Author: John Kagan
Edition: Model Aviation - 2012/04
Page Numbers: 134,135,136
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F1L — International EZB

by John Kagan [email protected]

My F1L model has been nominated for the National Free Flight Society (NFFS) Indoor FF Model of the Year, which is quite an honor. The airplane has been a good performer at the Indoor FF Nats, with five wins, five silver medals, and one third-place finish that was its lowest ever. That stellar record didn't take much effort, though; it is easy to fly. I've only built one and I only take it out of the box once a year. I launch a couple of test flights, and put it up for its usual times.

That got me thinking about what a nice starter category F1L is. It is a natural second model after Limited Pennyplane (LPP), which I discussed in a previous column.

F1L is limited to an 18-inch wingspan with a 3-inch chord, and has a set of rules keeping its complexity low (solid motorstick and tailboom, no variable-geometry propellers, etc.). The rules are the same as EZB, except for a minimum weight limit of 1.2 grams (modern EZBs weigh roughly 0.5 gram and can be as light as 0.3 gram).

What a difference half a gram makes! EZBs are finicky, fragile, and challenging to fly well. Each component is a delicate balance between weight and strength, and must be in perfect harmony with the rest of the model. Component flex is inevitable, and is actually used to tame launches (via motorstick bow) and emulate variable-pitch mechanisms (through flaring propellers).

By comparison, F1L models are relatively stout and simple. Wood selection is more important than in an LPP, but not as demanding as the bigger, lighter classes. Trim adjustments stay put, and motorsticks and wing spars don't contort excessively under launch loads.

PLUS:

  • Stroke watches
  • Indoor FF Nats update
  • Indoor Fling
  • Two new presidents

The rules, while restrictive enough to keep things simple, still allow a fair amount of design creativity. Indoor FF enthusiast Kang Lee took a look at the top F1L models of the 2011 Nats. Variations include use of tiplets, amount of dihedral, CG location, Warren-truss wings, and droop booms.

When a particular model tops the standings in its category, people tend to copy it. You end up with a bunch of look-alike models in the air and it can be hard to find yours. However, in F1L, a clear favorite has not emerged. The times of various models are still close enough that competitors are comfortable pursuing their own special nuances. Viva la différence!

If you are looking for your next challenge, consider F1L. There are many designs to start with, and plenty of variations to explore. They are fun to fly in all ceiling heights, and will help prepare you for more complex models.

Indoor FF Tools: A Stroke Watch

Top times in low-ceiling sites invariably involve some sort of energy management—usually through the propeller. The goal is to use the high-torque portion of the energy release (instead of backing it off) without out-climbing the site, and to keep the model in the air during the low-torque tail end.

Without such energy management, you are left with a relatively small section in the middle of the torque curve, and you lose the energy and associated time on either side. Models such as the F1L get their energy management through aerodynamic deflection of the propeller blades—called flaring propellers—because variable-geometry mechanisms are not allowed. Propeller blades are offset, with their center of pressure in front of the spar so that high loads twist the blade to a higher pitch. It is tricky to get the right amount of change. Sanding the blade or spar can increase the amount of movement, but if you go too far there is not much you can do to go in the other direction. A propeller is tuned for a particular ceiling height, so a collection is needed if you fly in more than one site.

Other classes benefit from variable-pitch and variable-diameter propellers. The mechanisms are harder to construct, but easier to fly. Springs, hinges, and adjustment screws provide a deterministic method of dialing in the flight characteristics for a particular site.

The first milestone is adjusting the propeller so that a no-backoff flight stays under the ceiling and uses almost all the turns in the motor. But even with such an accomplishment, there are tweaks that can improve performance, such as adjusting the amount of time the propeller stays at high pitch, or how quickly the propeller changes to full low pitch.

This is where a stopwatch that has a "stroke-rate" feature comes in; it is the easiest way to measure these variables. You program the number of events you will time (e.g., paddles on a rowboat, miles in a lap of a racecourse, or revolutions of a propeller), and the units of the result (rpm, mph, etc.). My watch is programmed to time five propeller revolutions, and gives me the resulting rpm.

Armed with such a tool, you can determine when a propeller begins changing pitch. At launch, the propeller rpm will steadily decline (assuming there are no other variables such as flaring blades). After a period of time, the rpms will level out or begin to increase. This indicates that the mechanism has moved off the high-pitch stop and is in the process of transitioning to low pitch.

People often ask me if my F1D model has "switched to low pitch yet," as though it is a singular event, similar to flipping a light switch. I tell them that it has been changing since approximately 6 to 8 minutes into the flight, and will continue for roughly another 2 to 7 minutes.

The time of the initial change is not the only variable that can be measured. When I am tuning a new propeller or adjusting to a new flying site, I will often map the rpms at 2-minute intervals for the entire flight.

The resulting graph can be analyzed to determine such factors as launch rpm, minimum rpm, transition start, maximum rpm, transition finish, transition rate, and final rpm.

One strategy is to fly at a very high pitch initially, to use the high motor torque as slowly as possible without gaining a lot of altitude, and then transition enough to climb to the ceiling as the torque starts to come down. My flying buddies and I call that "climbing on the spring." At the 2008 F1D World Championship, I theorized that it would be more efficient to climb on the initial burst, with a less extreme initial pitch, and then transition only enough to maintain a level cruise as the torque declined.

While I was restructuring my flight profile, German competitor Lutz Schramm logged some great test hops. Teammate Brett Sanborn and I took a seat and mapped one of his flights using a stroke watch. No need to quiz him or dig through his flight log; we saw by our graph that Lutz was using a nearly identical strategy, which was useful corroboration.

After you have stocked your toolbox with the Indoor FF essentials and you progress to variable-geometry propellers (it might even help with flaring propellers, though I haven't tried that yet), consider a stroke watch to expand the amount of data at your fingertips.

Indoor FF Nats Update

If you have ever thought about attending the AMA Indoor FF Nats and NFFS US Indoor Championships at East Tennessee State University (ETSU), this is the year to make it happen.

The school's basketball conference has required ETSU to install a new set of banners that obstruct the main flying area. This is tragic for Indoor FF, because this is one of the best sites we've found so far. Rock-solid air stability and immunity to outside weather conditions make the Mini-Dome ideal for delicate models, despite the introduction of "Big Blue," the scoreboard, a few years ago which chopped off a slice of the flying space.

The good news is that AMA executive director Dave Mathewson has generously agreed to finance the removal and reinstallation of the banners one time, allowing the 2012 event to take place. The bad news is that the future of the event at this site is uncertain.

Come enjoy five days of flying in this legendary site, May 23–27, 2012, as we concurrently try to find another venue and work to see if there is an affordable way to stay.

Indoor Fling

A late entry to the "notable 2012 Indoor FF contests" is the Indoor Fling in Pontiac, Michigan, jointly hosted by the Cloudbusters Model Airplane Club and the Detroit Balsa Bugs. After two previous sites—both inflatable domes—blew down, the May 6, 2012, version will now be held at the Ultimate Soccer Arena's permanent Category III–height building.

The contest features AMA and Flying Aces Club classes, plus a Phantom Flash event for beginners. Two on-site restaurants complete the picture.

Join the fun, and help make this contest a success at its new site.

New Leaders

Congratulations to AMA's new president, Bob Brown, and new NFFS president, John Lorbiecki.

Bob's campaign statement highlighted the value he places on AMA and FAI competition, vital parts of Indoor FF. The Indoor community has some important work ahead, and will certainly benefit from AMA's continued support. We look forward to working with Bob to keep Indoor FF alive and well through projects such as the Indoor FF Nats, flying-site procurement, and the World Championships program.

John has international competition experience—his son is a Junior F1J world champion—and has already posed some interesting ideas for the Indoor community, including rotating the Indoor FF Nats across the country, and eliminating the Builder of the Model rule. Whatever is decided, Indoor FF will benefit from the attention and fresh thoughts.

More good times lie ahead, and this is the perfect time for everyone to get involved and help guide our progress.

Correction

In my previous column I identified Brett Sanborn's new Category IV F1D record as 38:03 (my previous record). His new record is 38:36.

Sources

Transcribed from original scans by AI. Minor OCR errors may remain.