Thunder Tiger PRO 36
This engine is in essence, an OS 32 knockoff. It certainly doesn't have the power of the OS 32 but it is a nice, clean little engine. Of all the Taiwan engines the Thunder Tiger is my favorite. Their engines appear to be made of better metals and implement better QC practices. The fit & finish is excellent.
This editorial isn't another run of the mill opinion as found throughout the Internet. What you'll find here is a specific application and how the engine was modified to fit the application. Plus, how well the Pro 36 performed within the circumstances.
The application is to squeeze a Thunder Tiger PRO 36 into a "PARK FLYER" sized airplane and see how well it performs. The biggest difficulty in a project like this is weight. The engine weighs a lot relative to the airplane size, and the shear mass of the engine will be difficult to deal with in general. The first item is to select a suitable PARK FLYER capable of carrying engine mass and vibration. I narrowed the choices down to:
(a) E-FLITE Mini Ultra-Stick
All of these airplanes are built-up using balsa and lite-ply. The Rogue has the largest wing-area and would be a great choice, however I'm told that spares are difficult to come by.. so it's out. The Ultra-Stick and Brio both have 325 sq. in. wing area, and spares are readily available. I chose the Brio 10 because it has an engine cowling, it's mid-wing, and it just looks like an airplane.
There really is a purpose to my madness here...
To start this off, I'm actually working with 2 Pro 36 engines. The first engine is a broken-in engine which has seen lots of use. The other is a brand new engine. I began with the older engine and made some modifications to fit it to the airplane. The mods included a radial mount, and a custom exhaust system. The whole story can be seen at the high-lighted link above.
The NEW engine got a little extra attention...
The radial mount does three things. It frees up mounting space, it substancially reduces the overall weight, and provides ridged support for the engine. These are very important aspects in fitting a BIG engine in a SMALL airplane.
Here is the radial mount installed on the older TT 36. There are two things to observe here, One is the small footprint of the radial mount, and the other is the lack of mounting materials beyond the radial mount. The radial mount weighs a mere .41 oz. That's less than half the weight of a conventional nylon engine mount. The radial mount is bolted directly to the firewall. This provides a ridged support for the engine which evenly distributes the vibration without adding any harmonics to the airframe. As noted in the photo, the backplate screws were enlarged to 3mm to ensure good holding strength of the engine.
This is a photo of my custom exhaust. It too weighs considerably less than the OEM muffler. It also provides a re-directed exhaust below the airplane, to keep things a little cleaner. I had to make two changes in my original design. The pressure tap was too close to the firewall and was moved to the side. The other change was to add a small restrictor to the exit stinger. The restrictor was needed in order to get more pressure to the fuel tank. This had virtually no effect on the engine performance other than getting fuel to the carb during extreme maneuvers. The stinger length was tuned to 1/4 wavelength at 14,000 RPM. This provides optimum horsepower at peak RPM.
The performance of the older TT 36 Pro in the Brio is incredible to say the least.
The NEW TT 36 got a few additional "changes". The horizontal mounting lugs were milled off to reduce weight.
The new engine got modified to accept a radial mount. The backplate flange (on the new engine) was turned down to reduce weight and provide a good flat fit on the mount.
When up-sizing to M3 there's ZERO room for error! This must be done using a SHARP blind-hole tap, lots of cutting oil, and carefully tapped to the bottom of the hole. One mistake here will render the crankcase a POS.
Here you see the new engine fitted with the radial mount and the turned down backplate. Removing the mounting lugs from the engine only reduced the weight 1/3 of an ounce. But it all adds up in the end. It also gives the engine that High Performance appearance, like a Pylon Racing Engine. Other modifications included re-timing the crankshaft intake, enlarging the oil hole in the connecting rod, and raising the exhaust port 20 degrees. This effectively moves the power-band up about 500 to 1000 RPM. The reason for this is that the prop I'll be using is a low-pitch, large diameter 3D type prop. This engine will be no stranger to upper RPM during 3D maneuvers. While looking at the photo, I came up with another way to mount the engine and reduce the weight even further.
It's still a radial mount. The difference being, the backplate screws will mount everything through the firewall and eliminate the 4 outermost mounting screws and the flanges. The overall size is reduced by 50%. The installation & removal will be a little more difficult but the weight savings is worth it. As you can see, this radial mount is much more compact and will fit into tighter cowlings.
The TOTAL Weight of this engine INCLUDING the mount is 9.5 ounces! The original weight was 11.06 ounces without a mount. That's a 1.56 ounce weight reduction or 15%. In a "Park Flyer" that is a significant amount of weight.
The new radial mount basically does nothing more than provide additional mounting surface area, as opposed to simply bolting the engine to a firewall. However, it could be done.