LIMITED-B Prop Tests please ?

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sgilkey
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Post by sgilkey »

OK, Brian and I finally got out to do some testing. Weather was still hot and humid, but not so bad as to be "abnormal" for summer. Two test planes, both old B ships at about 2.75 pounds, with smaller wing area than currently in vogue, so wing loading probably heavier than current standards.

All tests on same day, within a period of two hours, with 10% fuel, standard plug.

Plane 1, engine Magnum 28XL with stock muffler and small stock carb (there are at least three different carbs for this engine,most recent ones I have gotten have all had the smaller carb)

MA 9x4 16.9k
APC 10x3 14.7k
MA 10x4 14.3k

Plane 2, Norvel Big Mig .25 with stock carb and muffler, but muffler tailpipe reamed out. Based on previous testing, this adds perhpas 2-300 rpm over stock unreamed muffler

MA 9x4 17.4
APC 10x3 15.0
MA 10x4 14.7k

Note that though the Big Mig out-turned the Magnum on every prop, the magnum powered plane was faster in a straight line, and held speed thru the turns better, in every instance. I think this is because of the reamed muffler on the Big Mig. To get it lean enough to not be blubbering when flying straight and level, it was too lean in turns and would not power thru turns as well, so i had to pick a kind of "in-between" needle setting not optimal for either. So as a side note, I conclude the reamed muffler is not good on the Norvel with a suction fuel system.

The 9x4 gave best speed and overall performance. Contrary to my previous posts, the APC 10x3 was second. Somewhat slower straight-line speed (though surprisingly, not as slow as expected/hoped), but excellent sustained speed thru turns, probably at least as good as the 9x4. Climb actually better, with unlimited vertical. The 9x4 plane could also climb straight up, but was trading speed for altitude- the 10x3 maintained speed better in the climb. Overall, the 10x3 gave slower but still very crisp performance.

The 10x4MA was slowest in straight line, and also bled off speed faster in sustained turns. Turning performance was degraded comapred to the 9x4 baseline. Climb was again unlimited, but not with as much authority as the 10x3APC. One thing that was really noticeable with the 10x4 is the down-line speed (i.e. in dives, etc) was noticeably slower than with the 10x3, the 10x4 acts as a very effective brake when descending. Overall, the 10x4 is inferior to the 10x3APC, but is by no means a "paint stirrer,", the performance was still very good. in fact, we flew multiple heats and were quite pleased with the 10x4 and found it to give very "fun" performance, though again certainly inferior to the other two props.

Conclusions: 1) reducing performance ONLY by eliminating tuned mufflers is not enough. Planes are still very fast on 9 inch prop. We only need to recall how stellar the performance of clean designs such as the T-Rex (and assume contempraries such as the Cobra) performed with a BM 25 and stock muffler just a few years ago- those things smoked! 2) Therefore a 10 inch minimum diameter is a good additional performance limiter. The 10x3APC gives better performance. However, the objective here is not to maximize performance, but to limit it. One thing I don't like about the APC is it is too brittle. I used to use APC when I started in combat, and switched to MA when I got sick of breaking APC on landings. Sure enough, on his second landing Brian broke his 10x3, and it was NOT a bad landing- it just wasn't a perfect "greaser". Considering their cost, not to mention the hassle of balancing, plus the ability to withstand some midairs, I prefer the toughness of the MA.

Therefore we recommend the MA 10x4 as a "spec" prop. ALthough we'd not protest too loudly if the 10x3APC is adopted, as it is a much-needed step in the right direction, if that is what it would take to compromise. But we would much prefer the MA. And remember we count as two votes!!!

Final note, Brian likes the speed and excitement of current B, and is a hard sell for slowing down B, but when we were done, he agreed that 10x4/stock muffler combat was a LOT of fun, more relaxing, and he is fully behind it!

p.s. don't be surprised to see us use some of this info in our RCR column....

Scott Gilkey
Jimbo
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Post by Jimbo »

Does anyone have any 0% fuel? I'm very curious to find out what the RPM difference would be between zero nitro and 15% in the same engine.
Scott, thank you very much for the report !!!

Limited-B
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Rabbit Leader
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Post by Rabbit Leader »

Scott, we also tried the MA 10-4 on my Mustang when she first flew last year. The 10-4 just didn't slow her down as much as we wanted, although she flew okay. You have to remember that most 2548 fighters are coming in at 3 and a half pounds, or more, and they are limited to 48 inches maximum, so the flight characteristics of our scale birds and the 2.75 B ships are going to be quite dissimilar. We found that the Mustang launched better and was just more fun to fly on the APC 10-3 than the MA 10-4..also, the APC seems to be a bit more self-regulating, i.e when we pulled her out of a dive at full throttle, the plane slowed down much faster than with the 10-4. The 10-4 might be a real good spec prop for limited-B, but it just doesn't seem to work within the confines of a 48 inch scale plane at a higher wing loading, which is where the APC 10-3 shines. Anyway, I appreciate the tests, especially with the Mag28..we've been needing the data for some time now. I MIGHT get a chance to fly Sunday, and if I do, I hope to have a Graupner 10-3 to test..

Cash

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sgilkey
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Post by sgilkey »

I'll bet significant portions of my anatomy that a Jett will well exceed the proposed rpm limits on a 10x3 APC. I flew at a meet against Phil Rossman, who ran the 10x3APC on his Jett, and his planes flat smoked my OS/Ultrathrust-powered planes running 9x4s. The speed and pulling power through the turns of Phils planes was simply amazing. Jett and 10x3APC (or 10x4MA) would NOT be a limited-B combo!!!

I hate to sound like a broken record but my own testing has convinced me the 10x3APC is a better prop than the 10x4MA. You guys win on that point! Keep thinking "limited B, LIMITED B!" The objective is to limit performance. I don't want to break more props than I need to and I think 10 inch APC props are easy to break on even good landings!

This is fun, guys, I am enjoying this discussion. BTW, when Brian and I flew our test flights, we were in full mano-a-mano combat, this was not just flying around. Needless to say, I smoked his butt, as long as you give me a suitable handicap, that is. In three test sessions, the total cut score is 20 to, um, ZERO. In one session, after he cleaned me early, I said, let's have you practice defensive flying and I will try to cut you. I did not. Egad, I really suck.

Which brings up one other point that I like, engines ran great, sucking every last drop from plain old 6 ounce suction tanks, with total WOT flight time nearing 9 minutes. Less vibration, fuel foaming, etc, and the engines seem really happy. Interestingly, we consistently got about 30 seconds longer flight times on the Mag 28s than the Norvel, so much for the vaunted fuel economy benefit of the Norvel.

Scott Gilkey
Jimbo
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Post by Jimbo »

Scott what muffler did your friend have on his Jett ? Limited-B does not allow tuned exaust of any kind.

Limited-B
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lightning
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Post by lightning »

Clarification please guys. I have no issue with the idea of 10x3 APC props even though (as Scott said) they do break easier than the MAs. But I've been using 9x4 and 9x5 APCs for Open B and 2610 so it won't be any worse.
My question though is in regard to mufflers. I've replaced all my stock OS mufflers with Mac mufflers (the black one piece one that I believe is an expansion muffler). They weigh less and give me 400-500 rpm over the stock OS one. HOWEVER, if I remove the OS baffle and open up the stinger, I get 300-400 rpm more than the MAC, but a helluvalot more noise.
As I read the proposed Limited B rules, I need to go back to the stock OS muffler, but removing the baffle and opening/removing the stinger is allowed?
Is this correct or am I out to lunch here?
BigCountry
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Post by BigCountry »

Lightning,

You're correct on all but one count. You do not necessarily have to go back to an OS muffler for your OS engine. The term stock is used but any muffler that is an expansion chamber muffler containing no internal pipe may be bolted up to your OS. Some replacement parts are definitely cheaper than others and we wanted to give folks an option in what they purchase to replace parts. As far as the stinger goes we've yet to have anyone test a muffler where the stinger has been removed. I can't say that I know one way or the other as to how it will affect the engine but if you try it please report back with your findings. I hope I answered your question...

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Jimbo
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Post by Jimbo »

As Travis said, a Mac one piece muffler is NOT a tuned muffler. They can actually cause some engines to drop RPM's. I know from experience. Just check your engine and don't show up to a contest taching over 15.5[8D]

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Devil Dog
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Post by Devil Dog »

Jimbo,

I’m not sure about the Mac muffler not being tuned. I agree that sometimes it causes engines to run slower, but I think that is because it is tuned and only comes up at a high range. If you are not in the tuned range, it is actually worse which is indicative of a tuned muffler. My observation here was with my friend Mark and a new OS25 FX. At first the RPM increase was nothing with 15% nitro, new engine and 15000 RPM. Ten tanks later, 30% nitro 19200 RPM, which is the same as my moose-can mufflers. It looks to me that I could tack low on the ground and open up in the air with a Mac pipe. If I can figure that out, eventually Lighting will too. Hay Lighting, “Hint, Hintâ€
sgilkey
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Post by sgilkey »

I personally feel the MACS one-piece muffler should be allowed, it is not tuned, has no inner pipe (other than a small internal "stinger" which is more for tuning exhaust note), and is just a light and fairly cheap and durable expansion chamber muffler. I don't use them but would not complain if someone did. I think removing tailpipe stingers should also be allowed but would not complain if I am out-voted. Sometimes you break one off in a midair, or when you are reaming the tailpipe out, and it would be nice to be able to use the muffler. Of course Phil Rossman's jett had the "stock" tuned muffler, otherwise he would not have been faster than a piped OS on a 9x4. only point is to be careful with wording of the muffler rule as some folks will say "the Jett (and MVVS "stock" muffler is tuned so i meet the rules, I have a "stock" muffler, the rules need to explicitly outlaw tuned pipe-in-pipe types.

Scott Gilkey
BigCountry
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Post by BigCountry »

Scott I believe we're covered as the rules are written now for Limited B. We address both no tuned mufflers as well as no mufflers with internal pipes. As far as the MACS muffler if someone has one and is willing to do a head to head comparison with a normal "stock" muffler then as long as the results are even I can't see why they would need to be restricted, same thing with no stinger. I never lost one on a stock muffler so I don't know how they will affect engine performance. Again if someone will do a head to head comparison and report what they find we can address that as well. Currently though the rules make no mention of a the stinger having to be present...

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lightning
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Post by lightning »

OK guys, my observations:
<ul><li>Motor - OS 25FX, broken in and in good shape, </li>
<li>APC 9x4 prop. (don't have any 10x3 APCs yet)</li>
<li>15% Ritches Brew fuel,</li>
<li>temp 75 degrees.</li></ul>
Results:-
<ul> <li>100% Stock OS muffler - 15,100 rpm </li>
<li>Mac muffler - 15,500 to 15,600 </li>
<li>OS muffler minus baffle and stinger - 15,900 to 16,000 </li> </ul>

Hence my conclusion that the Mac gave me 4-500 rpm and the modified OS another 3-400.

So if the MAC is not allowed (as it "Maybe" tuned) no problem, I'll use heavier and noisier <b>legally</b> modifed OS mufflers (if I can find enough of 'em laying around!)
Of course I realize these may be all out the window with a 10x3
Jimbo
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Post by Jimbo »

The Macs muffler is NOT, and I repeat NOT tuned. That's not to say it will not cause your engine to add or drop some RPM's. A Tower .46 muffler will do that too. All I can tell you is that if it puts your engine over the limit, don't use it. If not, don't worry. Thats why we need to do random taching. The most important thing is that you don't tach over 15.5 on the ground. Combat contests are not won and lost on the amount of RPM's your engine will unload in the air. If that were true Mike Fuller and I would have won every contest we went to.We have a year to work out the details so lets have some demos and see how it goes. Thanks again for the input guys.

Limited-B
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Jimbo
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Post by Jimbo »

Does anyone out there have a Webra.25 they can test soon? If not I'll order a couple tomorrow to test myself.
Thanks

Limited-B
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Pat_Willcox
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Post by Pat_Willcox »

Jimbo,

I bought some but they still in box and I am short on time to try and do anything. Next month on my days off I plan to devote some time to getting my limited B stuff dialed in.

Pat
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