Hurricane Mk103

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pictsidhe

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Scott, I had a quick look at your website the other day. A very Hurricane-esque fuselage!

4.8x8 wheelbarrow tires are very close to scale. I'm really tempted to use rigid gear, which would facilitate retracts. Lightweight teles are a pain to improvise. Maybe after I fold rigid ones... I was clearing out some junk earlier and an old office chair was chucked out, then I had 2nd thoughts and extracted the gas spring thing. It still has a hefty bracket to cut off one end, but it looks like it might be useful. If it is, I'll wait for goodwill to have a matching pair...
Scale prop would be 86", but that reduces clearance by 4", so 78" is as big as I'd go. Ideally, that would want 2000rpm if can manage 40hp. Yes, I'll need an airspeed sensitive throttle to stay legal.

I scaled one of those draewings to 1:25 and had a go at working out pilot position. It's really, really tight. I need to decide how long the engine will be and build a cardboard cockpit before committing to 2/3. Doesn't help that I'm 6'6"...
A very quick look at tail loads and coro might work as a stressed skin with no spars on fuse, fin and stab! I need to do hinge loads and do it much more accurately. I have a spreadsheet that works out 2nd moment of area for hollow airfoils now. If I can do monocoque everything behind the pilot, that saves a lot of fiddly and weighty framework, to mitigate all that coro. I have another bending idea to try for small radii.
The tail airfoils look like 8% for the fin, 12% for the elevator on the drawing. I'll likely go fatter 00xx unless someone has a better idea?
 

Tiger Tim

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With regards to tail surfaces, why not just go with a single layer of thick coroplast? This is all just off the cuff but my first instinct says to attach all your hinges to an aluminum channel then bond a sheet of coroplast into that channel. Most of the work could be done with a single tool:
 

pictsidhe

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With regards to tail surfaces, why not just go with a single layer of thick coroplast? This is all just off the cuff but my first instinct says to attach all your hinges to an aluminum channel then bond a sheet of coroplast into that channel. Most of the work could be done with a single tool:
Bending loads, weight.
Large radius bends are easy-peasy. A thin coro sanddwich is going to be lighter than stuff thick enough to slide suitable carbon spars inside. A coro sandwich can be monocoque. I may need a hinge spar, and wrapping it round the LE may not happen, so maybe a wood or composite profile there. Otherwise, thin coro takes the loads and is lighter than a flat plate. I do need to run proper numbers, but the ballparking figures yes.
 

pictsidhe

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A few thoughts. 4mm is similar weight to oratex over 1"x3/8" stringers at 8" intervals. If loads are carried by seperate truss, a hurricane type fuse will probably be lighter in coro than a truss and crudely framed skin.
Scott, I've been thinking of mechanical retracts. I estimate the up position to need around 15ftlbs each side at the pivot. That's going to be a bit of a heave. However, If I had an over centre spring, with the centre maybe 20 degrees retracted, I could drastically reduce that force and give very positive down locking. With at least some pull needed to retract, a cable would do the job. With a cable, I could also use a funny shaped pulley so that loads are fairly constant on the operating lever.
 

pictsidhe

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Looking at engine options. A 503 with C box is 102lb. That'll likely be too heavy, the B box is only 6lb lighter. It would be nice to have the option of 'sufficient' hp! It may also clash with my feet if I'm squeezing into a supine 2/3 scale cockpit.
On the cockpit. I made an adjustable experimental supine 'seat'. A door leaning against wall, small bit of ply leaning on the door. That gave me some numbers. In a pretty comfy position, I am 34" high and 67" long. That does fit in a 2/3 cockpit with my backside on top of the wing. If the engine isn't too long (like a 503),,. A bit more upright and I need to sink between the spars.

The bad is that the view will be lousy. A full size canopy is 12" above the canopy end of the nose. My eyes are 5" below the top of my head. Even with only an inch headroom, that's eyes just 2" above the nose at 2/3 scale. Something needs to move. Likely the canopy. With a few more inches of headroom, I should be able to squeeze a 503 upfront if I can find the weight, though I'm more likely to start with a v-twin industrial.
 

cluttonfred

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If you can afford it, a 36.5 hp liquid-cooled Polini Thor 250 DS might work out well, more than enough power for Part 103 and you've already got a place to put the radiator.

THOR_250_DS.jpg

https://www.polinithor.com/en/thor-250-thor-250-ds-2/

If it turns out that the radiator needs to stay closer to the engine, then you could "cheat" by building a North African campaign Hurri with the big chin air filter and a fake hollow radiator housing. Tank-busting 40mm cannons are optional. ;-)

b56ef10236e135d8a6041f2290d7b0f5.jpg
 

pictsidhe

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Don't start me on cannons. I was pondering how to make rapid fire propane cannons while cutting the grass earlier...
The Thor is a bit pricey, but it would work. The rad is tiny, shouldn't be too hard to squeeze in somewhere.
If I go aircooled, even a small gap between the 15" spinner and cowl will let plenty of air in. Hot air out through the 'engine' exhausts. Some ducting and the same scheme could work for water cooling. The 'radiator' housing under the wing looks more like a very nice little baggage pod to me. I just need to balance any weight there with enough beer, etc in the LE 'fuel' tanks, which should be sorta accessible with the gear down.
 

cluttonfred

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For the gun, we had a thread on an All-electric simulated machine gun? (flashing light and speaker) that actually got more traction over at the EAA Forums. Ron Wanttaja even shared the design in the attached PDF. I don't think there are any wing radiators on a Hurri, maybe you're thinking of a Spitfire?

Hurricane_Fl_GB_4303_3-view_p029_W.png

Of course, for Part 103, just staying within the maximum empty weight is going to be a problem but I think it could be done with careful attention to weight in a thick cantilever spruce-and-plywood box spar, fabric over stick ribs, and a stick-built or light welded steel tube fuselage. If I were really going to tackle something like this, I'd put a Hurricane, Mustang, P-40, Yak-3, K-61 Tony, etc. in a blender and come up with a universal foundation to which I could add different cowlings, wingtips, canopies, turtledecks, rudders, and paint for a stand-way-way-way-off replica of any inline, low-wing, inward-folding gear WWII fighter.
 

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ScaleBirdsScott

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If I were really going to tackle something like this, I'd put a Hurricane, Mustang, P-40, Yak-3, K-61 Tony, etc. in a blender and come up with a universal foundation to which I could add different cowlings, wingtips, canopies, turtledecks, rudders, and paint for a stand-way-way-way-off replica of any inline, low-wing, inward-folding gear WWII fighter.
"stand-way-way-way-off" I love it. And it's true, that's the name of the game down at the weights of 103.

Also, no need to limit it to inline. Radials just need a fatter firewall is all. :shock:

(And I'm not even saying you have to put a real radial on it, for a p103 that Polini or something like it would be a strong contender, especially if one is interested in actually putting anything like retracts or a canopy on the bird. The upside to a radial cowl is that the big muffler isn't just hanging off the side of the thing. So why not a Tempest and/or Sea Fury?)


Also, with a fixed gear model you don't need to worry so much about how the original gear fold, so some more models open up.
 

cluttonfred

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Radials, too, I like how you think! I have never liked the knock-kneed look of the Spitfire or Bf109 outward-folding gear but you're right that it wouldn't really matter since it'll be fixed anyway and you can't see the wheels from the cockpit. The key here would be coming up with a base structure that can stand in for the largest number of aircraft.

It might still make sense to focus on the designs with generally straight-tapered wings and less-tapered horizontal tails (so a constant-chord stab and elevator with rounded corners won't be jarring). The curves of a Spitfire wing and tail, the old-school lines of a P-40 tail, the sharp taper of a Zero or Oscar's tail, would all be missed if left out, and the designs with straight leading edges would just look wrong with double taper.

Even within those limitations, there are some unusual designs that you could pull off. Fiat G.50 or Fairey Fulmar (with dummy rear cockpit) anyone? ;-)



"stand-way-way-way-off" I love it. And it's true, that's the name of the game down at the weights of 103.

Also, no need to limit it to inline. Radials just need a fatter firewall is all. :shock:

(And I'm not even saying you have to put a real radial on it, for a p103 that Polini or something like it would be a strong contender, especially if one is interested in actually putting anything like retracts or a canopy on the bird. The upside to a radial cowl is that the big muffler isn't just hanging off the side of the thing. So why not a Tempest and/or Sea Fury?)


Also, with a fixed gear model you don't need to worry so much about how the original gear fold, so some more models open up.
 

ScaleBirdsScott

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I don't see why a tapered/rounded trailing edge on the fail feathers is any great challenge, regardless of the material of choice.

I'm doing it all in aluminum tubing more-or-less and Airdrome WWI replicas have shown the method good for all kinds of fancy curved features: bending some tube over a wood template is no big deal.
 

pictsidhe

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Blender! But the Hurricane is already Baby Bear's porridge! Hang on guys, let me build the first one first, maybe then, I'll build something else. It's a real shame that the Mosquito cockpit is so far forward ;).
 
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cluttonfred

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Scott, it's not the fabrication that bothers me so much as the potential changes in aerodynamics. I was thinking that it would be good to take a page out of Bud Evans's playbook and keep the primary flying surfaces untouched except for varying the rudder outline and wingtips to suit.
 

pictsidhe

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Scott, it's not the fabrication that bothers me so much as the potential changes in aerodynamics. I was thinking that it would be good to take a page out of Bud Evans's playbook and keep the primary flying surfaces untouched except for varying the rudder outline and wingtips to suit.
This was my thinking. The Hurricane has been described as "a great, big pussycat". It's apparently also easier to fly than the Harvard trainer let alone the Spitfire. Slow it down and it should be even easier to fly?
I am struggling a bit with the root airfoil. I have drawings showing slightly different shapes. It is a Clark YH (mod) 19% on paper, but no ordinates I've found yet. If I scale a YH about the camberline, XFLR5 has a hissy fit and tells me it's truly awful. Reducing the nose radius, as in some drawings, fixes that. But I'd really like to get a definitive airfoil so I don't mess up stall behaviour etc. The YH tip airfoil works just fine at full and 103 scales.

Anyway, a picture of a Mk1, purely for reference, of course! Lose 2/3 of the engine (heresy, I hear you cry!) and a 3/2 scale pilot should still squeeze in. I've seen this one flying mild aerobatics in formation with a Mk1 Sea Hurricane :)

8713797440_1e6857eeab_b.jpg
 

cluttonfred

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With the very, very different power and wing loading plus the scale impacting the Reynolds number, I don't know much you should pay attention to those details of the wing. If you want to keep the reflexed airfoil to reduce trim loads and the size of the horizontal tail but need more thickness to reduce spar weight, you might try something like NACA 23118 tapering down to 23112.
 
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Himat

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In the making of a scale model of an aeroplane, there are two main choices in design philosophy. A scaled down model with the exact outline of the original can be made, or the outline can be changed more or less to make a flying model that behave well. Changing out wing and tail section to fit size and Reynolds number of the scale model is a modest deviation. If the wing and tail section thickness is kept, a different aerofoil may not be noticeable at all. At least not without the original parked alongside.
 

pictsidhe

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With the very, very different power and wing loading plus the scale impacting the Reynolds number, I don't know much you should pay attention to those details of the wing. If you want to keep the reflexed airfoil to reduce trim loads and the size of the horizontal tail but need more thickness to reduce spar weight, you might try something like NACA 23118 tapering down to 23112.
Yuck! The FW190 used 5 digit airfoils and was known was for its downright vicious stalls. After the RAF tested one, advice was given to try baiting FWs into stalls during dogfights. There's gun camera footage of a FW190 on youtube on a Mustang's tail. He stalls and does a 3 turn inverted flat spin before recovering... He eventually got the Mustang.

The YH tip airfoil works great at full size and 103 scales. I'll have a hard time finding anything much better so I'll likely stick with it. Simply scaling it to 19% works really badly at both full size and 103 in XFLR5. If the hurricane does indeed have a horrible root airfoil (surely they tested it?) Then I want one that will give similar whole wing stall characteristics, or my 'improvements' could result in nasty stalling. Likewise, I don't want to lose several points of Clmax by using a root airfoil that stalls much sooner than it needs to. I don't want to mismatch tip and root so that stall inception and progression changes.
This isn't about replicating the airfoil, it's about replicating the behaviour of the whole wing. To do that, I need to know the exact airfoils used at full size. I won't be using the 19% YH root as it's awful. There are other airfoils that have similarly low Clmax, Cm, but way lower drag. But maybe the actual Hurricane airfoil isn't quite a 19% YH and is usable. The 19% YH actually works slightly better at 103 RNs than at full size. That is suspicious... Reducing the nose radius makes a huge improvement both large and small size.
I'm nowhere near needing to decide on exact airfoils yet, plenty else to do.

The Hurricane used 12% tip, 19% root airfoils. I'll probably stick with that. That'll be a foot thick at the root of a Mk103.

Hmmm, Actually, this should be the MkCIII?
 
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