Scratch build McDonnell XP-67
01-16-2018, 06:34 PM
#52
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New wing plugs. Need a little cleanup work but much better than my original ones, airfoil is better. Taper is better. Got some twist built in this time. Might start the mold tomorrow.
01-16-2018, 07:44 PM
#54
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I needz monies! Lol. I’m at the expensive part. Electronics etc 
I’m working on a couple jobs that are just taking longer than I anticipated. I got to order some cabosil or micro balloons and start making some fuses. Have quite a few bulkhead templates to figure out.
I’m working on a couple jobs that are just taking longer than I anticipated. I got to order some cabosil or micro balloons and start making some fuses. Have quite a few bulkhead templates to figure out.
01-21-2018, 05:55 AM
#56
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I discovered my first major flaw. It’s fixable. Will require some work in the mold itself unfortunately. Needless to saw as this is my first scratch build, I have learned many lessons, for most of which is to develope a PERFECT jig. Spend 10x the time on the jig, maybe even double it. Make 5 of them for Christ sake until it’s more than perfect, god like even.......my wing roots were off by about 5mm at the trailing edge. Matter of fact the entire starboard side of the planes trailing edges were off about a millimeter near the very stab, to 5mm at the wing root. I have corrected the wing root issue and I’m thinking that the rest of the filleted fuse will not be a huge concern. Everything trailing edge from the nacelle inward is max 2 millimeters off. Will require a little extra trim no doubt, but I think it will be ok. The molding is done. I’m letting it kick. I realized my problem after I molded the lower wing half, I was looking and I was thinking something is crooked.......something is crooked.......lol........no no no.... it’s fine.......no something is very wrong.......but I can’t really tell......yea it’s ok.......no something is crooked........ah screw me.........so I had to pull them off. The detailing came out really good. Obviously getting my technique down...0 voids, no thin spot with bubbles. Very happy. As I’m looking at it now the dihedral may be a few degrees off, but it looks good. The lines flow right. I’m probably ok. I haven’t been sleeping well and I think I might just be being super critical right now. Anywho, ordered all my electronics for the plane. I chose some 370w motors, 30a escs. A 3700 3s battery rather than a 5000mah. The lower mah battery saved me about 7 ounces!!! Only cuts theoretical flight time by a quarter, I’m looking at 4.5min at wot now, bear in mind I’ll be running greater than 1:1 power ratio, I may end up going smaller and light motors and battery even still, but I thought....POWWAAA(Jeremy clarkson fans will get it). New landing struts are on their way. They aren’t especially scale looking, but they may require no modifications, which for something this small I think is more important at this point. I’ll update again when I start mold repairs. Putting me back about another week, but eh, who’s counting
Last edited by Mms_citrus; 01-21-2018 at 06:01 AM.
01-21-2018, 08:58 AM
#57
If it were easy, every one would do it. It is a trite saying but it still applies. Just attempting this puts you into the top 1% of people in the hobby. I'm looking forward to seeing the completed project. It looks like you could use the same technique to make a mold for a Gloster Meteor.
01-24-2018, 04:33 PM
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I spent 2.5 hours taping panel lines..........I spent the last couple mornings blending the wing to fuse joints. This morning I taped up the lines and brushed on some epoxy. I also added the elevator to my horizontal stab. It’s just gonna be easier to lay up. I also layed up a few test panels, trying to nail down my lamination schedule. I ordered som fabric from taylorcraft. I heard good things about their stuff. I had set up an account with a composites company here in Florida, I’m just not super happy with the cloth they have. I got some 4oz and it just doesn’t conform very well at all. And the cost was really just not that good. I’ve gotten used to the epoxy but it’s really thick. When I run out I may try a different company. Anyway, taylorcraft, I got 2.5oz. It lays out really nice. It came partially wrapped in this polyester fabric, not a woven cloth. Steve said it was some unbranded no spec polyester fabric. They bought some rolls from a traveling sales dude, so No one knows what it really is I guess.It’s really interesting. One of the test panels I did 2 layers 2.5, a layer of the unknown stuff, and another layer of 2.5. Im pretty impressed. I think this coupled with some strategic 1/16 balsa coring will Yeild pretty good results, plus a couple 1/8th ply bulkheads. The last 2 pics are one of the test layups. The honeycomb pattern is the mystery fabric. I also got some peel ply. That stuff is cool...I think I might lay up my first fuse tomorrow. You may see sexiness on Friday......
i need to bite the bullet and commit to vacuum bagging one of these days....
i need to bite the bullet and commit to vacuum bagging one of these days....
Last edited by Mms_citrus; 01-24-2018 at 04:39 PM.
01-25-2018, 09:30 PM
#62
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Thanks for that advice. I’m going to finish the layup tomorrow. It’s going to be a little heavier than I wanted cause I’m using more epoxy than I wanted to. It’s thick and not wetting out well. I am thinking I’m going to be 4-5 ounces heavier than I initially thought. Coming along well tho. Going to be plenty stronk I think. I may end up just cutting this one to pieces for easy bulkhead fab, so it doesn’t have to be perfect.
01-29-2018, 10:06 AM
#63
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Well prototype fuse is done. I pulled it apart just now. Came out ok for my first attempt. I need to shave 10 ounces. I don’t know how I’ll do that exactly. I have some ideas tho. I think I can shave 5 ounces for sure. It’s 27 ounces. I didn’t think the resin so I know my resin ratio is too high. I’m going to lay up the next one with heated resin so it’s thinner and wets out better. I didn’t want to thin it because it weakens it by like 35% at 10% thined. Overall I’m very happy with my first attempt. The mold is not perfect. The fuse will require a little bit of finish work but I think that’s ok. I’m going to lay up another fuse maybe tonight. I’m going to try some different methods and filet every edge and some other stuff to try to eliminate a couple of these small voids. I’m also not going to pre paint it. See how much weight I save. And I think I’m going to foam core with expanding urethane foam. So I’m going to eliminate a layer of glass and some reinforcement layers. I am also considering live hinge for the ailerons and elevator. Not even remotely scale but will be easier to do. I’m going to cut out all opening on this one and start figuring out my gear and servo mounts. If anyone has any suggestions for the layup or experience with the foam let me know your thoughts. I found one that says 1/2lb density. I’ve never seen anything lower than 2lb density so I emailed and am trying to see what it is.
01-29-2018, 09:07 PM
#68
Great effort!
01-31-2018, 06:04 PM
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I think I have it. I layed up a new bottom. I used a total of 4.2oz resin. I mixed up some epoxy/cabosil and applied it to all the edges and hard angles. Then I brushed a coat and let it tack. Then I heated the resin and brushed another coat. Then I layed down the first layer of 2.5oz cloth. I heated the resin with my heat gun as I wet it out. I applied the second layer of cloth and heated the resin as I wet it out. I’m laying up in pieces with about an inch overlap. The shapes are too complex to do it in one piece. At least for me. The center section ends up at 4 layers the way I do the overlap, and although I could get it to wet out 3 layers 4 was a little dry so I brushed on a little resin in the center. Then I cut some strips of this polyester fabric I got and added some stiffeners to leading edges trailing edges and the cowl joint. The nose area from tip to a few inches past gear door I layed up as 5 overlapping layers. The will be practically no foam core in the nose so it must rely on itself. Then I layed 5 layers plus the “coring” fabric on gear doors. I forgot to add it to the servo doors so I scuffed it all up tonight and I’ll work on it tomorrow. I would take pictures of the layup but it’s too messy, and it takes me almost 2 hours to do the cloth layup. It’s really tedious...I think I’ll make a couple fuselages then I may make a new better mold. This one leaves much to be desired...the price of learning.
02-01-2018, 04:58 PM
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THE bottom weighs 7.2 ounces. On target. I think I’ll be at around 18-20 ounces. Plus some foam. I layed up one half of the top. I think I can come out under 20 ounces. That will trim at least 7 ounces!! The way I figure it now is if it’s heavy just make it faster high stall speed? No problem, make it go 80mph just land it like a jet lol.
I reinforced the the tail area. I don’t want any death wobble. Nose section reinforced. Motor mount area reinforced. Leading edge same as bottom. The red line is the peel ply live hinge. Be cool to see how it comes out.
high stall speed? No problem, make it go 80mph just land it like a jet lol.I reinforced the the tail area. I don’t want any death wobble. Nose section reinforced. Motor mount area reinforced. Leading edge same as bottom. The red line is the peel ply live hinge. Be cool to see how it comes out.
02-03-2018, 12:25 PM
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So I’ve run out of epoxy so I’m working on other stuff. Did some tests with expanding foam. I like it. Front gear mount sorted. Elevator and rudder mounts sorted. Main gear, I have mounting plates made up but I can’t install until I bond and foam the fuse. Did some motor and prop tests. The online calculator I’ve been using has been dead on pretty much. I need more props. I tested a 6x5.5, speed prop. Drew 19 amps, 21 surge. 260 Watts. The 7x6 was too much. I saw spikes over 45 amp. I need more test props. I’m going to look at plastic retracts, see how much weight I save. May not be enough to make a difference. Still waiting on gear struts to show so I can see if they will fit or if I have to modify them.
anyone have any ideas on how to open and close the gear doors without extra servos? Maybe some kind of spring to open and a lanyard attached to the strut to pull it closed?? The steering arm just barely fits.....lol. I planned it like that...
anyone have any ideas on how to open and close the gear doors without extra servos? Maybe some kind of spring to open and a lanyard attached to the strut to pull it closed?? The steering arm just barely fits.....lol. I planned it like that...
Last edited by Mms_citrus; 02-03-2018 at 06:46 PM.