duncan_rtfm

I've been looking at the fuselage, and yes, there is plenty of space directly in line with the CG inside the box. Easy filler cap jutting through the fuse side comfortably below the knee joint. And since the seat is screwed on (not bonded), I should be able to get the tank in/out. This will work. Now I just have to Google how to make a composite tank. Ha ha. Thank you so much for these gotchas guys. I really appreciate it.

I spoke to Jared Smith from RAAus yesterday about the Fleabike, and he put me on to Bill Oakes who doesn't live too far from me. I'll contact him on Monday and discuss when would be a good time for him to drop by and inspect the fuselage. Duncan

Hi Kasper, I briefly considered a wing tank, but dismissed the idea because I thought it would affect the wing movement in flight. But if, as you say, this is not the case, then I'll definitely look into this. What would be a good material for this? There is a thread on one of the other forums about plywood gas tanks - suitably sealed, of course. Lots of varying opinions. Major drawback seems to be weight. But I guess aluminium would be preferable, except that I have no sheet ali skills or tools. Thanks.

Hi, I have also been uncomfortable with the gas tank position. It needs to be closer to the CG, but that is easier said than done. But you raise a very good point.

Sikaflex structural adhesive? I'll Google it. Thanks. Actually, Caboolture isn't that far from me. Thanks for the heads-up.

I'm confused. The heat distortion temperature of West system is 50 deg C.. Bote Cote is 55 deg C???

After a rather disastrous laptop infection by a virus which encrypted every file on my backup drive (thank goodness it wasn't my C drive) I finally found time to get back into the workshop and progress my wing. My wings are constructed in three panels on each side. Each panel hinges. Panel A is fixed, Panel B hinges upwards, and panels C/D hinges downwards, allowing the entire rear wing (5.75m span) to fold into a 2m wide "concertina" This is Panel A. Each rib sits in a cradle, ensuring there is no twist, the ribs are perfectly spaced and sit at 90 deg. The main spar consists of two 19mm x 19mm Hoop Pine spar caps, with a 4mm gap between them. This is to allow space for the (discontinuous) shear webs to be bonded in place between them. I know this is somewhat unusual - to have a discontinuous shear web - but I've had the numbers crunched, and the 9mm gap between each shear web segment is fine. Here's a close-up of the spar caps. Using West System with some adhesive filler, I bonded the spars in place on both panel A and panel B. Once satisfied that everything was true, and that every rib was at 90 deg, I weighed the spar caps down with my trusty bricks. By tomorrow morning, I should be able to flip the two panels, and bond the bottom spar caps in place. If I get an early start (and if it's not too cold) I might be able to start sanding the spar caps to the contours of the ribs. Regards, Duncan

Gave RAAus a call this morning. Office directed me to Tech Documents, section 3.1 All seems pretty clear. Then I went to join as a non-flying member, but the website wouldn't accept my application because I needed to supply a doctor's certificate to prove that I am fit to drive a car. This, for a non-flying member. Seems odd...

As usual, a sane and common sense response. Thank you. Problem is, though, I plan to live well into my 90's (yeah, right...)

Well, all ribs cut, and all four rib jigs cut. This is the first panel. Unfortunately, the entire wing half won't fit on my build bench. Mmmm. But since they need to be built separately, that's not an issue - just that it would have been nice to see the entire wing - especially since the last panel sweeps up and backwards quite dramatically. Oh well. The jig holds the ribs nice and square. One thing I still have to do is to angle the square cut-outs for the drag/anti-drag spar. You can see the fancy cut-outs in the ribs to accommodate the drag spar. Quite sexy. The CNC cuts them at 90 degrees. But not a big deal. I'll be sealing the ribs next. I was planning on using West System - but that's a very expensive option. So I got some Polyurethane sealer. I'll do that tomorrow. Fleas generally have the pivot at about 23 deg or so of chord. But since this is a tapered wing, I had to calculate the AC first, and then work out 23% of the MAC. Again, no big deal, but easy to miss. I'll also be attaching the pivot masts to a variable attachment, allowing the pivot to be moved from 22 deg of the MAC to about 24 deg. Final positioning can be determined during testing.

Done! Cut the rear wing ribs using the NACA747A315 airfoil. Nice and fat. A CmMax of 0.012. We'll see how it goes. Also cut the rib jig. Cooking with gas! Photos tomorrow. Duncan

As you say - the 23xxx is very thin. Not a lot of meat there. Perhaps my initial choice of the 747 might be a better choice, and my larger than average wing (6.9m, 5.7m span) will compensate for its relatively low ClMax? My router bits arrive this afternoon, and I'm itching to begin cutting ribs... Duncan

OK, so the Fraser airfoil seems a poor choice. The only thing I am hesitant about regarding the 747 is it's low Max Cl (1.36) Both the 23xxx airfoils seem to have a max Cl of about 1.5 Is there any value in something like a 23115? I might just play it safe, and go with the 23112... I'm busy researching Roncz, Horten and Hepperle at the moment. Duncan

OK, so the Fraser airfoil seems a poor choice. The only thing I am hesitant about regarding the 747 is it's low Max Cl (1.36) Both the 23xxx airfoils seem to have a max Cl of about 1.5 Is there any value in something like a 23115? I'm busy researching Roncz, Horten and Hepperle at the moment. Duncan

With regard to airfoil choice, it seems there are a number of contenders. The tried and true NACA23012 the supposedly superior NACA 23112 the 43015 (spoken highly of, but for which I can find no coordinates) the F5Fras15 (lower Cm that the 23012 or 23112 above) and out of left field somewhat the NACA747A315 (it has a very low pitching moment, good stall characteristics, and extremely low drag) I had been planning to use the 747A315, but the F5Fras15 is very attractive. I particularly like the rock-steady CP position, and the low Cm (0.05 in the cruise condition) Any thoughts/advice/experience with any of these airfoils? Regards, Duncan

Thanks for the info guys. I'll give RAA a call today. I got Peter Leonard round a month or two back. He looked the fuselage over, and was very happy. He said he'd put me in touch with someone to walk me through the process, but that turned into some documentation sent via email only. Since then I have built a second fuselage incorporating all the lessons I learned in the first one. Very easy to see inside, however, even though it is now all but finished, because a number of panels are screwed on, rather than bonded. Thanks again, Duncan

OK, I have a PPL, gained in New Zealand about 15 years ago. I understand I would need refresher courses in Nav, Law, Radio and probably a few others. That's fine, and I accept that. And I'd need some serious refresher stick time also. I'm now 69, so medicals are going to be a problem I assume. Duncan

A quick question: Yes, I know this has been asked and answered many times, but I'm still confused. I joined SAAA half-way through their financial year because I wasn't aware that RAAus had people to help and mentor builders (their main thrust is in pilot training). Since then I have learned that they do in fact have a building support program (although this is hard to find on their website). SAAA have just billed me for the 2021/2022 financial year, and I'm not sure this is the way I want to go. I'm building a Flea, and a watchful eye on my construction, as well as a guide to the necessary paperwork to get the plane into the air is what I'm after. I have heard some less than complimentary stories about RAAus being inflexible and expensive. Is this true? And if I join RAAus, will I be able to call on the assistance of qualified people to get me into the air? Sorry to be asking this again, but I need some help with all the political crap which seems to be the norm in and SAAA vs RAAus discussion. Regards, Duncan

Hi, Nice to know my idea isn't way out there. Just seems sensible. But please keep a watchful eye on my build and save me from further SNAFUs No building today - router bits didn't arrive. Bugger. Regards, Duncan

Great point, and it's great to learn from your experience. However, this is something I have already considered. The pivot will not be fixed, but will have an extension bolted to the main spar, something like this, allowing for ground-adjustable pivot point of 22%, 23% and 24% chord. This will allow me to sort out the optimal pivot position during testing, and permit pilots to choose a setting to their own preference.

Hi, I'm afraid you're right. I spent most of last night and then again at sparrows this morning working on the wing. Two spars. Main spar now at 22% chord, rear spar remains where it was. Checked out the HM360 and HM293 plans I have to verify pivot placement. I am very please you picked this up. I am now waiting for new router bits to arrive by express courier so that I don't lose too much time, and then I'll cut new ribs (fortunately, I had only cut the ribs for the inside panel, and I have extra ply in the shop, so no big deal as far as that's concerned. And speaking of time - while I'm waiting for the bits to arrive, I'll go and re-check the wing. Again. Duncan

Mmmm You have a point... You said: "Design concern - your pivot spar is not your lift spar therefore you are expecting the full lift forces to be passed from the lift spar to the pivot spar through the ply ribs - I would reconsider that and use the same full span spar as both your lift and pivot as you are then not passing significant loads through the ribs" I can't use the main spar as the pivot spar - the main spar is at 40% chord, while the pivot spar is at 22.5% (i.e. ahead of the CP). I'll have to think about this. Good catch. Duncan

Today I cut the rib "cradle" jig. The ribs rest in this cradle perfectly spaced and aligned. The spar caps (19mm x 19mm Hoop Pine) are then slid into the recesses in the ribs. There is a second cradle jig, so that I can turn the ribs upside-down and bond in the top spar caps. In the photo below, you can see: The "Pivot" mini-spar. This is set at 22.5% of the chord and has a 9mm shear web. This is where the wing actually attaches to the masts, and pivots on it. There are two spar caps at 40% chord (thickest part of the wing). You will notice a gap between them - this is to accommodate the 4mm shear web. I was going to use 3mm, but since I had a sheet of 4mm Gaboon ply, I again erred on the side of caution, and used this instead. I was going to use a single spar, but decided to use two, as you can see. I think this wing is going to be as strong as a brick SH** house. I'm aiming for 6G (though in a Flea, this is never going to happen). One of the nice things about a Flea wing is that is can be built in sections. My wing has three sections: the inner section (what you can see here), a middle section (which will fold upwards as per standard Flea doctrine, and a third outer panel, which will fold downwards. This gives me 5.75m span (on the rear wing) with an aspect ratio of almost 7 which is more than almost all Fleas.