[NSRCA-discussion] Odyssey CG
Dr. Mike Harrison
drmikedds at sbcglobal.net
Wed May 2 09:57:36 AKDT 2007
Anthony,
I think you will find 25% to be very nose heavy, I would opt more for 30%. This has been a great discussion regarding CG. It is important that the pilot learn early the way to find CG and then adjust to his personal likes.
Good Luck
Mike
----- Original Message -----
From: Anthony Abdullah
To: NSRCA Mailing List
Sent: Wednesday, May 02, 2007 10:50 AM
Subject: Re: [NSRCA-discussion] Odyssey CG
George,
That clears up everything! I guess that is why they call it mean aerodynamic CHORD. When I go home tonight I will use both the mathematic method and plug numbers into the calculator. I am fairly confident that they will be very close to each other. First test flight will be this weekend with the CG set at 25% MAC.
Once again, thank you to everyone, you guys are awesome!
Anthony
"george w. kennie" <geobet at gis.net> wrote:
Anthony,
He doesn't want you to go out 13.5 inches from the root section of the wing. He wants you to move out on the panel to a point where the wing measures 13.5 inches from the leading edge to the trailing edge, in other words, the point where the CHORD of the wing is equal to 13.5 inches wide, and that's probably going to happen around 17 or 18 inches out. On top of that, you're going to have to use the actual numbers ( chord/tip) from YOUR wing.
----- Original Message -----
From: Anthony Abdullah
To: NSRCA Mailing List
Sent: Wednesday, May 02, 2007 9:21 AM
Subject: Re: [NSRCA-discussion] Odyssey CG
A huge thank you to all that have provided information. I apologize for my ignorance, I am one of those people that tends to follow the plans as a starting point and fine tune from there. As such I do not have a firm grasp of the concept yet but love learning about it.
Simple question:
Does the 13.5 in the below example refer to the distance out from the center of the fueslage or from the root rib? As I understand it, if I go out 13.5 from that point (fuse center I believe) and draw a perpendicular line that will be my MAC. Setting the CG from there is just a matter of taking 25% to 30% of the MAC distance out (13.5 for example) and marking that on the fuse at the root rib?
Thanks again for all of your help!!
With any luck the next thing you hear from me will be a successful maiden flight report.
Anthony
"Dr. Mike Harrison" <drmikedds at sbcglobal.net> wrote:
Anthony,
They are all correct. That is 30% of MAC or mean aerodynamic chord. A reasonable estimate with double taper wing is to add root chord plus tip chord divide by 2 and take 30% of that. For example if the root is 18 inches and tip is 9 inches that adds to 27/2 equals 13.5 as your MAC. Go to your wing and locate it. It is about halfway out. Take .30 equals 4.05 inches, mark it and go perpendicular to the root rib and mark on the root rib. There is a very specific formula for this in Ron Van Putte's old articles, but this is quick and dirty and will get you there in the shop or at the field.
Mike
----- Original Message -----
From: george w. kennie
To: NSRCA Mailing List
Sent: Tuesday, May 01, 2007 1:27 PM
Subject: Re: [NSRCA-discussion] Odyssey CG
Anthony,
Not trying to start a war here, but if that thing has a tapered leading edge, I think you might want to move out almost half way on the panel and then go for your 30%. If you start at the root, you may find yourself flying a brick. Trimming on KE on a 45 degree upline might also be a worthwhile addition to your trimming regime.
G.
----- Original Message -----
From: Anthony Abdullah
To: NSRCA Mailing List
Sent: Tuesday, May 01, 2007 1:46 PM
Subject: Re: [NSRCA-discussion] Odyssey CG
Dr. Harrison,
Thank you very much for the information! I agree with you completely that the CG is pilot specific. I tend to like my planes just a hair tail heavy compared to others. What I was afraid of was having the CG so out of whack that the plane would not survive its maiden flight.
I know that 30% is the rule of thumb and I wanted to make sure that applies to the Odyssey. Just to summarize and for example, If I am looking at the wing root of one panel and the chord is 10 inches, I wand to start with the CG roughly three inches from the leading edge at the root (fuselage)?
I will follow that and let you know how it turns out.
Is there anything else I should know about the Odyssey?
Thanks again
Anthony
"Dr. Mike Harrison" <drmikedds at sbcglobal.net> wrote:
Anthony,
I designed the Odyssey and I can't tell you where it is, but I can recommend some guidelines. First, however let me give some opinion as to the value of cg location. I believe the optimum cg location is pilot sensitive, that is to say different flyers prefer different cg's based on how the plane is set up. For that reason I recommend a range that is easy to find then fly the airplane and change the cg until you like the way it flies. Some points to remember are to fly full speed then cut the throttle, the plane should descend very slowly. If it descends rapidly, then it is nose heavy. If it climbs, it is tail heavy. That will get you close. After that make very small changes to suit your style. On your root rib mark from 28 to 32 percent of the rib. That would be a recommended range. You might start at 30% and work from there. The stab is powerful on the Odyssey and requires expo for best results so don't confuse a powerful elevator as tail heavy.
Good luck
Mike
----- Original Message -----
From: Anthony Abdullah
To: NSRCA Mailing List
Sent: Monday, April 30, 2007 12:38 PM
Subject: [NSRCA-discussion] Odyssey CG
Does anyone know where the CG should be on the Odyssey?
TIA
Anthony
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