Why Strong Props Suck!

[scott]

I had always used the hobbyzone flexible props until I started reading about how great Master Air Screw and APC props were and how strong they are.

With this in mind I headed down to the LHS and grabbed me a handful of APC props. I like the price of them as well as how aggressive they looked.

I mounted one on my cub a (10x8) and headed out excited to fly my cub with the new cool prop. There was about an 8-10 mph wind that day but nothing I hadn't flown in before.

I'll cut this short- I came in for a landing and caught a little breeze close to the ground and nosed in a little on the landing. The propeller caught on the ground and my cub spun around. My first thought was "That wasn't all that bad of a landing I have had a lot worse and only had minor repairs." When I got up to my cub the entire nose was laying on the ground attached only by the wires from the ESC! WHAT! Upon further inspection I seen that the prop had actually dug into the ground about an inch breaking the nose off at the firewall.

Using cheap feeling flexible props has it's advantages! The parkzone props are wide and rounded on the ends which also make them difficult to dig in. I would rather break a prop than break my entire firewall, motor mount, and motor off. As far as I can tell with a watt meter they are pretty close in performance to the APC's.

[supercubnz]

I have been using APC props 10 x 5 and found that with multiple nose overs, the shaft ends up being bent. But I think APC props seem to provide better thrust/speed, compared to for instance GWS props. I have started using GWS 10 x 6 recently and found take offs are not as quick as with APCs. Will see how GWSs perform with next flights.

[flydiver]

Thrust will depend on the prop. You don't get anything free.
An APC 10x5 thin electric is almost identical in draw and performance to a GWS 10x6, but costs 2-3x more.
These are both 'thin electric/direct drive' props.

The old stock 10x8 is a slow fly as is the new 9x6. Slow fly props have fatter blades, more torque, but eat more amps than a similar sized direct drive.
An APC 9x6 Slow Fly may draw more amps than a 10x5 thin electric. I've never compared them so don't know that for sure.

I did a test with my buddy on his Multiplex MiniMag. We put a bunch of props and tested them while hooked t a wattmeter and an accurate scale. We bench proved that one of the GWS DD gave him MORE thrust at WOT with LESS amp draw than an APC SF. It was a more efficient prop. But, at the field he didn't like to have the throttle set as high to get the effect he wanted so went back to the APC slow fly. He just couldn't get his mind around the idea that 2/3 throttle on an efficient prop could be better than half throttle on a less efficient one (for that application and that motor).
Bench testing is not everything but is certainly an important place to start. Without it you are flying in the dark.

A wattmeter doesn't tell you everything either. You can hook up the right sized square stick and get exactly the same reading you get from a given prop. Of course you'll have no thrust at all, just churning air.
I know some folks like the Master Air Screw but they have been shown to not be very efficient in bench testing in some of the motor test forums. OTOH, the Cub is not a sleek plane and not breaking prop all the time is not a bad thing.

[scott]

Oct 5, 2010 11:15:27 GMT 1 supercubnz said:

I have been using APC props 10 x 5 and found that with multiple nose overs, the shaft ends up being bent. But I think APC props seem to provide better thrust/speed, compared to for instance GWS props. I have started using GWS 10 x 6 recently and found take offs are not as quick as with APCs. Will see how GWSs perform with next flights.

Yes I forgot to mention that too. The prop shafts that come on the Turnigy 35-xx series are pretty thick. I also managed to bend one for the first time using the APC prop.

I like to experiment too much to be using a prop that is so strong to not give any in a light crash and break my plane.

OTOH, the Cub is not a sleek plane and not breaking prop all the time is not a bad thing.

Not sure what you mean by this?

To me it's easier to just replace a prop rather than having to glue a motor mount back on or worse.

[flydiver]

The Master Airscrew props have been popular because they are hard to break. As you found, that force needs to go somewhere.

When I was learning I sometimes went home with charged batteries and a box full of broken props. I though prop savers were a pretty neat deal when I found out about them. I even had one on my Cub. Needed pretty serious bands or it would displace itself in flight and that was with NiMh batteries.

[Silverback]

I thought that the prop and motor size used on the SC was just about out of the range of what you could use reliably with the prop savers?

[flydiver]

As I said, I needed beefy bands and was using NiMh - less power than lipo.
A good prop saver, an excellent fit, and strong latex bands were necessary.
A radical maneuver could displace it if all the above criteria were not met. Terrible racket. Somehow I never broke a cowling, ever. Weird because guys break cowlings all the time.