Hi Gary,
I think the current 55cm F1Ds are a contradiction to 1.4 times the model
weight being the best way to go about optimizing the rubber weight. When
the rules were written it was thought that the 50% rubber weight rule would
drastically reduce duration but in actuality its has only reduced the
duration by about 20%.
Lew Getlow published a table in his book of optimal rubber to model ratios.
I do not have my copy with me so I cannot provide a page number. I think
information provided there may be a decent starting point. Personally I
have found that I do best when I fly motors that are about 100% of the
models weight.
Regards,
Nick
On Sat, Oct 26, 2013 at 7:50 PM, <Warthodson_at_aol.com> wrote:
> **
>
>
> 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
>
>
>
>
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>
>
>
>
Received on Sun Oct 27 2013 - 08:41:44 CET
This archive was generated by Yannick on Sat Dec 14 2019 - 19:13:48 CET