Welcome back to another journey into the fascinating world of radio-controlled aviation. Today, I’m heading to Hampton Farm Airfield in Ashford for Interglide 2025—a competition featuring F5J thermal duration gliders. This is completely new territory for me, and I’ve been fortunate enough to be invited by Mike Van Erp, an experienced F5J pilot who’s agreed to show me the ropes.
Meeting Mike: A Journey Through Aviation
After a two-and-a-half-hour drive, I arrived at the airfield to find pilots already setting up, camping out, and getting practice flights in. Mike’s background in aviation is remarkably diverse. He started with control line models and free flight rubber-powered aircraft before moving on to full-size gliding in Zimbabwe, where he went solo at just 15 years old. His journey has taken him through paragliding, a break from flying to focus on family life, and eventually a return to the hobby during COVID through drone flying—which quickly reminded him that his true passion was gliding.
The Aircraft: A Carbon Fibre Marvel
Mike’s competition glider is an absolute beauty—just under 4 metres in wingspan and manufactured in Slovakia. Eastern European manufacturers have established themselves as world leaders in composite aircraft construction, and it’s easy to see why when you examine the build quality of these models.
Construction and Weight
The glider is primarily carbon fibre with some Kevlar reinforcement. Unlike older hollow-core gliders, these modern F5J models use Rohar cell foam internally, making them more delicate than winch-launched gliders but offering superior performance and lighter weight.
Mike actually brought three of these gliders to the competition, each with different weights:
- A lightweight model just over 1 kilogramme (close to the FAI minimum limit)
- A midweight version at approximately 1.2 kilogrammes
- A heavier configuration at 1.5 kilogrammes (achieved by adding brass slugs as ballast inside the wings)
Understanding the Polar Curve
The reason for different weights relates to something called the polar curve—a fundamental concept in glider performance. Imagine a graph where the vertical axis represents your rate of sink and the horizontal axis shows your speed. If you fly too slowly, you’ll stall. Fly slightly faster, and your sink rate improves until you reach minimum sink. Beyond that point, as speed increases, sink rate increases exponentially.
In competition, pilots must constantly decide where on this curve to fly. When thermalling (flying in rising air), you want to be near minimum sink. When covering distance—say, returning from downwind to your landing spot—you’d choose the best glide angle, which is found at a tangent point on the polar curve. This is where you’ll cover the most distance for the least loss of height.
Electronics and Control Systems
Opening the canopy reveals a sophisticated array of electronics that would impress any RC enthusiast.
Servo Configuration
This particular glider features seven control servos plus an eighth channel for the motor:
- Two flap servos
- Two aileron servos
- Two elevon servos (on the distinctive anhedral tail)
- One rudder servo
The anhedral “Mercedes tail” (officially called a Revo tail to avoid trademark issues) is a modern F5J innovation. Whilst Mike admits he’s not entirely convinced whether it’s more marketing than functionality, it does appear to offer small advantages in turning tightly at low altitude—and it certainly looks distinctive!
Power and Safety Systems
The power system is surprisingly modest. Mike uses a 700mAh 3S battery for the motor, which is quite small because these gliders are incredibly efficient. A backup 2S battery provides redundancy for the receiver, with both batteries connected through Schottky diodes to prevent one attempting to charge the other.
The star of the electronics package is the Glider Keeper—an AMRT (Altitude Motor Run Time) device. This sits between the receiver and ESC, monitoring and limiting motor usage according to F5J rules. It measures altitude, records motor usage, and most importantly, cuts the motor after the permitted time to prevent any possibility of cheating.
F5J Competition Rules: The Challenge Explained
F5J, also known as thermal duration, is all about staying airborne as long as possible using only rising air currents after an initial powered launch.
The Flight Task
Here’s how a competition round works:
- All pilots in your group (typically 10, sometimes up to 17!) launch simultaneously on a buzzer
- You have exactly 30 seconds of motor run time—the Glider Keeper enforces this
- The goal is to stay airborne for 10 minutes (actually 9:59, as you’ll see why shortly)
- You must land before the 10-minute buzzer sounds or lose landing points
- Landing accuracy matters enormously
Scoring System
Points are accumulated through several factors:
- Flight time: One point per second airborne (up to 9:59)
- Landing accuracy: 50 points for hitting the spot, decreasing by 5 points per metre away (zero points beyond 10 metres)
- Launch height penalty: One point deduction per 2 metres up to 200 metres; three points per metre above 200 metres
The penalties for excessive launch height discourage pilots from simply blasting skyward with their 30 seconds of power. Mike practises spot landings obsessively and gets “pretty angry” with himself when he doesn’t score the full 50 points!
What Makes It Challenging
You’re not allowed telemetry—no variometer, no altimeter. Everything must be judged by eye and feel. Simultaneously, you’re managing:
- Optimal motor usage during launch
- Finding and centring thermals
- Watching competitors to gauge relative altitude
- Timing your flight
- Positioning for the spot landing
- Avoiding 17 other gliders in the same airspace!
Transmitter Setup and Flight Modes
Mike flies Mode 2 (as he says, “like all proper pilots should”—apologies to Mode 1 flyers!). However, there’s an unusual configuration: the left stick doesn’t control throttle in the conventional sense. It’s full up during normal flight, and pulling it down deploys the flaps as airbrakes for landing.
Complex Mixing
The transmitter programming is remarkably sophisticated, featuring multiple mixes:
- Ailerons to flaps: The flaps move with the ailerons (but less), improving roll performance
- Ailerons to rudder: Rudder automatically coordinates with aileron input
- Elevator to flaps/ailerons (snap flap): Pulling up elevator slightly increases camber for tighter thermal turns
Flight Modes
Different flight modes adjust the wing camber for various situations:
- Speed mode: Slight reflex (flaps slightly up) creates a flatter wing with less drag for covering distance quickly
- Cruise mode: Neutral position for general flying
- Thermal mode: Flaps and ailerons drop to increase camber, reducing minimum sink speed—perfect for circling in thermals
Mike uses templates created by Michael Shelum, a highly respected figure in the gliding community who develops glider programmes for EdgeTX and Ethos operating systems. These templates make the complex programming much more manageable.
Equipment Choices
Whilst the gliding community tends towards conservative equipment choices—lots of Futaba, Graupner, Multiplex, and Jeti transmitters—Mike believes RadioMaster offers the best value and most powerful programming options for gliding, despite being the most affordable option. The key is using proper templates to overcome the programming complexity.
The servos are standard KST units (some pilots prefer MKS), and the receiver is a RadioMaster ER8G glider receiver. Apart from the AMRT device and the multiple mixing, most components would be familiar to any RC pilot.
Getting Started in F5J
Interested in trying thermal duration flying? Mike recommends starting with the Barcs (British Association of Radio Control Soaring) forums, a subgroup of the BMFA. The community is welcoming and eager to help newcomers, though like many areas of the hobby, they’re concerned about declining participation numbers.
Cost Considerations
F5J isn’t the cheapest form of modelling—high-performance moulded carbon fibre gliders require significant investment. However, Mike suggests that £1,000 could get you a decent secondhand glider from a slightly older generation, which is an excellent place to start. As he points out, one of his friends flies a glider several generations older and remains incredibly difficult to beat—it’s far more about pilot skill than equipment.
Alternative Disciplines
If F5J seems daunting, consider these related disciplines:
- F3RES/F5RES: Built-up balsa gliders with limited carbon fibre, more affordable and available in both bungee-launch and electric versions
- F3K (DLG): Discus Launch Gliders—hand-thrown like an Olympic discus, no motor required
- F3F: Slope soaring speed racing over a 100-metre course—the Formula 1 of gliding
Small Details That Matter
Mike’s competitive edge shows in the small details. Whilst many pilots use VHS tape as a wind indicator on their transmitter aerial, Mike uses cotton thread—visible to him but much harder for competitors to see from a distance. As he admitted with a smile, he’s “pretty savage” when it comes to competition!
The wings break down into four pieces, held together with tape at the root and mid-section (with carbon joiners inside, of course). This makes transport much easier—essential when you’re travelling by bicycle, as Mike does!
Final Thoughts
Exploring F5J thermal duration gliding has been an eye-opening experience. The combination of aerodynamic knowledge, tactical decision-making, precision flying, and technical setup creates a discipline that’s both intellectually engaging and tremendously skilful. Watching pilots launch simultaneously, searching for invisible thermals, and then executing pinpoint landings demonstrates mastery that comes only through dedication and practice.
Whether you’re a seasoned RC pilot looking for a new challenge or someone drawn to the elegant efficiency of soaring flight, F5J offers a compelling blend of competition, community, and the timeless appeal of engineless flight.
If you’re already involved in any form of gliding, I’d love to hear about your experiences in the comments—what transmitter do you use and why? And if you’re considering giving it a go, the Barcs forums are waiting to welcome you into this fascinating corner of our hobby.
