Some early notes about test flying the Evolution Gas 35GT engine
With the introduction of the new Evolution Gas Power 35GT (and close relative the 26GT) have come many inquires about just how well the engine performs. The short answer is very nice, very nice indeed.
This engine is attractive with its blue anodized head and thrust washer but performance is the real story. The electronic ignition and conventional “model airplane engine” configuration make for easy mounting in existing models and minimal weight gain over a glow engine. I mounted it in one of our pre-production Extra 260 27%-size aerobatic models in order to get an idea of how it would perform as a typical sport flyer’s fun to fly airplane.
It was easy to mount the engine with the mounts included in the kit. A Bisson inverted wraparound Pitts style muffler was installed with plenty of room all around and only two screws to hold it together. The standard fuel tank supplied with the model proved to have plenty of capacity for 15 to 20 minute flights. The servos in this model just happened to end up being JR 9411 digital precision servos. Overall it is a very nice and easy assembly with minimal cutting of the cowl. Balance proved to be a bit tail heavy and the batteries (receiver and ignition) were relocated to bring the model in line with the manuals recommendations. By the way, flight tests were accomplished using the new JR NiMH receiver packs for both the radio and the ignition. This electronic ignition requires a 4 cell 4.8 volt pack and I choose the 2300mah (JRPB5001) pack. I have not been able to use even 30% of the battery capacity in a days flying.
Firing up the Evolution engine was a fun experience. No changes were made to the basic settings of the carb. The 35GT has a “Fast idle/Choke on” startup position on the carb so simply putting the choke “on” will have the idle in the best starting position. Before turning on the ignition it is wise to give the prop a few flips to get fuel to the carb (the Walbro carb has a built in pump/regulator). When powering up the ignition you will note that the LED will give you a bright red flash to indicate the power is on. After a few flips the engine was running. I followed the manual instructions for an initial minor breakin. This few minutes of ground running can be accomplished in the model at the field before the first flight. The startup indicated the engine was a little on the rich side but no changes were made until after the first flight.
I had selected a 20x8 Air Wild propeller for the first flights with this model. Performance in the air was acceptable but this proved to be a bit larger prop than optimum for the Extra 260. When the APC 19x8 was fitted and the carb tuned this baby came alive! The airplane has good power for 3D hover maneuvers as well as the more common aerobatic sequences. It certainly is not the hot rod that the bigger 50cc engines prove to be in these lightweight models but it is very nice to fly. Still, level flight is pretty fast with full throttle so throttle management during maneuvers is important.
The engine has been exceptionally reliable in this model to the extent that only one engine off landing was made…totally empty fuel tank! It is pretty easy to lose your sense of flight time when you are having this much fun with a combination like this. Now I flip the stopwatch switch on the JR transmitter at the beginning of every flight.
RPM with the 19x8 propeller is 8000 plus. This seems to be right in the middle of the operational “sweet spot” for this engine. I also used a Pro Zinger 20x6 turning 8600 rpm with moderate results, great low speed pull but not enough top end speed for this model. I also note that propeller speed has been increasing with more run-time on the engine. I suspect that power improves as the ring becomes fully seated.
All in all, everyone that has flown this combination has been satisfied and smiling after they land. It is great fun and the engine just becomes sort of a best friend, always ready to fly and no special equipment or procedures required. When you pick this engine as your first Gas Powered engine you are going to have a very enjoyable experience!
Using the LED RPM readout from the electronic ignition
The LED is very straight forward:
When you are ready to start your engine turn the battery switch to "on". The LED will give a bright flash to indicate the on position.
After you start the engine the LED will "glow" at the frequency of the engine rpm. It gives one flash per revolution. You can stick your optical tach on the LED and read the RPM directly without any interference from anything. Now it flashes at once per rev while the tach would normally see two propeller blades per revolution so you must double the reading that you get from the LED to get actual rpm. This is a key point. If the Tach is set to a three bladed prop or 4 bladed you must multiply the LED reading by the prop blade setting on the tach (normally 2 blades).
Then when you finish the flight and land you should shut the engine off with the throttle trim lever but leave the ignition turned on. If you then take a reading on the LED you will see the highest RPM the engine reached during that flight. Very cool! Gives you a good idea of performance in the air with the prop and needle setting you are using. When you turn off the ignition everything resets so you will erase that max rpm reading and start over.
Nothing very strange but is kind of nice feature to have. The bright flash when you turn on is very nice as none of the other ignitions show you that you actually have a "good to go" signal.