- Aug 8, 2009
Unless we are looking at very low speed, there's not a huge difference in efficiency of the two choices.But the Briggs can not direct drive the equivalent 5 foot diameter prop.
. . . . Low power is ok if high propulsive efficiency is included.
I don't remember the pitch. The diameter was 60" and 2900 rpm. I cut it to 58" and now it gets 3000 static and 115 pounds thrust. I should have reduced the pitch instead of cutting it down. It still needs reduced pitch for static at 3200rpm.Good to know. What pitch and diameter and static thrust/rpm.
Yes, it is a Honda derived engine. It has a redesigned head with better flow and a different cam, but most importantly, it is governed at 4250 rpm instead of 3600 rpm. Tillotson calls it a 10 HP engine. The actual dyno chart I have been able to get my hands on shows the power peaking at 9.1 HP. I don't know what density altitude conditions that test was conducted under, but until I have better data, I'm calling it a 9 HP engine. A better flowing air filter and muffler still has the potential to improve power. The rpm governor speed can be changed, but unless the flow through the engine is improved, there is no reason to raise it. In stock form, the power output is fairly flat at 9 HP from 4000 to 4500 rpm, after which it begins to fall off.The 212cc engine appears to be a Honda 200 clone.The Honda is about 5.5hp at 3600 rpm. I trust Honda numbers over racer numbers.
For a single seat design, I'm told that I don't need a multi engine rating, or even a private pilot certificate. I can get a student pilot certificate and get to the point where I'm signed off to solo the plane. I can then solo it as a student pilot, indefinitely.
You will likely need to make the hole in the propeller flange & short shaft smaller in diameter than the engine crankshaft. Then you can heat the propeller flange & short shaft in the oven it and the hole will get larger (the hole will get bigger in diameter as it heats up). Then it gets fun, it helps if you pack ice around the engine shaft or an engine that small put the whole thing in a freezer to get the shaft diameter as small as possible and give yourself a second or two before things normalize to the same temperature and you can't move them. Have everything prepared and ready and "tada" it is like magic. I would predrill a hole in the end of the shaft and tap it (lengthwise) so after you mate the two together you can put a bolt on the end, lol, so that it won't come apart somehow. If you figure out the right allowance to make the hole smaller when it cools down on the shaft they will be almost like one. You will be able to get it back off if you have to with a press or you can tap a larger size bolt hole in the flange when you make it, larger than the hole in the end of the crankshaft so you can just run a bolt into the flange end and as it pushes against the end of the crankshaft they will come apart. Use good material like normalized 4330 or something along those lines and don't heat it to hot and destroy it's temper. But a normal kitchen oven probably won't get it that hot anyway.I bought one of these Tillotson 212cc engines last December. I've got it mounted to an engine test stand for experimentation. I recently bought an Xoar 36x12 propeller to test with it. It should take 9 HP at 4050 RPM and 10 HP at 4200 RPM, but I need to figure out how I'm going to mount the propeller before I can proceed with any testing to verify any of this.
My first attempt was to draw up in CAD a custom propeller interface to mount to the shaft. However, having the parts made as I drew them is going to cost a bit more than the engine, so I'm looking at different designs now and other alternatives. If anyone has good advice on how to inexpensively add a propeller interface to a 3/4" straight keyed engine shaft, I'd sure like to know about it.
I figure there is about a 50/50 chance this engine investigation is a wild goose chase, but maybe it will bare fruit in the long run. Couped with the right design, it has the potential to be a part of a very affordable ultralight.
Get some instruction. Some people live when they fly without instruction, some don't.For a single seat design, I'm told that I don't need a multi engine rating, or even a private pilot certificate. I can get a student pilot certificate and get to the point where I'm signed off to solo the plane. I can then solo it as a student pilot, indefinitely.
If it is an ultralight, then I don't even need to do the student pilot certificate and the craft doesn't need registration or have any taxes. Obviously, this is the most desired if it is possible to meet the requirements. If not, the alternative is not that bad. It seems the single seat really simplifies things.