Rubber Speed Event

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kittyfritters
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Rubber Speed Event

Postby kittyfritters » Tue Dec 18, 2018 4:39 am

Well, there could be debate about whether or not this is really free-flight but the Black Sheep Exhibition Squadron has a Round the Pole Speed contest coming up in the next few months. A typical rubber powered speed model will be about 22 inches long, have about a 9 inch wing span and a 4 bladed prop. In round-the-pole contests they have landing gear since ROG is required.

The speeds are amazing. The model takes off and the speed timing is done on the second two laps. Since the models are flying on a fifteen foot line if the two laps take 1 second each the model is flying at 64.26 miles per hour! (Yes, we round to two decimal places.) However, the contest is for the total time on however many laps the CD decides.

I will post details on this thread and a thread about the model I build.

KF
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kittyfritters
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Re: Rubber Speed Event

Postby kittyfritters » Sat Dec 22, 2018 2:57 am

Here are the preliminary rules set for the Rubber RTP Speed event.

RUBBER POWERED RTP SPEED EVENT RULES
(Preliminary)

Pole
    The pole will be three feet tall with a headed nail in the top.
    The line will be fine sewing thread with a paper clip at each end as a swivel and a hook. The swivel to hook length, including the paper clips is 10 feet. This gives a circle of 62.83 feet. (1 second lap equals 42.84 mph.)
    A 1/8 inch high, foam, curb is placed across the path of the flying circle at one side as a timing point.
    Three people with stop watches will do the timing unless there is an electronic timing system


Models

    Classes

      Covered motor
        “Plausible scale” (i.e. must have a cockpit)
        Motor completely enclosed by fuselage
        Flying surfaces built up and tissue covered
        Landing gear has rolling wheel(s)
        Detachable dollies allowed
        (If you think you can make that work!)
        Hook attaches at wing tip
      Unlimited
        Motor sticks allowed
        All balsa flying surfaces allowed
        Landing gear has rolling wheel(s)
        Detachable dollies allowed
        (If you think you can make that work!)
        Hook attaches at wing tip

Competition

    For a qualifying flight the model must ROG, from the floor, from any point past the curb and must be airborne and clear the curb at the end of the first lap.
    The timing starts when the model crosses the curb at the end of the first lap. The model is timed for the second and third lap and the speed is calculated.
    Winner in each class is the fastest speed.

These rules are preliminary and will be revised after flight testing and experimentation.
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staubkorb
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Re: Rubber Speed Event

Postby staubkorb » Thu Jan 03, 2019 11:13 am

This should prove to be interesting! I know that the speed class was popular up thru the '50s and Outerzone has a couple of plans IIRC (I know that I have one or two in my collection).
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kittyfritters
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Re: Rubber Speed Event

Postby kittyfritters » Sun Jan 13, 2019 10:06 pm

Here is the preliminary drawing for The Speed Merchant, my Round-The-Pole rubber powered speed model, for the contest at Duarte on February 16th. Before I cut wood I'm considering moving the wing to the bottom of the fuselage. the tether wire will go from the right side of the fuselage, embedded in bottom of the wing about half way between the leading edge and the spar, to the left wing tip where it will have a loop. Will test both two and four blade prop. If other obligations permit I will have both the built up fuselage and rolled tube versions ready for test flying at Duarte on January 19.
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kittyfritters
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Re: Rubber Speed Event

Postby kittyfritters » Fri Jan 18, 2019 3:00 am

For those of you in California, in the Los Angeles, Orange County, San Bernardino area, you are invited to fly with us, or just watch, at the Duarte High School 3rd Saturday Night Indoor Flying Sessions. Bring a model or models and fly with us, This is where the Black Sheep Exhibition Squadron Rubber Powered RTP Speed event will be held on February 16. The attached poster has the details, or if you can't read it email ttraeger@duarteusd.org for details/
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kittyfritters
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Re: Rubber Speed Event

Postby kittyfritters » Wed Jan 23, 2019 12:30 am

Went to the Duarte High indoor flying session Saturday night. (Even got my wife to go with me.) Since we had not really done this before the intent was to test the indoor RTP setup for the Rubber RTP Speed contest next month. Boy! Is it different from straight line rubber speed! Dave Gee and I got it down to a science but it was a lot of work. At first we couldn't get the models unstuck in the first lap as required by our rules. We also discovered that these models need more wing than we anticipated. (Some people speculated that they wouldn't need wings at all.) They also need small props because the torque effects at the end of the tether are magnified. All of this had not shown up in our previous RTP flying with scale models and slip-togethers since we weren't trying for high speeds. RTP flight dynamics seem to become more critical at about 12 mph. We'll go over the results at the OFFC meeting this Wednesday and the Black Sheep Meeting on the 02/06. Be interesting to see what changes will be made in the models being built for the contest with the new information

KF
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kittyfritters
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Re: Rubber Speed Event

Postby kittyfritters » Thu Jan 24, 2019 9:27 pm

Here's a video of my test hack at OFFC Wednesday morning. Couldn't get it over 13.5mph at Duarte last Saturday, Changed to a smaller prop and cut the wings back down, in stages, to the original span and got a 24.43 mph flight out of it, probably the limit for that airframe, The vid was taken at the end of the session when the rubber was getting tired. It's only doing 16.34 mph in the video, Has too much incidence, jumps off the ground too soon and flies too high, but I think it give me the parameters for my real racer. Oddly enough, I think a scale D-12 Bonzo would do quite well.

https://www.youtube.com/watch?v=1MoqCCBgFmc

More Later!

KF
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kittyfritters
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Re: Rubber Speed Event

Postby kittyfritters » Wed Jan 30, 2019 10:37 pm

Jim Leuken brought his first interpretation of a rubber RTP speed model to the O.F.F.C. meeting this morning. It has some interesting features.

Jim_RTP_2.JPG
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The rubber motor is on the outside side of the model instead of on the top or bottom to add a little tip weight. The wing has a higher aspect ratio than most of the designs I have seen, the landing gear attaches to the wing, not the fuselage and it has a Y tail with an under rudder.

Jim_rtp_1JPG.JPG
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Flight testing showed it still needs trim sorted out and the right combination of rubber (A lot of rubber!)and prop. More designs are showing up. Dave Gee showed a sketch of one he is working on that shows his usual penchant for bending the rules. Don't think that one will be built. More next week.

KF
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kittyfritters
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Re: Rubber Speed Event

Postby kittyfritters » Fri Feb 08, 2019 6:23 am

At yesterday's O.F.F.C. meeting we did more testing for the RTP speed event. I brought another test hack, an ROG type stick model with the wing and tail surfaces of my Speed Merchant design. Jim Leuken brought his improved design from last week and we had the three foot pole called for in the rules. Bill Watson brought the electronic timing pylon that he built for the contest.

My test hack had the wing held on by a rather strong rubber band so I could easily adjust the incidence. As I had thought the airfoil I am using needs a degree and a half of incidence to get the model off the ground within the first lap. Although with the three foot pole everything seems to get off the ground in the first lap.

Three foot pole.JPG
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I was using a five inch, Guillow's red prop and easily getting up in the twenty mile per hour range with four strands of 1/8" flat, tan, sport rubber. One thing I did find is that winding a thousand turns, or more, into a motor with four to six strands of rubber will rip the free wheel dog right off the front of the prop. Since we don't need a freewheel for this kind of flying just bend the shaft over the front of the prop. A may actually use the test hack as one of my entries in the contest with a more aggressive prop, maybe a four bladed prop. Another thing I found was that if you forget to aim one of these short winged monsters out of the circle at launch the line will go slack and the torque will wind the model into the line. With these motor stick types the line gets wound into the motor. We will need to have spare lines at the contest.

test hack2.JPG
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Jim tried to find the maximum sized motor for his design. He is used to handling strong motors since he flies in international Wakefield competition. However, he found that he can make too strong a motor for this type of model since with a very large number of strands you can get tremendous acceleration on the first lap but if the motor has too many strands you can't put enough winds in it to finish the third lap. Since the timing is on the second and third laps it defeats the purpose.

Bill's timing pylon was a heavy, impressive structure made of particle board with the timing platform and line pivot arm on top. It had two methods of timing, a micro switch tripped digital stop watch and a Hall effect sensor with a remote readout. The aluminum arm had a disk center with a spiral groove track on the bottom. There were two holes drilled into the track for the start of the second lap and end of the third lap. The track ended in a circle after the third lap hole. A whisker, attached to the micro switch rides in the track. The micro switch was tapped into the start/stop switch in the stop watch which was attached to the platform on the top of the pylon. You start the model with the whisker at the outside of the track. As the model flies around the pylon the arm rotates starting and stopping the watch when the whisker hits the holes. You have to go to the pylon to read the time, reset the watch and the whisker for the next flight. After a few test flights we realized that this Rube Goldberg electronic timer was just too touchy to work reliably.

The Hall Effect sensor, on the arm, was connected to a remote box with the electronics programmed to do the timing on the second and third lap and calculate the miles per hour at the push of a button. It also has a reset button and an on/off switch. This rig worked flawlessly except that the miles per hour calculation needs to be reprogrammed since it did not take into account the length of the arm. There was some concern about the drag of the massive (relatively) looking arm but it was not justified since the arm was on a bearing from a CD player and did not lag behind the line by the end of the first lap. In any event, since the mechanically tripped timer will be deleted there will be a much less massive arm on the pylon next week. The electronic timer pylon will definitely be used in the contest because with the regular pole and stop watches we discovered that with multiple people timing the spread between the times of a run were plus or minus 2 tenths of a second. We will still get another test session next Wednesday before the contest on the 16th.

https://youtu.be/3X_Qm-9_uV4

The 4.9 second time is 17.49 mph on rather tired rubber.

At the Black Sheep meeting, last night, Tony Naccarato brought some cut down Skystreaks that he converted into RTP racers. These are the new, improved Skystreaks (Still have the grain in the tail in the wrong direction.) with cut down wings. added landing gear, and the motor hook moved to the extreme rear of the fuselage. (Not to mention the paint job that he gave them.) These should easily get up into the twenty plus mile per hour range and don't take much time to build. At Duarte, last month, Dana Wall got a virtually unmodified Jetstream, with a four strand motor, up to 17 miles per hour where as a completely stock one would only get to 12.
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kittyfritters
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Re: Rubber Speed Event

Postby kittyfritters » Thu Feb 14, 2019 4:31 am

Did some more testing at the O.F.F.C. meeting this morning. Bill Watson came in with two designs of his own and the new, improved timing head.

HEAD1.JPG
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The arm on the head is still sitting on a bearing from a CD drive but it now, lighter, tubular and has a counter weight. A slight breath on it will start it spinning for about thirty seconds and it has no appreciable drag on the line. At one point Bill had a tiny TV camera on it transmitting pictures to his cell phone. This worked but the playback looked like the model was standing still and the room was spinning which was a bit dizzying. Richard Cox (president of the Conejo Valley Silent Fliers) who built the readout box re-programmed it so that the miles-per-hour read out worked correctly. This did require making the line nine feet four inches long to take into account the length of the arm. The original line was 10 feet long, including the paper clips, and pivoted on the nail in the center of the pole.

Bill brought two models, one very conventional and the other, well, take a look.

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Bills3.JPG
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The push-pull propellers run off opposite ends of the same rubber band. When asked why he made six bladed props he replied, "I was going to make five bladed props but when I made the blades I had a couple more left so, why not?" He did get the fastest time of the day but it was only a marginally faster than my test hack. I was testing different propellers and found a very aggressively pitched Ikara prop in my stash that I thought would work well but it was only a tenth of a second faster than with a Guillow's five inch, red prop. I'm really thinking that the red prop is seriously underrated! My test hack seems to fly best on two loops of 1/8" flat. Four loops provides way too much torque although a couple of inches more wing span (current span 8 inches) might counter that.

The contest is this Saturday at the Duarte High School gym, at 6:30 PM. If you can make it come out!
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