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Author Topic: Bellcrank 3" vs 4"  (Read 13302 times)

Online Howard Rush

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Re: Bellcrank 3" vs 4"
« Reply #50 on: July 26, 2012, 05:24:36 PM »
Rich Porter did it, but nobody noticed.
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Offline L0U CRANE

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Re: Bellcrank 3" vs 4"
« Reply #51 on: July 26, 2012, 05:47:25 PM »
Agreed, Bill, yet Pete Soule' called it an accelerated catenary in an Aeromodeller Annual (1970-71?) article.

A catenary curve is the (parabolic?) sag of a cable of uniform load or weight, between its two supporting ends.

The "supporting ends" for our flying lines are at the handle and at the leadout guides. The vertical sag due to the lines' own weight is pretty negligible.

In terms of "sag aft" due to line drag: Air drag (load) on the lines increases with the square of velocity, and velocity increases with radius - from near zero at the handle to the airspeed at the leadout guide locations. Curvature tightens from the handle to the leadouts... We can see it as we look down the length of the lines... We deal with it (adjustable leadouts; CG shifting.)

Pete's 40+ year old formula is a good first estimate, given the other variables we can't put hard numbers on, regarding CL flight. I believe Pete's formula is very close to being a basis - or at least start point - for the LINE'XXX' apps, which add further refinements.

Got a notice about Brett's latest post - while I was writing this... I believe that good reasons for pivoting the bellcrank near the spar include these:

...The spar is usually near the greatest "rib" height, ... greater depth is good for 'bending strength'

...Max "rib" height is usually around 20% to 30% of chord, so there should be reasonable fore/aft space.

... The flying lines 'tend' to aim pull at the CG, through the leadout guides. If the leadout guides are properly located, the angle the lines make when they reach the guides can be continued, inside the wing, right to the CG. This should reduce friction on the guides. The friction may not be much, but leadout cables and/or guides can be damaged over time. ...cable saw, anyone?
\BEST\LOU

Online Brett Buck

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Re: Bellcrank 3" vs 4"
« Reply #52 on: July 26, 2012, 06:01:56 PM »
Rich Porter did it, but nobody noticed.

   I noticed!  Everybody has fun telling Rich Porter stories but what little time I spent talking to him was interesting and I certainly learned some stuff.

    Brett

Offline Trostle

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Re: Bellcrank 3" vs 4"
« Reply #53 on: July 26, 2012, 06:12:56 PM »
Hi Keith,

Success has little to do with the physics involved in the use of handle spacing twice that of the bellcrank spacing.

(Clip)

Ted

Ted,

I think I knew some of that.  I was just commenting on how one individual that we know trimmed his airplanes.  It worked for him.  I have flown some of his airplanes and -----

Keith

Offline Bob Reeves

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Re: Bellcrank 3" vs 4"
« Reply #54 on: July 26, 2012, 06:16:01 PM »
Pete's 40+ year old formula is a good first estimate, given the other variables we can't put hard numbers on, regarding CL flight. I believe Pete's formula is very close to being a basis - or at least start point - for the LINE'XXX' apps, which add further refinements.

LineIII actually uses Pete's original C source code for all the math calculations.

Offline Ted Fancher

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Re: Bellcrank 3" vs 4"
« Reply #55 on: July 26, 2012, 06:45:57 PM »
Ted,

I think I knew some of that.  I was just commenting on how one individual that we know trimmed his airplanes.  It worked for him.  I have flown some of his airplanes and -----

Keith

Keith,

Don't think for a moment I'm putting our mutual acquaintance down.  Nobody did what he did better than he did and, unlike many, I thought his patterns were very competitive in terms of corner, etc. with what was being flown in that era by the other guys.  He also flew (flies) pretty much flawless shapes which very few do (Dougie Moon and Ryan Young being the most recent examples I've watched who spend time making sure the tricks look like their names!)  Anybody notice, by the way, that on the one "non-overun" flight Ryan flew in the Walker Flyoff--which included two stalled out bottom right 120 degree corners--scored within the noise range of Doug's excellent Walker Cup flights?  These Texas guys might be shifting the stunt CG in a big way in the not too distant future!)

Getting on my soapbox, by the way, I'd like to comment on something I noted while at the Nats.  The first six conversations (give or take a number or two) I sat in on after arriving all bemoaned the lack of young fliers and generally ended up with comments like "what can you do about it?", etc.  Well, a week later I watched the usual crowd watching and nit-picking the top five flyer's patterns right up to  Doug's exciting final victorious flight.  I had judged the handful of Junior and Senior entries and missed the first two flyoff rounds but watched the ones that ended up counting in round three.  While judging the young fliers I was once again (after my experience as assistant team manager in Hungary) struck by the skills displayed by Ryan Young.  His flights had shapes and sizes ripped right out of the rule book and only an occasional airplane fart (his ship is heavy for its size and "will" stall if pushed too far) prevented scores in the stratosphere from both myself and the other four judges.

Well, I then watched the final round and stood around waiting for what I thought would be a very competitive Walker Cup duel between Doug and Ryan.  Alas, the duel for the cup petered out pretty quickly as Ryan promptly threw up two overrun flights which turned out to be the result of the tie wraps on his pipe being so loose they spun and the connector had, not surprisingly, opened up and destroyed any effect from the pipe.  Forever game, however, Ryan and his pit buddy Darryl patched up the tie downs and he went out to fly his third flight knowing full well he was dead as a duck in the flyoff as Doug had two fine complete flights to zero for himself.  This time the engine ran perfectly and the flight was marred only by a couple of give ups in one corner of the triangles and the last corner of the hourglass.  His score was only twelve points (IIRC) behind Doug's best effort and some of that was in appearance points!

What does that have to do with my conversations earlier in the week?  Just this.  The seats in the stadium were empty!  All the guys wondering why we didn't have more juniors and seniors were gone after the top five fly-off and missed the opportunity to see a kid who, I predict, will win more than a few Walker Cups in the not too distant future. 

Boy, did I get off track there!  Sorry.

No, Keith my comments about the big handle and the small bellcrank used by our friend were only addressed because of the subject matter of the thread and the direction it was (and is) going.  I'm 100% in the opposition when it comes to such a set-up but, like you, can only marvel that a man who handicapped himself in so many ways on the way to achieving his aspiration managed to do so nonetheless.

Ted

Offline EddyR

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Re: Bellcrank 3" vs 4"
« Reply #56 on: July 26, 2012, 07:37:58 PM »
No one has mentioned the 3.5" bellcrank. I use to use them before the 4" bellcrank was easy to get. I didn't make them but several people did make them .I think I ordered mine from Rollie McDonald. They were a big improvement in Twister size planes.My vintage Juno from 1988 has one in it.
Ed
Locust NC 40 miles from the Huntersville field

Online Howard Rush

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Re: Bellcrank 3" vs 4"
« Reply #57 on: July 26, 2012, 09:04:13 PM »
Boy, did I get off track there!  Sorry.

I thought it was a good diversion.  Ryan is a very impressive person, as well as a good stunt flier.  And I'll have you know I was in the bleachers. 
The Jive Combat Team
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Offline RandySmith

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Re: Bellcrank 3" vs 4"
« Reply #58 on: July 26, 2012, 09:13:09 PM »
 "" His score was only twelve points (IIRC) behind Doug's best effort and some of that was in appearance points! ""


Hi Ted

I thought that in the  past, APs  were dropped in the Cup flyoff, did they not use to do it that way?
Do you know when or if it was changed?
Regards
Randy

Offline Ted Fancher

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Re: Bellcrank 3" vs 4"
« Reply #59 on: July 26, 2012, 09:39:50 PM »
"" His score was only twelve points (IIRC) behind Doug's best effort and some of that was in appearance points! ""


Hi Ted

I thought that in the  past, APs  were dropped in the Cup flyoff, did they not use to do it that way?
Do you know when or if it was changed?
Regards
Randy

Randy, You're absolutely right and I was dead wrong to mention them.  The Walker Cup has historically been competed without the APs.  Still, 12 or so flying points behind a guy that had just beat the winningest flier in US stunt history is not a bad showing for a kid who had spent the entire week judging rather than flying.  I continue to stand by my predictions for Ryan's future!

Ted

Offline proparc

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Re: Bellcrank 3" vs 4"
« Reply #60 on: July 26, 2012, 09:42:35 PM »
OK, so who's going to be the first with a 5" or 6" bell crank?  Has it been done?

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Windy had a 5 inch in his Foam wing Sweeper, (Bob Zambelli has it) where he placed 17th at the Nats. John Wright told me he stuffed a 4 inch bellcrank into his Barnstormer which helped to give him his Nats win.  I believe the Russians were packing 5" or big levers into their stunt ships, but you didn’t hear that from me, ( ask Leon Panetta about that).
Milton "Proparc" Graham

Offline RandySmith

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Re: Bellcrank 3" vs 4"
« Reply #61 on: July 26, 2012, 09:42:44 PM »
Randy, You're absolutely right and I was dead wrong to mention them.  The Walker Cup has historically been competed without the APs.  Still, 12 or so flying points behind a guy that had just beat the winningest flier in US stunt history is not a bad showing for a kid who had spent the entire week judging rather than flying.  I continue to stand by my predictions for Ryan's future!

Ted

Hi Ted

No biggie, I was curious if it had been changed, and  I do agree  with you about Ryan, the young man has a boat load of talent.

Regards
Randy

Offline Ted Fancher

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Re: Bellcrank 3" vs 4"
« Reply #62 on: July 26, 2012, 10:29:23 PM »
No one has mentioned the 3.5" bellcrank. I use to use them before the 4" bellcrank was easy to get. I didn't make them but several people did make them .I think I ordered mine from Rollie McDonald. They were a big improvement in Twister size planes.My vintage Juno from 1988 has one in it.
Ed

Ed,

My late (and mostly unlamented) circular bellcranks I used in the published Imitation and Excitations were also 3.5" diameter drives.  They were nicely machined by John Schwickwrath but, unfortunately, the bearing material wasn't up to snuff and they got sloppy after a few hundred flights.  They did precede the switch to four inchers as well.

Ted

Offline Dennis Toth

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Re: Bellcrank 3" vs 4"
« Reply #63 on: July 27, 2012, 07:51:23 AM »
Guys,
The build project El Diablo is getting to the stage of installing the bellcrank. I have found a way of putting the 4" crank in without much trouble and very good support. BUT, the ED's wing is only an 1 1/8" thick and the crank fits between the top an bottom spars nicely problem is this leaves only a little over 3/8" for the pushrod to clear. I like to use cable leadouts with a brass tube "C" bushing so to get the pushrod to clear the leadout attachment it needs to come out on a slight angle. This all works except for the connection of the pushrod to the bellcrank. Normally I would use a ball-link connector but this is to tall on the 4" Brodak crank. So as I see it I can get a different style bellcrank that allows a lower profile leadout connection or use a heavy gauge wire that allows some weird bends and maintains strength.

Anyone offer a thin flat bellcrank with sideways leadout connectors?

Best,       DennisT

Offline john e. holliday

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Re: Bellcrank 3" vs 4"
« Reply #64 on: July 27, 2012, 09:08:37 AM »
Well, I hope you guys don't tell my Ringmaster that was built box stock by a young lad many years ago that it is not supposed to fly the way it does.   Mine flies an Old Time Pattern better than some of the planes I had before.   It will do it again in October. H^^
John E. "DOC" Holliday
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Shawnee, KANSAS  66203
AMA 23530  Have fun as I have and I am still breaking a record.


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