3 blade prop question

[K.A.R.]

I was thinking of trying a 3 blade prop on my 74" Extremeflight Yak 54 and was hoping to get some opinions.

Here's what I have now:

Motor Hacker A60-20M 170KV
Battery 10s Lipo Flightpower EVO 25 3700mah
Prop 22x10 PT model carbonfiber
auw just over 12 pounds

In flight measurements taken from a Jeti spinbox:
Max amps 53.5
voltage 39.86
RPM 5820
this adds up to 2132 watts in

The plane flies pretty well and has quite a bit of power but doesn't pull out of a hover with a lot of authority. I was wanting just a little more (65-70 amps and around 2500 watts.

So, what would happen if I went with a Mejzlik 3 blade 21x11.5n or 21x12? Would this be too much prop? Would I be better off with a 2 blade 22x12?

What about the narrow vs wide vs electric versions of the Mejzlik props? Is the wide version just better for braking and the electric version just lighter, or is there more to it than that? I did have to bore a hole in the face of my PT model prop to countersink the prop washer cause it was too thick to fit the spinner and hardware on the short shaft, so I assume I would have to do the same to the Mejzlik non-E props and am OK with that.

One last question: would I be better off increasing my voltage to get more power or am I OK with the 10s battery? Is my RPM high enough? I do like to run 2 5s packs cause they're compatible with smaller planes and give me more options.

I don't need a competition level 3D plane, I just want good power and good looks. I'm leaning toward the 3 blade cause I think it would look great. Any opinions are greatly appreciated. I tried motocalc and found it practically useless so I'm looking for real world experience from experts who've been there, done that.

Thanks,

Kevin

[mpope1]

I am running a hacker a60-16s(I think) the highest kv in the s a60 line. Was running a 16x10 master airscrew on a yak 54, flew great but really lacked in the vertical pull out. Switched to a 18x8 apc eprop and I didnt notice much of a difference in power but much better pulling out of a hover. I liked the look of the 3 blader.....

[Ed Lyerly]

Kevin,
I would try the APC-E 22x12W 1st. The APC "W" props pull quite a few more amps than the standard E props (and give a proportinate increase in thrust). If the 22x12W is too much, then try the 21x12W.
Ed

[jrb]

I assume the top speed is fine Kevin?

Then what you need is to spread your available watts over more blade area to get more static/hover thrust: via more blades, wider blades, or diameter!

Going to 12S gives you even more available watts; upping the current amps will too.

Can you afford some more amps out of your 10S pack(s)?

The 21x11.5x3 will perform very similar to a 22.7x11.5 two blader – both give you more blade area! They will consume more amps as well: these two 66amps, 22x12 @ 62, & 21x12 same as your current 22x10.

More diameter (blade area) is what you need not pitch – don’t do the 21x12.

[Ed Lyerly]

Jim,
Yes, he needs more blade area. That is why I recommended the "W" blades. The 22x12 "W" pulls more amps and makes more thrust that the standard 22x12 "E" prop, and the 22x12 "W" is also a more efficient "E" prop. Unfortunately the "W" blade is not available in a 10" pitch ..... or I would have recommended that. Agreed, the 21x12W is not as good a choice as the 22x12W.
Mejzlik also makes a 22x12 W-E prop in CF, expensive, but might be worth a look.
Ed

[3Deranged]

If you notice that pretty much all comptetition 3D planes use 2 blades and IMAC/aerobatic planes tend to favor 3 blades. You really don't need to go fast for 3D moves but you need good vertical and a little more tip speed for IMAC/aerobatics. You usually won't get as good static thrust from 3 blades on a Yak as you will using larger diameter 2 bladers(i.e. bucket cowl). Check out what the big boys setups are and you'll see what I mean. I don't think I've ever seen a 3 blade doing good 3D before. Not that they won't(mileage may vary with pilot) but generally I find on Yaks a big diameter 2 blade gets the nod for 3D. Ed's right, try the Wide props if you want to load up more on the amps and get more static thrust. My 2 cents. Keep 'em flyin'!

[GWRIGHT]

3 blades is the wrong way to go, you loose efficiency, plus you change the speed to thrust ratio for a given input power in the wrong direction. If you have a 22X10 on there now, then you need a 23 or 24 inch prop, with slightly less pitch, assuming you want to consume the same power. I've got quite a lot of time experimenting with various props for 3D on various models from 3 lbs to 16 lbs and everywhere in between. The best example I could list is a 9+ lb plane that did far better on a 24X12 at 1300 watts than it did on a 20X10 at 2000 watts (different cellcounts, but it's pretty amazing when you fly one setup, go down 35% in input power (yes, from 2000 to 1300 watts), and get better pullouts and overall better 3D performance. You want 1St gear, not 5th gear, larger diameter, lower pitch.

[twest]

Three blade props look cool.

Sorry, just an opinion. Never be afraid to try one, I've had good luck in the "40" to "60" sized electrics with them. The big drawback is lack of selection, oh and price.

Larger and/or higher pitch and/or wide two bladed props will be more efficient, but on a scale warbird or aerobatic model, the three blades look fierce.

[Ed Lyerly]

Kevin,
Another thing to view with skepticism is those numbers from your Spin Box. I have found my Spin 75 to be way off on amps. Although your amps seem reasonable, your voltage does not. My experience is that the better (20C-30C rated) lipos hold about 3.7 volts/cell under load (say 50-60 amps) while the 10C-15C rated ones struggle to hold 3.5 volts/cell under load. According to your Spin Box numbers, your cells were holding 3.99 volts (10 cells = 39.9V) @ 53 amps. I think that number is high. If you have an Astro Whattmeter, put it on the system and run it up to check this. If you are running a "Y" on those 5S EVO 25 packs .... and can't get to the main lead, just put it between one pack and the speed control and double the numbers you get. My suspicion is that you are pulling less than 2000 watts (say 1950 -1975).
Ed

[Ed Lyerly]

Gary Wright,
Thanks for your input. I don't know any electric pilot who has done more hovering (and punching out of same) than you :).
Ed


PS ...... here are some larger "E" props from XOAR that have lower pitch. These XOAR props are pretty fragile, but they are light and would rev up quicker .... which would be a good thing for 3D. Atlanta Hobby has them.
Ed

[K.A.R.]

Hey everyone,

Thanks so much for the expert advice.

Ed, you're right about the Jeti spinbox not being very accurate. Mine reads about 3 volts high. I forgot to mention that...shoulda known one of you guys would pick up on that. My overall watt numbers are fairly close though since I have also measured using my very accurate Medusa Research power analyzer and it ranges from 2000-2200 watts.

Maybe I'll take GWRIGHT's advice and try a 24x10. This should give me more efficiency and more power at the same time. Hopefully this will put me somewhere around 70 amps or so. My Evo 25s will deliver plenty of current since they're rated at 92 amps continuous and 185 amp bursts. I really like the PT model carbon fiber props but TBM seems to be out of the 24x10 so I may have to wait a while. I may also consider Mejzlik. Looks like Desert Aircraft carries the Mejzlik in 24x10. I tend to steer clear of the APC props cause they flex so much.

Thanks again everyone for your time. I still may try a 3 blade some day just because they look so good.

Kevin

[3Deranged]

Xoar makes a nice 24 x 10 solid beechwood e-prop too. :) A little easier on the wallet too. A lot of people prefer them over an APC. I love Xoars, they cut out a lot of unwanted cavitation(noise, wasted energy) and seem to perform better in hovers especially. My 2 cent deposit.

[GWRIGHT]

I agree with the 24X10 route, or maybe even a 24X8 first. Be carefull with the large outrunners when you load them up. The motors are fine (especially the A60's), but some ESC's have an issue with timing and you can get the "chatter" many people write about when they throttle up quickly, or be unable to throttle past a certain point without the chatter. You can bypass some of this by increasing the timing (20 to 23 degrees advance is the range to be in), and by decreasing the acceleration,..i.e. the throttle doesn't go from low to high as quickly even when you slam the stick forward,..kinda like if you slowed down a throttle servo. I'm running an A60L on a plane with 12S and a spin99.It's in the high 90's in current on hot packs, and somewhat over 4 kilowatts. On that setup I had to retard the throttle acceleration all the way to 1.7 on the spin (1.7 seconds from idle to full throttle) and timing just over 20 degrees. This is somewhat out of manufacturer's specs (running a 2500 watt motor at >4Kw <G>), but I've had good results with the setup. Took some time to get the acceleration delay and timing right to stop the chatter.

[K.A.R.]

Thanks GWRIGHT,

I actually ordered a 24x8 last night since TBM didn't have the 10. I also ordered a 22x8 for my other motor (Hacker A60-24s) since I have been having trouble with that motor stalling out under load. I contacted Ian from Hacker and told him about my setup and what it was doing and he wants to see the motor, so I'm sending it in for testing. I had the timing set at 24 and it stalled out regardless how much acceleration delay I had. I tried turning the timing down to 20, then 16 and thought I could fly it...then it cut out while taking off and had to put the plane down in a not-so-ideal spot. Some damage. Hoping the motor us faulty cuase the 24s is 5oz lighter and should deliver the power I need. I haven't had any such trouble with the 20M even with only .5 seconds acceleration delay.

[GWRIGHT]

I don't understand the "stalled out" comment. What i've seen is the "chattering" that many discuss with all the larger outrunners. Did you try a much smaller prop? If that eliminates the problem, then it's just too much load for the esc to work with when using that motor. In my last 90" planes, I wanted to use the short motors (24S actually), and at 2kw they could handle the power input fine, however, I couldn't use a large enough prop. I think it was a 20X11 that was as large as I could go (using 10S) before I would encounter the chatterring. Went to the lower KV "M" motor and all was OK. It was a shame to have to use the M motor in that fashion, because that plane would easily go 12 to 15 minutes on 10S/6000's, and land with the motor 3 to 5 degrees warmer than ambient even if I hovered 8 to 10 minutes constant (it wasn't even breaking a sweat), but I wanted the really large prop for thrust and didn't need speed. (22X10 on the lowest KV "M" motor and 10S) It's almost as if you can't overload the large outrunners because the ESC won't allow you to overprop them because they chatter and stutter on throttle up. Various ESC's would allow more or less prop before the chattering on throttle up, but there was still a limit with all.

[bigbobed]

As an experiment, I cut a 16" prop down to 14". It had significantly more pulling power than a standard 14" prop. I attribute that to more blade area.

Jim,
Yes, he needs more blade area. That is why I recommended the "W" blades. The 22x12 "W" pulls more amps and makes more thrust that the standard 22x12 "E" prop, and the 22x12 "W" is also a more efficient "E" prop. Unfortunately the "W" blade is not available in a 10" pitch ..... or I would have recommended that. Agreed, the 21x12W is not as good a choice as the 22x12W.
Mejzlik also makes a 22x12 W-E prop in CF, expensive, but might be worth a look.
Ed

[K.A.R.]

I don't understand the "stalled out" comment. What i've seen is the "chattering" that many discuss with all the larger outrunners. Did you try a much smaller prop?

I've seen what could be described as chatter under heavy load when using the CC85HV and 16s A123 and a 19x8 and a 20x8 APC. But with the 10s lipos and the spin99 it was a definite cut out/stall, or an abrupt end to all acceleration accompanied by a distinct squeal. It might have chattered if I had kept the throttle on but I was real quick to cut the power. Thanks very much for the explanation of your prop/chatter issues. Everything makes more sense now. My motor is probably fine but it's already on the way to Hacker for testing. I will try the 22x8 on the A60-24s when I get it back. I hope it works. It was close enough with the 22x10 that if I ran the battery down just a bit before taking off, It wouldn't cut out during flying.