• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

Simple Cub seems under-powered

#1
Hello everyone!
This is my first post on any forum let alone the FliteTest one so that just shows how desperate I am :p

I scratch built an FT Simple Cub (my first build) using a cheap A2212-6 22000kV motor, ESC and prop bundle from Amazon. I also preemptively bought a 3s 3000mah battery, hoping that it would last longer because of the larger number.
I later realised that this battery made the plane very heavy, especially with the 5mm foamboard I used. I ordered two 2s 1500mah batteries which, turns out, can't even push the plane forward on concrete. I suspect that 2s batteries of this size are made for RC cars rather than planes, but I'd like confirmation.

I ended up risking it and giving the 3000mah battery a go, but even this wouldn't push the plane forward much on the concrete. A hand launch got it flying with quite a nose-high attitude and full throttle, but the weight made it very difficult to turn and it ended upon the ground in a not-so-elegant 'landing'.

From what I understand, despite the battery being far too heavy for the plane, it should at least have enough power to get it to take off from the ground; the excess weight should mainly affect the handling once in the air, right?
So I suspect there may be something else at play, such as a problem with the motor or ESC. I know that a lower kV motor paired with a bigger prop such as an 8X4 would be better suited to a Cub, so I was planning on buying another motor anyways, but if there's an issue with the ESC or something else I'd rather know about that before I go and buy a new motor and smaller battery.

I live in the UK so some of the components on HobbyKing and especially BangGood take ages to ship, which is why I used Amazon for my current components, and am hesitant to buy something from them before having consulted the forum.

Thanks a lot in advance,
Niccolo

Components:
Motor and ESC - https://www.amazon.co.uk/gp/product/B07777ZH3J/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1
3000mah battery - https://www.amazon.co.uk/gp/product/B07DR7BL1Z/ref=ppx_yo_dt_b_asin_title_o04_s02?ie=UTF8&psc=1
1500mah battery - https://www.amazon.co.uk/gp/product/B074XQMF14/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
Foamboard - https://www.amazon.co.uk/gp/product/B00ALVPZYO/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1
If relevant, I use a Flysky Tx and Rx.
If photos would be useful, ask and I'll take some.
 

FDS

Well-known member
#2
If you are buying from Hobbyking you pick only items which are in stock on the UK or EU warehouse, not International.
Firstly, you have too high KV motor, you want something around a 1000kv swinging a 9x3 or 10x4 prop.
Second, UK foamboard is 40% heavier than the stuff used by Flitetest, so you are fighting all up weight already.
Third- You have far too much battery on the one hand and not enough on the other.
You need to look at several things-
Overall weight- weigh the plane with everything in. This will allow you to look at how much thrust you need to generate from the motor and prop to get airborne. Then you can look for a motor to power it.
Battery- The 1500 should just be able to balance the plane, it will be enough to power a better motor/prop.
CG/Balance- With the 1500 battery in, does the plane balance on the correct point as in the plans? A common problem with UK board is that it ends up too tail heavy, you then end up adding too much extra weight to balance it and a heavy plane gets heavier. The 2s packs you have are not the same as the 3s ones recommended for the Cub. They may still be too light to balance the plane.
The advantage of the 2s batteries is they are spinning your prop slower, so you may be able to run a bigger prop than the one you have.
The all in one motor esc combos on EBay are pretty awful. I wouldn’t buy them if you want a better experience. The two I got were both hopeless, the ESC got notchy and the motors were awful.

Solutions- Don’t second guess the plans, buy as close to the recommended battery weight as you can, Hobbyking is usually good for common sizes of lipo. In planes less weight = better handling and longer flight times. Very few planes use anything bigger than 2200mah size in any voltage.
Use FT board, even if you scratch build. It can be bought here from Model Shop Leeds, Sussex Model Center, Gliders UK, several other places. 3mm UK board can be used but the plans need adapting to reflect the narrower board. There is no light, cheap DTFB equivalent board in Europe, only the FT stuff is light.
You can build with 5mm UK board, the larger FT designs work but need modifications like extra length in the nose and light tails to compensate. You can take the paper off one side too, but that’s extra work.
I think a bigger motor will be a good idea. Your present ESC will run one, for the 2s batteries something like this 1400kv with a 10x4 APC prop will give you some grunt back. Push the motor as far forward as you can to get free nose weight to sort the CG and it should go better.
Those links are out of stock in the UK warehouse, will get you some alternatives as well.
Model shop Leeds- Motor and Prop for the 2s packs. Can’t guarantee that will all balance your plane, but the Thumper has some added mass vs your existing one, and with the firewall level with the front of the nose you might get enough weight forward with the 2s packs. If you decide to run a 3s you would want a lower motor KV and a 9x3 prop.
There’s lots of info in the UK sub forum as well.
@CarolineTyler, did I miss anything?
 
Last edited:
#3
Wow, thanks for the incredibly fast reply.
You're right about the Hobbyking UK warehouse, I hadn't noticed it and the shipping times are far better.

The plane weighs in at 420g without battery and 550g (1.2 pounds) with the 1500. (Everything included). It seems to balance fine even with the 2s if I put it just behind the motor.

The most sensible option on the UK warehouse seems to be the following:
https://hobbyking.com/en_us/turnigy-aerodrive-dst-1200-brushless-outrunner-motor-1200kv.html
Alternatively, for more money,
https://hobbyking.com/en_us/turnigy-park480-brushless-outrunner-1020kv.html

The pages say that they're both more than powerful enough for the current weight of the plane.
Is the 30A ESC from the last motor fine for these or is it better to replace that too?

The apparent best prop option is a strange colour but matches what you said:
https://hobbyking.com/en_us/gws-style-slowfly-propeller-10x4-5-green-ccw-4pcs.html

Sorry for spamming links, it's just difficult to gauge what motor will be able to pull what plane.
Thanks again for the help!
 

FDS

Well-known member
#4
1200kv may be a little slow for 2s. Most people recommend 1400kv for 2s. Both those motors will have enough power to pull the Cub.
The motor specs are on the FT plan page if you look, as well as on the power pack details in the FT store. Then it’s all about searching like you have done for the right equivalent. HK also don’t help by measuring all their motors differently to everyone else.
Only horrible prop colours left in stock, you can tell it’s summer!
Good that it balances right, my Sportster was really tricky to balance. 30A esc should be fine, both the motors linked are under 20A peak.
FT list the weight of their Cub kit as 285g dry.
 
#5
Wow the FT Cub is significantly lighter; next time I'll use the FT foam and be more sparing with the glue.

There is a 1500kV which is slightly less powerful than the others:
https://hobbyking.com/en_us/turnigy-2205-34-1500kv-brushless-motor.html
but I think I might as well be safe rather than sorry and go for the 1200kV, and get the recommended 3s 1000mah or 1300mah to stick as close as possible to the recommended, as I should have from the start. Then I can still try my 2s 1500 and see how it works out with the new motor. After all if I optimise it around the 2s I'll regret not spending the extra and getting the 3s and appropriate motor.

Thanks for all of the great advice, I'll definitely be sticking around the forum.
 

Hai-Lee

Old and Bold RC PILOT
#7
The Simple cub does not like being heavy as the wing incidence is insufficient as the weight is increased.

You are advised to use 3S batteries 1300 to 1500mA/Hr.

I use the heavier FB here is Aus and for mine I use a CF2812 1534 Kv motor from HK swinging a 8x3.8 prop and increase the wing incidence using a paddle pop stick under the wing LE where it rests on the fuselage top.

With this setup the Simple cub can take off at half throttle and fly around quite slowly with even less throttle and still have a turn of speed at full throttle when wanted.

I also have 3 inch wheels on my version to keep the landings and take offs easier as I use grass strips.

Once sorted the Simple cub is a sedate cruiser with reasonable flying characteristics.

It works for me!

Have fun!
 
#8
The Simple cub does not like being heavy as the wing incidence is insufficient as the weight is increased.

You are advised to use 3S batteries 1300 to 1500mA/Hr.

I use the heavier FB here is Aus and for mine I use a CF2812 1534 Kv motor from HK swinging a 8x3.8 prop and increase the wing incidence using a paddle pop stick under the wing LE where it rests on the fuselage top.

With this setup the Simple cub can take off at half throttle and fly around quite slowly with even less throttle and still have a turn of speed at full throttle when wanted.

I also have 3 inch wheels on my version to keep the landings and take offs easier as I use grass strips.

Once sorted the Simple cub is a sedate cruiser with reasonable flying characteristics.

It works for me!

Have fun!
I didn't know that the angle of incidence could compensate for weight in this way, I'll definitely try the popsicle stick beneath the wing to increase it. Thanks!