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  #371  
Old 01-20-2016, 09:45 PM
KnotKrazy KnotKrazy is offline
 
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Okay, this guy gets the 'builder dedication' award!!! Holy Cow! Or should I say "cowl"?
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  #372  
Old 01-21-2016, 12:56 AM
crabandy crabandy is offline
 
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Shoot, I haven't even considered a plans built airplane.....yet....
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  #373  
Old 01-21-2016, 05:33 AM
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DanH DanH is offline
 
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Quote:
Way back when, Steve Smith (a highly qualified source) was good enough to point out that exterior shape around the inlet was critical to drag. A sharp edged pitot-type shape may result in a flow separation starting at the outer edge of the inlet ring radius. The above photo illustrates to point very well. Look closely at the exterior curvature of the original Vans inlet vs your new shape.

At the time, Steve said to look at the shape of modern fanjet engine nacelle inlets for guidance. I had seen similar advice previously, thus the exterior curvature below. Is mine optimum? Heck, I dunno, but the point is valid.



See posts 15, 18, 30, and 35 here:

http://www.vansairforce.com/communit...ad.php?t=68241
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Last edited by DanH : 01-21-2016 at 05:42 AM.
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  #374  
Old 01-21-2016, 03:45 PM
crabandy crabandy is offline
 
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Well, I was going for lips like Angelina Jolie.....

It's easier to see the differences in radius now things are split, I think the aforementioned picture really makes it look pointy and sharp. Here's a pic of the same inlet from another angle, it is a sharper radius than Van's but not by much.



It did turn out flatter than I wanted and will massage the curves a bit. Besides it's just fiberglass, I can always grind it off and start on version 3!
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  #375  
Old 01-25-2016, 08:47 AM
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Andy, had a opportunity to shoot a few detail photos this weekend. Some of the other photos you've seen may have fooled you; it can be hard to judge curvature. These were shot at right angles.

Outboard quadrant:



Above the inlet. Without a width constraint, I worked in a tad more curve:



I can't claim either one is perfect, but note the similarity to the Vans cowl, and to various low drag radial cowls:



My humble understanding is that your current sharp pitot shape will promote separation as the freestream tries to flow out around the cowl.

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Last edited by DanH : 01-25-2016 at 09:32 AM.
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  #376  
Old 01-25-2016, 05:46 PM
BillL BillL is offline
 
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My My My, it looks like I will also have some work to do on the SJ inlets. I have a little extra clearance to work with, but the original shape is sharper than Andy's.

Do we know how big the correct shape needs to be? Surely all scales of the same profile are not equal. Dan - I see yours is not as large as the original Vans shape. Any guidance for Andy (and others . . ).
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  #377  
Old 01-25-2016, 06:10 PM
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1001001 1001001 is offline
 
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Does anyone happen to have a 3D CAD model of these various inlet shapes? I happen to have an unused CFD workstation here at home and may be able to play around with it a bit. It may take me a while to remember how to run it (and get the mesh set up) but I might give it a shot.

Come to think of it, a 2D mockup might be a better way to start...
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  #378  
Old 01-25-2016, 06:46 PM
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Quote:
Originally Posted by BillL View Post
Do we know how big the correct shape needs to be? Surely all scales of the same profile are not equal. Dan - I see yours is not as large as the original Vans shape. Any guidance for Andy
Nope. I just try to follow along when the smart people talk. The goal is to keep the flow attached, but as stated, I have no idea if my own is an optimum shape. It would be great if Dave (above) fired up that CFD tool.

Recall that we talked about stream tube diameter in a previous post. At 175 knots the stream tube would be about 3.2" D, and the rest of the air approaching the 6" inlet must flow outboard and around the inlet lip.

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Last edited by DanH : 01-26-2016 at 10:24 AM.
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  #379  
Old 01-26-2016, 11:15 PM
crabandy crabandy is offline
 
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DanH sent this to me in a separate email, it illustrated the point nicely for myself. I need to lower the AOA of the inlet lip.



I re-foamed one side, that's all the pour foam I had. The good thing about the pour foam is it is ready to sand in less than 30 minutes and it sands easily. The bad part is it is easy to sand past the desired shape, and acetone doesn't dissolve the cured foam like the pink/blue insulation foam. It's as far as I'm going to sand for now, I want to split the cowl and see the curve from that view. I don't care for the aesthetics as much, we'll see. The outside of the cowl by the split line is gonna take some work to blend in the larger curve.





The other inlet I stuck 1/4 foam window insulation to the cowl and then wiped a lip of epoxy flox/filler with a piece of bent/curved cardboard. I just did a couple inches in case I end up sanding it all off.



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  #380  
Old 01-27-2016, 09:23 PM
crabandy crabandy is offline
 
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I think the foam strip guided epoxy/flox/filler lip may do the trick, the lip radius is looking better and I think I can fair it into the cowl a couple inches back. I think using the foam as a guide will help to make a more consistent shape around the lip.



The fatter foam shape on the other hand retained the more pointy and less curvy shape, probably just me visualizing and sanding the same mistakes over again.



I test fit the cowl to the airplane, the prop has 3/8 inch plus clearance on both sides from the front of the inlets. The new cowling shape opened up more room along the front of the plenum/cowl area, I'm still trying to visualize which path to take.



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