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05-22-2007 04:26 AM  13 years ago
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ProModeler

rrElite Veteran

Sanford, FL (Orlando area)

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BBC update
I thought this would be a good time to update folks on the BBC (big block conversion). We're having some teething pain, but nothing insurmountable.

The clutch hubs came in (I only had four prototypes made up) in order to build up some helicopters and try (between me and some friends) to see if they were ready for prime time. The hubs are beautiful and size-wise are very similar to the standard P50 part, but shorter to account for the physically larger engine.

Accompanying them were the special tapered engine nuts, 5/16" instead of 1/4" thread, of course. These, together, were the major source of trouble. Let me explain.

The nuts are 12mm vs. the 10mm socket the standard nut uses, i.e the hex are 12mm on the side. The problem is the hole for the nut had to be made larger to acocunt for this. First problem, the hole in the fan hub is how the clutch unit itself self-centers. With a bigger hole we lose the self-centering feature - oops! So we took some of the nuts to a machine shop and machined the 12mm sides down to 10mm. This worked nicely, so we're going to make up some more at 10mm a side, which allows using a standard socket and we don't have to open up the ID of the fan hub and thus, we regain the self-centering benefit. This, of course, takes time but at least we know where we're going with this

Meanwhile, the new long tail boom and drive belt are working just fine. Frankly, it's nice to have "something" work out right.

Unfortunately, the sample 85-tooth gears aren't quite right, but this is fixable too. Again, it takes time.

So there you have it, nothing insurmountable in the BBC, just more time to get it right. So (to cop a phrase from Ernest and Julio Gallo) there will be no BBC before it is time!

Hang in there folks, it's coming.

John Beech
AMA # 47381
IRCHA #745
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05-22-2007 04:36 AM  13 years ago
rcadd1ct

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Richardson, Texas

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Wouldn't it be easier to drill and tap a 10mm nut than shave a 12mm nut to 10mm?-RCA .......... Making Cuisinarts Fly!!!!!!!
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05-22-2007 04:41 AM  13 years ago
ProModeler

rrElite Veteran

Sanford, FL (Orlando area)

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Yes, but the 10mm nuts are hardened and thus, drilling and tapping is not a trivial exercise. Meanwhile, the 12mm special nuts are prototypes and haven't been hardened yet.
John Beech
AMA # 47381
IRCHA #745
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05-22-2007 05:08 AM  13 years ago
rcadd1ct

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Richardson, Texas

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Cool.

Details.

Something about devils and details?
-RCA .......... Making Cuisinarts Fly!!!!!!!
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05-22-2007 12:31 PM  13 years ago
CHARGE

rrApprentice

FUTURE PLANET EARTH

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Hi john sometime in the automotive buss i find that toyota does occasional make nuts with a small head to get into tight places and what should in all reality take 14mm socket takes 12mm socket.i'll see if i can find the source i'll pass it on i know with a little research maybe you can find what your looking for already made.pm me with the info and i'll ck with my supplier.TomA positive outlook is all that is required
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05-22-2007 02:13 PM  13 years ago
ProModeler

rrElite Veteran

Sanford, FL (Orlando area)

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Alas if it were so simple, but remember, the engine nut is tapered, and hence is custom made.
John Beech
AMA # 47381
IRCHA #745
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05-23-2007 09:49 PM  13 years ago
Gearhead

rrMaster

Vt

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that would be "JB on BBC"

Jim
Jim
Buzz Buzz Buzz
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05-25-2007 05:57 PM  13 years ago
cwoodstx

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Plano, TX

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John, I have some novice questions about the BBC. Why is it necessary to have a longer boom? If more tail authority is needed wouldn't a longer tail blade suffice? As long as you had a governor to prevent over reving could you still use 600 mm blades?
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05-25-2007 09:40 PM  13 years ago
ProModeler

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Sanford, FL (Orlando area)

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a) A governor would certainly prevent over-revving.

b) More tail authroity is not an issue in the least. The Pantera 50 product has a 5.3:1 tail gear ratio vs. the significantly slower (and thus weaker) 4.5:1 tail gear ratio found in Raptors, Sceadu, etc. Those models are frequently equipped with a longer tail rotor blade as modelers seek more power (thrust), which we deliver through higher RPM instead (i.e. via design).

c) A longer boom permits longer blades - this is the purpose. Why longer blades? To permit harnessing more horsepower is the general reason. For example, a 50 makes about 2 horsepower. A 91 make more like 3 horsepower. A 61 makes about 2.2 and a 70 more than this but less than a 91. A 91 (and the 70) is physically the same dimensions (externally) as a 61, which is the engine we designed the BBC for.

I leave it as an exercise for the student to figure out why I'm trying to keep one step ahead of certain folks by coming up with a longer boom/belt combo.

Finally, thanks for giving me the opportunity to respond, and please, in the future never worry about "novice" questions. In a previous life I was not only an engineer, but also a secondary school math and science teacher. Like you, I was not born knowing more than how to cry and wet my drawers and everything else I learned from someone patient enough to teach me. The fact is every single soul here on RR learned what they know about helicopters from someone elese (in some way or fashion). For this reason I frequently say, "There are no stupid (or novice) questions."

My 2¢

John Beech
AMA # 47381
IRCHA #745
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05-25-2007 09:55 PM  13 years ago
cwoodstx

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Plano, TX

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Thanks John, your responsiveness, patience, and of course excellent products are the reasons I bought 3 Panteras and will buy more as soon as the BBC is available. I gave one away to a worthy cause, one is still flying, and one being built for backup.
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