Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by rtfm, Jul 11, 2008.

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1. Aug 23, 2008

### rtfm

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Hi guys,
Thanks for the kind words. Yes, she is a real looker, and when she is built, I think she is going to fly really nicely.

I'm in Wellington at the moment, and have just returned to the hotel after a gruelling day of Ballroom competition. We made the final of the Waltz and the Tango, so we are "on show" tonight for that event. Tomorrow we dance three dances in the group above us, so we don't expect to do very well. But it is a great weekend.

I'm back home on Monday, when I am hoping Mac790 will have been able to slice this cute little plane like a salami into many bulkhead templates, so that I can start building it.

Photos as soon as I have something to show.

Regards,
Duncan

2. Aug 24, 2008

### Mac790

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Personally I thought about "standard" method with plugs, moulds, etc. But If you want to use that "superkr2" method you can make it more "professional". I've found a really nice webpage about boat hull construction.
http://www.amateurboatbuilding.com/articles/howto/foam_sandwich/index.html
I think it's a good idea to use some planks "strip of wood" over these plywood templates. I've read that some people cover wooden structure with a sheet of plastic foil to prevent the resin from leaking through gaps and bonding to the jig. I think its a good idea. I'm not familiar with that "aerosol spray glue" but personally I believe that filling these gaps between the foam with an epoxy is a better idea.

Check out that page a guy builds a plane fuse with a very similar method.

Seb

btw I did few renderings for these method.

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3. Aug 24, 2008

### Rom

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From the amateur boat building link I can see why they do the one-off method from the outside first using a male form. It appears that with a large structure such as a boat, one needs to be able to walk inside the boat hull in order to finish the structure. The way I am doing the strips https://www.homebuiltairplanes.com/forums/showthread.php?p=30491#post30491 with a female form there is no need to walk on the fuselage to do the interior laminations because of it's size. I believe that fairing the outside should be much easier because the shape won't distort because the inside is already glassed and foam being already rigid.

4. Aug 24, 2008

### orion

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One consideration to examine: The baseline Airex foam is a great material but may have one drawback in that it is not a rigid, cross-linked foam. While this does provide the material with excellent durability and toughness, when applied over a series of wooden frames it may kink, creating a series of facets along the fuselage. Given the relatively gentle curves, you might want to consider a cross-linked product like Klegecell or Divinycell.

5. Aug 24, 2008

### Mac790

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Personally I've never heard about Airex before so its hard for me to judge, I thought rather about
Divinycell or Klegecell. But I'm afraid its too late.

.

I believe that both methods have some advantages and disadvantages but its like discussion "what was first the chicken or the egg". I have some experience with plugs and moulds and for me its easier to work with the male plugs than with the female ones. It's easier to shape, with the female mould/plug you cant be sure about outside shape till it comes out. Btw Thans for the link I was a little bit busy and I missed it Nice job, When are you going to remowe your fuse from the mould?

Seb

6. Aug 24, 2008

### orion

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Female moulds can be quite difficult to work with, especially if you're after a nice fair surface. I too would rather build on a male tool rather than a female tool.

Our current projects use female tools but in that case all are CNC cut so there's little or no finishing - just a bit of surface prep for the laminate applications.

So far I've worked on about half dozen projects where a male pattern was used as substructure for strip planking and each time I'm quite sure it was much easier than if I would've gone the female route.

7. Aug 24, 2008

### rtfm

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Hi guys,
Thanks for the contributions to the build thread. Actually, I haven't placed the order for the foam yet, because I have been competing in the National Ballroom championships, and things have been a little busy of late because of it.

So, if Divinycell or Klegecell are the preferred options, I still have time to investigate these. It may be that availability is the deciding factore here in New Zealand, but we're not exactly backward as far as composite construction is concerned, so these foams may well be available.

Mac790 - it appears that your approach seem to be to build one half of the fuselage at a time. To be honest, I had not considered this. I had thought to mount the templates on a central beam suspended between two stands. But building each side separately would be a great idea. For one, it would be relatively easy to position the templates, and also relatively easy to secure them in place.

Duncan

8. Aug 24, 2008

### Mac790

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I did quick a check using an area tool and it seems that you will need about 45 square foots of foam per side. CG for the fuse skin is in the middle (I know its only skin so it doesnt mean anything)

Seb

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9. Aug 25, 2008

### LGM

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RTFM,

You might also spend a little time poking around on the various Vision builders sites. The Vision uses a similar build technique as the KRSuper2. It's built in 2 halves.

Good luck,

L.G.

10. Oct 26, 2008

### rtfm

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Hi guys,
I have gone though a month or two of belt-tightening, and have done relatively little on the Razorback build. However, I have come though the tough patch, and have a bit of disposable income to apply to the project. Trouble is, I seriously doubt that I have the skills to pull this off. It seems that no matter how simple a task is, I cock it up.

For example - Seb worked with me to produce a very lovely design, and he helped further by producing 21 templates for me. To save on printing costs, he printed them 7 or 8 to a sheet. I had these printed, cut them out, glued the paper to hardboard sheets, sanded them to exact dimensions and then began fitting them to a central beam.

Bugger. I had no idea in what order to mount the templates. It was not simply a matter of smallest at the nose, and bigger ones further back. It took me ages to get the sequence correct. Then I tried to mount them (each was in two halves, left and right) on the central beam. Again, major head-scratching. I had carefully routered out a recess in each template to perfectly fit over the 2x4 beam, but either the beam's dimensions are not precise/regular, or my measurements were a bit off. Some were too tight to fit, others too loose, and couldn't be held in place long enough to glue. I have now completed half of them - held together with masking tape and hope. When I get all of them lined up and stable I have to figure out how to make sure the entire superstructure is accurate and rigidly in place before I start laying the foam "planks".

All this drama, and I haven't really started yet...

Whoo boy - this is going to be a rough ride...

One thing I have discovered, however, is that it is just not possible to move in one half of a double garage with a full-size aircraft fuselage taking centre stage. This is ridiculous. So I have arranged to move into a workshop hangar out at the local airfield. This will obviously give me more space, but will also allow skeptical eyes to wrinkle in amusement at my ham-fisted attempts to build the aircraft. It's a tough trade-off...

When I finish the template mounting (later today?) I'll take a photo, and post it here for your amusement...

Regards,
Duncan

11. Oct 26, 2008

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Stick with it, Duncan. You'll get there eventually. You've already heard "measure twice, cut once", so I won't say it again (oops). Remember that for your jigs, it's much easier to cut outside the lines and sand to size than to fix it once you've cut too far... but (again, for jigs) shims work pretty well too. Tightly pulled cables give straight lines, as do lasers, if you can stack your templates and drill a few holes through them, so you'll have something besides the beam to give you alignment.

But yeah, realizing that both design and building were huge undertakings was what drove me to build a kit design (with the same construction style as my imaginary design) first; so I learn to use the tools and the techniques with support and instructions.

12. Oct 26, 2008

### PTAirco

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Hey, this happens to the best of us. Today I cut a piece of metal ( a kind of luggage shelf underneath the panel). It needed three flanges, and I bent two out of three the wrong way......

13. Oct 26, 2008

### Blackhawk

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Hi rtfm,

Just out of curiosity, how many aircraft are you going to call 'Razorback'.

Here's a photo of a German gyro thats similar to yours from 1972.

Blackhawk

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14. Oct 26, 2008

### Midniteoyl

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Believe its the same dream, only different....

15. Oct 26, 2008

### rtfm

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Hi. It's a changing target, Blackhawk. I just like the name, and since I didn't build the gyro, why not transfer the name to something else?

That's a pretty neat looking gyro - isn't it strange how often we think we have a unique idea, and lo - you discover you're late... I doubt I could have made such a great looking gyro as he did, however. Good on him. Thanks for the photo.

Duncan

16. Oct 26, 2008

### Mac790

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Hmm Sorry Duncan but I dont get it. Why did't you ask me for help? I sent you pictures with proper order (attachment) Did you receive them? I thought you quit/resigned, changed your mind or something. Next time please ask me for help life is short enough there is no time to waste.

That what I was waiting for.

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17. Oct 26, 2008

### AVI

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Re: 3D Lofting

Mac790:
That's really nice work. I'm still stuck in 2D AutoCAD myself, but would like to learn 3D. What program are you using and what would you recommend?
Alex

18. Oct 26, 2008

### Mac790

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Re: 3D Lofting

Alex
All these renderings I did with different Autodesk Inventor versions (10, 2008 and 2009)
hmm My first question is are you a student? Because students can get almost everything for free (Autodesk Inventor) or for small amount of cash (Solidworks, Solidedge, Pro/Engineer, Rhinoceros etc).
If you arent student my second question is how much money are you going to spend (we are talking about offical, legal way). And third question what are you going to do with that software.
In my opinion you have two possibilities (one relatively cheap):

-Rhinoceros (Orion uses it) its a very good software special for complicated parts like cowlings, etc. (but I only "played" with it for about half an hour so I don't have to many experience with it)
+ good for surface modeling
- price (you cant get private version commercial cost over 1000$) you can't make FEA (finite element analysis) tests more info here Modeling tools for designers -You can buy Pro/Engineer private version even if you are not a student for about 368$ it's about 20 times cheaper then commercial version.(or maybe even more I dont remember commercial version price)
+ price, proffesional engineering software (top class), FEA (mechanica included)
- with private version you cant exchange files with commercial version,

COMSOL ONLINE - PTC Pro/ENGINEER Wildfire 4.0 SE Academic Use / Private Use

I dont have experience with "cheap cad programs",like freecad etc so I can't help.

Seb

Last edited: Oct 26, 2008
19. Oct 26, 2008

### rtfm

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Seb,
Hi. I didn't ask for help because I didn't want to appear too stupid :gig:

But I've now hit another snag. I have all the templates on the central beam, and there is NO ROOM to move in my workshop. I have about 18" at best either side of the fuselage - really very awkward. I keep bumping stuff, and knocking stuff off the walls. This will never do.

I have secured a large workshop (basically an entire hangar) out at the local airfield, at a very reasonable price. The current occupier moves out in a couple of weeks time, which is great. So I think I may just number the templates very carefully, and dismantle everything. MUCH easier to move on the back of a small pickup if it is all in pieces...

Then I'll spend a weekend transporting my entire workshop to the hangar, and set everything up again. At least that way I'll be able to (1) get everything transported and (2) once there, be able to work in relative comfort...

Duncan

20. Oct 26, 2008

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