Author Topic: Re: Prop selection revisited (Read 3854 times)

William DeMauro · « **on:** March 20, 2009, 12:58:30 PM »

Speaking of RC Dude has anyone tried any of the xoar props yet?

Mark Scarborough · « **Reply #1 on:** March 20, 2009, 01:23:59 PM »

William,
I have a selection of Xoar props,, from 12x4 electric and glow,, through a 13x6 glow. I have snow on the ground still so have nt been able to fly them yet. I have talked to and read articles by people using them and they sound VERY promising. I know that Crist has some he plans on trying. I think he has done some testing on the ground. The magazine article I read tested them head to head with the APC electric 12x6 and the Xoar drew less amps for the same rpm, produced more thrust and flew the airplane with better authority.
I hope in the next two weeks to get some flight time on my electric ship and try some of these out. They are a beautifull peice of work! the finish on them is better than any wood prop I have ever seen, ( excepting one that has been customized by the user perhaps)
there is another source of props too, wood,, they are called Vess and its the sports series, very well done props,, I will be testing them as well.

Alan Hahn · « **Reply #2 on:** March 20, 2009, 03:20:48 PM »

Quote from: Mark Scarborough on March 20, 2009, 01:23:59 PM

William,
I have a selection of Xoar props,, from 12x4 electric and glow,, through a 13x6 glow. I have snow on the ground still so have nt been able to fly them yet. I have talked to and read articles by people using them and they sound VERY promising. I know that Crist has some he plans on trying. I think he has done some testing on the ground. The magazine article I read tested them head to head with the APC electric 12x6 and the Xoar drew less amps for the same rpm, produced more thrust and flew the airplane with better authority.
.....<snip>

Hmm, did they recharge the battery during the flight too??

Somehow I doubt this, and for the following reasons:

1) The thrust was probably measured statically, so it probably doesn't have a lot of relevance to actually flying.
2) The lower Amps was probably due to lower effective pitch could give rise to the higher static thrust at full throttle (more rpm too I bet!).
3) Flying with greater authority?? Probably flying a 3D like plane (which does approximate flying at zero airspeed), so the lower pitch (probably) and higher rpm did give him more zero airspeed authority.

Now I could be wrong, but most of the stuff you read about props is basically garbage. On the other hand if Crist tells me he flies the pattern with 10% less battery juice with the same lap speed and with the same vertical "authority", then I'll line up to buy some too!!

William DeMauro · « **Reply #3 on:** March 20, 2009, 04:42:49 PM »

I think I will wait for a few reports on all these props,but will keep an open mind, I have enough "firsts" going on already with this plane,and don't need to add another to the mix. I still haven't even tried out the 12x6 EP prop I bought for my Cardinal.

Dean Pappas · « **Reply #4 on:** March 20, 2009, 05:04:31 PM »

Hi Guys,
I split this one off. Seems too good to hide under an unrelated name.
Alan has an excellent point, static tests are useless for anything other than hovering your Bi-Slob.
Dean P.

Mike Anderson · « **Reply #5 on:** March 20, 2009, 08:12:36 PM »

Also, if the voltage is the same, and the amps are the same, the RPM can't be greater. If rpm is greater, amps must be lower. (This doesn't mean the prop is better or worse - just that the load line can't have zero slope).

Mark Scarborough · « **Reply #6 on:** March 20, 2009, 08:19:15 PM »

Static tests are valid for SOME comparisons. I agree you cant look at a static test and conclusively prove or disprove anything. However, when you run a static test, and the current draw is less, the thrust is higher, and the rpms are the same dontcha think you can gain some insight from that? mostly about the efficiency. I do,, if you dont thats fine,, now as for the rest of my comments, a note about my comments about in flight comparisons. they were NOT doing 3D hover flying, it compared the acceleration and vertical performance as well as level flight speed. I will try to find the article and I can be more explicit then.
Some hands on observations, the blades are thinner,, and have a spectacular finish on them. ( compared to any other wood prop available) the blades are more rigid and resist tip flex more than the APC electric. Most if not all prop comparisons are subjective and are strictly valid as a point of reference and until you bolt the thing on YOUR setup and fly it, you really don't know
while I agree that some thoughtfull observation is appropriate, I think that until some flights are put on them, it would benefit us all to remain open minded about them and resist the skepticism.
I am pretty optimistic about them, but then I have talked to people that fly them on electrics,, granted they are RC and I have about 15 or 16 of them different sizes in my hands so its easier for me to have a feel for how well they are made.
I will let you know what I find out when I manage to fly them, Hopefully within the next couple weeks.

Alan Hahn · « **Reply #7 on:** March 20, 2009, 09:01:31 PM »

Mark,
I'm open minded and skeptical!

However it is important to measure the actual application. Comparing static thrusts of props with purportedly the same pitch means very little. As I mentioned on some other thread, I see major differences between the APC 12-6 tractor and pusher props at the same rpm which made the pusher basically unflyable (for me at the tractor rpm). I was hoping to do a blind test of whether CCW and CW rotation makes a "real" difference by letting a friend fly and not tell him which prop it was, but because of the pitch difference, I gave up. (This doesn't mean that CCW or CW is better, but my blind test couldn't be done--at least not easily by simply replacing the prop. I haven't noticed a big difference when I replace a broken tractor 12-6 APC with another identical prop so my guess is that it must be something in the molds. I am a great believer in blind testing where you truly don't know what's what!

For example, I was reading a recent article on Pattern batteries in Model Aviation (I think). I don't dispute the general findings of the author, but I do dispute comments like "battery x seems to have more ...." especially since the observations aren't made in a blind manner (the author knows which pack he is flying with) and what his discharge graphs look like.

On a similar note, there is so little data on what we do, it is worthwhile to be skeptical about the latest greatest things--especially when the same guy had 180 degree opposite comments a few years back. I am sure that we all believe what we write (I know I do), but without real data (like numbers) it doesn't mean much to me. When I read---"airspeed stays constant during maneuvers...." (or something similar in a recent thread here on SH) referring to a PA flight, I lose a lot of belief in the author's point. I don't think any of us fly at a constant airspeed. The physics just isn't there.

So like I said, if someone shows me that input power drops but the flight still holds together, then I will really be interested.

Dennis Toth · « **Reply #8 on:** March 22, 2009, 01:00:34 PM »

Guys,

This prop sounds interesting and I agree that the only way to determine if it works for you is to try one for a few flights. You may have to adjust rpm to get the prop to its best working range. Some props that are dogs at low rpm come alive at 500 rpm more. This is particularly true of narrow thin blades with flat back airfoils. So if it seems like a dog move the rpm and once the prop is happy adjust the line Length to get the lap time were you feel confortable.

On the static thrust, I believe for stunt the one thing this shows if how quickly it can re-accelerate the plane after a corner. As we go through a corner even if it is very smooth (and big) the ship will slow some. Our electrics react fast to the increase in load and hold the rpm but the prop then needs to bit and pull the ship. If the prop has high static thrust to me it indicates it bits. For light ships it is less important but if you have a bit of extra paint on it or maple hard balsa then you will see the difference between props after a corner.

I think we keep and open mind and see what results Mark and William get.

Best, Dennis

Dennis Adamisin · « **Reply #9 on:** March 22, 2009, 10:30:42 PM »

Yup, what StuntGuy-Dennis said.

One more factoid - as Unca Deano has pointed out the inertia means a lot to power spikes too weight & inertia of props comes into play. MA-gas stple props, APC-Gas props and even certain wood types are just too durned heavy and/or have a lot of weight out in the blades adding inertia to the aerodynamic loading on the prop.

Ain't no substitute for flying and "measuring" results.

William DeMauro · « **Reply #10 on:** March 23, 2009, 09:47:49 AM »

Actually, I'm with you guys, I'm going to wait to see what results Mark and Crist come up with,especially in the 12x5,12x6,12x7 range. Then if it looks promising, I will get a few and give them a try. I will keep an open mind and also realize that what works on their planes may not work on mine and vice-versa.

Crist Rigotti · « **Reply #11 on:** March 23, 2009, 11:11:47 AM »

Fellas,
I'll post what I come up with. I'll only compare the APCE 12x6 with the Xoar 12x6. Apples to apples so to speak. I wish APCE had a 5 pitch to compare with Xoar. One thing for sure, the Xoar props are lighter than an APCE equivalent.

Alan Hahn · « **Reply #12 on:** March 23, 2009, 12:25:36 PM »

Does anyone have a picture of the 12" XOAR next to the APC 12-6 E. I'm just curious how it appears size wise (blade width mainly) to the APC that I am familiar with.

Mark Scarborough · « **Reply #13 on:** March 23, 2009, 12:42:43 PM »

Alan, I dont have one here at work, but I will try to take one tonight when I get home.

Crist Rigotti · « **Reply #14 on:** March 23, 2009, 01:24:10 PM »

The 2 props appear to be identical in blade shape.

William DeMauro · « **Reply #15 on:** March 23, 2009, 05:17:30 PM »

Crist,
Thanks in advance cause I am looking forward to those results. As far as the other 2 sizes it more of a curiosity thing to see how the perform.
William

Crist Rigotti · « **Reply #16 on:** March 23, 2009, 05:54:12 PM »

Here are some pics of an APCE and an Xoar 12x6 props.

Alan Hahn · « **Reply #17 on:** March 23, 2009, 07:00:25 PM »

Well it looks like someone avoided R&D costs!

It will be interesting to see how the XOAR works out. My guess is that it won't be a lot different than the APC--probably some "effective" pitch differences, but that's fixed by rpm tweaks.

Crist Rigotti · « **Reply #18 on:** March 23, 2009, 07:13:38 PM »

I agree Alan, there won't be much difference. Now the weight is 25% lighter (or 33% heavier)....that's where the most difference will be. It will be able accelerate quicker than the "heavier" APCE. Of course the overall weight of the plane will be about 1/4 ounce lighter too. Free lightness! I think the Xoar props seem stiffer too (more efficient?). I'll come up with a Deflect-O-Meter to measure them.

Alan Hahn · « **Reply #19 on:** March 23, 2009, 07:19:05 PM »

Crist,

Well I am not big into angular acceleration---after all, my rpm stays constant (acceleration=0!). Actually a "flywheel" effect minimizes rpm losses in fast maneuvers, so for constant rpm running, heavier is actually better.

It will make a small difference in the gyroscopic effect--but these electric props are so light compared to props like the ubiquitous APC 12.25x3.25, I doubt that it matters a whole lot.

I am just amazed that they can cut that wood so thin!

Crist Rigotti · « **Reply #20 on:** March 23, 2009, 07:39:49 PM »

Alan,
If heavier is better, try this APC 12x6 and let us know how it works out:

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LX1566&P=ML

Alan Hahn · « **Reply #21 on:** March 23, 2009, 07:46:37 PM »

Quote from: Crist Rigotti on March 23, 2009, 07:39:49 PM

Alan,
If heavier is better, try this APC 12x6 and let us know how it works out:

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LX1566&P=ML

well if you want your car engine to run smoothly, do you use a flywheel or not?

I think a lot of us don't understand basic kinematics!

We are not accelerating propellers (which means rpm changing).

Crist Rigotti · « **Reply #22 on:** March 23, 2009, 08:05:31 PM »

Alan,
So you are saying that in the fixed rpm mode there is absolutely no rpm change to the motor/propellor? Even when I hit a hard corner?

Mark Scarborough · « **Reply #23 on:** March 23, 2009, 08:34:10 PM »

Alan,
please remember its not just about the propellor, and rpm change, its about the airframe slowing down when you manuever and needing to reaccelerate it.

Dennis Adamisin · « **Reply #24 on:** March 23, 2009, 09:36:10 PM »

Remember our prize is control of acceleration & braking - I think it is hard to make a case for flywheel (high inertia but slower response) AND active feedback loop control (fast modulation) - they are counter-productive.

The only other concern for the Xoar is the stability & consistancy of the media (wood) versus molded composite. The proof is in the flying and campaigning over a season.

BTW I'm surprised no one has mentioned the electric 3-BLADE Xoars that look mighty impressive too!

Crist Rigotti · « **Reply #25 on:** March 23, 2009, 09:54:42 PM »

Dennis,
I missed they offered 3 blades! Hmm..........

Mark Scarborough · « **Reply #26 on:** March 23, 2009, 10:22:20 PM »

I saw them, but the last time I looked they didnt have anything that worked for my power system at least,,
Hopefully with the finish they have on these props it will help to mitigate changes in the pitch at least from moiture absorbtion

Dennis Adamisin · « **Reply #27 on:** March 23, 2009, 11:07:05 PM »

Xoar lists the 3 blade electric series starting at 10" diameter with .5" pitch increments up to a 7" or 8" pitch.

http://www.xoarintl.com/props/ma/PJI-E.html

Xoar claims a 2-cote finish - which should be pretty good. My worry is whether even their NC milling can cope with wood reshaping itself after they start carving it to shape and the wood starts unstressing. OK so I worry too much!

Alan Hahn · « **Reply #28 on:** March 24, 2009, 07:39:58 AM »

3 blades sounds very interesting.

Now back to physics 101---Sum of all Forces = mass*acceleration, or the torque equivalent, sum of all torques=I*angular acceleration. I is just the moment of inertia (proportional to the mass of the prop in our case).

Now at any given time the last equation can be expressed as

Torque(motor)-Torque(load)=I*ang_acceleration.

Now our governor is trying very hard to keep rpm constant, and according to my data recorder, doing a pretty good job of it--I don't see any correlation of rpm glitches with hard corners, at least on the time scale of 0.1 s recording intervals. So basically the angular acceleration (which is the change of rpm divided by the time interval it is changing) is really close to zero. So the impact of the mass of the prop (in "I") is close to zero (identically zero if there were absolutely no rpm change).

So when the load changes, like in a corner, or in the climb as airspeed drop, the motor current goes up, increasing the motor torque, exactly balancing the increasing prop load. So as long as the rpm stays constant, the prop mass is basically irrelevant. This is for our stunt mode where we run constant rpm. There are other flying modes---carrier comes to mind, where in the slow speed, you can need quick applications of power--which increase the rpm, where the prop mass may be important. I am not sure how much it matters there.

So to recapitulate-there is no problem with using a lighter prop, but there is also no big advantage either, at least as it pertains to rpm control in stunt!

Now I will shut up!

John Cralley · « **Reply #29 on:** March 24, 2009, 07:59:16 AM »

Alan or anyone else,

I have been running 10/6 or 10/5 APC E or Master Airscrew E props on my Ringmasters. If I wanted to switch to 3 bladed props, what would be the approximate equivalent in a 3 blade prop? I see a ground clearance (less grass mowing LOL) advantage to using a 3 or 4 blade prop.

Alan Hahn · « **Reply #30 on:** March 24, 2009, 08:01:44 AM »

Just looked at the 3 blade XOAR--it does look a bit different in blade profile to the 2 blade version. Does anyone know where you can buy one of these--I see RC Dude carries the two blade versions (I must say that the APC are cheaper!), but he doesn't seem to have 3 blade versions--unless I missed it somewhere.

Mark Scarborough · « **Reply #31 on:** March 24, 2009, 08:35:47 AM »

don't think the three blades have hit the market yet, my source shows them as "coming soon"

as for propeller mass, there is another HUGE factor that is being ignored here, that being gyroscopic precession. the more mass you are rotating, the higher the higher the induced yaw on corners becomes. This is a very significant factor in successfully flying our craft through the pattern. in this case it cannot be disputed that lighter is better.

Alan Hahn · « **Reply #32 on:** March 24, 2009, 10:43:27 AM »

Quote from: Mark Scarborough on March 24, 2009, 08:35:47 AM

don't think the three blades have hit the market yet, my source shows them as "coming soon"

as for propeller mass, there is another HUGE factor that is being ignored here, that being gyroscopic precession. the more mass you are rotating, the higher the higher the induced yaw on corners becomes. This is a very significant factor in successfully flying our craft through the pattern. in this case it cannot be disputed that lighter is better.

Mark (no rant on or off

)

If you look at my post up above, I specifically mentioned that point of gyroscopic precession--so I wasn't ignoring it. However I dismissed it, at least with regard to the APC Thin Electrics props, since we already use much heavier props--the APC 12.25 x3.75 for one, in glow stunt applications without major gyroscopic effects (not everyone uses a Rabe rudder).

To be honest, nothing is full on/off---there are always gradations of effects. My claim is that where we are starting from (APC Thin Electric) so we are already pretty light and in addition we are not flying 3D RC where you might want the extra capability (~30% if I remember Crist's weights correctly) to quickly increase prop rpm (aka prop angular acceleration) that the XOAR might provide. However you also need to include in the moment of inertia of the outrunner shell which is also rotating--but I am guessing the small radius of the shell compared to the prop minimizes its addition even though it is pretty heavy (moment of inertia goes as mass * square of radius). Maybe it is worth a calculation though!

I am also interested in hearing how these XOAR props work for people. I'm curious if they are worth the extra cost or not. They sure look prettier. I really have been wanting a 3 blade APC electric prop since I am out of ground clearance as is.

I am thinking about doing what Crist did last year--cutting down an APC 13" prop to 12", mainly to get the wider blade. I am not sure how the efficiency will go, or whether the prop authority (delta_thrust/delta_airspeed at fixed rpm) will be better. I am guessing the efficiency will drop and authority will go up.

Dean Pappas · « **Reply #33 on:** March 26, 2009, 09:59:38 PM »

Hi Alan,
I know we disagree, but I still say that lighter is better, though the airfoil thickness of wooden blades may negate the advantages due to lightness.
Flywheels resist the tiny transient RPM changes which signal the ESC to change the POWER applied to the prop.
We want more power to be briefly applied at the moment the corner creates extra induced drag.
better resolution data-loggers are needed.

later, Dean

Mark Scarborough · « **Reply #34 on:** March 26, 2009, 10:13:11 PM »

Dean,
just a FWIW, the XOAR props I have been harping about have very comparable blade thickness to the APC props, they are very similar

Dennis Toth · « **Reply #35 on:** March 27, 2009, 09:24:05 AM »

Guys,

Building on Deans last statement about needing a momentary boost in power (and rpm) can we adjust the ESC gain to produce a slight over shoot in responce to load give the momentary pop in rpm ?

Best, Dennis

Alan Hahn · « **Reply #36 on:** March 27, 2009, 09:51:27 AM »

Quote from: stuntguy13 on March 27, 2009, 09:24:05 AM

Guys,

Building on Deans last statement about needing a momentary boost in power (and rpm) can we adjust the ESC gain to produce a slight over shoot in responce to load give the momentary pop in rpm ?

Best, Dennis

Didn't we go through this a while ago? The problem with trying to boost the gain and get an overshoot is that the overshoot is probably followed quickly by an undershoot. Maybe there would be a gain, but you really do need more than a 0.1 s burst, because the plane is losing speed during the climbing part of the maneuver too.

If you go back to 4-2-4 "glow lore"

, a perfect run was when the motor would just break into the 2 stroke near the top of the maneuvers. Actually that's where I find (from my data) the airspeed just about the lowest (actually ~45 degrees up), and where the prop load should be the biggest. Sort of implies it is the engine load that causes the break and not the leaner mixture,---but hey, this is electric and we shouldn't get into a 4-2-4 battle here!!

Author Topic: Re: Prop selection revisited (Read 3854 times)

Alan Hahn

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