3D How to "build it light"

[David Shriver]

I see this phrase in the forums fairly often
"If you build it light it will fly great". How does someone build an ARF heavy or light? In my days of building kits there were lots of ways to shave weight and if not careful excess weight could build up. But with an ARF all the building and covering is done, so where can someone save weight? I suppose engine and battery selection can make a big difference but are there other tips/tricks to "building it light"?

 

[Bunky.F.Knuckle]

Engine choice, battery choice, exhaust choice...... Just to name a few....

Im glad we are in a day and time when we dont need to use true 1/4 scale servos, 6-8oz each servo. Can you imagine outfitting a 40% with 13 of thise servos........

 

[David Shriver]

I remember the first 50% Extra I saw fly. It was outfitted with these

 

[Terryscustom]

Making smart decisions on what you put in and how you mount it. For instance, don't build a plywood platform for batteries if it is not needed, same with RX. Use a water bottle or pre-built light fuel tank like taildragger sells (saves 40% or more than regular tanks). Even Tygon is pretty heavy, don't have an extra foot of fuel tube if you don't need it in there (plan your fuel system). Wheels, spinner choices, type of batteries, eliminate the ignition battery / switch, tailwheel choices, pilot figures, Ti gear servos if they are an option.........

Lots of options to shave weight. 1/4 ounce here and there adds up quick.

 

[BalsaDust]

Agree with everything others have said. Proper choice of equipment makes a huge deal. I picked up a Carden cap from a buddy. When he was flying it it weighed right at 20 pounds. By the time I was done with it it only weighed 18 pounds. I never expected to be s me to cut that much weight but I did and it makes a big difference in how the plane flys. On landings my buddy how to keep his speed up and now being lighter I can slow it down a lot more on landings.

 

[pawnshopmike]

Yup. Best way to save weight is K.I.S.S.

I recently saw an add for a 30cc plane that was outfitted with enough gear for a 40% plane. With the exception of servos of course. Why on earth would someone put a power expander and dual 5200 packs in a 30cc plane?! Just crazy overkill.

 

[Xpress]

Why on earth would someone put a power expander and dual 5200 packs in a 30cc plane?!

That's another important aspect as well. Power expanders, as someone stated, are an eloquent solution to a problem that doesn't really exist. With how many channels modern radio systems have and the types of power input options receivers use, there is zero need for a power expansion system unless you absolutely need one. Even if you're limited to 7 channels you can still have a 30-35% setup without a power expander, especially since a lot of modern digital servos can be ganged together and programmed to center and move exactly the same. I have all 4 of my aileron servos on my 107" Yak setup on just 2 channels because I was able to match them to each other.

Ditching a full canister exhaust system may make the airplane a bit louder and make the engine perform a little differently but it can save a lot of weight, so can removing huge battery systems, or masses of additional options like smoke or ignition batteries, running an IBEC instead. Options like opting to run a HV servo setup so you don't have to use regulators or big LiFE batteries so you can run a pair of 2s LiPOs instead, stuff like that can save weight.

 

[BalsaDust]

KISS is exactly how I cut the weight from my cap.

DLE55 over a evo58
Stock exhaust
Solar D772's on all the surfaces
Standard servo on throttle
Fiji water bottle fuel tank
Pair of 2500mah 2S life packs
And a single 8 channel reciever.

 

[Terryscustom]

Wow, Solar servos......so you don't even need batteries then except ignition?

Just promise us you will not use solar servos in anything larger

 

[David Shriver]

I've often wondered if we will ever get to the point where we use alternators instead of carrying batteries.