Fei Bao MiG-21 Build Thread
12-30-2008, 11:22 PM
#26
RE: Fei Bao MiG-21 Build Thread
Back to work on the MiG after a break for Christmas.
Saddle Fuel Tanks
The saddle tanks are approximately 5" long x 7" high x 2" wide (at the widest point) and have a capacity of 30 ounces each (60 ounces per pair). Since the length of the tank is less than the height, it was a bit of a challenge to plumb the clunk line to reach the bottom, back, and top of the tank so that fuel flow would be maintained regardless of the attitude of the model when flying.
The photos below show the fuel lines within the tank. I bought a length of 5/32" brass tubing from the LHS and annealed it using a blowtorch to allow it to be easily bent using a Dubro tube bender. Dubro fuel line barbs were soldered to each end of the brass pieces. [link=http://www.bvmjets.com/Pages/fuelcells1.htm#KA]BVM #2804 Fuel Line[/link] was used to connect the individual pieces of the clunk line since it maintains flexibility even when immersed in kero for long periods. Tygon tubing was used as an extension for the vent line since it tends to stiffen with longterm exposure to kero. All connections are secured with safety wire.
Initially I tried a clunk line made of a single piece of BVM tubing but found that it tended to curl up and didn't reliably allow the clunk to move. Adding the 2" length of brass tubing to the clunk line improved matters but the tubing didn't quite have the flexibility to allow the clunk to reach the bottom and top of the tank. Eventually, I made a slight (approx 10 degree bend) in the brass tubing at the stopper as shown in the photo below to bias the line allowing the clunk to reach the bottom of the tank.
The bend prevents the clunk from reaching the last 4 oz of fuel in each saddle tank when the plane is inverted. This is not an issue since the saddle tanks feed the main tank. If the model is rolled inverted when the saddle tanks are almost empty, fuel will be supplied from the main tank. Once the model is returned upright, any fuel left in the saddle tanks will immediately be drawn into the main tank.
Regards,
Jim
Saddle Fuel Tanks
The saddle tanks are approximately 5" long x 7" high x 2" wide (at the widest point) and have a capacity of 30 ounces each (60 ounces per pair). Since the length of the tank is less than the height, it was a bit of a challenge to plumb the clunk line to reach the bottom, back, and top of the tank so that fuel flow would be maintained regardless of the attitude of the model when flying.
The photos below show the fuel lines within the tank. I bought a length of 5/32" brass tubing from the LHS and annealed it using a blowtorch to allow it to be easily bent using a Dubro tube bender. Dubro fuel line barbs were soldered to each end of the brass pieces. [link=http://www.bvmjets.com/Pages/fuelcells1.htm#KA]BVM #2804 Fuel Line[/link] was used to connect the individual pieces of the clunk line since it maintains flexibility even when immersed in kero for long periods. Tygon tubing was used as an extension for the vent line since it tends to stiffen with longterm exposure to kero. All connections are secured with safety wire.
Initially I tried a clunk line made of a single piece of BVM tubing but found that it tended to curl up and didn't reliably allow the clunk to move. Adding the 2" length of brass tubing to the clunk line improved matters but the tubing didn't quite have the flexibility to allow the clunk to reach the bottom and top of the tank. Eventually, I made a slight (approx 10 degree bend) in the brass tubing at the stopper as shown in the photo below to bias the line allowing the clunk to reach the bottom of the tank.
The bend prevents the clunk from reaching the last 4 oz of fuel in each saddle tank when the plane is inverted. This is not an issue since the saddle tanks feed the main tank. If the model is rolled inverted when the saddle tanks are almost empty, fuel will be supplied from the main tank. Once the model is returned upright, any fuel left in the saddle tanks will immediately be drawn into the main tank.
Regards,
Jim
01-02-2009, 05:20 PM
#27
RE: Fei Bao MiG-21 Build Thread
It's been a busy last few days in the workshop, but the MiG is coming along.
Pneumatic Tubing Install - Retracts/Gear Doors/Speedbrakes
While this model is 98" long, the fuselage is only 7-1/2" wide and 8-1/2" high and the hatch for the engine compartment is only 5" wide and 12" fortunately, the main gear doors and speedbrakes provide a bit more access but there isn't a lot of room to work and a long pair of surgical hemostats (clamp) makes things a lot easier.
[link=http://www.dreamworksrc.com/catalog/product_info.php?products_id=124]Dreamworks Tidystrips[/link] (thanks Len for introducing them to me) are invaluable in making a clean installation. [link=http://www.jetsnstuff.com/BUY_NOW_%21.html]Jets N Stuff Airline Safeties[/link] are da bomb and save a lot of time over using safety wire. Also, their one-piece T-fittings and X-fittings eliminate potential air leaks and breaks compared to regular plastic fittings or multi-piece fittings. I didn't have quite enough T's for the install so I used three Y-fittings included with the FB hardware pack.
Attaching the pneumatic lines to the nose gear door cylinders (which were pre-installed with this kit) was quite difficult due to limited access through the gear door opening. In order to pull the Airline Safeties onto the fittings, I made a puller tool by putting a 90 degree bend in a Dubro Ball Link Release Tool and gluing it to a strip of hardwood. The notch in the tool is just a bit larger than the tubing yet smaller than the Airline Safety.
Regards,
Jim
Pneumatic Tubing Install - Retracts/Gear Doors/Speedbrakes
While this model is 98" long, the fuselage is only 7-1/2" wide and 8-1/2" high and the hatch for the engine compartment is only 5" wide and 12" fortunately, the main gear doors and speedbrakes provide a bit more access but there isn't a lot of room to work and a long pair of surgical hemostats (clamp) makes things a lot easier.
[link=http://www.dreamworksrc.com/catalog/product_info.php?products_id=124]Dreamworks Tidystrips[/link] (thanks Len for introducing them to me) are invaluable in making a clean installation. [link=http://www.jetsnstuff.com/BUY_NOW_%21.html]Jets N Stuff Airline Safeties[/link] are da bomb and save a lot of time over using safety wire. Also, their one-piece T-fittings and X-fittings eliminate potential air leaks and breaks compared to regular plastic fittings or multi-piece fittings. I didn't have quite enough T's for the install so I used three Y-fittings included with the FB hardware pack.
Attaching the pneumatic lines to the nose gear door cylinders (which were pre-installed with this kit) was quite difficult due to limited access through the gear door opening. In order to pull the Airline Safeties onto the fittings, I made a puller tool by putting a 90 degree bend in a Dubro Ball Link Release Tool and gluing it to a strip of hardwood. The notch in the tool is just a bit larger than the tubing yet smaller than the Airline Safety.
Regards,
Jim
01-02-2009, 05:48 PM
#29
RE: Fei Bao MiG-21 Build Thread
Bypass and Turbine Installation
My understanding is that the FB prototype didn't have a bypass (correct me Wagner if I'm wrong), but I'm installing one on this model. The installation is simplified if you perform it prior to bolting on the rear fuselage.
I found that the turbine mounting rails were a bit too low causing the bypass to interfere with a fuselage former. As such, a 1" wide piece of 3/8" thick plywood needed to be installed on top of the rails. I glued 3/8" thick hardwood strips to the top of the bypass flange to center the JetCat P-120 turbine in the bypass since the flanges on JetCat mounting straps are above the centerline of the turbine. Notches were then cut in the upper bypass to accept the hardwood strips and Jetcat flanges. All of this was initially laid out on the workbench and later installed in the model. A couple of coats of BVM Heat Shield was also brushed onto the aft area of the bypass.
Some modellers use woodscrews to screw down the turbine to the mounting rails but I prefer to use socket head cap screws and blind nuts (particularly in tight installations when there is limited access to the screws and a ball driver is needed). After drilling pilot holes for the mounting screws, I counterbored the back side of the 3/8" thick plywood strips I added and installed the blind nuts. The strips are later glued to the top of the mounting rails and this "captures" the blind nuts preventing them from ever falling out when installing the cap screws. Velcro strips (from Home Depot) were used to hold the top of the bypass in place.
Edit: Added photos of upper bypass.
Regards,
Jim
My understanding is that the FB prototype didn't have a bypass (correct me Wagner if I'm wrong), but I'm installing one on this model. The installation is simplified if you perform it prior to bolting on the rear fuselage.
I found that the turbine mounting rails were a bit too low causing the bypass to interfere with a fuselage former. As such, a 1" wide piece of 3/8" thick plywood needed to be installed on top of the rails. I glued 3/8" thick hardwood strips to the top of the bypass flange to center the JetCat P-120 turbine in the bypass since the flanges on JetCat mounting straps are above the centerline of the turbine. Notches were then cut in the upper bypass to accept the hardwood strips and Jetcat flanges. All of this was initially laid out on the workbench and later installed in the model. A couple of coats of BVM Heat Shield was also brushed onto the aft area of the bypass.
Some modellers use woodscrews to screw down the turbine to the mounting rails but I prefer to use socket head cap screws and blind nuts (particularly in tight installations when there is limited access to the screws and a ball driver is needed). After drilling pilot holes for the mounting screws, I counterbored the back side of the 3/8" thick plywood strips I added and installed the blind nuts. The strips are later glued to the top of the mounting rails and this "captures" the blind nuts preventing them from ever falling out when installing the cap screws. Velcro strips (from Home Depot) were used to hold the top of the bypass in place.
Edit: Added photos of upper bypass.
Regards,
Jim
01-03-2009, 01:43 AM
#30
RE: Fei Bao MiG-21 Build Thread
Horizontal Stabs - Fitting
The H-stabs slide into a really solid trunion bearing block which is pre-installed on a fuselage former. The axles are aluminum rod and have a notch for alignment with the control horn. The stab root chord has a "Z-bend" which fits into a matching notch in the fuselage. This scale notch makes the H-stab install a bit more of a challenge to install than a stab with a straight root chord if you want to minimize the gap between the stab and the fuselage yet allow the stab to rotate through the required travel.
Initially I installed the stabs using the furnished plastic washer sandwiched between the stab and the fuselage. The gap between the stabs and the fuselage varied between 1mm to 5mm and this comprimised the look of the model (see 1st & 2nd "Before" photos below). I locally sanded portions of the root chords, eliminated the washer, temporarily double-face taped a piece of 1/32" ply to the fuselage root chord, and then filled the remaining gap with spot putty and sanded it to shape. After removing the ply/tape, this produced a consistant 1/32" gap (see 3rd & 4th "After" photos below). I did have to sand away so much of the left stab that the front that the fiberglass root was eliminated. A piece of 1/16" ply cut to shape and installed in the root with Hysol, puttied and sanded flush is the fix.
Now that the gap was minimized, the vertical face of the notch at the fuselage root was cut away to allow the H-stab to rotate (see 5th & 6th photos below). This area is covered by the stab so it's not visible when the stabs are at neutral; you won't see them when the model is in flight either!!!!!
You might notice in the photos that the trailing edge of the right stab extends about 5mm further rearward than the left stab (the left stab trailing edge ends forward of the fuselage fairing but the right stab ends aft of the fairing). I'll check out some 3-views to figure out which is scale and will sand/putty the other stab to match.
Regards,
Jim
The H-stabs slide into a really solid trunion bearing block which is pre-installed on a fuselage former. The axles are aluminum rod and have a notch for alignment with the control horn. The stab root chord has a "Z-bend" which fits into a matching notch in the fuselage. This scale notch makes the H-stab install a bit more of a challenge to install than a stab with a straight root chord if you want to minimize the gap between the stab and the fuselage yet allow the stab to rotate through the required travel.
Initially I installed the stabs using the furnished plastic washer sandwiched between the stab and the fuselage. The gap between the stabs and the fuselage varied between 1mm to 5mm and this comprimised the look of the model (see 1st & 2nd "Before" photos below). I locally sanded portions of the root chords, eliminated the washer, temporarily double-face taped a piece of 1/32" ply to the fuselage root chord, and then filled the remaining gap with spot putty and sanded it to shape. After removing the ply/tape, this produced a consistant 1/32" gap (see 3rd & 4th "After" photos below). I did have to sand away so much of the left stab that the front that the fiberglass root was eliminated. A piece of 1/16" ply cut to shape and installed in the root with Hysol, puttied and sanded flush is the fix.
Now that the gap was minimized, the vertical face of the notch at the fuselage root was cut away to allow the H-stab to rotate (see 5th & 6th photos below). This area is covered by the stab so it's not visible when the stabs are at neutral; you won't see them when the model is in flight either!!!!!
You might notice in the photos that the trailing edge of the right stab extends about 5mm further rearward than the left stab (the left stab trailing edge ends forward of the fuselage fairing but the right stab ends aft of the fairing). I'll check out some 3-views to figure out which is scale and will sand/putty the other stab to match.
Regards,
Jim
01-03-2009, 02:21 AM
#31
RE: Fei Bao MiG-21 Build Thread
Horizontal Stabs - Servo/Pushrod Install
The H-stab servos are mounted on plywood plates that are pre-installed in the fuselage. The plates are quite a distance down in the rear fuselage so this install is literally done "at arms reach". First thing was to roughen up the surface of the plates with some course grit sandpaper. Unfortunately, the plates have no features or cutouts to serve as a guide for installing the servos and the left and right plates were of different sizes and slightly different locations. This was a bit of a surprise as FB did an excellent job with pre-cut mounting plates for the rudder and aileron servos. I recommend that they create a similar solution for the H-stab servos.
I used aluminum brackets and hardwood blocks as servo mounts as well as the clevis and pushrods that come with the kit to make a servo "sub-assembly" on the workbench. A series of little holes were randomly drilled in the back face of the hardwood blocks which will be glued to the ply plates in the fuselage. The FB blue anodized rod ends were then attached to the control horns and locknuts installed.
The servo sub-assembly was then placed into the rear fuselage and the rod threaded onto the rod end with the H-stabs taped to lock them at neutral. This positions the servo in the fore/aft direction. Vertically, the servo position was done "by eye" such that the control rod seemed to be horizontal. I then placed a strip of 1/4" square balsa against the servo and tack-glued it to the plywood plate. The strip serves as a jig to quickly locate the servo when gluing it's mounting blocks in place. After a quick check to ensure the left and right stab servo positions matched, I glued the hardwood blocks to the plates using super thick CA. The servos were then removed, and the glue joint between the hardwood blocks and the plywood plate was reinforced with fillets of Hysol as well as pieces of 3/4" balsa triangle stock.
The H-stab trunion blocks extended into the opening for the exhaust duct so the edge of the blocks was ground away to match the curvature of the opening.
Regards,
Jim
The H-stab servos are mounted on plywood plates that are pre-installed in the fuselage. The plates are quite a distance down in the rear fuselage so this install is literally done "at arms reach". First thing was to roughen up the surface of the plates with some course grit sandpaper. Unfortunately, the plates have no features or cutouts to serve as a guide for installing the servos and the left and right plates were of different sizes and slightly different locations. This was a bit of a surprise as FB did an excellent job with pre-cut mounting plates for the rudder and aileron servos. I recommend that they create a similar solution for the H-stab servos.
I used aluminum brackets and hardwood blocks as servo mounts as well as the clevis and pushrods that come with the kit to make a servo "sub-assembly" on the workbench. A series of little holes were randomly drilled in the back face of the hardwood blocks which will be glued to the ply plates in the fuselage. The FB blue anodized rod ends were then attached to the control horns and locknuts installed.
The servo sub-assembly was then placed into the rear fuselage and the rod threaded onto the rod end with the H-stabs taped to lock them at neutral. This positions the servo in the fore/aft direction. Vertically, the servo position was done "by eye" such that the control rod seemed to be horizontal. I then placed a strip of 1/4" square balsa against the servo and tack-glued it to the plywood plate. The strip serves as a jig to quickly locate the servo when gluing it's mounting blocks in place. After a quick check to ensure the left and right stab servo positions matched, I glued the hardwood blocks to the plates using super thick CA. The servos were then removed, and the glue joint between the hardwood blocks and the plywood plate was reinforced with fillets of Hysol as well as pieces of 3/4" balsa triangle stock.
The H-stab trunion blocks extended into the opening for the exhaust duct so the edge of the blocks was ground away to match the curvature of the opening.
Regards,
Jim
01-03-2009, 05:33 AM
#32
RE: Fei Bao MiG-21 Build Thread
Exhaust Duct Installation
The FB double walled tailpipe is very well made and has stiffening rings at the both ends. The outer pipe tapers slightly and it was an excellent fit in the rear former such that it is snug with the pipe recessed about 5/8" forward of the end of fiberglass tailpipe which preserves the scale look of the plane.
The inner pipe fits INSIDE the bypass which surprised me as I was expecting it to fit around the exterior of the bypass (thus preventing hot exhaust gases from escaping between the pipes or having the high speed exhaust flow potentially partially collapse the pipe. A bead of high temp RTV silicone around the exterior of the inner pipe solves this issue but makes the pipe a bit tougher to reinstall should you ever need to remove it. The pipe was a bit too long so I cut off 1-3/8" from the front inner pipe. I'll shorten the outer pipe by cutting about 3/4" off the front after a quick trip to the LHS for another cutoff wheel.
Mounting the pipe was quite simple using the "ears" that are spot-welded to the exterior pipe. I shortened the ears by about 1-3/8" and marked where they intersect the fuselage former. Each ear was then bent 90 degrees and drilled. Holes were then match drilled in the former and button head cap screws installed to hold the pipe in place.
All in all, this part of the build was simple....the toughest part was drilling the holes in the former as they had to be done with a pin vise due to limited access so the ol' fingertips are a bit sore.
Regards,
Jim
The FB double walled tailpipe is very well made and has stiffening rings at the both ends. The outer pipe tapers slightly and it was an excellent fit in the rear former such that it is snug with the pipe recessed about 5/8" forward of the end of fiberglass tailpipe which preserves the scale look of the plane.
The inner pipe fits INSIDE the bypass which surprised me as I was expecting it to fit around the exterior of the bypass (thus preventing hot exhaust gases from escaping between the pipes or having the high speed exhaust flow potentially partially collapse the pipe. A bead of high temp RTV silicone around the exterior of the inner pipe solves this issue but makes the pipe a bit tougher to reinstall should you ever need to remove it. The pipe was a bit too long so I cut off 1-3/8" from the front inner pipe. I'll shorten the outer pipe by cutting about 3/4" off the front after a quick trip to the LHS for another cutoff wheel.
Mounting the pipe was quite simple using the "ears" that are spot-welded to the exterior pipe. I shortened the ears by about 1-3/8" and marked where they intersect the fuselage former. Each ear was then bent 90 degrees and drilled. Holes were then match drilled in the former and button head cap screws installed to hold the pipe in place.
All in all, this part of the build was simple....the toughest part was drilling the holes in the former as they had to be done with a pin vise due to limited access so the ol' fingertips are a bit sore.
Regards,
Jim
01-03-2009, 07:29 PM
#34
RE: Fei Bao MiG-21 Build Thread
If you can recall what the Big Picture is,,,,,,, Vin's "Fishy" put in a appearance at SVF..
as usual the Experts put in their suggestions 
And Ron Flew his F 16... Just like Butter .....no gongs at all . Center cut [sm=wink_smile.gif]
Semper Fi
Joe
as usual the Experts put in their suggestions And Ron Flew his F 16... Just like Butter .....no gongs at all . Center cut [sm=wink_smile.gif]
Semper Fi
Joe
01-22-2009, 07:36 PM
#38
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RE: Fei Bao MiG-21 Build Thread
Is there any update photos, seems like it has been about a month since I herd anything about this jet. [size=4]Loosing interest!!![/
Ron
Ron
01-22-2009, 07:44 PM
#39
RE: Fei Bao MiG-21 Build Thread
ORIGINAL: arizonasun25
Is there any update photos, seems like it has been about a month since I herd anything about this jet. [size=4]Loosing interest!!![/
Ron
Is there any update photos, seems like it has been about a month since I herd anything about this jet. [size=4]Loosing interest!!
01-30-2009, 10:35 AM
#46
RE: Fei Bao MiG-21 Build Thread
I've been pretty busy "wrenching" on the MiG and have made lots of progress. I'll follow up a bit later with a more complete post with some details but, in the mean time, here are some photos to show you how it's all coming together. The turbine, pneumatics, fuel tanks, turbine accessories, and equipment tray are all installed. The servo extensions and battery installations are next on the To Do list. The plan is to have it ready to maiden on Sunday and then spend a few more days next week getting it all tidied up for Speedworld.
Regards,
Jim
Regards,
Jim
