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Old Apr 30, 2010, 02:23 PM
In speed lies safety
Aerogance's Avatar
USA
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Quote:
Originally Posted by rothlisburger View Post
As long as you're looking at laminar airfoils, maybe you should use the P-51D tip airfoil, just for the cool of it.

-David
That one resembles my original choice.

If I meet with success, I may try using the SHM-1 (15%). It has been extensively tested and has improved stall characteristics.
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Old May 02, 2010, 10:43 PM
In speed lies safety
Aerogance's Avatar
USA
Joined Sep 2008
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Cores

My new work bench and foam machine still have a few wrinkles to iron out, but I did manage to punch out some cores this weekend.

Currently:
95" wingspan
847.5 square inches
AR = 10.6 : 1


If I add 1 more center section:
118" wingspan
1082 square inches
AR = 12.9 : 1

If I just use the wing tip secitions:
47.5" wingspan
380 square inches
AR = 5.9 : 1
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Old May 09, 2010, 02:58 AM
In speed lies safety
Aerogance's Avatar
USA
Joined Sep 2008
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It looks like Prototype #1 will be 60" span, 480square inches and AR=7.5.

Attached is a PDF of the design concept. The fuselage shape is unique and may have enough room in the tail for a big servo. The fuselage plug will be turned on a lathe. I plan to use a steel spar in the wing.
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Old May 09, 2010, 10:49 AM
Detail Freak
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Harbor City, CA
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What is the purpose of having the fattest part of the fuselage aft of the wing saddle??

Just curious, thanks.

R,
Target
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Old May 09, 2010, 11:48 AM
In speed lies safety
Aerogance's Avatar
USA
Joined Sep 2008
2,712 Posts
Quote:
Originally Posted by target View Post
What is the purpose of having the fattest part of the fuselage aft of the wing saddle??

Just curious, thanks.

R,
Target
A few reasons:

-Stiffer structure between the wing and tail (less flex = better control)
-Torsionally stiffer between wing and tail (less twist = better control)
-Possibly higher parisitic drag but potentially lower overall drag at speed
-Lots of room for radio gear and ballast
-Potentially lighter weight tail boom since less material required for given strength.
-Shape can be turned on manual or CNC lathe

This plane will be small enough to exploit the fuselage shape. A huge plane may not benefit at all. I thought it would be worth doing it since the potential for improvement over conventional shapes exists.

I have to evaluate where the wing is going to be located. In the middle as drawn may not be the best. High wing would be more stable and easier to build plus stronger fuse at wing saddle.
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Old May 09, 2010, 12:08 PM
I DS slower than I build!
Cory's Avatar
Idaho Falls
Joined Jul 2006
2,349 Posts
A mid mound would be easiest. If you do a high mount you will need to fair it in to avoid interference drag.
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Old May 09, 2010, 08:30 PM
Registered User
Sydney
Joined Apr 2009
716 Posts
Sounds interesting - have you ever looked at the design theory behind the AR- 5 homebuilt record holder?(1992)

http://www.ar-5.com/

The section relating to interference drag and the relative locations of wing and fuselage, are interesting.

John
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Old May 14, 2010, 10:18 PM
In speed lies safety
Aerogance's Avatar
USA
Joined Sep 2008
2,712 Posts
Wing Tip Shape

I settled on the wing tip shape for the first prototype. I remembered back to my first few planes and they had a very simple wing tip design that was elegant in its simplicity and finished off the wide and thick tips of those old planes nicely. The planes were the Gentle Lady and the Trainer 40. Both planes were rather unexceptional but were good for their intended purpose.

Researching the wing tip shape some more turned up the "Horner Tip" design, claimed to add 5mph to a 200 mph plane while eliminating tip stalls and improving high-alpha behaviour. I was going to round and sand the wing cores to achieve a basic tip shape, but old data suggests that the Horner style tips produce smaller tip vortices and thus reduce drag compared to simple rounded tips. And they are incredibly easy to create on foam cores as evidenced in the photos below:
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Old May 15, 2010, 09:08 AM
Deniable plausibility
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Derbyshire, UK
Joined Aug 2008
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Interesting wing tip shape. I seem to remember from the Nic Wright, 'how to build an Electra F3B' paper, he also advocated that shape... but that was in 1989

Always interested to see what others design and build,

S
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Old May 15, 2010, 10:51 PM
In speed lies safety
Aerogance's Avatar
USA
Joined Sep 2008
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Quote:
Originally Posted by Shedofdread View Post
Interesting wing tip shape. I seem to remember from the Nic Wright, 'how to build an Electra F3B' paper, he also advocated that shape... but that was in 1989

Always interested to see what others design and build,

S
Yeah, it goes way back to even before 1989. But it should be better than my "Plan A" tips and it is easy to build true and symetrical, so for a simple planform it should work just fine. I would use something more high-tech on cnc mould however...
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Old May 15, 2010, 10:57 PM
In speed lies safety
Aerogance's Avatar
USA
Joined Sep 2008
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Final Cores

So, I made quite the pile of "test cores" while dialing in my bench/bow/wire/power supply/pully etc. Everytime I would get it perfect, I would change or break something (i.e. bow size, material being cut, pulley/bow rig etc). I was having trouble with wire temp when I switched to a 36" bow because the powersupply I built was designed for 24"/48". Today I made the trek over to radioshack (pun intended) and picked up different resistors for the power unit. Some solder fumes later and wire temp was much improved (still not perfect but I know how to fix it). I finally have a matching set of cores ready to be processed:
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Old May 16, 2010, 04:31 PM
In speed lies safety
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USA
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Mowin' wings

I joined the cores today and turned the leading edges. After sanding everything out, I cut the mylars. I still need to cut the wing tip shape before bagging (no spar for this first wing since bugs need to be worked out and it may become a plug):
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Old May 16, 2010, 07:02 PM
In speed lies safety
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USA
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Got the wing tips formed and sanded out this afternoon. The dihedral is such that the top of the wing is flat:
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Old May 16, 2010, 11:35 PM
In speed lies safety
Aerogance's Avatar
USA
Joined Sep 2008
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Almost in the bag

I assembled all my tools/supplies to get this sucker glassed and in the bag. Mylars are waxed, glass is cut, breather/saver is cut to size, custom vac bag assembled. I decided to call it a night. After speaking with Jason, I am considering shooting the mylars with auto primer to prefill any holes. I usually do this but thought I would prime after bagging this time:
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Old May 16, 2010, 11:49 PM
Detail Freak
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Harbor City, CA
Joined Oct 2003
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I think the only bonus of bagging non-painted mylars is if you want to see how well you are doing with the layup....
But it seems like no paint makes pinholes much more likely.

If you wanted the best of both worlds, I suppose that you could use a coat of clear on the mylars, then layup.

I plan on doing that on the next wing I layup that has an all carbon wing, but I will spray broad stripes over the clear to make a naked carbon/striped wing bottom.

R,
Target
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