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Cargo pod for a 9?

this confirms the problem we expected. I need to add the actual cowl, internal cowl cooling flow and the fuse and then do some parametric studies. but firstly, I need to stain and urethane a bunch of windows for my wife.... such is life. why do women like windows so much?

Could exhaust augmenter tubes be incorporated into the cargo pod to solve the exhaust pressure problem?

Dan H. / Steve Smith should weigh in here -- could this pressure increase at the cowl exit actually be a "good" thing; ala Shrinking Exit?
I am not danh or Steve Smith but maybe you should consider incorporating a boat tail exhaust exit dirctly into the front of your pod. Vetterman built a beautiful one on his RV. It is detailed on the Vetterman website: http://www.vettermanexhaust.com/
 

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kicking shapes around. it's begging for a boat tail of some kind, like someone earlier suggested. maybe I could do a small one.

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wife's windows in process, 3 coats urethane. she becomes very pleasant when I do things for her.

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Where did you get the CAD files from? Looks to be the originals. I would like to design & make a 3D printed RV-8 RC model (and share the files), but I don't have access to the native cad shape for reference. So I'm curious..

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Airlines will not allow lithium metal and lithium-ion batteries to be in the cargo compartment because of fire concerns. What type of batteries are in the bike and is there a possible heat issue with the location that could cause a runaway?
 
Some comments from an old CFD guy:

1. You need really top notch CFD and an excellent quality mesh for analyzing vortex generators and/or flow separations in this sort of situation. Probably not what's in SolidWorks.

2. Any big round or steep corner at the upper, leading edge is going to produce a region of stagnation pressure near the cowl vent opening, reducing engine cooling. It would be preferable to use a sharp-edged ramp there, the shallower the better. The ramp should run from just aft of the cowl seam to the max thickness of the pod, in order to minimize ramp angle and hence static pressure increase.

4. I agree with earlier comments that the relatively blunt trailing edge of the shown pod shape could produce a large drag increase - probably more drag than the rest of the fuselage. Fairing it in such a way as to prevent flow separation could easily reduce pod drag by 50% or more. You might consider a row of (alternating direction) vortex generators a few inches upstream of the lower, aft "corner". I believe Aircraft Spruce sells some inexpensive experimental VG's.

Always interesting ideas in your posts... Thank you for posting them.

-Paragon
Cincinnati, OH
 
6 inch spacing of the pod from the engine cooling outlet results in a .2 psi back pressure to ambient. that's a lot. needs to be resolved.

on the plus side the drag from the aft side of the box is not as bad as I thought it would be. it's workable.

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Make an exhaust pipe / cowling extension tunnel that ends at the low pressure area on the front bottom of the pod.
 
Is that at zero AoA?
What about in a climb?

yep, climb is a factor for cooling. that big speed brake deflects even more during a climb.

added a taper to the box and a boat tail and knocked off 20 lbs of drag. now I am down to 28 lbs of drag but heavier with the boat tail.

I can wiggle down to 24 lbs of drag with a steeper nose but when you get too close to the cooling exit the airflow is affected. so, in this case distance away is better than a steeper nose. I am using 5 inch of water pressure at the cooling outlet, an estimate, I don't know what the real numbers are, presure will vary with speed and AOA. I suppose I could take an actual measurement on my aircraft.

anyway, here's a photo of the latest. I need a way to make a hinging door for that boat tail in order to be able to load the bikes. fun stuff!

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cruise condition, 130 kts

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That pod is looking better and better as you tweak.

One more possibly helpful comment:

If the pod closeout is not extended sufficiently far to fully prevent flow separation, then one probably wants to terminate the pod closeout with an abrupt, blunt, rectagular trailing edge (or in 3D, trailing face), rather than a rounded or ramp-like shape. (VG's a few inches upstream can extend the separation point farther around a turn, but what's shown here will presumably still separate at some location.)

Why an abrupt Trailing Edge?

What one does not want is a vague separation point. There may be some airspeed range where the flow separation is unstable, hence inducing loud vibration into the airframe. It would be better to close out the pod as much as possible without flow separation, then abruptly cut it off so the separation point is fixed at that location.

-Paragon
Cincinnati, OH
 
Steve, why not make the bikes mount on a belly door and swing it up into place in the pod?

it could be done that way but you would need to climb under the aircraft to load the bikes on the swing tray and then lift the 75 lbs of bikes to attach the swing tray to the pod. the aerodynamic loads on the bottom of the tray is 170 lb downwards, so 75 + 170 = 240 lb the hinge would need to support in cruse flight with no g loading. I feel better about having the bikes totally enclosed in a rigid box.

Pod corner brackets note: in cruise flight with no g loads the four corner brackets of the pod will need to support on average, total pod weight =130, aero load = 170 , 300/4 = 75 lbs each. add 4.4g to the pod + bike weight = 130 x 4.4 = 572, add aero total for total max load = 572 + 170 = 742 lb., 742 lb / 4 = 185 lb avg max gust load on each corner bracket. and then you need to add some load for gasket cushion compress loading. 250 lb load is probably a good number to design the corner brackets.
 
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That pod is looking better and better as you tweak.

One more possibly helpful comment:

If the pod closeout is not extended sufficiently far to fully prevent flow separation, then one probably wants to terminate the pod closeout with an abrupt, blunt, rectagular trailing edge (or in 3D, trailing face), rather than a rounded or ramp-like shape. (VG's a few inches upstream can extend the separation point farther around a turn, but what's shown here will presumably still separate at some location.)

Why an abrupt Trailing Edge?

What one does not want is a vague separation point. There may be some airspeed range where the flow separation is unstable, hence inducing loud vibration into the airframe. It would be better to close out the pod as much as possible without flow separation, then abruptly cut it off so the separation point is fixed at that location.

-Paragon
Cincinnati, OH

yes, that's a good suggestion. I simply rounded the this one off. you can see the effects. I don't know if the movie will play.

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movie

[URL="https://hosting.photobucket.com/images/hh519/semelton500/Animation.avi"][URL="https://hosting.photobucket.com/images/hh519/semelton500/Animation.avi?width=1920&height=1080&fit=bounds"]https://hosting.photobucket.com/images/hh519/semelton500/Animation.avi?width=1920&height=1080&fit=bounds[/URL][/URL]
 
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Don't forget G loads for the pod, not just normal weight and aerodynamic forces.....

How about pressure recovery on the rear section like the wheel pants.....
 
Instead of a pod on the belly how would a small pod on each side work out? Might not make any difference to the total drag component and you wouldn't have to bend over and fight putting the bikes underneath. Also no interruption of air flow for the engine cooling.
 
Instead of a pod on the belly how would a small pod on each side work out? Might not make any difference to the total drag component and you wouldn't have to bend over and fight putting the bikes underneath. Also no interruption of air flow for the engine cooling.

like Squirrel cheeks?
 
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