# Some design musings

Discussion in 'Hangar Flying' started by rtfm, Jan 14, 2014.

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1. Jan 14, 2014

### rtfm

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Hi,
HITC and a few other mates drove down from Brisbane and the Gold Coast to the annual airshow at Evans Heads last weekend. It was a great day, hot as hell, but thankfully there was a bit of a breeze to cool things down somewhat. I saw my first F1-11. I had no idea how BIG it was. I've been looking at my diminutive (10ft) Razorback for too long I think... I also saw the awesome Grumman Avenger. Wow. What a lovely plane. Those folding wings look just like a bird folding its wings when it lands. Elegant and so quick...

Apart from these two stand-outs, I have to confess there was little else to pique my interest, design-wise. Whole rows fast glass clones. Some even had indistinguishable names (Sting/Sling). At a glance I was hard pressed to tell them apart. Then there were four or five amphibians, all of which looked like they came out of the same sausage factory. A bunch of high-wing clones also (Light Wing, etc etc). And then the Warbirds. Again, I have to confess, we were struggling to tell the Harvards apart from its clones.

So all in all, a case of the Clone Wars as far as variety was concerned.

A couple of things did stand out for me, however:
1. There were no 'rough-and-ready' homebuilts. Simply not in attendance. Which was a pity.
2. Without exception, every commercial offering was as well appointed as a modern sports car. Which is perhaps why the cheapest kit on offer was upwards of $75k. Which made me take note that if I ever want to sell Razorback kits, I'm going to have to spend an awful amount of time and money getting it up to showroom standards. There was also a lot of discussion about how these prices were unrealistic, especially given that the market is miniscule. Some suggestions of$40k as being a realistic price. Interestingly, Chris Conroy's planes (he was also there, with a little stand touting his Sparrowhawk two-seater) sells for $45k if I remember correctly. So it can be done. 3. All the commercially available planes there (including the gyros and the trikes) had fitted racing-style, beautifully upholstered seats. Gone now is my plan to make my own. The Razorback would look positively home-made by comparison. 4. There was also quite a lot of discussion about how many kit manufacturers there were (someone mentioned 131 - but I think this was a global-figure?) and what one would need to do in order to stand out from the crowd. Some thought STOL was the way to go, since it made for a far more practical plane. I leaned to fast glass, but at a very competitive price. ie Well within the$40k suggested figure.

So, although as far as a designer is concerned, the show was very ho-hum, the very fact that there WAS a dearth of design innovation was encouraging. If I had arrived to see something like the Razorback, or a Horten-like flying wing, I think my heart would have dropped. As it is, the field and the race is anyone's at the moment.

One other thing which did emerge from the show - there were no single-seaters - except for a lone RV-3. Everyone wants two side-by-side seats. So the Razorback will have no chance I think of attracting much interest when I finally get one flying.

When I got home, I went off to check out the Friedrichschafen 2013 airshow in the hope of seeing some really innovative new designs. Fat chance. High wing clones, low wing clones, tadpole clones, etc etc. Talk about the Clone Wars...

So I sat down, and began thinking.

The Razorback will have to be my personal plane. I will love it but I recognise that it will be a personal plane and not for sale. I will definitely need a two-seater if I want to sell any kits. So here is what I came up with.

Based strongly on the Razorback, still very small, but departing completely from the "usual" plan view. A bit weird at first glance, but it kinda grows on one. A bit like the plan view of Formula 1 racing cars, don't you think? 42 inches at the shoulders. The side view is very sexy, however. I will have to think long and hard about the CG issues this will present. But those are details I can worry about later. Maybe it's time to build my first model to see what it looks like in the flesh...

Regards,
Duncan

Regards,
Duncan

Last edited: Jan 14, 2014
2. Jan 14, 2014

### Aircar

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Check out the Polliwagen Dunc - backsweep your finl and stick the horizontal tail on top .... Isn't this then recloning ? --bet there weren't any flying cars in the line up...

3. Jan 14, 2014

### Aircar

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PS check your drafting software --the nose on the side view is clearly much longer than the plan and likewise the distance from wing TE to tail -- (based on the root wing location -or are you showing the MAC ?)

4. Jan 14, 2014

### wizzardworks

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Duncan, Along long time ago in a place far far away there was a side by side razorback called F2. You have template printer files for it already.

wizzardworks

5. Jan 14, 2014

### rtfm

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Hi Aircar,
You're right. Two independent drawings, and they don't match up. But you get the general idea. I rather like the plan view of the fuse, however... I'll do some actual work on them, and see if I can get them to line up. Maybe a dead end, but a great way to spend an afternoon.

Duncan

Last edited: Jan 14, 2014
6. Jan 14, 2014

### rtfm

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Hi Wiz,
Aha! I found them on my old laptop. Time to brew another coffee, and take another look at them I think...

Thanks mate,
Duncan

7. Jan 14, 2014

### wizzardworks

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Duncan, I think the Razorback F2 was for a BMW R1100 motorcycle engine conversion. Everything was scaled off your sketches so we need to do a 3d of the engine and make sure it fits. The Corvair conversion
might fit and it is 100 HP and as a potential kit make sure a Rotax 914 fits in there. Sure would be nice if you could use the same wing on every variant. The F2 is a similar size with an extra 200 pounds
of passenger weight so the same wing would increase take off and landing speeds, but lift is related by velocity squared so the speed increase might not be all that extreme. And people building a fast
glass 2 seater might appreciate the higher speed of a relatively higher wing loading.
Just a thought. If you are not anticipating multiple copys of the single place Razorback why not just pull parts off the plug and surface finish like a Rutan design. Save the mould cost for the future F2
which is more likely to be series production. Since the single place has a cowl mounted fuel tank you can hot wire the wings and do Rutan construction on those also. Then pull moulds off the wings for use on the F2.

wizzardworks

8. Jan 14, 2014

### rtfm

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Hi again,
Well, deep into my third coffee, and my fingertips are tingling a bit. Eyesight's gone south, and the afternoon's getting ready to pack up. So am I.

As luck would have it, I didn't save my original doodlings, so had to start again. But this time, Aircar, I think I did a better job of it (as is often the case).

Here we go - things line up this time. Still has the "jellybean" plan view, and still has the long-nose-short-tail profile I like. Also, very small (Why make it bigger? Small = light and fast). I haven't done any weight estimations yet, so the CG may be way off. As may the placement of the wing. But it's somewhere to start. If Glenda gives me some time off this evening after dance training, I'll start the weight & balance calcs and see what I end up with.

Wiz - you will recognize the pedigree of the original F2, with the addition of the straight tail, the forward swept inverted gull wing, and it's smaller, of course.

Comments welcome (and gratefully accepted). I get side-tracked very easily, so your combined voice of sanity is almost mandatory in my case...

Regards,
Duncan

Last edited: Jan 14, 2014
9. Jan 14, 2014

### flyvulcan

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Hi Duncan,

As for single seaters not selling, I understand over 100 kits for the Onex were shipped in its first year of release. The Onex has affordability, simplicity and manufacturer credibility as its pluses but it seems to have reasonably mediocre performance, certainly not scintillating.

I wouldn't necessarily count the Razorback concept out yet, particularly if you can get decent performance out of it.

Cheers,

Dave

10. Jan 14, 2014

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But if you're tired of "traditional fast glass", why not do something really radical?

I too was tired of the dozens and dozens and dozens of virtually identical side-by-side Rotax-powered low wings at Friedrichshafen.

That's why my design too looks very different..

11. Jan 14, 2014

### ultralajt

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It is pretty late in the project progress to start doing market research now.
Any deviation of the project layout means waste of the aready produced plugs and molds... wasting money&time...
Mitja

(P.S.: personally I am scared of flying with short coupled planes. Would never purchase a plane that optical seems to me "short coupled", no mather what stability calculations says. Of course, I am looking trough eyes of "sunday" pilot, not a commercial proffessional pilot. I never overated my flying skills..I rather think conservative...

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12. Jan 14, 2014

### rtfm

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Hi,
Such is life... My life doesn't always (ever?) go according to plan. What's the alternative? Proceed doggedly down a chosen path just because you chose it? As Dave says, if the Razorback proves to be a real little performer on a tiny (and cheap) engine, it may just have some appeal. We can only wait and see. So I'll proceed with the plug as planned. But I certainly won't be the first designer/builder who has changed horses a few times before reaching the finishing post.

Short coupled? Maybe. But the proof of the pudding's in the eating, not just checking it out in the cafe window...

Regards,
Duncan

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13. Jan 14, 2014

### ultralajt

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Pretty nice sentence, trying to disarming me, but loss is not on my side.

I can say for myself, that during many years of my interes in aviation, I got pretty good eye for what looks right and wrong in aeroplanes.
Of course, this doesnt mean that I rely only on my eye. But my eye and drafting talent are the first step in design, and second (of course more important) are aerodynamic and structural design and analysis.

Once I was visiting my friend in Brno (Czech republic) and his friend show me photographs of his new all metal ultralight. He said how good is that plane and that he is satisfied with its performance.
It vas reall wery cute plane, but I noticed rather small vertical tail (small by my opinion.. "checking the pudding trough a cafe window".. by your words) and ask him how it behaves in a sidewind take of.
He suddenly blushed in face and told me that it not handle sidewind well by its small vertical tail.

That was not the only ocasion, when my "eye" serve me well, so I have confidence in myself.
As probably dont know, I build more than 4 flying machines and fly with them (hang gliders, paragliders, trikes..). All of them perform as I planned.

Every design I started with making eye apealing to me and next step, checked things with math.

The only design where I make many changes is the Footlaunchable sailplane presented here in Light area section, but this is still called "Preliminary design".
When preliminary design will be finished, there will be no more major changes. Only changes will be regarding some minor details regarding ease of manufacturing assembly and decorative parts.
The cheapest modifications are these made on the paper. (Homework)
So, one must define as much as possible on the paper, not to do "hot water discovery" at the building process.This could be a mjod drawback.

I follow your work for many years now, (remember, I made even some renderings for you of your early designs when you weighted between hihg or low wing concept) and I cant stop thinking of your early design drawings, comparing them with these newest developments.
It was said somwhere in the start, that you want to build fast. Look how many years went by and you stil did not came to final layout.

As you said, many two seaters are available... so, stick to your one seater racer! Be unique!
You dont need 1000 customers... 10-20 will be just as fine...

Mitja

14. Jan 14, 2014

### rtfm

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Hi,
I note that when someone makes a long reply, it often means they have been offended. I didn't mean to criticise you Mitja. And I'm sorry if I gave that impression.

I will definitely be finishing my single seater. In fact, I'm working on it every day. That's my number 1 goal. If I ever get round to building another plane, it will be a two seater, which may (or may not) look like my "preliminary design" here. Just throwing out ideas at the moment, that's all.

And yes, I remember your renderings of my planes. I have one of them as my screen saver! The low winged one looks very similar to what I am now building.

One of the reasons it has taken me so long to get this far is that I have changed my mind a number of times, that's true. But there have been other reasons too. Moving from New Zealand to Australia got rid of my first attempt, because I couldn't bring it. Then I found that I didn't know HOW to build a plug. I had a few failed attempts at that. Round about version four looked very good, but the guys on HBA convinced me to change the tail. And then when Wizzardworks rendered that design in 3-D, it showed that my engine would not fit in the nose.

So I started again, this time with CAD templates.

So I have had a number of false starts.

And see - this is a long reply, which shows that I am being defensive. So I'l end now.

Cheers mate,
Duncan

15. Jan 14, 2014

### cheapracer

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The \$64 question is Dave are those 100 the market fillers? Will another 100 sell in the next year or the next 10 years?

It might be you just being normal actually, it's called "The Golden Ratio" of visual asthetics. Shapes that fall outside tend not to be trusted or purchased by the masses ...

Golden ratio - Wikipedia, the free encyclopedia

16. Jan 14, 2014

### Tiger Tim

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Let me preface this by saying I think what you're doing is awesome. I can only wish I had the time, money and drive to prototype a kitplane.

Well, since you asked, I think it's ugly. It has too many different aesthetic concepts going on at once, like it was designed by either a committee or a duck billed platypus. The wing is swept forward, the stabilizer swept back and the fin is straight up: it all just clashes to my eye. The fuselage side elevation just feels wrong to me too, my gut says flow separation behind the wing and marginal directional stability but I suppose proper analysis can prove me wrong there. I'm also going to need to see more about that Coke bottle cowl, I'm just not sold on it yet.

Does this airplane have potential? Of course it does but IMO it needs a lot of refinement.

-Tim

17. Jan 14, 2014

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IS it actually short-coupled? A quick glance suggest a tail arm (0.25C to 0.25C) of 2.5 or so. Short, but not uncommon or is that glance incorrect?

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18. Jan 14, 2014

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I fully agree with your opinions about the “war of clones”, Duncan - or, better said, the ”frozen-in-project” uniformity of that tsunami of side-by-side, low wing 912-powered glassy tractor biplaces seen at the aero-fairs.
Though, this lack of evolution has some motivations on the practical side - involving egonomics, simplicity, costs, maintenance etc (that’s maybe also why birds don’t have low wings ). Observing this stagnation does’n mean that I like it, me too being haunted by the same originality-obsession (is it a virus maybe?) driving the idea-turmoil of so many HBA colleagues.

One important aspect is that the generalisation of this trend for light A/C makes much more difficult the goal to design new configurations - original AND efficient in the same time, but also easely accepted by the public, which is already “frozen” psycologically in the same concepts - if someone designs with this target in mind (to sell it.)
And this is a point connected with Mitja’s or Tiger Tim’s posts: “subjective” aesthetic impressions are indeed premonitory signs of successful designs in aeronautics too (being a principle functioning in every domain linked to rapid transportation and, inherently, efficient aero- or hydrodynamics.)

Following your open invitation to sincerity, I’ll point some… weaker points (IMHO) of your actual design, as a simple amateur RC-modeller (not talking now about proportions etc. - as an ex-professional editor AND designer, even if only in the motorcycle-field.)

1. The fuselage form might be aggressive indeed (due to the long and somehow… phallic nose), but I think that there is too much unused space behind the firewall, and also too little space behind the seats.
This leads to a very abrupt “thinning” to the fin (Vstab) and consequently a disruption of the air-flow (remember the golden rule of max. 7-8 degrees panels-inclinations.)

2. Generally, a normal fuselage must produce some lift too - and I doubt that your actual profile would be able to do so. Maybe it will achieve some negative lift (see its bottom line.)

3. I also guess that, by using a more balanced crew positioning, there won’t be any need for a forward-swept wing.

4. If the swept wing is still an irresistible idea, I’d personally go for a tandem biplace, optimising the CG with the passenger put ahead of the spar root.

5. Those wing tips are still wrongly rounded (upside-down - another subjective or even wrong opinion maybe, but I stick to it.)

…Wow, in the end I realize that I’m also on the… long-posting side,:gig: but I’m convinced that you won’t take it on the harsh side, Duncan - I still admire sincerely your astounding strong will to materialize your dream, but also your open mind when it comes to discuss constructive issues.

Last edited: Jan 14, 2014
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19. Jan 14, 2014

### Autodidact

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Duncan, my biggest complaint about your design decision process is that you have a tendency to complicate things. I don't want this to turn into a Duncan bashing session, which would be according to human nature, so I'll say that my biggest complaint isn't a large one; I just think that the tendency is there but that you've slowly and methodically dispensed with some very radical ideas and come around to more conservative ones - I personally think that a balance between the two is most interesting. For the one-seater version, I think that the inverted gull wing is a bridge too far. It's bound to be heavier and more difficult to build, and the drag reduction would be small. The forward sweep is interesting enough; I think a nice straight wing would be best. An inverted gull wing puts the center of lift lower in relation to the CG and this makes the aircraft a little less stable. Your design is not "short coupled" per se, but it is a small aircraft and these tend to have quick response times to control inputs. JMO

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20. Jan 14, 2014

### rtfm

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Hi guys,
Ha ha. Well, I DID invite honest criticism. I have just woken up, have coffee in hand, and am reading your comments. Gosh - Ugly, designed by a duck billed platypus, wing needs to be changed in a number of ways, wrong nose/tail proportions. Why don't you just say what you really feel?

I guess I do wear my design heart on my sleeve, rather than designing in private and showing only the final result. But I like to share my ideas, and value criticism along the way. Remember, the new design is my first paper napkin doodle only, and offered as a talking point. Which it is certainly proving to be.

Aesthetics:
In the eye of the beholder. The first time I saw a Rutan design (the Long EZ) I thought it was hideous. I still do. But many people love the look. I think the Verhees Delta is an eyesore. It's all a matter of taste. So, my chosen configuration for the single seat Razorback is here to stay, because I like the look.

Aerodynamics:
The first sketches of the two-seater obviously needs some more work. I put in the FSW because it was already drawn (for the Razorback). But it will go. I need a simpler, lighter wing. Point taken. The aggressively swept rear section - I'm not sure I buy the old "7 to 8 degrees" rule of thumb. The Questair Venture had just on 18 degrees of sweep aft of the cockpit, and it is one of the most aerodynamically clean aircraft out there. I think I'll investigate it further.

Profile:
Yes, all my designs have a long nose, and short tail section. Again, I like the look. It is certainly nowhere near the extremes of the Gee Bee with almost no wing, almost all engine, and the pilot practically sitting IN the tail. However, my design preference is certainly not idiosyncratic. It is shared by many racing aircraft. Here's a nice one (and notice the upswept aft belly also).

So - I'm off to the workshop now to continue work on the Razorback (F1). I'll doodle some more on the two-place (F2) when I get back. In the meantime, why not fire up your CAD and have a go at the F2 yourself - show me what you think might be better...

Cheers,
Duncan

Last edited: Jan 15, 2014
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