.049 and a electric starter???

"I don't know how much help this is going to be.

1) Engines are pressure fed from a bladder in the fuselage. Each engine is controlled by a pressure regulator.

2) The venturi is custom made and started out at appx. .300 inside diameter. There is no spray bar going through it. It is fed by pressure and has a "spigot" type feed. It was later "choked" down" to a .250 inside diameter.

3) It used Sig 10% champion fuel.

4) Props generally were APC 9x4 or 9x5. The 9x4's were used in France. Ground rpm was approximately 11,000 rpm.

5) The 15 FP's I have have a "normal" bypass in the case. I don't think the bypass cut in the sleeve would be bad. There is generally much more volume in the bypass ports than required. Remember that one fix for the Fox 35 is to plug up some of the volume to keep the rich burp from occuring.

This setup in the B-17 is not for most beginners, or even for most advanced fliers. Some expert fliers saw the system and would have no part of that type of system.

Hope this was of some help.

Good luck.

ps, Dave Gardner is working on an article for Stunt News covering the fuel system in the B-17. I have simplified the system here.

Later

Paul"

Paul's venturi size was .250 with a spigot, so this would give a choke area of about .0412748852 (I have been watching too much Star Trek. Thank, you, Mr. Spock.)

The normal choke area for a stock engine this size would be about .008, so this really throws any comparisons for single engine sport flying right out the window. Paul would obviously be able to swing a much larger prop and at a much faster speed then one using suction.

His comment about the bypass was interesting, though. The early copies of this engine that I had worked with had the bypass cout out of a rather thick sleeve, making it impossible to block off in the normal way and modify these engines as I do the larger versions. If, however, they are now being made "normal", it does make for another possibility to modify, enabling it to turn a larger than normal prop on suction. Maybe we will all gain something from this anyway.

Out of curiosity, if any of you have been using a stock FP 15 in sport/stunt flying, what prop, launch rpm, and fuel have you been using?

regarding the 15FP

I have one, and have not yet had a chance to run it. A while back. David and I did have the opportunity to try out a local flier's 15FP/kit Ringmaster system. Didn't have a lot of flights, but we ran it with both a 8-5 and a 9-4 Master Airscrew, pretty much full-out, just backed off enough to get it to pick up in the corners. It flew the plane extremely well (once we got the controls slowed down appropriately) even though it was no lightweight, having been built straight out of the kit with no wood substitutions. It would fly the entire pattern very easily and was very relaxing to fly as it was so solid and predictable. It was a real eye-opener, in fact, if flew so easily that it led to all of our subsequent experiments with the Veco 19, and the OS20/25FP.

My gut impression based on this is that the engine would be ideal for the smaller "35 sized" models like the Ringmaster and it's bretheren. I do know that the Veco 19 and even more so, the 20FP, are overkill for a Ringmaster, and need some special help in the form of either a $27 prop with 3.25 pitch, or some very-much-not-recommended backing off with the needle. Run the way the engine likes with available props results in some serious speed - Ringmaster+20fp+9-4 APC+medium 2-stroke+60 foot lines = 3.8 seconds! That's a little quick. It can be made to 4-stroke, and may make it without running away 6 times out of 10, but tht's clearly not what it likes.

Another thing I have found with the 20FP is that it runs *much* better with the stock muffler. Paul also ran the more or less stock mufflers on the 15 (for noise considerations - I can tell you from up-close experience that the 4 15's on tongue mufflers were LOUD), and also found that in addition to being very quiet, it also ran better. I think all Paul did to his was to bore out the outlet to a constant diameter vice the stock tapered outlet.

Note also that the 25FP has an unfortunate tendency to "home in" on particular revs (on the ground, something like 11,200-11,300) almost no matter what you do with the needle. My interpretation of this is that the mufflers act as 1/4-wave tuned pipes. They even look like tuned pipes, with convergent tail cones and even internal baffles. The 15 and the 20 don't seem to do this quite as readily. As the 20 provides more than enough power for the average Twister/Banshee/Nobler sort of airplane, I generally recommend the 20 vice the 25.

Another thing they don't seem to like, at least on suction, is being over-loaded with too much diameter. The 20fp will eaily turn a 10.5" prop without overheating, but it's too dead in the corners, and gets unstable. I run a light 9" prop on the 20, and I would guess that would be about the max for a 15. The 25 is similar, and those who run heavy-load 10-4's generally have some stability issues. Light-load 10" props seem better, and I would really like to see most running 9-9.5 light-load props instead. I have no experience with the 15 yet, but an 8-5 was too much pitch, and the 9-4 Master Airscrew seemed close to the limit.

Bottom line is, the series tends to run *very well* stock, as long as you run them the way they like. Even more importantly, they fly the airplane extremely well, as long as you don't overpower it. I guarantee the 15FP flew that guy's 32-34 oz Ringmaster way better than that other motorand it's kin.

When I get around to sticking the 15 on the Skyray, I'll report back (either here or in SN)

Paul used a light Cobra as an engine testbed. The .15 would pull it, but had none too much power.

One virtue of these engines is that they are very easy to start, particularly for a plain-bearing engine, once you figure out how to do it.

Do you think an FP .15 or clone would be about an ideal engine for one of GMA's built up fuse Peacmakers?