rhklenke

My Feedback: (24)

I just came back from FL Jets 2006 with a renewed determination to get my BVM AFS Mig-15 in the air this season - in primer if nothing else. I just started on it this afternoon. I'm willing to do a build thread on it if there is some interest. What say you?

Bob

siclick33

Always interested in build threads

I have considered the Mig in the past but I will have to wait for a while as I am just about to start another project. I will watch your thread with interest and you never know, it might just tempt me.

swansons

My Feedback: (3)

Bob,
Having just completed the building phase on this kit I can tell you there are a few omissions and errors in the plans and the instruction book. None of these should be a big problem for an experienced builder, just don't take the directions with the kit as gospel. This was my first BVM kit and I guess I expected it to be perfect. It wasn't! The folks at BVM, including Bob himself, have been very patient and helpful when I have called in. They have stated that they are not perfect but will try to weed out these problem areas. Be sure you have the latest drawings on the pneumatic systems. My kit had an earlier version pre AFS and need to be corrected for this later model.

LOL, PM me if you need or want any specifics.
John Swanson

rhklenke

My Feedback: (24)

John,

Well, poking around a bit in the instructions I see that the plumbing of the main wheel cover air cylinders is not included. Did you plumb them from a button switch activated by the main gear legs? I see that's how then have the nose wheel activated. I did a nose gear door for a KingCat that way, and it works OK, but its not my favorite method. I'd prefer to have a seperate set of airlines for the gear doors and activate them from a sequencer, but that means each wing has five air connections instead of only three...

Also, did you use the EZAir system to connect the air system into the wing?

Bob

swansons

My Feedback: (3)

Bob,
I think you may have an old schematic for the air system. The most current is BVM # 17568-1 dated Oct 2005. It is still incorrect but it is closer than the June 1999 version of this drawing. I plumbed the main doors with separate lines and quick disconnects, to the nose gear circuit. It is actuated by the small button switch for the nose gear that you referred to.

I did use the EZ air connectors for the main gear and brakes. I have not pressurized them yet but they look like a pretty good fit. I will let you know how they work.

John S.

PS. I think you already know that you will need to furnish a third air tank. BVM only gives you two in the kit.

Gordito Volador

My Feedback: (1)

Bob,

I am all eyes and ears on your build thread. I have one of those puppies right here in the box that I need to get started on. No time like the present since you have so kindly volunteered to do most of the thinking !

Regards, Bill

rhklenke

My Feedback: (24)

OK, so I'll go ahead with it. I've already started a bit and I'll post the pictures as soon as I get some good batteries for the camera so I can get them out of it

I do have a BVM F-100 that is coming back from plating soon, so I can't promise that I'll keep ahead of you Bill, but I'm fully intending on having the Mig RTF in primer by Liberty Jets in August, so we'll see...

Now lets talk about the gear plumbing. If you look at the kit addendums on the BVM site:

http://www.bvmjets.com/JetKits/MiG/mig-15.htm#AD

It has an updated air system diagram that has the main gear doors on it - which are missing from the one in the kit. The thing is, the kit comes with three EZAir connections per wing that are supposed to be for the retract up and down lines, and for the brakes. That's all well and good, but the main gear door cylinders are in the wing...

The photo in the addendum area talks about the main gear door cylinder mounting and states: "The arrow points to the 1/8" 5-ply tab that is glued in as the cylinder mount. This installation simplifies the wing removal and installation time." That seems to suggest to me that they intend to have you unbolt the main gear door cylinders and leave them attached to the fuse when taking off the wings. Granted that's only three screws, but I have to carry the plane in my trailer with the wings off, so I don't want to be messing with that every time I take the wings off and on. At the same time, it seems silly to have three lines on an EZAir and two (for the main gear doors) on separate quick disconnects...

The solution will be that I will either mount five EZAirs on the wing, or go to all quick disconnects. I'm leaning toward the five EZAirs, but will decide on that later when I get closer to that point and I can talk to some folks (maybe here) about the reliability of the EZAirs...

The second issue is that the plans show the gear door cylinders (both main and nose) being activated from the retract lines by a button valve. The button valve goes into the door "close" line is is setup so that when the nose gear comes up, it hits the button valve at the top of its travel and closes the doors. Then when the gear is commanded down, the doors will stay closed until the nose gear leg moves off of the button valve. Thus, you typically have to slow down the "down" gear action so that the doors have time to open after the button valve is released and before the gear hits them.

Like I said, I did a KingCat nose gear door that way and it works, but there are too many variables to change and potential ways for it to screw up for my taste. Thus I will modify the system to have a separate two-way valve for the gear doors and either move both valves with a mechanical mixing scheme or simply pay an extra $100 or so for a sequencer and extra cylinder...

http://www.minihobby.com/electronics/mhgdc.htm

Also the UP-3 is an option...

http://dreamworksrc.com/catalog/prod...roducts_id=204

Photos of the build start to come...

Bob

George

My Feedback: (57)

Bob, when I get home I'll let you know how my Mig is set-up on the air system and can send you some pics as well. Mine is set-up with door cylinders in the wings, so all I have to do is pull the wings and I'm done. The old system required you to undo the one cylinder rod from the door because the cylinder was attached in the fuse. I should be able to get you the info. before you get to that part considering your pace (jab, jab) .

Talk to you soon,
George

rhklenke

My Feedback: (24)

Thanks George!

Here's the first pictures. The first steps involve tapping and mounting the CF gear hold-down plates and checking the gear clearence. These AFS wings are a work of art, and the BVM gear are really nice. No doubt BVM stuff is top dollar, but it goes together better than any other jet I've built for sure. Be sure to keep the outer cores for the wings - they make good saddles to lay the wings down on during the build and also, the wing trailing edge is flexible in the flap area until you glue the flap lining piece in there and you'll need the saddles to hold the wing in the proper shape when you do that.

You are supposed to adjust the gear here so that it fits into the wells, but I think its early to do this - just be sure that both gear retract into the wells in the same place. You can adjust the height of the aft strut - and thus where the wheel falls into the well later once everything is in place. Also, I ground off much of the rib that is under the wheel to keep it from contacting the wheel when its retracted. I've seen many a KingCat land with the nose wheel up because something inside was pressing on the wheel in the up position and the retract wouldn't unlock to come down...

Bob

rhklenke

My Feedback: (24)

So...

After the gear are mounted and aligned, the next step is to glue on the 1/4" balsa root rib and add the CF alignment dowel - straightforward and you should see them in the future picts.

Then the manual talks about the wing-to-fuse alignment, but you really can't do much with that until you finish the fuse former installation much later in the build, so on to the flaps.

I built the flaps on a piece of glass as per the advice of my semi-local BVM rep, Tony (some day I want to build as fast and as well and as often as that guy... ). That helped, but they still took a bit of a warp after the top 1/32" ply sheeting was put on because it was so warped. Its important that they be dead flat as they are used to set the inner liner in place and that determines how straight the trailing edge is in that area.

I decided to glass the flaps on both sides at this time to help straighten them out and keep them straight. I use the method described by Dan Parsons - Envirotex Lite thinned by 50% with alcohol and simply brush it on over the 3/4 oz. glass cloth. It penetrates the wood very good and really stiffens up the structure without adding much weight. I blocked the flaps flat as the epoxy cured to get them straight. They came out basically right on...

rhklenke

My Feedback: (24)

Flap glassing pictures...

rhklenke

My Feedback: (24)

Then, after the flaps are glassed, they are used to glue the liners into the flap pockets in the wing. You have to sand out some of the foam, particularly along the trailing edge, in order to make room for the 1/32" liner and still have the flap even with the trailing edge. You hold them in with weights on the flaps with the wing in the foam cradle (told you to hold on to those, didn't they?). The result is a trailing edge that is quite stiff in this area. I will still probably go ahead and strenthen it with 2 oz. glass cloth and let that cure with the flaps in and weighted down like this to be sure it stays straight.

NickC5FE

My Feedback: (31)

Nice work! keep it up, with the pix. nick

George

My Feedback: (57)

Bob, I made it home finally and have had a chance to check out the air system as it pertains to mains and gear doors.

Mine uses 4 EZ-airs per wing, 1-brakes, 2-gear up, 3-gear door closed, 4-gear down & gear door open. The fourth connection "T's" gear down and door open. The amount of air required to open the door is much less than to drop the gear letting the door open before the gear come down. You could also place a restrictor in the "down" line on the retract to ensure door opening, but I don't think it is necessary, the gear will push the door open anyway.

I can shoot you a pic, but it won't show much except 4 EZ-airs and their placement, let me know.
Hope this helps,

George

rhklenke

My Feedback: (24)

George,

OK, your plane uses the button valve on the nose gear to close the doors. That's the setup shown on the latest version of the plans except they don't show the fourth EZ-Air. I may go with that, I'll have to think about it. Its simpler, but I have been having good luck with the UP sequencing valves...

Bob

swansons

My Feedback: (3)

Does anybody have an air system schematic for the MIG-15 that they know for sure is 100% correct??? I am going nuts trying to make mine work the way the latest one that I have(BVM # 17568-1 Oct 2005) shows it should be. I suspect that it is still incorrect.

Any help here would be appreciated.

John Swanson

rhklenke

My Feedback: (24)

John,

From what I can see, that is the latest version of the air diagram. It looks correct except it still doesn't have any EZAirs or disconnects in the air lines to the main gear door cylinders. I believe that in the original design, you were supposed to take the main door cyliners off or the wings and leave them attached to the fuselage via the airlines when you took the wings off. From George's desctiption above, his was modified to put the"T" for the door open/gear down inside the wing and a 4th EZAir was added to the door-closed line which is actuated by the button valve...

Except for that issue, the diagram you are using should result in a system that at least works (although that's not how I'm going to set it up). What's the problem you are having?

Bob

swansons

My Feedback: (3)

Bob,
I do have the door cylinders in the wings and I did the same thing with the "T"off the line to the wheels. I also used a quick disconnect on the fourth air line. I only have three EZ Airs fittings on each wing.

I think there are at least a couple of problems in my set-up. Number one is the small button valve. It has three ports on it, not two as shown on the drawings. I deduced that the third port which is on the bottom had to be blocked. Number two is the little 4-port air junction boxes they supplied. No where in the instructions does it tell you the little line couplers have to be glued into the main block. So they all popped out as soon as I put air in the system. If you look at the top center note on the drawing you see an arrow pointing to a"T" and this "T" is identified as being in the "down" line. If you trace this grey line back up to the main retract selector valve you will notice that this valve has to be in the "up" position before this grey line has any air pressure on it. Therefore the main valve drawing has to be mis-labeled as to the "up" and "down" position.

All this has led to my being one more confused puppy. Oh,BTW you also have to slow the retract servo way down to let the wheels retract before the doors can close. It just has be worn out and not thinking very clearly. What am I missing??

John Swanson

rhklenke

My Feedback: (24)

John,

Yes, you are right, the "gear up" and "gear down" arrows on the main valve are mislabled. The red line is the retract and the grey line is extend. They have the Smooth Stop "T"ed off of the extend line so you can use gear air (when the gear is down) to activate the brakes. I'll probably find a place to put a small tank for the brakes. I would especially recommend that you do that if you use a Smooth Stop. Maybe its me, but I prefer *not* to use a Smooth Stop as they always seem to leak - which would be bad if it was using gear air and all of the air bled off before you retracted the gear the first time in the flight...

On the button valve, you do have to be sure that when the button is released, the air can get out of the line going to the cylinders - otherwise, the pressure won't be released and the doors won't open. Also, you have to be sure that the nose gear is the last to go up - otherwise it will trigger the doors closed before mains have come all the way up.

Like I said, I'm going to use 5 EZAirs in the wings and a UP valve to sequence the doors - much simpler and I think more reliable.

Bob

Silver182

My Feedback: (2)

I built one of the early kit M-15's.. the all build wing version. Boy you guys really have it easy with those beautiful AFS wings! The gear mounting area looks to be very strong, an area that I had to make stronger as time went along.

I used the supplied three port Ez-Air units, and two more separate quick disconnect air connectors, also supplied per wing. The inner door cylinders are mounted in the wing wheel wells not the fuse. NOTE: The only gear failure I’ve experienced over the years was caused by a slightly shallow fit of my right wings EZ-Air three port unit. During construction the wing to fuse fit is critical for these ports to be airtight! I found adjusting them to be easy by putting thin spaces behind either the wing-mounted unit or the fuse-mounted unit.

The real gear sequencing trick for me back in 1999 (I could find a good sequencing valve at that time)… was to mount the air retract value, and the supplied air switch (button) on a tray in such a way so that the last 1/8 inch servo travel actuates the air switch. Then by programming the radio so the gear retract servo moved as slow as possible, (servo slow feature set to max), inner main gear door & nose wheel gear door delayed sequencing was achieved.

Futaba’s (conditions) allows totally separate travel settings, totally separate settings for all channels parameter’s in fact, and in that way I could set up the gear sequence to be totally automatic upon gear switch activation…. Slow but after about 8 seconds the gear is up and inner & nose wheel doors then close.

I tried setting it up so the nose gear actuated the air switch but that didn’t work, even with air restrictors in the nose wheel airlines! Today I’m sure there must be a gear sequencing value that will do the complete job with out special radio programming.
Lee H. DeMary
AMA 36099

swansons

My Feedback: (3)

Bob,
I have a dedicated tank for the smooth brake system. It seems to work fine with no leaks.

If I understand you correctly the button valve has to have the third fitting (N.O.) unplugged to release the cylinder air when in the doors open position. This could be part of my problem. I will experiment with this tomorrow. BTW my button valve is activated by the retract servo located on the equipment plate below the cockpit, not the nose gear.

Thanks for the help. Let me know if you think of anything else.

John S.

swansons

My Feedback: (3)

Bob,
I have a dedicated tank for the smooth brake system. It seems to work fine with no leaks.

If I understand you correctly the button valve has to have the third fitting (N.O.) unplugged to release the cylinder air when in the doors open position. This could be part of my problem. I will experiment with this tomorrow. BTW my button valve is activated by the retract servo located on the equipment plate below the cockpit, not the nose gear.

Thanks for the help. Let me know if you think of anything else.

John S.

rhklenke

My Feedback: (24)

John,

Its been awhile, but I did a nose gear door on a Kingcat I built for someone and that's the way it needs to work. When the button is NOT pushed, the line coming from the pressure side is closed, but the line coming from the cylinders needs to be open (vented) so that the air on that side can release and allow the cylinders to move the other way. Then when the button is pushed (either by the gear itself or the retract servo), the pressure line is connected to the cylinder line to pressurize the cylinder and move it in the correct direction for doors closed.

Personally, I'm going to use a UP-3 valve - I've had good luck with the UP-2 and UP-4 in my Eurosport...

http://dreamworksrc.com/catalog/prod...roducts_id=204

Bob

mr_matt

My Feedback: (10)

Hi Bob,

I love those UP valves. They are a great company to do business with. Their hose is the best as far as I am concerened, and now they have 5 colors.

I use their door cylinders as well. They make a larger 7/16 inch diameter cylinder. It is only 1/16 (in radius) bigger than the normal size, but it has twice the force. Nice

The reason I wrote, is that unless something has changed, that push button door switch thingy has a bit of a problem. When you switch to "gear up", you have no air holding the door open any more. Air loads can push the door closed enough to foul the gear coming up. I much prefer a positive air up and air down system.

Good luck looking forward to more of the build thread.

Foxbat711

My Feedback: (29)

What turbine will be utilizied?