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Simple Cub - scratch build but way tail heavy?

#1
Hi - pretty happy with the Simple Cub as a build but putting the motor and battery in and discovered that in standard position for the motor with the battery full forward the tail won't even leave the bench with a CG test. What's going on here? Is it because the foam board I use is heavier than the FT stuff? My marked CG is 45mm from the leading edge per the data sheet. At this rate I would have to have the motor sitting 10cm forward to get any kind of balance. Didn't expect it to be that far out. Using a 1500mah.
 

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CarolineTyler

Well-known member
#2
I had exactly the same issue when building with heavier foamboard. The best thing to do is when building remove all the inside covering in the tail to lighten it. Instead of adding dead weights, run a larger battery, you will add flight time. The Simple Cub has a big enough wing to handle a fair bit of extra weight.
 

BATTLEAXE

Well-known member
#3
Hi - pretty happy with the Simple Cub as a build but putting the motor and battery in and discovered that in standard position for the motor with the battery full forward the tail won't even leave the bench with a CG test. What's going on here? Is it because the foam board I use is heavier than the FT stuff? My marked CG is 45mm from the leading edge per the data sheet. At this rate I would have to have the motor sitting 10cm forward to get any kind of balance. Didn't expect it to be that far out. Using a 1500mah.
Have you tried a 2200 3s inside the pod?
 

Hai-Lee

Old and Bold RC PILOT
#4
Hi - pretty happy with the Simple Cub as a build but putting the motor and battery in and discovered that in standard position for the motor with the battery full forward the tail won't even leave the bench with a CG test. What's going on here? Is it because the foam board I use is heavier than the FT stuff? My marked CG is 45mm from the leading edge per the data sheet. At this rate I would have to have the motor sitting 10cm forward to get any kind of balance. Didn't expect it to be that far out. Using a 1500mah.
As already stated it would have been better if the internal paper had been removed from the fuselage prior to commencing construction.
On mine, (also built with heavier FB and all of the paper), I fitted much larger and heavier wheels and a very large prop adaptor.
When you get it to balance be aware that the extra weight may cause a few handling issues in standard trim. If you do experience strange flight characteristics you may need to increase the main wing incidence angle by propping the wing LE up with a paddle pop stick or similar. The extra incidence increases the wing lift and returns its handling to more trainer like!

Have fun!
 
#6
Some good thoughts thanks. The Cub has such a short nose that it takes a tonne of extra nose weight to make a difference. I am going to try a 2600mah 4s as I have a couple of them. Maybe tune it down throttle wise? It just, just balances with that in.
 

FDS

Well-known member
#8
That will make it pretty pitchy, you reduce the moment of the tail if you do that.
A nose extension or bigger motor is still better, I never like to add ballast, it seems silly when it’s sapping power.
If you find out how many G weight or extra length in the nose is required to balance it, by adding small coins to the nose until it balances or by pulling the power pod out until it balances with the battery on, then you can look at a solution. You could use a heavier battery and you would then know how much heavier as coins are a known weight, even if you don’t have gram scales. Similarly the weight difference between motors could be factored in then too, or moving the motor right out the body by pulling the power pod forward and spacing the motor off the flywheel would also be a quick n dirty fix.
I wouldn’t chuck that big 4s in there, extending the nose is easier and better if it’s a lot of weight required.