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Oct 29, 2008, 07:52 AM
Winging it >
leadfeather's Avatar
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Quote:
Originally Posted by dz1sfb
Hi Dan,

Love watching your threads. Did a quick drawing in TurboCAD for this one. See if you would like any annotations. I just put the minimum in for now.

I'll add the skids into the file.

On the annotations, if you write them the way you would like them to appear, I can just copy and paste.

Adam is quite an artist on the paint job!


Ken
Ken,

Adam does a great paint job and he seems to keep getting better.

The drawings look really good. The best anotations I've seen were right on the plans. My SloFly templates were done like this and the notes are right there wen you need them. I'll send you my notes soon...not that many really for this simple design.
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Oct 29, 2008, 07:59 AM
Ken's CAD Models
dz1sfb's Avatar
Dan,

I like doing these simple designs. It took about an hour and a half to get this much. When I put in your notes, I will simply update the post with the attachment and post a notification of the update with a link back to my original post.

Lotsa fun,
Ken

Edit: I'll add the skids as well. Is it okay to tab them into the KF step? Also update for 9mm EPP. I mistakenly designed at 10mm. Only the slot on the vertical fin is affected.
Oct 29, 2008, 08:54 AM
Registered User
Gold and Lead (interesting dichotomy), Years ago, we did research at the lab on the sources of noise from computer fans. The same thing happens with our props either in a slot or at the rear. The airflow is always disturbed when leaving the wing so it comes off the rear of the surface similar to the flow of air around a wire cage protecting the fan. That forms an aeolian harp type of flow but since the wing or wire is too stiff, the airflow is "split" into a top and bottom flow separated by a turbulent boundary. The prop "chops through" this layer and creates a pressure change (or effectively a pop) each passage.

I experimented with the sound of a prop centered on the rear of my wing vs. elevated above the trialing edge and found the higher the prop (like up on a plastic mount like a wild wing) does change the "tone". It would be fun to run an FFT on the sounds and look at how the wave frequency and phase correlates to the RPM and height. Wow, I just came up with a research project for one of my students!!!

The cleaner the rear edge of the wing does reduce the turbulent layer but you still have a pressure difference and that will make noise. I just tell people, it's still quieter than a nitro!

Just my 1 cent since the economy is in the crapper my 2 cents went the way of my retirement....
Oct 29, 2008, 10:08 AM
Winging it >
leadfeather's Avatar
Thread OP
Quote:
Originally Posted by rocketree2000
snip...

The cleaner the rear edge of the wing does reduce the turbulent layer but you still have a pressure difference and that will make noise. ...snip

Rocketree, really good information.

Based on this statement then it would seem that tapering the forward edge of the slot should help reduce noise. Further, tapering it from the bottom up; kinda like reflexing the airfoil a little; might help reduce the pressure difference from top to bottom and help a bit more...maybe.

p.s. Less noise should mean more efficiency.
Oct 29, 2008, 10:43 AM
Registered User
Lead,
I read about someone who tested the thrust vs. distance of blade and thickness of rear wing. The results were much as expected, with pusher props, the blade moves in disturbed air and losses efficiency hence thrust. The waste energy is called our enemy: NOISE It is an interesting situation, prop in front, plane is in disturbed air: efficient prop, inefficient aircraft, switch to our system and you get our problem.

The rear of the slot is a different matter. I think a test should be done with a slot that is square, tapered symmetrically (pointed), angled flat on top, flat on bottom and both one one each side of the prop. If someone has the time, please try this. I'll see if one of my slaves (aka students) is willing this semester. If not, I have a few spring semester who will have several projects now. I'll post the data when they do it.
Oct 29, 2008, 11:01 AM
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j2m2t2's Avatar
I went through all the posts and I cant find the CG. Lead?
Oct 29, 2008, 11:23 AM
Registered User
J2,
on the basic plan sheet is a dot about 9.75 inches from the nose. I didn't realize it at first but used the Palos website to compute it and got 9.6 inches. At that point I realized there was a dot there on the drawing. Mine was docile at 8.5-9 inches but with 30 mph wind, I haven't gotten to test it anywhere but my shed.

I hope that was it or a fortuitous stray mark which worked.
Oct 29, 2008, 11:23 AM
Winging it >
leadfeather's Avatar
Thread OP
Quote:
Originally Posted by j2m2t2
I went through all the posts and I cant find the CG. Lead?
j2,

It is 9.5" back from the nose. I move the battery further forward when flying in windy conditions.
Oct 29, 2008, 11:59 AM
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j2m2t2's Avatar
Thanks lead and rocketree2000. I will be building soon.
Oct 29, 2008, 09:03 PM
Ken's CAD Models
dz1sfb's Avatar
FYI,

The plans have been updated here.

https://www.rcgroups.com/forums/show...1&postcount=58

Ken
Oct 29, 2008, 09:26 PM
Registered User
adreher's Avatar
Ken,

Very nice job on the plans! Step 12 on the build steps is great, made me laugh. I will be the first to say that a good paint job makes it fly better
Oct 29, 2008, 09:45 PM
Ken's CAD Models
dz1sfb's Avatar
Adam,

Got a quick note from Dan indicating that the skids were further apart than he designed, running them into the LE. I just made the correction and updated the post.

Ken


Edit: Deleted plans as the latest version is in the following post.
https://www.rcgroups.com/forums/show...&postcount=740
Last edited by dz1sfb; Feb 21, 2009 at 09:57 PM.
Oct 29, 2008, 09:57 PM
Winging it >
leadfeather's Avatar
Thread OP

Thanks Ken


Great job on the plans Ken, thanks!

I'll add a link in the first post of this thread to these plans.
Oct 30, 2008, 07:29 AM
Fly,Crash,Repair..Repeat!
Ultralight's Avatar
Thanks to all who have created and made the plans available. I have a few questions. Where do you get your EPP and what size sheet do i need? I got to reading on the updated plans and it said something about Welders glue. Has anyone got a link for that stuff? Whats the best way to cut EPP? Sorry for all of the questions but i have never used EPP before and i want to build this puppy right. Thanks.


Jason
Oct 30, 2008, 07:40 AM
Ken's CAD Models
dz1sfb's Avatar
Jason,

You can get Welders Glue at your local Wal-mart.

EPP is available here;
http://www.rcfoam.com/cart.php?targe...category_id=83

This is where I purchased mine from;
http://www.flyingfoam.com/foamsheet.html

And you would not be complete without the EPP tips and tricks thread;
https://www.rcgroups.com/forums/showthread.php?t=703115

Ken


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