I also wanted to include 3 key features in this mod

- Minimal battery box changes (preferably none)

- Ability to switch between using Lipo and the NiMh battery types

- Ability to monitor Lipo usage

The pre-requisites for this mod are:

1. To convert the ESC, Charger and Batteries to Deans Ultra connectors (or some other
   type better than the stock connectors).
2. To mark on the fuselage (just under the wing) the centre of gravity (CoG) of the
   stock plane with stock battery. Using a finger either side of the plane
   under the wings and marking the balance point with a Sharpie.

The first objective, to avoid battery box changes is mainly achieved
through the selection of your Lipo battery. This limits you to a maximum length
of 67mm which are the ‘square’ shaped batteries usually between 1000mAh and
1300mAh capacity 3s (11.1v) batteries. While this is a capacity limitation from
the 1800 to 2200mAh 3s average, I felt it worth the compromise.

Many people on forums chose the Thunderpower which should be ‘drop-in’.
I chose the cheaper $21 hexTronic 1300mAh from Hobbycity which is supposed
to be 65mm long. In fact the hexTronic was about 10mm longer that the spec
which was very annoying.

Getting this slightly over-sized Lipo to fit required me to remove the
rear side of the battery box using a scalpel / craft knife. The white battery
box plastic carves quite easily with a sharp knife and this could be done without
removing the box from the plane. This allowed the battery to lay horizontally
in the box using the stock battery box door, the receiver could be kept in the
stock location above the battery box and velcro strap was still functional.

Next was adding a switch to select between Lipo and NiMh LVC (low
voltage cut-off). This was achieved by using a standard receiver switch to
control the LVC jumper on the receiver. I re-used the lead and connector from one
of the ACT sensors I had previously removed to extend the length of the switch
wires. I connected one side of the switch to the jumper header on the receiver
and ‘shorted’ the other side using the previously removed jumper. (Note, a
future mod would be to cut, join and solder the wires on this other side of the
switch to save a gram or two).

The switch now controls the LVC jumper. When in the ‘on’ position, the
jumper is closed, which is the NiMh position for a lower LVC. When the switch
is ‘off’, the jumper is open, which is the Lipo position for the 9v LVC. The switch can now be tested using a
multimeter circuit tester. It is then a good idea to test the LVC is working as
expected by connecting a charged stock 8.4v battery and switching to Lipo mode
(9v LVC). The propeller should turn as normal until the throttle reaches ~ ¾
and then cut out. Changing the jumper switch should allow the throttle to be
opened up to the max without anything cutting out.

For easy access (and easy removal if required) I located the switch at
the bottom of the plane in the middle of the holes already in the plane
fuselage. It was secured in place by the face plate compressing the foam and is
not going anywhere.

The final part of this mod was to utilize a $5 Lipo battery monitor
(Maxpro from Hobbycity). This monitor fits onto the battery balancing
connector, has a really small current
draw (~ 5mA) and automatically indicates the battery voltage with an LED and beeper
as follows:

-
above
11.0v it’s bright blue

-
between
10.0 and 11.0v it’s blinking blue

-
between
9.8 and 10.0v it’s bright red

-
under
9.8v it’s beeping and blinking red

I located the
battery monitor where the lower ACT sensor used to be, between the battery box
and the holes used to hold the LVC switch. I feed the monitor wires through the
sensor hole to the battery box area. I then marked around the sensor and then used
a hot soldering iron to increase the sensor recess to fit the monitor flush
with the bottom of the fuselage. The monitor was secured with a few drops of CA
glue and some temporary tape to hold it in place while the glue dried. Once
dry, the sensor was covered using clear and then nylon reinforced packing tape
(which helped hide the green circuit board)

I then changed the stock propeller (10×8) for a 10×7 one to reduce the
power draw on the ESC. Many forum entries and the propeller testing on this
site recommend the 10×6 size and being optimal but I was worried I wouldn’t
have enough power for the test flight and so decided to try the 10×7 as a
compromise first.

Finally I re-checked the centre of gravity and confirmed that it had not
measurably moved from the previously marked position.

The final Lipo ready setup looks like this:

Flight Testing with the Lipo …..

The blue light obviously comes on as soon as the balancer plug is
connected. The red light and beeping would continue until the balancer plug is
removed… seems a bit annoying, and I toyed with the idea of putting in another
switch, but when you think about if the voltage is below 10v, you really shouldn’t
just be getting the plane down, you need
to remove the battery to stop the battery drain of the receiver. So annoying is
a good thing. Actually I think the blue light when flying looks really cool,
especially at dusk.

Power. With the stock battery, the throttle started turning the prop at
about 1/3 of the way up and progressively increased the rpm to full throttle. With
the Lipo the propeller started turning earlier at ~1/4 of the way up and the
increasing rpms seemed to top out at about 70% of the way up. No noticeable
increase between 70% to 100% throttle. However there was definitely more
incremental control between 25% and 50%.

50% throttle gave significantly more power than my upgraded 8cell (9.6v)
NiMh battery at full power. I did most of my straight and level flying at ~35%
throttle. Brief wide open throttle got the SuperCub climbing steeply. Cruising
at 70% throttle needed work at keeping the plane level, but I didn’t spend much
time at this speed and didn’t bother trying to trim for it (on my first
flight). I couldn’t say if there was any
noticeable difference in the air between 70% and 100% and there was absolutely
no need to go above 70%.

Rolling and hand launched takeoffs were very easy with the SuperCub
leaping into the air at 70+% throttle. This was noticeably much easier and more
positive. Pulling loops was easy although with NiMh batteries I had never
bothered to reduce throttle after passing over the top. With Lipos, once over
the top with max throttle the plane accelerated like a rocket towards the
ground (luckily I had plenty of height), but this really showed me what the
plane was now capable of once I graduate from my current straight and level style
of flying.

General handling and landings were no difference to normal. The battery
monitor blue light was clearly visible whenever I flew near, even at ~500+
feet.

After two flights and a touch and go circuit for 15+ minutes the blue
light was still on, so I can’t comment on the red light or beeping.

Once home, I checked the battery and it was still at 11.4v, so the
monitor was correct (blue > 11v). Also after charging, the 15+ minute flight
had used only 850mAh of the battery, amazingly only 65% of the 1300mAh rated
capacity. This length of flight would have previously taken me about half way
into my second NiMh batteries. It made me smile as I had taken 2 x 1300 Lipos,
and both my old 7 and 8 cell NiMh batteries to the field, just in case !

This confirmed what I had read, that the Lipo conversion is relatively
easy to complete and pays dividends with additional power AND flight time. I
have already changed the prop down to the recommended 10×6 size for my next
flight which should lower the max power a little (there’s tons to spare so I
don’t see this as an issue) and further increase flight times.

I think the LVC switch of this mod may prove redundant as I can’t see
myself using NiMh out of preference and the 2 Lipos I purchased will be more
that enough for my flying.

PS – You may have noticed my wing strut fastener mod… a bent paperclip
which slots under the battery box door latch. One end is closed and the other
end slightly open like a hook. This makes removing the wings quick and easy
with no need for a screwdriver.

The first graph shows the results for selected 10" props:

The second graph shows the results for selected 11" props against the stock 10×8 prop:

The last chart is an expanded view that shows all tested props at wot using a ThunderPower 2200, 11.1 volts – I would consider this the top limit of what can be powered through the stock ESC and 480 motor (HobbyZone does not certify this setup beyond the 9.6v NiMH; I do not recommend the Lipo setup). A number of Super Cub owners are using an 11.1 volts Lipo reporting no problems:

The Prop Load Factor is a number which shows the load a given prop puts on a motor – it's computed by multiplying the prop's diameter cubed times its pitch (thanks to Lucien Miller of Scorpion for this). All other things being equal, a prop rated at 8000 will require 50% more power than a prop rated at 4000; however, all props are not equal and you may see differences among props with the same diameter/pitch due to their designs.

IMHO there are two clear winners:

 

• GWS 10×6 HD: I use this and it's a nice alternative to the stock 10×8, giving good thrust although at higher rpms; it's not a "power" choice but is more efficient that the stock prop, achieving about 8% more thrust for the same power input at higher watt levels.

   

• E-flite 11×4.7 SF: I have not used this in flight but on paper it's a clear winner – achieving about 8% more thrust for the same power input at higher watt levels.

From an efficiency standpoint – yes. From a power standpoint? Less so. Don't expect to see dramatic improvements – the table below shows the difference is Thrust/Weight Ratios at wot assuming a flying weight of 25 ounces:

The GWS 1060 HD, while more efficient, is rpm limited to a lower thrust level at wot; however, the EFL 1147 SF is not and as such achieves about an 8% higher ratio at substantially the same power as the stock 10×8. However, this will not linearly translate into more speed – increase in speed, increase in drag, more speed to overcome increase in drag, etc.

I found the E-flite SF props to be stiffer than equivalent GWS SF props – this should translate into more effective thrust, as the E-flite props should hold their shapes better than the GWS SFs at high rpms.

Either the GWS 1060 HD or the EFL 1147 SF are good choices to try against the HobbyZone stock 10×8 prop, each for reasons stated above. Overall the E-flite 11×4.7 SF looks like a fine replacement for the stock prop.

Note: The E-flite 11×4.7 SF requires drilling out the hub slightly to fit the 480's shaft and requires a lock washer to keep it from slippng – the hub will not fit over the 480's nut.
The E-flite 10×8 E will fit directly over the 480's nut but will not clear the motor – this requires adding a second nut to the shaft to achieve clearance.

NOTE: This article has been updated to extend the data by using a ThunderPower Extreme 2200 mah 11.1 volt Lipo with the stock HobbyZone ESC.

The Super Cub RTF ships with a brushed 480 motor that is apparently used in other HobbyZone RTFs. I tested one that came with the Super Cub with three props – the "stock" 10×8 that ships with the Super Cub, a GWS HD 10×8 and a GWS SF 11×8 – these three show a wide range of results. The first chart compares Thrust vs RPM:

The second chart compares Total Watts into the motor (I used a laboratory power supply) vs RPM:

The GWS SF 11×8 is power hungry compared to the others – extending the curves, I would think that it will top out at about 4000 rpm with a thrust of about 600 grams – assuming you have the battery to supply the required power and the ESC can tolerate the power load.

UPDATE: The GWS SF 11×8 with the 2200 Lipo topped out at 658 grams thrust, 151 total watts, 4578 rpm.

The stock 10×8 prop is a good fit for the Super Cub – extending the curves, I would think that the stock setup could top out at about 5000 rpm with the thrust hitting about 600 grams, but taking something like 130 watts to hit these numbers.

UPDATE: The stock 10×8 with the 2200 Lipo topped out at 624 grams thrust, 143 total watts, 5189 rpm.

Finally the GWS HD 10×6 shows a very interesting curve – much flatter than the other two. I suspect this prop could rev pretty high and the limit will be where the 480 tops out.

UPDATE: The GWS HD 10×6 with the 2200 Lipo topped out at 566 grams thrust, 105 total watts, 6569 rpm.

UPDATE: The Lipo pushed the motor and ESC pretty hard. Pushing 150 watts is about double the 8.4 volt NiMH pack. A thrust of 600 grams is about 21 ounces – this gives a thrust/weight ratio for the Super Cub of 0.84, greatly transforming the Super Cub's performance characteristics, although with higher stress levels.

A number of Super Cub owners are using a Lipo with the stock motor and ESC without problems, but it is clearly way over spec. I think running WOT for an extended period might not be the most prudent thing to do.

The stock 10×8 prop which for the HobbyZone 480 is a good fit (what did you expect?) for the Super Cub's 480 brushed motor, keeping rpms and power usage at tolerable levels for the ESC. Getting this combo to something like 5000 rpm at something like 120-130 watts should result in a significant and noticeable improvement in flying characteristics, although the increased load on the electronics is out of spec.

I personally like the GWS HD 10×6 as an alternative to the stock 10×8; although not as powerful, it's more efficient and lengthens flight times – a nice prop for high-flying photo missions.

The GWS SF 11×8 is much flatter and looks more like a "power" prop. Using the stock ESC and 8.4 volt battery, this prop will deliver about 10% more thrust for 10% more power compared to the stock 10×8 at WOT.

I set up the Super Cub's receiver and motor on my Home Brew Motor/Prop Tester to test out a number of different propellers using the SuperCub's stock 480 brushed motor. The tests were conducted using the standard 7 cell battery @ 8.4 volts and then with a laboratory power supply.

The props used were to give a range of results, ranging from a 9×4.7 to 11×8 to compare results to the stock Super Cub 10×8 prop.

After this test, I then used a laboratory power supply to hold the voltage constant at 7.90 volts and let the amps float – the results below:

The closest alternative to the stock 10×8 is the GWS SF 10×8; however, the blades are not as rigid as the stock 10×8 and in flight under high stress circumstances may not perform up to the stock prop; I've used the GWS SF 10×8 and not noticed substantially different performance.

The most efficient prop is the GWS HD 10×6 – this will give increased flight times due to its lower power requirements.
I think this one is the best alternative to the stock 10×8 – even though the thrust is a bit lower, it is more robust than the SF props and most likely holds its shape better under stress. It also fits directly over the nut on the 480's shaft – the other SF props require a lock washer to hold them in place.

The GWS SF 10×4.7 is puts up some good numbers on the bench; however, I used this and did find that it does not perform as well as the numbers indicate – for example, I found loops a bit of a struggle from level flight. I think this prop flexes under stress and as a result it's losing pitch, resulting in less power.

If you want more power, then the GWS 11×8 is a nice upgrade. I've used this one also and it does give more power but it will cut into flight times as it needs more power.

Last, I tested the 9×4.7 to show the performance difference – I would not recommend flying this one.

Prop selection is to a large degree based on what you expect out of your Super Cub – if you want longer flight times and good performance, the GWS HD 10×6 looks like good all-around choice. The GWS 11×8 SF is a "power" choice and the GWS HD 10×4.7 could be an interesting one to try out.

Users with the 9.6 volt / Lipo as power sources will show better numbers due to higher power, although without reading amps/volts with a wattmeter, I'd hesistate to guess by how much.

Finally, it's interesting to note that with 400 grams of thrust – 14.1 ounces – the Super Cub's spec thrust to weight ratio is 0.52, about what you'd expect for a trainer.

I would very much appreciate emails from others with experiences with these and other props.

This is a fairly easy mod that almost doubles the Super Cub's flying time. First step is to relocate the receiver and then open up the top of the battery box – I used two balsa strips on which to zip-tie the receiver:

I fashioned a plate for the bottom of the battery box out of 1/16" plywood:

I then made up a new two-prong battery connector using Dean's plugs – VERY IMPORTANT – the batteries MUST be connected in parallel – a series connection will double the voltage and probably fry your receiver; the pic below shows how to wire the batteries in parallel – two reds into one, two blacks into one:

The batteries installed and ready to go – what's nice about this mod is that while the weight is increased by the second battery, the CG is not affected, since the original battery was laid flat and now it's just doubled in volume while in the same location:

I found flight times almost doubled; the extra weight does require about 10% more cruising throttle (60% now vs 50% with one battery). The Super Cub handles the extra weight easily – a tribute to its great design.

NOTE: This is a new site so please consider it a "work in progress". I would greatly encourage readers to send in articles for posting on AmpAviators. In contrast to a forum, finding articles of interest will be TONS easier here.