How much is to much???
After a dozen flights on the EF Laser 200 and I was a bit unsure where to go next. Don’t get me wrong, this is a really nice flying plane and the power system is outrageous… 3600 to 4100 watts peak depending on prop is just plane silly… and I love it! The problem is that the manufacturer recommends the motor for 3500 watts and that only for short bursts. I don’t want to abuse the motor so I need to keep a close eye on this. Generally I’d say I need to stay with the smaller of the two props I have run (the 20×10) but of course there’s a compromise to be made.
When I went to purchase a prop I picked up a couple of the recommended sized (a 20×10 and 21×10) and bolted on the 20×10 for the early test flights. After flying the 20×10 for a few flights I was unhappy with the prop due to excess speed and lack of braking. What I needed was a larger diameter prop with less pitch. I had the 21×10, but I’m pretty sure it would still be fast and even though larger diameter props typically add more drag when you decrease throttle I expect it wouldn’t be hugely better. What I really needed was lower pitch. According to my calculations a 22×8 is 3 or 4% less loading than the 21×10 and that big diameter would make a much better brake so I picked up one of those.
Testing with the new prop was very encouraging from a flight perspective. The plane has much better in down line braking with unlimited vertical and reduced top speed. Just what the pilot ordered! Unfortunately, the peak amps hit something around 90A instead of 80 and 4000 plus watts instead of 3600 which means increased risk of frying the motor and less flight time as the battery has to provide more current when you reach for all that pull. At least that’s the expectation based on the telemetry I have from a couple short flights. Now it may be that the short bursts of power won’t really hurt the motor since I will rarely even push it that hard and if I stay out of the throttle the flight times may not be as bad as I think… but it may be wiser to give up a little power (no problem) and probably some of the braking and drop to a 21×8 or maybe even a 20×8.
Now the question becomes, just how much is too much and which Prop to try??? Each time I pick up another Xoar prop it’s a $25-$30 investment and if I swap for cheaper brand prop it may change the whole formula. All props are NOT created equal and the shape and thickness varies between manufacturers so sticking with the Xoar is safest. Besides, I have always enjoyed the Xoar propellers. They seem to perform well and the quality of the wood and finish is top notch. So what to do next??
What I’ve decided is to go back to the 22×8 and fly some more flights paying strict attention to battery life and trying to moderate my throttle through a set flight routine. Probably will go up and fly the basic IMAC routine through two sequences and try to use only the throttle necessary to present the maneuvers properly. Then I’ll land and check the battery levels and watch my temps on the speed controller and battery. After a couple flights I should have an idea whether the prop will work or if I need to move down a little… or a lot! As long as I don’t let the smoke out it should give me the info to pick the right alternative.
Another thought… If I do decide that I need to downsize a bit I could always order a 20×8 and simply trim the 22×8 down to a 21×8!!! Then I could compare both options. I’ve done a prop “trim” like this before to get the exact prop I want and with a little care and proper balancing it can work out well.
I once had a gas motor that really needed a 17×6 wide blade APC to perform the way I wanted. Unfortunately they only made 16×6 and 18×6 in wide blades so… a bit of grinding and voila.. the worlds only APC 17×6 wide blade. I ran that prop for a couple seasons and it was exactly what I wanted on that plane.
If I go that way and the 21×8 “special” works well I can always order a 21×8 PJN factory standard with some confidence and just keep the special as a spare. If it’s still a bit to much I can just move on to the 20×8 which is even less load than the 20×10 I’m currently running so I’m sure will give me longer flight times and protect the motor and speed controller… At least I’d only be buying one additional prop!
Wish me luck. Hoping to get the test flights in tomorrow on the 22×8. Praying for smoke free day!!