I'm not real familiar with the 65cm rules but it was my impression that
there was a 1.4g rubber weight limit and a 1.0g minimum model weight.
Maybe someone who actually flew those models can confirm or correct this.
Gitlow's chart shows optimum rubber weights of about 130% for 65cm F1D,
110% for IS, 95% for Ministick, 90% for EZB, 80% for PP and 68% for LPP.
(all these are my approximations from his chart). The only one of these
I've got experience with is LPP. The chart would indicate about 2.1g
for LPP which is less than I use.
On 10/27/2013 11:41 AM, Nick Ray wrote:
> 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
> <mailto: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 <mailto:lasray_at_gmail.com>>
> To: Indoor_Construction Indoor_Construction_at_yahoogroups.com
> <mailto: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 Sun Oct 27 2013 - 08:57:08 CET
This archive was generated by Yannick on Sat Dec 14 2019 - 19:13:48 CET