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Author Topic: My first flying F1D  (Read 281 times)
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ffadict
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« on: December 09, 2019, 08:12:29 AM »

Over the last year, I've slowly pieced together an F1d. It came out at 1.5g, and only had one major problem: it wouldn't fly. The smaller problems came from sloppy construction, broken spars glued too many times, and not enough boron reinforcement. I finished out that build rather discouraged in late October. In November I had the good fortune to come across https://www.indoorffsupply.com.


Several emails with the owner, Dave Lindley, boosted the moral significantly, and more importantly the supplies and tools department. Especially helpful is the Estate Wood section of his store. I was lacking some motor stick and rib wood, and it was an easy way to place an order (as well as reasonable at $5 a sheet). His business model is admirable, focusing on supplying materials not already available rather than competing with current suppliers. I highly recommend his store. Although not mentioned on his website, he's located in Chicago, so a plus for those in the US ordering wood. Anyway I'm reinvigorated and have begun a new F1D, which I anticipate being my first flying model of the class.


I've built some more jigs and have gotten a friend to 3D print me a prop block of the dimensions for Kang's Salt Jr. I'll be using this plan in all sections except the wing and possibly the rudder. These designs will come from his more advanced model (the extra rib in the Salt Jr. just doesn't sit well with me).


Anyway, I've made myself a pre-New Year's Resolution: finish the build before 2020. At this point I've built the motor stick and put some of the trimmings on it. I still need to attach the the rear motor hook to the MS, install the wing posts, and make the extension on it.


To make the MS I used a piece of .25" KS tubing and the motor stick form from Mike Kirda's excellent form set that includes the TB, ext., ribs, and the front and rear webs. It's fairly straightforward; just set the form over the balsa, mark the holes, and cut along the exterior. I, being a dunce, forgot that the MS form was 12" long instead of the required 9", presumably leaving the option for omitting the ext.. I managed to cut out the whole 12" length when I only needed the 9", leaving the rest of the sheet unusable for motorsticks...measure twice, cut once.


Once on a roll of destruction, it takes a lot to stop me  Grin I used some of the mini drill bit set I purchased to drill holes in 1/4" cherry fixtures to push wire through and support the motor stick as it dried in the oven. If you look closely in the picture, you can see three holes. These are where the remains of the 1mm, .9mm, and .8mm bits are buried  Roll Eyes  If at first you don't succeed, try try again didn't apply here. Note to self, skinny bits don't like to be hand drilled into hardwoods...But as to the actual motor stick, I can't complain too much. The weights of installed pieces is as follows:


MS Blank: 118mg
Seam Glue: 22mg (ouch!)
Boron Weight: 11mg (Yay!)
Pigtail Bearing: 20mg
Front Web+Glue: 13mg

Total MS weight minus posts and ext.: 236mg

Goal is to be 10-20% overweight

To put the boron on, I used a jig like one of them mentioned in the 2010 build log. I ended up tensioning it with a finger rather than a weight for more control. I have had some boron popping up, but have been ungluing it the rest way with acetone and then gluing the offending section. Then I add more acetone to the fine section to reactivate the glue, and press it back down. I understand what Kang meant when he said that while working with boron you should "be diligent". I diligently shoved a length of boron half an inch down my finger, and had it break off under the skin at both ends. Fortunately, it was close enough to the edge so that it could still be seen. Dad was called into action for surgery, and it was pushed out with a pin far enough to be pulled with tweezers.

Edit: The boron has continued to pop up despite my best efforts. Any tips on how to keep it down or why that happened in the first place?

I made the rear hook and pigtail bearing out of .013" wire, and had better luck bending than usual. On the rear hook, I cut out the web and bent the hook as close as possible. Oh then trimmed the web a little bit for a close fit. On both the pigtail bearing and rear hook I attached the web by wrapping it with kevlar and putting a small tissue bandaid overtop. This was a little overkill, but the kevlar was half of the thinnest thread sold on the thread exchange, sliced with a razor and then pulled apart. I would like to finish this build by 2020, so I've got a lot of building to do!


I haven't attached the rear web yet, but I'm very happy with the fit of the wire on the web. This level of fit was far superior to that of my building; this comes from a new trick I tried this time. I made the hook the best I could, and then trimmed the web to fit it reasonably well. I think this will result in an acceptable structure and will be stronger than if it had gaps and was the exact size originally intended (no material came off the top or bottom so it should still fit). I still need to put Kevlar thread over it, and possibly some tissue. On the front web I Kevlar wrapped and then added tissue as there was still some looseness with the Kevlar. This time around I split my Kevlar thread in two with a razor so I had extra thin stuff. I can't remember the original thickness anymore, but it was the thinnest stuff sold on the thread exchange.  


I think I should be done with the MS and ext. today, and make a start on the tail boom.
On a happy note, I'd thought I had lost this whole post, and rewrote it while I was out and about. When I came back to my computer, I found it still had the initial post up and I was able to copy and paste it even though it was no longer part of the web! Strange things...

Pic. 1: Workbench with new tools/wood
Pic. 2: More tools
Pic. 3: MS wood
Pic. 4: I'm looking at the piece stamped 00001 Micro X Ultra. Are these just multiple peoples stamps, or is this really the first piece of wood Micro X cut?
Pic. 5: MS drying jig
Pic. 6: The Love of Three Drill Bits (Prokofiev anyone?)
Attached files Thumbnail(s):
My first flying F1D
My first flying F1D
My first flying F1D
My first flying F1D
My first flying F1D
My first flying F1D
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ffadict
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« Reply #1 on: December 09, 2019, 08:14:24 AM »

Pic. 7: Boron gluing jig
Pic. 8: Boron popping up Sad
Pic. 9: MS weight
Attached files Thumbnail(s):
Re: My first flying F1D
Re: My first flying F1D
Re: My first flying F1D
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Crabby
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« Reply #2 on: December 09, 2019, 09:06:35 AM »

ffadict, I have long heard of the use of boron in indoor duration models but never had the guts to ask what its purpose is? I do know it can be hazardous if it gets broken off inside ones finger, in fact thats the first thing that comes to my mind whenever I hear the word. Anyway what is its purpose, what is the cost and where do you get it?
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« Reply #3 on: December 09, 2019, 09:40:10 AM »


Edit: The boron has continued to pop up despite my best efforts. Any tips on how to keep it down or why that happened in the first place?


You should always pull the boron using a weight or a rubber band to straighten it when gluing. I use rubber bands.

Aki
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ffadict
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« Reply #4 on: December 09, 2019, 09:44:53 AM »

ffadict, I have long heard of the use of boron in indoor duration models but never had the guts to ask what its purpose is? I do know it can be hazardous if it gets broken off inside ones finger, in fact thats the first thing that comes to my mind whenever I hear the word. Anyway what is its purpose, what is the cost and where do you get it?

I believe that boron is used as a stiffener for the balsa. It's brittle, so has very little give to it and seems to be stronger than the balsa. It's available at https://www.indoorspecialties.com for something like $18 per 100 24" long pieces. I think that it also has a sub-purpose of being used to brace fingers   Wink

You should always pull the boron using a weight or a rubber band to straighten it when gluing. I use rubber bands.
Aki
Hmm, that makes sense why it popped up. Maybe I'll try ungluing the popped up section to the end and reapplying it with tension.  
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strat-o
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« Reply #5 on: December 09, 2019, 09:53:59 AM »

The alternative to boron seems to be carbon fiber tow which is raw carbon fiber thread.  I too share crabby's visions of bits of boron circulating through my system!

https://indoornewsandviews.com/2017/11/20/substituting-carbon-tow-for-boron/
« Last Edit: December 09, 2019, 10:05:53 AM by strat-o » Logged
faif2d
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« Reply #6 on: December 09, 2019, 10:36:27 AM »

My first F1D was test flown in my fathers haymow that was empty because the horses were long gone. They were not very successful but I finally got enough elevator (actually wing) angle in it that it did fly.
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Olbill
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« Reply #7 on: December 09, 2019, 11:29:25 AM »

Balsa and boron react differently to humidity. Balsa moves a lot in response to humidity changes. Boron hardly at all. It's pretty difficult to keep them joined if they're exposed to humidity levels that are different from when the boron was applied.

It's important to note that boron doesn't accomplish anything if it's loose and not very much if it isn't straight.

Tensioning the boron may accomplish getting it straight initially but doesn't guarantee it won't come loose if the balsa shrinks or expands.
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ffadict
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« Reply #8 on: December 09, 2019, 10:35:25 PM »

Thanks for all the boron thoughts here. I completely removed the boron on one side and replaced it due to a break that I made trying to re-position it. I applied it using the rubber band method this time. I initially glossed over the rubber band part of Aki's reply, but then it struck me this afternoon that it had mentioned rubber bands. At first test, it seems to work better for me than the jig I had made. No popups yet, keeping my fingers crossed. The other side hasn't fared too well. I might try replacing it too; the weight from the former replacement was only a 1-2 mg penalty.

It's important to note that boron doesn't accomplish anything if it's loose and not very much if it isn't straight.
Tensioning the boron may accomplish getting it straight initially but doesn't guarantee it won't come loose if the balsa shrinks or expands.

I know the first part all too well Roll Eyes The boron on my first airplane looped all over the place from me just gluing some popups to the side, and it did nothing for the MS but add weight. I don't experience very large humidity swings in Michigan, so I think that I should be good unless I start traveling to contests (which I hope to do in the future).

Carbon fiber tow...don't tell me that I need more supplies! I had enough trouble today. I was running out of polyimide tubing a couple of months ago and no one had it for sale anymore. I proceeded to request samples from a couple of companies, and ended up with one sample two weeks ago. I thought the other company had just ignored me, but today I received a 7.5' long package in the mail today, containing the tubing in 5' sections...mother was not happy. Enough supplies for the moment  Grin

Boron through the circulatory system...I wonder what happens when it reaches the heart Shocked
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lincoln
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« Reply #9 on: December 10, 2019, 05:24:57 AM »

Tow in the amounts you need can be very cheap. At least if you get it as tow rather than cloth. One possible source is Soller Composites. I don't know WHICH tow would be best. Maybe just get the scraps, cutoffs etc. that they list at $2/lb. But you can get spools of some other types for $18/lb. That ought to be enough for a number of F1D's. ;-)

I wonder if it wouldn't be better to split off little bits from pultruded carbon, which is nice and straight.

I'll admit I've had NO experience with boron or F1D. but I've seen the difference straighter fibers can make elsewhere.

It may help to keep in mind that some varieties of carbon fiber have a much higher elastic modulus than others. I think that may be more important than the somewhat lower yield stress,some of these fibers have.
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USch
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« Reply #10 on: December 10, 2019, 07:03:03 AM »

Just a few numbers to clear the fog about carbon tows. It may help to choose the right article for reinforcing your indoor model.

Carbon tows are normally called ROVINGS.
The distinguishing factors are type of fibre with different mechanical properties and number of single fibres forming the roving/tow.

The different types are called:
General, all round carbon fibre = NF, T800, if there is no specific annotation that's what you normally get as carbon fibre.
High Tenacity = HT
Intermediate Modulus = IM
High Modulus = HM
Ultra High Modulus = UHM

Tensile strength means the fibre resist high loads in traction, high modulus means the fibre is very rigid, but less resistant to traction.

The number of single fibres composing the roving is determining the section it forms together with the resin. The most found numbers are:
1k - 3k - 6k - 12k - 24k
The numbers are indicating thousands of fibres, 3k equal to 3.000 fibres forming a section of about 0,11mm2 dry and about double impregnated with resin.

Other parameters are "Elongation at Break" and "density" but that's a different story.

On indoor models the preferable reinforcing fibre is a high modulus typ to increase the stiffness of the single components disregarding the tensile strength.

Urs

PS: if I remember correctly Mike Kirda on propblocks.com sells small quantities of high modulus roving
« Last Edit: December 10, 2019, 07:38:15 AM by USch » Logged

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ffadict
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« Reply #11 on: December 11, 2019, 10:42:31 PM »

If I remember correctly Mike Kirda on propblocks.com sells small quantities of high modulus roving

I forgot to mention in my first post that Mike Kirda closed his store and combined with IFFS. At this point, carbon tow hasn't made it over in the transfer.

I used to think that F1D's were simple machines but hard to build. My impression is definitely changing...

I got the the TB and the offending piece off the MS. The ext. is rolled and drying. Weights of each and pics coming soon.

Paul
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Tapio Linkosalo
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« Reply #12 on: December 12, 2019, 01:45:11 AM »


One thing about carbon is that it comes in loose filaments (in both cloth and tow), and needs a matrix (some resin or glue) to bond the filaments together. Typically epoxy is used. This adds a level of complication in construction compared to boron. FWIW, I tried to make "carbon-boron" by soaking thin rowings of carbon (extruded from an uni-directional cloth) with celluloid glue, and attach these to a prop outline in a similar fashion as boron is used. However, the result was a disappointment - obviously celluloid glue is not hard enough matrix for the carbon fibers.

Having said that, carbon can be used for construction, but it takes more tooling and effort. I have build my latest F1D wing spars and ribs from carbon-balsa-carbon sandwich. Starting with the thinnest uni-directional carbon I have found (~10 grams per square meter if I recall right), I make a sheet of material, laminating the carbon on top and bottom of light balsa. For ribs this is done on a carved mold to gain the curve of the rib. After curing, individual ribs and spars are then cut out with a miniature table-top circular saw and a diamond cutting wheel. The issue with the thin carbon is that it is pre-preg - meaning that the fibers are pre-soaked with epoxy. This special epoxy needs to be heated (to 100 degrees centigrade) to cure, and to ensure proper adhesion I found that the laminate needs to be made in a vacuum bag. So you need vacbag that can handle the heat and an oven to heat the laminate for curing! The result, however is good, I feel that the wider carbon strip holds better to the underlying balsa than narrow strips of boron.
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