Hi All,

A discussion regarding different propeller types was"hijacking" the JAS Integral thread, so I have started this thread to continue the discussion.

To recap / provide context -
- APC has a substantial amount of information on their website regarding prop design, testing, evaluation, etc.
- APC has a long history of proactively and continually revising/improving their propellers based on new science and field testing.
- APC has focused on an injection molding production process to provide very high quality, high performance propellers at a reasonable price.
- APC has produced propellers using carbon materials, but this has been very limited (to date) due to the substantial increase in production time and end cost to the user, and anticipated limited number of consumers.

Most would recognize the APC-E line of props as the most often used electric prop and certainly it is the most comprehensive line of props for electrics. In recent years, electric power systems have rapidly grown in peak power levels, and the stresses on props increases as well. As noted in the prior thread, there have been some motor/structural failures in pattern planes that were using APC props. Post mortem is often not possible to positively identify the nature of the failure and the contributing factors - which can be very complex when evaluating resonant frequencies of individual components and systems as a whole, especially when considering the wide variety of airframes, mounting methods, motors, props, and RPM combinations.

My history of testing/tweaking/conversing with APC regarding propellers for pattern applications began in the late 1980s when they sent out test samples of their initial propellers for the pattern market (I believe all NSRCA VPs received test propellers at that time). With the recent discussions about stronger propellers being needed for greater safety and/or improved performance, I exchanged some email with APC. APC does not monitor web forums, but is interested (as always) in feedback, and are currently evaluating several data sets regarding high power electric applications, and design/material improvements for future offering. From the CF laminating of APCs I've done in the past year (which APC has seen), APC has reviewed test data and (with an increase in weight of ~10%) can increase the torsional stiffness of the E props. Thoughts regarding, for example, a 20.5x14 weighing ~115 grams instead of 105 grams?

I have no financial interest in APC. However, I (and APC) am interested in gathering data for APC (to be compiled by me) for the purpose of improving APC props, which should provide a benefit to all us.

To that end goal, there are two types of data groups I can see that would be beneficial to have -
1. Any application (pattern or similar) in which an APC is not the best performing prop.
2. Any application (pattern or similar) in which a problem has occurred - structural failure of plane or prop, resonance, unusual noise(s) on ground or in air.

The more data, the better, including-
Prop(s) used
Age / number of flights on prop
Range of operating RPM
Motor
Mounting method
Prop mounting (threaded shaft, thrust collett, etc)
Spinner?
Fuselage construction
Logging data (ESC, Eagletree) or telemetry or timing/radar gun
Maneuver being performed

The intent here is to gather data (post to this thread, or PM to me), and find out what improvements can be made.

Jeff / Brenner, Certainly you know more than I from engineering/process/production perspectives, please feel free to jump in.

Regards,

Dave Lockhart

Do 3-blade props offer better down line breaking than 2-blade props?

Without going into details, it depends. Primarily, the braking is increased as the area of the prop blades increases, and in most cases, a 3 blade prop of similar load to a 2 blade prop will have more blade area and yield a slower downline.

Regards,

Dave

Man that's interesting. Dave have you ever experimented with 3 or 4 blade props E. props? If not why? Thanks, Mike

Mike,

There are not a whole lot of 3/4 blade props out there that I am aware of for E (not that you couldn't use a glow 3/4 blade).

With glow, the practical options for increasing downline braking are limited, and extra blades can be quite effective at increasing downline braking - but - it comes at the expense of efficiency. For a given amount of input power, less speed and thrust will be generated (assuming all other design parameters of the prop are equal) - quite simply, 1 big wing is more efficient that 2 or more smaller ones. Some of the speed/pylon guys use a counterbalanced 1 blade prop seeking maximum efficiency and speed, but for most applications, the small increase in efficiency is not worth the hassles (ground clearance, balance, lack of 1 bladed hubs, props, etc).

With glow, less efficiency at the prop generally means running higher throttle more often, and consuming a little more fuel (no big deal, assuming top speed and thrust were more than needed with the 2 blade setup).

With electric, less efficiency means using more amps......generating more heat....and increasing the load on the whole system - not a problem if accounted for in the setup, but it will still be less efficient (which generally translates to more weight and/or shorter lifecycle on the batteries). With electric, there is the option of using the brake on the ESC to control downline speeds, and this does not compromise the choice of prop for best speed / thrust. If the downline speed can not be slowed enough with the ESC brake, then revisiting the propeller is in order, but I've yet to see an electric that responded better with a 3 blade higher pitch prop than a flatter 2 blade prop. Granted I've done very little running of 3 blades on the electrics, but I don't plan to until I think electric is at the point where adding load to the system will have negligible effect on the longevity of the batteries.

Regards,

Dave

Thanks Dave.

Hello Dave,

What is the advantage or the concept behind the WPN props vs the regular pattern prop?

Thanks

Alejandro

Hi Alejandro,

The first "PN" props I saw were used the 18x10PN by Chip at the 2003 US Team Trials. He had a newer YS DZ in his Double Vision bipe, and the goal of the prop was max thrust for the weight and drag of the bipe. The prop did pull quite well, but it was louder than the scimitar shaped regular pattern props. As motors got stronger, the 11 pitch versions showed up, and the WPN was to hold down RPM and increase downline braking. I've not run the WPN back to back with the 18.1x11 or 18.1x12 for sometime, but I recall the 18.1 stuff being quieter in the air. I know Adrian Wong in the US and some of the Asians were running modified WPN props, but I don't know the details.

Regards,

Dave

Good info, thanks.

Alejandro

Dave, do the data logging ESC's provide enough information for your needs? I would like to try a couple of props and send you the data. I'm hearing that XOAR props are performing pretty well and would like to try and compare both.

Joe,

I've used the Castle ICE ESCs on smaller stuff, and they correlate extremely well with Eagletree logging, and are sufficient for purposes of prop evaluations. I've not run any other logging ESCs, but have seen some data that did not appear to be accurate in terms of ground RPM / amps compared to in air RPM / amps.

Regards,

Dave

Thanks. I might check out one of those Eagle Tree loggers. I'm between that and holding out 'til next Spring to see if there is an upgrade to the HV85. In relation to the other thread, I'm going with a bigger power system in my plane and would like to consolidate as much as possible.

I'm really curious how the data works to draw comparisons. I'm personally interested in the affect that the shape of the tip has on performance, and how that turns up as logged data.

I just heard from Castle Creations production manager that they are just running their first production run of an HV Phoenix ICE controller! It is their HV ESC with full programming and data logging capabilities. Can't wait to get one.