Friday, September 26, 2014

Pushing Simple Planes to Greater Duration

It would sure be nice to have a very large open area to fly free flight model airplanes but more commonly only smaller areas like a schoolyard or a soccer field are available. Flying from the somewhat risky flying site, I normally fly the simpler rubber powered models that would not be a big financial or building time investment  loss if the model could not be recovered from a flight.  Last evening I grabbed several simple rubber powered models and headed to a small field because the wind was almost still.

Collection of Simple Rubber Powered Free Flight Airplanes

The first model into the air was an AMA Racer which is a really simple flat wing design with triangle shaped flying surfaces. Normally this plane is built on the plan material but I covered with tissue paper instead to save weight and because I think it looks better. For a simple plane it really flies pretty well and achieved a fair altitude. Next in the air was an Easy Built IMP which is a ROG type plane with a single surface curved airfoil. This provides good lift but the glide is really steep into the ground, after the rubber winds down the airplane is on the ground within a few seconds.  Most the small simple planes do not glide very well when the propeller starts freewheeling.

AMA Racer 

Easy Built IMP

Flew the original plane I had designed that has the tail surfaces of a Denny Dart and a flat wing with winglets; vertical fins on the wing for stability. I had curved the ribs while wet to give an airfoil with a small amount of curve but not too much that it caused excessive drag. This airplane flies well but seems to require a proper launch or it can crash right after launching. Last plane to be flown is plane with an airfoil covered on both sides that normally will climb slightly higher than the other airplanes I brought out.

Plane of My Design

Two Surface Covered Wing Airplane

The longest duration of any of these planes without much thermal help appears to be one minute at the very best. This makes for a nice flight over a small field but I was thinking about how more duration could be obtained using this size of airplane with a 6” diameter plastic propeller. I think the key is to reduce weight more by lighter covering or structure so that the airplane can fly with thinner rubber strip that will accept more winds without breaking.  Using 1/8” wide rubber strip 97 turns per inch is considered maximum but if the airplane can climb on 3/32” rubber turns per inch is 129. 

Anyway this has me wanting to try to get a flight of at least 1 ½ minutes outdoors without thermal help. 

Bill Kuhl

Monday, September 22, 2014

Slope Flying Contingency Plan

On the third Saturday of the month there are a group of us that gather for a thermal duration contest of some type organized by Wayne Norrie. When this first started it often happened to be on a windy day; we would gather and talk for a while and then go home. Wayne has been working hard to find suitable slope soaring sites with hills facing all directions which gives us a contingency plan for windy weather; last Saturday we were at another dam site that will work for east or west wind.


 Lift was good for a small hill and a variety of gliders were flown. Ray landed at the edge of the water a couple of times to start with because he was having trouble controlling his glider. Turns out he had too much control and the glider was not responding well, when he adjusted that his flying wing was flying very well. Wayne flew his Sig 2 meter riser which quickly rose fairly high compared to some of the smaller foam planes I was flying. 

 After mentioning to group we could try some type of timed racing event without much response; Wayne decided he would go for the one hour slope flight. After the first launch his Riser was back on the ground after not very long, it was launched again and the flight duration kept stretching out. On a couple of occasions the Riser came within a few feet of the top of the dam but Wayne nursed it carefully back to altitude. When it looked like 60 minutes might be within reach, the wind shifted slightly and the glider landed at 38 minutes. Rather disappointing but a darn good flight from such a small slope.

 Dave flew a Hyper DL glider; I just purchased a used one that I think flies very nice. George who had been flying his Alula but changed to his 2 meter Radian and powered up to altitude to check out the thermal lift. Even though it was windy, there was some huge thermal lift over the land areas to side of the water that appeared to be rather stationary. 

 It was a fun morning of flying and the pelicans on the water didn’t seem to mind us being there at all. 

 Bill Kuhl

Monday, September 15, 2014

Goodbye to My First Tip Launched Free Flight Glider

Sooner or later it was bound to happen, the Maxima tip launched free flight glider I had built the winter before would be lost.  It seemed almost like this glider was leading a charmed existence, it had endured; getting stuck high in a tree, flying over a small pond and landing in a tiny strip of land before houses, and flying over small woods and a four-lane road.  When I started to learn to launch a tip launched glider it repeatedly smashed into the ground but all the repairs were rather minor. This was the first free flight airplane that I had installed a dethermalizer on and that was a learning process.

Last Flight of Maxima TLG 

Over the course of the flying season it became apparent that the biggest weakness in the glider was at the critical hinge point of the tailboom, it broke in that area many times. After the carbon boom was no longer breaking from the wood hinge block the then plywood surrounding started to break from the wing. In repairing this area I think the pivot operation might have not been as smooth as before.

A couple of flying sessions before the last I had replaced the DT spring and the rubber band it seemed to work fine, but it could have been a failure variable. I thought I was getting pretty good at setting short DT times to keep the glider on the small fields I flew from.  Last Saturday I had the chance to fly from a larger field but not huge by any means, the wind was gusty at times but it appeared to be a day that should create good thermal lift. The morning started barely above freezing and it warmed to the mid 60’s by the afternoon.

Swinging Boom Must Pivot Easily

For the start of the flying season I was content just to see the glider launch high and glide smoothly down. As the season progressed I wanted to see the glider floating effortlessly in a bubble of rising air. Funny thing just that morning I was rereading the NFFS Symposium #45 Really Random Thoughts from the World of Outdoor Hand Launch Glider Flying Tim Batiuk. Quoting from the article, “One thing that has remained consistent since history of HLG is that in order to get a max you must have a thermal.”  For my own enjoyment getting thermal flights was the really cool part of free flight flying.  It was the same as flying my radio control gliders when there was no lift, pretty darn boring.

Start of Flight

Last Seen Flying Over the Trees

Last Saturday I had the chance to get to a larger field, I started with some short DT flights. The glider came down and the boom had popped up.  I thought I had the DT set short again but then the temperature was now 15 degrees less than during most of my previous flying; that could be another variable. Waited for the calm and gave it a good launch, the glider was circling perfect, not really getting higher but not coming down.  I started walking towards the glider but the ground was too wet to be able to run on.

Turkey Vulture Would not Tell me Where Glider Was

Hard to judge time when you are watching something so cool but it seemed like it had been flying a heck of a long time. It is getting so close to trees at the end of the field, why doesn’t it DT I keep thinking. Pretty soon it appeared to be past the trees, a turkey vulture was circling low over there also, if only it could have told me where it landed. I had done RC slope soaring off the hill behind the trees before but that was early one spring but now I found it was cornfield past the trees. Made a couple of passes through the field but I had to give up.

Larger Field to Fly From

I plan to build a couple of TLG gliders this winter; this has been one of my bigger thrills in model aviation. There is much for me to learn about dethermalizers and still I realize that planes will be lost on occasion.

Bill Kuhl

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Wednesday, September 3, 2014

Using Trig to Estimate Height of Small Slope Soaring Hill

As Paul Naton said in his first soaring video “there are a lot more small slopes than large slopes”, that is sure the situation where I live. With the availability of small foam ready-to-fly gliders such as the UMX ASK-21 and UMX Radian I have been having a great time flying several small slopes and always looking for more to try.  I have been curious to just how tall these slopes were and was thinking that by using trigonometry an approximate height could be arrived at.

Hill to Estimate Height

Slope Flying UMX Radian 

Using the Estes AltiTrak device that I had purchased for computing the apogee of model rocket launches I was able to measure the angle of the face of the slope  (22 degrees), no doubt some type of carpentry level could be used as well. Then I measured the length of the slope using a tape measure (39 feet), this would be the length of the hypotenuse of a right triangle which is the basis of trigonometry. 

Measuring  Face of the Hill - Hypotenuse

Estes Alti - Trak to Find Slope of Hill

For myself math skills become rusty because I do not use math enough, I posed the scenario of what I was trying to calculate on model aviation listserve and someone provided an example of the correct trig function to use; the sine function. Sine = Opposite / hypotenuse so the height of the top of the hill would be the opposite side of the right triangle. Rearranging terms the height of Slope =sin(angle)*hypotenuse or   =sin(22)*39ft = 0.375*39ft= 14.6ft  the height of the slope.

There are other small slopes that I would like to compare to this one as to available lift. It would be interesting to see if there was significantly greater lift from a slope that was 30 feet tall compared to 15 feet. No doubt there are many more variables to the lift than slope height. My guesses to slope height tend to be rather optimistic, this slope I thought was close to 25 feet tall.

Bill Kuhl

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