SEN 1288<

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Category: Archive 2009
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Table of Contents SEN 1288 - 4 March 2009

  1. Hot air or not?
  2. Scat ANN
  3. Q for it



In Reply to Air temperature and trim changes
 
From: Ken Bauer


I have a question to pose to SEN readers:  How does air temperature,
humidity, density, altitude, etc, effect model trim changes?  Is there a
definite, scientific, documented trend that we can rely on?
All these features affect air dencity, and this has an effect on the lift and drag of the airfoil/wing/tail. It then depends on the airfoils, the matching of the lift/drag slopes of the surfaces, whether a change on air properties affects the trim or not. The change is more pronounced here in Finland, where we fly at winter time in freezing conditions, and in much milder weather in the summer. Some models require a considerable re-trim from winter to summer, some fly on the same trims. I think the modern ships with larger incidence and smaller tailplane are less sensitive than older models, where the incidence between wing and tail was smaller.

However, another feature that may affect your trims as day proceeds, is thermal expansion of the control mechanisms, as well as temperature drift of the servos. I have found this phenomenon especially serious on wakefields, for two reason. First of all the control linkages that I use are one-side pull cables against a spring, so dissimilar thermal expansion of the wire versus fuselage changes the trim. Second, small servos (in the 4 gram or below range) seem to have rather serious changes in the centering as temperature changes, a feature not as common/serious on the larger servos. Unfortunately there is no room, weight-vise, to pack larger servos into the pylon, in you prefer to use a direct drive of the control surfaces from the servos. The solution for this problem is to add a temperature sensor to the timer, and program a temperature compensation that adjust the centering of the servos depending on measured ambient temperature.



-Tapio-




SCAT ANNUAL
March 14 & 15, 2009 at Lost Hills Field, CA


AMERICAS CUP & NATIONAL CUP Contest                   Sanction No. 09-xxx
For FAI Classes A,B,C,G,H,J,P & Q          Trophies for 1st places, Medals thru 3rd

Saturday, March 14: F1A, F1B, F1C & F1P
Seven   one hour rounds start @ 8AM with extended max times:
F1A rd 1 max is 210 sec
F1B rd 1 max is 240 sec
F1C rd 1 max is 300 sec
F1P rd 1 max is 210 sec  [note: 7 sec max eng run per '08 FAI rule]
Remaining rounds maxes are 180 sec.  ABC Flyoff Schedule TBA

Sunday, March 15: F1G, F1H, F1J [Note: 5 sec motor run rule] & F1Q
Note: F1Q added for AM Cup points purposes.  No award. $3 fee.
F1Q Rules: 5 rounds, 20sec motor run, 3 minute max.

Tie-breaker 'No-Max Flight'! H & Q @ 8:00-8:10AM, then G & J @ 8:15-8:25.
Then five 2007-12-18 13:15:58 45 minute rds will be flown: 120 sec maxes, starting @ 8:30AM.
Rd 5 should end by 12:15PM. Mini Event Flyoffs to begin approx 12:30PM.
FO maxes start @ 240, then go up 2 min, etc.
If ties remain @ 2:30PM, Tie-breaker times decide final placings.

National Cup Events, Trophies for 1st places
Saturday: Hand Launch Glider & Nostalgia Wakefield  8AM-4PM
Sunday: Catapult Glider, Classic Towline Glider & Vintage FAI Power 8AM-4PM

Entry Fees: FAI first event, $20 Open, $5 ea for additional FAI events.  
National Cup events and Juniors, $10 for first event, $3 additional events.
Junior Hi-Time Trophy.      
All-In Fee of $30 to fly any & every event you want!

Memberships in AMA & Lost Hills Field Assn are MANDATORY.
We will be glad to sign you up at field for either one.

Contest Director                                               Contest Organizer
Lee Hines                  Jim Parker
376 Magnolia St                  9534 Ruffner Ave
Costa Mesa, CA 92627              North Hills, CA 91343
[949]645-4850                  [818]892-4110
This email address is being protected from spambots. You need JavaScript enabled to view it.This e-mail address is being protected from spam bots, you need JavaScript enabled to view it               This email address is being protected from spambots. You need JavaScript enabled to view it.This e-mail address is being protected from spam bots, you need JavaScript enabled to view it




SCAT ANN F1Q

Mike,
 
Thanks for the hint re F1Q.
We will shorten the Flyoff motor runs by 5 sec increments,
down to 5 sec minimum.
 
As far as long chases go, just pick down air, come down quick!

CU there,
Lee
---------------------------------------------------------------------------------
PS to Roger M:
Please post the above note and the flyer as reminder in next SEN.
TU,
LRH




...........................
Roger Morrell<