Author Topic: Naca scoop and gear leg finishing. (Read 12166 times)

GlennBob · « **on:** April 07, 2012, 01:23:42 AM »

Hey guys,

I've got my bird inverted in my garage, . .refinishing the underside. I'm gettin' close, . .but I'm reworking the NACA scoop. (updraft cooling). Does anybody know, . .at the front of the scoop, . .is it supposed to be a sharp step down ? or is it a blended flow down from the preceeding body ?

Also have my transponder antenna just prior to the carb and it is indented about a quarter inch. I plan to bring that up flush to smooth the air before the carb.

I think I have found a neat way to deal with the gear leg fairing flex problem. I had used some plastic advertising sign material ( for sale etc ), to make a nice clean line in my nose gear leg. I mixed the micro and squeegied it in on both sides of the sign material. Then when cured, I simply pulled out the sign material. It had a good enough sheen not to stick. This left a nice clean line. So . .I tried it on the gear leg fairings. With the bird upside down, . .there's no load on the legs so they should be the same as when in flight. I finished the fairings directly to the body and legs and then cut a thin line around the whole leg, . so as to allow for flexing. I jumped up and put weight on the legs and they flexed o.k. So . I planned on using the sign material trick again. But this time, . I couldn't get the material out. So . .I think I'm just gonna leave it in there. I jumped up and put weight on the legs and got them to break loose and flex, but then with no weight, they go back to the finished position. I can't sand them as smooth as I'd like because the sign material must be harder than the micro, . .but it just leaves a small line around the legs. I think it's gonna work out just fine ! ! I'll send pics if anyone's interested.

glennbob

Vandy12 · « **Reply #1 on:** April 07, 2012, 07:23:38 AM »

I'm interested in seeing those photos. My VEZ is also in the 'static inverted' position right now. Hopefully not much longer!

Can you post them here? If not, please email to

brian_strack@hotmail.com

Thanks and good luck!

Brian

GlennBob · « **Reply #2 on:** April 10, 2012, 11:58:14 PM »

Here's a link to the photos of my gear legs, naca scoop, and strake windows.

http://s773.photobucket.com/albums/yy14/glennbob3/

Glennbob

dorr · « **Reply #3 on:** April 20, 2012, 03:24:05 PM »

Any joggle or bump at the mouth of the NACA will disrupt the flow some. Smooth is best.

Don't put antennas or other things ahead of it either...

Beagle

flyingwaldo · « **Reply #4 on:** April 20, 2012, 03:57:09 PM »

Take a look at the information presented in this slide from a drag reduction presentation. It will explain why Beagle mentions not putting anything like it in front of your cooling inlet.

GlennBob · « **Reply #5 on:** April 22, 2012, 11:42:43 PM »

I had heard that early disruptions in the naca flow would cause turbulence and less efficient flow into the naca scoop.

What I was wondering is the leading (small) edge of the naca scoop, . .should that depression be abrupt or blended smooth into the preceeding body. Sounds like from Beagle,. .it should be smoothly blended.

My antenna (transponder) is just prior to the carb in the large mouth of the Naca. I think as long as this is as smooth as poss. it should be ok right ? ?

Glennbob

dorr · « **Reply #6 on:** April 24, 2012, 03:24:13 PM »

The edge of the NACA should be a wing shape, what is more, some guys also get better cooling with a expander after the floor (roof when looking up at the aircraft) runs out.

I'd move the antenna somewhere else, were it me. We put them inside the strake with a flat plate of aluminum for the base. Some did it in the nose.

Beagle

GlennBob · « **Reply #7 on:** April 24, 2012, 10:35:32 PM »

The last portion of the NACA scoop is where you're suggesting to put an extension into the cowl for better cooling . . .otherwise known as a " diffuser ". I had planned on doing that when the bird is on it's feet again.

The antenna should be able to be mounted just about anywhere since fiberglass is invisible to radio signals right ? I like the idea though. Then I can get a clean shot into the Naca.

Bruce Hughes · « **Reply #8 on:** April 25, 2012, 01:53:39 PM »

My antenna is to the right side of the NACA scoop. I dremeled a small hole from the
passenger's space downward. The hole is directly under the passenger's armrest about
half way from the the seatbelt hardware to the area directly below the stick. The
antenna sits below a 6" aluminum plate (I hope that is large enough for a ground
plane). Almost 1/2 of the aluminum sticks out into the air. I faired it in as well as
possible. The coax attaches to the antenna directly downward and IIRC was sealed
with a silicone glue. I believe I remember some foam in the area; if so, I removed a little
foam all around and replaced the foam with flox before inserting the coax and antenna.

I am NOT recommending anything; I am NOT an engineer. My advisor never said it was
wrong.

Bruce Hughes

flyingwaldo · « **Reply #9 on:** April 25, 2012, 07:24:23 PM »

"Almost 1/2 of the aluminum sticks out into the air."

You're kidding ...... right?

Bruce Hughes · « **Reply #10 on:** April 25, 2012, 09:04:12 PM »

The aluminum that sticks out is fairly thin (but thick enough to not vibrate).
I feel sure it adds less drag than the step on the other side. Anyway I
took the step off so it should equal the drag. Nobody will run into it as
it is under the strake. So what is your problem?

Bruce Hughes

GlennBob · « **Reply #11 on:** April 25, 2012, 10:45:19 PM »

Yikes ! !

Don't want to start WW 3 here ! !

I'm thinkin' I might want to put it inside the main spar. Don't want to give up precious strake room. I remember the antenna guru saying that you'd want to have a sheet of aluminum foil between this antenna and the gib to eliminate radiation that was similar to a microwave!

Glennbob

Bruce Hughes · « **Reply #12 on:** April 26, 2012, 03:01:31 AM »

O! The word "microwave" finally gave me a clue of your concern. I suppose
you know that the radiation in a microwave is absorbed by water in the food
and converted to heat. You need a lot of watts for that to work.
Your transponder puts our very few watts.

The aluminum ground plane is between the antenna and the passenger. It could be
supplemented by more aluminum or a copper grid under the passenger. It think that
is gross overkill of a "problem". Placing the antenna inside the main spar will give the
passenger even less protection from the "microwave effect".

I think your "guru" may have been "pulling your leg". Did he tell you that on April 1 ?

DON'T drill a hole in the spar for the antenna. So what will support it? What will be the
ground plane? Most of those antennas are mounted on aluminum airplanes and the
entire wing or fuselage acts as a ground plane.

If you put the antenna inside the main spar, the coax will always be in the way. The
nose is a better location, if the battery is not in the way of the coax. Of course it has
to be to one side due to the nose wheel.

Bruce Hughes

srothert · « **Reply #13 on:** April 26, 2012, 09:00:31 AM »

Bob Archer used to make a transponder antenna that was on a circuit board. I RTV mine to the end of the C/S where it meets the wing.

Steve Rothert
Long-Ez N49SR

flyingwaldo · « **Reply #14 on:** April 26, 2012, 12:23:28 PM »

Quote from: Bruce Hughes on April 25, 2012, 09:04:12 PM

The aluminum that sticks out is fairly thin (but thick enough to not vibrate).
I feel sure it adds less drag than the step on the other side. Anyway I
took the step off so it should equal the drag. Nobody will run into it as
it is under the strake. So what is your problem?

Bruce Hughes

Well, have seen a lot of canards and none done with sheet aluminum hanging out of the fuselage. We'll see how it works (and looks) when you get it flying.......
You would have found that step kinda handy now and again, at least I do even with electric nose gear. Beagle lived without one for a few years but he's in pretty good shape......!

Hangar Flying

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