RE: how to figure out the CG on this wing?
Pollemix, Great project! How to determine the center of gravity for your model? There are on-line calculators. For a wing of this particular shape, you need to break it down in surfaces for which it is easier to calculate the area’s centroid. I have attached five schematics that describe the graphic method. You will obtain more than one area’s centroid (or aerodynamic center) and more than one mean aerodynamic chord (MAC) for one semi-wing. Then, you will have to combine those into one equivalent AC and one equivalent MAC. By definition, the equivalent AC will be located at 25% of the equivalent MAC. That is the point where all the lift and drag created by your complex wing will act. However, your model is more than two semi-wings; it has other surface that also creates lift and need to be considered. You will need to determine the AC of the horizontal tail, in a similar manner. For your model, it will be simpler, because the shape is a rectangle. Next, you will calculate the neutral point (NP). That is the point where the moments of both lifting forces get balanced. Now you know where your limit for locating the CG is located. That CG must be forward the NP for balanced flight. The distance between the two points is selected by you, and it is called Stability Margin. A margin of 20% of the equivalent MAC is a normal recommendation for the first flights. All these calculations can be easily performed here: http://adamone.rchomepage.com/cg2_calc.htm http://www.geistware.com/rcmodeling/cg_calc.htm#cg Regarding the second mystery for you, if the part of the wing that goes inside the fuselage is to be considered for the calculation: I would say no, do not consider it, since I believe it does not create any lift. However, several references and books say do consider it. Note that I have performed my calculations considering this hidden area. You could run your calculations excluding that area, and comparing the two CG locations. Be aware that these calculations are only approximate, since many other surfaces of the model contribute to drag and lift, and that the final location of the CG will need to be determined for you during the first flights of your model. Best luck building and flying it; just keep us updated!!
Posted on: 11/20/2009 4:56 PM by Author "lnewqban" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9268143

RE: Out of trim trainer
“Trim the model of a new pilot and he will fly for a day. Teach a new pilot to trim his models, and he will fly for a lifetime.� Chinese Proverb[:)] Training in proper trimming is frequently overlooked; however, it is very important. Trimming from the Ground Up (Three parts article): http://www.masportaviator.com/ah.asp?CatID=8&ID=141
Posted on: 11/20/2009 1:20 PM by Author "lnewqban" in the forum "Beginners"
http://www.rcuniverse.com/forum/fb.asp?m=9267732

RE: Acceptable wingloading
You are welcome, hellyeh. The specifications of your model indicate that the normal wing loading should 32.2 ounces/sqft, for a total weight of 187 ounces. You have calculated the weight of your model to be 13.5 pounds = 216 ounces For that weight, the wing loading will be 37.1 ounces/sqft. Here you can calculate the stall speed of your model: http://www.ajdesigner.com/phpwinglift/wing_lift_equation_surface_velocity.php I have just done it (see attached calculations), using CL=1.0, as recommended for landing by the book I have. I have used normal air density of 0.0752 lbm/cuft (@ 68 F) The stall speed for your model should be around 30 miles/h. The landing speed should be a 20% higher than stall; hence, it will be around 36 miles/h (53 ft/second).
Posted on: 11/20/2009 12:46 PM by Author "lnewqban" in the forum "Questions and Answers"
http://www.rcuniverse.com/forum/fb.asp?m=9267681

How to internally clean a glow engine
How to internally clean a glow engine: While trying to find information about the best way to internally clean one of my glow engines, I have found this good article, which I would like to share: http://findarticles.com/p/articles/mi_qa3819/is_200605/ai_n16488075/?tag=content
Posted on: 11/20/2009 9:25 AM by Author "lnewqban" in the forum "Tips & Techniques"
http://www.rcuniverse.com/forum/fb.asp?m=9267247

RE: Color scheme for best visibility
What about this one? http://www.rcuniverse.com/forum/m_9073974/anchors_9076359/mpage_1/key_/anchor/tm.htm#9076359
Posted on: 11/19/2009 10:48 PM by Author "lnewqban" in the forum "Beginners"
http://www.rcuniverse.com/forum/fb.asp?m=9266593

RE: Delta wing CG
James, The stability margin for delta wings should be between 5% and 10% MAC. If you enter the wing tips and tail area as zero into this calculator, you will get the exact location of the CG for any delta wing: http://www.geistware.com/rcmodeling/cg_calc.htm#cg Just for verification, if you enter the values shown in the second attached schematic into the calculator, you will get the same shown results. You can find more information about balancing any model here: http://adamone.rchomepage.com/index5.htm
Posted on: 11/19/2009 4:32 PM by Author "lnewqban" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9265664

RE: I can fly, now I want to build...
barndawg77, You can find excellent articles about model building at this site: http://www.airfieldmodels.com/
Posted on: 11/19/2009 12:52 PM by Author "lnewqban" in the forum "Kit Building"
http://www.rcuniverse.com/forum/fb.asp?m=9265259

RE: Acceptable wingloading
Check this old thread: http://www.rcuniverse.com/forum/m_7624877/anchors_7738986/mpage_1/anchor/tm.htm#7738986
Posted on: 11/19/2009 12:33 PM by Author "lnewqban" in the forum "Questions and Answers"
http://www.rcuniverse.com/forum/fb.asp?m=9265207

RE: help with non-planing shapes
[quote]ORIGINAL: gregow Thanks, right now thd blades trail back at a 60 degree angle, with a total cutting width of 1.5''. Would there be any aerodynamic advantage in decreasing that angle and lengthing the blades to achieve that same cutting width? [/quote] No, I rather see an aerodynamic disadvantage, which is higher possibility of flutter of the blades. The pivoting capacity of the blades eliminates any torque or perpendicular force over the shaft, which eliminates any possible plane effect. The CG of the blades is aft the pivot point; hence, they could enter into resonance vibration or flutter. The longer the distance between pivot and CG, the worst the flutter may be. That is in theory, but only experimentation will tell you the truth.
Posted on: 11/19/2009 7:56 AM by Author "lnewqban" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9264725

RE: Flaps
One more caveat about flaps: Do not retract flaps to normal flying position until the model reaches the speed that will sustain flight with no flaps. If not, the model will just drop because it is flying too slowly for no-flaps conditions. Flaps increase the chamber of the wings and their pitch down tendency, as well as the down flow that leaves the trailing edge. The angle at which that down flow strikes the horizontal tail will determine if the model will pitch up or down when flaps are deployed. Regarding the droops: Their function is to eliminate tip stalls, which will be followed by a sudden and unwelcome roll. Especially for tapered wings, the stall tends to start at the tips. That may be desirable for a model that needs to be agile in roll, but not for a trainer. The concept behind the removable droops is progressive training and agility. It is up to your confidence to decide when they can be removed.
Posted on: 11/18/2009 4:42 PM by Author "lnewqban" in the forum "Beginners"
http://www.rcuniverse.com/forum/fb.asp?m=9263404

RE: help with non-planing shapes
I believe yours is an excellent idea from the Aerodynamical point of view. However, I have no clue about how it will work for the arrow's mission. Keep us updated, it is quite interesting!
Posted on: 11/18/2009 4:41 PM by Author "lnewqban" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9263403

RE: help with non-planing shapes
The only non-planning shapes are a sphere, a semi-sphere and a cylinder or rod perpendicular to the air stream. Any other flat shape will introduce an aerodynamic force IF it faces the air stream with some angle of incidence. I have seen that arrow shafts bend substantially during fly; hence, any plane perfectly aligned with the axis of the arrow will eventually present an incidence angle to the air stream. The force created by that surface will change directions if the arrow shaft also rotates. However, the CG of an arrow follows a projectile trajectory rather than fly. That CG is located by the mid section of the shaft. Any perpendicular force that appears at the head or tail will only rotate the whole arrow in pitch around the CG. Besides playing with shapes at the head, I suggest increasing the stability margin (or distance between the CG and the center of drag) as much as possible. That will give less mechanical advantage to any force at the head and more to the forces at the tail. There are two ways to achieve a big stability margin: 1) Moving the CG forward (which increases the total weight of the arrow and reduces acceleration at launch). 2) Increasing the tail surfaces.
Posted on: 11/18/2009 4:08 PM by Author "lnewqban" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9263318

RE: help with non-planing shapes
What is wrong with the head shown on the right hand picture?
Posted on: 11/18/2009 12:46 PM by Author "lnewqban" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9262862

RE: Nifty 80
Sorry! One of Yarrish's books, "Getting Started in Radio Control Airplanes", includes a construction description of the Forio's Nifty Fity. The book may be available at your public library.
Posted on: 11/16/2009 8:51 PM by Author "lnewqban" in the forum "Sport Flying"
http://www.rcuniverse.com/forum/fb.asp?m=9258926

RE: Profiling control surfaces
You can find a couple of good articles here: http://charlesriverrc.org/articles_construction.htm
Posted on: 11/13/2009 1:24 PM by Author "lnewqban" in the forum "Kit Building"
http://www.rcuniverse.com/forum/fb.asp?m=9251148

RE: Nifty 80
You can find 230 articles written by him here: http://findarticles.com/p/search/?qta=0&qt=Gerry+Yarrish's%20&tb=art&qf=all&x=0&y=0
Posted on: 11/13/2009 1:08 PM by Author "lnewqban" in the forum "Sport Flying"
http://www.rcuniverse.com/forum/fb.asp?m=9251123

RE: Penetration
[quote]ORIGINAL: CrateCruncher [quote]ORIGINAL: lnewqban It seems that high wing loading is good for wind penetration. But I don’t believe so, or at least I don’t understand the physical reason. I insist on that low drag is the key for good penetration. Some birds have to glide thermals and penetrate wing, according to the circumstances. How do they do it without adding ballast? Modifying
Posted on: 11/4/2009 2:29 PM by Author "lnewqban" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9227925

RE: Pull Pull servo placement
If your levers are equal, there is nothing to worry about. Right over the hinge line will be just find, sorry for the confusion. Check the schematics:
Posted on: 11/4/2009 2:01 PM by Author "lnewqban" in the forum "Questions and Answers"
http://www.rcuniverse.com/forum/fb.asp?m=9227808

RE: wing
edmoor, You may find some guidance for re-design here: http://users.mo-net.com/shirl/Design.html There is a practical relation among wing surface, stab surface, dihedral and vertical fin surface. Deviations from that relation may cause problems with roll control, like Dutch roll or spin instability. If it is marginal now, you also may need to increase the tail area, or the control surfaces of the tail for the new wing. Not to be scared; I recommend replacing the wing and test fly it; then, making small changes as needed. Be aware the original CG will shift after replacing the wing; just use an on-line CG calculator. Regards!
Posted on: 11/4/2009 9:34 AM by Author "lnewqban" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9227356

RE: Pull Pull servo placement
Trax540, You can use it or not, just try it if a regular set up gives you problems. Many problems with pull-pulls come from slight misalignments’ and different lever lengths’ for servo and horn. Here is another good link with examples and pictures: http://members.cox.net/bdfelice/Pull-pull/pull-pull.htm
Posted on: 11/4/2009 9:15 AM by Author "lnewqban" in the forum "Questions and Answers"
http://www.rcuniverse.com/forum/fb.asp?m=9227319

RE: Balancing a canard or tandem wing biplane for initial flight.
[quote]ORIGINAL: rc bugman I don't dis-believe your explanations but somehow I am missing the logic. [/quote] Let's try the logic of the arrow: Feathers in an arrow create an artificial drag that is necessary in order to achieve a stable flight. The CG (located by the middle point of the arrow) is forward of the center of drag, or vice-versa. Then, the airstream will keep that center of drag directly behind the CG (around which the arrow rotates for any disturbance). If the arrow starts flight with the feathers pointing forward (case similar to a tail heavy airplane, for which the CG is aft the center of drag or aerodynamic center or neutral point), the airstream will force the arrow to rotate around the CG by dragging that point of resistance or center of drag, and placing it directly behind the CG, as it should be. In other words, a tail heavy airplane (regardless the type or configuration), will be forced by the air stream to fly tail first, with disastrous consequences.
Posted on: 11/3/2009 10:14 PM by Author "lnewqban" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9226532

RE: Penetration
It seems that high wing loading is good for wind penetration. But I don’t believe so, or at least I don’t understand the physical reason. I insist on that low drag is the key for good penetration. Some birds have to glide thermals and penetrate wing, according to the circumstances. How do they do it without adding ballast? Modifying the area of their wings by extending o retracting them. However, increasing the wing loading is a sub-product of reducing lift capacity and both types of drags. A diving hawk has a tremendous penetration and diving speed, and it can also slow to zero in a few feet.
Posted on: 11/3/2009 8:58 PM by Author "lnewqban" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9226344

RE: Show your Precocious little pilot
Congratulations!! You have a little precious aviator at home.
Posted on: 11/3/2009 8:32 PM by Author "lnewqban" in the forum "Beginners"
http://www.rcuniverse.com/forum/fb.asp?m=9226291

RE: Pull Pull servo placement
My response to your questions is yes. Both must be in line and symmetry; rotated positions around that line are non-critical. Check this out: http://members.cox.net/bdfelice/Ackerman/ackerman.htm
Posted on: 11/3/2009 7:48 PM by Author "lnewqban" in the forum "Questions and Answers"
http://www.rcuniverse.com/forum/fb.asp?m=9226186

RE: BAE HAWK FLAPS
.....and the tail will need to be strong enough to keep the wing and the flap at the right angle, fighting the increased pitch moment. Consider that the strong downwash created by the deployed flap will reduce the AOA of the stab; ie, the airstream will heat the stab and elevator from above.
Posted on: 11/3/2009 7:02 PM by Author "lnewqban" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9226058

RE: BAE HAWK FLAPS
Check this mechanism out: http://www.freepatentsonline.com/6010097.pdf
Posted on: 11/3/2009 7:34 AM by Author "lnewqban" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9224559

RE: 83
bcatone, The real airplane was big, having a wingspan of 42' and a length of 29'. Checking the scale of your model: 83�/504� = 0.165 = 1/6.07, 1/6 scale approximately. In order to be more accurate, you should do the same for the length, as da Rock as explained above. I have just measured my bust, and it is around 18�, then, depending on where the pilot’s bust is cut: 18�/6 = 3� tall bust Your pilot's figure: 2.85" x 6 = 17" height of real bust I believe is close enough.
Posted on: 11/3/2009 7:21 AM by Author "lnewqban" in the forum "Questions and Answers"
http://www.rcuniverse.com/forum/fb.asp?m=9224539

RE: Penetration
[sm=thumbs_up.gif]..........and I will add: Flying faster is a privilege of low drag and/or overpowered models. Profile drag depends exponentially of the air stream velocity; just as the needed thrust does. That is one of the reasons that airliners have to fly at 30 000 feet high, since high altitude equals low air density and viscosity.
Posted on: 11/3/2009 6:55 AM by Author "lnewqban" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9224509

RE: Balancing a canard or tandem wing biplane for initial flight.
According to that logic, a tailless aircraft couldn’t be either nose heavy or tail heavy. However, pitch stability is not determined by the location of the stab respect to the main wing. The more or less authority of the stab, wherever it is, comes from how much the airstream helps it or not to stabilize the main wing. In conventional, layouts the stab works against the lift produced by the wing. In canard layouts, the stab helps the main wing to lift the aircraft, and then a smaller wing is possible. This website has animated pictures with very clear explanations. http://www.geistware.com/rcmodeling/articles/aerodynamics/centerorgravity.htm Just click on the tabs under each picture to activate the animation.
Posted on: 11/2/2009 7:47 PM by Author "lnewqban" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9223584

RE: Help me figure out this mechanical advantage in the servos
Is this what you described?
Posted on: 11/2/2009 6:50 PM by Author "lnewqban" in the forum "Questions and Answers"
http://www.rcuniverse.com/forum/fb.asp?m=9223424