FF Indoor
Bud Tenny, Box 830545, Richardson TX 75083
New Glider
Bill Gowen has put forth an incredible effort to develop a Hand-Launched Glider (HLG) that is proving to be a formidable contender. He began with Mark Drela’s 1980 Upstart A design, and created a glider using carbon-fiber rods as construction elements in the wing.
At first glance it seems that the wing might be too weak to withstand a launch of reasonable force, but this hasn’t been a problem.
The glider has a span of roughly 20 inches, with 60 square inches of wing area. After flight-trim was complete, the model weighed 4.3 grams.
The fuselage, stabilizer, and fin are balsa, and the wings are constructed entirely from carbon-fiber rod. The carbon-fiber rods Bill used are called Carbon Micro Rods, and they are available from Matt Gewain at www.ostales.com.
Bill’s early discussions of the project were discouraged by most fliers; fortunately, he wasn’t easily deterred.
We discussed the project via E-mail, so I heard most of the early concepts and comments. Bill was largely working on expectations until he actually had a working machine.
It took a while, but (typical of most HLG models) working with the glider taught Bill what launch techniques the model wanted. After that, it was no longer a curiosity, but a competition machine.
Good work, Bill!
There are two interesting aspects of this glider. One is the covering material: it is covered with Ultrafilm, which is more commonly used to cover lightweight indoor models.
The other is that Bill used three rods to make the wing spar: 0.05-inch rods top and bottom, with a 0.02-inch rod sandwiched between the other two.
Kroger® Bags
Sometime earlier, Bill had reported that veggie bags (the rolled kind in which fruit and vegetables are sold) from Kroger® grocery stores weigh 0.0035 grams/square inch and are heat-shrinkable. In comparison, the veggie bags fall between 0.0025-inch Mylar® and Ultrafilm in weight, and are lighter than light condenser paper.
Bill tried the material on an earlier built-up indoor glider, but shrinking the film applied too much force to the airframe and warped it.
Now Bill uses Ultrafilm exclusively, but he must still use care to avoid warps when shrinking it.
Novice Pennylplane (NPP)
Bill Gowen developed an NPP model and, via E-mail, we discussed problems and successes related to this model.
One early discussion thread started this way:
“I had such gross problems with my Pennylplane yesterday that I never got to do them. I eventually had the best time of the day but the airplane was incredibly bad-mannered.
“The airplane was my third-generation Fin-Pen with no dihedral but having tip plates on the wing and stab. The prop is a very wide-blade prop from Vladimir Linardic’s Mylar Doll design, set initially to 24 inches pitch.
“After setting the cruise attitude with very low power I added a small increment to the launch torque, using about 20% of maximum winding torque. With the added power, the model invariably flew straight ahead for 50 or 75 feet before starting to circle.
“As it got down to lower speeds it would settle into a nice turn radius. I tried everything I could imagine to get an initial turn. I added left thrust, left rudder, more stab tilt, and finally washout in the left wing. Nothing helped.
“Someone suggested that the wingtip plates might be overriding the turn adjustments. I tried removing the bottom portion of the left tip plate, leaving about 1/2 inch of tip plate above the wing. This seemed to help a little so I did the same thing to the right wing.
“The airplane flew fairly well at the 20% torque. (I’m using a percentage because my winder is not graduated in inch-ounces or any other unit that I’m aware of.) Again, when I added more torque, the airplane rolled to the left in an extreme bank attitude and still tried to turn right.
“When I added still more torque it went into acrobatic mode, eventually rolling upside down. Since time was running out, I put in a couple of flights at about 30% torque and kept the airplane in the air long enough for it to reach a slight climbing cruise.
“My best flight was 6:20 with the airplane never getting more than 20 feet high. For about the first one minute of that time it was circling at about four feet of altitude; heeled over in a left bank with the nose pointing to the right.
“I’m now suspecting that the following things were wrong and would like your comments on these ideas:
- Prop blades are flaring unevenly and going to a too-high pitch condition. I noticed as more torque was added that I was getting a severe vibration from the prop that was shaking the airplane. I had checked the balance and pitch of the blades, so uneven flare is the only other thing I can think of that would cause this.
I used this prop that had the Nats with a conventional tip dihedral wing and also had stability problems at high torque.
- Wingtip plates need to be a little larger than my final configuration to prevent the roll instability I was seeing.
- Possibly more rudder area would have stabilized the airplane and overcome the too-high prop flare. The rudders on this airplane were much smaller than on my first Fin-Pen, which was extremely stable in all phases of the flight but was overweight.”
My reply:
“Two or three things must be happening. First, that prop is obviously unstable. Use a smaller prop that doesn’t flare much—or not at all. Be sure the new prop weighs the same as the first one.
“Once the model problems are sorted out, you can switch back to a more flexible prop to gain the higher performance they afford.
“Second: make sure that no part of the model distorts when you hook up a wound-up motor. Most likely, the stab tilt changes (less tilt, or even reverse tilt).
“If the motorstick is twisting, most likely the wing is also.
“Finally, the model may be effectively nose-heavy.”
Feedback
After sorting through my suggestions, Bill sent the following information.
“I’m happy to report that my efforts are bearing sweeter fruit! I flew at the monthly TTOMA indoor meet yesterday and took two firsts and a fourth.
"The most important part of the story is that the LPP flew beautifully. Every flight was picture-perfect—at least until it got to the ceiling.
"The LPP had the following changes made from the last time we talked:
- New prop with laminar blades and 1/4-inch less chord.
- Wingtip fins rebuilt larger and lighter.
- Stand rudders from Pen-Fin I installed to give about twice the rudder area as Pen-Fin III.
"The model hung a wingtip on a cloth sound-control pad twice; I had to bring it down in pieces twice. After repairs I finally got in a successful flight of 6:54. I was using a 13-inch loop of .085 wound to .8 in.-oz and backed off to .2 in.-oz. It went dead-stick at about three feet altitude.
"Since this time was a half-minuter better than anyone else's, I didn't try it anymore. I think with a longer and slightly smaller motor I should get in the eight-minute range next time.
"I haven't done the rpm checking yet. Now that the airplane is flying reliably I can start concentrating on the fine-tuning stuff.
"In response to your question about structural stability, the fuse is very stiff and does not really show any twisting at the torques I'm using.
"It is made from a large piece of very light wood sanded into an I-beam shape. The stab and rudders used were very heavy but the total weight was exactly 3.1 grams.
"With the weight reduction that should be possible with a rebuild, I hope to do some experimenting with two-surface airfoils.
"Thanks for your help!"
Steering
Depending on the circumstances, steering an indoor model can be a luxury or an absolute necessity.
We are allowed to use a variety of mechanisms to steer a model away from an obstacle or to help prevent our model from fouling another model.
A balloon is the most versatile steering tool, but there are some problems unique to balloons. They must have enough lift to give a strong and steady pull; otherwise, effective steering of models higher than 50 feet is almost impossible.
For really high ceilings, the balloon should lift two or three pounds to give effective feel and quick response.
A "soft" balloon can be used to retrieve models stuck in the overhead, but it won't follow a model quickly enough to score it.
Most balloons are rubber; some fliers buy surplus weather balloons to get high lift.
However, rubber balloons don't stay properly inflated very well. It is well worth the effort to obtain a Mylar® balloon.
Mylar® balloons have advantages over rubber balloons:
- Low-pressure Mylar® balloons don't explode when snagged on a splinter or rusty metal in the top of the site.
- Mylar® balloons lose helium much more slowly than rubber balloons.
- Mylar® is lighter per unit volume than rubber, and filler fixtures can be lighter with low-pressure Mylar®. Lower weight on a balloon means better lift for a given volume.
Where do you get Mylar® balloons big enough to do the high-altitude steering? Ray Harlan made his.
He made a heated roller (discussed later) that he used to seal the edges of five gores that, when assembled, made a Mylar® balloon that was approximately 20 inches in diameter.
The fill nozzle isn't strong enough to attach the line to, so he has a three-strand cradle that surrounds the balloon and provides an anchor for the line.
Ray notes that this balloon only has to be topped off daily during a multiday meet. He cautions that this balloon is too fragile to be taken outside while still inflated—a true "indoor" balloon!
The heated roller was machined from aluminum and consisted of a cylinder just large enough to fit over a 200-watt soldering iron. The roller attached to the cylinder and conducted heat to the Mylar®.
A variable-voltage transformer allows the amount of heat to be set high enough to seal the plastic, but not too hot to melt it rough.
The plastic Ray utilized was a special multilayer type used for making balloons. Normal covering plastic used on models won't heat-seal, but some people have used double-stick tape to seal the edges of balloons made from covering Mylar®.
Transcribed from original scans by AI. Minor OCR errors may remain.
