FAI Rules Changes for Indoor Free Flight 

By Don Slusarczyk | [email protected]

As seen in the May 2024 issue of Model Aviation.

SEVERAL WEEKS BEFORE the 2018 FAI F1D World Championships for Indoor Model Aircraft, the FAI Jury published its ruling regarding whether using a purchased variable-pitch (VP) propeller hub on a model was considered a violation of the FAI Builder of the Model (BOM) rule.

The 2018 Jury decision allowed the use of purchased VP hubs, but this ruling was never officially codified in the FAI rules. Since then, a rules proposal was submitted to the FAI about purchased VP hubs, as well as clarifications of the BOM rule.

The final proposal that was agreed upon made two changes to the FAI rules. The first change codified the FAI Jury opinion of 2018 and allows the use of a purchased VP hub in FAI Indoor Free Flight (FF) classes. This means that for F1D, F1R, and F1M, VP hubs no longer have to be built by the modeler; they can now be purchased.

In contrast, AMA Indoor FF classes that allow VP hubs still require the modeler to build their own hub as part of the BOM rule. Contestants and contest directors need to be aware of this distinction, especially if they are flying one model that fits both an AMA and FAI class.

An example is an F1D model flown in AMA Hand-Launched Stick (HLS). If the model has a purchased VP hub, it is legal for F1D, but it would not be legal for HLS. Similar crossovers could potentially happen with F1M and Pennyplane or F1R and Intermediate Stick.

The second change was to adopt the BOM limitations and interpretations that currently appear in the AMA Indoor FF Competition Regulations rulebook. The good news about this is that the AMA and FAI rules now both have the same wording in regard to the BOM, with the VP hub being the only difference between the two sets of rules. The new FAI rules went into effect on January 1, 2024.

Carbon-Fiber F1D VP Hubs

With the new VP hub rules in effect, I decided to go ahead and buy a few F1D VP hubs to try out. Because the FAI rules now specifically allow it, I will take any perceivable advantage that purchasing them will give me. I believe that being able to buy a VP hub is a considerable advantage over making one by myself. The time savings are quite significant because the hours that would have been needed to develop and build the tooling, as well as the actual building time, are no longer required. That is now bypassed by purchasing the hub.

The hubs that I purchased were made by Dmytro Sednov, a Ukrainian F1D flier. These hubs are all carbon-fiber construction with wound carbon-fiber tubes for plug-in propeller blades and a machined, solid, carbon-fiber screw yoke, as well as a carbon-fiber bar. The adjustment screws have a tight tolerance for no backlash and are made from high-strength aluminum.

Carbon-fiber F1D VP hubs made by Dmytro Sednov weigh only 95 mg each.

A closeup view of the Sednov F1D VP hub.

The hubs are built and assembled with specialized tooling and fixtures. They appear to be identical to each other, which is a sign of a rather well-honed manufacturing process. They each weigh 95mg, as seen in the photos.

If you are interested in obtaining some of these hubs, contact Dmytro’s business partner, Vladimir Linardic, for current pricing and lead time. His email address is listed in "Sources."

New Rules Proposal Cycle Begins

With the previous rules cycle being delayed by one year because of COVID, the "odd years" rules cycle for Indoor FF has now become an "even years" rules cycle, which means that we are now in the beginning of a new rules cycle. Rules proposals must be submitted through the AMA website and can be proposed by any current AMA member. Proposals must be submitted online before March 15, 2025.

3D-Printed O-Ring Slicer

I have always had keen interest in the tools and gadgets that other people develop for Indoor model flying. Chuck Andraka has designed a handy tool for slicing O-rings. It is a small block that holds the plastic tubing, with a slot for a razor blade to be inserted to cut the tubing into O-rings.

A set of 3D-printed O-ring cutters for F1D and Pennyplane.

Because these are designed for 3D printing, I decided to download the files and print a set out. There are three different sized blocks, as well as a "finger saver" razor blade holder.

The parts printed fine; the only small issue I had was that the slot for the finger saver was a little undersized for the razor blades that I use, so a little tweaking was needed to get the back of the razor blade to fit correctly.

After the blade was installed, I sorted through my nylon tubing collection to find tubing that fit. The blocks are designed for use with .125-inch outer-diameter (OD) tubing, Du-Bro pushrod #511 (.134-inch OD), and Du-Bro #700 (.187-inch OD). The .187 size is intended for use with larger motors for events such as Pennyplane or F1M. The larger tool also cuts a thicker O-ring of 1.5mm instead of 1mm.

Simply pressing down the razor blade is all that is needed to slice an O-ring from the tubing.

Using the tool is quite easy. Push the tubing in until it stops, make the cut with the razor, then pull the tubing back a little to release the O-ring. The O-ring will fall out of the slot on the bottom of the block, or just tap the block on the table to get it to drop out. In a matter of a few minutes, I had a nice pile of O-rings. I measured them and they were between 0.97mm and 1.03mm wide.

Thanks to Chuck for making this handy tool available. If you would like to download and print one for yourself, the files are available on Thingiverse, or they can be purchased online from Indoor Free Flight Supply.

It only took a few minutes to cut all of these 1.0mm thick F1D O-rings.

SOURCES: