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RE: SIG Ryan STA special Plan needed!
I agree with the others. It's nice that you guys are sharing your builds. Despite this being a popular kit for decades I have seen only one partial build thread on the internet. This kit is in my stack so anything I can learn from your experience is much appreciated. One thing I have heard is that the plastic material included in the kit for making scale hinges has a reputation for being quite fragile and prone to breaking unexpectedly. (Has anyone else heard this?) I like the scale hinge look but will likely opt for Robart's point-style as a substitute.
Posted on: 1/6/2010 1:46 PM by Author "CrateCruncher"
in the forum "RC Scale Aircraft"
http://www.rcuniverse.com/forum/fb.asp?m=9392549
RE: Climb on speed change
BMathews, How did you conclude the CG of the model in question was set too far forward? The original poster doesn't have the plane in the air yet. He was referring to the model's reputation "in general". The plane's reputation might be suffering from any one of a host of maladies: poorly matched wing lift/weight, excessive decalage setup, insufficient downthrust. Another point: Adding downthrust actually helps reduce pitch-up caused by thrust moment in high-wings. Further, chopping the throttle of a plane with downthrust will cause it to momentarily pitch UP, not down. Regarding constant climbing planes, fiddling with elevator trim etc. Is this some new form of macho? "only real men fight their airplanes"(LOL). I prefer to control mine with dynamic feedback. Regards.
Posted on: 1/6/2010 1:30 PM by Author "CrateCruncher"
in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9392504
RE: Climb on speed change
Vic, A wing generates lift in proportion to the square of it's velocity. So, when all other things are held constant the plane climbs when prop thrust and airspeed increase. Notice I said "proportional" not equal. The wing also generates lift in direct proportion to the angle of attack of the wing. Why am I bothering to mention this? We can use one to compensate for the other. Here's a common example. When landing everyone knows you have to steadily increase up elevator as airspeed falls in order to maintain a constant descent rate to touchdown. What you are doing is [i]increasing[/i] lift with angle of attack of the wing to compensate for the [i]decrease[/i] in lift due to falling velocity. Designers use the same technique to automatically maintain altitude with an airspeed increase. Think of your Pilatus as a yardstick attached to the ceiling by a string. The string is attached to the yardstick at it's center of gravity so it is balanced level. If we tape a quarter to one end of the yardstick that end sinks slightly and the yardstick is no longer level. Downthrust in an engine is just like adding weight to the end of the yardstick. A prop with 0 degrees of downthrust directs 100% of the force horizontally. But if the engine is angled down at 2 degrees, about 0.1% of that thrust is [i]straight down[/i] just like adding the quarter to the end of the yardstick. Even better is the fact that the downforce increases in perfect proportion as velocity increases. In a nutshell, we put some downthrust in our prop so that as lift increases in proportion to the square of the plane's velocity, it also decreases due to downthrust pulling the nose down and decreasing the angle of attack of the wing reducing lift. When everything is designed correctly there is no climb when speed is increased.
Posted on: 1/5/2010 11:58 AM by Author "CrateCruncher"
in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9389054
RE: Scratch-built Fokker Dr.I 1/6 scale
Happy new year everyone! This officially ends the holidays for me so I'll have to leave the world of Fokker Dr1's soon and get back to work. But I have done a little more digging and discovered the airfoil used on the Dr1 and it's lift curve. It was the Gottingen 298, named after the university wind tunnel that first published the research on it. In John Anderson's book The Airplane - A history of it's technology there is an interesting excerpt I thought Dr.1 enthusiasts might enjoy: [link=http://books.google.com/books?id=FrvrkXYDCL8C&pg=PA144&lpg=PA144&dq=gottingen+298&source=bl&ots=bAkb6VT2b2&sig=VDKk5WLumCBM_ro-zM2sJoA7GWY&hl=en&ei=yQA-S9rAJ4GCMeKixQY&sa=X&oi=book_result&ct=result&resnum=4&ved=0CBIQ6AEwAw#v=onepage&q=gottingen%20298&f=false]The Airplane Excerpt Link[/link] Looking at the graph in Figure 5.11, page 150, you can clearly see that the 298 airfoil begins to generate positive lift at -7 degree angle of attack (AOA). In addition, the airfoil makes a huge amount of lift even at shallow angles. This combined with the enormous wing area is not only the secret to the Dr1 maneuverability but also to it's reputation as a good climber despite anemic Oberursel power. After looking at several in-flight photo's from the period (as well as the excellent video US185Damiani linked) I've come to the opinion that the tail does indeed ride high at cruise attitude. Looking at low fly-by's at 3/4-full throttle the turtle deck line is almost horizontal. (Landings are misleading. When approaching to land the tail sinks to add wing AOA to maintain lift at lower speed). Ok, I am speculating here, but I suspect the Dr1 was designed with the wings at -2 like most planes from the period on the assumption the airfoil would perform similar to a thin one. Fokker had an inch taken out of the tailpost (+3.5 stab) after flying the prototype with constant forward stick pressure to maintain level flight. This made the wings effectively -5.5 and was much easier than redesigning all the wing mounts, fairings, etc. Abu, I have no idea what airfoil you used to make your ribs so this may be immaterial. I hope someone has found it interesting and good luck with the build.
Posted on: 1/1/2010 9:36 AM by Author "CrateCruncher"
in the forum "RC Scale Aircraft"
http://www.rcuniverse.com/forum/fb.asp?m=9377231
RE: Scratch-built Fokker Dr.I 1/6 scale
Ok, after looking over my Dr1 plans I see the point Vertical Grimmace is referring to. I had forgotten that the portion of the fuse frame that the h. stab rests on is not parallel with the upper longerons. It has obvious positive slope "with respect to" the upper longerons (about +3.7 deg on my plan). Assuming [i]that[/i] surface is supposed to be horizontal in level flight with a neutral elevator then the stab is likely +3.7 with respect to the upper longerons. The lower wing is +1.3 with respect to the upper longerons (or -2.4 with respect to the h. stab) on my plan. (We still don't know what the actual wing incidence should be without a lift curve). I hope this underlines the point I and many others at RCU have discussed ad nauseam, that choice of datum line really doesn't matter. It's just an imaginary reference. It's the angles "with respect to" that are all-important. I propped up the tail of a Hasegawa Dr1 I have so that the stab is horizontal. The tail looked kinda high and the fuse looked like it was pointed down in a shallow dive. Is this a scale attitude? It looks pretty draggy. Perhaps it was done to improve pilot visibility? Fokker being a pragmatic sort did they change it because it was easier than redesigning all the wing mounts? I also discovered something I didn't realize I had. In the back of Paul Leaman's book [u]Dr1 Triplane[/u], I discovered a technical paper from 1918 discussing the relative contribution of the wings on page 216. In a nutshell, they found the upper wing most effective, the lower wing next most effective and the middle wing contributing less still! This may afford some insight into how best to tune the incidence angles so the lift center is close to the center of mass. For example, adjusting the angles at -3 upper, -1 middle, -2 lower, may balance them so they all do roughly equal work.
Posted on: 12/31/2009 1:53 PM by Author "CrateCruncher"
in the forum "RC Scale Aircraft"
http://www.rcuniverse.com/forum/fb.asp?m=9375262
RE: Scratch-built Fokker Dr.I 1/6 scale
I think we're all saying the same thing. The choice of datum line often makes this topic more confusing than it should be. Abu, the first thing is to determine how you want the fuselage to fly at cruise throttle setting. In my earlier post I assumed having the top longerons horizontal at cruise was scale but you've seen a lot more Dr1's than I have and its your plane. I'm curious what the datum line is that you are using. I'll assume it is an imaginary centerline through the fuselage side view with the top longerons about +5 relative to it. So setting the horiz. stab at +5 and the wings at +3 relative to the centerline datum would be exactly the same as setting the stab at 0 relative to the upper longerons and the wings at -2 relative to the stab. Not having seen the lift curve for your airfoil this rigging seems reasonable. In the air a stab wants to weather vane to a 0 AOA so I try to set my fuselage angle first, then zero the stab angle to it, then set just enough wing incidence (lift) to hold the plane in the air. This (hopefully) results in the lowest possible drag at cruise. On a racer you set everything to top speed, not cruise.
Posted on: 12/31/2009 12:10 AM by Author "CrateCruncher"
in the forum "RC Scale Aircraft"
http://www.rcuniverse.com/forum/fb.asp?m=9373882
RE: Scratch-built Fokker Dr.I 1/6 scale
Here are some points about incidence I've had to learn the hard way: 1) Incidence is the trim setting which makes the plane cruise level with the fuselage/tail aligned at the least amount of frontal area. 2) The easiest way to set incidence is to align the horiz. stab with the fuselage then dial in enough wing incidence (relative to stab) to support the weight of the plane at cruise speed. 3) Wing incidence angle is measured from a line drawn through the extreme outer points of the airfoil cross-section, not the bottom of the airfoil. 4) Only symmetric airfoils generate 0 lift at zero angle of attack(aoa). Cambered airfoils have 0 lift at some negative number (Clark Y is - 4.5 deg!). 5) Model airplanes generate slightly less lift at a given velocity and aoa than their full scale versions because of scale effect (ok, difference in chord length in this case). Engineers use the Reynolds number to neutralize the scale effect when they compare data. If you look at a typical lift curve plot there are often a series of nested curves reflecting different Reynolds numbers. Reynolds for a fast .60 sport plane is about 500k, for a full scale Cessna 150 about 1M. You can probably skip worrying about Reynolds, I just mentioned it because I know your curious about it. If it were my plane I would set the horizontal stab level with the top longerons of the fuselage. I would try to determine the lift plot of the airfoil used in your wings. I would email Glenn Torrance and ask him how he set the incidences of his wings relative to one another to get the best flight performance on a model Dr.1. Then, given the estimated weight of the plane and lift curve of your airfoil I would apportion the lift to the wings in the arrangement Glenn recommends. Frankly, it would not surprise me if he says (-4,-3,-3) or something. The Dr.1 has a huge wing area relative to it's weight. If you set the wings with a lot of positive incidence it will still fly but the tail will stick up in the air and you will have to fly with down trimmed elevator. The relative incidence between the wings is important for good performance. Often, model biplanes fly best with the top wing at a slightly lesser angle than the rest to compensate for it's higher efficiency. I[i] think[/i] the reason for this is that the lower wings lose lift due to high pressure disturbance of the lower surface of the wing above it as well as fuselage interference.
Posted on: 12/30/2009 1:14 PM by Author "CrateCruncher"
in the forum "RC Scale Aircraft"
http://www.rcuniverse.com/forum/fb.asp?m=9372074
RE: My Kit Collection: Comments wanted
[quote]ORIGINAL: tarvma02 I am developing a library of airplane kits.[/quote] (Yea, me too!)[quote][color=#3300FF][/color]Not to hoard but to build and reproduce later if needed. I am very worried about the future availability of kits; almost to a point of hysteria![/quote] Yep, same here...[quote]Some are currently produced but many are discontinued ones. Here's what I have so far: Goldberg: Bucker Ultimate Chipmunk -I need an Extra, Sukhoi, Cub, and Gentle lady[/quote]OK, I'm envious that you have a Bucker Jungmann but man, do you really NEED a Gentle Lady? [quote] Great Planes: Aeromaster Super Skybolt Giant Aeromaster Ultrasport 60 Super Sportster 60 60 size Cap 21...believe it or not, these things actually fly great light. Don't deserve the Snap 21 rep. -Can't think of any more I need Sig Hummer King Kobra Kougar 4 Star 60 4 Star 40 I would like a Kobra, 4 star 120, 1/4 scale cub, and the new 1/5 scale laser cub[/quote] Wait a second, that's THREE Piper Cubs you've mentioned...What Ultimate flyer needs (or really wants) ONE cub?! [quote] Midwest big Cap 232 big Extra 300XS Others wanted: Pilot models 1/3.5 Bucker...yeh right I'll ever find one Balsa USA 1/3 scale Cub with floats[/quote]Thats a GREAT scale Cub but you gotta LOVE Big Cubs AND Scale for this one![quote] all the Top-Flite warbirds; big and small. I'm really not a scale guy but I like their warbirds (never built or flown one though) BTE Venture 60 kit Cloud Dancer 60 Seamaster 120 Direct Connection Ultimate Kaos 60 UltraSport 1000 Anyone have any comments. I think you can read the above list and tell what type of planes I like. Mike [/quote] Well, you already have a big collection so rather than adding iffy stuff which waters it down, I would recommend thinning it a bit by selling some of the kits you're not crazy about. Take the money you make and buy something really rare and special. This is the way most high-end collectors do it. Over time the collection stays the same size but keeps getting better and better. Don't worry about Kaos kits and such. Those are so popular someone will probably always kit it. Try to focus on really rare BUT popular kits that would be difficult to reproduce. An example might be '70s pattern planes with fiberglass fuselages. They need a mold not just a laser pattern. Happy collecting.
Posted on: 12/23/2009 5:13 PM by Author "CrateCruncher"
in the forum "Kit Building"
http://www.rcuniverse.com/forum/fb.asp?m=9354831
RE: Dirty Birdy Build Thread
Jeff, Please record the airframe weight before and after glassing for us. Thanks!
Posted on: 12/9/2009 1:14 PM by Author "CrateCruncher"
in the forum "Classic RC Pattern Flying"
http://www.rcuniverse.com/forum/fb.asp?m=9316643
RE: Scratch-built Fokker Dr.I 1/6 scale
[quote]ORIGINAL: abufletcher Well, the brass frame didn't fly to pieces. In fact, it doesn't look like a single joint failed during the test runs. There's quite a lot of vibration and torque, but that's to be expected on such a completely unsupported frame. Just placing my hand on the top of the frame settled it down. This was also simultaneously the break-in for this new Saito 56. [/quote] Don your test looks really good. In my opinion it's a worse case than the finished plane because a portion of the frame is held rigid. A free-standing plane can absorb some shock simply by wobbling about. I'm also glad you used silver solder over the soft stuff. That adds to the strength in itself and your joints look smooth and well made. Ok, I know filing the joints down makes them pretty as heck (yes, I do it too) but it also weakens them so don't go crazy, leave some meat. That frame has a natural frequency. When the engine vibration matches the natural frequency it will start to shake itself apart (resonate) and should be avoided. Resonance will "likely" happen somewhere near idle but it's hard to know exactly. As a rule the more rigid the system the higher the natural frequency. Because of this you might luck out with the finished plane idling above it's natural frequency. Only testing the finished plane will tell you definitively. Then there is fatigue. This occurs when a joint is repeatedly loaded and unloaded to a limit that in itself is well below failure yet after millions of cycles (maybe billions) fails anyway. Bottom line, you will want to visually inspect every joint every time you fly and anticipate how you will re-solder breaks with additional reinforcement. The pro's use finite element analysis to find hot spots of excess stress concentration while still in drawing form but the rest of us must develop by the wait till it breaks method. If you see unusual amounts of vibration ground it until you know why. And always fly with a well balanced prop. I'm just adding some thoughts that came to mind when I saw your test. Good luck with it and keep the updates coming. As a hobby we need to get away from rigid mounting our engines to our airframes. I think there's a market need for isolation mounts but have never found anything.
Posted on: 12/6/2009 4:13 PM by Author "CrateCruncher"
in the forum "RC Scale Aircraft"
http://www.rcuniverse.com/forum/fb.asp?m=9308479
RE: TF Stinson SR9
Scalenut, There is a TF SR9 thread in the kit building forum that has been running for years with several of these planes being built by the contributors. Try there if you have any additional questions. And congratulations on getting this far on such an enormous project. [link=http://www.rcuniverse.com/forum/m_6417717/tm.htm]TF Stinson Thread[/link]
Posted on: 12/4/2009 11:44 AM by Author "CrateCruncher"
in the forum "RC Scale Aircraft"
http://www.rcuniverse.com/forum/fb.asp?m=9303082
RE: Curare Build
[quote]ORIGINAL: doxilia Interesting... what does that do to the integrity of the alloys? Not that I've been there but I'd imagine one could potentially start having fissures in the metal matrix (liner or case) - but maybe they are more robust to abrupt temperature changes than I'd imagine. I admit that I still have a liner stuck in a YS AR that I haven't tended to... David. [/quote] The aluminum alloys used in cases are quite ductile so local temperature gradients aren't a concern. One potential threat is reduced temper in the case alloy but one would have to get the aluminum very hot (500+ F) for that to occur. You just [i]warm[/i] the barrel of the crankcase evenly until the liner slides out. It shouldn't require much. The idea is to have the liner at 40F and the case at 200F. With that temperature differential the heat will transfer to the liner very quickly so work fast or you'll have to start all over. This technique has been used for generations of automotive engine rebuilders to remove stubborn crank pins from aluminum pistons. It's where I acquired it. When replacing the new liner cold soak it in the freezer and heat soak the case in the oven at 250 and they should go together without fuss.
Posted on: 12/4/2009 10:24 AM by Author "CrateCruncher"
in the forum "Classic RC Pattern Flying"
http://www.rcuniverse.com/forum/fb.asp?m=9302919
RE: Curare Build
[quote]ORIGINAL: jmb52760 I am having second thoughts about the Rossi. I am trying to rebuild it with new bearings, but I can't get the fool thing apart. The piston liner is currently stuck halfway out. I heated the case to 300 degrees and pushed a piece of plastic into the exhaust port from the top and turned the crank (with a prop hastily bolted on). That worked, but only as far as the piston will push it. Any suggestions? [/quote] If the interference is still too great to pull the liner out you can reduce it further by making the liner cold and the case hot. Try cold soaking the engine in the freezer a couple of hours. Then heat the outer barrel with a flame while pulling on the liner. A gas stove works well. Just try not to heat the liner and work quickly. It should slide right out. I don't own Rossi's but I have successfully removed stubborn liners from other brands doing this.
Posted on: 12/3/2009 11:42 PM by Author "CrateCruncher"
in the forum "Classic RC Pattern Flying"
http://www.rcuniverse.com/forum/fb.asp?m=9302222
RE: Curare Build
I too am interested in building a Curare and will be watching your progress. I think I'd like to build mine with foam wing and stab but undecided. What led you to pick the foam version. Thanks for sharing.
Posted on: 11/29/2009 6:30 PM by Author "CrateCruncher"
in the forum "Classic RC Pattern Flying"
http://www.rcuniverse.com/forum/fb.asp?m=9290075
RE: Wing, hor stab incidence and CG affect on flight attitude
Splais, Reading the description of your Bf109 attitude in level flight I would suspect the incidence in both the main plane and stab were too positive relative to the fuse centerline but about right relative to one another. Shame the plane isn't around to check. (Oh, and I agree that moving the cg back would have been a mistake.)
Posted on: 11/28/2009 9:19 PM by Author "CrateCruncher"
in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9288064
RE: How to build
I think one of the most effective ways to build straight is to focus on what is critical. As builds get increasingly complex you will be forced into making a few trade-offs. Knowing how each inaccuracy effects flight performance will get you consistently nice flying planes without unnecessary tedium. For example, gluing two wing panels together with a [i]two[/i] degree angle between their chord lines is a minor disaster but a bulkhead that's [i]five[/i] degrees off square in the fuse is just cosmetic and isn't worth fixing.
Posted on: 11/24/2009 12:39 PM by Author "CrateCruncher"
in the forum "Kit Building"
http://www.rcuniverse.com/forum/fb.asp?m=9277367
RE: Penetration
After thinking about this for a while I'm not as enthusiastic as I once was about adding mass to powered planes for penetration. Gliders are a different story. In an uplift, the airstream (and by definition, drag) has a small vertical component that can be countered with increased weight. Without a propeller any small increase in forward acceleration is important. Looking at it graphically using force vectors it's apparent how adding mass improves "penetration" by offsetting the drag. When we apply down elevator to add forward speed it's the same thing. We are pointing some of the weight vector in a direction opposite the drag.
Posted on: 11/24/2009 12:13 PM by Author "CrateCruncher"
in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9277307
RE: Wing Loading....
[quote]ORIGINAL: tonyg11780 Please correct me if Im wrong, but to calculate the wing loading of an airplane...is the following the correct method? 1. Divide the weight of the aircraft by the wing area 2. To get it to oz / inch, multiply your number by 144, as there are 144 square inches to a square foot 3. Multiply that number by 16, because there are 16 oz per pound? this just doesnt sound right to me, but the numbers look right...as an example on an edge 540 with a 75'' wingspan and a 26cc engine... Weight-Lets say 10 lbs Wing area-990.7 sq inches 10 / 990.7=.010093873 .010093873 x 144 = 1.453517712 1.453517712 x 16 = 23.25628339 Would this put the wing loading as 23.3 oz/sq inch? I seriously think I am overcomplicating this, but someone here should be able to tell me. Thanks in advance! TonyG [/quote] TonyG, There is one problem with your calculation. When you multiplied your number by 144 you converted from "per square inch" to "per square foot". The final number is 23.3 oz/sq ft. I'm sure that's what you meant and no one else bothered to mention it. An easy way to do conversions is to think of the units as fractions separate from the numbers. Here is how I would work your problem: 10 (lb) / 991 (in^2) = 0.01 (lb/in^2) 0.01 (lb/in^2) x 144 (in^2/ft^2) = 1.45 [(lb)(in^2)]/[(in^2)(ft^2)] = 1.45 (lb/ft^2) The in^2 terms cancel. 1.45 (lb/ft^2) x 16 (oz/lb) = 23.3 (oz/ft^2) Again, the lb terms cancel one another because lb/lb is 1.
Posted on: 11/24/2009 11:37 AM by Author "CrateCruncher"
in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9277228
RE: Penetration
Well first off thanks for actually reading the post everyone. I figured I'd only hear crickets after posting it. Second, I admit I have very little hands-on experience with park flyers. I used a cute little lightweight advertised in a recent Tower flyer as a guinea pig. Third, the disparity in Re# for models vs. published AOA data becomes even more of a problem when we start getting into these tiny planes. Fourth, a 20 mph wind seems reasonable to me. I fly in 20mph winds all the time around here. The electrics pack up at 10! Lastly, I picked a slender symmetrical I had data on (naca 0006) because I felt a cambered airfoil would confuse the data with negative AOA's contributing positive lift. Dick since you have the most heartburn with the conditions how about suggesting some better ones. I'll redo the numbers and see what happens.
Posted on: 11/4/2009 5:56 PM by Author "CrateCruncher"
in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9228345
RE: Penetration
A pilot of a very light (1/2 pound) electric plane is flying in calm conditions at 40 mph ground speed. A front rolls in changing the conditions to a headwind of 20 mph and a 60 mph airspeed required to maintain the same ground speed. (1) What is the effect on AOA due to change in speed AND an added ballast of 3/4 pound? (2) How is control sensitivity effected by the change in weight at the higher airspeed? weight(mg)= 0.5 lbm (slugsft/s^2) weird units huh? wing area= 1.29 ft^2 V1 = 40 mph(58.7 ft/s) V2 = 60 mph(88.0 ft/s) airfoil: naca 0006 (cl/AOA data from Abbott, pg.452) air density (R) = .002378 slug/ft^3 1) Starting with the equilibrium between weight and lift we have: weight = 0.5*(air density)*(velocity squared)*(wing area)*(lift coefficient) or mg = .5R(V^2)S(Cl) Rearranging terms to get Cl: Cl = (2mg)/[R(V^2)S] Airspeed w/o ballast(.5) w/ballast(1.25) Cl AOA(deg) Cl AOA(deg) 40mph 0.10 1.0 0.24 2.5 60mph 0.04 0.2 0.11 1.0 Notice the AOA of the plane without ballast is very close to zero at the higher airspeed while the ballasted plane restores the AOA for level flight back to one degree. 2) Sensitivity of +/- 0.5 degree change in AOA at 60mph: Weight AOA Cl Net Force(Fr) Fr/W*100(%) 0.5lbm +.7/-.3 +.1/-.05 +.7/-1.1 +140/-220 1.25lbm +1.5/+.05 +.2/+.05 +2.4/+.6 +92/-52 Pitching the plane half a degree has a dramatic effect on the plane without ballast. In the last column the unbalanced reaction force is divided by the total weight of the plane. The unballasted plane is virtually uncontrollable.
Posted on: 11/4/2009 1:35 PM by Author "CrateCruncher"
in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9227817
RE: Penetration
[quote]ORIGINAL: Bozarth [quote]ORIGINAL: CrateCruncher The added ballast does more than just damp turbulence with it's inertia. It moves the airfoil angle required for level flight to a more reasonable positive aoa and makes pilot inputs to that angle less important. With additional ballast the plane's weight is better matched to the lift and drag forces acting on the airframe. [/quote
Posted on: 11/3/2009 10:55 PM by Author "CrateCruncher"
in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9226637
RE: Penetration
[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 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. [/quote] Inewgban, One of the things I remember living near the ocean was feeding seagulls from my outstretched hand. In a stiff breeze they could effortlessly hover by changing pitch and wing area. I assume they have much better piloting skills than the average biped but I remember that to "penetrate" or gain ground in wind they flapped their wings. When raptors tuck in a dive its to maximize speed so drag reduction is everything. Big scavengers split their air miles between soaring in uplifts and gliding to the next one. It's during the gliding part that they need good penetration. But they also have another trick planes can't pull off. Again, they can flap! Bird physiology and planes are so different that I have trouble comparing them on specifics like this.
Posted on: 11/3/2009 10:33 PM by Author "CrateCruncher"
in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9226578
RE: Penetration
For most glow powered planes talking about penetration is admittedly kinda silly but considering all the tiny electrics I've seen lately and the windy conditions here in Central Texas it is becoming relevant. The added ballast does more than just damp turbulence with it's inertia. It moves the airfoil angle required for level flight to a more reasonable positive aoa and makes pilot inputs to that angle less important. With additional ballast the plane's weight is better matched to the lift and drag forces acting on the airframe. I used the term while slope soaring. Launching into a constant 70 mph gale at the top of a ridge, proper ballast is critical for good "penetration".
Posted on: 11/3/2009 7:20 PM by Author "CrateCruncher"
in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9226106
RE: Penetration
[quote]ORIGINAL: Bozarth How is ''wind penetration'' any different from simply flying faster? Kurt [/quote] "Penetration is in my understanding, the ability to make forward progress (ground speed) in extreme wind [i]while remaining pitch stable[/i]." Kurt, simply adding power to the plane will not cure the problem of pitch stability. As airspeed goes up so does lift sensitivity. The gusty, unpredictable behavior of extreme wind conditions near the ground makes the problem more acute. The pilot get's into an uncontrollable pitch oscillation without additional ballast. The pilot must add the ballast to reduce the pitch sensitivity back to a manageable level.
Posted on: 11/3/2009 10:47 AM by Author "CrateCruncher"
in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9224844
RE: Penetration
Onewasp, After reading this discussion I can't seem to find a direct answer to your question regarding penetration. Penetration is in my understanding, the ability to make forward progress (ground speed) in extreme wind while remaining pitch stable. A good example of penetration is in slope soaring. These unpowered planes can accelerate to very high ground speeds because of their ability to "penetrate" using added ballast weight. At the top of a ridge the airstream is flowing with a vertical component. If we assume a 45 degree slope that means for every foot the wind travels horizontally it must also flow one foot straight up and "0" AOA is a 45 deg nose down pitch relative to ground! In a light wind a glider with no ballast will move slowly forward horizontal (relative to the ground) by assuming a tail up attitude as viewed by the pilot. However, the plane really has a high positive angle of attack relative to the airstream and that generates lift to maintain altitude. The plane can even fly backwards. However, as wind speed increases the plane will quickly gain altitude because of excess lift and the pilot must dive the plane but pitch ultimately becomes uncontrollable. [i]Adding ballast allows the plane to generate more aerodynamic force (sum of lift and drag) without gaining altitude.[/i] As the pilot adds more down elevator to a properly ballasted plane the tail lifts higher and the aerodynamic force tilts further and further forward until there is a forward component accelerating the plane to a higher ground speed. If the wind speed dies the plane becomes a rock. Flying powered planes on level ground is basically the same. A lightweight electric in a high wind must dive to prevent the generation of excessive lift and becomes uncontrollable. Adding ballast allows the plane to "penetrate" into a headwind because the added ballast counters the higher lift force. (Recall that a plane at "0" AOA still has drag that must be overcome.) The plane MUST fly faster (airspeed, not ground speed) so it needs more power too.
Posted on: 11/2/2009 11:55 AM by Author "CrateCruncher"
in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9222391
RE: Arizona Models (again & final)
Having Jaime Johnson for a business partner won't last long enough for the ink to dry on their agreement. I predict Belaire will either to cut and run or double down to buy JJ out of the business. Let's hope it's the latter.
Posted on: 10/18/2009 10:41 AM by Author "CrateCruncher"
in the forum "RC Scale Aircraft"
http://www.rcuniverse.com/forum/fb.asp?m=9182544
RE: Shear Webbing
Try looking at it this way. Take a 1/2" sq stick of soft balsa 3 feet long and draw lines on it every inch ina direction perpendicular to the length. Now bend it into a curve. You'll discover the lines you drew are still straight BUT no longer parallel. Instead, they now all point toward the center of the radius of curvature. Therefore on the outside surface of the stick the material has stretched outward due to tension and the inner surface of the stick has compressed. Axial stress occurs when you try to pull on the ends of a bolt. Shear stress occurs when you use the bolt to clamp two plates together and then try pulling the plates apart. The bolt is said to be loaded "in shear". Thats why big scissors are called "shears" Back to the 1/2" stick. If the outer surface is stretched and the inner surface is compressed, then we have internal shear. The shear is tangent to the arc of curvature in pure bending. No g-loads, webs or balsa heterogeneity to clutter up the concept either. What Rodney failed to understand in all of his study in this area is that the shear in a cantilevered beam varies from zero at the tip all the way up to the full bending moment divided by the second moment of inertia at the root yet the vertical load is constant. Therefore at some point in the wing the shear will be at 45 degrees but it's different everywhere else. Furthermore, the point of maximum stress in web shear is dominated by the pure bending shear at the root where the worst case occurs. Shear in pure bending is horizontal as illustrated at the beginning with the 1/2" stick example.
Posted on: 8/31/2009 6:46 PM by Author "CrateCruncher"
in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9059765
RE: Shear Webbing
I don't think anybody can make a plane on paper that is optimized and ready to produce without building a plane or three and burning some fuel. But preliminary analysis cuts out perhaps 80% of the cut n' try by getting you in the ballpark before you ever start cutting wood. Best of all, it can quickly eliminate all those "cool and sexy" ideas that we often fall in love with but are DOA by exposing them to Newtons world. Frankly, I think you need a lot of both.
Posted on: 8/29/2009 10:48 AM by Author "CrateCruncher"
in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9054082
RE: Shear Webbing
[quote]ORIGINAL: Rodney This is an old argument that always gathers much comment. If you check out your Strength and Materials handbook, you will see that the stresses in any web is at a 45 degree angle to the span so it really makes no difference in whether the grain is vertical or horizontal in the webbing, both are equally strong in shear loads. Now, if you are worried about crushing (say the cat or dog steps on your wing) then vertical grain is the strongest. If you want maximum shear strength, you need the grain at 45 Degrees to the span but; if you go inverted the shear stresses reverse by 90 degrees so now that same 45 degree is the weakest direction. That is why the specifications for shear webbing on homebuilt planes usually calls out plywood with the grain at a 45 degree angle to the span to give maximum shear strength for both positive and negative G loads. In our models, don't worry, either spanwise grain or vertical grain is equally effective. [/quote] You sound [i]very[/i] confident like you've done a lot of analysis in this area but I'm a skeptic. I'd like to see your work to be properly convinced. Using your knowledge of typical RC flight loads and beams in pure bending I'd like to see proof that maximum shear stress occurs at 45 degrees. As I'm sure you already know, there are several methods for showing stress transformation so just use the method your most comfortable with. [;)]
Posted on: 8/28/2009 10:29 PM by Author "CrateCruncher"
in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9053272
RE: Rudder on Big Stick 40
[quote]ORIGINAL: P-40 DRIVER You would want 0 to the datum line not horizontal stab anyway. [/quote] Well, the following doesn't have anything to do with the thread but since you brought it up.... A datum line is just a convenient reference line. It may or may not be parallel with the airstream when the plane is in level flight. The horizontal stabilizer, however, is always designed to be parallel with the airstream at optimum trim. Thats why I said "perpendicular to the horizontal stab". I was covering my behind because I have no idea what his plan uses for a datum line. Thanks for keeping us on our toes though.
Posted on: 8/25/2009 11:04 PM by Author "CrateCruncher"
in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9045404
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