Hi Howard,
I should have guessed I would find you here.... !8-D

Howard,

It looks like you are using a couple of APC propellers. How it your machine performing. I have measured some propeller performance data for APC props for electrics up to 16" I also have some software to match props, gearboxes, motors and battery packs.

James

James

Howard,

I think that I have a paper on coaxial propellers, I will try to dig it out today.

I'd be interested to compare results with you. I'll be travelling today so I will see if I can find the paper on coaxial propellers tonight.

James

Howard,

I found the name of the paper on the coaxial propellers, unfortunately, I did not keep a copy of the document itself.

Here are the details:
'An Experimental Investigation of Low Speed Single and Dual Rotating Propellers', Ronald Helmut Lorenz, University of Toronto, MSc Thesis, Department of Aerospace Science and Engineering.

I believe that it can be obtained through the library at the following URL: http://cisti-icist.nrc-cnrc.gc.ca/main_e.html

If you would like me to prepare a report for any specific combinations of propeller, motor, cells, please go to my website www.flightsolver.com and select the link for 'database summary' which is grouped with two other links near the top of the page.

I believe your comment that the second propeller should have a higher pitch is correct. The difficulty is determining how much. Another question arises, ie, is it better to have a space between two coaxial propellers.

James

Howard,

I searched through the ~1,900 presolved powertrains generated by the FlightSolver program. These powertrains are generated by the FlightSolver program according to minimum performance criteria and battery and motor current and voltage limits for use with airplanes.

The APC 12x8P and APC 12 x 6E are not in the database, but I have the APC 12 x 8E (tractor) propeller in the database.

I found a presolved powertrain with a APC 12x8E that reached about 4.7 grams/Watt at zero airspeed (ie in a hover). The thrust in a hover is 17 N and the powertrain mass is 0.37 kg (3.7N), so the powetrain can lift its own weight.

The current drawn by the motor in a hover is about 31 Amp which slightly exceeds the battery pack current limit of 30 Amp. Flight time is thus quite low, about 2 minutes.

The complete powertrain is as follows:
propeller: APC 12 x 8E
motor: AXI 2826/12
battery: FlightPower (UK) EVO20 1500 4S1P

I have the complete report generated by FlightSolver in pdf form. I can't figure out how to attach it to this email, however, I will figure it out and send it along in a separate email.

James

Commenting on your post in my forum topic:
What CAD Software did you use for your board? I'm using Eagle and it doesn't have the Sayno or the Fairchild and that's really annoying :(

dear howard,
sorry to ask a question blunt like this but would this blimp be for sale?
jorislaarman@gmail.com

Hi Howard,
did you make any progress with your sparse stereo? I was checking your page for some sample images.
I'm currently trying to implement something pretty similar. Eventually the algorithm is supposed to track features in consecutive frames from one camera but as it doesn't really come at additional efforts i'm currently using it to match features between the frames from a stereo pair.
My current approach is a fixed point implementation of the harris corner detector in connection with a sum of absolute difference matching of some neighborhood around detected features (though normalized cross correlation might be equally fast and more reliable). Though i'm currently using non rectified images (it takes forever to load the distortion tables onto the board) the first results look promising.
I would be glad to hear about your progress and ideas.

Joern