RE: CG On flying wing?
The links suggested in this discussion give some good info about conventional airplanes, ie. with tails, but the flying wing is a special case. Normally, the horizontal tail(HTail) influences the location of the Neutral Point(NP) by moving it rearward. The NP is somewhere between the Aerodynamic center of the wing and that of the HTail. But, your plane doesn't have an HTail, so the NP of the plane is at the NP of the wing, which is normally very close to 25% of the wing Mean Aerodynamic Chord(MAC). This being the case, the CG must be located a safe distance forward of the NP. For typical sport flying, a Static Margin would be about 10%. So, since the NP is at about 25% of the MAC, putting the CG at 15% of the MAC would give you a 10% static margin. My recommendation is that you start test flying the plane with the CG at 10% of the wing MAC, ie.a 15% static margin, which should be a little nose-heavy. Then, when you are more familiar with flying the plane, move the CG rearward in 1 or 2% increments until you are comfortable with the way it flys. I wouldn't go much lower than a 10% static margin. In order to be confident in what you're doing here, it is very important that you calculate the Neutral Point location accurately, which depends on the HTail area, shape, efficiency and some other important factors. It is equally important that the MAC is correct. For example, any calculation must include the effects of wing tips. If a CG Calculator doesn't use these factors and use them correctly, then you are risking the safety of your plane. You can read a more complete description of the analysis, at the RC Aeronauts website. Good luck
Posted on: 8/1/2012 5:43 AM by Author "edsplane" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=11177021

RE: CG On flying wing?
The calculator used in the previous message, is limited to a single-panel wing and does not include the effects of the wing tips. If your flying wing is similar to this simple configuration, the calculator results should get you within about 10% of the actual CG location. If your flying wing is multi-panel, the true results can be very different. If the wing shape is more complex and/or you want a closer estimate, I suggest that you read the description of a multi-panel wing analysis, including wing-tip effects, at the RCAeronauts website.
Posted on: 7/31/2012 4:55 AM by Author "edsplane" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=11175662

RE: New CG application that does multi-panels
I have tried a 4-panel example using the referenced CG calculator and find that the answers it gives, don't agree with my hand calculations. One reason is that the wing tips are ignored. Another is that the tail efficiency doesn't appear in the neutral point calculation and has a strong influence on the results. I get a much more accurate solutions using the techniques at www.rcaeronauts.com , which can accommodate up to 7-panel wings and 4-panel tails.  Edited to add a space after the URL so the link will work.- BMatthews
Posted on: 7/22/2012 9:36 PM by Author "edsplane" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=11139761

RE: New CG application that does multi-panels
of luck. Edsplane
Posted on: 7/15/2012 6:34 AM by Author "edsplane" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=11155852

RE: CRAZY YAK 100
From your original description of the problem, it sounds like the CG is too far aft. I wouldn't deviate from the manufacturer's specs for incidence and thrust line until the CG is located correctly. The first thing I'd try is to use a very reliable way to make sure the MAC is the correct length and it is located correctly. Next, locate the CG at 20% of the M.A.C with the incidences and thrust line set to specifications. It should fly a little nose-heavy but be very stable. Next, check to see what % of MAC that the Mfgr recommended for a CG location. They or maybe you, have made a mistake there. With the CG at 20% of MAC, see how it flies. If it is nose heavy, change the CG to 23 or 25 % of MAC and retest. Above 25%, move the CG aft in 1% increments until you get the performance you want. Caution: be sure to find the neutral point location before you go aft of the 25% of MAC point. For a better description of this, look at www.rcaeronauts.com. Good luck.
Posted on: 7/10/2012 8:20 AM by Author "edsplane" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=11149947

RE: New CG application that does multi-panels
I don't know what you're using for these calculations, but, just because something is in the calculations, doesn't mean that it is correct. I suggest that you get the best possible set of equations and do a hand calculation to see if the results you are getting, are close to correct. If you read through the discussion on determining the neutral point , at www.rcaeronauts.com, you will get an idea of what I mean. Good luck.
Posted on: 7/9/2012 6:06 AM by Author "edsplane" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=11148485

RE: Figuring wing loading
R8893 is absolutely correct. The ailerons are always included in the wing area, as is the portion of the wing that's covered by the fuselage. Also, in case you don't have this, a convenient equation you can use, to find wing loading in ounces per square foot, is, wing loading = 2304 times (airplane weight in pounds divided by wing area in square inches) = ounces/sq. ft. So, for your plane, WL = 2304 x (6/840) = 16.46 oz/sq ft It may be a little sensitive to wind gusts, but should fly great. Best of luck
Posted on: 7/4/2012 5:37 AM by Author "edsplane" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=11142367

RE: Aerfoil data - drag and lift coefficients
I have a copy of a report that gives the x,y coordinates to plot a Clark Y airfoil. It also has the lift coefficient vs Angle of Attack which you probably want and lift and drag coefficients at various Reynolds number values.What equations are you looking for? The report title is "A Catalog of Low Reynolds Number Airfoil Data For Wind Tunnel Applications" Feb. 1982, by S.J. Miley I got the report many years ago from the U.S. Dept. Of Commerce Information service. Try looking it up on the Internet. Hope this helps. Ed www.rcaeronauts.com
Posted on: 6/25/2012 9:40 AM by Author "edsplane" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=11131110

RE: Beginner question regarding CG
The calculator you referenced, and others I've seen, do not handle wings with more than one panel. Aside from the Trainers, most of the model aircraft are really 2 or 3 panel airplanes. Treating them as one-panel throws the accuracy of the CG and NP calculations off. Secondly, the program is extremely user friendly and familiarizes the user with the technology behind the calculations. And, it is fast and accurate if your measurements are taken correctly. When I'm paying $26.00 for a gallon of glow fuel, I consider the CG Optimizer cheap insurance to have the CG and NP located with confidence.
Posted on: 6/20/2012 2:44 PM by Author "edsplane" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=11125650

RE: Beginner question regarding CG
You will find a good discussion on CG location at www.rcaeronauts.com. You should know that the CG must be located forward of the Neutral Point. The farther forward of the NP, the more stable the plane, but the less aerobatic. So, you must also find out where the neutral point is, as well as the CG. The information at the rcaeronauts website should give you an idea of what to do. Good luck.
Posted on: 6/20/2012 5:47 AM by Author "edsplane" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=11124928

RE: Complex shape flying wing/delta CG calculator
HI Mike. Please do not "simplify" the drawing of your complex wing. You will only build more errors into your CG calculations. There is a small program that is available, to do exactly what you want. It is specifically designed for complex wing shapes like yours. It's easy to use, there's plenty of free tech support and you get accurate solutions in just a few minutes. It will give you the CG and Neutral Point of your plane, so you can easily tell how stable the plane will be and it lets you adjust these values, so that you fine-tune the performance of the plane to your level of flying skills. And, all of the math is done for you. Look at www.rcaeronauts.com, for a good discussion and the answers you need. Best of luck.
Posted on: 6/20/2012 5:31 AM by Author "edsplane" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=11124911

RE: CG on a Royal Kit
No matter what plane you have, it is easy to locate the CG. All the information you need is on www.rcaeronauts . You can accurately locate the CG and NP for any single- or multi-panel conventional airplane and all of the math is done for you. Calculators typically approximate the CG location for single-panel wings. If you have a multi-panel wing, the accuracy from a calculator, will probably be off. Caution: It is not the CG location alone, that determines pitch stability, but the location of the CG relative to the neutral point. An accurate way to find both the CG and Neutral Point, is crucial.
Posted on: 6/19/2012 5:37 AM by Author "edsplane" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=11122141

RE: CG location when fuel is burned
Hey Guys, Let's try this a different way; forget the moment arms for now. The balance point for the airplane is, by definition, where the CG is located. If you put the CG of the fuel tank at the CG of the plane, there will not be any imbalance of the plane, no matter what the fuel level is in the tank. If the CG of the fuel tank is forward of the plane's CG(with Tank empty), then any fuel in the tank will tend to make the plane more stable in Pitch(nose up & down). You can eyeball the tank CG at about half the length of the tank. That's why the pattern guys put the tank CG right on the Plane CG. And, that's why we never put the tank CG aft of the plane's CG. Now, back to the Moment question. If you take the sum of the moments about the plane's CG(with fuel tank empty), the sum of all moments is zero, thus the balance point. If the tank CG is not at the tank-empty plane's CG, then any fuel that's put into the tank, will cause an imbalance about the Plane's CG and the sum of the moments will not be zero. In other words, the plane's CG has now been moved. If the plane's CG is moved forward, the plane becomes more stable in pitch and will be less aerobatic, but safer. If the tank is behind the Plane's CG, the more fuel that's added will make the plane less stable and less safe. If the tank is located behind the plane CG far enough, then the plane will be unstable in pitch. There's more on this at www.rcaeronauts.com. Hope this helps.
Posted on: 6/17/2012 7:56 AM by Author "edsplane" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=11121118

RE: CG location when fuel is burned
There is no contradiction. What you say is absolutely true. It is customary to calculate the CG location with the tank empty, I think because you want the plane to be stable when you are ready to land. The fuel tank is normally forward of the CG, so when it is full, the plane will be even more stable. In a pattern plane, you don't want any variation in performance, depending on how full the tank is, so if the tank is located on the CG, you eliminate this variable. The key factor that many people miss, is that the pitch stability of an airplane depends on the CG location, in relation to the plane's Neutral Point(NP). Just putting the CG at 25% of the Mean Aerodynamic Chord(MAC) only does half the job. Where is the CG relative to the NP? The Neutral Point location depends on tail location, tail efficiency and some other factors. It can be very different from one plane to the next. I suggest that you find this out and locate the CG accordingly. There's more information on this at www.rcaeronauts.com . Good luck.
Posted on: 6/16/2012 7:56 AM by Author "edsplane" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=11120132

RE: Beginner question regarding CG
Hi, I think that the advice you've been given above, is good as far as it goes. You can learn more on my website www.rcaeronauts.com , since it goes into the location of CG in more detail. As a beginner, you probably fly a high-wing trainer and the usual CG position is at the 25% of MAC(Mean Aerodynamic Chord) position. I would even go down to 22 or 23% of MAC to start out. Just be sure that you measure the 25% correctly. If you have a rectangular wing on the plane, it's just one-quarter of the wing chord, back from the leading edge of the wing. If your wing is not rectangular, refer to my website for some ideas. This is a great hobby and the best way to enjoy it is to learn correct techniques from the outset, both on and off the field. Best of luck and happy landings.
Posted on: 5/11/2012 12:42 PM by Author "edsplane" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=11077158

RE: great planes floats question please:
Here's my opinion. Always cover the floats with either fiberglass, silk or similar fabric, painted with fuel-proofed dope or really thinned epoxy paint. Covering them with film over bare wood, is really asking for trouble. And always glue chunks of the very light type of styrofoam between the float compartments. Doing these things will better keep the floats water-tight and hold them together better in a crash. Also, the styrofoam will give you better floatation if the floats get damaged. You can do all this and still keep the plane light and it really helps when you need to find and recover the pieces if you crash. Hope this helps. rcaeronauts.com
Posted on: 4/24/2012 9:01 AM by Author "edsplane" in the forum "Seaplanes"
http://www.rcuniverse.com/forum/fb.asp?m=11054925