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Old Aug 04, 2007, 04:02 PM
dougmontgomery's Avatar
Glendale,Az.
Joined Oct 2004
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Discussion
kevlar vs. Carbon-pod lay-up for 1.5 meter Dlg

Kevlar vs carbon. While working on projects between kits in wee hours of the night I decided to do a lay-up of 5mil kevlar. it is at 90degrees, one layer of 2ounce fg on the bias and a piece of 5.7ounce carbon reinforcrcement in between the two layers also on the bias in the vulnerable spot in front of the boom directly below the LE.

Carbon vs kevlar

carbon compresses more and tends to leave either dry spots or too much resin in places.
It is easy to seam, trim, sand.
my carbon pod weighed in at 27 grams

Kevlar isn't easy to sand or trim but leaves a better finish when rolled with two paper towels before squashed into the mold with the silicone.

here is my latest 1.5meter kevlar pod weighing 14 grams unseamed as shown.

Doug
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Last edited by dougmontgomery; Aug 04, 2007 at 06:32 PM.
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Old Aug 04, 2007, 06:24 PM
Jay Garcia
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Huntsville, AL
Joined May 2006
305 Posts
Nice pod dougmontgomery!!!

How does this pod compare with regard to stiffness when you put it next to the carbon pod?

-Jay
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Old Aug 04, 2007, 06:31 PM
dougmontgomery's Avatar
Glendale,Az.
Joined Oct 2004
3,540 Posts
jay-
The pod is a little more compressive compared to the Cf but the Carbon does not give at all. It is still really strong around the le area, the wing will be pylon mountes so the pod is just for the gear and fairing to attach the boom to.

I am waiting on booms from Denny right now so I cannot test. The lighter pod will allow me to use a heavier 25-30 gram battery. With the Cf pod, I end up being nose heavy with a 350mah 4.8v battery.

Doug
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Old Aug 04, 2007, 10:08 PM
Look out! The lever!
bobthenuke's Avatar
United States, AZ, Peoria
Joined Feb 2005
2,625 Posts
Looks great, Doug!

...bob
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Old Aug 05, 2007, 10:13 AM
wishes this caption was longe
will_newton's Avatar
wilson, nc, usa
Joined Dec 2005
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Doug, is this a clamshell pod or will there be a hatch?

What weight is 5mil kevlar close to? 1.7 oz? I might be a bit concerned about not having enough strength near the tip to take a hard dork landing. Maybe you could use a bit of 2 oz fiberglass in the layup from the carbon patch to the nose on the lower pod half.

How far does the boom insert into the rear? Does it go up to the carbon patch? You could save some pod weight by cutting off some of the pod behind the wing saddle.

To ensure a good epoxy finish on a carbon pod. I like to apply epoxy to the fabric, then flip it over and roll in some more. Then continue as usual with the layup. This ensures good epoxy coverage on the outer layer of carbon.

I don't try for super dry pod layups or apply a lot of pressure to roll the fabric. I have a metal roller (www.joewoodworker.com) and let it do the work. As for the puddles you are getting, I'd have to see a pic of your molding setup and an idea of where the puddles are forming.

My gut tells me the carbon pod is too heavy (weight) and the kevlar one too light (layup), but they both look cool!

I don't mean to slight the nice job you did, but just give you some suggestions that might help you fine tune the design. I always like that you post up whatever it is you're working on. Nice job!
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Last edited by will_newton; Aug 05, 2007 at 10:39 AM.
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Old Aug 05, 2007, 10:35 AM
dougmontgomery's Avatar
Glendale,Az.
Joined Oct 2004
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Will- I think 5mil is 2 ounce but not for sure.
I made two top molds so I could form the hatch seperately
the Boom does go 1" in front of the forward pylon. Whish is appx ~1-1/2 back from the LE.

My latest model I am flying with the Lighthawk wing and my boom and tail surfaces weighs in at 8.5 ounces auw-this is with a 27 gram CF as shown above. I would be perfectlly happy alway flying a 8.5 ounce DLG- I think it is a perfect all around weight for up to 8mph winds. Then I go to my tank-10.5ouncer.

I am no to fond of using formers and wing pins to hold the boom in this style of kevlar pod.

The kevlar saddle doesnt have any support value, it is more of a fairing.

Doug
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Old Aug 05, 2007, 10:40 AM
Come out swinging
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San Diego
Joined Mar 2005
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Personally, I prefer the all-carbon pods, or carbon/Kevlar hybrid pods.

I like the rigid nature of the mostly carbon pods.

Doug, you could try a lighter weight carbon fabric, like 2.9oz carbon, to reduce the carbon pod weight.

Sean
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Old Aug 05, 2007, 03:49 PM
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Tel Aviv-Yafo Ben Gurion, Israel
Joined Sep 2004
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Nice work Doug, your'e work is emproving all the time!
keep up the good work!
Eitan.
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Old Aug 06, 2007, 02:42 AM
dougmontgomery's Avatar
Glendale,Az.
Joined Oct 2004
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Pod Lay-up schedules

Sean- I really don't want to buy another yard of 2.9 ounce Cf for pods- I think I can modify my CF lay-up to do away with the second 5.7 layer that extended from 1/2" from the back to three inches in front of the Le- Then I will replace it with a piece of 1.7 ounce kevlar. I will post a layer drawing-

Eitan-Thanks- your pod also turned out beautiful also-my pods for the 1.5 meter are for myself only- I only wish I could get the seams better on the Kevlar- but I do not want to have to adjust my molds for a bladder of sillicone presses to join top and bottom.

Doug
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Old Aug 06, 2007, 06:01 PM
wishes this caption was longe
will_newton's Avatar
wilson, nc, usa
Joined Dec 2005
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in your carbon pod drawing, try replacing the fiberglass layer with the light kevlar on the bottom half, just use two carbon layers on the top half

should save you a bit of weight and epoxy.

sometimes you can get kevlar to behave a bit better if you use a layer of 3/4 oz fiberglass on the outside
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Old Aug 06, 2007, 07:54 PM
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Jim Walker's Avatar
United States, TX, McKinney
Joined Jul 2001
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Nice looking pods Doug. My suggestion on the kevlar pod is to use .7 oz glass on the outside instead of 2 oz. Or you might try none, my next pod will be molded with only one layer of 1.7 kevlar and CF to save weight. I don't know if it will be strong enough or not. My current ones with the glass on the outside are plenty strong. I took a direct hit from a launched plane at low level, (full speed in other words), right in front of the wing on the pod. It cracked but kept on flying. After the round I just wicked in thin C/A and am still flying it.

Also you could back off on the CF too. That's way more than I use. About half that much cut into three strips would probably do it. CF sure likes to suck up resin, it's thirsty material. I'll bet you could get your pods down to 1/2 ounce easy and still be plenty strong.
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Old Aug 06, 2007, 08:19 PM
dougmontgomery's Avatar
Glendale,Az.
Joined Oct 2004
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Quote:
Originally Posted by will_newton
in your carbon pod drawing, try replacing the fiberglass layer with the light kevlar on the bottom half, just use two carbon layers on the top half

should save you a bit of weight and epoxy.

sometimes you can get kevlar to behave a bit better if you use a layer of 3/4 oz fiberglass on the outside
Will-One of the issues I have with the Glass on the outside is the mold process I am using- same as some some others but way more hillbilly. I do not want to sacrifice the Kevlar finish by having a delam or airbubble.....The seam I can deal with.

I may try the smaller Cf reinforcement and maybe 3/4 ounce glass as the third layer to shave weight. i would be happy with a 15 gram pod auw with canopy.

Doug
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Old Aug 06, 2007, 08:25 PM
dougmontgomery's Avatar
Glendale,Az.
Joined Oct 2004
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Lay-up

Quote:
Originally Posted by Jim Walker
Nice looking pods Doug. My suggestion on the kevlar pod is to use .7 oz glass on the outside instead of 2 oz. Or you might try none, my next pod will be molded with only one layer of 1.7 kevlar and CF to save weight. I don't know if it will be strong enough or not. My current ones with the glass on the outside are plenty strong. I took a direct hit from a launched plane at low level, (full speed in other words), right in front of the wing on the pod. It cracked but kept on flying. After the round I just wicked in thin C/A and am still flying it.

Also you could back off on the CF too. That's way more than I use. About half that much cut into three strips would probably do it. CF sure likes to suck up resin, it's thirsty material. I'll bet you could get your pods down to 1/2 ounce easy and still be plenty strong.
Jim- I dont think I can get these pods down to ~6.5grams. Right now i am using a 4.8v 1/3AAA battery waying 19 grams. If I use Aradhanas battery at 27 grams- I have 8 grams to play with. In the Cf pod it balances Perfect with Aradhanas battery. So once I get the tail surfaces down to 10 -12 grams, from 14 grams. The kevlar pod will be the chosen Pod without moving the wing on the boom. Should way in at 8.1 ounces Auw.

I will Try some different lay-ups schedules- if anybody is interested in these prototypes Pm Me. Then i can continue to Lighten up the pods.
Doug
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Last edited by dougmontgomery; Aug 06, 2007 at 09:08 PM.
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Old Aug 06, 2007, 08:38 PM
Registered User
Joined Oct 2005
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Wow, you put a lot of carbon into a DLG. Two layers of 5.7 carbon!

My bubble dancer has two layers of 4.5 S-glass and 1 layer of 1.4 S-glass and a 3/4" strip of uni CF. Takes dork landings with 24oz of ballast besides the 35 oz weight to start. Two layers of 1.7 kevlar and a bias of 1.6 of glass isn't enough?
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Old Aug 06, 2007, 09:38 PM
Come out swinging
sporter's Avatar
San Diego
Joined Mar 2005
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Doug,

You'll be fine. Just make sure you make the rudder stiff.

Sean
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