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Old Sep 03, 2012, 01:09 AM
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1st time scratchbuilding - Comments/tips appreciated!

Hi all I'm scratch building my own plane for fun. To be honest I am pretty inspired by all the amazing scratchbuilds here.

Here is a pic of my plane.. I pretty much got the airframe down except for the rudder.

I tried throwing her and she seems to be able to glide.

Size is 32inches wingspan. The tailfin foam is lighter than the main wing foam.

I'm thinking of installing an old motor from my 50cm Ezysky Cessna that I decommisioned recently. Runs on 2S.

I hope that it will be a nice slow flyer which can do some mild aerobatics.

I'm still deciding how to secure the motor on and also the main wings as its my first build.

I've decided to name her the flying guppy.

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Last edited by kilotango; Sep 03, 2012 at 11:24 PM.
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Old Sep 03, 2012, 04:54 AM
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I would follow plans for your first scratchbuild. Easier to understand the techniques required that way, and you don't have to worry too much about whether or not it will fly.

If you love tinkering and trial-and-error, by all means! Make sure your CG is right (there are CG calculators to help estimate, but you will need to do glide tests to confirm). Make sure your power system is suitably matched to the plane (enough thrust to weight) and to itself (battery, ESC, prop, motor). Many more things to think about which won't matter for your first plane :P.

It looks like you are using 3mm depron for your horizontal stab. Is it the Artfriend one? It is likely to be too weak. There also appears to be a crack in your fuse.

I regularly fly some of my scratchbuilds at tamp field. Saturday mornings from 7 ish. If you want I could bring some along this weekend and you can take a look-see.
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Old Sep 03, 2012, 06:28 AM
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Thanks for the tips!

Yes I like to tinker and have some trial and error!

It doesn't matter if it doesn't take off first time, I will try to get it right in the end.. thats the challenge for me.

I did look at some of the plans for the scratch builds here but decided to do something of my own for the sake of satisfaction. Something really 'from scratch'.

The horizantal stab is 5mm foam.. not sure what kind! I bought it from SHS. They had 5mm and 10mm stuff. Came plastic wrapped. Ok I may reinforce it with some CF.

Yes there is a crack in the fuse because I decided to glue back the piece I had taken off.. I couldn't figure a way to have a vertical stabilizer otherwise without alot of trouble.

Oh cool thanks for the offer.. I may take it up with you.. sat mornings 7 ish is fine for me .. I'll let u know. Would love to see some of your scratchbuilds!!
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Old Sep 03, 2012, 10:18 AM
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Hi Guys! Great to see more SG scratchbuilders here!

Cute Guppy.. tho I'm a little concerned about the short tail moment. May make COG hard to obtain and balance out he plane. Also the smaller Horizontal stab. You may end up with a pitchy plane. But then again...thats the best part about scratchbuilding. Mostly have fun doing it.

I've been building for over 2 years with Compressed foam and EPP and gone through tons of planes from this section on RCG. Everything from 3D profiles to nutballs, PBF's, deltas, pushers...crashed some, invented some....list goes on..lol!

If you need help feel free to PM me. We can chat over the phone or if your nearby perhaps for drinks. Lemme know! Cheers and welcome to the world of foam scratchbuilding!
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Old Sep 03, 2012, 03:52 PM
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Love the shape of your Guppy. Will be keeping an eye on this thread to see her first flight.
Make sure you get all of the electrics before fitting anything. That way you can stick everything onto the foam roughly where you want it and test that you have CoG right. It's always worth using a length of hook and loop tape to fix the battery as that will allow you to fine tune CoG once you get her flying.
Make sure your control rods are strong and there is no play in the connections to both servo and horn.
When hinging your control surfaces make sure the hinges (whatever they be made of) flex really easily. A plane of that size will require fairly light servos and you don't want to add any undue resistance.
Good luck. Have fun.
TCF
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Old Sep 03, 2012, 09:28 PM
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Cute looking plane!
Do you know how to check your CG using two index fingers? Your CG should be just a bit in front of your wing spar. Clip a weight on the nose such that the CG will be where suggested, then give it a glide toss. If the nose goes up during the gilde, increase the weight and vice versa.
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Old Sep 03, 2012, 09:47 PM
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Hello Tim and TCF, thanks guys for the warm welcome!

Tim- ok great to meet another fellow singaporean! I may drop you a pm too to ask for help if needed. Yah I'm beginning to discover there is an amazing variety of concepts and profiles one can tinker and build. Its really good fun and mind stimulating! Roger that on the COG... I might stick the motor out front a little more so as to balance it properly.

TCF- thanks for the tips!!! Great tip about sticking everything onto the foam roughly to test the COG. I will do that. I have the electronics ready... just have to stick them on. :P Yes I have long strips of velcro (hook and loop?) ready too for the battery position.

I have plastic hinges ready too.. thanks for the tip.. I'll make sure the control surfaces play freely. I'm still thinking of how big the ailerons I want to make. I will probably cut then sand them down for the taper. I'll be doing a lot of sanding down on all the other rough edges.

Btw I had a lot of trouble cutting the foam to have clean edges even with a new blade on my art knife. Maybe its just my knife technique.

Does anyone use a hot wire foam cutter here? Does anyone have experience with this? I am trying to look for one.

best regards! :P
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Old Sep 03, 2012, 09:53 PM
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djacob7- thanks for the comment and the tip!

Yes will do a few more glide tosses as suggested. I'll probably stick on all the electronics and see how she glides. :P
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Old Sep 03, 2012, 10:07 PM
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Hobbyking has a knife for something like US$2, and spare blades that come in packs of 10 for US$1. I bought 3 or 4. Not as sturdy as the Xacto no. 2s, but it gets the job done and is thinner and much cheaper, even considering shipping.

When cutting foam, don't try to make the cut all the way through the foam on the first run. Unless your blade is ridiculously sharp and you are on a smooth hard surface, you will get raggedy edges on the bottom end. I take 2-3 passes to cut my 6mm depron. Thicker foam takes more passes.

To keep the blades sharp I sharpen them every now and then with 1000 grade sandpaper. The important part is to keep the tip sharp. If the tip breaks, replace the entire blade, and use that broken blade for nonessential cutting work.

I used to have a battery operated hotwire cutter a long time ago. I found them fiddly to work with unless you have a lot of space, clamps and a steady hand, to make sure your edges come out nice and true. Maybe I just wasn't too good with the cutter. I don't know where mine is now.
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Old Sep 03, 2012, 10:17 PM
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Ok thanks Ray for the knife tips! (no pun intended).

Yes I think I cut too deep on my first score.. probably the reason for the ragged edges.. lol..

Hmm yeah i think need a really steady hand and clamps as well to use the hot-wire cutter accurately.. will also end up with a different kind of ragged edge otherwise!!!

I was thinking of using the hotwire cutter mainly for the curves as I can't really cut nicely with the art knife round a bend.
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Old Sep 04, 2012, 11:04 PM
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Hey there KT!

Always a pleasure. Feel free to PM me for help. We can exchange cell numbers and take it from there.

As for cutting compressed foam, I use an OLFA knife with the NT cutter 45 degree blades. Been used to it from my days of signage and display work..lol! I'm too lazy to sharpen them with a stone so I just cut and break them off. I do buy lots of packs whenever I'm at Popular Bookstore tho..hehe. Never used a hot wire cutter as I don't have such patience. Since I'm not into airfoils and there is the tried and trusted KF airfoil,..scratchbuilding has never been easier.
For cutting compressed foam, if you don't have a steady hand, make sure the blade is sharp by breaking off a section or 2. Do a first cut halfway through with a Steel Rule. Don't rush and appply enough down pressure on the ruler especially with longer length cuts where you have to move your hand holding the ruler down the length as you cut otherwise as you end the cut, the ruler may slide off the line.
After the first initial cut you will have a nice channel to make the final cut all the way through. I find standing up and being over the cut makes for neater and straight cuts. This way you can see your blade perpendicular to the ruler as your cutting. Sitting and cutting makes you have less pressure on the steel ruler and you may get slanted cuts.
Sometimes slanted cuts are expected, but I just run a piece of old phone card, ruler, something flat and straight along the slanted cut side to flatten it...hehe.

You should also get a nice slit sound when your cutting. If you hear small crunching noises or crackles then your blade isn't sharp anymore. I find investing in a large cutting mat, long steel ruler and a knife worth it for long term scratchbuilding. Besides, their great stationary to have at home when needed. I have 2 knives, a larger Stanley Heavy duty one for plywood and balsa and a smaller metal OLFA model. The NT Cutter 45 degree blades have a sharper acute point on the blades. Do be careful of a few things when cutting tho.

These 45degree blades are sharper!! Trust me,,,hehe. The sharper pointed front allows you to jab your blade into foam and make nice curves. when cutting a line watch where your Thumb is!! I've seen too many people have their thumbs at the rear of the ruler over the cutting length and while cutting run the knife over them!! Don't cut with too much pressure on the knife!! The blade may snap so extend only what is needed and not more! Also steady pressure ensures your blade won't skip the ruler and cut your hand!! Hence the first channel cut!

Hope that helps! In the end,...the more you build the more you will find where cuts need to be better, where less glue is needed, where CF rods are needed and end up with much better builds!

Do get in touch...I live in the East side so someday we can exchange geek talk!
Cheers
Tim
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Old Sep 05, 2012, 02:38 AM
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I've thought about setting up a hot wire cutter but came to the conclusion that there would be no benefit for me. Partly because I'm no expert with electrics but mostly because I think hot wire cutting only comes into its own when producing lots of identical components. For one offs the work required to make templates seems equal to or greater than just cutting the foam.
Just my opinion.
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Old Sep 05, 2012, 05:46 AM
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Thanks guys for the opinions on the hot wire cutting. Yeah its not a must have for me... I can always sand down the ragged edges and curves by hand.

I did a test glide! I taped on the motor and battery as recommended and tried gliding it.

The COG is right at the carbon spar. Had to adjust the batt all the way forward... the motor is a small one meant for a 50cm Cessna.

Was the test glide a success? :P

There are 2 tries..
Glide test- Flying Guppy - Scratchbuild (0 min 9 sec)


and
Test Glide 2- Flying Guppy - Scratchbuild (0 min 11 sec)


Obviously my daughter does not appreciate the finer points in airplane construction. hmmph.
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Old Sep 05, 2012, 05:58 AM
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Tim- thanks for the detailed knife work information! Greatly appreciated.
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Old Sep 05, 2012, 09:03 AM
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Glides looked ok to me. Difficult to judge as you were indoors. In a headwind your glide may be vastly different from better to possibly worse (I doubt the latter).

I'd put ailerons on it and elevator and not worry with a rudder. That thing looks like it'll be a fun flyer.
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