Thursday, October 26, 2017

Why I Like Free Flight III - Probability

This series of articles on why I like free flight has been really popular so I am adding another and discuss probability. My view of how the world works is everything is based on probabilities. There are factors that one can adjust to increase the probability towards a more favorable outcome.  In free flight competition the top competitors have identified factors that gives them the highest probability of scoring high in contests most of the time. In outdoor free flight the factors give a higher probability their models will climb very high and glide as long as possible consistently. In outdoor free flight there is also the big factor of launching into thermal air currents, something I definitely need to work on.

Launch to High Altitude on Very Limited Motor Run

Besides what might be obvious factors such as using a very powerful motor or building the plane to just over a minimum weight, there are smaller factors that can influence the reliability of the model over time. This could be such things as the proper materials used to cover the model with, and how the power system and timers are setup. 

Covering With Very Thin Plastic Instead of Tissue

Another thing I really have noticed in the contests I have been to which really isn’t that many, is time management is a big part of it.  Now we could make it easier on ourselves and only fly a couple of events but most of us try to fly more events than we can comfortably handle in a day, this is a good thing as there needs to be enough entrants in the various events. To improve what can be flown in limited time factor, we want everything to be as reliable and trouble free as possible. Anytime you have to spend time doing field repairs, trying to get a motor running, etc. is time that could have been spent flying. Another big waste of time in outdoor free flight is retrieving your model; this is why I purchased a used tracking system. A motorcycle would be a big help also, but cannot be used at our club contests.

Walston Tracking System

No doubt how I waste the most time from official flights and I know a lot of people are in this situation, is that I do not have a proper place to test my models until I get to the contest. At least I have enough space available I can check out the power pattern on electric models and the transition to glide. It really doesn’t give me a good idea what the duration will be when trying for a 2 minute flight on a larger field. When I flew indoor free flight contests I had a place locally to trim models and a mentor to offer constructive criticism; that was a huge advantage to people that came to contest with untested models.

Power Pattern Tested for E36 Starduster on this Small Field

Rubber powered models make it easy to try short flights because you can just put fewer winds in the rubber motor. This really doesn’t give you a good idea of what a contest flight will be like when there is much greater torque provided by the rubber motor. I sure found that out on a rubber model this year that appeared to climb nicely on 200 turns but went into huge stalls at 400 turns.

Testing on Small Field - Not Great

Building season has started where I live but there still can be some flyable weather but only during the day. I want to think about how I can improve my probabilities for consistent flights for the next contest season.

Bill Kuhl

Tuesday, October 10, 2017

Mousetrap Car Demonstration at Nursing Home

Last week I gave a demonstration of mousetrap cars for two different groups in a nursing home. I was concerned how interesting they would find my presentation but it was well received and they are looking forward to me presenting another project idea, I proposed model aviation.

Mousetrap Car Race 

Below is an outline of what I wanted to present, it worked well for a 40 minute presentation:

My Basic Outline for Mousetrap Car Demonstration

* Talk about my father and his farm machinery inventions.

* My interest in model airplanes led to building and flying events for kids, I wanted to expand to more types of model projects and came across mousetrap cars.

* I watched some videos of mousetrap cars on the Internet and was amazed at the number of views.

First Mousetrap Car I Design Built from Bamboo

* My purchase of the Doc Fizzix book on mousetrap cars gave me the background to design my own cars using different materials; the first car was built mainly from bamboo. I also purchased Doc Fizzix kits and started an online friendship with Doc Fizzix, Alden Balmer a truly outstanding teacher.

College for Kids Class Mousetrap Cars

* In teaching a project building class at local university, I had students build mousetrap cars every year.

Lever Arm Attached to Spring on Mousetrap Car

* Mousetrap cars are a wonderful for teaching force and motion, I would mention Newton’s Laws of Motion especially the first law relating to getting an object at rest moving.  

Large Drive Wheel Mousetrap Car

* I would demonstrate mousetrap cars with long lever arms which moved slowly, cars with short leverage arms were much faster, and a mousetrap car with a very large drive wheel is also slower.

Start of Mousetrap Car Race

* There would be a mousetrap car race between two cars. By attaching a length of yarn to mousetrap car, a person sitting could easily release the car.

Bill Kuhl

Related Links

Monday, October 9, 2017

Oktoberflug Free Flight Contest

It was the best weather this year for the final outdoor free flight contest in Minnesota. The wind was very light in the morning but switched around almost 360 degrees throughout the day. To start out the morning drift was towards the trees which worried me, better flyers were getting their models to fly over the trees. I flew my e36 Super Pearl before any contest flights with fairly short DT to avoid the trees; it flew perfect as it had the last time.

Gordon Dona Flew Model Past the Trees

My main goal was to get some longer flights on my Wilbur rubber model, at the last contest when I increased turns from 200 to 400 it was going straight up and sliding backwards. Adding some side and down thrust appears to have cured that. It stalled in the glide somewhat but it caught some lift on one flight and was staying up even with the stalls, next flight I had fixed the glide but didn’t find any lift. I still did not have anywhere near maximum turns but it was drifting towards the corn almost 180 degrees from the drift before. It is fun to see the propeller fold back and I did get in three contest flights with no damage.

Wilbur Rubber Model Folded Prop
Wilbur Landed

Before the wind came up I wanted to try my Peewee 30 model Basic Yeller. The first flight did not get super high but the glide was perfect and stayed up until the DT brought it down but now the drift was behind us. I tried another flight and it went to the right into the ground, no damage. Thinking it was just a bad launch I tried it again and this time there was damage, broke the pylon off. I noticed there were only two wood screws on one side holding the motor on. My thought is that it was loose before causing sidethrust giving a severe turn. I plan to fix it with bolts instead of wood screws.

Basic Yeller Landed Behind Pit Area

Pylon Broken in Crash

I flew my Polecat X P30 in the contest for the first time and it went very well. Still I was not up to maximum turns which no doubt would have taken it higher. I am using the 3/32” rubber motor that gives a long run but a slow climb. During the long run there is a good chance it will encounter lift which it did but the pop off wing brought it quickly down.

My Polecat X Brought Down by DT Before Cornfield

Just before I left I tried one flight of my Jetstream towline from a launcher. By now the wind was up and I was not familiar with that. It rose quickly and I stopped running but the wind took it up like a kite until it came off the hook and banked sharp into the ground. Only damaged one wing tip but I can see I have more to learn about towing in different wind conditions.

Starduster X

I used my binoculars when timing flights for others as I want to get better at following the model this way.  Also hoping to take some video but I only got video of a Starduster X flying one flight. At least I had rubber boots for this contest and did not have to leave with wet feet from the morning dew. 

Pearl e36 with my new Boots 
Flying Aces Moth

Bill Kuhl

Related Articles

P. Visser's "Wilbur" Nostalgia Mulvihill per Zaic '53    Item ID  NOSR9   Propeller Blanks  Pearl Free Flight website to Purchase Polecat X

Starduster Video

Tuesday, October 3, 2017

Why I Like Free Flight Part II

I have been overwhelmed by the number of views to my last post so I have decided to expand on that and share a little more about myself.  One thing that bothers me, is wasting anything and I am really impressed by things that are efficient.  I know I could do a better job of not wasting and I realize that other people have different needs; you are not going to pull a horse trailer with a Prius. What impresses me most of about my hybrid car is that the engineering that has been done in so many aspects to improve the gas mileage. The factors that contribute to the total result working together are many but the end result is I drive car that averages 60 mpg in the warmer months. Just some of the areas where improvements were made were recapturing energy from coasting and braking, drag reduction, increased thermal efficiency in the internal combustion engine, constantly variable transmission, and using battery power to help power the car some of the time.  It is a total system working together.

Typical Large Glow Engine Powered Free Flight - Dave Edmondson
Hybrid Car System of Engineering Ideas Work Together

Now how does this relate to free flight?  I see the competition free flight airplane as a total system that is optimized in many ways to give the longest duration given the constraints such as size, power, and minimum weight.  There are so many factors that can be optimized such as; the aspects of the construction materials such as balsa density and grain, building structure types, covering material, and warps built in to give the proper flight path for a free flying model airplane. With power system if it is a motor it should have a high power to weight ratio given constraints to the competition classification. Aspects of the propeller such as diameter, pitch, and pitch ratio can make a difference in power models including rubber powered models.

This Balsa Structure Made for Very Stiff Balsa Wing

Bob Hanford has Flown Free Flight Contests from a Young Age 
Beyond keeping your competition free flight model aloft consistently above a specified length of time, you want it to come down reliably after that specified time. This is where the dethermalizer system (DT) comes in to bring the model down quickly without damage while lifting air (thermals) can be trying to carry it higher still. There are many systems that are used but it is often a tradeoff between weight, cost, and what the builder prefers to use. The DT system can often take a fair amount of tweaking to work as reliable as possible.

Pressurized Fuel System and DT Timer on Dan Berry's Plane
Now after the model is built, you need to test fly it. With no control from the ground to save it should it fly in a path that results in a crash, you develop procedures to slowly lengthen the time of the motor run and length of glide before DT. If this model is rubber powered you use less turns of the rubber motor but you must be aware that the model might fly radically different with more turns of the rubber and increased power. For any type of model test glides are done first but this might only give a very rough idea how it will fly under power.  To me this is the most interesting and sometimes frustrating aspect of free flight models, the adjustment process. In getting your model to fly properly it calls on your knowledge of aerodynamic theory and putting it to practical use. Like any good experiment you want to change only a single variable at a time.

Rubber Powered Model Needs Propeller and Rubber Strands Matched - Skeeter Surgine

If you are flying indoor free flight it is a rather controlled environment but flying outdoor free flight which I have greater interest in now, has many additional aspects you must consider. There is the thermal air currents that you want to launch into but there is also sinking air, turbulence, and wind that will drift your model to parts unknown.  This year I purchased a used radio telemetry system which am I learning to use. A small radio transmitter is attached to the airplane that sends out a signal that you locate with a directional antenna.

Tiny RF Location Transmitter

Directional Antenna and Receiver 

My Indoor Rubber Powered Model
As the investment guru Jim Cramer likes to point out, here is the bottom line. Outdoor free flight model aviation gives one endless opportunities to learn engineering skills and practice real world experiments. By just timing the flight duration over a series of many flights you can see the results of many factors working together in a system operating in a changing environment. As a bonus for those of us passionate with the hobby, the thrill of seeing the model airplane flying with no external control is a major high.

Note: I did not mention gliders, topic for another post.

Hank Sperzel a Big Inspiration to Me

Bill Kuhl

Related Blog Articles

Related Links to My Short Videos - My Background in Free Flight Model Airplanes - Learning to use Walston Tracking System - Guillow's Lancer with fuse DT - Texas Timers Micro DT - High Speed of Glow Powered Free Flight Ruth Bane