Hi guys
So the below wing started out as a Ritewing Z1. pure EPP. Anyway she spend a month floating in an estuary before I got her back- and after salvaging most of the electronics I wanted to make the most of the airframe. The centre section was knackered anyway- so I cut this apart, removed the carbon spars and bodged together two halfs to make a 42" EPP wing.
(http://i63.tinypic.com/2e4kopg.jpg)
She's now fully built, laminated, and has all her electronics present.
However, I'm struggling with her CG. She's building incredibly tail heavy. Her current CG is around 9" from the nose. Given the Z2 which is 56" had a 9" CG this seems way too far back.
For reference the Ritewing TW40 CG is around 7.5" back. So I'm aiming for 8".
Anyway- she's going to need 200g of nose weight to get her around 7.5". She's weighing 1.3kg fully loaded so I don't want to add another 200g.
Some of my components are quite far back- but I'm using existing holes and cut outs so would rather not dig the video tx out and reposition it. It's not that heavy anyway.
https://i.imgsafe.org/3832169a5e.jpg (https://i.imgsafe.org/3832169a5e.jpg)
So- could someone please give me some advice on where I should aim for the CG. I will prob end up shifting a few things forward if I can and then adding 100g of nose weight and seeing how she copes with a few hand launches.
Hi,
See if either of these CG calculators helps out
http://fwcg.3dzone.dk/ (http://fwcg.3dzone.dk/)
http://www.friendlyflyers.org/cg-calc.html (http://www.friendlyflyers.org/cg-calc.html)
PK :)
Ah nice that second link is pretty idiot proof for me to follow thanks :)
Could you get the motor the other side of the mount? Would help a bit.
The mount is actually designed to have the motor on the inside like Stellaship suggests, however it all depends on what motor he's got and if he can get his shaft to poke through far enough to use a collet style prop adapter. In all honesty though, I much prefer the bolt-on-can style prop mounts.
Ah I'm running a short shaft NTM with the shaft bolting on so I fear that won't work :( shame as I expect it would have helped a fair bit.
If I can keep the weight around 1300g I think it has the potential to be a good flyer. It's carrying a 4000 4s - the same as my z3 and that weighed 2.5kg or so.
I will put the figures into the CG calculator and if needs be hack into her again and move the motor further forwards another inch or two. Mind you the motor only weighs 80g so even removing it entirely would only negate 80g of nose weight from the predicted 200g required. I could dig the tx and Rx out and make new holes for them further forwards but they really aren't that heavy and I'm just not convinced it will help much tbh.
If I hadn't messed about with stepping the voltage down for the video system I would have considered running a small 3s battery up front just for the video setup.
I maidened this yesterday and after gradually removing 150g of nose weight the CG came out at about 8.5" from the nose. I was surprised tbh- for a 42" wing that seems awfully far back. But nevermind- just need to integrate a flight cam properly now and try and put her on a diet- she's quite lardy at 1400g and the little 250W motor needed at least 50% throttle to keep her level.
I was surprised at her slow speed tbh. I'm running a 8x4 prop so was hoping for some more thrust. The motor came back slightly warm so I could perhaps up the prop a little to get a bit more thrust. Will see how she performs after her diet first. I have removed her 40A esc and seperate bec and replaced it with a 18A esc- plus I have moved the video Tx a few inches further forwards in the hope I can save some nose weight. If I can shave 50g from her I will be pretty lucky so she's still going to be a bit heavy :(
One question guys- how vital are wing tips to a wing? Do they do a lot to increase low speed lift? I ask as removing them will save a flew grams and they are behind the CG at the moment.