Rubber Motor lenght / Motor Stick length

banilmd
Member
Member
Posts: 5
Joined: February 11th, 2019, 10:01 am

Rubber Motor lenght / Motor Stick length

Postby banilmd » February 11th, 2019, 10:10 am

Hey all,
This is my first time competing in this event so forgive me if some of the questions I ask have obvious answers. Recently I competed at an invitational, and I saw some teams had a very long motor stick and long rubber motor. From my understanding, the reason for the long motor stick is so that you can decrease the angles of both the wind and stab and therefore reduce the overall drag. As for the longer rubber motor, I assume it is to allow for more turns as the length of the motor does not affect the torque. My question is one, am I understanding what is happening properly, and two how would I go about experimenting with longer motor sticks and rubber motors.
Thank you all very much!

bjt4888
Member
Member
Posts: 392
Joined: June 16th, 2013, 12:35 pm
Division: C
State: MI

Re: Rubber Motor lenght / Motor Stick length

Postby bjt4888 » February 11th, 2019, 12:09 pm

Basil,

Yes, in general, you have one of the benefits of the long motor stick correct. If a longer stick allows a longer tail moment arm (essentially, the distance from the wing TE to the Stab LE), this moves the center of pressure more towards the stabilizer which allows, generally, the CG to be moved more towards the stabilizer which allows a shallower decalage angle (difference between the wing and stab incidence angles). Lower decalage angle will generally reduce drag. Whether this is optimal or not you would have to build and test.

If you want to test longer motor sticks, I would build and try. A difference of at least one inch would probably be significant.

To test longer motors, I would keep thickness actually density in grams per inch) constant and try longer and shorter in two inch increments (loop length) initially. The, of course, try different densities too. Lots of testing is the route to success.

Good luck,

Brian T

banilmd
Member
Member
Posts: 5
Joined: February 11th, 2019, 10:01 am

Re: Rubber Motor lenght / Motor Stick length

Postby banilmd » February 11th, 2019, 2:50 pm

bjt4888 wrote:Basil,

Yes, in general, you have one of the benefits of the long motor stick correct. If a longer stick allows a longer tail moment arm (essentially, the distance from the wing TE to the Stab LE), this moves the center of pressure more towards the stabilizer which allows, generally, the CG to be moved more towards the stabilizer which allows a shallower decalage angle (difference between the wing and stab incidence angles). Lower decalage angle will generally reduce drag. Whether this is optimal or not you would have to build and test.

If you want to test longer motor sticks, I would build and try. A difference of at least one inch would probably be significant.

To test longer motors, I would keep thickness actually density in grams per inch) constant and try longer and shorter in two inch increments (loop length) initially. The, of course, try different densities too. Lots of testing is the route to success.

Good luck,

Brian T


Thank you very much Brian!
So basically i would just go inch by inch testing the longer motor stick. I’m assuming I would have to test with my rubber motor length as well. However by increasing the motor stick length would it throw off any proportion in relation to the tailboom? I am using an unmodified 2019 Freedom Flight kit for reference. Also there must be a point where the CG gets too far back. Would i be able to identify this by stalling, etc. Thank you!

bjt4888
Member
Member
Posts: 392
Joined: June 16th, 2013, 12:35 pm
Division: C
State: MI

Re: Rubber Motor lenght / Motor Stick length

Postby bjt4888 » February 11th, 2019, 4:19 pm

Banil,

The stock FF kit design has a high static stability margin and can accommodate a CG that is further back towards the stab. So, extending the motor stick one or two inches is unlikely to cause stalling issues.

A long motor stick is more prone to bending due to motor tension though, and this is not a good thing. So, the stick needs to be light and very strong.

Motor length and stick length are not related. You’ll want to see the other threads that discuss this. Coach Chuck and I both have comments in these other threads that will be helpful for you to read.

Stick length may have only a small effect on duration, if any. Best to focus on propeller design, pitch and rubber density and length and winding procedures.

Brian T

banilmd
Member
Member
Posts: 5
Joined: February 11th, 2019, 10:01 am

Re: Rubber Motor lenght / Motor Stick length

Postby banilmd » February 12th, 2019, 9:43 pm

bjt4888 wrote:Banil,

The stock FF kit design has a high static stability margin and can accommodate a CG that is further back towards the stab. So, extending the motor stick one or two inches is unlikely to cause stalling issues.

A long motor stick is more prone to bending due to motor tension though, and this is not a good thing. So, the stick needs to be light and very strong.

Motor length and stick length are not related. You’ll want to see the other threads that discuss this. Coach Chuck and I both have comments in these other threads that will be helpful for you to read.

Stick length may have only a small effect on duration, if any. Best to focus on propeller design, pitch and rubber density and length and winding procedures.

Brian T

Thank you very much for the information. After going through this years thread on ikara props and changing the pitch, i have decided that i want to venture into making my own balsa props seeing how too many pitch changes may break the ikara prop. In addition, balsa props usually weigh less. Is there any place where I can find information on how to make the varying styles of hubs, the design of the blades, how to actually make the different types of blades (flaring vs. non-flaring), and the materials that may be necessary? I know that it will come down to matching the prop design / pitch to the rubber, but I am rather confused as to where to start.

jander14indoor
Member
Member
Posts: 1505
Joined: April 30th, 2007, 7:54 am
State: -

Re: Rubber Motor lenght / Motor Stick length

Postby jander14indoor » February 13th, 2019, 5:53 am

INAV, Indoor News and Views, the LONG time newsletter of the hobby/sport.
https://indoornewsandviews.com/
Has all the old newsletters and articles. Many on building props, I'd focus on the ones for Penny Plane props as they are closest to weight and size for SO events.

A general search of the web for Penny Plane build info will also be productive.

Jeff Anderson
Livonia, MI


Return to “Wright Stuff C”

Who is online

Users browsing this forum: No registered users and 1 guest