Newsletter June RC BEES of Santa Cruz County, Inc. Thursday, June 21st, 2012, at the EAA building, Aviation Way, Watsonville Airport, 7:30 PM.

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1 RC BEES of Santa Cruz County, Inc. Newsletter June 2012 Next Meeting Thursday, June 21st, 2012, at the EAA building, Aviation Way, Watsonville Airport, 7:30 PM. Treasurer s Report Editor: Alan Brown, 388 Aptos Ridge Circle, Watsonville, CA Phone: (831) alangwenbrown@charter.net. Web site: However, Steve Boracca noted that there was an error in the newsletter. Jacob was not at the Day in the Sky event, and so did not assist with flying. All, however, agreed that the event at the Watsonville Airport went very well. We will almost certainly be re-invited next year, with the possibility of a larger flying area. Beginning Balance $ Income Fuel Sale $60.00 Subtotal $60.00 Expenses Field Toilet Service $64.80 Bank Fees $3.00 Fun Fly Expenses $80.78 Office Expense Misc Subtotal $ It was also proposed that we should start making arrangements to participate in the Annual Fly-In scheduled for the Labor Day weekend in September. Old Business Dan Southwood s stainless steel box is now installed above our storage container complete with working field viewing camera. The installation was completed by Allen Ginzburg and John Williams. Thank you both. Ending Balance $10, May Meeting The meeting was called to order on May 17th at 7:40 p.m. by Steve Boracca with fourteen members present. Bob Carr of the local EAA was present as a guest. He flies regularly at the Monterey Bay Academy. The treasurer s report and minutes from the previous meeting were accepted unanimously. Don Good said that he would pick up runway crack sealing material and, with help, would complete the job. The $800 weather station was again discussed with the idea of voting on whether the club should purchase one. Unfortunately we did not have a quorum present, so the vote could not be official. However, all fourteen members present voted against it, as representing too large an investment for the relatively small return. So unless a sizeable

2 number of members disagree with this decision, no further action will be taken. Alan Brown brought along his half-completed 1920 s Heinkel floatplane, shown below. New Business President Steve Boracca has contacted CalTrans regarding getting some stone grindings to reinforce our entrance and pit area. He has had no reply so far. It was noted that a fairly large truck would be required, and Bill Boone pointed out that we have had an eighteen-wheeler on the property before doing similar work. There were some thoughts about finding an easier way to get down to the river for floatplane flying, but nothing that could be done prior to the following Sunday s fun-fly for floatplanes. Show and Tell It is being built from a much modified stand-off scale plan originally published in RCM magazine in The reason behind it is that Alan s uncle was in the British Royal Air Force in the 1920 s and gave him a box of photos of airplanes from his air base. It included a visiting Swedish Heinkel floatplane shown below, which is Alan s subject. Richard Tacklind showed his Sparky, kit-built and featured in an article he wrote for the October 2010 RC Sport Flyer, opening page shown below. Richard has apparently done several review articles for that magazine. Bravo, Richard! Those float/wing struts are going to be interesting! At that the meeting was adjourned. Floatplane Fun-Fly This year s event only attracted two competitors, Bob McReynolds and John Williams, but they brought multiple models, and have frequently flown at a lake near the Sierras. Here s their combined fleet together with Bill Boone, who performed yeoman work putting their airplanes into the water. No, Bob s Hawk ornithopter, left foreground, did not swoop down on the seaplanes as they took off!

3 Two of the planes are identical scale model ICON A-5 s. Bob and John bought them at Aero Micro just two days before the competition. They are amphibians, and each one got its maiden flight off the runway before John converted his to the floatplane configuration and flew it into second place. This ARF model got front page coverage in both the May issue of Model Aviation and the June issue of the British magazine Quiet & Electric Flight, and was highly recommended by both sources. The competition involved static judging, take-off, horizontal figure-eight beyond the levee, and return for a water landing. The turns from the river to the land and back were made well to the west of the audience to ensure safe operation. The hardest part of the operation was passing the models down to Bill Boone for launching and subsequent retrieval. The electric powered models were not much of a problem, but puttng Bob s Sea Dancer in the water with a big four-stroke engine running wasn t easy. We ll have to think of an improved method in future. The picture below illustrates the situation as John Wheeler helps Bill. - and taxiing after landing. Bob s T-28 took first place, here seen taxiing home after a successful flight, and his Sea Dancer came third. Bill brings the T-28 out of the water after a successful flight. And here it is with a Monterey County backdrop - Here are John and Bob with their magnificent second and first place certificates!

4 Ducted Fan Fun-Fly As usual, Bill Moore did a fine job of keeping the hungry mob fed! This will be held on the Sunday after the July monthly meeting, July 22 nd. Plenty of warning so competitors can be thinking about what to bring, and what the events should be. Last year s events included a slalom taxi, a speed run, a spot landing and a best-guess duration flight. This year should we include static judging, a horizontal figure eight, a pilot s choice maneuver, a maximum duration from fixed motor run, and/or a pylon race? Please let the editor know, or discuss at the June club meeting, any ideas you have for improvements. It was decided last year that different models could be used for different events. Not my preference, but again, let us know yours. Down by the River Open flying after the fun-fly saw Johnny Skoch with his Giant Super Sportster, a very pretty airplane, and Richard Tacklind flying a 32-year old plan-built Electra Lite glider. A Letter from Brian Lacey Brian left for the U.K. last week and asked me to put this letter in our newsletter a fine tribute to our members. Fellow Club Members, I ll be leaving for the UK soon for an extended visit. I wanted to take a minute to thank all of you for your support and help. I especially wanted to thank Don Good and Steve Jones for the hours of training and assistance they have given me. I have really enjoyed being a part of this flying club. I ve never been involved with an association as friendly and helpful as you all have been. Many thanks, hope to see you in the future. Brian Lacey Richard s brother, David, in the foreground. Most of this day s photos are by John Williams.

5 Dennis Kanemura has had a couple of his pattern aircraft down at the field recently. Christophe Paysant le Roux designed the Caprise (combination of "CAP" for the CAP 21 and "surprise".) He flew his plane in the world s championships a few years prior to Dennis buying a kit directly from him, and it was shipped from France. Dennis flew the plane in Hollister recently and it still flies great, if he can keep the YS 140 running. Here it is as flown in the Gold Country pattern contest who seems to be coming out with a new airplane every week. Don Good got his amazing photo of the two biplanes in flight. (I know how hard this was to do; I ve tried unsuccessfully myself). Here s my more pedestrian effort, which Stefan suggested I could Photoshop to eliminate the ground background and the propellers! Dennis s newer pattern plane is an ARF Angel S, 50 size, designed by Italian F3A pilot and champion Sebastiano Silvestri and manufactured by Sebart, his company. It has close to 100 flights on it and he brought it out to test a new motor. He apparently burnt out the original Hacker so replaced it with a new version that supposedly handles more watts. It flies on a 5 cell 5000mah pack. The interesting feature is an air-cooled spinner as lathe-turned by Dennis to keep the motor cooler. It can be seen clearly in the picture below. This is Gary s 1930 s Henschel 123 fighter in flight (flown by Marcelo) and on the ground. Recent entertainment has come from Marcelo Montoreano and Stefan Warnke flying their Nitroplane Dynams Peaks 42 span biplanes together, and from new member Gary Gonzales, (In flight photo by Don Good).

6 Meanwhile the old stalwarts aren t sitting on their hands. Johnny Skoch has a very attractive new Decathlon, seen here next to his Christen Eagle.. Here s an array of some of Gary s airplanes. An A- 10 in the foreground, followed by a Focke-Wulf 19o, two T-28 s (everyone should have a pair!) and the Henschel. And Don took a great picture of one of his Sticks taking off. Emmett White doesn t get a photo of one of his airplanes in the newsletter very often, so we ll close this section with his foamie Cessna in full flight. Stefan and Marcelo each have F-35 s of different sizes. Stefan s is the newer, larger one shown here. Aero 101 High Speed Stalls This and the subsequent article are in response to a member s request. What is a high speed stall and why does it happen? Marcelo put the identical motor and EDF unit into his smaller airplane, and it is, as you would expect, much the faster of the two. You just can t beat power/weight or thrust/drag ratio! Typically, it might occur while the airplane is performing a loop or pulling a tight turn. Let s start with the loop. Suppose we enter the loop at 50 m.p.h., which is just over 73 feet/second, and suppose that we perform the loop at 50 feet radius or 100 feet diameter. At any point in the loop, the centrifugal force exerted is given by W/g times

7 V 2 /r, where W is the weight of the airplane in pounds, g is the gravitational acceleration constant, about 32.2 feet/ second 2, V is the velocity in feet/second, and r is the radius of the loop in feet. So on entering the loop for our example we will be pulling 3.3 g s (V 2 /rg) from the centrifugal force. Now, in general, we will not keep constant speed in the loop unless we are very good pattern pilots, and the airplane will tend to slow down as it climbs into the loop. Thus the centrifugal force will tend to diminish as the plane slows down while we keep the radius constant. The net force on the airplane wing will also be reduced as we approach the top of the stall by the weight of the airplane acting downwards while the centrifugal force acts upwards. So at this point, instead of having 3.3 g s acting on it, it will only have 2.3 g s, and even less if we allow the airplane to slow down. Clearly, if it slows down enough the airplane will fall out of the loop; because the centrifugal force falls as v 2 falls, but the weight remains constant (give or take fuel usage). However, for us mediocre pilots, our airplane will accelerate on the downward leg of the loop, and because the speed is building up and the centrifugal force is increasing, we find the ground coming up towards our airplane ever faster! In addition, the weight term for the bottom part of the loop is additive, and so as we approach the bottom of the loop, if we are at our original speed, the airplane will pull 4.3 g s, which means an even higher angle of attack. So the bottom of the loop is the most critical part. If we pull more elevator which tightens the loop radius, bang the airplane stalls and drops out of the sky. So what happened? Let s look at the basic lift equation for the wing. It goes as follows: L = ½ x x V 2 x S x C l, where L = lift in pounds, air density, V = velocity, S = wing area, and C l is the lift coefficient, an almost linear function of the angle of attack that the airfoil presents to the airstream. As the angle of attack increases, the lift increase steadily until it nears the critical stall angle, where it maxes out. and then starts to fall, sometimes rapidly. Our airplane flying steadily at 50 m.p.h. might be at about 3 0 angle of attack. When it enters the loop, we have already seen that it will be pulling 3.3 g s, so its angle of attack will now be about 10 0 to handle the apparent increased weight of the airplane, which might have a stall angle of, say, At the top of the loop the angle of attack will have dropped by 2.3/3.3 to about 7 0. If we increase the speed, the lift on the wing will go up, but so also does the centrifugal force. So the angle of attack is only a function of the radius of the loop and the relative direction of the weight of the airplane. It increases as the airplane goes from inverted at the top of the loop to upright at the bottom of the loop, at which point in our example, it would be about When we now tighten the loop radius slightly, the airplane stalls and probably crashes. End of airplane! Now let s look at horizontal turns. A good first example might be turning to come in to land at our field. I haven t measured the dimensions, but the runway is about 30 feet wide, and I m guessing that its centerline is about 50 feet from the center of the levee. So a downwind approach might be 100 feet from runway centerline, giving a 50 foot radius turn. If our landing speed is 30 m.p.h., then the centrifugal force generated will be 0.36 times our previous example, or 1.2 g s. This gives a bank angle of 50 0, and the lift required to sustain this is 1.56 times that for level flight. If, as in our original example, we needed 3 0 angle of attack for 50 m.p.h., then we ll need for 30 m.p.h. [(50/30) 2 x 3 0 ] and 1.56 x or about 13 0 in the turn. This is getting close to the stalling angle of the wing for what seems like a fairly benign approach. However, at 30 m.p.h. this really doesn t classify as a high speed stall. Let s look now at some high speed maneuvers that might give this result. Let s fly our same airplane at 70 m.p.h. and see what sort of turn radius is needed to stall the airplane at this speed. The level flight angle of attack will now drop from 3 0 to about [3 x (50/70) 2 ]. To get it up to 15 0 we need a centrifugal force of about 10 g s (sine and tangent are about equal in this range), which we can achieve with a turn radius of 33 feet. So that s the condition for our high speed stall. Remember that these are just examples, and different wings fly and stall at different angles. I hope that this explains some common flying situations.

8 Aero 101 Washout Although this subject was covered quite well in the March issue of Model Aviation, the subject has been raised within the club recently, so I ll attempt to add to what has already been written. washout because it will stall at the root first, while a wing more sharply tapered than an ellipse must have washout, or it will inevitably tip-stall. The first thing to understand is that lift on a wing is generated by positive pressure under the wing and negative pressure on top of it. Positive and negative are with reference to the atmospheric pressure in the region of the wing. Looking at the wing from the front, it is fairly clear that near the wing tips, the high pressure air under the wing wants to leak around the wingtip and fill in where the low pressure is acting. If you look at this in plan view, you can see that the forward velocity of the airplane will cause the high pressure air to spiral around the wingtip causing what we call a wingtip vortex. However, it s not quite that simple. Vortices are generated all across the wingspan as shown below. An elliptical wing will generate equal strength vortices all across the span (local lift times local taper ratio). The effect of the vortices is to generate some downward flow, which reduces the effective angle of attack of the wing at that particular spanwise point. A parallel chord wing will generate much higher vorticity and therefore a lower angle of attack close to the wingtips. A wing which is more sharply tapered than an elliptical wing will have higher vorticity nearer the wing root, and so will have its lower angle of attack in this region, and higher angle of attack out near the wingtips. Thus an elliptical wing has the highest efficiency, all parts of it acting at the same angle of attack (hence the Spitfire). It may, however, in practice, need some washout to ensure that when it does stall, it will stall at the root first, and not disastrously nearer the tip. An untapered wing doesn t need