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Update

Some of the comments are on using larger propellers and one 3-bladed and a 2-bladed, and there is a question on using a spreadsheet for single propellers.

  • The single propeller spreadsheet may be a compilation of experience on using one single propeller. However, you will be driving two propellers.
  • A main selling point for your set-up is elimination of torque. Use one 3-bladed and one 2-bladed propeller, and the difference in drag will re-introduce torque. You have 4 blades in total already, no need to add a 5th or more for any purpose.
  • A larger propeller uses more horsepower than a smaller propeller, and you're driving two propellers. If your engine can drive 2 larger diameter propellers, by all means go ahead.
  • Your vehicle travels at a maximum of 70 km/h, the propellers won't have an issue with attracting enough air.
  • Increasing output RPM would be a good way to increase thrust!

Update

Some of the comments are on using larger propellers and one 3-bladed and a 2-bladed, and there is a question on using a spreadsheet for single propellers.

  • The single propeller spreadsheet may be a compilation of experience on using one single propeller. However, you will be driving two propellers.
  • A main selling point for your set-up is elimination of torque. Use one 3-bladed and one 2-bladed propeller, and the difference in drag will re-introduce torque. You have 4 blades in total already, no need to add a 5th or more for any purpose.
  • A larger propeller uses more horsepower than a smaller propeller, and you're driving two propellers. If your engine can drive 2 larger diameter propellers, by all means go ahead.
  • Your vehicle travels at a maximum of 70 km/h, the propellers won't have an issue with attracting enough air.
  • Increasing output RPM would be a good way to increase thrust!
6 Two 2-bladed
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  • Add this to the velocity triangle and you end up with a blade tip angle of 10°. That equates to a blade pitch of 22 inch for the forward propeller. Select the standard pitch closest to 22 inch (24" ?). The next one up to 22" should be the best choice, because the aft propeller will be pulling in air and add to the free stream velocity.
  • The aft propeller runs the accelerated air from the forward propeller and must have a higher blade pitch than the forward propeller. Select the next available pitch up (28" ?).
  • Naturally, one propeller must be clockwise and one must be counter-clockwise.
  • Both propellers should be 2-bladed. That will result in four blades in total, more than enough for this application. Adding more blades will cost horsepower and not result in any useful thrust increase.
  • Add this to the velocity triangle and you end up with a blade tip angle of 10°. That equates to a blade pitch of 22 inch for the forward propeller. Select the standard pitch closest to 22 inch (24" ?). The next one up to 22" should be the best choice, because the aft propeller will be pulling in air and add to the free stream velocity.
  • The aft propeller runs the accelerated air from the forward propeller and must have a higher blade pitch than the forward propeller. Select the next available pitch up (28" ?).
  • Naturally, one propeller must be clockwise and one must be counter-clockwise.
  • Both propellers should be 2-bladed.
  • Add this to the velocity triangle and you end up with a blade tip angle of 10°. That equates to a blade pitch of 22 inch for the forward propeller. Select the standard pitch closest to 22 inch (24" ?). The next one up to 22" should be the best choice, because the aft propeller will be pulling in air and add to the free stream velocity.
  • The aft propeller runs the accelerated air from the forward propeller and must have a higher blade pitch than the forward propeller. Select the next available pitch up (28" ?).
  • Naturally, one propeller must be clockwise and one must be counter-clockwise.
  • Both propellers should be 2-bladed. That will result in four blades in total, more than enough for this application. Adding more blades will cost horsepower and not result in any useful thrust increase.
5 Both 2-bladed of course
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  • Add this to the velocity triangle and you end up with a blade tip angle of 10°. That equates to a blade pitch of 22 inch for the forward propeller. Select the standard pitch closest to 22 inch (24" ?). The next one up to 22" should be the best choice, because the aft propeller will be pulling in air and add to the free stream velocity.
  • The aft propeller runs the accelerated air from the forward propeller and must have a higher blade pitch than the forward propeller. Select the next available pitch up (28" ?).
  • Naturally, one propeller must be clockwise and one must be counter-clockwise.
  • Both propellers should be 2-bladed.
  • Add this to the velocity triangle and you end up with a blade tip angle of 10°. That equates to a blade pitch of 22 inch for the forward propeller. Select the standard pitch closest to 22 inch (24" ?). The next one up to 22" should be the best choice, because the aft propeller will be pulling in air and add to the free stream velocity.
  • The aft propeller runs the accelerated air from the forward propeller and must have a higher blade pitch than the forward propeller. Select the next available pitch up (28" ?).
  • Naturally, one propeller must be clockwise and one must be counter-clockwise.
  • Add this to the velocity triangle and you end up with a blade tip angle of 10°. That equates to a blade pitch of 22 inch for the forward propeller. Select the standard pitch closest to 22 inch (24" ?). The next one up to 22" should be the best choice, because the aft propeller will be pulling in air and add to the free stream velocity.
  • The aft propeller runs the accelerated air from the forward propeller and must have a higher blade pitch than the forward propeller. Select the next available pitch up (28" ?).
  • Naturally, one propeller must be clockwise and one must be counter-clockwise.
  • Both propellers should be 2-bladed.
4 Account for tip losses.
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