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Author Topic: combat kitten weight problem  (Read 2334 times)
Augsburger
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« on: January 25, 2017, 05:04:38 PM »

How much should a combat kitten weigh without the motor and fuel tank? (i.e. using a cox bw .049)  Mine is too heavy and I need to recover and redo.  It will only fly if the Black Widow decides to unload which it has only done once.  I plan on using the first build to do a first try with monocote or some other covering for practice before building the second kit.  Any other tips on getting the original airframe lighter would be appreciated.  I also plan on using the tuning tips for the engine.  Thanks

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Dan Berry
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« Reply #1 on: January 25, 2017, 06:58:42 PM »

Cover it with Ultracote Lite.
Or jap tissue.
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badbill
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« Reply #2 on: January 26, 2017, 04:41:57 AM »

My Kitten is from the PDK kit, and it goes like hell on 40' lines with a black widow... Running a 5-3 cox prop on 25% cox fuel. I don't know about unloading, we just lean it out, let it go and hang on. It's covered with regular monokote. Booms and engine mount painted.

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Bill Davenport
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Augsburger
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« Reply #3 on: January 26, 2017, 07:44:23 AM »

BadBill... I was hoping you would reply.  If you have an opportunity to weigh your Kitten next time the engine is off would you do that for me?  Your Kitten looks great.



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Wilder Eber
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« Reply #4 on: January 26, 2017, 07:52:15 AM »

I'll weigh it this evening when I get home from work.
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Bill Davenport
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Augsburger
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« Reply #5 on: January 26, 2017, 08:13:40 AM »

a better picture...


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Wilder Eber
Augsburger
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« Reply #6 on: January 26, 2017, 08:16:11 AM »

I'll weigh it this evening when I get home from work.


thanks, can't wait...
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Paul Smith
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« Reply #7 on: January 26, 2017, 12:40:30 PM »

If you're concerned about weight, don't use Top Flite Super Monocote. That's the heaviest covering the world of modeling.   
OK, except for plywood with fiberglass.

In addition it shirks with enough force to crush a small airplane.


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Paul Smith
badbill
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« Reply #8 on: January 26, 2017, 12:53:36 PM »

If you're concerned about weight, don't use Top Flite Super Monocote. That's the heaviest covering the world of modeling.   
OK, except for plywood with fiberglass.

In addition it shirks with enough force to crush a small airplane.

Not true at all, several brands of solartex and coverite weigh WAY more than monokote. And I'd be hard to convince that silk and enough dope to fill the weave to make it anywhere near as smooth as monokote would weigh less. And with all that said, mine is covered with monokote and it goes like a raped ape with a stock BW .049.
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Bill Davenport
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« Reply #9 on: January 26, 2017, 03:10:59 PM »

               There's really no fat to trim here. You have the leading edge, trailing edge, spar and sheeting. You can't compromise any of them by eliminating them. The booms can be flat sanded and tapered as well as the elevator but truth be told, they really need all the strength offered. I have built several of them and never weighed one of them nor did I ever have an issue with a Black Widow flying one. All of mine have had Black Widow engines aside from the current one I have with a Tee Dee. If your engine isn't up to the job, I would be seriously looking into it. As Bill mentions, 25% nitro and a small prop like the 5x3.
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Augsburger
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« Reply #10 on: January 26, 2017, 04:31:51 PM »

I probably doped and painted it way more than I should have.  Just cutting out the silkspan between the ribs has dropped the weight almost 1/2 oz.  While stripping away the material and doing some light sanding I was amazed at how strong the wing really is and that most of the unnecessary weight was put on by me using silkspan and trying to over fuel proof with lots of dope.  Now I have to go dig out my Higley books and start reading while I try to strip the paint off the balsa sheeting.  Thanks for the help and I will keep you all posted.
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badbill
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« Reply #11 on: January 26, 2017, 05:53:13 PM »

Mine weighs 4.9 oz
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Bill Davenport
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Augsburger
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« Reply #12 on: January 26, 2017, 06:01:15 PM »

Thank you sir.  That gives me something to shoot for.
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Paul Smith
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« Reply #13 on: January 28, 2017, 01:27:08 PM »

I ran some stuff across the scales:

Two homemade foam 1/2A's, built for TD's with some repair weight added, contest winners: 4.0 ounces.
TD .049 : 1.85 ounces.
Fora .049 (probably 2 to 3x the power of a TD): 2.38
AP Wasp .061 RC with muffler & prop:  2.02
Pacifier with tube etc:  0.25 oz
Cox Little Stinker RTF:  3.6
Hollow log Super Cub with Black Widow, built for speed & racing: 4.27
Sorry, no Black Widows off the plane today.


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Paul Smith
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« Reply #14 on: January 28, 2017, 02:19:27 PM »

Now I have something to go on.  When I weighed my Kitten it was 128 grams or 4.5 ounces.  I have already decreased the weight to 3 7/8 and haven't removed the paint and silkspan from the balsa sheeting yet, so I am hopeful.  I also started the upgrades on the BW, swaged or tightened the piston rod connection.  The Cox literature that came with the tools says .001 to .003 play.  When I looked at my .002 feeler guage, I think it would be difficult to know what that feels like, but I think it tightened a bit without being restrictive.  Thanks for the info everyone.  I appreciate it.
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« Reply #15 on: January 28, 2017, 09:10:19 PM »

1/2A foamie.

This is right at 4 ounces, less engine, and that includes a lot of patch work. The TD, prop and tank should bring it to about 6.4 ounces.

It's covered with GBC laminating film, which is just about the lightest you can get in covering.


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Paul Smith
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« Reply #16 on: January 30, 2017, 12:01:54 PM »

Now I have something to go on.  When I weighed my Kitten it was 128 grams or 4.5 ounces.  I have already decreased the weight to 3 7/8 and haven't removed the paint and silkspan from the balsa sheeting yet, so I am hopeful.  I also started the upgrades on the BW, swaged or tightened the piston rod connection.  The Cox literature that came with the tools says .001 to .003 play.  When I looked at my .002 feeler guage, I think it would be difficult to know what that feels like, but I think it tightened a bit without being restrictive.  Thanks for the info everyone.  I appreciate it.

After all that, yours weighs less than mine?Huh LOL. I can assure you, put a decent running motor on there and it will be fast enough  Devil
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Bill Davenport
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« Reply #17 on: February 01, 2017, 03:03:03 PM »

Now I have something to go on.  When I weighed my Kitten it was 128 grams or 4.5 ounces.  I have already decreased the weight to 3 7/8 and haven't removed the paint and silkspan from the balsa sheeting yet, so I am hopeful.  I also started the upgrades on the BW, swaged or tightened the piston rod connection.  The Cox literature that came with the tools says .001 to .003 play.  When I looked at my .002 feeler guage, I think it would be difficult to know what that feels like, but I think it tightened a bit without being restrictive.  Thanks for the info everyone.  I appreciate it.


You should be able to haul around a 8oz plane with a black widow and still be enjoyable. I haven't weighed them, but by feel the lil hackers I have are heavy and they fly great on a golden bee. If you're unsure of how to make the engine run great, that's where I would focus the energy. Your plane sounds like it is just fine.
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« Reply #18 on: February 01, 2017, 07:43:51 PM »

The Merlin 1/2a glowplugs do wonders over the stock ones.
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« Reply #19 on: February 04, 2017, 11:13:55 PM »

I'll second what Dane said, based off your original post I keyed in to the fact that your Widow wouldn't unload. Your weight is fine.

Now, nothing against tanked reedies as I love them, they just don't lend themselves well to stunt,  and combat requires even more out of them. With a lot of fussing you can get them to run right, but a TD on pressure would be the hot ticket on a little combat job. If you want to go tanked a Medallion would be a good choice. Good luck in whatever you decide.
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Augsburger
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« Reply #20 on: February 25, 2017, 04:36:30 PM »

Update and making progress.  Here is the Kitten after having been stripped of dope and silkspan and sporting my first attempt at Ultracote which I chose for the weight advantage.  I made many mistakes especially around the motor mount but it was a lot of fun.  The motor mount area was tough because I couldn't remove the mount and had to cover around, over and on top of if.  The picture shows the first attempt although I redid about 4 times.  I really like the way the material works.  I trimmed the weight from 4.5 to 3.25 oz., or, 128 to 92 grams.  After the engine tune with tips from forum members I got the Black Widow to go from 11K to a consistent 17.5 to 19.2 K rpm's.  I can't wait for a calm morning and will report on the attempt to fly soon.  Thanks for all the help.  Cheers.



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« Reply #21 on: June 18, 2017, 09:53:09 PM »

That thing should scream now.  Sounds like 99% of the problem was your engine.  Now that you have got it sorted out AND reduced weight, well, I hope you can keep up with it.
I built one way back in the 70's, had the skill level of a typical 13yo, silkspan/dope finish and a Golden Bee for power and it was all over the sky. It was capable of more than I was.
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