LIMITED-B Prop Tests please ?

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sgilkey
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Post by sgilkey »

Mike F, I have a THEORY that your concerns are somewhat overblown, and here it is. In SSC, 500 rpm makes a big difference in performance. The theoreticians say that rpm x pitch = speed, and 500 rpm on a 3 pitch only means a couple of mph so it's no big deal. I disagree, as 500 rpm means a BUNCH more thrust, so in SSC, 500 rpm makes a substantial difference in turning, climbing, etc. Real-world flying seems to confirm this.

For Limited B, even at 14,500 rpm, it appears we have sufficient thrust to overcome drag of any airframe all the way up to the theoretical, pitch-constrained top speed. Even when looping and climbing, we can overcome gravity and drag with the available thrust. So therefore, in this case, a 500 rpm increase truly means only a couple of mph- we already have a surplus of thrust, so it will have a LESS dramatic effect on turning/climbing ability.

Just a theory. We have yet to see this tested- i wanted to run a test of a "clean" airframe running the spec prop at 15k (or whatever) vs. a "dirty" one at same rpm, to see how much of a difference we got in level speed. My guess is not much, but I may be in for a surprise. I haven't had time to do this test, if someone else has representative airframes that would be good, I'd love to see their results.

I do agree with you that some, or many, folks will do what they can to get to the rpm limit. Juggling plugs, head spacing, nitro, etc.- that 15.5k limit is just too tempting. With the 10x4MA we see typically 2-300 rpm lower on the same engine, compared to the 10x3APC. On all the engines we have tested, we have seen below 15k on the MA 10x4, except a 28F that I put a huge carb on (otherwise stock, 15% nitro). I suggest we consider a 15k limit if we go to the MA 10x4, since the 15.5k limit proposal was, I believe, based on a 10x3APC prop. No sense in setting up a HP war, it will be easy to stay under 15k (virtually all demos have been run at that rpm and performance was good) with low nitro, or other means, as necessary. Tests to date have indicated that most engines are already there anyway, lets' not set a ceiling that many will inevitably strive for!

Scott Gilkey
sgilkey
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Post by sgilkey »

Mike "Dr. Evil" F.- the Webra you ran in Open B last weekend was very strong! Brian's webra has been disappointing for power, so if I do an rpm check on it, I fear it will give misleading results. Can you check your Webra with a stock OS muffler (no baffle) with the 10x3 and 10x4 props? Thanks.

Scott Gilkey
RHorton
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Post by RHorton »

Why do we need another class is my question?[?] This is Combat and only combat, we don't have tach races, nor fly around pylons nor do precision aerobatics. The RCCA is here to keep us all together and promote combat. Two or three classes is enough to satisfy anyone needs. I have been at this for a long time and I have been trying to get combat slowed down for the past three years. What I am saying is that if Colorado wants to fly open B as it is and we fly limited B then we have deluted our combat pilot pool for a given contest. Why is it so hard to just slow open B down with a Muffler and prop restriction. Sure we could go back and fourth between Limited B and open B but why. IS it just for speed. Jimbo I am with you all the way in slowing the planes down. We will see more people fly if everything was slowed down. I just don't see the need for two classes of B sizes planes.

We have to come together and gve a little here and there for this (RCCA) to work. Don't give up just bend a little. [:)]
Lou Melancon
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Post by Lou Melancon »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by RHorton</i>
<br />Why do we need another class is my question?...[?] [:)]
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

Ron,
I think I can answer this question, but first lets clarify the discussions. There are actually three proposals on the table, they are:
<ul>
<li>Let's leave Open B alone</li>
<li>Open B but remove the mousse cans, pipes and return to stock mufflers, plus a prop limit</li><li>Limited B where the engine and/or airframe is limited </li></ul>
The AMA Open B rules cannot be changed until Janaury of 2007, and the RCCA rules follow the AMA change dates. This means that we cannot "officially" modify the rules for either AMA or RCCA combat before the change date. That leaves us with the "Provisional" route. This is a good thing because it allows us to test both the concept and the sustained level of participation.

Lou Melancon
Alpharetta, Georgia
RHorton
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Post by RHorton »

Only the AMA rules are in effect till the next rule cycle, but the RCCA can adopt a different set of rules to keep us all flying open B and 2610 and ssc. Didn't the Board of the RCCA change the NPS rules after the season ended[?] It just takes the Board to change our rule cycle!
Lou Melancon
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Post by Lou Melancon »

Good questions,
The current board voted in late 2002 to bring the RCCA rules change cycle into sync with the AMA cycle. Prior to that it could be changed annually.

SSC is a provisional event, as would be any modification of a class to have that modification flown separately. This is the path that the folks in this discussion are pursuing. Are you saying we should change Open B to limit it to stock mufflers and/or stock props for the 2005 NPS calendar year?

To do that the RCCA board would have to vote to change the rules cycle and also adopt changes to Open B. If this were done then contests that are flown for Open B, which are flown by different rules than AMA, could not be sanctioned as rule book events.

I think it is a good idea to have the rules cycles syncrhonized with AMAs cycle.

Lou Melancon
Alpharetta, Georgia
RHorton
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Post by RHorton »

<font color="red">"To do that the RCCA board would have to vote to change the rules cycle and also adopt changes to Open B. If this were done then contests that are flown for Open B, which are flown by different rules than AMA, could not be sanctioned as rule book events."</font id="red">

So what you are saying is that it's OK to let a class die in order to be in line with the AMA and have any number of provisional classes being flown. How many SSC events were flown under the AMA rule book[?] Answer NONE!

We flew under a class C sanction until we got open B and 2610 in the AMA rule book. We can still fly a class c events instead of class A if that is what it takes to keep us together.[:)]

And didn't the AMA change the rules so we could fly a 3.5lbs 2610 instead of the 3.0lb AMA rule. And arn't all 2610 events flown with the 3.5lb rule instead of the 3.0lb AMA rule. So every 2610 event flown by RCCA 2610 rules is out of step with the AMA rules.

What am I missing here[?]
RHorton
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Post by RHorton »

I meant to say the AMA let us fly 3.5 lb planes at the Nats when the AMA rule book says 3.0lbs. [:D]
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Which_way_is_up
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Post by Which_way_is_up »

Ron,

So a vocal minority should cram a set of rule changes down the throat of the entire membership for the good of the membership to ensure that the entire membership is happy and stays with the RCCA?

What am <b>I </b>missing?

<hr noshade size="1">

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Lou Melancon
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Post by Lou Melancon »

Ron,
The AMA allowed us to fly 3.5lbs Scale 2610 planes at the Nats because the AMA Combat Contest Committee had approved the increase in weight to 3.5lbs for the 2005 rule book, and because we (RCCA) petitioned them to allow it.

Whatever the majority of fliers want flown is what will be flown. You cannot force participation by limiting classes, or changing rules. SSC is not killing B, nor will Limited B kill SSC they will co-exist with levels of support reflecting the interest of the membership.

Many of the folks on this thread want the Limited B concept to work and are working hard to do it. They are testing concepts, exchanging ideas and I believe understand that success comes from participation.

Incidentally in my opinion SSC did not kill Open B, nor do I think Open B is on life support. I believe a lot of folks got tired of the carnage rates and wanted something slower and more survivable. That "something" could have been .25 SSC, but the folks who took the time to develop the Five SSC Commandments agreed on .15s, and no one stepped forward to develop a .25 SSC class.

If you take the difference in engine displacement between SSC and B and multiply the SSC airframes to that factor you will come up with very large, hard to transport, expensive airframes. A .25 is 1.6X greater than a .15. Multiply as follows:
<ul><li>Span - 64" X 1.6 factor = 102" span </li>
<li>Weight of 2.5 lbs X 1.6 = 4lbs minimum </li></ul>

This would seem, to me at least, to be a the size plane you need with .25 engines to achieve the same level of performance/survivability/and speeds that have made SSC so popular.

Lou Melancon
Alpharetta, Georgia
Jimbo
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Post by Jimbo »

I wouldn't want Limited-B to be another SSC. I would like to see it become more of a pursuit style class. Dr.Evil has come up with some ideas that may help that.We just need some more testing done first.

Limited-B
Try it,you'll like it !
drewjet
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Post by drewjet »

Well after putting the stock muffler with baffle and 10X4 MA prop (14,000 RPM) on my Open B plane, I can tell you that it was enjoyable. We didn't check weight, but I think it is within a few ozs of 3 lbs. I found I had to richen up the engine a lot more than normal, otherwise it would heat up,lean out and shut down after a few minutes.

Slam did the same thing, except he used a 10X3 APC. The speed seemed very even. With no wing optimization they still turned pretty tight, but not as tight as when in Open B mode. I would have no problems flying it in a furball. Sure the furball would be bigger and maybe that would reduce carnage, but just the same I am sure a furball would happen. Of course me and Slam hit(his engine on my tail, my engine on his wing leading edge), as we seem to usually do, and I think the was less damage then had we been going 10 to 20 MPH faster. He sliced my vertical stab and broke my elevator horn and I had no vertical control and put it down in the weeds, he had some leading edge damage.

So what does this mean? I think this class has merit, and our next contest may well be a open B contest with a gentleman's agreement to be limited b (of course anything RCCA legal in open B would be allowed, but props and mufflers will be made available to contestants if they choose to give it a try). I love the way my 25FX runs over the way .15's run. I like having all that thrust to make downwind launches easier. I like having vertical climbing ability. I like the idea of a spec wing, but if not a spec wing it needs a maximum limit on wingspan. In general I like it, and hope it works out.

Drew







you only crash when you run out of airspeed altitude and ideas at the same time, or get T Boned by me!
Jimbo
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Post by Jimbo »

We have to run them a little richer too, like I do my sport planes. I kind of like seeing a little exhaust trail on my combat planes.

Limited-B
Try it,you'll like it !
BigCountry
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Post by BigCountry »

That's cause it gives you something to look at once I take your streamer[:D][;)][:p]

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RHorton
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Post by RHorton »

Wich way is up could I ask who this is[?]

It's a vocal minority that is cramming the rules we have down our throat now, we can't change the rules to keep up with technology so we need the provisional rule to keep combat going. What if we had leader that would not have allowed SSC to get started, then would have Lou quit flying combat because open B and scale were to fast for him.

Lou you completely missed the point. We fly 2610 not by the AMA rules but by the RCCA rules, what is the differance in open B if the RCCA members want to get rid of the tuned pipe and run a 10x3apc. I say none. It doesn't matter the AMA 2610 rules say 3.00 lbs, in 2005 they go to 3.5lbs. For now to sanction a RCCA 2610 event it must be a class c event, next year if 2610 is still alive it can be sanction a class a event.
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