Flying Aids

Winders, Stooges And Retrieval Systems

Retrieval systems

For many years the radio direction finding system sold by Jim Walston was the gold standard retrieval system for free flight planes. A small transmitter attached to the plane sent a series of beeps and the pilot found the bearing to the plane using a directional antenna on a UHF receiver. Walston no longer supplies these systems, but they are still available according to an NFFS forum. Apparently, Walston got his systems from a supplier to Falconry hobbyists ( Systems are also available from Falconry transmitters weighing as little as 4 grams are available from
The transmitters are tuned to channels about 10 KHz wide in a HAM Radio band near 220 MHz. Walston systems used a WMI TRX-3S receiver with a frequency range of 148 to 222 MHz, which can be tuned to 3 channels.

Remote Dethermalizer Activation by Radio

In addition to on board Clockwork or Electronic Timers and fuses, it is now possible to activate a dethermalizer (DT), such as a pop-up stabilizer, from the ground via radio control. While for the biggest planes a battery, receiver and servo might weigh in excess of 20 grams using normal R/C plane gear, recently lighter gear based on garage door opener technology is becoming available. One source in the UK has a system to burn through a rubber band to activate the DT Eagles are testing this system for activation range. A longer range transmitter, “B2”, is also available. 

In the U.S., a 434 MHz transmitter for RDT has to fall under the rules for FCC Regulation Part 15.231 governing periodic operation at low power. Since RDT only needs momentary activation, this should not be a problem.

Eagles are testing both the original and longer range systems for activation range.

RDT Range testing results as of 5/7/2023:

Mike Kirda and Jeff Annis both tried out the original version. Mike has an .020 powered Sniffer with a servo DT mechanism and tried it out initially. Mike reports that the plane flew well enough and the DT worked positively down in Muncie, as far out as he could see it. No distance measurements were taken.

Last summer, Jeff installed a bandburner in addition to his fuse on an unlimited design. He was lucky to get it back as the RDT did not work when needed downwind. The fuse burned through the band eventually and the plane was not lost. Mike was quite surprised at this.

The following day, Mike and Jeff did some ground range testing and found that about 1000’ was the limit. Any further and the unit did not function on the ground. They tried raising the model and standing on a picnic table to increase the height of the transmission. Also a brand new battery. This was very interesting to Mike especially as others have reported DT ranges in the air far in excess of 1000’.  Right about the same time, BMK released an 8x higher powered version of the transmitter called B2. Soon afterwards, BMK’s GPS system became available, along with the compatible FlexiDisplay.

On May 7th, 2023, Mike Kirda and Jeff Annis did range testing at the Wind Lake Turf Farms flying site. There are electrical lines along the road and irrigation equipment in the area. The area is basically flat, with one small ‘hill’, just more gradual elevation than a hill.

Response using the B2 transmitter was intermittent with the receiver at 0.8 miles away, nothing at 1 mile.

Mike’s FlexiDisplay, which shows GPS data on his phone, was working at 1 mile and stopped at 1.2 miles.

Realistically in the air, range should be 1.3-2x further , according to Mike.  The BMK designer points out that this is likely a severe underestimate: as long as the plane is roughly 100’ in the air, the range should work out to 5 or 6 miles out.

This was completely acceptable to Mike and Jeff. They feel a lot more confident now, but wish they had the chance to do a real air test.  Before Mike could get his Mulvihill in the air the weather turned.