Lim B and Open B questions

Any Open Class topic can be discussed here. Come on in and share your knowledge or ask a question. Best place on the Net to hang your hat on a windy day!

Moderator: hbartel

Fred420
Posts: 277
Joined: Thu Feb 10, 2005 8:36 am
Location: USA

Lim B and Open B questions

Post by Fred420 »

Ok ... now it's time to go up a class and I am going to build a couple of B ships. What are the specs for both Limited B and Open B and is it possible to fly both with the same plane?

It's been a great season and Lynn and I are looking forward to next year.
Hat Trick
Posts: 1540
Joined: Thu Mar 15, 2001 6:58 pm
Location: USA
Contact:

Post by Hat Trick »

Open B has a max weight of 3.5# Limited B has a minimum weight of 3.25#
Open B you can do whatever you want with the engine. Any prop any RPM.
Limited B you must use a MA or Kavan 10x4 or a APC 10x3 max RPM 14,500. Stock engine and muffler. You can remove baffles in the muffler and bore out the stinger.

I build light for Open B and add weight for Lim B and change the muffler and prop.
Fred420
Posts: 277
Joined: Thu Feb 10, 2005 8:36 am
Location: USA

Post by Fred420 »

Can we use any .25? I have a couple MVVS's, Or are they restricted to a price as with SSC?
sgilkey
Posts: 2351
Joined: Mon Mar 19, 2001 8:26 am

Post by sgilkey »

Dave, if you go to the RCCA homepage under "start combat" you can view the rules for each class. Basically for LimB or Open B you can use any engine you want, no price limit. HOwever, while for Open B you can use a tuned muffler, MCP, Ultrathrust, etc (factory or aftermarket) up to 8 inches length, for LimB you have to use a non-tuned, expansion chamber type muff (commonly called a "stock muffler" though some engines like certain MVVS came "stock" with a tuned muffler which would not be allowed for LimB. Any engine, including engines such as the Webra 25GT which don't come with any muffler can use another mfg muffler, ie the OS 25FX muffler will fit the Web 25GT, or you can use an OS muffler on a magnum 28XL, etc. Parts swapping, removing muffler baffles, reaming out the tailpipe, etc are all allowed as long as you don't exceed the 14.5k rpm figure on the spec prop. you can also use aftermarket mufflers such as the Mac's one-piece (black).

If you want to fly both classes you might want to consider an engine that is good for both classes. I'd say for that, it's hard to beat the 25FX. It is about perfect for LimB, will turn at or near the rpm limit, is reliable as an anvil and easy to operate, smooth and durable, easy on plugs and not finicky on fuel. Put a MCP on it and it is a very competitive OpenB engine, though not the most powerful. The Web 25GT, on the other hand, is a very stout Open B engine, though a bit finicky and durability is questionable (some last awhile, some blow up soon, many blow up sometime!), appears to be a dog on a stock muffler and the spec LimB prop. The MAg 28Xl is an excellent sport engine and great for limB, it is also quite powerful and makes a nice Open B engine but at the Open B rpm it is a vibrator and durability seems to suffer a bit.

In its day, the MVVS .26 was a very strong Open B engine (on a pipe), though a bit heavy and quite finicky (inconsistent carb, they did better with an OS carb). Don't know how the MVVS do on stock mufflers.

FOr running both classes, especially for starters, I'd say you'd be hard pressed to find a better all-around engine than the 25FX.
User avatar
boiler
Posts: 3336
Joined: Wed Jan 01, 2003 8:16 pm
Location: Ohio
Contact:

Post by boiler »

Hard to beat the 25fx.
Captain America
Posts: 1009
Joined: Tue Aug 09, 2005 2:33 pm
Location: Middle of f'n nowhere

Post by Captain America »

Right now im favoring the new B2 style wing usable for both limited and ssc with the same wing. My new fence post I use with the B-s style wing can be run for ssc or limited with just a motor swap and weight adjustment. If I were not flying open where i needed dual servos int he wing one stock wing could be used in all 3 classes. certainly can be the case for lim and ssc. I have not flown the b-2 wing in ssc form myself yet but it seems to be a good setup. My only concern at this point is durability of the soft leading edge in open combat. My wing broke in the midair sunday, I need to disect it but it was a much different break than the normal fiberglas rod LE wings I was running. Flew great though up to that point.
User avatar
lightning
Posts: 1444
Joined: Sun Jan 19, 2003 10:53 pm
Location: USA

Post by lightning »

hey Capn, I'll trade ya your ONE broken wing for the TWO I've got!!
EK
Posts: 338
Joined: Fri Aug 22, 2003 6:36 pm
Location: Aubrey,Texas

Post by EK »

Using the same basic setup for SSC and B has it's advantages. I build for SSC looking for the 40oz package using 25# foam for the wing. B wings are of 40# foam but use the same template and can be flown for SSC if needed (and vice-versa but an SSC wing will be hard pressed to make it through a B hit). Fuses are also from the same template but for SSC I take an inch from the tail and add it to the nose.
Damage comes in many forms. A wing to wing hit won't usually break open a wing but a prop cut or a center punch sure will.
jj
Posts: 729
Joined: Mon Jun 03, 2002 11:45 pm
Location: USA
Contact:

Post by jj »

The Avenger B2 runs great for either Open B or Lim B. Same thing for SSC, but I usually only use one aileron servo for SSC whereas I use twin aileron servos for Open or Lim B.
Fred420
Posts: 277
Joined: Thu Feb 10, 2005 8:36 am
Location: USA

Post by Fred420 »

Is the 72" wing going to be allowed in '07 for B?
jj
Posts: 729
Joined: Mon Jun 03, 2002 11:45 pm
Location: USA
Contact:

Post by jj »

The B2 Avengers have 64" wings and they turn as tight or tigher than the 72 inch wings.
sgilkey
Posts: 2351
Joined: Mon Mar 19, 2001 8:26 am

Post by sgilkey »

any wing span is allowed in B. For Lim B there is a 64" max, but a "grandfather" clause which allows 72 inchers to compete this year. The original thought was to limit performance with the 64"max but as JJ states, the current crop of 64" planes such as the AVENGER B2 are the hardest-turning planes out there, so the 72" span has, to me, not demonstrated any advantage. So to encourage participation by those who have 72 inchers still in their inventory I will propose a rules change to LimB to remove the 64" restriction (still keeping an area restriction which I believe still has merit).
jj
Posts: 729
Joined: Mon Jun 03, 2002 11:45 pm
Location: USA
Contact:

Post by jj »

Scott,

Agree.

Given the lack of differnetiation in flying characteristics why on earth would we want to keep someone from flying in Lim-B just because of having a longer wing. If performance were a factor it would make sense.

More participation == better

This allows for a simple muffler / prop swap to enable participation in more events at lower costs.

jj
Hat Trick
Posts: 1540
Joined: Thu Mar 15, 2001 6:58 pm
Location: USA
Contact:

Post by Hat Trick »

I'm ok with grandfathering 72" wings but I do think the max wing area and max span rules should eventually be solid. Right now it doesn't make to much differance but I'm totally convinced that an increase in wing area or span is an advantage and we definately don't want 72" wings to be required to be competative.
AIM
Posts: 801
Joined: Fri Aug 19, 2005 7:22 am
Location: Montpelier, Ohio

Post by AIM »

Weren't 72's grandfathered last year? And the year before? Seems funny that everyone says they have NO advantage yet they seem to want an exception to the rule every year. I say let's chisel LimB rules in stone for 07. But thats a different discussion.

To give fred420 my opinion is that I like LimB more than open. The planes are slower. It's easier to build for, and the rules tend to make you design around durabilty instead of ultra light weight and flat out speed.
I don't fly open at all. Not necessarily due to the speed or anything. It's just that when you go to an event LimB usually comes AFTER open and I don't have enough planes to do both. You may also find (as I did) that it's easier to build a competetive plane for LimB. I fly ALL full size gear and even a 600 mah battery and my planes weigh right at 3 1/4 and are hitting the 14500 rpm max with ease. That being said, my planes built with common radio gear should "in theory" be JUST as fast as anyone elses out there.
In open alot of guys are turning 18 plus with 2 3/4 lb planes and I choose to not try to keep up.
I am probably wrong with this next opinion but I see LimB becoming more popular than open in the future simply because of the limitations. Guys tend to get frustrated with not being able to keep up with the "Jones's" so to speak. In limB just about everyone can run side by side. My planes can't turn like some do, but in a run across the field I can keep up with just about anybody.
Post Reply