RE: Golf ball dimples
Right I was able to reduce the drad further when I tried to see how a flying car version of that low D car could look like. The suspension could be like in Gumpert Apollo. It also seems to have almost no room to work for the suspension albeit it has 700 hp engine on it.
Posted on: 11/3/2009 2:37 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9224338

RE: Golf ball dimples
I tried to figure out how to make a real small drag into a 4 seater car, thus going 55 mph at 0,5 gallons / 100 km ( MPH 124 ). I had roughly drag coefficient 0.17 here. This mean very low and clean body...not very practical for inner city driving. Dimples would certainly lower the drag.
Posted on: 11/2/2009 8:01 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9222024

RE: Golf ball dimples
I just wanna add that my 250 m stroke had a touch and go at 200 m flight ( GIR ) but skidded of the green. Mike Austin is a legend of having hit a ball 515 yards of the tee. I hit mine from a position where the ball was lower than my shoe soles and at delofted club face angle ( loft i3 equivalent ) at very high speed at least 110 mph where the ball leaves the club face at 160 mph having 0.5 N of drag. I was also in slighty elevated postition in comparison to the green ( 5 meters / 15 ft ). I was told it was a flyer..but maybe it only had less rotation than normally hit balls.
Posted on: 10/31/2009 7:25 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9217115

RE: Golf ball dimples
[quote]ORIGINAL: davidhand Very interesting reading reading, particularly the one on the aerospaceweb. In the case ov the car which is not rotating do you not think that it would only be necessary to put the dimples in say the last third of the vehicle? Or perhaps some simpler way of creating turbulance, as on the Gloster Javelin. [/quote] Golf ball that does not rotate creates even less drag...called a flyer. I once had a 250 m ( 288 yards ) stroke with an i5 ( 10 years ago ).
Posted on: 10/30/2009 9:49 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9214741

RE: pusher vs. tractor
[quote]ORIGINAL: TFF Hartzell's on Piaggio PT6s have life limits on either the blades or blade and hub because of the exhaust. I dont know the limits. Hartzell manual 158 is where to find it. [/quote] I did notice also LF 2100 prop blades looked pretty nasty after a while...I think the exhausts could be made to go through the prop hub !
Posted on: 10/25/2009 11:37 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9200523

RE: pusher vs. tractor
There is some efficiency involved here...a 2 seater with 4.5 m2 wing area and 100 hp engine; http://www.youtube.com/watch?v=YjlE5Gl4N9I&feature=autofb
Posted on: 10/19/2009 2:10 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9184486

RE: pusher vs. tractor
[quote]ORIGINAL: da Rock How about the fact that a fuselage in front of a pusher displaces air away from that prop. In fact, how many pushers do you know of that see a fan's worth of air? They can't, can they? They're going to see less air and it's going to be turbulent. An example of what turbulent air that's been disturbed and displaced is shown on TV 15-20 weekends a year. Watch the front runner in a NASCAR race when he's in clean air. He has an advantage and the guy behind is at a disadvantage. That's more of an example of a design that's at a disadvantage in ''dirty'' air. But there's another. Car's running close behind another lose downforce. Downforce on those cars is a function of the quantity and force of air the car sees, and the following car sees less that is weaker. They're the pusher prop that's not getting a full fan and what it's getting is ''thinned''. Formula 1 is a better example. They have even worse problems when their car is the ''pusher''. [/quote] I think this could be overcome with prop design; more pitch for the prop in the root and tips more effective than in tractor..by adding more blades or making them othervise more efficient. But the root of the prop should acceletate the flow in order to make that suction possible for the zero speed cooling to work. Tractor prop throws the airflow onto the surfaces and causes more drag too.
Posted on: 10/15/2009 3:42 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9174639

RE: pusher vs. tractor
[quote]ORIGINAL: da Rock [quote]Like golf swing..gotta consider all variables to execute a perfect stroke and make a double eagle.[/quote] You don't make a double eagle with just your drive, or your approach, or your putt. But are you after a lower score or a longer drive. The Cessna achieved a lower score with two engines on the same line. It isn't faster (drives the golf ball farther) with just one engine is it? If you wish to consider all things, then consider that the pusher receives disturbed air no matter what. The Cessna example actually does suggest something to that idea. Very disturbed air to the pusher really screws up the efficiency of the climb and evidently operating the front alone isn't as efficient as the rear alone IN A CLIMB. Disturbed air increasing drag appears to be a significant problem with a pusher. And that can cause problems. Be prepared. It would be interesting to see where you are in your years of development. Any pictures? And experimental results? [/quote] I agree there is disturbed air....but one has to deal with that ( and take advantage of it ); http://max3fan.blogspot.com/2009/04/zero-speed-ram-air-cooling-by-prop.html http://max3fan.blogspot.com/2009/04/airscrew-design.html LF2100 used several props before a 4 blade fan was found out to be the most efficient back in the 80ies.
Posted on: 10/14/2009 6:22 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9172008

RE: pusher vs. tractor
[quote]ORIGINAL: da Rock The pusher prop is almost always going to have a fair amount of the air that's presented to it affected significantly by some structure or another .... [/quote] Right..but this would have to be considered and not just built "a strange tractor plane with prop in the rear pushing". You see/know what I am after ? Like golf swing..gotta consider all variables to execute a perfect stroke and make a double eagle.
Posted on: 9/9/2009 5:32 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9080965

RE: pusher vs. tractor
[quote]ORIGINAL: Sport_PilotPusher is more efficient, but tractor has more elevator and rudder authority at low speeds. [/quote] I think you have a point, but also a pusher has the suction caused power steering option..not many realize that !
Posted on: 6/4/2009 4:13 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=8824409

RE: pusher vs. tractor
[quote]ORIGINAL: HighPlains All the really fast prop airplanes have always been tractor designs. Nothing likely to change. [/quote] If you study history of aviation really carefully this is not quite true. But I agree that the "absolutely" fastest is not likely to be a pusher ( for various reasons ), but most economical it could be. 1. New Avanti Piaggio goes 740 km/h ( name a faster turbo prop passenger craft ) 2. Learfan 2100 was more economical and faster than Citation I Bizjet 3. Mixmaster did the same as B-17 but with 2 engines and was 100 mph faster 4. Edson Fessenden Gallaudet flew 130 mph in 1912 with a pusher. I could also mention that Lars Giertz whose VMax Probe was demolished in testflite mentioned his plane could go ( calculated estimate ) 240 mph at 50 hp and was after 300 mph at 80 hp. I do appreciate your input..there is lotsa variables to consider. Also the Molt Taylor dream of a really economical pusher Micro Imp never realised it became 240 kilo plane. Jerry Holcomb was able make a one ( Perigee ) at 166 kg. I think to accelerate the flow at fuse and reduce drag the fuse would have to be really clean and the turbulent air to the prop would have to come somehow projected evenly pressurewise...you know what I mean ? This is why I have the wing throwing the "turbulence" middle of the prop arch in my MAX III. The fan/prop would then have to deal with this wash as efficiently as possible. new ellipse prop for instance could have an answer. I think the biggest obstacle in pusher systems so far is the cooling and maintenance of the engine. ( Second is the CG management..they tend to be tail heavy ). More about my pusher here: http://max3fan.blogspot.com
Posted on: 6/4/2009 2:41 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=8824298

pusher vs. tractor
Recent FLIGHT magazine and pusher pusher story by Peter Garrison made me think if a pusher is a "dead end" after all. I have been very keenly developing a pusher design during last 8 years and last 5 months actively. I got the impression tractor is more efficient if you have fuselage dia more than 50% of the prop dia. Did anyone read the story ? Pushpull Cessna is know to be 33% more efficient ( climb rate ) when running with pusher prop alone than in tractor mode. The drag and turbulence and several other factors were mentioned but seems that real comprehensive data is vague. Is pusher technology still like a new frontier in aviation ? Also the Piaggio Avanti P-180 loud noise was mentioned.
Posted on: 6/3/2009 9:37 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=8821871

RE: What is the physics behind 150+ mph slope soarers without engines?
I think ( IMHO ) the slope soarers and sailplanes use pretty much same way wind energy as sail boats but in different direction. Also the cleaniness of the sailplanes and large low drag lifting area contribute to the speed.
Posted on: 5/19/2009 2:11 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=8780819

RE: TWIN, INLINE, DUCTED FAN'S = TWICE THE TAILPIPE VELOCITY?
[quote]ORIGINAL: SPEED JUNKIE [size=3]Who need's two fan's in one thrust tube anyway?[/size] [/quote] Not very common in subs nowadays..or iz it ?
Posted on: 5/19/2009 2:02 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=8698384

RE: Need a lite Me-109 G-6 ?
I saw the model is in my storage..looking pretty dead ( maybe I rehabilitate it..I did that to my LS 1 glider ). What made it strong was the two piece wooden roof for the canopy ( same 10 mm balsa piece to the rudder..in canopy a 1 mm plywood on top )...no curving parts needed from plexi. Here is how it was colored...approximately. BTW: Chinese have 29 symbols for asteroids...svastika was one them. So it is actually a star ( svastika ) spraying materia into space .
Posted on: 4/13/2009 10:24 AM by Author "topspeed" in the forum "RC Combat"
http://www.rcuniverse.com/forum/fb.asp?m=8676498

RE: Measuring Total Plane Drag
I was designing the gear and discovered that the landing gear can make 60% of the total drag...looks innocent little gadget but can kill the whole economy of the plane when you don't have enuf power to leave the ground. So watch it.[:D]
Posted on: 4/13/2009 4:59 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=8675986

RE: Prop efficiency, 2 versus 3 blades
[quote]ORIGINAL: CrateCruncher Airplane drag tests will show the in-flight force required to propel the plane at a given speed. And after 40 years of speculation and argument we can be the generation that provides evidence one way or the other. [/quote] This is very important..you have to know the drag. Also all aircraft are usually designed for some speed region...also you have to choose the prop accordingly. There are lotsa variables here. What I am wondering at the moment is how much different is the prop in front of the plane compared to one aft of the plane. Does the laminar flow in fuse become disturbed with lesser props...I am leaning into at least 7 props fan...with high pitch and small diameter instead of two blades. Seems to me the bigger the prop is the further will it throw the wash. There is no need for that in a pusher...slipstream is smooth. The suction will affect airflow at least 3 feet in front of the 800 mm dia prop at 5 - 6 000 rpm.
Posted on: 4/12/2009 1:01 PM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=8673709

RE: Prop efficiency, 2 versus 3 blades
Is this even better for a pusher ?
Posted on: 4/7/2009 12:44 PM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=8657894

RE: Need a lite Me-109 G-6 ?
I have had 2 Mustangs too. I like it a lot. I had one destroyed when I had a radio interference. Scaleish P-51D plunged into the Bothnic Sea.[&o] 109 is slightly more challenging to fly. Gotta keep the speed at landing and never pull the elevator fully back...g-stall occurs.
Posted on: 4/6/2009 6:47 AM by Author "topspeed" in the forum "RC Combat"
http://www.rcuniverse.com/forum/fb.asp?m=8653372

RE: Need a lite Me-109 G-6 ?
Thanks Max, I have to look for the pics. The plane is pretty worn out by now ( let's say no longer very photogenic ). It was in the Model Airplane News center fold in 1990-1991 ( or some similar mag ). It was long ago. It was totally different AC at 750 gr weight than later after few low altitude snaps and repairs with 950 gr. Rudder was of lower type and no twist ( I seem to have left out an S from the word Messerschmitt ). rgds, Juke
Posted on: 4/5/2009 11:12 AM by Author "topspeed" in the forum "RC Combat"
http://www.rcuniverse.com/forum/fb.asp?m=8650506

RE: Need a lite Me-109 G-6 ?
I think a Me-109 G needs a scale spinner. Here is how I modified the existing spinner to make a cheap "scale" one. Needs a lathe ( I used the Makita drill to rotate the spinner tip glued from plywood pieces ) and some sanding paper. Back plate is the key word and a new screw. This will bring some more weight to nose, but plane flies just great.
Posted on: 4/5/2009 11:07 AM by Author "topspeed" in the forum "RC Combat"
http://www.rcuniverse.com/forum/fb.asp?m=8650268

RE: Measuring Total Plane Drag
I used the AR-5 site for the Bruce Carmichael example following drag calculations for my pusher ac.
Posted on: 4/5/2009 9:23 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=8650257

RE: Can I really design my own airfoil?
[quote]ORIGINAL: dick Hanson PS the Wright Bros airfoil is almost a dead ringer for current,indoor microfilm competition models [/quote] I have a really small "F-14" delta wing sling flyer and it has the "same foil" inverted and flies awesome.
Posted on: 4/3/2009 4:45 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=8644208

Need a lite Me-109 G-6 ?
I used the draw these 10 years ago. [IMG]http://i136.photobucket.com/albums/q168/topspeed2/me-109G-6_high_tail3.jpg[/IMG] Slightly bad scanning but drawing will help to make a 650 gr-720 gr .10 - .15 powered 109 G. I have flown one over 150 flights and it is still flyable.
Posted on: 3/27/2009 8:42 AM by Author "topspeed" in the forum "RC Combat"
http://www.rcuniverse.com/forum/fb.asp?m=8621215

RE: P51d mustang aerofoil section
[quote]ORIGINAL: sir crashallot yeah topspeed what sopftware are you using there [/quote] I have profili ( unregistered ) 2.15b version. I have discussed which version I should have with Stefano Duranti via e-mail. It costs only 10 €:s. Duranti Stefano via della Casazza, 43/B 32032 Feltre (BL) - ITALY Phone ++39 0439310326 E-mail info@profili2.com - st.duranti@tin.it This is how my plans looked
Posted on: 3/26/2009 8:45 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=8617749

RE: Can I really design my own airfoil?
http://www.raes.org.uk/cms/uploaded/files/SG_HPAG_aerofoils.pdf There is a 1977 study of human powered AC foil.
Posted on: 3/25/2009 7:04 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=8614320

RE: P51d mustang aerofoil section
Yeah go for it ! I have SD 6060 in my TS2 racer model ( see my profile ). What do you Ben Lanterman think of that Dr.Selig creation ? rgds, Juke PS: I saw F-15 first time in Farnborough air show in 1996. Bird was in bicentennial colors back then.
Posted on: 3/25/2009 6:39 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=8614289

RE: P51d mustang aerofoil section
Right, See the models loads on the left side ( near origo )..those kites are really lite..but they have to be due to Reynolds effect.
Posted on: 3/24/2009 7:53 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=8610679

RE: Can I really design my own airfoil?
[quote]ORIGINAL: dick Hanson The short answer is yes There are no tricks or secrets involved Best yet , the results may be better than the ones you find in endless charts. A sharp pencil , a ruler (a scale) and a couple of French Curves and you have all the tools you need Oh yes an eraser is a good idea. First decide what the finished model (this is all about model aircraft ) will be How large is it to be? How much will it realistically weigh.? Will it have to go fast ? will it have to be very maneuverable? OK think about those questions Now , can you pick n choose the materials you will need or are you stuck with a limited type of materials. Airfoils are not really critical for most sport type model airplanes so as we pick n choose this airfoil , remember some compromises may be needed and in the end , the results won't depend on some "exact" line. Let's start by sorting out the basics : Thick wings can be stronger than thin ones . Pretty obvious . Thick wings TYPICALLY can operate over a wide range of angles - called Angles of Attack- (AOA) Why? because the shape is less critical. think of a rolling pin as the least critical shape and a flat sheet as the most critical somewhere in the middle -is a shape we can use -if we streamline it a bit . Thin wings can offer less drag and do other neat stuff but lets pick a decent compromise for the first effort. Lets assume we want to build a sporty flyer about 4 pound and about 50 "span- no scale model but a nice looks like a model type. some really rough rule of thumb says well 500 square inches is pretty good for 4 pounds This gives a wing loading of about 15 ounces for a squarefoot. At that weight the model will fly easily . A good shape for our use then will be oh- 10"chord by 50" span (500 sq inches) Wow! we are ready to pick and design the airfoil . Where do we start Let's look at how thick should it be experience shows that a variety of materials can be used in this size wing and get good results . balsa - Obechee- pine (yes) fibreglass but lets make it easy and figure on mainly balsa and some spruce for the top and bottom of a main spar located about 1/3 of the airfoil ( chord) This is like designing a bridge and so the engineers call the spar design a beam and the the weight it can carry the beam loading. Thru trial and error we have foundthat on this type of a wing ,in this type of application - a beam about 1 to 1.5" thick is a good working range This means the airfoil will be 10% to 15% as thick as it is long. Let's compromise and go for about about the center of that range or 13% Now for the curves - the critical part of the drawing !! Not really critical! we have already done the critical part! So ... The drawing should give us lines which are easy to accurately build. The leading edge is best if it is a part of a circle and this then blends to the spar and then continues in two straight lines which meet at the rear. That's all? Not really This is where the curve comes in Let's make the airfoil symmetrical- really this allows you to make panels which can be matched up easily to check for differencs (accidents) in building so draw a straight line 10" long. This is the centerline of the airfoil . now measure back 1/3 from he leading edge and place the spar ( 1.3" thick)centered on the line. Leading edge shape ? draw a 1/2" diameter circle at the leading edge centered on the line Now grab the French curve and juggle it around till yo u get a nice blend from the leading edge to the center of the spar flip it over and draw the bottom line. Using the ruler (a straightedge) draw straight lines from the top and bottom of the spar to the trailing edge. Now again with the french curve, lay it over one of these straight lines and blend from the top of the spar into the straight line as smoothly as possible We actually want the aft section of the airfoil to be straight lines! Why? easier to build and duplicate and the shape is as good as any . You may wnt to slightly seperate the lines at the trailing edge to permit the aileron to be stronger (thicker ) a sharp trailing edge gains you nothing on this model. Ther you have it "my first airfoil" and for this application as good as any and better than some It will be good for slow speeds or aerobatics and on the thinner side (11%) goes like stink ( many Quicky 500's were exactly this shape") My old "quicky"weighed three pounds with a K&B40 and I always had to add ballast to race (rule) It also flew very slowly if I wanted i to and I used it to practice new maneuvers . vertical eights -spins whatever ' perfect manners in a great aerobatic trainer! [/quote] This is just the way Gustave Eiffel did his foils I assume...but he also built a windtunnel to test them. I guess when you have a good grasp on these lift coefficients etc you can just tune the foil thickness by heart ( like making a good sounding violin ). I used to do wing foils with french curves before there was a computer..I traced the foil from an existing foil. Very easy indeed...and planes flew nicely ( not so well the ones that I hastily drew with french curves after looking at the photos from existing planes...not recommending this approach ). But I am sure that a good mathematically gifted dude with a gift to draw well can do the job and define a well flying AC with his own foil. This needs the understanding of the speeds, weights and liftcoefficients needed for the project and basic understanding how foils with low reynolds area actually perform ( bubbles etc ). Wing geometry has a lot to do here too ( and lotsa MOJO and SWAG :)). Easier would be getting a Profili program.
Posted on: 3/24/2009 7:21 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=8610628

RE: P51d mustang aerofoil section
Michael Luvara had a similar task when he made a model of Tsunami with laminar foil. http://members.tripod.com/~tsunam/ The Hergett Mustang gives 9 pages in google ( The eppler 203 foiled Mustang)...so it is pretty popular. You are more after the scale effect and thus search for the "right" foil may give you extra credits for appearance as well. You have some good comments here of modelists and real AC engineer...I think you will find the answer soon ( use the "force" or go for a stroll and it all clears for you I am sure ). Good luck !
Posted on: 3/24/2009 3:55 AM by Author "topspeed" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=8610453