Thanks Nick,
Just for the record, I was not looking at the absolute value of the predicted flight time when modeling A6's using the Hunt program, just the relationship of the results & the % difference between them. For example, I might model my current A6 & an identical one with a tail boom that was 2" longer & see what the affect was on predicted time. In this example I might assume that I could simply make the tail boom longer but not increase the weight of the boom or I might decide to increase the weight of the boom proportionally to the length & assume I could save that amount of weight somewhere (like the motorstick). If the predicted time increased by 2 seconds I would probably have decided that it was a dead end, but if the time increased by a significant amount (what ever that is) I might try building & testing one.
I am interested in the premise that the rubber weight should be 1.4 times the model weight for all classes. Nick, have you or anyone else examined this premise to see how well it holds up in the real world? In classes where the front bearing to rear hook dimension are limited, like A6, the 1.4 might not be applicable, but in classes with more dimensional flexibility I would be interested in knowing if the 1.4 is proving to be a reasonably accurate guide line.
Gary H
From: Nicholas Ray <lasray_at_gmail.com>
To: Indoor_Construction Indoor_Construction_at_yahoogroups.com
Hi Gary,
You are correct that the Hunt program is mainly concerned with the models sink rate as a glider. Hunt figured out a factor, 14.63 divided by the sink rate times prop diameter efficiency factor. This equation accurately predicts duration of old rules F1Ds with a 1.4 gram motor.
The duration prediction corrected for the low rubber ratio is the rubber weight divided by the 1.4 times the model weight. Based on this equation, I believe that Hunt thought the rubber weight should be 1.4 times the model weight for all classes. However, as the rubber weigh decreases, the sink rate improves. So, there may be a good compromise between sink rate and rubber weight some where in between.
For A-6, the prop efficiency factor is considerably outside the expected inputs of the program. The program compares everything to an 18 inch F1D prop. A prop less than 18 inches is considere d less efficient with a factor less than one, while a prop greater than 18 inches has an efficiency factor greater than one. Because A6 uses small flat bladed props I would be wary of any duration predictions the program makes.
Regards,
Nick
Sent from my iPad
Received on Sat Oct 26 2013 - 16:50:48 CEST
This archive was generated by Yannick on Sat Dec 14 2019 - 19:13:48 CET