LiteFighters: P-40/P-36 and beyond

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Dana

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There's a group restoring a Corsair at my home field. The center section carrythrough (I think that's what it was) is an elaborate forging and they couldn't find a serviceable one. Last I heard they were working on designing a new built up one, which was only possible because they wouldn't flying at full combat weight.

When I asked the project leader when they expected to fly the plane he said, "in about a million dollars."
 

Dana

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Sounds like they have almost completed the restoration.

If you get a chance, sit in the seat and look at all the space and stuff below.


BJC
Hah! They've got the plane all apart, with bits and pieces all over the country being worked on by various people. If they get all the pieces back it'll be a miracle.

They've got a Wasp Major on a trailer that they bring to shows and start up to attract attention and hopefully donations... hopefully more than the $1000 it costs them every tine they fire it up.
 

ScaleBirdsScott

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Corsair spars are definitely a cool example to look at. They're made from a number of various pieces all bolted together, the way they have bent channels for the top and bottom cap strips and then formed 'cap' webs bolted to those cap strips is quite interesting. Then the main spar web is stiffened frequently with hat sections. I like aspects of it. There do seem to be some major machined forgings as well, near the gear and such.


fg1d_r_hr_66.jpg
 

ScaleBirdsScott

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So, it's been a while but we finally have our oil tank modified and ready to go back into the P-36.

300907276_1259779424759150_3046780982195080880_n.jpg

Changes include adding a bunch of holes to the top of the forward part of the tank and then adding a 'dog house' (at least that's what we call it) to the top of that area which is approx 1.8l in volume. The perforations between hopefully acts as some baffling between the lower sump and the upper air chamber. Beyond that, the biggest 'engineering' adjustment is I've re-routed the tank return into a cyclonic separator that acts as tank diffusion inlet and 'downcomer', one that empties down into the main reservoir with a sizable gas vent up through the middle. The bottom of the cyclonic cylinder has anti-vortex cross baffles and then the cylinder comes within a very tight margin of the bottom of the tank, with the forward section of that cylinder cut away, facing opposite our pickup line, so that oil will flow into the main reservoir at least mostly away from the pickup.

Cyclone_1.jpg 299612743_451548393586700_7264302495204016464_n.jpg

I hope that those changes to the tank alone prove enough to solve gas entrainment/foaming/etc from overwhelming our reservoir.

Tank_Cutaway1.jpg

But just in case additionally I had our welder convert our 'dumb toob' of an expansion column to something more appropriately called an air-oil separator. (In reality we definitely should have just bought an off-the-shelf one from the get go as we paid our guy more than the cost of the ASA one to weld and then modify that thing). If what we made works as a true separator, it's certainly a huge one. Anyway it's also a cyclonic type, with a series of baffles towards the bottom of the main chamber to slow and disturb the flow coming down so that it knocks off any last gas before it drains back down to the tank at the bottom. The middle of the cyclone vents to a chamber above, which then has a baffle before the final breather pipe exit in the middle vents directly down and out the bottom of the aircraft, facing slightly aft.

Sep_Cutaway1.jpg

One thing I have avoided is adding fine-pack 'filter' type stuff like steel wool or woven mesh or one idea I had which was reach into our buckets of aluminum lathe swarf which basically forms various sized 'springs' which could certainly be stuck together and wound into a chamber. Mostly because I haven't got the time to develop a way to open a filter area up and replace/clean the filter area fully. And that seems to be a common concern. So better to leave it out for this one. Being a radial we aren't worried about a little oil mist escaping, as we'll loose oil regardless from other means. But I do want to keep the system from just pumping the oil out in bulk, and, I don't think that's the problem the mesh would solve.

All told, I hope what we have is a system that efficiently keeps gas from even entering the main tank reservoir, allows what gas does get in there to effectively escape with minimal resistance, and whatever mix does wind its way up out of the tank into the breather system, is further encouraged to be split and sorted appropriately, either out of the aircraft or back with the rest of the oil, in our separator.

I stopped short of cutting open the lower sump tank to add myriad labyrinthine baffles and trap doors, with the intent there to force the lower flow to go all the way around the tank before it can get to the pickup sump area, with the theory that gassy oils would spend a longer dwell time in the reservoir being able to aerate before getting to a point those oils can be picked up. And then keep them low enough that anything over a min volume would just flow over top the doors like a sinking Titanic. Before I got fancy with that, I was told not to get too carried away. Maybe in the future. Honestly no-one else doing these Verner installs is going to such lengths, not even of this new, current tank. But I'm experimenting and having fun exploring all the options and talking with my race buddies and watching the videos out there about all this stuff. Lots to learn.

In any event I'm looking forward to get it all on there and see what happens. I'm sure in due time we'll be back in bizniss.
 

Dana

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When I built my separator (with a copper scouring pad as the coalescing media) I made the end caps removable. The caps are grooved, with o-rings, and a long tie rod through to hold it together and support the internal baffles.
 

ScaleBirdsScott

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When I built my separator (with a copper scouring pad as the coalescing media) I made the end caps removable. The caps are grooved, with o-rings, and a long tie rod through to hold it together and support the internal baffles.

That's not a bad idea! I had been thinking needing threaded endcaps or some kind of flange, but really just a machined little cap with O-rings and a simple central bolt could work for something like this.

Will keep that in mind.
 

Hawk81A

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I gotta wonder what kinds of problems Glenn Curtiss went through. Hope this settles it for you. Dennis
 

ScaleBirdsScott

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Well his problems started at the very beginning and kept going, so I'm sure they had their share.

We're mostly just playing catch up with a little novelty, as a treat.


So we got the tank in today, had to do a little work to make some things fit because we simply don't have the entire FWF planned out 100% in CAD, only major stuff like the mount and engine and cooler and the like. I don't have little things like pressure senders, the exact arc of the throttle cable, wiring for the starter and so-on all 100% accurately modeled. I mostly go by the numerous photos as reference to correlate with our CAD to see if there's a potential hit in a given area. But it does mean what often looks like 'miles' of room in computer-space sometimes translates to "negative half an inch" in reality.

But we got it all sorted and other than needing to order one new hose, and ideally switching from a 90 degree AN elbow to a 120 degree elbow, we are good to try running it tomorrow.
 

J.L. Frusha

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@ScaleBirdsScott
Something to consider... With different empennage, canopy, a belly scoop, wings and landing gear your fuselage isn't that far off from a P-51 B/C. Could even offer up the Malcolm Hood/Canopy.

I'm sure I make it sound easier than it is. I was just looking at the profiles, with the P-51 B/C overlaid.
 

radfordc

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@ScaleBirdsScott
Something to consider... With different empennage, canopy, a belly scoop, wings and landing gear your fuselage isn't that far off from a P-51 B/C. Could even offer up the Malcolm Hood/Canopy.

I'm sure I make it sound easier than it is. I was just looking at the profiles, with the P-51 B/C overlaid.
You forgot a different engine! Basically a completely different plane....nothing to it.
 

J.L. Frusha

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You forgot a different engine! Basically a completely different plane....nothing to it.
Good morning. Maybe you haven't had enough coffee? P40 was a V12, not a radial, like the P36... Means they are already planning an airframe for other than a radial.
 
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Hawk81A

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While their existing plane is a radial (what I believe he means by different engine), I believe that heir plan is to move on to a P-40 with inline engine, and eventually expand to other planes using the basic framework. Dennis
 

ScaleBirdsScott

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So been a while since posting much. I had a big hot machining job to deal with that took up the last month with tons of setups and setbacks to muddle through so I did not make a lot of time to mess with the plane. But also because while we've flown the P-36 a few times the news isn't particularly exciting or conclusive yet.

We're shy of most of our numbers, but not out of the ballpark. Just decidedly an infield hit just short of the baseline, just right of 2nd and rolling towards the outfield. But no home run yet.

We've had some opportunities to test different configurations on the propeller, cowl flaps, with/without baffles and so-on all to see what moves the right needles. For example tightening up the cowl flaps to fully closed earned us 10mph level and only about a 2-3 degree difference on the CHT. So getting the ability to adjust or set them to entrain in flight is going to be a must.

The big take-away so far, without getting too fancy with the testing, is that the exposed landing gear without fairings has to be a huge source of slow-down sauce. (A realization that many could and did predict.) But how much sauce we got on these wings is still TBD. So we're going to work on some spats and trousers for the leg and wheels that are somewhere between the original Curtiss look and the Fokker D.XXI style. I doubt they'll be a final design that we stick with for the fixed-gear long-term but should be good enough to see if reducing the drag from the gear hanging in the breeze moves us appreciably towards the intended goal.

Other low hanging fruit on the slow-down-tree are dome head rivets on the leading edges (in particular but also generally on the whole wetted area), a less than optimal termination to the lip inside the cowl, and some of the panel seams. But landing gear certainly look to be the biggest thing to address. Retracts would really help of course. (OK and so would switching to a P-40 nose with a 150hp inline but that's a different thing)

Another take-away but one we have to do some more analysis on is that for our mission, a bit more wing area and flaps would probably help a lot. We aren't making any firm conclusions yet but signs point to high wing loading for the power and drag we have on this machine vs the paper estimates done years ago when we initially sized things. Looking into it a bit, we can definitely grow the wing a foot or two before it starts to appear out of sorts for the scale. So I see potential there.

If it turns out to be correct thinking, I'm going to be looking into the viability of putting together a new center-section that adds flaps, provisions for full retracts, and pushes the wingspan outboard a little bit. These are all things we've more-or-less already known we'd need to work out anyway, so just puts a priority on it for this machine vs waiting until later on.

So the P-36 as we built it, was done with fixed or ground-adjustable everything, dome head everything, etc. Partially to save time, but mostly excused to see how simple and straightforward the design and construction could be (thus hopefully saving money and build-time) and still get the right look and hopefully perform well. It proves it can look OK, and that it flies, but we've probably got to take a few things another step up to get the performance inline with expectations.

I'm trying to compile some of the video from these flights, but it'll take a little time to get caught up.
 
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cluttonfred

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Thanks for the update, Scott, glad to hear you are plugging away and making progress despite the "distraction" of your actual job. ;-) I'll just say again that while many people will dream of a retractable gear P-36 (or P-40), the realities of LSA rules in the USA and the relatively low skill level of most recreational pilots mean that a relatively low-powered, fixed-gear Hawk 75 (or a P-36 or P-40 that looks like a retractable but isn't) is a better fit for most people. Increasing the wing area to reduce the wing loading also seems like a great idea for the same reasons.

1664173492516.png
 

ScaleBirdsScott

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Yeah the Thai/Chinese/Argentinian Hawk-75M type spats are a good point of reference. The main thing is I am fairly sure they built completely new gear legs/wheels for those to fit in, since they were ditching the whole retract thing; so for us to keep the P-40 style gear legs/wheels and throw a big fairing over, it won't quite be able to pull off the same contours. Plus they're just a bit stubby? I kindof like the slightly more teardropped Fokker D.XXI spats which are otherwise similar. Working on a model now so we can make some patterns and do some hotwiring. I really don't feel like firing up the CNC router to carve foam for that job.

One detail with those export versions was the use of the Curtiss-Wright 9-cylinder vs the Pratt 14-cylinder radials. So if we really had to, we could throw a Verner 9-cylinder on the nose and use the larger, blunter style cowl that Curtiss did when using a 9-cylinder vs the 7+7. Of course then I'd have to debate whether to go for a ROCAF livery or go Thai-mode 😅
 

flitzerpilot

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Scott, I entirely agree with your analysis of what's needed at this (early) stage in the flight test programme. It matches what I'd considered with my paper study of the Fokker D.XXl in particular with the relative simplicity of the fixed landing gear and the slimmer leg and spat contouring - not the broad trouser leg of the Argentinian Hawk which looks clumsy in my view.

Regarding oil temperature, the 124 hp Verner 7U in the Flitzer Schwalbe was higher than hoped for on the maiden flight and that's been addressed with cooling air through the ventral tank tunnel, but further testing has been delayed due to a house move, etc. Regarding wing area increases, I feel that, despite the excellent RoC (flown solo with 1/2 fuel uplift) I am considering extending the span by 2', to 22' for later plans-built Z-2's which should further increase climb rate and reduce the landing speed.

Best of luck with the modifications you are considering with the Hawk.
 

edwisch

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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!
 
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