Wright Stuff C

[bjt4888]

Klast,

If you cut the blade shape at about a 30 degree angle from a standard “party plastic cup”, which is about 4.5” tall with a diameter at the rim of about 3 7/8”, you should have usable pitch distribution.

As the rules this year will produce an airplane that will need to fly relatively fast (high wing loading; meaning relatively heavy for the flying surface area), I am thinking that a modified version of the Ikara flaring prop would be a better choice than plastic cup blades. Plastic cup blades are pretty flexible unless supported by a longish spar.

Brian T

[klastyioer]

Klast,

If you cut the blade shape at about a 30 degree angle from a standard “party plastic cup”, which is about 4.5” tall with a diameter at the rim of about 3 7/8”, you should have usable pitch distribution.

As the rules this year will produce an airplane that will need to fly relatively fast (high wing loading; meaning relatively heavy for the flying surface area), I am thinking that a modified version of the Ikara flaring prop would be a better choice than plastic cup blades. Plastic cup blades are pretty flexible unless supported by a longish spar.

Brian T

gotcha! thanks so much. ps we were trying to make props from the water bottles that are pretty tall and look like the smart water water bottles so the degree angle will be a bit different. plus plastic party solo cups have ridges which arent ideal for this experiment. we have both resources and materials to make our own propellors as well as ikara flaring props so we should be all good to go this year. we are just trying some things out until game time to test our ideas out.

thanks for the help again,

katie

[bjt4888]

Katie,

Actually, as a water bottle has a smaller diameter than a solo drink cup, the angle would need to be greater in order to produce a prop blade with close to helical pitch. There is a spreadsheet tool that a number of us use that employs an “ordinary least squares” regression model to find the optimal angle on any particular diameter cylinder to produce a blade pitch distribution, for a particular target propeller pitch, that most closely approximates helical. 30 degrees is pretty close for a solo cup because it tapers from rim to base. 30 degrees is also pretty close for a typical 2.5” diameter water bottle.

Brian T

[bjt4888]

Katie,

Sorry, I’m going to correct myself. I was trying to do the process in my head. I put the 2.5” water bottle diameter into the spreadsheet along with a 9.4” diameter prop and a target pitch of 15” and the best angle To
cut the blade from the bottle is 17 degrees. This angle of cut from the bottle will produce a pretty close to helical pitch when the blade is mounted on the prop spar to produce a 15” pitch as measured at the 3” radius.

Brian T

[klastyioer]

Katie,

Sorry, I’m going to correct myself. I was trying to do the process in my head. I put the 2.5” water bottle diameter into the spreadsheet along with a 9.4” diameter prop and a target pitch of 15” and the best angle To
cut the blade from the bottle is 17 degrees. This angle of cut from the bottle will produce a pretty close to helical pitch when the blade is mounted on the prop spar to produce a 15” pitch as measured at the 3” radius.

Brian T

so i would take the bottle and cut the blades out at a 17 degree angle? im not sure what the aprox. diameter of the prop is though, could you emphasize on that and maybe even share the spreadsheet with me?

[klastyioer]

Katie,

Sorry, I’m going to correct myself. I was trying to do the process in my head. I put the 2.5” water bottle diameter into the spreadsheet along with a 9.4” diameter prop and a target pitch of 15” and the best angle To
cut the blade from the bottle is 17 degrees. This angle of cut from the bottle will produce a pretty close to helical pitch when the blade is mounted on the prop spar to produce a 15” pitch as measured at the 3” radius.

Brian T

so i would take the bottle and cut the blades out at a 17 degree angle? im not sure what the aprox. diameter of the prop is though, could you emphasize on that and maybe even share the spreadsheet with me?

and the water bottles that we usually use are around 2.75" or 7 cm in diameter, should i just lower the angle to 16 degrees or would i get away with 17?

[noah.blome21]

I am just wondering what flight times other people are getting?

[bjt4888]

Katie,

18 degrees angle of blade on the 2.75” dia. bottle. 15” pitch as measured at 2.7” prop radius now.

As I’m sure you realize, a pitch of 15” is a reasonable starting point for initial testing. Try more pitch than this and less. Less will probably match to thinner (lower density) rubber and more pitch will probably need thicker rubber.

The spreadsheet I am using was developed by an international class F1D flier.

Brian T

[bjt4888]

Katie,

Sorry, l missed your two questions above. Yes, the blade is cut at an18 degree angle from the bottle. See the picture of a propeller blade angled on a cylinder in Jeff Anderson’s attachment.

I don’t believe that forum has the capability to share documents like the spreadsheet.

Brian T

[FermiGod]

Been a while since I’ve been here lol. Is it necessary to color in the wing black or can we just leave it without coloring it in? Also what do you guys think mostly invitational scores will be raw time?