Limited B: Not so limited

This is the thread to aid in development of new ideas and classes. Post working rules and gather feedback!

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sgilkey
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Post by sgilkey »

Thrust is only part of the equation. Do you mean to tell me that a Q40 pylon plane will be faster with a 10x6 prop than the itty bitty toothpick under-8-incher it's spinning, because the 10x6 makes more static thrust??? Try making that argument to the pylon racers and see if you convince them to run bigger diameter props! When I flew IMAC, I had an 8.5 pound plane with a 1.4 c.i. engine spinning a 17" diameter prop, probably making 14+ pounds static thrust. In other words, thrust to weight ratio way above our Open B combat planes. But any SSC plane would be about as fast as my old IMAC ship, it was speed limited by its pitch/rpm constraints, no matter how much thrust it had. It ACCELERATED to its top speed real quick, and climbed striaght up quite nicely, even from a dead stop. Still slow, though.

Impact destruction is all about dissipating kinetic energy. KE goes up with the square of velocity, but only linearly with mass. Therefore reducing velocity is the most fertile ground for limiting impact destruction. We never said Limited B would eliminate destruction, but it will have the opportunity to reduce it considerably. You get center-punched with a hard point like an engine, there's still going to be damage, even at the lower speeds. But it's hard to argue that lower speed=lower energy=less likelihood for damage, all other things being equal.
jfromm
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Post by jfromm »

Scott,

I got to admit that I never seek guidance or insight from a 16 year old and that you would be too much of a challenge to explain flow theory to on this forum. My Masters is technical and not in education. Let’s just leave it at “you are smarter than meâ€
boilermaker
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Post by boilermaker »

Easy there Scott, you must have not read my previous post about being a smart ass. Of course I wouldn’t tell the pylon guys to change props, but when it comes to trying to fly vertical at 25 thousand feet a 10x4 is going to yield about the same results as a 9x4 isn't it?

Next time I'll just go with those two props pulling 800lb planes at sea level and 72 degrees. They'll both be pulling the planes at the identical speed of 0 mph relative to the ground :)

Of course, me simplifying things to thrust is no different than simplifying impact to kinetic energy.
Jimbo
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Post by Jimbo »

Limit-B is much slower than OpenB. It's not matter of opinion, it's a matter of fact.
Cross Check

Post by Cross Check »

Hi All,

What RPMS does a new(broken in)OSFX turn a MA10-4 on no-low nitro fuel?

Could that be a happy max. limit?

As the engine gets tired the nitro could be upped to make the max. RPM.

Take care,
Have fun,
Dave'crosscheck'Fallowfield
Maac 6437
Unabashed Combat Team
boilermaker
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Post by boilermaker »

Sure it's slower, was speed all you wanted to limit? Was speed limited enough to have any significant effect? A 3.25lb plane flying 55mph has the same momentum as a 2.5lb plane flying 71.5mph. Take two of either one and have them hit each other from the same angle. The impulse time is going to be about the same on both, and the impulse force is going to be huge on both.

It's like taking two glass bottles and hitting them against each other. Get slightly heavier bottles and smack them at half the speed and they'll still break. Sure you may have cut the kinetic energy by 75% when you cut the speed, but the force at impact that does the breaking doesn't change. All the extra kinetic engergy on the fast moving version just means the pieces that break off land farther away from the point of impact.
Jimbo
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Post by Jimbo »

If you are looking for SSC, try SSC, not limit-B. Are try some E-Combat.
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Which_way_is_up
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Post by Which_way_is_up »

Eyee me mates, "Arrrr try some E-Combat"!
boilermaker
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Post by boilermaker »

double post
boilermaker
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Post by boilermaker »

Is that tail end charlie, or one eyed willy?

I got it, if you're looking for SSC try SSC. If you're looking for speed, try open B. If you're looking for Scale, try 2548 or 2610. (Ignoring for a moment that the SS part of SSC is considered by many to be an unattainable). If you're looking for _________ try Limited B.

What goes in that blank that would point yout at Limited B and not any other event?
Feathers
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Post by Feathers »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">I got it, if you're looking for SSC try SSC. If you're looking for speed, try open B. If you're looking for Scale, try 2548 or 2610. (Ignoring for a moment that the SS part of SSC is considered by many to be an unattainable). If you're looking for _________ try Limited B.

What goes in that blank that would point yout at Limited B and not any other event? <hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

Actually I can think of quite a few very good things that could go in that blank. However, something tells me that they're not going to make any difference to you. Frankly, everyone has to fill in that blank for themselves- nobody can do it for them.

I can understand that the idea of a Limited B event would not appeal to everyone. I have a little trouble with why someone would have a problem with a Limited B event appealing to others. So, as you don't have to fly any event you don't want to- why the fuss?
Bo_Connolly
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Post by Bo_Connolly »

As anybody even flown a Limited B Event Anywhere in the Country Yet?

There Are No Limited B Scores in the Provisional NPS. It is May.
drewjet
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Post by drewjet »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by boilermaker</i>
<br />Is that tail end charlie, or one eyed willy?

If you're looking for _________ try Limited B.

What goes in that blank that would point yout at Limited B and not any other event?
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">
A contest with slower speeds better survivability and still have the reliability of a .25 FX
sgilkey
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Post by sgilkey »

I tried this analogy before, looks like I need a repeat.

Try this test to teach yourself the difference between MOMENTUM and KINETIC ENERGY when it comes to dissipating crash forces.

STEP 1: Walk into a wall face first. Note pain level.

STEP 2: Pick up a 50 pound bag of sand, put a kid on your shoulders, or somehow increase your weight. Walk into the wall face first. Note your pain level.

STEP 3: Discard your 50 pound weight. Heck, take all your clothes off, go on a diet, whatever, LOSE weight if you want to. Then jog into the wall. Note your pain level.

STEP 4: Let us know your findings.

There is a reason that the federal government mandates, and occasionally increases, SPEED in crash testing for automobiles, not MASS. SPEED is the greater contributor to destructive forces in an impact. If you look at any accident reconstruction, the SPEED of the impacting vehicles is estimated/recorded, nobody goes and WEIGHS the involved vehicles. Of course weight matters, but nowhere near as much as speed.


WHY Limited B? Reduced (not eliminated, of course) potential for crash damage through lower speeds compared to Open B, while offering much better launch authority (especially with strong tail winds) and better overall flight characteristics due to much better thrust-to-weight ratio than SSC. (A side advantage: If you get a sick run with SSC and you are 1000 rpm below the max, your performance will be significantly degraded. Launching will be a challenge, dragging streamers gets tough, etc. A limited B ship running 1000 rpm below the max will still launch with authority and give excellent flight attributes due to the abundant thrust.) Also the engines suitable for Limited B are generally perceived to be easier to handle and more user friendly than the SSC engines. Finally, with the minimum weight and wing area/span limits proposed, it's a piece of cake to build a Limited B ship at minimum weight with cheap, durable full-size gear, while a minimum weight SSC ship will generally (though not always, of course) need mini servos.

Locally, we've had several Limited B demos including two with a pilot who speaks with some authority on these issues, Mike Fredricks. He wholeheartedly endorses the Limited B concept and I tend to think he knows what he's talking about. Brian and I have flown probably in excess of 100 "rounds" of Limited B as that is what we fly for fun/practice. We've flown a few rounds and won or placed at a few contests in Open B and SSC as well, and I think we know what we're talking about when we say that Limited B is slower than Open B and yet still a different breed of cat from SSC. As Tim says, if you don't like it, nobody's making you fly it. But please stop denigrating the class by trying to argue against physics, reality, and real-world experience. I don't think a few rounds flown in horrid conditions at the last Havoc constitutes a real validation (or refutation) of the Limited B concept. The observations are welcome and interesting, but let's not trash the class based on four rounds in humongous winds.
Bo_Connolly
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Post by Bo_Connolly »

Hey Guys:

Please, Please, Please, I'm not trying to trash Limited B.

[ I'm reading this thread cause I'm curious about what is going on ]

How many rounds of it have been flown so far this Year?
Was Havoc the first and only ?

From what I've heard of Havoc, that wasn't a fun day...

Anybody who thinks that Limited B is as fast as Open B wasn't in Paris Texas
for the 2005 Lone Star Nationals.

Open B is Very Very Very Fast.

Take Care,
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