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  #381  
Old 01-28-2016, 08:31 AM
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DanH DanH is offline
 
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Bill, I dug around on my hard drive, as I had forgotten what I was looking at circa 2008. My project prior to the RV-8 involved radial engine development, and I got hooked on the old NACA papers for info. Try this one for fundamental drag information relating to shape. As previously noted, a radial engine cowl is merely a low Vi/Vo inlet, and as such, a lot of the information transfers nicely.

http://naca.central.cranfield.ac.uk/...report-745.pdf



The focus is on drag rise due to compressibility, which is of no interest with our RVs. However, there is some good stuff starting on page 297....





....with more on 298.

Andy, there are ordinates, Table 1, page 289.
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  #382  
Old 01-28-2016, 09:40 AM
BillL BillL is offline
 
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Quote:
Originally Posted by DanH View Post
Bill, I dug around on my hard drive, as I had forgotten what I was looking at circa 2008. My project prior to the RV-8 involved radial engine development, and I got hooked on the old NACA papers for info. Try this one for fundamental drag information relating to shape. As previously noted, a radial engine cowl is merely a low Vi/Vo inlet, and as such, a lot of the information transfers nicely.
<snip>
....with more on 298.

Andy, there are ordinates, Table 1, page 289.
Thanks Dan, very timely, I was just searching my drives for that paper. I could have sworn that I saved it the last time you posted. This adds some dimensions, sorry for you having to do my homework.
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  #383  
Old 01-29-2016, 09:22 AM
Stewie Stewie is offline
 
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Default Kuchemann and Weber

The first several chapters of Aerodynamics of Propulsion by Kuchemann and Weber covers intake design theory and experimental results and is the best guide I've found on the subject (in addition to the NACA and Cranfield papers). A smaller radius has less drag at a particular design point, but the larger radius has a larger range of effective operating angles (both AC aoa and Vi/Vo). My guess is that the drag saved from an optimally sharp radius over a fatter radius is minimal, but that the cooling drag/problems from an excessively sharp radius causing separation/turbulence at the head of the cooling system can be significant. For an RV-type airplane, I would err on the side of a fat LE radius lip, and then use adjustable exhaust outlet flaps a la Dan Horton to recover a bit of velocity.
The book is out of print but you should be able to find one at a good engineering school to make a copy.
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  #384  
Old 02-02-2016, 10:57 PM
crabandy crabandy is offline
 
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I've been gone for a couple days, just so happened I was in a window seat just forward of the engine. When takeoff power was applied fog/vapor was forming around the inboard edge of the inlet until approximately 60 knts. I'm guessing the engine was sucking air from behind the lip until airspeed was delivering the correct amount of air, at that point it was spilling over the sides. Unfortunately I didn't get my phone out fast enough to take a pic of the vapor/fog.



The NACA report DanH mentioned in a previous post used a 10.4 inch diameter cowling, my inlet diameter is 5.75 inches. My 6th grade math is solid, after that I have a general idea but I usually need the answer to work my way backwards through the math problem.
To get a properly sized curved lip for my size of inlets should I set up a ratio like: 10.4/5.75=1.81 inches to correctly size the curve to my diameter inlet?
If the diameter of the inlet is the "y" plane, and the distance behind the inlet is the "x" plane should I divide both the x and y distances by 1.81 to correctly size the curve for my inlet? I remembered this little conundrum only after ploting out the ordinates in the charts on some foam graph paper. Ordinate Chart from the NACA report (Wikipedia has a good explanation of "ordinates"):


Here's the ordinates from the chart graphed out on some cheap foam graph paper (Walmart), I graphed inlet curve 1, 2, B and C and cut out C since it was the lowest drag shape. Looks like my original shape was close to 1, and my newer lip shape fits C nicely up front. Being the ordinates are for a radial engined cowling that tapers much more than my cowling I have a little "customizing" to do. I think I can disregard the aft 1/3 of the ordinates and blend it into the existing cowling shape.





Lip radius as originally shaped.

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Last edited by crabandy : 02-02-2016 at 11:09 PM.
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  #385  
Old 02-12-2016, 07:24 AM
crabandy crabandy is offline
 
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Of course things seemed to have shifted slightly after making the cut, I tweaked things back in shape and laid up 5-6 plies to make a flange on the inside of the cowling to attach the hinge to. I'm still trying to figure out the best way to build more curve into my lips.



In the spirit of progress and getting at least something done I switched to making "Man Glitter." Version ## (i forget how many brackets I threw away) is on I think will serve it's purpose. I added a doubler to the middle of the center baffle and used a bracket on each side of the middle.







By some miracle the rear baffle bracket version 1 seems to fit well.



I drilled and cleco'ed the plenum to the baffles and laid up the front flange of the plenum. I was pretty happy with how the front flange turned out, until I started putting my fiberglass supplies away and realized I used West Systems instead of AeroPoxy. Sigh, I was planning on adding more plies on the inside of the flange of the plenum anyway, I'll add a ply or two on the outside both made with AeroPoxy (if I don't grab my trusty West Systems again). It may turn out like a hot Ice-Cream sandwich, we'll see.



I'm still dreaming up some protection for my EFII crank sensors.



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Last edited by crabandy : 02-12-2016 at 07:27 AM.
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  #386  
Old 02-12-2016, 09:05 AM
BillL BillL is offline
 
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Hi Andy,

FYI - I plotted the same dimensions and noticed that was for a diameter of 10 or so inches. I was thinking about scaling the curve down proportionally to the diameter of the inlet. Once I did that it is not much different than the SJ original shape, a flat spot and progressive curve.

Oh - Really nice looking progress on that front plenum flange. Hot ice cream sandwich - I like that visual description.
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  #387  
Old 02-12-2016, 09:58 AM
crabandy crabandy is offline
 
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Quote:
Originally Posted by DanH View Post
Bill, I dug around on my hard drive, as I had forgotten what I was looking at circa 2008. My project prior to the RV-8 involved radial engine development, and I got hooked on the old NACA papers for info. Try this one for fundamental drag information relating to shape. As previously noted, a radial engine cowl is merely a low Vi/Vo inlet, and as such, a lot of the information transfers nicely.

http://naca.central.cranfield.ac.uk/...report-745.pdf



The focus is on drag rise due to compressibility, which is of no interest with our RVs. However, there is some good stuff starting on page 297....





....with more on 298.

Andy, there are ordinates, Table 1, page 289.
Yes the study did use a 10.4 inch opening, I thought about scaling the curve down as well but not sure that it needs to be rescaled.....but I can make cases for both in my uneducated opinion.

I think the radius 1 is very similar to my original shape and that of SJ's cowl lips, maybe 25% ish more drag mirroring the same flat curve as lip B and C.

I'm going to let the ideas marinate for a few more days.
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  #388  
Old 02-14-2016, 07:20 PM
jmodguy jmodguy is offline
 
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Crabandy - "I'm still trying to figure out the best way to build more curve into my lips.".

Botox???

Sorry I couldn't help myself......
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  #389  
Old 02-23-2016, 11:53 PM
crabandy crabandy is offline
 
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I plotted the ordinates "x" and "C" on a piece of cardboard, I then took C/2 and plotted the curve underneath. I averaged/drew a curve between the two and made a template for my lip curvature. The new curve seems doable to shape into my existing cowling. I made a short and a long template, the short template shows the inner lip next to the spinner was already close to the right shape.







My final version of the paper template for the ignition pick-up armor.



I forgot my die grinder at home so the final curve was cut with a #30 30 times over.



It seems pretty stout, the top bracket doubles as an attachment for an adel clamp holding the wires on the aft side of the baffling with a solid 1/8 inch clearance from the rear of the ring gear support.



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  #390  
Old 02-25-2016, 01:28 PM
crabandy crabandy is offline
 
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I think My fiberglass skills have progressed to the next level, I now do lay ups and spread epoxy/micro/flox in my regular clothes. I'll save the pants and shoes spattered with little crispy spots and dallops of micro for the next pro-seal session.
I made a couple of "custom" spreaders for my epoxy/cabosil/flox/micro mix, I bent a Popsicle stick under warm water and taped it to some cardboard to make a larger slightly curved spreader. I've found pop/beer boxes to be useful impromptu spreaders, the cardboard shapes nicely and epoxy doesn't stick to the outside painted/waxy surface.







A couple of regular plastic spreaders cut/sanded to shape.



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