RE: Zero history question??
The American's test flew captured examples in bare metal ( with US markings ), but that's about all you'll find, I think.
Posted on: 10/31/2009 10:35 PM by Author "wellss" in the forum "RC Warbirds and Warplanes"
http://www.rcuniverse.com/forum/fb.asp?m=9218842

RE: Stab twist: one side. Effect?
Don't worry about it. It'll cause a slight left roll, nothing the ailerons can't compensate for......same with elevator trim
Posted on: 10/31/2009 1:52 AM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9216891

RE: OS .52 4-stroker prop
http://manuals.hobbico.com/osm/fs-52s-manual.pdf
Posted on: 10/26/2009 12:26 PM by Author "wellss" in the forum "Beginners"
http://www.rcuniverse.com/forum/fb.asp?m=9203184

RE: Full flying elevator question.
The biggest concern is aerodynamic balance and flutter. Hinge line should be close to 25% chord, or a little forward. Incidence is set the same as a fixed stab, only it is adjustable.
Posted on: 10/26/2009 8:36 AM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9202705

RE: Golf ball dimples
[quote]ORIGINAL: hugger-4641 The Navy does the same thing to the skins of nuclear submarine. I woudn't think 12 percent is too big a stretch. [/quote] I reckon that's more to do with reflecting sound waves to become harder to detect, rather than a decrease in drag ? But, if it serves both purposes...I suppose it's a good thing.
Posted on: 10/24/2009 6:35 PM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9199074

RE: pusher vs. tractor
[quote]ORIGINAL: alasdair [quote]ORIGINAL: wellss One of the main differences is the effect on pitch stability. Tractors are destabilizing, and require greater stabilizer surface with less control power. The opposite for pushers. [/quote] wellss, I have heard that too but not seen it explained or quantified. Where did you get that info? Was it accompanied by any quantitative analysis? [/quote
Posted on: 10/24/2009 5:03 PM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9198916

RE: Golf ball dimples
Inside the dimples are stagnant vortices ( air that just sits in the hole, spinning around in circles ). This basically gives the object a cushion of air surrounding it and allows energy to transfer from the vortices to the streamlined airflow as needed. The streamlined air doesn't stick to the vortex air as easily as it does to the surface of the object and so drag is reduced. At least, that's how I understand it. I'm sure there's a lot more to it than that. Maybe think of it as an invisible ball bearing inside the dimple ?
Posted on: 10/23/2009 5:34 PM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9196728

RE: AILERON TRIMMING.
Don't most computer radios save the trim settings for each model? If not, that's dumb...
Posted on: 10/21/2009 8:17 AM by Author "wellss" in the forum "RC Radios, Transmitters, Receivers, Servos, gyros"
http://www.rcuniverse.com/forum/fb.asp?m=9190348

RE: naca foil datas
It is higher drag that causes lower maximum lift at low Rn. Why the drag is higher....I believe is due to the boundary layer not scaling and so is thicker, relative to a smaller airfoil.
Posted on: 10/19/2009 9:08 AM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9184856

RE: naca foil datas
The original NACA report is here, http://naca.central.cranfield.ac.uk/report.php?NID=1087
Posted on: 10/18/2009 1:48 PM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9182933

RE: Wing load for L-19
A G-23 will fly a 15 pound PT-19 just fine, so I'd imagine that a 26cc would handle 16.5 pounds in a cessna, no problem....very scale like. Probably won't be able to loop from level flight ( or just barely ), but hammerhead turns would be possible. Not that you would fly those maneuvers with that plane, but just to give an idea of excess power.
Posted on: 10/16/2009 4:27 PM by Author "wellss" in the forum "Giant Scale Aircraft - General"
http://www.rcuniverse.com/forum/fb.asp?m=9178533

RE: how to calculate dihedral angle?
Of course there is, but it may not be simple. There are several balancing of torques. For example, take the fin/rudder... It is above the CG usually and so acts like half a wing. In sideslip, there would be a tendency to roll. A sideforce from the left may want to turn the nose to the left, but will cause a right roll. The effective angle of attack of the wing due to sideslip with dihedral is a simple formula, angle of attack change = dihedral angle * sin ( yaw angle ) You would need to figure out the resulting rolling torque and balance it against the fin/rudder. In a turn, there is also the effect of the outer wing travelling faster than the inner one. It's a small effect, but must be accounted for as well.
Posted on: 10/13/2009 5:18 AM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9168931

RE: Seriously, need advice from a master mechanic (car trouble)
A had an incident with my car, where it was using lots of oil ( 4 litres in 100 km ). It turns out the oil filter blew up as a result of using too thick of oil ( 10 w 30 ). I now only use 5W30 synthetic with a heavy duty K&N oil filter. My mileage also improved significantly ( almost 100 km per tank ). Not a Honda, but still.... I can't imagine that you would have to use a thicker oil in a warm climate. The temperature inside the engine is not likely to be that greatly affected.
Posted on: 10/12/2009 8:22 PM by Author "wellss" in the forum "Off Topic Forum - Cars, Trucks, Buggies and more"
http://www.rcuniverse.com/forum/fb.asp?m=9167897

RE: Double Reflex Airfoil
I don't know if this profile is the same, but maybe similar? I "reflected" the curve aft of the highest point, to the trailing edge. It looks like this, [image]http://www.iaw.com/~general6/double_reflex.jpg[/image] The analysis at Reynolds number of 200000 ( The Magnum flying at 25 mph ) doesn't look promising, when compared to the NACA 0012. It is inferior in every way. The higher drag leads to earlier stall and quite possibly very abrupt as the code was unable to perform calculations beyond the end of the line, whereas the NACA profile clearly shows a gradual approach to maximum lift. [image]http://www.iaw.com/~general6/dr_lift.jpg[/image] [image]http://www.iaw.com/~general6/dr_drag.jpg[/image]
Posted on: 10/12/2009 2:54 AM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9165813

RE: Double Reflex Airfoil
Could you scan the profile from the magazine? If I knew the thickness ratio and chord location of maximum thickness, I could construct a similar profile and run it through some analysis software and compare it to a typical NACA section, for example? Or, you know what....I'll construct such a profile with maximum thickness at 30% chord, say 10% and 15% in thickness and compare to NACA 0010 and 0015. We'll see what happens...stand by
Posted on: 10/11/2009 11:37 AM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9163665

RE: angle of attack limited by landing gear
Holding more elevator than is needed to keep the tail on the ground is a waste and only "takes away" lift, helping to keep the model on the ground longer.
Posted on: 10/5/2009 12:45 PM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9148328

RE: Double Reflex Airfoil
Very similar to a Joukowski profile, which is a natural streamline shape and the earliest mathematical or theoretical airfoil application, dating to 1910 or so. Good for lift, but draggy. Therefore, may work well at low Rn. I have no experience with such a profile and it would be very difficult to quantify any difference from any other profile, I'd imagine. However, in real world application, the Republic P-47 used a modified Joukowski section ( with finite trailing edge thickness, ie Karman-Trefftz ) wrapped around the NACA 230 mean line to give minimal pitching moment while avoiding the rather abrupt stall with the NACA thickness distribution. Hmm, Dan Santich designed the original Top Flite P-47 with a similar airfoil as he mentions it having a little of the double reflex built in. I flew a Hots years ago, but I can't remember what airfoil it had...but it flew well. I'd say that it will depend on the chordwise location of the maximum thickness. The further back it is, the more abrupt the stall will likely be. Joukowsky airfoils are at 25%. Modifications can move that point rearwards. NACA sections ( 4 and 5 digit ) are at 30% and are considered general purpose sections. Beyond that, your goal is to reduce drag at the expense of maximum lift and stalling characteristics.
Posted on: 10/5/2009 6:46 AM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9147562

RE: Mean aerodynamic chord
It's not even a good approximation and results in nearly twice the moment from the aero center. Placing CG at 1/4 mean aero chord is an equally good approximation. Better safe than sorry. If you wanted to use a rule of thumb type approximation, you could take the 'simple' formula, using only areas, and cut in half, the resulting distance from the aero center of the wing. I'm not trying to criticize, but someone reading this thread that doesn't know any better might use that formula as a "good approximation" and crash their airplane.
Posted on: 9/25/2009 10:01 PM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9124376

RE: Wing spoilers vs. ailerons??P-61 Black Widow had spoilers....
The P-61 used spoilers because it had full span flaps. The F-14 was similar in concept
Posted on: 9/25/2009 9:50 PM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9124337

RE: Mean aerodynamic chord
Neutral point based only on areas and moments are only half of it and NOT accurate. One should be using the lift slopes of the wing and tail ( varying with aspect ratio and sweep ). The latter being about 1/2 due to downwash from the wing and the effect of thrust ( destabilizing in pitch when in front of the CG ) is not accounted for.
Posted on: 9/25/2009 2:34 AM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9122260

RE: Right Wing drops suddenly
You would be able to test HighPlains idea in level flight. If it only drops the right wing in turning maneuvers but not in level flight, then it's probably gyro. If it does the same in level flight, it's probably out of trim, for whatever reason. Just feed in some left rudder trim until it doesn't always snap to the right
Posted on: 9/24/2009 12:09 AM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9119499

RE: Anti Yaw Device
I haven't read the article, but it sounds like the guy is trying to think outside the box a little bit. I can see how if weight is added to the right side, that side of the plane will accelerate more slowly, causing a right yaw in order to cancel the left yaw caused by the propeller. The uneven wing loading will of course affect stall characteristics with the engine off. Hmm....what if the wing area was also increased on that side? The added weight and drag from that could allow for some of the other wingtip weight to be removed and the idea would be to keep an even wing loading. I think the Macchi 200/202/205 series fighters from WW2 did something like that, with one wing longer than the other one.
Posted on: 9/24/2009 12:08 AM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9119495

RE: Flaps - a question of interest
Let's say flaps reduce landing speed by 20%. If your trainer already flies 20 mph without flaps, a reduction of 4 mph is not really significant. What's that, walking speed? A mild breeze can do the same thing. As the plane gets heavier, it becomes more significant.
Posted on: 9/18/2009 1:44 AM by Author "wellss" in the forum "Beginners"
http://www.rcuniverse.com/forum/fb.asp?m=9104867

RE: pusher vs. tractor
One of the main differences is the effect on pitch stability. Tractors are destabilizing, and require greater stabilizer surface with less control power. The opposite for pushers. Thrust decreases with speed and so in theory, a pusher should be able to operate at greater efficiency if the air entering the propeller is slowed down, albeit smoothly, rather than turbulent.
Posted on: 8/29/2009 8:55 AM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9053909

RE: Induced Drag
Your formula is right, except AR should be in the denominator Cl^2 / ( pi * AR ) not, Cl^2 / (pi) * AR <- AR is actually in the numerator here
Posted on: 8/29/2009 8:38 AM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9053878

RE: Do not exceed speeds for model airframes...
Excellent point, I've seen several trainer type airplanes fall apart from normal training use. I sent e-mails to Hobbico and other manufacturers to at least try to determine the extent that the models are designed or tested. Of course, I got no replys.
Posted on: 8/29/2009 8:30 AM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9053867

RE: Let’s discuss facts about stall-spin
The AoA is directly related to the elevator angle, provided the airplane is stable. Find the specific angle by test flying and don't exceed it at any time. No stall.....no spin....no crash. Attitude/Airspeed doesn't matter. No guessing required.
Posted on: 7/20/2009 5:04 AM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=8948045

RE: Extra airfoil thickness
The optimum thickness for models is 12%. Thicker airfoils don't show improvement until high Reynolds number ( full size ). Looks like Mike Hurley knows what he's doing.
Posted on: 5/16/2009 1:29 AM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=8773075

RE: P51d mustang aerofoil section
Check the UIUC Airfoil Coordinates Database http://www.ae.uiuc.edu/m-selig/ads/coord_database.html
Posted on: 3/18/2009 9:35 PM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=8592430

RE: Software for testing
Javafoil does 2d flow analysis http://www.mh-aerotools.de/airfoils/javafoil.htm For vortex stuff, you'll need 3d and it gets expensive http://www.hanleyinnovations.com/multisurface/
Posted on: 2/15/2009 9:05 PM by Author "wellss" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=8480823