Newsletter December 2010

Transcription

1 RC BEES of Santa Cruz County, Inc. Newsletter December 2010 Next Meeting Editor: Alan Brown, 388 Aptos Ridge Circle, Watsonville, CA Phone: (831) Web site: Old Business Thursday, December 16th, At the EAA building, Aviation Way, Watsonville Airport, 7:30 PM. Treasurer s Report Beginning Balance $ Income Donations $40.00 Fuel Sale $ Dues $ Subtotal $ Expenses Field toilet service $65.40 Sound meter $60.08 Subtotal $ Ending Balance $ November meeting Eighteen members attended the meeting on November 18th, President Bill Moore called the meeting to order at 7:35 p.m. and the minutes of the October meeting and treasurer s report as published in the November newsletter were approved. The latest on the field camera is that a new 22-foot pole has been put up, but the camera is not yet mounted on it. Allen Ginzburg suggested that a fairly cheap pressure-sensitive pad could be put on the roof connected to a 105 db noise generator, which perhaps would scare away potential thieves. The sound meter, which has now been purchased (see treasurer s report) was shown to members. It will be demonstrated at the field shortly. Relative to runway upkeep, questions were asked as to whether sealing the cracks was adequate, or should we reseal the entire runway. Bill Moore noted that total resealing was quite expensive, based on previous history, and has not always been done well by commercial contractors. Don Good suggested that we might do a 30-foot section using volunteer labor from the club to see whether it would be worth while continuing. Bill Moore has a pump which could use river water to clean off the runway as required. We do not yet have a replacement windsock. New Business Jay Friedland proposed and Don Good seconded that we have a fun-fly on the Sunday after the January meeting. Before a vote was taken, Alan Brown proposed and Don Good seconded that starting in January, and on alternate months thereafter, we designate the Sunday after the monthly meeting as a club day, when we would

2 have some sort of special event, perhaps a fun-fly, or a floatplane day, or pylon races, or whatever. This way all members could be aware of a club calendar for the year, and plan accordingly. The January event would be a fun-fly as we have held in the past. This was voted on and carried unanimously by the membership. at the field soon. The price is remarkable even by today s standards. $127 gets it to your door complete with servos, motors and ESC s! And here it is. It really looks very good, doesn t it? Accordingly, the following Sundays are to be set aside for special club events. Take note! January 23rd: fun-fly. March 20th. May 22nd. July 24th. September 18th. November 20th. The little guy to its right is John Williams E-flite Micro Beast, which has a very good flying reputation. Show and Tell Oh, and Rick has a ready-to-go F-18 for sale for $150. Call him if you are interested. A good showing this month, with photos taken by Don Good. Nominations Don Wilden, who is one of our premier model builders, brought two of his airplanes to show us. One is a gull-winged sports model aptly called Gulliver, and the other is a glider which he calls Pfalz Alarm (yes, Pfalz was a WW I German aircraft manufacturer). Here they are. How would you like to make that gullwing from scratch?! Check the number of ribs. The final item of business was to solicit nominations for officers for Bill Moore has been president for some time, and would like to step down, so Steve Boracca volunteered to be in the running for president. Alan Brown half-heartedly tried to get out of being secretary/newsletter editor, a job he has been doing for more than eight years, but no replacement volunteers leapt to their feet! If anyone would like to take on this highly interesting and rewarding job (it pays $48 per year, i.e. your annual dues are waived), please put your name into the ring for voting at the December meeting! No other nominees were put forward for the other posts, and final voting will be counted up next week. It should be noted that the request for votes for governing positions put in the last newsletter got an absolute zero response. Obviously, the request wasn t well explained! The meeting was adjourned at 8:30 p.m. to allow the board to hold their first meeting in several eons! Board meeting Rick Sullivan brought along a Cessna 310 ARF from Nitroplanes which he has put together for Ricky Wright. He s assembling another one for himself, so we ll look forward to seeing them both This was attended by president Bill Moore, vicepresident Bob McReynolds, and board members Allen Ginzburg, Don Good and Rick Sullivan. Alan Brown, secretary, took notes. The main purpose of the board meeting was to relook at the existing constitution and field rules, noting that there have been considerable changes in

3 the last seven years (the last time there was a revision) in the types of aircraft being flown, (park flyers, e.g.) and the auxiliary equipment, such as transmitters, batteries and electric motors. The constitution and field rules were gone through step by step, and the secretary s best assessment of what the conclusions were was ed to the board members on November 23 rd for their review. That is where the matter currently stands. Note especially the following rule in the constitution. Flying Site Policy Change: No rule change having an effect on the flying operations at the Club flying site shall be voted on without being published in the Club Newsletter and circulated to the membership and posted at the flying site for a minimum of four consecutive weekends prior to the meeting at which the said rule change will be voted on. This shall not preclude the enactment of an on the spot temporary rule change made necessary by the circumstances at the time. This implies that any modifications to the rules regarding flying operations must be open to member comment prior to final acceptance. Down by the River One of the more interesting sights from your reporter s point of view was Marcelo Montoreano launching Stefan Warnke s Avro Vulcan discus style by one wingtip. The airplane magically finished up flying in a straight line away from the pilot, to my amazement if no-one else s! Marcelo has also been flying an F-35 and an F-18 recently, shown below, very nice photos by Don Good. Late news: Marcelo is now flying yet another jet for his collection, an L-39. It did very well on December 12 th. Here s Paul Weir s F9F coming in over the mountains followed by Dennis Kanemura s Tantrum and Mike Evans P-51. Rick Sullivan has a couple of very different-looking airplanes, a Fairchild PT-19 (if I remember correctly), and an out-and-out 3D foamie.

4 The foamie, mercifully has made it to the next page, so we don t need to look at it along with all these nice scale models. At least we don t have to wonder which way is up! it is with the PT-19 and Ricky Wright s Super Stearman and P-40. Membership renewal Just a last minute reminder that RC Bees membership must be renewed before the end of the year. The gate code will be changed on January 1st. Thank you all. Balloting for officers Now an F-5 Tiger, and I m ashamed to say that I m not sure who it belongs to, Stefan Warnke or Benno, or is it another of Marcelo s squadron? Dan Southwood has made for us a very nice stainless steel box to hold our camera. Here he is showing it to Allen Ginzburg. Hope it isn t so nice that thieves attempt to take the box and leave the camera behind! Thank you, Dan, for a very nice job. As mentioned earlier in the newsletter, we need nominations and votes for officers for The final voting will be completed at the December meeting in a few days time. recipients can reply to this letter with your suggestions directly. Those receiving the newsletter by US mail can give me the information at the field this week or at the meeting. Those officers not mentioned earlier in the newsletter are currently Bob McReynolds, vicepresident, Dennis Kanemura, treasurer, and Steve Boracca, Allen Ginzburg, Don Good and Rick Sullivan, board members. Now here s a very experienced group. If I figure it out correctly, the combined ages of John Nohrden, Nick Marinovich and Chuck Sullivan are 262 years. How could you go wrong with this trio running the show?!!! Photo again by John Williams. Thank you! Rick Sullivan s Cessna 310 shown at the previous meeting made it to the field on December 7th. Here

5 Aero 101 Wing Lift and Drag This column comes about for two reasons; one because Jacob, one of our younger members, has built a wind tunnel for a science fair and wants to test some wings in it, and compare his results with analysis, and the other more pragmatic reason is that I need to fill an odd number of pages to make the U.S. Mail issue come out right. Jacob had found that lift, L = ½ ρ V 2 A C l where ρ is air density, V is the vehicle velocity, A is the wing area, and C l is the lift coefficient. He found another equation which said that C l = 2 π α, where α = the angle of attack for the airfoil, and that's about where he came to a halt. So let s look at what these equations mean, and how useful they are. First of all, the lift in steady 1g flight will be approximately equal to the weight of the aircraft. The air density is essentially a constant for the place where we are flying, and the wing area is also a given for the particular aircraft. So the weight or lift is proportional to the product of the lift coefficient and the square of the velocity. I think we all know that we need to fly at a larger angle of attack to get a higher lift coefficient when we reduce the aircraft speed. Jacob s second equation wasn t explained well in the text that he took it from, and in fact only applies to a wing with an infinitely large aspect ratio, the ratio of span to average chord. In other words it doesn t account for the losses we get with a finite wing when high pressure air from below can spill around the wing tips to the low pressure region above the wing, causing wingtip vortices. It also applies to the angle being in radians, not in degrees. Over most of the operating range of the wing airfoil, i.e. prior to flow separation near stall, the relationship between the lift coefficient and the angle of attack is a straight line and its slope is only a function of the wing aspect ratio, and is essentially independent of airfoil shape. We can define this slope as a and the slope for infinite aspect ratio as a 0. Then the lift curve slope for finite aspect ratios is given by 1/a = 1/a 0 + 1/πA. Sorry to say that this is for α being in radians, not degrees. It is also strictly only true for elliptical wings, but it s close enough. In other words, a 0 is 2π as in Jacob's equation above, and when A is infinite the second term goes to zero. If we convert the equation to one with α in degrees, then we get the following numerical results. A inf a Aspect ratio 1 corresponds to a delta wing with 76 0 sweepback, think even more sweepback than Concorde. As each wing will have about the same maximum value of C l if they have the same airfoil section, then our infinite aspect ratio wing may stall at, say 15 0 (think high performance sailplane), the aspect ratio 2 wing will stall at 30 0, and the aspect ratio 1 wing will stall at The Concorde airliner typically lands at about 35 0 angle of attack. What s the physics behind this phenomenon? As the aspect ratio decreases, the wingtip vortex gets more and more dominant, forcing the air downward behind the outer part of the wing. The information about this downward motion gets transmitted forward of the wing (we re traveling much below the speed of sound), and the wing sees air which is deflected downward and so sees a lower angle of attack. Now we have another situation coming into play. The lift force acts at right angles to the local airstream, and so gets bent backwards as the aspect ratio is reduced. That means that part of it acts to support the airplane and part of it is in the drag direction. This latter force is called induced drag, and is in addition to the profile drag which is associated with friction and protuberances. This is why low aspect ratio airplanes need a lot of power when flying at slow speeds, e.g. landing, and high aspect ratio airplanes float forever, it seems. Earlier I said that the slope of the lift curve is essentially independent of airfoil shape, which makes one wonder how we get so much lift out of high-lift and flapped airfoils. The reason is that although the slope of the curve is unchanged, it crosses the y-axis at progressively higher values of lift coefficient. So while a symmetric airfoil will have a zero C l at zero degrees α, a cambered airfoil may cross the zero degree line at a C l of 0.2 and a flapped airfoil may cross the axis at a C l of 0.5. Their stall C l values will be correspondingly higher, but their slopes to reach those points will be only a function of aspect ratio. Sorry I ve no room to add these graphs; perhaps some other time.