LiteFighters: P-40/P-36 and beyond

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cluttonfred

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There does seem to be some variation in the wheel spats on the different iterations of the fixed-gear Hawk 75. I do agree that the Fokker fixed gear is more appealing, but then I'd love to see a Fokker D.XXI replica kit as well. Or maybe something in the spirit of the Flitzer, a simplem fighter-like, radial-engine sport plane that channels both the Fokker D.XXI and Koolhaven F.K.58 so it looks like it could have come from the drawing board of Erich Schatzki without being a replica of anything.

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ScaleBirdsScott

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I'm not enough of an aerodynamicist to know how much reducing the span loading, in addition to the wing loading, will help -- but I've got a good seat in the cheering section!
I'm not either to be fair, just reporting some of what we've been looking at.

Ultimately I think we're not that far off but we do need to clean things up, and I'm going to have to look at some ways to do a weight reduction of our setup for next time. There's a lot of obvious places I can shave a few morsels here and there. Then again, being a replica some things need to stay and they all weigh something, and some have a direct impact on drag as well (like fake guns, etc). So may have to simply adjust the baseline assumptions to reflect more or less what we have, now that we have some flight data.

If we do decide to stretch the wing with a new center, then the question is whether we would choose to re-build the outer wing panels as well, which would let me shave a few more pounds and clean up a few things.
 

flitzerpilot

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The Verners open up a huge range of radial fighter types for replication, but most monoplanes will feature retractable undercarriages, unless one goes back further into the inter-war fighter biplane era. Although creating a non-specific 'fighter' monoplane, which would allow a more relaxed approach to design, I feel it would be missing the point. The Prowler is a good example of this approach, although having the refinement of a retractable landing gear, but, like my fixed gear Baturin 'fighter trainer' design, it would fail to arouse much interest because it lacks the kudos of a glorious history.

Part of the appeal of scaled Hawk. Fokker D.XXl,or with retracts, Hellcat, Zeke, Fw 190, I-16, La 5FN or with say, an Aeromomentum, Spitfire, Bf 109, Yak 3, P-51 etc., is that the ego of the frustrated 'fighter pilot within' can be massaged when looking out at a familiar wing shape with appropriate national markings and through a reflector gunsight over a familiar cowling.

For fixed gear types, although limited to two prototypes, the Avia B.35 is an excellent choice for an inline motor, using a one-piece 'flat' wing (dihedral due to thickness taper only) but its appeal would be reduced for the reason of its obscurity and lack of a production order, this being reserved for its retractable offspring, the B.135.

For sure the highly-polished prototype of the fixed-gear Hawk 75 would be marvellous to behold and if the 9-cylinder Verner were to be an option, scaling it up a little to take advantage of a bigger wing and reduce the constraints imposed by the smaller scale would make it sensational. The additional power would not de-stabilise a slightly bigger machine and the thicker wing could be fabricated without much weight increase imv factoring in the greater spar depth with a deeper, perhaps more slender, spar boom. Just my observations.

What a rip-roaring ship this could be for a little recreational aerial combat or display flying: big enough to fool the eye, manoeuvrable without being over-sensitive, allowing a scale canopy size; a salute to the progenitor of a redoubtable fighter series that took the war to a relentless foe in the early 1940's.
 

ScaleBirdsScott

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Haven't updated in a while, but my old man did put together a video so thought I'd link it:



Since that footage was shot we've run into a snag. A hard bounce on landing last week or so caused the lower tube leg of our starboard landing gear to bend to the point of deformation, which caused the tips of the composite prop to abrade away on the runway. The leg did not give out entirely, and Sam never even really noticed anything was wrong until the engine was shut off and got out. So it's a good sign if the right wheel can be bent about 10-20 degrees of negative camber and everything stays controllable. Unfortunately we did not have cameras running on that flight as I wasn't there helping set up.

I have more investigation to do but I think that we might have had a machining issue causing more material to be removed than I had originally designed when turning down the lower leg tube. I plan to cut the tube into some sections and take measurements and see if I made it wrong, or if the design is insufficient for the sideloads being placed on that tube, or if we just had exceeded a reasonable impact.

One thing we did notice from previous flights is that the spring for the gear shock was overly bouncy and the thing really needs to be converted to Oleo type shocks. So I guess that's definitely happening now.

Without a suitable propeller, we probably are down for the winter.

It also gives us a chance to work on flaps and some engine cooling and the like so it'll be productive time.
 
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ScaleBirdsScott

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So regarding propellers, we're looking at trying a different propeller than the one we had on as a start instead of having the same blades re-made as they were. (Also not sure what the situation in Ukraine means for availability) We're talking things over and thinking that particular blade profiles may not be well enough optimized for our engine and setup. Decent enough climb but couldn't get reasonable cruise performance dialed in. Plus we went for a rounded-tip replica look, and ultimately there are trade-offs there since we had to have the mfg modify their blade shape, so it wasn't a totally bespoke blade profile. I think we probably need to do a little more work, and maybe for now find a blade that does the job even if it doesn't fully look the part.

So if anyone's got some thoughts on a lead for a good propeller option that would do a good 3-blade for 120-130hp, 2350rpm max direct drive, 72" max dia, and isn't backlogged to the summer, I'd be open to hear it. We've looked at a number of places but may not be aware of everything.
 

Marc W

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Meglin has a carbon fiber 3 blade for up to 150 HP available right now. He didn't give diameter so you would have to check on that. Blade shape wouldn't be period correct but he has it in stock. It only took 9 days for my prop to get here from Ukraine. That was in July or August so during the war. Good prop and the price was right!
 

ScaleBirdsScott

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Thanks for the thought. We are reaching out to NR prop to see if they have any availability and thoughts on performance for us to work from, but, want to open up the options to see what else is available.
 

Tiger Tim

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For the purpose of flight testing would a ground adjustable prop make the most sense? That sounds to me like it would allow some variation to let your
customers choose pitch for their own machines to suit their circumstances.
 

ScaleBirdsScott

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We've had a ground adjustable on already, and an electric in-flight adjustable would be even better, we're just wondering if the blade geometry we have is ideal. Not being a propeller expert it starts to get beyond me.
 

Dana

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GSC does both ground and in-flight adjustable props. Wood blades, so they could probably do a different tip shape.
 

aodem

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Hi HBA, so some of you might have caught on that my project, ScaleBirds, has been working on a new thing. I thought I'd make a thread for it, instead of trying to shift the topic of some other thread.

We put up a news item today that is showing the latest with our new development:

The Frontal Assault

You can also read some older articles and see a little bit of the progress if so interested. Or, if you're like me, that page may not pass your work filter. So I'll link a few of our images here for those who can see the HBA at least.

In short, we're working on a single-seat LSA-qualified light fighter replica, the idea being that if WWI replicas can do well with simple, affordable single-seat replicas then there has to be at least a few tin knockers who want in on that game vs the tube and fabric boys. In general, even the tube-and-fabric guys will be right at home with our construction method. In keeping with our whole ScaleBirds concept, we're building a tube truss frame that can accept various skins to take on various shapes. We used an aluminum tube and gusset construction held with stainless pull rivets. After seeing the builds of the Airdrome replicas, it seems like a viable method for this level of homebuilding.

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The first model is being built a P-40. And it is designed for a Rotax 912 under a nice composite cowling I've labored countless nights over. And of course it would look good with teeth and eyes and a massive spinner:

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But the plot thickens! Since getting a new Rotax 912 is quite expensive, and our options for getting an affordable pre-owned model locally have not gone as we originally planned, we're looking at this Verner 5Si radial engine we just ordered to put on airplane #2(which was to be a Zero, then changed to being a Hellcat, and for now is in limbo)

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And now its got us thinking "well, we have an airframe going together and we have a sick engine on the way, maybe we need to make something of these two?"

Or, at least I'm thinking that, since P-40 Warhawk + Radial Engine = P-36 Hawk. And I happen to think the P-36 = Super Awesome Looking Warbird. But apparently because it was an early war fighter that was superseded by more famous planes, it's not the best 'marketing' choice to make a P-36... figures.

Even so, it may well be a thing we do before we find a viable 912 to put on. I mean I control the CAD right? So that gives me a bit of veto power. And anyway when we do get a Rotax and it's P-40 time, just would be a case of swapping engines and cowlings and the other tweaks should be minor. Now, the only other technical challenge, is all of our aero has been done assuming the pointy nose; and so for that reason it may be that we need to stick to the in-line option full-stop. But I'm still rooting for the radial. Even if the cowling took only minutes to draw (and not weeks). I mean, just look at it:

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So I'd tweak a few things, this was a quick mockup. We'd add guns to the cowl and proper scoops and vents, and the fuse forward of the windscreen would get provisions for the 'machine guns' up top, and we may flare out the fuse a bit to better match the round cowl up front. But that's all minor stuff. I just wanted to get a sense of how the Hawk would look and I love it.

Now, speaking of radials:

The other thing I figure I'd share, is we are now signed on to be dealers for Verner Motor in the USA. We ordered our own engine and it will arrive next week, and I'm really excited to see this thing we've been dreaming about for years now; I've been following these motors since the ScaleBirds project started, basically. Back when all they had was a radial for helicopters and this Scarlett 7 engine was a new thing, we were hoping to see more come of the Verner line. And, well they are starting to really get moving in Europe. But it is still a new product line especially here in the USA. So while discussing our engine order, both parties agreed that if ScaleBirds wants to be using these motors in our potential fighter fleets (and we do!) then it makes a lot of sense to be able to source them directly. And, more than that, we want to help grow this emerging market of small, general aviation radial engines. Because they are cool. Because they are actually pretty darn good engines. And people agree, as the demand is obviously there; and companies like Rotec are doing a great job demonstrating to the world that these are still real things that can power an airplane. And now there are more options for a round-engine fix especially at the low-power end which is always a good thing.

We are just starting this deal, and only just in the next few days getting hands on with our own engine; and so some things are still being ironed out, and I don't want to say anything I'm not supposed to yet. But, by Oshkosh I'm hoping interest in these engines really jumps off. That all is mostly for a different discussion in probably another section of this forum, if at all. Anyway, I'm just excited for this, for real. And thanks for checking it out.
Anyone on here tried to make a WW1 replica using lighter plastics?
 

ScaleBirdsScott

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You could always get blades with the most efficient tip shape and make up some rounded tips that stick on, like Spock‘s ears, when the plane is on static display. Just add “remove Spock’s ears” to your preflight checklist...

That might be tough for a saber-type blade but, I've heard stranger ideas regarding blades.
 

ScaleBirdsScott

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All those could be fun. We definitely need to get through this first one first. And P40. And the Hellcat. And just having a kit that is viable in general.

Feeling in a bit of a low point at the moment as we didn't get nearly as much testing in as we figured. We're running out of time for this year before the cold really sets in, which isn't a hard cutoff but it means less opportunities to get out to the airport to fly overall. As it is, we're waiting on repairs and a prop which we have to decide on. Maybe try some new blades from Ukraine, or Sterna apparently can get something in a week or two but that's a whole new blade and I've got no real experience whether those are a good option or not.

Still trying to work out the best way to address some of the performance challenges without a lot of data to pull from. Ultimately I was hoping to be using this time working on the first tail kits, and we're just not on the right track to work on that yet.

I think the biggest LiteFighter project to work on now for my part, would be to get back to work on the retractable gear set, and for it a test rig so I can nail down the dynamics and do some drop tests. But on the other hand that's one of those aspects that for kit builders is only needed towards the back of the build schedule. So I can't plan to get a lot of useful progress done right now, and that's got me wondering where to focus efforts for the maximum near-term gain.9

On the other hand I've got to be putting some time into our Verner accessories and trying to streamline and standardize the accessories we make for those engines. So far most parts have been mostly custom one-off configurations, and that has been hell from a planning and execution standpoint. So we're trying to narrow down our designs to a core set of options and then a few upgrade accessories.

At some point we may look at making our own replica-style 3-blade hub from billet for someone's blades. I have all the equipment I'd need to CNC a nice hub set, even if I have more manual setups than someone with a fancy 5th axis. Those hubs ain't exactly cheap to begin with, nor do they look correct, so for the relatively few we'd have to make for the Verner fleet of 3-blades it probably would pay to just do our own. Ultimately we probably need to work with someone to develop a set of custom Verner blades too. Something that is meant to get ideal performance in the lower RPM range while providing good flow down at the root of the blade for cooling, and has the right blade shape. Something that can work on the 7 and the 9 since the ground clearance will be similar challenges between the two at around 70"

As it is, all of this stuff is expensive, and shop space without a lot of projects to fill them is expensive, and hangar space is getting a lot more expensive in the area especially if the weather is bad where we can't do much test work. And without the performance meeting our expectations at the moment we haven't committed to any orders yet so the budget will be stretched thin over the winter as well.
 
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