 port valve to the reservoir return and then each line before the tee in turn, this will prove valve bypass.

Lastly squeeze off each line connected to theROD end of the cylinder in turn. It is unlikely that more than 1 piston will have failed, this being the case if you squezze off one of the lines and the gear stops dropping then that is the offending seal. Becasuse all the cylinders are connected together, then 1 bad seal will drop all the cylinders.

Just keep in mind, as I mentioned in an earlier post, if the oil is not on the ground then it has to bypass back to the reservoir and this being the case there are only 3 area's it can do this.

Finally, you have installed the Festo pilot check valves on the gear down side of the cylinders, these valves are classed as leak free and as such the oil stays trapped in them forever until you let it out. However on the gear up side, the oil is held in the cylinders only against the check valve on the pump pressure line through the 5 port valve. The 5 port valve is NOT classed as a leak free valve (for the spool to slide it must have clearance, any clearance no matter how small will bypass oil). Technically we class them as 5 drops per minute, but in our planes it's probably more like2 drops an hour or more. My gear will stay up for days (unlike me) but after about a week it will start to push the doors open. Compare this to the original air design without up locks that would drop the gear like a stone as soon as power to the jetronics valves was lost, we are still miles better off.

I am sure you will find the offending item

RE: Jetlegend Mig 29 Fulcrum
 

Bart, i vote you for you "Hydraulics RC man of the year" !

RE: Jetlegend Mig 29 Fulcrum
 

Great stuff Bart. I do indeed have a check valve (Festo) but I did notice when I was bleeding the system that air bubbles seemed to be flowing back through the check valve towards the pump so this will be the first thing I check. I checked my cylinders under water and with air so I think they are sealed pretty good since I saw no bubbles. I will check all out and report back with my findings.

Also, does anyone else have a suggestion for a better check valve?

RE: Jetlegend Mig 29 Fulcrum
 

John,

The upgraded mains have arrived so I'll post them off to you.

Jeff

RE: Jetlegend Mig 29 Fulcrum
 

Great, Thanks Jeff.



John

RE: Jetlegend Mig 29 Fulcrum
 

So I did a little testing at home during lunch and I think I found the problem. Seems that my check valve is not "checking" ;);). I retracted the gear and right when the pump shut off I clamped the tubing between the check valve and the distribution valve and the wheels stayed up! SO, seems that would be the problem. I have 2 new check valves on their way (in case one of them is bunk) so I am hoping this will help.

At the same time I noticed a bit of an issue. When the gear is fully retracted into the plane they are still hitting the doors a little (just the mains). Seems that the stroke of the cylinders are not enough to get the gear all the way into the wells. I have not hooked up the doors yet but that is my next project. I am hoping that they will perform better while under pressure, we'll see. I will update again when that is up and running.

RE: Jetlegend Mig 29 Fulcrum
 

How about a hydraulic system with the upgraded mains, and connect the retraction side of the "locking" cylinder of the mains with a T to the doors closing line ? that might help out a bit in locking the gear up, and might cure the issues you are having as there would now be an added "push" to lock the gear up ?

RE: Jetlegend Mig 29 Fulcrum
 

My kit came without the little nose wheel steering arm :(
can anyone give me the measurements of this part so i can make it by CNC myself ?

EDIT: my builder found it in the LG where all the valves are so all good. :D

RE: Jetlegend Mig 29 Fulcrum
 

You guys that are flying the Mig. Do you find the fuel tank capacity large enough for decent flights, using a 160 turbine? I had thought of adding some more capacity, but there ain't much room available.
Also what CG are you using? I thought of setting mine on the spar, just rearwards of the factory setting, which someone said was too nose heavy.

RE: Jetlegend Mig 29 Fulcrum
 

Also, where did you have to mount your battery packs to get her to balance well ?

RE: Jetlegend Mig 29 Fulcrum
 

To get mine to balance on the spar ( if that is the accepted point), I have two 2300ma lifes in the nose area close to the canopy end & a 3000ma lipo for the turbine in the rear of the equipment tray. Getting it to balance will not be a problem, there is no need to keep things forward, or back.

RE: Jetlegend Mig 29 Fulcrum
 

Jim

After taliking to John, I set mine on the spar and I love it, I think John has moved a little more than that now. If you take into account where the tanks are and the fact that there seems to be no need for any trim change during the whole flight, you start to get a feel for just how much lift there is from the shoulders.

RE: Jetlegend Mig 29 Fulcrum
 

Thanks Shane. I remember from my Avonds F15 (being the same shape), CG was not critical & had quite a range to play with.

RE: Jetlegend Mig 29 Fulcrum
 

I received my new check valves so I will be testing them out at lunch today to see if they will do the trick.

RE: Jetlegend Mig 29 Fulcrum
 

EUREKA!!!! Looks like I got this problem worked out. I replaced the Festo check valve with an SMC one and it seems to be holding nicely, no more sagging gear. I am going to clean off my bench and I will make another video showing the movement and how I ran all the lines for anyone who may want some ideas as to how to get their system going.

RE: Jetlegend Mig 29 Fulcrum
 

Ian,

Good work! Like you, I've got mine working with the SMC check valve. Seems to hold the pressure better than the Festo valve. What sequencer are you intending to use? I've tried the Jettronic sequencer and am unhappy with it. Not consistent. Have a Tom Cook one on order which should arrive this week. Once we get the gear doors sequenced with the gear, it is going to be toooo coooool!

Look forward to your video.

Rob
F15driver

RE: Jetlegend Mig 29 Fulcrum
 

Rob, I am going to try the RCBee I got from Todd at Dreamworks. The price was right and supposedly there is a wide range of times to configure between the operation of the door valves and the gear valves.

[link]http://www.rcbee.com/index.php?Page=11[/link]

RE: Jetlegend Mig 29 Fulcrum
 

Post 361 shows where I have my CG. It balances with no lead. With the standard fuel tanks I am flying for 8 minutes and landing with a lot of fuel. (Merlin160 power). I do not have a sequencer but operate the doors by programming my (Futaba 14mz) radio. It works fine.


John

RE: Jetlegend Mig 29 Fulcrum
 

damn that's inexpensive!!!!

RE: Jetlegend Mig 29 Fulcrum
 

Thats what I am talkin about Buck. I played with it a little tonight and I have it delaying at 8 seconds right now but I think it might be able to go a little longer. Right now I am plumbing my gear doors and brakes. As far as the hydraulic conversion though everything is looking real good. I raised the gear at lunch today and it is still holding, 11 hours now, sweet!! Video and details coming soon!!

RE: Jetlegend Mig 29 Fulcrum
 

Finished building mine. I have used the new U/C as supplied & it appears to work fine. Test flights will be Saturday, if it is not too windy. Wren 160 for power.