# Pusher cowling ideas

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#### Eugene

##### Well-Known Member
Fearless free-thinkers like yourself are what we need in these troubled times. I am offering you a once in a lifetime chance to get into an exciting aviation product - for a small amount of money every month, I will send you exciting videos of my [-]flying car[/-] personal transportation device and promises that it will be ready "soon".
You really don't want to miss out, so sign up now and be ahead of the crowd!

* objects in the video may be smaller than they appear. Your mileage may vary. Contents may settle after packaging.
For a brief moment I was thinking that I am on the wrong website. Feels like shopping for used vehicle or something like that. Thank you for waking me up and making me think

BJC

#### AdrianS

##### Well-Known Member
I could have posted that in the Raptor thread, the new Raptor thread, the Moller Skycar thread (if there is one), or many others.
It's multi-purpose.

Anyway, back to homebuilts. Sorry (not sorry) for the sidetrack.

#### WINGITIS

##### Well-Known Member
Coeffiecient of drag is a coefficient--a ratio--the denominator of which can be based on any measure desired (e.g. frontal area, planform area, total wetted area, etc.). I, for one, always believe everything I see on the Internet, so I believe that an elliptical shape has less drag than a streamlined body, because the Internet told me so.
There is the CD and the CDA, the CDA takes into account the frontal are, so that makes it unsure what that provider is trying to do there.

He then lists the last one as the based on planform area...which is basically a shape to analyze just like the others.

So I agree something strange is going on there, I was primarily looking for a chart with an image of an ellipse with the ration of 3.25 as Eugenes is...

Perhaps others can find one......!

#### WINGITIS

##### Well-Known Member
Here is another with the SAME numbers for the ellipsoid..

What is missing of course is the Reynolds number and fluid density it was measured at.

Someone may also want to do the exact calculation for Eugene....

You will notice that example with the formula also shows the airfoil as worse!

So a description of WHY everyone does that is required.........by someone......

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#### Eugene

##### Well-Known Member
Fearless free-thinkers like yourself are what we need in these troubled times. I am offering you a once in a lifetime chance to get into an exciting aviation product - for a small amount of money every month, I will send you exciting videos of my [-]flying car[/-] personal transportation device and promises that it will be ready "soon".
You really don't want to miss out, so sign up now and be ahead of the crowd!

* objects in the video may be smaller than they appear. Your mileage may vary. Contents may settle after packaging.
I forwarded this message to many people today. Many of them were very confused in the beginning. They really didn't expect this from me. I guess I'm not that kind of guy in their eyes. We had a good laugh!!! Thanks again!

#### thjakits

##### Well-Known Member
Still doing my paperwork….
Just found god way to incorporate the rocket inside of air-scoop. I think it’s correct way

View attachment 113952

NO idea if this was mentioned already - I am just starting with this thread...
Maybe you want to have a look at Hoerner, Fluid Dynamic Drag, Chapter IX, "Drag due to internal flow systems", starting on page 156 in my pdf copy....
Even if the formulas don't make much sense - just reading the text and looking at the figures and tables gets you going quickly!
page 9-4 (as the book is numbered) shows a in-wing radiator installation with a huge area of stalled flow and reverse-flow.... figure 4
page 9-5, figure 5 then shows a radiator installation on a Me-109, with the diffuser shaped like a parabolic curve (...I think it is a parabolic curve...). I remember Paul Lamar doing a lengthy piece on that! ....how to perfect cooling intakes!
[In a different piece he demonstrated images that showed "standing fuel fog clouds" on top of carburator intakes caused by harmonic sound waves - I think it was the 4-rotor LeMans engine - and how that was solved by perfecting the carburator intake bells into a parabolic (...I think!) trumpete shape...]

I remember him explaining HOW you get your parabolic shape according to your radiator face and area.
I think he said he would get the edges down to 2-3mm to the radiator face...Then cut the difuser at the planned cross-section area.
According to his research the flow doesn't separate until nearly at the face of the radiator....and it is safer (against stalls and flow separation) and a LOT SHORTER than the usual 7° diverging difuser....
[Exit is of course a different story - looking at the pictures of the machine at hand - there is not much chance to converge after the radiator according to best practises, but you might be able to do something at the cowling outlet...

Right there with that figure 5, Me109 radiator at 9-5 - it also mentions that it is critical to have a as perfect as possible seal to avoid pressurized cooling air to spill where it is not supposed to - that is a HUGE loss if it occurs.....

I am sure the guys with the experience here will have something to comment on Hoerner and Lamar!

Cheers,
thjakits

#### Eugene

##### Well-Known Member
NO idea if this was mentioned already - I am just starting with this thread...
Maybe you want to have a look at Hoerner, Fluid Dynamic Drag, Chapter IX, "Drag due to internal flow systems", starting on page 156 in my pdf copy....
Even if the formulas don't make much sense - just reading the text and looking at the figures and tables gets you going quickly!
page 9-4 (as the book is numbered) shows a in-wing radiator installation with a huge area of stalled flow and reverse-flow.... figure 4
page 9-5, figure 5 then shows a radiator installation on a Me-109, with the diffuser shaped like a parabolic curve (...I think it is a parabolic curve...). I remember Paul Lamar doing a lengthy piece on that! ....how to perfect cooling intakes!
[In a different piece he demonstrated images that showed "standing fuel fog clouds" on top of carburator intakes caused by harmonic sound waves - I think it was the 4-rotor LeMans engine - and how that was solved by perfecting the carburator intake bells into a parabolic (...I think!) trumpete shape...]

I remember him explaining HOW you get your parabolic shape according to your radiator face and area.
I think he said he would get the edges down to 2-3mm to the radiator face...Then cut the difuser at the planned cross-section area.
According to his research the flow doesn't separate until nearly at the face of the radiator....and it is safer (against stalls and flow separation) and a LOT SHORTER than the usual 7° diverging difuser....
[Exit is of course a different story - looking at the pictures of the machine at hand - there is not much chance to converge after the radiator according to best practises, but you might be able to do something at the cowling outlet...

Right there with that figure 5, Me109 radiator at 9-5 - it also mentions that it is critical to have a as perfect as possible seal to avoid pressurized cooling air to spill where it is not supposed to - that is a HUGE loss if it occurs.....

I am sure the guys with the experience here will have something to comment on Hoerner and Lamar!

Cheers,
thjakits

Here is great videos from Russ, from 21st-century:

#### Eugene

##### Well-Known Member
Made the conclusion this morning that I need to establish some sort of trailing edge between the wing and muffler opening on engine cowling.

Also found on this video very cool sending tools that those guys used. I made something similar as well. My project looks so much smaller than what they have going on.

#### Eugene

##### Well-Known Member
This is looking really great, Eugene. You might consider making the fillet on the top side as an expanding radius (as it appears you have done on the bottom). As a way to finish off the fillets at the back (where we see a little pink foam), you could consider an extension that completes itself something like this:
View attachment 116390
View attachment 116391
Finally starting to understand how this intersection supposed to look like between wing trailing edge, engine cowling and fuselage. Sort of reminds me how flying bats look like.

If I see this correctly bottom part of my fuselage will have a similar intersection between landing gear and tailboom. And will be probably similar approach. Landing gear will look like two little wings.

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#### Eugene

##### Well-Known Member
Not sure if I am doing it right. But I am doing it. Don't know exactly what shape this two little wings supposed to be ( left and right from air outlet). Would it be better for them to have outer radius, straight line, or inner radius? If only I can move propeller out of my way by 12 inches or so, I would be able to do such a beautiful job! But it's not an option.

#### Eugene

##### Well-Known Member
Looking at this three-quarter inch plywood that I used for trailing edge on my cowling mold below the wing. Will it need to get sharp at some point, or can stay this way as three-quarter inch sharp end? You can see something like this an iconA5

#### Voidhawk9

##### Well-Known Member
Don't make it sharp, you do want a 'square edge' (NOT rounded!) of some width. 3/4" is probably just fine in this case.

#### mcrae0104

##### Well-Known Member
It's common practice to cut off an airfoil at 99% chord. The 3/4" surface you have is buried well within the boundary layer. I wouldn't worry a bit about it.

#### Eugene

##### Well-Known Member
Not sure how I supposed to finish trailing edge on this cowling. What is more important, to follow the shape of the wing from top or from flat bottom?

#### Guinart

##### Member
Hello,

I wish to help, but I´m wondering how much clearance is available for the fairing design before the spinner location. Seems like the spinner goes right behind the dish in the picture, isn´t it? Forgive my limited English.

Another question: Is there an exhaust tubes or hot air exit included in the design?

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#### Eugene

##### Well-Known Member
Hello,

I wish to help, but I´m wondering how much clearance is available for the fairing design before the spinner location. Seems like the spinner goes right behind the dish in the picture, isn´t it? Forgive my limited English.

No room at all. This is it. 14 inch round plywood is the beginning of the spinner

#### mcrae0104

##### Well-Known Member
Not sure how I supposed to finish trailing edge on this cowling. What is more important, to follow the shape of the wing from top or from flat bottom?

The expanding-radius fillet on top follows the curved top surface of the wing and the expanding-radius fillet on bottom follows the bottom surface. The curved trailing edge is at the intersection of these two cone surfaces. You can take that general idea and adapt it to your situation.

#### rv6ejguy

##### Well-Known Member
Remember the basics of recovering lost cooling air momentum here- you must have less outlet area than inlet area to do this. In order to cool in the climb and accomplish lower drag in cruise, you'll need a variable area exit door, just like all WW2 liquid cooled aircraft did.

#### rv6ejguy

##### Well-Known Member
figure 5 then shows a radiator installation on a Me-109, with the diffuser shaped like a parabolic curve (...I think it is a parabolic curve...). I remember Paul Lamar doing a lengthy piece on that! ....how to perfect cooling intakes!

I am sure the guys with the experience here will have something to comment on Hoerner and Lamar!

Cheers,
thjakits

In my e-mail conversations with the late Paul Lamar, it was clear that he had little understanding of cooling drag or momentum loss. He never flight tested any of his concepts with instrumentation. Many of his recommendations conflict with basic physics and with what most successful, low drag liquid cooled aircraft employ for radiator and duct configurations. Look to Voodoo and Strega for the most highly refined rad and duct layouts for minimum drag. I cover these in one of my YT cooling vids.