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Hi I have reached the point with my plug preparation where I am just about ready to wax on, wax off. I.e. start making my molds. However, I would really like an experienced eye to give my plug the once over and provide me with a sanity check before I carry on. I have reached the 150grit stage, all the blemishes have disappeared and as far as I can see all is ready. But what do I know? So, if you live in the Brisbane area and have a half hour to spend this weekend, I'm looking for some assistance. Regards Duncan

Good grief. What a self-rightous bunch you are turning out to be. For goodness' sake - chill guys... This finger pointing and tut-tutting is unnecessary. Duncan

Hi Daffyd, Hi. Hey look... I'm not trying to be awkward... Just asking an inncocent question. You have answered it quite comprehensively above, so thanks. Cheers, Duncan

Hi, Thanks for all your helpful insights and answers. I will be using 10mm 3-D Core as the meat in my CF sandwich. My test pieces are extremely rigid, and surprisingly light. The entire fuse (inclusing vertical tail) will weigh in at just on 21kg, and since the fuse is roughly circular, and only 3.9m long (12.8ft), it is going to be extremely rigid. There will only be two bulkheads. Well, three if you include the structural control panel. (Firewall, control panel, seat back). No longerons. Tricycle undercarriage, with the main gear attached to the inverted gull wing. The spar= single piece, although I am considering folding the wing at the elbow just outboard of the landing gear (like the Corsair). Engine = 900cc Generac (Valley Engineering Big Twin. 116lbs wet (ie running), including starter and redrive. 50hp. The wing skins will be made from 3mm 3-D Core foam and CF. Again, extremely light and rigid. It was when I showed my 3mm test piece to another local composite designer/builder, that he thought it would be more than sufficient for the fuse skin also. Hence the reason for my somewhat idle question. Just wondering, I guess. At the moment, I am almost finished the plug. A final dusting of black paint this afternoon, before (hopefully) the final rub-down tomorrow, and onto increasingly fine sandpaper till I have a mirror-finish. Within a week I hope to start making my molds. Regards, Duncan

Pal, I asked a simple question. Do you know the answer or not? I didn't expect (or deserve) a talking to about doing my homework. Sheesh. Duncan

Hi, This is my own design. I have been advised that the "standard" (in the US anyway - eg: Glasair) is 1/2 inch sandwich for the fuse. I went ahead and bought 10mm foam designed specifically for infusion. However, a local builder said that this was way overkill, and that the 3mm foam I bought for the wing skins was more than adequate for the fuse as well. So the question remains - does anyone know how thick the sandwich skin of the Jabiru is? Regards, Duncan

Hi guys, Does anyone know how thick the composite skin of the Jabiru is? For that matter, does anyone know how thick composite skins usually are? I have received advice that a fuselage skin thickness (sandwich) of 3mm is more than enough, and other sources insist on 12mm. Are either of these in the ballpark of what would be considered "normal"? Regards, Duncan

Hi, If it's what I THINK it means, its a VERY "free" translation. Nice. DuncanTop of Page

Hi, I have only just stumbled across this thread today. Don't know where I've been hiding... As HITC mentioned very early on, there was a protracted discussion about whether it was possible to design a really inexpensive Part 103 plane on another forum (which will remain nameless, to protect the innocent). Much discussion on materials, basic design (pusher/tractor/tailwheel/trike/2-stroke/4-stroke etc). A lot of sharp minds there, but no consensus. For my part, I proposed a "profile fuselage" concept. Basically, a sheet of 100mm foam, cut to a pleasing profile, glassed, and with wings, engine and undercarriage bolted on. I got as far as actually building the fuselage, and then got enthused about my Razorback design, and put the profile concept aside. It is still hanging on my workshop wall. If you're looking for SIMPLE, cheap and quick, this will take a lot of beating. The airframe is a single composite piece - what is simpler than that? And you can build it in a weekend. Once the fuselage has been glassed, you add the wing, any engine up to about 55kg and bolt on the undercarriage. Some controls, and that's basically it. There are some structural details to work through yet, but I still think the concept has promise. My 2c Duncan

But that's exactly the point... IF the unexpected and potentially catestrophic happens, WHAT ARE YOU TO DO? Duncan

Hi djpacro. You said: You've got the cart well and truly before the horse, mate. In designing a plane, one doesn't have the luxury of flying it first to check its PIO tendencies. One has to look at "simple geometry" and try to predict whether or not it will exhibit excessive PIO tendencies or not. So one aims for a generous horizontal tail volume coefficient. And one shoots for a healthy static margin. And aims for a healthy Couple Index. One does it all, and then possibly fly it in X-Plane as a sanity check. And if you have a mate who's into RC, you might get to see it fly as a RC. In short, do it all. But you can't fly it first. But a nice report - I've read it before. Thanks for reminding me of it again. Cheers mate Duncan

Bloody hell - that's scary... I'm scared witless just sitting in an open cockpit! But don't you just love that terribly stylised way of speaking adopted by early announcers? Duncan

Ah, yes. I was assuming reasonable values for Cvt and Cht. I have selected 0.85 and 0.065 respectively. But while the tail volume coefficients chosen certainly affect the dynamic stability of the plane, these do not affect the short-coupledness of the plane. That is another matter. Regards, Duncan

Yes... I see he's added some colour to his site since last I visited it. I agree - some of the designs are fascinating. Duncan

Hi, I get this every time... A short-coupled aircraft is a function of the relative distance between the wing and the stab. Not the actual distance. If you scale down an RV so that the actual distance between the wing and the stab decreases, it doesn't change the relative distance between them, which is why RC models of RV's are just as pitch-stable as full sized ones. Here's a re-post from HBA (with some edits to remain current): In the flight sim, as corroboration, the Razorback flies with no pitch sensitivity at all. Regards, Duncan

Hi, I have the templates in DWG format, so I was thinking of scaling them down (10% maybe) and checking to see if my construction method works, and to have something to play with in the shop while waiting for resin to cure. I have no RC experience, however, so to embark on a proper RC project would be too big a distraction I think. Regards, Duncan

Hi Jim, Yes, it has been a long often disappointing road so far. Although I have evolved the design considerably from when I first started, my MAIN issue has been with construction. I have no background in building anything - apart from two or three foam surfboards back in the early 60's. And even then, my father did most of the work. I simply didn't have the necessary skills. Fortunately I now have Alan Clarke as my mentor, and he has all the building smarts I lack. I was promised a brand new engine so long as I specified the Thunder engine as standard on any kit I produced. Too good to be true, unfortunately. And yes, if I hadn't already bought the Valley Engineering Big Twin, I'd fork out the extra and get the BMW 1200. With that engine, the little Razorback would truly go like the proverbial bat outta hell. But at 74kg, it would be a challenge to get the CG right... Cheers, Duncan

Hi fly_tornado, No I haven't. I have often thought I'd do so, but never got round to it. What I AM doing, though, is I've created an X-Plane model, and have spent some time trying to fly it in the sim. I have no sim flying experience, so it is easier said than done. No spatial awareness, no control feedback. All I do is crash, mostly... Do you have any RC building/flying experience? Duncan

Hi folks, I have posted extensively on the HBA web site regarding the little Razorback airplane I have designed and am now about to start building. I thought I'd use this forum as my primary one, since it is Aussie, after all. I am in the process of moving out of my old workshop into new (much larger) premises, and so everything is in a state of suspended animation till that job is completed. But I have the stand all ready, the templates on file, and very soon now, I'll be forking out for new foam, and some CNC cutting of the templates. I promise to post lots of build photos. Basically, I'll be building a plug, from which I will take molds, and then use these molds to make the actual fuselage and wings. I could have built a single one-off plane, but where's the fun in that? If she flies as well as the spread sheets suggest, there may well be others who might want to build one. So I went with the molds. Till next time Regards, Duncan

Hi Mark, Thanks for the kind words. Unfortunately, I'm in Brisbane, otherwise I'd jump at the opportunity to have some help. Movable weights? Yes, I've considered this from time to time. The difficulty is in the logistics of it. Probably the most weight-efficient way to do it would have been to move the battery fore/aft. But that's not a particularly quick job, and since the battery I want to use only weights less than a KG, that idea went out the window. I'm toying with the idea of fitting Fowler flaps to the h-stab also, to be deployed as required - either to counteract the pitching moment of the wing when the 40% chord Fowlers are deployed, or to simply increase the tail volume coefficient should a heavier pilot be in the plane. But the jury's out on this one. Cheers, Duncan

Ha ha. Not really. I LOVE the design phase, but only LIKE the building phase. Problem is, I'm having to learn by trial and error. It is a damn side easier to learn how to design a plane than to actually build it. But I'm getting there. This one is the charm, I think. And with my half fowler, half split flap design, I should be able to tootle around low and slow with the best of them. Regards, Duncan

Hi guys, I joined this forum a few years back, and for some reason it dropped off my radar. I have just been reminded of its existence again, and so here I am, back again. I know this is an old thread, but hey - since when has age ever been a barrier to folks like us? There are very few amateurs today who actually are designing brand new aircraft starting with a blank sheet. I'm one of them. And I'm glad to find some others here as well. I started out planning to build a KR2. But I couldn't find enough decent wood (I was living in Auckland at the time). So I bought a set of Sonex plans, and discovered that I didn't like the zillions of little bits of aluminium which had to be rivited together. Besides, I didn't like working with the stuff. So I began to think composite. My dad and I built a number of very early composite surfboards way back in the 60's when no-one knew what the hell they were doing. But I liked the process. So I began looking for suitable composite kit planes. There was nothing I could afford. The idea struck me that I should save money, and design my own. HAH! Save money? Not... Almost four years later, I have finally got a grasp on what aircraft design entails, have received a lot of peer advice (and criticism), and have thrown away more than a dozen "final" designs. I've also discarded a half dozen plugs. One only got as far as the basic shell. I have completed five other plugs, made adjustments to them, fixed errors, changed dimensions etc till they were so mutilated, I had to chop them up and begin again. One of these was abandoned when I moved from Auckland to Brisbane. Each time I restarted the process, I went into lockdown mode, and made significant changes to the basic design. I have tried low wing, high wing and now I've settled on a mid-wing configuration. I've gone from tailwheel to tricycle. Over the years I've acquired three engines: a Suzuki 3-cylinder (sold it - too hard to convert), a BMW K75 (trying to sell it - too heavy) and now a Valley Engineering Big Twin. This is an already aero-converted engine, 50hp, 116lbs including reduction drive, started, alternator, oil. With the aid of WizardWorks (a 3-D Wizard mate on the homebuiltairplanes.com web site) I now have plug # 6 ready to go. All template files are currently at the CNC shop, and foam is on order. The last plug took me 8 months of sometimes daily labour to get to the stage where I was ready to make molds. Then I decided to change the tail for better spin recovery, and to widen the cockpit. The new plug (with new and improved construction method) will be ready for molds within a few weeks from starting. Well, that's the plan. So - if you're reading this thinking that you might give designing a plane a go - do it, mate. Do it. But don't expect it to be quick, cheap or simple. Hopefully, however, you will end up with a unique and ultimately satisfying design you can truly call your own. More info on my design can be found on my web site: http://rtfmaero.wordpress.com/ Regards, Duncan

Hi, I have just moved to Brisbane, and am living in a tiny one-bedroom apartment in the West End. I have designed a single seat low wing aircraft, and I'm looking for a number of things - I'm hoping someone reading this post can help with some answers... First - where can I source carbon fibre, glassfibre, foam, resin etc? Second - without a lockup garage, I need to rent a garage somewhere so that I can begin construction. Any ideas? Third - while we currently live in the West End, we plan to move north of the city - which would make Caboolture a good bet as far as a home airfield is concerned. Comments? Suggestions? Any help getting me building would be appreciated. Also, I'm wanting to get back into flying after a rather long break (4 years). I have a PPL, but would like a recreational licence. Any ideas regarding a good flying school? Regards, Duncan