CriCri MC-15 in NZ

Discussion in 'The light stuff area' started by MadRocketScientist, Jun 19, 2009.

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  1. Aug 22, 2009 #41

    MadRocketScientist

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    Today I made the new cockpit edges, they worked out a lot better than the plans ones. I think I can reduce the curve slightly and then they would fold even better although I will be using the ones I made today. I made a pattern from 0.020 for marking out the holes along the topsides of the cockpit. It makes it a lot easier to line things up. The pattern is visible in the pics, its the straight edge where the cockpit should be curved.

    I also made the formers for folding the canopy bows, I hope to cut these out and fold them later tonight.

    Made the mounting bands for the rear canopy too.

    There is also a picture of the nose gear clamps, I need to get some more welding done on them as the previous small rod parts didn't weld very well

    Shannon.
     

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  2. Aug 23, 2009 #42

    MadRocketScientist

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    More progress today (and last night) Lots of aluminium forming. The front upper skin went all crazy when I formed the flange, I will have to tweak it until it goes flat again. The nose access holes are good for putting clamps through as you can see in the pics. I also folded the hoops for the canopy frame although they need a lot more work. Lots of wrinkles to smooth out, the 2024 work hardens really fast. I have to re-temper it often.

    I also cut a trial of the front cowling out of PVC as the plans mention that this piece may need to be shaped to fit, it fit perfectly right off the machine, not sure what all the fuss was about. I then cut it out of the 0.020" 2024.

    Also pictured is the LPG turbo torch, soap and water for tempering the 2024.

    Shannon.
     

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  3. Aug 24, 2009 #43

    MadRocketScientist

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    I have been beating the canopy bows into shape and it takes a while to get them to my satisfaction. The 2024 work hardens rapidly when being cold worked, even after it has been freshly tempered.

    Starting with the front bow halves (smaller and less material to waste if I wrecked them:devious:). I removed the front upper skin from the fuselage and mounted it on one of the curved jigs I had made for drilling the corner fuselage angles. I hammered the bows over their formers until they were close enough to test fit, then carefully worked them until the angles were a good fit against the skin. I managed to get them pretty close although I may look at them again for another tweak. A few flutes go a long way to make things sit flat. It is amazing how stiff the whole front section becomes once the bows are clecoed in place. The vast majority of the fuselage is out of 0.020" 2024T3 yet makes for a very rigid structure.

    I have yet to get the front skin sitting flat, the flange needs a lot of attention. It does sit down with clecos holding it but I would like to have internal stresses in it when I install it. I may attack it tomorrow.

    The front canopy area keeps reminding me of the Statue of Liberty with all those clecos in it.

    Shannon.
     

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  4. Aug 29, 2009 #44

    MadRocketScientist

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    The last few days I have folded and drilled the brackets that hold the canopy hoops in place. As in the first pic, all the lower parts of the hoops were too wide for a good fit, a re-temper was the order of the day and then reshaped the hoops over the modified formers. The front brackets had to be remade as the plans ones were about 12mm (1/2") too short in height. I made them by hand so I will have to take them off and measure them and change the CAD drawings to suit. (The thin strip of aluminium visible in some of the photos of the front brackets is there to hold the sides the correct distance apart while I install everything)

    Tonight I cut the doublers for the hatches in the nose, I decided to use 0.032" for safety although the local LAME's said that 0.020" would be fine. I think I will have a better peace of mind with it slightly thicker. The weight increase for the hatch modification over the stock skin will be around 100grams for both hatches (includes rivets and nutplates etc.)

    In the last photo I also attempted to get the long attachments for the rear canopy sorted out but still needs more attention until I am happy with the fit.

    I didn't think I had done much but it looks more when I go to post about it here.:grin:

    Shannon.
     

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  5. Sep 7, 2009 #45

    MadRocketScientist

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    Next round of build pics.

    I have been experimenting with a DIY dimpler made out a of a pair of bolt cutters. Makes very nice dimples but it does take a few tests to get just right for a certain size dimple. Although I am very happy with the quality of the dimples, a V2 DIY dimpler is in the works:gig:.

    Machined the odd part or two on the CNC, there's still more to come.

    I also fitted some of the small fittings into the fuselage. 1, The lower cable guide brackets for the nose gear steering. 2,The seat back mounts and 3, I continued with the structure around the lower seat area.

    Included next are pictures of the trim lever and its base and pictures of the firewall reinforcements.

    I have only just realized that I have made a mistake with the upper skin, it is located 1mm further back than it should be and causes the holes in the frames to not line up:depressed. I have only drilled them to 1/16" on the CNC so the shift shouldn't be an issue. I did wonder why the template for the holes between the two canopy frames seemed a little too long. This means that all the holes in the upper front skin need to be shifted forwards around 0.5mm when I drill them out to 3/32"

    If you look closely, the holes in the upper firewall reinforcements are slightly off center from where they should be. Some of the discrepancy is in the drawings (easy to fix up) but doesn't account for the whole error. More investigation is in order.

    Also found a handy tip when I was reading my younger brothers aircraft engineering manuals. It mentions using on size drills and then a clearance drill just before final assembly to make sure the holes fit really well. ie; 3/32 holes to start with and then a #40 hole when ready to prime or assemble.

    Shannon.
     

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  6. Sep 7, 2009 #46

    MadRocketScientist

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    This time we have the firewall or F1 with and exploded view, there's the odd part there.

    The center picture is of the large nut and cap screw that I used to make the 2.0mm thick conical washer for the trim lever. I covered the nut and cap screw liberally with masking tape to stop it marking the washer, then used a bench vice to squeeze it. I sanded the top and bottom to a small flat to give the mating surfaces more area. The lower middle picture has the assembly partially complete.

    I have some cheap flanging pliers that I use for folding some of the small parts, I have filed a radius on the top edge so that it is suitable for bending the 0.5mm (0.020") parts. I was going to shape the opposite edge to suit 1.0mm thick material folding, but as yet haven't needed it.

    Shannon.
     

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  7. Sep 18, 2009 #47

    MadRocketScientist

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    Time for another update, did I mention there are a lot of small parts in a CriCri;);). More CNC cut bits, but wait there's still more:nervous:.

    I worked out how to fold the hat section without having to make any fancy tools. I folded the center of the hat to about 45 degrees to allow for bending of the outside flanges in the folder. I then clamped the hat section over a piece of acrylic or mdf (whatever happened to be the correct width) which pulled the sides parallel. I then carefully used a mallet to flatten the top of the hat into its correct fold angle. Making the hat sections in one piece is a bit more tedious than in two parts (the plans show both ways) but the result means less rivets and less weight.

    I also made the lower tail section in one piece. The plans allow the rear tapered part to be polycarbonate or 0.020 2024. If using the 2024 it has a music wire tailskid (more weight:dis:) I decided to make both parts out of clear polycarb and have it in one piece (less work and less weight:devious:;):gig:) In the second to last phot you can see the sides of the fuselage tip starting to splay out slightly. I don't know if this would be an issue or not but I may but a small piece of 0.020 2024 to join them together.

    I had to temper the corners of the formers (first pic in the bottom row) as they both have a couple of joggles to allow them to sit flush on the upper skin. I had a think about how to go about it and decided to fold the flanges in the folder to get a straight fold. I then tempered the aluminium and formed the joggles with the hammer and dolly. The joggles are only 0.5mm but make a big difference in how the formers fit.

    Shannon.
     

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  8. Sep 18, 2009 #48

    Topaz

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    I'm impressed as hell at how quickly and well you're moving along with this. Just sayin'.
     
  9. Sep 18, 2009 #49

    MadRocketScientist

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    Thanks Topaz,

    I think its going very slowly;);). I seem to take twice as long working out how to make something as actually making it. If I build a second one its going to be a really really fast build.

    Today's progress includes the front fin attachment angles that mount on the bulkhead. They started out as 'L' angle and I CNC cut the curved side to shape. The jig on the CNC took longer to make than the cutting :ponder: I cut the riveted side with the bandsaw and filed it to finish it. The lower holes on the two fin supports are slightly too close to the lower edge, they're still passable but the drawings are changed to fix it on the next ones. The tops (sticky up bits) need a slight twist to match the fin skin but I may leave that until I have a skin to bend it to match.

    I also finally cut the fin spar caps and started fitting them to the spar web. I used a 1/8" rod to check that the top fittings were square. I hindsight I should have drilled the holes to final size before setting the caps onto the web. I will have to be very careful when drilling them now.

    I do like the shiny metal look. The white PVC covering gets boring fast:dis:.

    Shannon.
     

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  10. Sep 18, 2009 #50

    MadRocketScientist

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    Hmm I have made very good progress today.

    More and more and more parts. I cut up the remainder of the angle only to realize I am 1ft short (short of angle not my height:gig:) I have used 60' of 3/4"x 3/4"x1/16"thick angle. I will get another piece from the shop at the airfield in the morning.

    I also remembered to get a few pics of the process of CNCing the parts. I have cut a MDF jig with slots in it to wedge the 2024 angle into to hold it for machining. I cut the angle to length and the jam it in the slot in pairs of parts. I then drill the holes and cut out the shape (sorry about the blurry pic.) It takes me far longer to prepare the parts for CNC cutting than it takes to CNC them. I may try cutting multiple parts out of longer lengths of angle next time.

    Although its not strictly necessary I then hit all the parts with a file and sandpaper to clean off the tooling marks. I also round off the sharp edges of the parts. I had better watch out for magpies with all the shiny stuff laying around;).

    Shannon.
     

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  11. Sep 18, 2009 #51

    MadRocketScientist

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    Before I forget, Topaz if you are reading this I am considering putting the air intake for pilot cooling in the nose cone (a la glider style.) I was looking at a self powered glider at the airfield the other day and they have the pitot tube inside the air intake. What I don't understand is how the vent doesn't affect the airspeed measurement. I think it would be great to have a nose air vent with a protruding pitot (I want to use an angle of attack one.) I am just not sure how having the vent so close to the pitot won't affect airspeed measurement.

    Shannon.
     
  12. Sep 18, 2009 #52

    Topaz

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    It doesn't affect it because it's all just ram pressure at the tip of the pitot and the vent intake. Oh, there might be a transient effect if you slam the vent shut, but I tend to doubt it unless you're going tooling along at transonic speeds. Which would be quite a trick in an Cri-Cri. :gig:


    Think of it this way:
    1. Vent Closed: With the vent closed, the air pressure in the vent tube builds up to ram pressure (q) and stays there, since there's no place for the air to go but spill over the entrance lip. The pitot is always closed off at the back, so it's always at q, which is what a pitot tube measures anyway. Since the pressure in the vent tube and pitot are the same, there's no error created.
    2. Vent Open: The vent tube now has an opening at the back, and air is able to escape the vent tube. The pressure is lower, but still above ambient due to losses in the tube and the fact that the opening in the cockpit probably isn't full-diameter (there's still a restriction). The pitot still doesn't have an opening in the back of the system, so the little 'column' of air that it intercepts still pushes it up to q. It reads the same as the vent-closed case.
    If you could somehow get enough suction in the vent tube to actually pull air out of the front of the pitot while all the air goes by, then you'd see some airspeed error due to the vent line. But in this case, the pitot and vent lines are exactly the same as if you had two concentric pitot tubes and the outside one has a leak. The inside one is unaffected.

    I can't vouch for this arrangement working if the pitot open end is down inside the vent tube - that is to say, its opening is farther aft than the lip of the vent tube. It'd probably still work for the reasons I've outlined, but I could see pressure drops in the vent tube starting to have an effect if the pitot opening was too far down inside. So long as the pitot starts either in the same fwd-aft plane as the vent tube opening or anywhere forward of it (sticks out a bit, even just an inch), you should be fine. Our 1-26 at the soaring club has this arrangement, and I've never seen a difference in indicated airspeed with the vent valve in different positions.
     
    Last edited: Sep 18, 2009
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  13. Sep 18, 2009 #53

    PTAirco

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    I think the Cri-Cri wins the prize for the most complexity crammed into the smallest possible airframe. It definitely does not look like a project for a total beginner - I can just imagine the hours involved in making all those complex pieces with hacksaw and file. Still, I like a nice bit of (over-?) engineering.
     
  14. Sep 20, 2009 #54

    MadRocketScientist

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    You might like the complexity of the elevator trim lever, I really enjoy making a well engineered piece of engineering;). I think you could be right about a bit over over engineering, but the weight on this eensy weensy itsy lotsa bitsy:gig: aircraft is fairly critical.

    I have cut a few more parts like the friction washers for the trim lever and the few aluminium parts pictured.

    I have also reduced my extra 1' of 3/4"x3/4" angle to small parts ready to assemble.

    Shannon.
     

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  15. Sep 30, 2009 #55

    MadRocketScientist

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    Progress is ticking along.

    I bent the front fin mountings so they are lined up with the slots in the top skin. They still need to be angled over slightly but I will do that when mounting the fin.

    I cut out a lot of the fold formers for ribs etc. I made special formers to press the flanges around the lightning holes. They seem to work really well.
    The last two pics are some of the structure for the nose gear support. Now I have those two parts folded I can assemble a lot of the internal structure in the nose.

    Also have the fin spar mounted (sorry no pics yet)

    Shannon.
     

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  16. Oct 3, 2009 #56

    MadRocketScientist

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    The first shot is of a self powered glider pitot tube, the tube entry is recessed about 1/2-3/4" inside the lip of the cabin air entry opening. Speaking to the pilot, he said the the airspeed doesn't change when the cabin air vent is opened or shut. Looks promising for a nose vent on a CriCri, I may have my pitot protruding with a AOA pitot instead.

    I have fitted some of the nose gear support structure. I still need to fold and install the pedal tray rails.

    I started fitting the main landing gear and then went onto folding the flanges on the upper fin rib halves.

    The last two pictures are of the modified nose vent. The plans one has a series of 6-8mm diameter holes to vent the cabin air overboard. A small round hole in a flat sheet is about the most inefficient shape to push air through so I decided to try out a different vent shape. I also wanted to make the vent flush with the skin rather the the protruding one as per plans. I can easily change the vent to match the plans if it doesn't work to my satisfaction.
    The top of the vent just clears the bottom of the pedal tray in it foremost position.

    I have only been drilling a few of the holes in each part out to 3/32", I will go through and drill all the holes to final size when everything is ready to start the dimpling and countersinking process. If I end up making another CriCri I have a much better idea of which holes can be drilled to the final size on the CNC and which ones need to be undersize to allow for small amount of folding variations. Some will be best to not be drilled at all and be left until after the parts are folded.

    Shannon.
     

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  17. Oct 3, 2009 #57

    PTAirco

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    After all this, you should be able to produce some very nice quality kits for Cri-Cris. I am so envious of your CNC stuff - I realize all that can be made by hand, but it's nice to see such useful technology filter down to individuals.
     
  18. Oct 11, 2009 #58

    MadRocketScientist

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    A little more work on the landing gear, the mechanism that stops it moving sideways is done. I still have to weld up the parts for the actual supports but thats not going to happen very soon. I also need to source/make the rubber bushings that go in the main U/C mounts.

    I have assembled most of the front internal fuselage structure. I gave up on the fuel filler cap redesign for the time being and set the flange thickness at 2mm. I need a custom formed flange that is also attached to the pipe that goes to the tank. Deciding that the flange will be 2mm thick means I can get on with the rest of the front fuselage assembled and sort the filler out later. I will take the fuselage out to the local airfield for a check with the engineers there about the nose hatch modifications. I am generally happy with the hatches but getting other advice is always good (even if you don't end up using it)

    I started fitting the reinforcements to the wing spar box as they don't affect the fit with the spar. The spar box is assembled after the spar as the spar has to fit neatly into the spar box, small variations from the plans in spar size can then be accommodated.

    Shannon.
     

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  19. Oct 17, 2009 #59

    ultralajt

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    Wonderful! Thanks for sharing building progress with us.
    I really enjoy visiting this thread

    Regards!

    Mitjs
     
  20. Oct 17, 2009 #60

    MadRocketScientist

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    No problem, I am really enjoying the build so far.:):)
    I have made more of the landing gear mounts but have yet to take some pictures. Hopefully in the next few days.

    Shannon.
     

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