Every gram counts! - RC Groups
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Apr 18, 2015, 07:26 PM
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Every gram counts!


We love flying our F3P airplanes! We loved them at 125 grams, we loved them more at 100 grams, we loved them even more at 80 grams with a Coax, and now at 60 grams/coax we think we are in heaven until we look at the weights of the top competitors at the World Championships. Now we know we are not in heaven yet! Their weights are in the low to mid 50 grams with a 2s battery. My 60 gram mylar covered foam airplane is 67g with a battery.

If you think it is too hard to build a really light weight airplane you are mistaken. It just takes attention to detail and making every gram count. If you think a really light weight airplane is too delicate you are mistaken. First of all they make you a much better pilot because they fly so slow, they donít hit as hard and if you do make a mistake the mylar holds the foam in place for an easy repair.

Here are the steps i took to get to 60 grams.

1.Weigh your foam. I found a difference of 8% in my foam stock! The heaviest was the foam i paid extra for as it was advertised as super light. To be fair they did say that their weights were + or - 10%. 100g/square meter is a good weight.
2.Donít be afraid to cut away as much foam as you can before covering with mylar. I tried about 5mm width on the foam i left behind. My foam, ready for covering weighed 19 grams.
3.Buy some 2um mylar and spray adhesive. I used 3M but Loctite is good. If you settle for 5um mylar you are not making every gram count.
4.Adhesive spray needs to be very light. A dusting is all you need.
5.Avoid tape hinges. I used some really small tape pieces to join the ailerons to the wing and the elevator to stabilizer before covering. Once covered the mylar is the hinge.
6.Use all tube carbon except for minor braces which can use .2mm rod. The heaviest tube i used was 1mm and only for the main wing braces and nose gear. My design used tricycle gear. My assembled airframe weighed 30 g.
7.You must get rid of any insulated wires and all standard connectors. My control system weighs 10.5 g. That is 3 TGY 1290 servos, Deltang reciever, YEP 7 esc and 32 gauge magnet wire. The only connector was a micro for battery. The battery was stripped and rewired with magnet wire. My TGY 120 mah battery weighs 7.5 g.
8.Donít waste weight on the landing gear. The airplanes don't spend enough time on the ground! My gear consisted of a short 1mm tube nose gear and the extension of .5mm rod supports for the lower winglet. See photo
9.My main wing spar was only .4mm thick flat. I did not use any carbon bracing on the ailerons or elevator.
10.Carbon control arms and small control horns
11.Carbon props from Glavak. 11x3.8 lightweight.
12.Coax system weighing 12.5 grams w/o props.
13.Micro velcro from Horizon.

Here is complete wgt break down:
Airframe=30g
Coax motor=12.5g
Props and o-rings=5g
Control system= 10.5g
Control arms/horns=2g
Total=60g
So where do i find another 10 grams or so without going to an all carbon airframe??? I have some ideas but can use more!
Last edited by Vince Caluori; Apr 18, 2015 at 07:28 PM. Reason: Photos next
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Apr 18, 2015, 07:35 PM
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Here photos:
Apr 19, 2015, 12:52 AM
"Free" in Christ! #F3P
Free's Avatar
I like this, it is a nice breakdown of how to build a simple, yet light F3P plane. Good job.

About how to loose 10 grams. I think you can get the airframe to be lighter, maybe 27 grams.

You can also lose a couple of grams on the motor. The pros use 10 gram motor systems.

Free
Apr 19, 2015, 01:29 AM
Registered User
Free, What is so interesting is that the lighter you build the slower they fly and the slower they fly the lighter you can build them!

As much fun as our DIY coax's have been i'm getting really tempted to spend some $$ on a Glavak coax. Bang! There goes 5 grams! Besides the Glavak units are so pretty(and well engineered) you just want to have one.

If we could make our DIY coax work with a 5 gram motor and light props (balsa)
we might get close to Glavak weights.

Vince

ps, with the dollar as strong as it is we get a nice savings buying overseas.
Last edited by Vince Caluori; Apr 19, 2015 at 01:30 AM. Reason: correction
Apr 19, 2015, 11:07 AM
Registered User
Glavak coax system is work of art. 5g to the good. More aggressive airframe as Free suggested. 3g to the good. Still looking for at least 2g more!!

The 1290 servos are great. How much potential weight loss in modifying the 1290s?
Apr 19, 2015, 04:17 PM
C.H.E.A.P.
MICKEL's Avatar
Sand down your CF a little.
Apr 19, 2015, 05:17 PM
Build to fly, fly to fix
Quote:
Originally Posted by Vince Caluori

ps, with the dollar as strong as it is we get a nice savings buying overseas.
Ironic, with our (CDN) $ sucking all RC related acquisitions have been put on hold. Including US ( No Toledo this year), Chinese, HK, purchases.

Not sure what the answer, but in the grand scheme of things it's not really good for anyone.
Apr 20, 2015, 04:19 AM
Registered User
Quote:
Originally Posted by Vince Caluori
The only connector was a micro for battery.
No experience with so far, but I'm thinking about pin headers for connecting the battery with the ESC.
Apr 20, 2015, 01:49 PM
Registered User
Hans, I used the micros from Hobbyking . They are symmetrical but with power on the center and one side they can't short out. If you plug them in backwards you just get no power.



6pin Micro Plug (10pairs/bag)
Apr 21, 2015, 05:20 AM
A.K.A sir Crashalot
methuso's Avatar
Why not substitute some of that carbon for fishingline or even kevlar thread from the flyfishingshop? where only "pull strength" is needed.
There was even a schematic some years ago of howto "brace-up" your airframe with it.
I've tried it and it works as good as carbon rods along the fuse and to stiffen up wing and tailplanes.
In that plane i only used carbon for the landinggear... not even in the wing.
/Ulf
Apr 21, 2015, 05:45 AM
Registered User
Quote:
Originally Posted by Vince Caluori
Hans, I used the micros from Hobbyking . They are symmetrical but with power on the center and one side they can't short out. If you plug them in backwards you just get no power.

6pin Micro Plug (10pairs/bag)
These are pin headers

Today's depron airframes go below 20 gr. Typically they don't have those depron crosses or Xs in the cells anymore (or not as much).

Serrano F3P (2 min 10 sec)
Apr 21, 2015, 11:44 AM
Registered User
Hans,
"These are pin headers"
I don't understand? What did you mean?

Love the video!

Methuso, That diagram is from Foamy Factory. I can see using Kevlar thread for the rear fuselage bracing but i can't picture bracing the wing and maintaining alignment. It seems that that method of bracing was done on heavier models that had some basic stiffness to start with .
Last edited by Vince Caluori; Apr 21, 2015 at 11:53 AM.
Apr 21, 2015, 01:22 PM
Registered User
Quote:
Originally Posted by Vince Caluori
Hans,
"These are pin headers"
I don't understand? What did you mean?

Love the video!
The HK micro connectors you use are known as pin headers in electronics (male and female). You can buy them up to 30, 40 in a row and cut them with a hobby knife.

http://upload.wikimedia.org/wikipedi...Pin_Header.jpg
Apr 23, 2015, 09:18 AM
Registered User
You could try the 2 gram Spektrum A2010 servos.

But why stay with foam? With carbon you should be able to easily save 10 grams on the airframe. If you buy smaller more expensive carbon then 15 grams is possible. The carbon airframe will be much, much stronger meaning fewer repairs. I built my first (heavy at 71 grams) carbon plane in January and I will never go back to foam. It was actually easier to build than milled or carved out foam. The carbon I used was heavier than needed so my next one will use 0.8mm or smaller carbon rod. I believe the Donatas Victory S1 uses 0.7mm and smaller carbon. I believe the airframe weighs quite a bit less than 20 grams.

Dave
Apr 23, 2015, 12:34 PM
Registered User
Dave,
The 2010s are interesting if they really only weigh 2g. Horizon doesn't show a weight for the servo And i've seen it spec'd as 2.5g.

I'd love to have a carbon airframe but i see top guys at world championships within a gram or two of carbon with foam. For me, foam is so easy while wrapping dozens of carbon joints is not something i look forward to.

Why did you find it so easy?


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