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rickofudall
Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA
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 Posted: Mon Jul 23, 2012 10:24 am Post subject: A fairing for the Mk III |
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There hasn't been a lot of building activity on the forum for some time.Attached are two pics of the composite fairing I made for the aft end of the fuselage pod on Ken Holle's Mk IIIX. I call it a duck tail for short. The idea behind it is to help smooth the inflow to the prop, gain a little efficiency and maybe decrease drag a little.
The first pic shows the profile of the duck tail and illustrates the construction method used to make it, your basic Burt Rutan moldless composite techniques. The shape was derived from pressure recovery shapes developed for sail plane fuselages. The second pic shows the part mounted on the airplane.
From a block of large cell (flotation billet) Styrofoam I hot wire cut the first side with the divot at the trailing edge and glassed it with two plies of BID at 45 degrees. Peel ply was placed over the lay up and wetted out. The drop from the cut was put aside to be used to hold the part for the second cut and when the second lay up was done. TIP: When you make the hot wire templates for a part like this, layout the nail holes (the templates are attached to the foam with 10 penny finishing nails) in a symmetrical pattern, stack up the templates and drill them all at one time. That way you can pull off the first template, attach the second and they line up perfectly.
The first lay up was rough trimmed with a box knife while the glass was in the "green" stage. The second template was applied, the hot wire cut was made and two more plies of BID were laid up and peel plied. Once again the drop was retained for use later.
This second lay up was rough trimmed in the green stage too. I mixed up a batch of heavy micro (glass micro balloons and epoxy) TIP: When the epoxy will not absorb any more micro balloons put a drop or two of denatured alcohol into the mix and it will absorb more. The idea is to make the mix as light as possible. The heavy micro was used to fill the divot, and scraped flush with the edges. A single layer of BID wide enough to cover the micro in the divot was wetted out an a strip of plastic sheet, a second piece of plastic sheet was placed over the glass and a squeegee was used to push out as much epoxy as possible while still keeping the glass wet (this method is known as the poor man's vacuum bagging technique). The top layer of plastic sheet was carefully peeled off and the bottom sheet was used to transport the lay up to the part. This lay up was applied over the micro fill to seal it. This, too, was green trimmed and the whole part was allowed to cure for a few days.
After the part was fully cured it was placed between the drops from the hot wire cuts of the OML and the sandwich of part and drops was lightly clamped with a few rail clamps. The hot wire was charged and most of the block on the inside of the part was cut away. The inside of the mounting surfaces were scraped with a Surform tool to remove all the residual foam and the part was ready to trim to length and fit around the boom tube.
The mounts are two lengths of 1/2" X 3/4" 2024-T3 aluminum angle .062" thick. They are held to the "H" frame uprights with three custom formed Adel clamps. At 5 inch intervals Nut Serts were installed so the duck tail could be attached with thin head 10-32 phillips screws.
The duck tail, the mounting rails, and all the hardware weigh less than a pound and a half. Flight testing will be in a few days and we'll see if it actually does anything or if it just looks cool. IMOH :-}
Rick Girard
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Zulu Delta
Mk IIIC
Thanks, Homer GBYM
It isn't necessary to have relatives in Kansas City in order to be unhappy.
- Groucho Marx
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Richard Pike
Joined: 09 Jan 2006
Posts: 1670
Location: Blountville, Tennessee
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| Posted: Tue Jul 24, 2012 3:31 am Post subject: Re: A fairing for the Mk III |
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Very nice. The prop pulses will not be kind to it, so give us a few long term endurance reports along with the efficiency reports.
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Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0
Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing. |
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undoctor
Joined: 21 Oct 2008
Posts: 212
Location: Bethelhem, PA
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| Posted: Tue Jul 24, 2012 8:13 am Post subject: A fairing for the Mk III |
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Kolbers,
When Don G. built my FlagFly he fabricated one out of aluminum. I don't
know how the weight compares with glass, but the pulses from the prop
have no effect upon it's integrity.
Dave Kulp
Bethlehem, PA
FireFly 11DMK
On 7/24/2012 7:31 AM, Richard Pike wrote:
| Quote: |
Very nice. The prop pulses will not be kind to it, so give us a few long term endurance reports along with the efficiency reports.
--------
Richard Pike
Kolb MKIII N420P (420ldPoops)
richard (at) bcchapel(dot)org
Kingsport, TN 3TN0
Now faith is the substance of things hoped for, the evidence of things not seen.
Hebrews 11:1
Read this topic online here:
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rickofudall
Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA
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| Posted: Tue Jul 24, 2012 1:10 pm Post subject: A fairing for the Mk III |
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Dave, Well aluminum would certainly be cheaper than composite. :-} I had the glass, styrofoam, and epoxy, but didn't have a sheet metal brake so I went with what I had on hand.Sure is a pretty FireFly.
Rick Girard
do not archive
On Tue, Jul 24, 2012 at 11:12 AM, David Kulp <undoctor(at)ptd.net (undoctor(at)ptd.net)> wrote:
| Quote: | Kolbers,
When Don G. built my FlagFly he fabricated one out of aluminum. I don't know how the weight compares with glass, but the pulses from the prop have no effect upon it's integrity.
Dave Kulp
Bethlehem, PA
FireFly 11DMK
On 7/24/2012 7:31 AM, Richard Pike wrote:
| Quote: | --> Kolb-List message posted by: "Richard Pike" <richard(at)bcchapel.org (richard(at)bcchapel.org)>
Very nice. The prop pulses will not be kind to it, so give us a few long term endurance reports along with the efficiency reports.
--------
Richard Pike
Kolb MKIII N420P (420ldPoops)
richard (at) bcchapel(dot)org
Kingsport, TN 3TN0
Now faith is the substance of things hoped for, the evidence of things not seen.
Hebrews 11:1
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=379078#379078
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--
Zulu Delta
Mk IIIC
Thanks, Homer GBYM
It isn't necessary to have relatives in Kansas City in order to be unhappy.
- Groucho Marx
[quote][b]
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The smallest miracle right in front of you is enough to make you happy.... |
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