jeff sewell

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You lot are so impatient!

I'm off in the workshop now to try and get some done...

Jeff

yeahbaby

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ditto

nt flyer

Subscribed. Can't wait to see this one fly!

Greg

JohnMac

That's good. You can have it ready for Sunday then!

jeff sewell

My Feedback: (1)

Well I would but its not mine...

Jeff

Aussie Bart

Well I started to catch up with my other build projects and repairs so it was time to take a closer look and start some actual work on the mig.
I have a great like for hydraulic retract systems (I design hydraulics for a crust) after using it in my Catalina a few years ago and just recently in my 1:5 KS Vampire and JL T45. This being said, I could not wait hook up to the main gear just to gauge how long it was going to take to operate those big ass cylinders, I can happily report that the work extremely well and at a very scale speed and performance and am looking forward to getting all 3 legs running on oil in a couple of weeks.
I had a good look at the mounting plates for the mains, and whilst I would prefer to see some flex plates being predominantly a grass strip flier, I don’t believe the heavy duty alloy mounts are going to fail anytime soon.

Aussie Bart

I then removed the Stabilizer mounts to have a closer look and to set up the servo’s. These are accessed from inside the fuse and are held into the rear former by cap head screws and are a snug fit into the former mount, it was actually a bit difficult to remove the mounts even with all the screws removed. The mounts are fitted with some very smooth and close tolerance bearings that support the Titanium stab shaft. Because of the distance from the bearing mounted clamp and the outrigger bearing, the stabilizer support is very strong.

Aussie Bart

One of the most difficult jobs it seems on the mig is just how to get the nose wheel steering setup. Now it must be said, that JL do not provide allot of build info with their product other than a 1:1 cad drawing of “most” of the important bits. However I can say that after building the JL 1:8 F16 as a kit, the JL Gripen as a kit, the JL T45 as an ARF and now the mig, the airframes are well designed and really are not too difficult even without a page by page assembly instruction.
Anyway back to the nose gear, when I unpacked the front fuse half that has the gear installed, and cycled the gear up and down by hand, it became very obvious that the JL team had come up with something very special but the servo connection eluded me other to say that I also found this small crescent shaped alloy plate in a bag taped to the inside of the box, this bag had the innocuous words written on it saying “Nose Wheel”.
Upon inspection and a fair bit of trial & error, I found that you actually mount the Crescent shaped plate to a standard round servo horn and then trim the plastic back to the shape of the plate, mount it to the servo, then mount the servo inverted into the frame. This was tried a couple of times and I found that I could not use servo horns that were too thick and the only servo I could find in my stock with a low enough splined shaft were Hitec’s.
My final combination was to use a standard White circle horn from a HS 5475, mount the alloy plate (the 2 holes in the alloy plate line up perfectly with the outer holes of the horn) and then mount that all onto a HS 7985. The 5475 would fit as well but I don’t think it would take the abuse of grass strips too well.
The other mod I made was to ‘concave’ the face of the alloy plate that pushes on the steering cross bar this in turn will ensure that all the forces are pushed laterally and not tend to deflect away from each other.
Lastly I have some photo’s of the gear folding to show how the wheels are pulled up (collapse the suspension) with the aid of the centre rod running through the oleo, this allows the long leg to clear the wheel well.

Aussie Bart

Leg Shots

yeahbaby

My Feedback: (21)

fantastic pix amigo!!!!! please keep 'em coming

Jeremy_D

Looking good Shane!! I love the nose leg and the way it retracts in to clear the fuse. I'm still waiting on an answer for you about hydrolics.

Cheers

Jeremy

Aussie Bart

Yeah Yeah I know, I start off with such a flurry and then nothing, just left it all hanging, well your'e starting to sound like my wife.
Anyway after some serious work time selling stuff (more money = more jets) and finishing off my Facet repairs and replacing the wing on my JL T45, I have finally got back onto the Mig.
Time to get serious, so started off with the control surfaces and the elevators were first on the list. As with most people, I like to strip all the pre-assembled mechanisms down to check for loose bolts etc, whilst not falling apart the bolts in the elevator mounts were not very tight. A little bit of loctite later and all was good. These are tuff little puppies...

I mounted the HS 7955 TG’s which showed up the acute angle between the control horns. JL supply very nice M3 ball links with the kit but no pushrods?? (not even on the packing list) but I had some spare high tensile ones.

Once hooked up the whole assembly is smooth and strong. I have not mounted back into the fuse yet and looking at it may be a little fun as the servo is covering the mounting bolts so it may be done in 2 steps.

Aussie Bart

As for the ailerons, I elected to use HS 7895's for the ailerons and analogue 15 kg servo's for the flaps. I found that the aileron cavity is just a bit shallow for the full size servo but if sand the supplied wooden mount down a little on the trailing edge side it fits like a treat.

I did find however that the position marked on the drawings for pin hinges and horn mounting blocks was not what you got on the real thing, in particular the aileron horn. All of the control surfaces come pre drilled and recessed for the pin hinges but when you go to mount the fibreglass horn it is quickly evident that you would have to cut directly through the pin hinge.
I found the only solution to this was to offset the fibreglass horn and use ball links to cover the offset.

The aileron travels listed is +/- 32 mm which is seems allot. I found that I needed to cut the top & bottom shroud back and extra 3mm to try and relieve some of the resistance and in addition run a warm covering iron along the shroud with the fully deflected aileron to ease the pressure.

Flap travel is 54 mm and again I had to cut the bottom shroud back 3mm and warm it up with the flap fully deflected.

In both cases, there is still a huge amount of shroud overhanging the control surfaces so there will be no danger of air bypassing through and generating flutter.

jair

Hi,

are the pneumatic rams self-locking?

Julian

jair

What´s the weight of the MiG kit so far?

Aussie Bart

Hi Julian

The main pneumatic cylinders have a locking mechanism built internally at both ends, it works very well. I will actually be using a hydraulic system to operate the legs and the locking still works very well. As for the weight, I have not had a chance to check it but I should be able to get a figure soon.

Aussie Bart

Sorry for being so slack but too much work on and spare time has been spent getting the Mig ready for one of our bigger meetings here in Aus last weekend. End result is a jumpy and short video of the maiden, well a compilation of the first couple of flights anyway.

I am still trying to sort out a couple of minor issues with the retracts but all in all she flies like a treat.

http://www.youtube.com/watch?v=cRyHzMXYb74

I hope to get some time this weekend to finish uploading the minor mods and tricks I found during the build.

jmalone1982

My Feedback: (1)

Bart, pure filth!! Porn for the kero lovers. And those landing gear, my wife thinks i stay up late looking at skin sites but when she sees the history she thinks im even more afflicted. OH WOEISME. How do i tell my wife that i have spent the cash on one of these?

Tis far easier to ask forgiveness than permission I say.

Aussie Bart

Well here is the rest of the info I promised.

THe elevator servo assy is very robust but can be a little tricky to assemble. The kit was supplied with 3mm bearing rod ends but no pushrods so I used 3mm stainless steel allthread. The linkage length is very short. You will need to fit a high torque servo not only for the size of the elevator but also due to the fact that the servo arm thrust direction is not in line with the control horn so you will lose about 20% of the power, I used Hitec 7955 TG's.

Aussie Bart

The Aileron & Flap installation went smoothly except if you use a full size servo on the Aileron you will need to profile the mount to fot it all into the wing,

Aussie Bart

Now the biggest problem I had was with the landing gear and had developed after I had finished building and started testing all the systems extensively. After about 20 or so landing gear cycles I noticed that one of the main legs started to retract very slow, which seemed like it was binding somewhere. When I removed the air from the cylinder it moved extremely smooth but once the air was on it would "grind" to a stop.

This of course annoyed me to no end so it was time to strip the landing gear down.
As I had mentioned earlier in the thread, the landing gear is very substantial and is not made up of the usual trunnion and fork arrangement but instead some form of locking mechanism in the cylinder itself.
Once I stripped it down it soon became obvious how this mechanism worked as well as why it was failing.
The cylinder piston is hollow and fitted with a “shuttle” that has an O ring seal arrangement. This shuttle is machined with a land in the centre and a taper on each end. Around the taper are 3 steel balls that are housed in the piston and each protrude through a tapered window in the piston.
Near the barrel end is a machined groove (one in the mains 2 in the nose). When the piston has travelled to the end of stroke and bottoms out, the air pressure will continue to move the shuttle an extra couple of mm forcing the Taper under the steel balls, pushing them further through the windows into the machined barrel groove, this in turn locks the piston to the barrel in the DOWN position.

Aussie Bart

When the gear is put into retract mode, air pressure is shifted into the end where the piston has bottomed out and because the piston is locked by the steel balls the air shifts the shuttle the other way thereby moving the taper from under the balls thus releasing them, this then unlocks the piston allowing it to travel to the other end. On the mains, the balls are only in one end of the piston, the photo’s here are showing the nose leg cylinder piston that is set up with balls both ends of the piston to lock in the up & down position. Due to reliability issues I ended up removing the balls from the up lock portion.
The reason that the leg was failing, was the shuttle is made from aluminium and as the shuttle moves back & forward the steel balls were pressing a groove into the taper. This in turn would allow the balls to start “riding” up the shuttle taper as the piston was moving which would try and push the balls into the cylinder wall and start to jamb. If you have a close look at the photo you can se the tracks starting to form.

Aussie Bart

So, with the steel balls making these tracks in the soft aluminium, the only solution I could see was to modify the shuttle. I ended up machining the damage area down to 5 mm, and using some 6 mm stainless steel hydraulic tube, I machined it out to be a press fit onto the machined area of the shuttle, this was then dressed to meet the original shuttle profile. End result after a few hours was a much tougher surface for the steel balls to run on.

Jim Cattanach

I was thinking about one of these, but I am slightly put off by this U/C problem. It has been some time since the last post. Anyone got any updates or longer term experience with this model?

Aussie Bart

Hi Jim

Have sent a PM