Monday, June 23, 2014

Herr Champ First Flights

Building a rubber powered model free flight model airplane that looks like a full-scale airplane is fun and challenging for me.  It can be frustrating at times as there is a good chance the model will be broken from clumsy fingers during the construction process. Covering the many surfaces without wrinkles or warps is not easy for someone new to this either. Adjusting the model can take considerably more effort compared to the rubber powered beginners models. When it all comes together and the model that looks like a full-scale plane is making perfect circles in the sky with no control from the ground it is well worth the effort.

One of the common challenges comes from the fact that the full-scale airplane has this heavy motor in the front while your rubber model only has a propeller in front and the rubber motor is located along the length of the fuselage back almost to the tail. If possible, building the tail as light as possible saves having to add excessive weight in the nose to balance the airplane and reduces the overall weight. On the Guillow's Super Cub I built the tail by curving the wood while wet to create lightweight tail surfaces, this plane flies very well without any nose weight.

Other challenges come from the lack of dihedral and the smaller tail surfaces when building a model that looks closer to it's full-size counter part. In the links below are short videos of some my previous rubber scale airplanes that did not fly too well at first. With some adjustments the planes all flew better but not perfect. It has been a learning process and I try minimize problems during the building phase based on my previous experiences if possible.

Last winter I constructed the Herr Engineering Aeronca Champ rubber powered airplane. Plans are adequate but not as detailed as with some kits, the wood was good but not excessively light. When completed I thought it looked fairly well for my skill level but I am no master builder.

Start of the Construction

For the first flights it became apparent the plane had too much turn to the right, in the field the only way I had to correct was clay on the left wing tip. With a gentle right turn the plane would climb very steep and hang on the propeller resulting in a stall to the ground. Clay was added to the nose until the climb seemed about right, this put the CG as indicated on the plans. As seen in the video clip I took the flight path is rather wobbly yet, I am trying washout in the wing for the next flights.

IMP Model Flew Perfect With No Adjustments 
The Easy-Built IMP model pictured above is a typical beginner's model for comparison. Lower wing loading, more dihedral, higher lift wing, and larger tail surfaces make for an airplane that flies slower and was easy to adjust.

Hopefully I can get another video clip when this plane is flying smooth.

Bill Kuhl

Flight Videos of Some of My Other Rubber Models

Guillow's Super Cub
Guillow's Cessna 180 - bad flight
Dumas Curtis Robin - some stalling
Minnow ROG - flies perfect every flight

Friday, June 13, 2014

Lost Model Plane - What Can I Learn

I lost a cheap rubber powered model airplane the other evening that I had little invested in, a Peck ROG. This kit sells for $5 or less and it builds quickly but it is a wonderful flyer.  My wish was if I had to lose it was to see it spiraling upwards in a thermal until it was a tiny speck. Instead I did not launch far enough from the Bermuda Triangle of my flying area, the small trees and tall grass.  With too many winds in the airplane to start with after not flying for some time to check the flight pattern the plane went out and came back heading right for the trees. I thought I had watched carefully where it went into the trees but not careful enough.

Peck ROG

Spent at least 15 minutes walking the brushy area and shaking the small trees hoping my plane would come out of some small tree, no such luck. Gave up looking and flew other airplanes but it still bugged me that I had watched the plane fly away but could not find it. I have been trying to get a better visual line exactly where I see a plane land and walk straight to it. 

Front Area of Trees Plane Flew Into

Tall Grass on Top of Ridge

The next evening I was out in that area so resumed my search. After not much looking I came across another small plane I had lost last year, the Klutz Shooting Star. It was not in very good shape but the small propeller assembly appeared good. It gave me a little encouragement that I could find a model plane in this small jungle but I think it just made me more frustrated in my search. 

Plane Lost Last Year Found

After covering the same area again, I tried looking farther out. Then I tried to apply more logic to my search tactic reasoning that I did not remember seeing it stop flying into the trees in front it must have flown over the trees and could have landed in trees on the back side of the small ridge or in an area of tall grass. I wish now I would have tried to take a picture of it flying into the trees, your memory of where you last saw it quickly starts to fade.

Rear of Ridge and Trees

Sure wish I could have found this airplane just because I would like to know how I could have missed it in my search. Could I have walked by it time after time? Had it penetrated some area of tall grass to be covered up. Last year I had lost a small hand launch glider in another brushy area and the Shooting Star in the trees you would think I would learn better how to search for missing planes.

More Brush on Other Side

I remember years ago walking a cornfield with a bunch of people including my father looking for a missing radio control airplane. Someone asked my father if he had spotted anything and he replied no but he thought he might have seen Jimmy Hoffa in the cornfield.

Bill Kuhl

Tuesday, June 10, 2014

UMX Radian Initial Impressions

Not to be left out of the fun, I purchased the UMX Radian radio control glider from my local hobby shop Everything Hobby. This is a smaller version of the popular 2-meter Radian glider, the wingspan of the UMX is just under 29 inches with a weight of 1 ½ ounces. For the last couple of years I have been flying the Radian Pro 2-meter glider which adds ailerons and flaps. I have also been flying the ASK-21 glider which is similar size but does not have electric propulsion.

At this point I have only flown the UMX Radian for one flying session and this was only thermal flying, no slope flying.  The airplane was very easy to setup and bind to my Spektrum DX9 transmitter. It uses a single cell 150 mah lipo battery which I use in three different airplanes so I have several. USB charger is included but I have an AC charger that charges two batteries at once. Like the ASK-21 gliders the UMX Radian has the built-in gyro technology known as AS3X. In reading forum comments some people thought it was great and other people were wishing there was an easy way to turn it off.  The positive opinions were that the smaller glider would fly in windy conditions better with AS3X but some people wondered if the glider would indicate thermal lift with it on as well as with it off.

It is amazing how well this glider climbs on a single cell battery. Obviously with such a small size the glider gets hard to see fairly quickly.  I did have it climbing in thermal lift but flying the Gentle Lady 2-meter glider the same day I could rise in thermals much easier with the larger glider. From reading the comments on forums it seems there is a differing in opinions as to how well it thermal soars with some people thought it was great and others not very positive. The wing is rather thin so it does penetrate wind better than one might think for a glider so small.

The main reasons I think people are purchasing the UMX Radian are:
Price only $90 ready to fly without transmitter
The ability to fly from smaller flying sites both thermal and slope 
It is so small that it is easy to leave it in a vehicle and be able to fly almost anywhere

As I get more experience with this glider I plan to write another report.

6/10/2014 Update

I flew again late afternoon in somewhat gusty conditions from 4:45 to 5:20 p.m. Several times the UMX was climbing in lift but I did not let the glider get real high as it was getting downwind rather far. It helped to get rather high and try to find the thermals. Trying to circle up from a thermal at 50 feet probably would not work too well which isn't easy with any glider. I find myself more relaxed flying a glider that costs less than $100.

Bill Kuhl

Thursday, June 5, 2014

Still Learning With 2.4 MHZ RC

After replacing the nickel metal hydride battery in my Shadow 2-meter glider I thought my troubles were over with battery issues in that airplane. I found out I had more to learn when it comes to 2.4 radio systems. I flew the glider with the new battery for some test flights and then flew it again without a full charge. The expanded scale voltmeter showed the battery was still well into the green but after a couple of short flights my glider went into a spiral dive crashing into the ground just next to a street.  I was really amazed there was not more damage, only an area around the wing hold down area of the fuselage was broken.

Shadow 2-meter Sailplane

After the crash I thought the receiver was flashing which I learned afterwards indicates an error condition in the receiver. I tested the voltage again with the expanded scale voltmeter and it was still in the green.  From questions I asked on the RC Soaring and Sailplane Society forum on Facebook, I learned that in flight battery voltage can easily drop if there is a large load causing receivers to fail.  Expanded scale voltmeters are not that accurate for testing either, the battery needs to be tested under load. This glider has 6 servos and two of the servos are rather old, this can be a large load. Many people are using another cell or some type of lithium battery with a regulator to keep the voltage from being too high for the receiver. 

After the Crash

I epoxied the broken piece back and tried to fly the glider again. Someone with a mild electric winch took the plane up. We noticed the canopy fall off on launch which has never happened before, this should have been a clue that something was wrong. I flew around fine but on landing I noticed the wing was not straight, sure enough my repair had failed.  Someone with the same type of glider gave me good advice how to do a proper repair covering a large area of the fuselage with fiberglass cloth and using a slower drying epoxy.

Area With White Patches was Repaired With Fiberglass

Canopy Held on With Wire at Both Ends

Last evening I flew the Shadow again with a full charge and with the two flap servos unplugged; now there were only four servos draining the battery. The glider flew perfect, after a couple of gentle launches I pulled back harder on the hi-start and got better altitude. Soon the glider was in lift; and going up. It was after 5:00 p.m. so I was rather amazed to find lift so good but there had been big puffy cumulus clouds all day.  This was really fun, the glider flew rather fast but it was going up.  I tried the thermal mode preset I had set on the ailerons and it did slow the glider down.  Normally I am flying this glider when there is more wind and it is 
hard to see the speed difference. Landing was rather fast without flaps but that is fine.

Data Logger Worked on Receiver in my Radian

Voltage was still well into the green after flying for a total of 25 minutes, I called that enough. I have not been able to get the flaps to change with the ailerons in different flight modes on my new Spektrum DX9 transmitter yet. The manual leaves much to be desired, it does not go into enough detail about how all the many functions operate.  I purchased the Spektrum data logger but I found out the particular receiver model I have is not listed as one to work the data logger. 

This might sound very frustrating but I am really having fun with this glider. It flies so smooth and handles the wind so much better than my trainer gliders. When I obtain another glider of this type, I will look into a different battery system and a receiver supported by the data logger. 

Bill Kuhl

Nickel Metal Hydride Battery Story

Comparing Two 2-meter Gliders