LAST EDITED ON Jun-07-04 AT 05:57 PM (CDT) > I take no credit aside from typing it into the internet.
>Ted got David and I turned in the right direction on the
>Eather props. back in the early 90's. And of course, Brian
>designed and makes them.
Eather rules!!!
Anyone know why his e-mail does not work?
> 12-3.75 UCT (red) I take it?
Yes. That was the prop you told me to get, right? I also got the 11.5 UCT (more undercamber than the 12"). Haven't tried it yet.
That's a lot more load
>than the 12.5-3.75 flat-back. But both sound pretty close to
>a shaft run for a 82 4-stroke....
Well, yes, but that is kind of the point.
Starting with the info that was given to me by Paul Walker, Doug and I started trying new configurations (also, the info gleaned by Frank Williams was very helpful).
The idea has always been that the 4 stroke is completely different animal from the 2 stroke, and must be approached with a "clean slate" point of view. There are several advantages to the behavior of the 4 cycle stunt run (and the 4 cycles themselves) and several disadvantages.
Disadvantages:
1. Weight. It can be a little frustrating that everyone else around you gets to brag on how light there planes are. You take the engine, spinner, and prop out of one of my planes and I guarantee you would not say they are heavy. Put the motor in and the weight once again appears to be less than stellar. Put on an extra coat of clear and all the sudden I am pushing the design limits of the wing. (Just a minor bitch).
2. Lots of moving parts. Not necessarily the smoothest engines compared to the pipe motors. You will need very strong mounts and be prepared for some stress cracks in your airframe, if you skimp on construction.
3. No boost (4-2 break if you will). This could be considered a good or a bad depending on what point in the pattern you are talking about. In the past it could really kill your hourglass if you had the engine loaded and pitched for soft 5' corners. If the engine was set for strong overheads and verticals the corners suffered (Argh!)
4. Poor fuel draw. We already discussed this issue. I am content that I have solved it for my own uses, and I did not even need to resort to a pump (pain in the tookass).
Advantages:
1. No 4-2 break. I know I said this was a disadvantage before, but I mean there is no "duel mode" behavior. What you see is what you get. I have seen the 4 stroke set rich and allowed to "boost" to a leaner setting in the corners and verticals, but that simply has never been for me. I like the linear behavior, good or bad.
2. No rich "4 cycle mode" to deal with. Because the true four stroke is run at a nuetral needle setting, there is no excess charge of fuel trying to blow out the plug. This is a real problem when trying to "underload" a 2 cycle engine (example would be putting a 10" prop on a 65). The 2 stroke engines are succeptable to running "too cold". I believe you spoke of having some issues with the RO Jett when it first came out because of the potential difficulty of running smaller than needed props. The 4 stroke simply does not suffer with this issue. You can put very little prop on a 4 stroke and it will run just fine, showing no signs of trying to "blow itself out". The underloading simply makes the run steadier, as the engine is barely seeing a change between the verticals and the downlegs. There is no "boost" to create speedup when the engine is set well past the peak of the curve.
So a "shaft run" can be a good thing.
3. Great fuel economy. Lets you spend more money on neato fuels.
