- Category: Archive 2015
- Hits: 335
- Miles stone
- Cost Management ?
- Fuss about timing F1S Motor runs
- French Frequency
- Thicker towline
From: Jim Bradley
Let me be the first,?likely not really the first, to congratulate you on the 2000 issue of SEN.? Your contributions have effected the entire Free Flight community through the world.? Thank you very much.
Jim Bradley, USA
editor .... you were the first Jim , thanks for the kind words
Congratulation for reaching a mile stone
Amazingly SEN has reached to 2000th issue! What an achievement!
Congratulations Roger for an ongoing job well done!
Further thought on cost control/limiting
From: Gene Ulm
Dear Grand Master Sen,
There is an additional advantage to limiting to two models (in addition to cutting new model expenses in half, not making models obsolete and putting a boon of cheaper models on the resale market), allowing only two models would also cause modelers to "hedge" on radical, super cutting edge technology. If you only have two in the box, they will likely be more firmly under the bell curve rather than the extremes. That said, if flying a more extreme model is what a sportsman wants to do, that is their choice too.
Two models is not a revolutionary idea. That's the way it used to be.
Again, incentives for change rather than cost-escalating banning of aircraft types.
The fuss about timing F1S motor runs
Why fuss about not needing to time F1S motor runs (10 and 5 seconds)? The reason is that timing of electric motor runs is notoriously inaccurate. Motors hum and the props of F1Ss are too small. The US proposal specifies that a F1S motor run can be measured statically BEFORE the flight (allowing the battery to be switched) or AFTER the flight. This is accurate, fair and practical. Given the velocity ranges of an F1S, say to 35 foot/sec, the power coefficient Cp hardly changes in the air and we are talking about minimal altitude gains.
In contrast, engines using mechanical timers (~98%) are different. The reason is that their rotating scroll is reset before every flight. (Intriguingly, since an e-timer can’t be easily reprogrammed, one might hypothetically statically test motor runs of models with e-timers. If timed statically say at 4.9 seconds, then its motor run would still be legal even if it’s clocked at say 5.4 seconds! Of course, the flooded motor would have to be cleaned and the model would have to be refueled. So Static Engine Run Testing (SERT) might prove to be a great incentive to develop e-timers for F1C models in this hypothetical case.)
Back to F1Ss. We are dealing with simple e-timers, not ones with secret back doors programmable through the internet. The more sophisticated e-timers can be reset with Palms or IPhones, but we only allow a flier to switch their battery after a pre-flight static test. A post-flight static test can be performed if there is any doubt. And if a cheater is ever caught, their reputation will be seriously tarnished.
In other words, the electric world is different and simpler in some respects. It’s time to shed the old baggage of timing motor runs and enjoy the simplicity of the event.
Regarding the French GPS locator:
One concern is that it operates at 868 Mhz. That is a license free band in Europe and other parts of the world but not in the USA and North America. A 915 Mhz model would be needed to be legal here.
Re: Thicker F1A towline
From: Martin Gregorie
A small factoid about thicker towline: back when I could still tow
models in 2003/4, the best line I ever used was 100lb kite bridle line.
This was a Spectra core inside a woven Dacron cover. It was 1.4mm in
diameter according to my electronically enhanced calipers. It gave me
the consistently highest launches I ever had. Its extreme inelasticity
(the 5kg pull stretched it around 150mm, mostly due to the weave
straightening out as the first 1-2kg of load and with very little
extension thereafter) also provided very good feel for what the model
was being towed through.
If anybody still has any Russian Rod, which was considered to be
excellent line, please measure it and let us know its diameter.
Bottom line: I don't believe that setting a minimum line diameter will
do anything except require bigger reels on some towline reels.
PS: I'm still flying a balsa glider off Spectra line: its just that the
line happens to be 3.5 - 4 mm rope and the unflapped glider is 15m span.