Re: [RCSE] Initial CG on a scratch ship...
Title: Initial CG on a scratch ship... That is a good start for the CG, but the other part of the equation is the horizontal stab. How big is the tail, how far from the wing is it it and what is the decalage? Here's something worthwhile reading: http://www.fatlion.com/sailplanes/decalage.html Is this a scale ship?? Frank - Original Message - From: George Voss To: 'Douglas, Brent' ; soaring@airage.com Sent: Thursday, April 20, 2006 12:20 PM Subject: RE: [RCSE] Initial CG on a scratch ship... You need to find the MAC or Mean Aerodynamic Chord, which is the average chord. Assuming a straight leading edge and a tapered TE, if its a straight taper , measure the root, add the tip and divide by 2. That is the average chord. So, make a mark 8 back from the LE and thats the average chord. 30% of 8 is 2.4, just like you calculated. Id start there. If the TE has more than one taper, you will need to take into that into account. George Voss From: Douglas, Brent [mailto:[EMAIL PROTECTED] Sent: Thursday, April 20, 2006 12:39 PMTo: soaring@airage.comSubject: [RCSE] Initial CG on a scratch ship... Just trying to get a rough idea where to start here, what formula you might use to come up with a starting CG . Picture a 200 inch wing, root chord about 11 inches, tip about 5, straight leading edge, tapering TE. Modern airfoil, HQ 2.5, 12 - 10 percent thick. My thought was to go mid span, take some percentage of the chord there, then mark the root that far back - example: 30% of 8" becomes 2.4 inches - mark the root at 2.4 inches from the leading edge. 2 questions - how far off is that logic, how far off is 30%? I'm towing this ship for the first flight, so I'd like to be pretty close, erring to the nose heavy side. Thanks!Brent
Re: [RCSE] Initial CG on a scratch ship...
Title: Initial CG on a scratch ship... Brent. . .I would never tow a ship on its first flight. Can't you find a little hill or mound and start with some hand tosses? Having quite frequently seen inquiries about an initial CG, it might be of value to follow the steps I do with a new ship to avoid calamity. All of mine are scratch built and each is a little different, so it has to be sorted out for each one, step by step. Just go to the Genie pages at http://genie.rchomepage.com/ and get into File 8. - Original Message - From: Douglas, Brent To: soaring@airage.com Sent: Thursday, April 20, 2006 10:39 AM Subject: [RCSE] Initial CG on a scratch ship... Just trying to get a rough idea where to start here, what formula you might use to come up with a starting CG . Picture a 200 inch wing, root chord about 11 inches, tip about 5, straight leading edge, tapering TE. Modern airfoil, HQ 2.5, 12 - 10 percent thick. My thought was to go mid span, take some percentage of the chord there, then mark the root that far back - example: 30% of 8" becomes 2.4 inches - mark the root at 2.4 inches from the leading edge. 2 questions - how far off is that logic, how far off is 30%? I'm towing this ship for the first flight, so I'd like to be pretty close, erring to the nose heavy side. Thanks!Brent
Re: [RCSE] Initial CG on a scratch ship...
Your logic sounds quite reasonable for your planform. Bill Swingle Janesville, CA 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
RE: [RCSE] Initial CG on a scratch ship...
Title: Initial CG on a scratch ship... You need to find the MAC or Mean Aerodynamic Chord, which is the average chord. Assuming a straight leading edge and a tapered TE, if it’s a straight taper , measure the root, add the tip and divide by 2. That is the average chord. So, make a mark 8” back from the LE and that’s the average chord. 30% of 8 is 2.4, just like you calculated. I’d start there. If the TE has more than one taper, you will need to take into that into account. George Voss From: Douglas, Brent [mailto:[EMAIL PROTECTED] Sent: Thursday, April 20, 2006 12:39 PM To: soaring@airage.com Subject: [RCSE] Initial CG on a scratch ship... Just trying to get a rough idea where to start here, what formula you might use to come up with a starting CG…. Picture a 200 inch wing, root chord about 11 inches, tip about 5, straight leading edge, tapering TE. Modern airfoil, HQ 2.5, 12 - 10 percent thick. My thought was to go mid span, take some percentage of the chord there, then mark the root that far back - example: 30% of 8" becomes 2.4 inches - mark the root at 2.4 inches from the leading edge. 2 questions - how far off is that logic, how far off is 30%? I'm towing this ship for the first flight, so I'd like to be pretty close, erring to the nose heavy side. Thanks! Brent
