i3dm

My Feedback: (51)

Yes, some of us have. it is my personal conclusiont that they are not flight worthy as the lock on the mains hardly locks anything, and the nose doesnt have a lock at all - there is a detailed description by myself earlier in this thread.

ianober

My Feedback: (12)

Lior, yes, the SU-27 uses essentially the same cylinders as the Mig, same internal components.

ianober

My Feedback: (12)

Bart, I got a quick scenario for you. I got the system all hooked up tonight and it is working about 80%. The reason I say 80% is this, the nose gear works great, flawless but the mains are sluggish and don't retract fully. I played with the overload to no avail. So I thought maybe I was getting some blow by in my main cylinders so I pulled them out and tested them with air and under water. Both seemed to be air tight, no bubbles under water so I don't think I am getting any blow by. Any ideas?

Aussie Bart

Sorry to do this to you, but there are a couple of important principles you guys might need to see to help you plan installations.

The hydraulic pump (as they all do) has a maximum pressure rating, in this case about 120 psi. This rating is not so much where things fail but at what point it stops pumping efficiently.

All pumps suffer from slippage, ie where the oil actually slides back past the gear teeth internally from the pressure outlet back towards the suction inlet.

Pumps are rated in displacement or flow, in this case the UMS pump is rated at so many millilitres at full pressure, if the pressure goes higher because of restriction then the output flow will actually drop and continue to drop reletive to pressure

Pressure is DIRECTLY related to resistance, when the cylinders bottom out, the pump is still running but all the oil that should be coming out is just slipping back to the suction port (unless you have cylinder bypass)

If you have high restriction when operating the gear, then you might only be getting 50% of the potential oil flow, therefore the gear has not got to where it should be in the time alloted by the controller.

Pump flow is affected by battery voltage, the higher the voltage, the higher the potential pump flow, however if the pump can only deliver say 50 ml of flow because the pressure is too high due to restriction, then no matter how fast you spin the pump you will still only get 50 ml of flow.

So Ian, in your case your pump is located in the nose, the front gear is very close to the valve so pressure drop (loss) is minimal however the largest amount of oil (for 2 cylinders) has to travel all the way down to the mains through 1 pair of lines, oil pushed down there is one loss, oil coming back to the tank at the same time is a second loss.

Looking at your photo's, I can't really tell what size lines you are running from front to back, but from what I can see you are using mostly 3 mm od. The total pressure drop on 3 mm line over that distance is huge (in therms of this system). From experiance, you will get better results if you run 4 mm od line everywhere possible, in one of my earlier posts, I talk about 4 mm from tank to pump to valve, once I come out of the valve I would then split off into 3 mm lines to the cylinders, but my pump & valve were right in the middle of the mains and it was only the nose leg that had to travel the distance (1 cylinder). By the way, my mains start to move before the nose!!

You can test this by blocking off one of your main legs (just fold the line over to crimp it) and cycle the gear, this will result in only half the oil flow is needed to get down the back. If it cycles properley you have a couple of choices:-

A/ Up the line sizes from the valve to the rear of the fuse to a bigger size and only drop down to 3 mm after you split off.
B/ Have a close look at the lines running from through the fuse for kinks or crushing from cable ties etc, These are restrictions.
C/ Are you using sewing machine oil? any other oil will have a higher viscosity (thickness), a 10% increase in viscosity greatly increases friction in the lines and therefore how much pressure it takes to push the oil through.
D/ If you want to check your cylinders for bypass, squeeze the tube coming from the rod end of the cylinder with a pair of long nose pliers (not too hard, you just want to close it off) while the cylinder is trying to extend!! if the cylinder stops and stays there, then the seals are usually fine, if the cylinder continues to extend (while the pump is running) then the seals are bypassing cause the cylinder is regenerating.

Ironically, you could also squezze off the line on the other end of the cylinder when it is retracting and the cylinder will stop and start extending if the seals are bypassing!!!!

Hope you get it sorted.

i3dm

My Feedback: (51)

Bart, can you post some pics of where you installed each hydraulic component in the fuselage ?

ianober

My Feedback: (12)

Great info Bart, thanks. Yes, I am running all 4mm tubing from tank to pump to valve. Once I leave the valve it is all 3mm from there. I see what you are saying about the distance. The oil is sewing machine oil so that's no problem there. I did put some cable ties on some lines to keep them neat so there may be some restriction there so I will cut those loose and check. I think I may have to either relocate the pump or up the tubing all around.

i3dm

My Feedback: (51)

Good info guys ! i think i will go with 4mm tubing all along my conversion with 3mm reducers as close to the LG as possible.

F15driver

My Feedback: (24)

Bart,,

I agree the request for where you have located your major components. It appears you've put the retract pump on the right side, on a platform next to the turbine. Where is your 5-line controller valve and its related servo? Retract battery? Retract oil tank? Retract control box? I see you put your ECU on the left side on a platform and the solenoids on the other side on the turbine rail. As big an airplane as the Mig 29 is, there isn't a lot of room to install stuff when you're trying to keep some items close for hydraulic loss. I assume your pneumatic stuff is up in the nose on a tray?

Aussie Bart

Hi Guys

Yep, Hydrau;ic pump and tank are located on the starboard engine rail, the tank is directly under the pump, the controller sits immidiately behind the pump. Hydraulic battery (2200 Mah 2 cell lipo) sits directly below the wheel when it is stowed next to a smoke tank. 5 port valve & servo are located directly below the turbine cover. The tray in the nose has the door gear sequencer and jetronics electronic valve for the doors.

Struggling to load photo's, but will keep trying.

ianober

My Feedback: (12)

Yeah, my room is running low too. I think Bart has his valve right below the turbine, there was a picture if I am not mistaken, can't remember the post # though.

At this point I am thinking about relocating my items back under the airbrake and having them right close to the mains. I was also thinking about changing where the oil enters the "main trunk" from right before the nose gear to back by the mains. My only worry about swapping out all the 3mm line for 4mm is that I will get done and it wont work :-(, that would really suck, but I guess live and learn.

Check out post #93 Rob!

johnls

My installation is similar to Shane's. The controller and pump sit together on top of the reservoir, with the control valve on the fuselage floor underneath everything. I have shown a photo showing where my model balances and where the stab neutral point is.








John

Aussie Bart

Hi Jeff

I have heard from one of the boys in Iran who maidened with the upgraded gear, smooth landing, mains held but nose leg simply collapsed at 100 psi? Have you had a chance to try yours??

i3dm

My Feedback: (51)

Thats the problem. the nose gear is not locked at all, and can be retracted without too much force even with 100PSI. mind you that the nose gear retracts to the back, so the load of the plane moving forward wants to retract it.

jeff sewell

My Feedback: (1)

I'm not totally convinced about the upgrade on the nose so I'll get in touch with JL about it.

Close to finishing but just not had the time...as usual.

Cheers

Jeff

ianober

My Feedback: (12)

I got my order placed for more 4mm connectors and tubing so I am hoping it will be here tomorrow or Friday at the latest. I am going to try replacing all the tubing with 4mm and see how it goes first, if that doesn't work then its time for some surgery.

Jim Cattanach

Have received my Mig 29. Many thanks to Jeff Sewell. It looks very well built & engineered. Only thing I don't like, are the rubber bands holding the rear mains gear doors to the oleos. I will use something else.
I have tested the retracts on mine & there are no leaks at all. This is the first jet, I have had that did not have leaks. The mains are locking solidly when the air pressure is reduced to zero. The nose does not lock, but with reasonable air pressure, it takes some force to move it inwards. I don't think this will be a great problem, as the mains take the initial landing force & the nose should gently settle down. Even in a poor landing, it should not retract enough to cause a problem. I intend to at least give it a try, as I fly off a smooth tarmac runway.

johnls

Best of luck Jim. I'm test flying mine again tomorrow.





John

JohnMac

Good luck John. Any chance of a video?

Jim Cattanach

Good luck John.
After a further look & a few ups & downs of the retracts, I have found the nose gear does indeed have a positive lock in the down position. It just needed a few cycles to get it to work. I wonder if they have further modified the nose gear to incorporate a lock. I can hear a click inside the cylinder as it locks. So looking good for using the gear as it comes.

marc s

Wow you guys are working hard to fix this problem, hats off to you.
I have a Mig29 kit which uses a totally servo driven gear system, and whilst I am sure its not going to be right for your particular senario the method used to lock the nose gear might be.
On this kit the forward mounted 'ram' has a sprung plate fitted to the top face, on the end is a locating lug which drops into a hole to lock the piston in place and hence the nose gear. The lug is connected via a thin wire (I will replace to fishing wire) to a small servo in the nose well. As the gear comes down the lug just snaps into the hole as the wire is slack, before the nose gear retracts the servo is sequenced to withdraw the lug freeing the gear to move closed.

There may be a way to incorporate some of this system with your gear, maybe not, but worth a mention.

Good luck.

marcs

i3dm

My Feedback: (51)

Marc,

Perhaps you could post some better pics of that system ? it does sound interesting and perhaps doable !

Also, can you post some pics of the gear doors and how they are operated with the rubber bands ? i would like to add doors to my F-15 and thought about operating them mechanically, so would be interested to see how they work with those bands.

F15driver

My Feedback: (24)

Jim,

I disassembled my new nose cylinder and it doesn't have an internal lock. All they have done is replace the two part internal piston that had the 3 ball bearings with a solid piston. So, bottom line is, no lock. I assume mine is the same as yours as I just received mine from JL in China. The main locking system looks like it might work just fine. I'm proceeding forward with hydraulics on all three gear. Worst case, I could always use JL's pneumatic system on the mains and a hydraulic system on the nose. As Bart pointed out in one of his earlier posts, the pneumatic system on the nose will not prevent enough of a collapse of the gear to avoid damage to both the strut and the pitot tube in a hard landing as his picture clearly illustrated.

I suggest you disassemble the nose strut and check the internals.

Regards,

Rob
F15driver

Jim Cattanach

Hi Rob. I tried to disconnect the nose gear cylinder from the oleo, but failed. It is a very tight fit & without resorting to a hammer & punch, I doubt if I could remove it. I don't want to use force to dismantle it, as it all works fine & I don't want to cause problems. I have taken some photos, as my oleo looks different from the one Shane posted. Mine has steering dampers & a crossbar with pins in the ends? It looks like a steering bar, but it's not. The locking mechanism must be inside the air cylinder. It is a solid lock, & clicks when it's in place.

johnls

The cross bar looks different. It would help if JL adopted a bit of communication wouldn't it? I'm off to fly mine now, I'll see if I can get someone to video it.




John

JohnMac

Looks as if mine is ready to ship.