This is indeed a very interesting post by Mark Drela on servo requirements.
Did anyone else notice that the calculated flap servo torque requirement (62 in-oz) is higher than the specs on all commonly used servos other than the Volz Micro Maxx HP. The JR DS368 is spec'ed at 53 oz-in. The thin wing servos, JR DS-168 and Hitec equivalent at 46.6 oz-in. The Volz Wing Maxx XP optimistically is only 59 oz-in while the regular Wing Maxx is optimistically at only 49 oz-in. The regular Volz Micro Maxx is advertised at 56-67 oz-in and may work if one can believe the advertised specifications. The advertised specification for the Volz Micro Maxx HP is 67-82 oz-in, but it was independently measured to have a maximum torque with 5 volt input of 3920 g-cm or 54.4 oz-in. See http://www.teaser.fr/~osegouin/aeromode/servos.phtml or more easily (since I don't read French) http://www.rcgroups.com/forums/showpost.php?p=5010862&postcount=43 If I am interpreting things correctly. This really gets one thinking about the flap servos and what one is/has used for flaps. don -----Original Message----- From: Mark Drela [mailto:[EMAIL PROTECTED] Sent: Saturday, February 18, 2006 11:08 AM To: soaring@airage.com Cc: [EMAIL PROTECTED] Subject: Re: [RCSE] Carbon Supra #48 flies - weight < 61 oz ! Molded Supra launch hinge moments are listed below, for a 200 lb tow load (hard F3j launch). For smaller tow loads, hinge moments will be proportionally smaller. wing camber = +10 deg rudder defl = 30 deg wing CL = 1.2 lift = 200 lbs q = 0.16 psi = 1104 Pa V = 95 mph = 42.5 m/s Flap hinge moment = 4.87 in-lb = 78 in-oz = 5.62 kgf-cm Ail. hinge moment = 3.15 in-lb = 50 in-oz = 3.60 kgf-cm Rud. hinge moment = 2.12 in-lb = 34 in-oz = 2.45 kgf-cm To get the servo moment (torque), this hinge moment must be multiplied by a linkage geometry factor, which is approximately by the ratio of servo/surface horn lengths. This is between 0.7 - 0.9 for most installations. Assuming a horn length ratio of 0.8, the servo moments are: Flap servo moment = 62 in-oz Ail. servo moment = 40 in-oz Rud. servo moment = 27 in-oz RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off. Email sent from web based email such as Hotmail and AOL are generally NOT in text format RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off. Email sent from web based email such as Hotmail and AOL are generally NOT in text format
