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Feb 08, 2015, 03:26 AM
U down with EPP? Ya u know me!
Aerogance's Avatar
Build Log

Featherweight JW


With Weaselfest right around the corner, I thought now would be a good time to build an ultralight JW. For the build, I am using the JW60 UL kit. I have swapped the standard joiners for lighter kite ferrules (saves 3/4 oz) with the expectation that the loss in strength is tolerable if the plane is kept light (edit: kite ferules are now standard with the UL).

Rather than put a few ounces of lead in the nose, I plan to build a custom battery that will satisfy balancing requirements. The thinking is to avoid as much dead weight as possible. Bigger battery = longer flights vs lead = dead weight.

I plan to use MKS DS6100 servos since they are light but fast with sufficient torque. The MKS will limit me to a 4cell nimh pack to stay within voltage limits. The battery will either be AA cells or AAA cells depending on the nose weight requirements.

Target weight is sub-25 oz.
Last edited by Aerogance; Aug 03, 2018 at 11:01 AM.
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Feb 08, 2015, 11:17 AM
Registered User
Feb 08, 2015, 11:49 AM
U down with EPP? Ya u know me!
Aerogance's Avatar
Spars are dried and the wing is now nice and strong. To fill the top of the spar I smeared a layer of white Gorilla glue and let it air cure (it's raining so no need for added moisture). The top spar filler is drying now. I also glued the back of the fuselage together with white Gorilla to keep the weight down.

I am contemplating the way I want to finish the plane. Originally I was going to use a few strategically placed narrow strips of strapping tape and then use colored packing tape for the finish. But now I am thinking that the wing will benefit from 1.7 or 3 mil lam film. If I go with lam film then I could add one or two stripes for visibility at the expense of a raw looking plane. I may opt for a lam film d-box to save weight.

Radio location is another area I am working out the details. I considered putting the battery, RX and servos in the nose and then running carbon pushrods to the surfaces. The drawback to this will be the increased risk of flutter because the control horns will be located all the way at the root.

I plan to use the coroplast tail but will experiment with alternatives, in particular depron. I can't imagine saving much weight at the fin but a little less weight = a lot less needed at the nose to counterbalance.
Last edited by Aerogance; Feb 08, 2015 at 12:02 PM.
Feb 08, 2015, 12:27 PM
Afflicted with DDD
Soarhead00's Avatar
Aaron
Just got my UL kit yesterday. Thanks for the fast shipping.

I want to copy your ultralight ultralight JW so will be following with interest.
First question, where did you get the kite joiner for your spars? Also, would a balsa (swissed) tail be lighter than a coroplast tail?

Bob
Feb 08, 2015, 01:37 PM
foam is fun, but glass is fast
Redfarren's Avatar
You guys should really give epp a try for your vert stabs, extremely light covered w lam film they should be fine, might get bent over when combating a weasel but not broken like Depron, then you would be done for the day..
The guys building zulu's did a bunch of testing at the beginning of their thread.
James
Feb 08, 2015, 02:43 PM
U down with EPP? Ya u know me!
Aerogance's Avatar
Quote:
Originally Posted by Soarhead00
Aaron
Just got my UL kit yesterday. Thanks for the fast shipping.

I want to copy your ultralight ultralight JW so will be following with interest.
First question, where did you get the kite joiner for your spars? Also, would a balsa (swissed) tail be lighter than a coroplast tail?

Bob
I had a couple of kite ferrules laying around so I decided to try them. They are brittle so it took a few tries to get the bend in them. These are not the normal 3" kite joiners, instead they are 2 1/2" machined ferrules with center stop. The stop makes them break when bent. I don't think they will fail under normal flight loads but if you fly in huge wind they might not be the best. I will see if I can rummage up a couple and send them to you to check out.

As for swissed balsa tail, it should be easy to lay I e up and compare the weight. I will let you know if I find an alternative tail material.
Aaron
Feb 08, 2015, 02:46 PM
U down with EPP? Ya u know me!
Aerogance's Avatar
Quote:
Originally Posted by Redfarren
You guys should really give epp a try for your vert stabs, extremely light covered w lam film they should be fine, might get bent over when combating a weasel but not broken like Depron, then you would be done for the day..
The guys building zulu's did a bunch of testing at the beginning of their thread.
James
I will look for the Zulu testing. Coro is fairly light already but a little more weight shaved at the tail is a lot saved at the nose on the JW. Depron is easily damaged so not sure if that is ideal.
Feb 08, 2015, 03:27 PM
U down with EPP? Ya u know me!
Aerogance's Avatar
More progress on the JW UL:
Last edited by Aerogance; Feb 08, 2015 at 03:33 PM.
Feb 08, 2015, 03:38 PM
Afflicted with DDD
Soarhead00's Avatar
Quote:
Originally Posted by Aerogance
I had a couple of kite ferrules laying around so I decided to try them. They are brittle so it took a few tries to get the bend in them. These are not the normal 3" kite joiners, instead they are 2 1/2" machined ferrules with center stop. The stop makes them break when bent. I don't think they will fail under normal flight loads but if you fly in huge wind they might not be the best. I will see if I can rummage up a couple and send them to you to check out.

As for swissed balsa tail, it should be easy to lay I e up and compare the weight. I will let you know if I find an alternative tail material.
Aaron
Appreciate the offer but I did a search and found a Kite store in Boulder that I should check before you go to the trouble. If I can't find some there, they are pretty cheap on the web.
Bob
Feb 08, 2015, 06:16 PM
Secret clown business
gizzo's Avatar
I don't think MKS DS 6100 is up to the job in a JW. Got plenty of power for sure but the gear train strips really easily. If you're landing and backing it in, the elevon snags the ground and they're gone. I've wrecked a couple even in my Typhoon on rudder/ elevator on fairly mild tail slap landings.
Just my 2c, YMMV etc.
Feb 08, 2015, 10:06 PM
U down with EPP? Ya u know me!
Aerogance's Avatar
Quote:
Originally Posted by gizzo
I don't think MKS DS 6100 is up to the job in a JW. Got plenty of power for sure but the gear train strips really easily. If you're landing and backing it in, the elevon snags the ground and they're gone. I've wrecked a couple even in my Typhoon on rudder/ elevator on fairly mild tail slap landings.
Just my 2c, YMMV etc.
I have had great luck with the ones in my Sunbird, but it doesn't get the abuse that a foamy does. Good to know they are easily stripped, will look at alternatives. I tend to plow in when I land so I am not familiar with snagging
Feb 08, 2015, 11:16 PM
U down with EPP? Ya u know me!
Aerogance's Avatar
Got pretty far on the UL today, but hit a stopping point. I need to get my radio gear sorted before proceeding. I should have it figured out this week. For now, I sanded the Gorrila glue on the tips and nose, cut elevons to length, got my Eneloops charged and tinned.
Feb 08, 2015, 11:48 PM
U down with EPP? Ya u know me!
Aerogance's Avatar
Quote:
Originally Posted by Soarhead00
Appreciate the offer but I did a search and found a Kite store in Boulder that I should check before you go to the trouble. If I can't find some there, they are pretty cheap on the web.
Bob
Bob,
If the kite shop didn't have the correct kite joiners you can cut down the supplied joiners from 6" to something like 3" to reduce weight. A hack saw should work well.
Feb 09, 2015, 02:52 PM
Objects in mirror are losing
1000MPH's Avatar
Go Aaron, go!
I'll be using HS-225's on mine which I believe were popular on JW's before we started building them extra heavy.
Servocity.com has them listed as 27g for the nylon gear version and $18/ea.
MKS 6100 are 9.5gr.
Feb 09, 2015, 03:06 PM
Afflicted with DDD
Soarhead00's Avatar
Quote:
Originally Posted by Aerogance
Bob,
If the kite shop didn't have the correct kite joiners you can cut down the supplied joiners from 6" to something like 3" to reduce weight. A hack saw should work well.
I like that Idea.


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