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Old 06-22-2022, 02:29 PM   #1 (permalink)
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Question Ideas for aero-ing a piano hinge?

Howdy all!

I'm currently designing a nose cone for Champrius. The key to the nose cone will be a variable area inlet for the radiator right at the tip. I've bought these piano hinges:
https://www.amazon.com/dp/B07PP1XXQT
and plan on having a 24" x 3" opening for the inlet, with one hinge on top, and the other on bottom. That will give me 0-72 sq ins which should be enough to cover all cold to hot weather conditions. Viewed from the side, it's basically the leading edge "front" of a triangle whose base is the radiator (though with some more curvature to guide airflow).

Everything I've read says that aero-shaping for radiator inlets is crucial to proper airflow. It's the reason why virtually every grille in the world is inset slightly in some kind of curved bumper / fender. So I want to make piano hinges like little aerofoils / curve them smooth somehow.

Does anyone have any ideas on how to do that?

Keep in mind the main constraint: whatever we do has to be tough. This part will, without doubt, receive more wear and abuse than every other aeromod on the car. Not only does it have to withstand a constant +15-60 lbs per sq ft of pressure above atmospheric, it's going to get peppered by road debris and other crap while driving.

I'd also like to use a common part or material and re-purpose it, rather than having to custom make something myself. To give an example, the rest of the nose cone will be made from a Brute plastic trash can, cut up and attached to an aluminum frame. That has the natural curved shape we want already, and is tough enough to withstand the aero-abuse.

I've thought about slicing a pipe, but not only could I not find a pipe small enough, I couldn't think of a way to adhere it to the hinge. The hinge has holes in it, so we can potentially use screws if needed.

Any thoughts?

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Old 06-22-2022, 03:33 PM   #2 (permalink)
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If you curve the hinge it will be stuck either up or down.
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Old 06-22-2022, 03:36 PM   #3 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
If you curve the hinge it will be stuck either up or down.
Sorry; I should have been clearer. I want to keep the piano hinge itself flat and straight and cover it with something curved, like an aero cowl of some sort. I don't have the equipment to bend / shape metal.
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Old 06-22-2022, 03:49 PM   #4 (permalink)
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Quote:
Keep in mind the main constraint: whatever we do has to be tough. This part will, without doubt, receive more wear and abuse than every other aeromod on the car.
So, no titanium skid plate then? The parts you have should withstand small mammals.

I'm trying to picture a situation that would require flaps on the top and bottom of a three inch opening. All I come up with is flaps ahead of the opening that create a variable bellmouth.

It's all in a positive pressure gradient. Why not a single flap that completely covers the opening, with speed holes?
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Old 06-22-2022, 04:07 PM   #5 (permalink)
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Originally Posted by freebeard View Post
It's all in a positive pressure gradient. Why not a single flap that completely covers the opening, with speed holes?
Ur, I would do that, except I don't know what a speed hole is, or what you are describing.

Let me whip up a pic to give a better description of what I'm planning and looking for. Maybe you can suggest a simpler approach.

I want to have a ducted inlet to the radiator from the nose. So there will be a 24" by 3" opening right at the front. But I don't want to use all that all the time. If I just cover it with something flat, then I only get part of the aero benefit of covering it. So I want something reasonably like a curved surface, both to continue the tip, but also because everything I've ever read or seen on radiator inlets stressed how important smooth curved surfaces are.

In the pic I just made, I'm looking for the orange part that goes over the blue hinge. Am I making any sense?
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Old 06-22-2022, 05:09 PM   #6 (permalink)
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All I come up with is flaps ahead of the opening that create a variable bellmouth.
Like that then. Technically, not speed holes but a semipermeable membrane.



One hinge in the middle of a split flap?
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Old 06-23-2022, 12:28 AM   #7 (permalink)
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Quote:
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Like that then. Technically, not speed holes but a semipermeable membrane.



One hinge in the middle of a split flap?
Ah, the way I understand things that would be heinously bad aero for the front of the car. Holes like that would not only increase pressure (which we don't want) but also create turbulence behind it (which we also don't want).

The way to reduce drag on the front is to minimize the area that high pressure forces push the car back. In an ideal world, the outlet of the radiator is perfectly matched to the inlet (in pressure, size, etc.) so that minimal pressure buildup occurs at the tip to begin with.

I'll settle for just reducing the area that the high pressure acts over. The maximum pushback area in the 4.0 nose cone design is 24"x3", but I want to reduce that even more to the bare minimum. Hence the hinges to reduce the inlet, but in an aerodynamic fashion. If I cover it with a flat flap, then I'm still getting high pressure buildup in the whole area.

We could avoid that by having a completely curved nose in the z axis (looking down on the ground), but I don't know if I can engineer and construct that kind of inlet. I'm barely able to make a flat, rectangular inlet work out.
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Old 06-23-2022, 10:19 AM   #8 (permalink)
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If it were an internal duct like an air curtain I could see it, but right in front of the radiator there is a pressure gradient.

It looks like you're trying to reduce the stagnation point down to the variable size of the opening.

Which might work for a transonic needle nose.

Alternatively, you could modulate the flow with an exit flap, like the P-51 Mustang.
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Old 06-23-2022, 10:50 AM   #9 (permalink)
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Rubber membrane sealing tape like for roofing or window installation. Sticky as heck, bends and shrinks, small rodent proof. Want airfoil, stick it with hinge point on outside, want smooth, stick on flat side of hinge.

Julian Edgar was doing things with increased radii corners, not necessarily an airfoil although he did use a gawd awful Gottengen profile windmill blade (mostly because he could get them easy/cheap)
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Old 06-23-2022, 12:56 PM   #10 (permalink)
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Rubber membrane sealing tape like for roofing or window installation. Sticky as heck, bends and shrinks, small rodent proof. Want airfoil, stick it with hinge point on outside, want smooth, stick on flat side of hinge.

Julian Edgar was doing things with increased radii corners, not necessarily an airfoil although he did use a gawd awful Gottengen profile windmill blade (mostly because he could get them easy/cheap)
Oooh roof seam tape. A very good idea. I could curve the tip with either a small dowel inside or just layering the tape, depending on how big I wanted it.

I also looked into trying to get an actual wooden airfoil, like for a model airplane or somesuch. But they are all made out of balsa wood and I don't know if that will be able to withstand the conditions. If I did use them, attaching with some screws covered by roof seam tape sounds like it would be secure and waterproof.

Thanks for the idea!

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