One detail is missing from your description. Do you use a 1 gram dummy for the other half of the motor when you do half motor tests? I would guess that you do - just making sure. Otherwise what you are describing is a good technique.
As far as the full motor having more torque - that's not the problem. The problem is that the full motor will deliver high torque for twice as long as a half motor. So if your model is about to act ugly on full torque on a half motor, there's an even better chance that something bad will happen on the full motor. For instance your model might be beginning to power stall on the partial motor, but will not actually stall because the torque is dropping off. On the full motor this same trim might result in a full blown stall and ruined flight. Another possibility that I am very familiar with is the outboard wing might be beginning to washout on the partial motor flight but the torque will drop fast enough that the model will recover. The full motor will just keep pulling until the model does a death spiral.
----- Original Message -----
From: calgoddard
To: Indoor_Construction_at_yahoogroups.com
Sent: Monday, December 04, 2006 6:00 PM
Subject: [Indoor_Construction] Partial Motors
I tried to post a similar message the other day, but it seems to
have disappeared. I apologize if this is a repeat.
Some prior posts seemed to imply that full motors will exhibit
higher torque than partial motors. Maybe I misread the posts.
My experience has been that, for a given rubber type (e.g. specific
batch of Tan II stored the same way) and thickness (e.g. .093
inches), if, for example, 800 turns on a half-size motor indicates a
torque reading of 1.0 on a torque meter, then 1600 turns on a full-
size motor will also indicate a torque of 1.0 on the same torque
meter. I measure the motor "size" by weight, although I understand
many experts go by the length. Obviously, you can't extrapolate
torque for a motor wound, for example, two times previously to one
that has never been wound.
This is the basis on which our team does half-motor flights and then
extropolates height and time that should result on full motor
flights. We have observed that on a full 2.0 gram motor, double the
winds and the same torque will fairly accurately double the flight
height and flight duration of a flight with a 1.0 gram motor (again
assuming same rubber type, thickness and prior wind history). Of
course, you have to fly the same plane trimmed the same way under
the same conditions.
Apparently the smaller the partial motor is as a percentage of the
full motor, the less reliable the extrapolation. In other words,
half motor flights are generally a better predictor than quarter-
motor flights.
Am I missing something here? Maybe there are minute differencs in
torque but it shouldn't be significant in predicting the performance
of a Science Olympiad plane on full motors based on partial motor
flights. Perhaps it matters in F1D.
Calgoddard
[Non-text portions of this message have been removed]
Received on Mon Dec 04 2006 - 18:10:32 CET
This archive was generated by Yannick on Sat Dec 14 2019 - 19:13:44 CET