Quick question on bellcrank mounting

[andy borgogna]

I am building a plane and the plans show the bell crank installed with the push rod hole pointing to the inside of the circle.  Why is this better than the conventional method of mounting the bell crank with the push rod hole pointing to the outside of the circle.  I seem to remember this being explained a number of years ago but I can't for the life of me remember what the explanation was.
Andy

[Tim Wescott]

With a normal elevator horn it puts the up line in front, without having to cross the leadouts inside the wing.

There's been some discussion here lately on the advantages of having the upline in front vs. in back, particularly in relation to whether you have a CW or CCW prop.  There's also some people who feel that you should be able to adjust leadout spacing as well as center position.  Since one of these fellows is named Paul Walker, I nod my head "yes" and do it, even though I don't much understand why (it's something about cross-coupling between yaw and elevator.  It's all very confusing).  Hopefully I'll understand it all, someday.

[Mike Haverly]

With the down line in back, it can induce excessive yaw during outside maneuvers.  This is exacerbated with a left hand (pusher) prop.  And, individually adjustable leadouts are a big help.  I've have had this exact problem and was set straight by that guy, Paul.

For proof, just fly an airplane set up this way with a left hand prop in some wind.  You'll get a major sphincter contraction on the lower outside of the clover.   I've had one set up like this and, being electric, there is no CG shift.  It makes it worse yet.  Lesson learned.

[andy borgogna]

Thanks guys, since I intend to convert this plane from glow to electric and will be using a pusher prop turning clockwise rotation I will install the bell crank per the instructions.

[Mike Haverly]

One of my pet peeves is definition of prop direction.  As far as I know, prop direction is determined from the cockpit perspective, or pilot.  By this criterion, a clockwise rotating prop is standard, or right hand.  Props rotating in the opposite direction are left hand, not pusher.  Boats are the same.  I have a boat with one RH and one LH, both by definition are "pushers".  Most boats are not pulled through the water unless they're being pulled by another boat.

If I'm all wet I would like to get it straight.

[Mark Scarborough]

One of my pet peeves is definition of prop direction.  As far as I know, prop direction is determined from the cockpit perspective, or pilot.  By this criterion, a clockwise rotating prop is standard, or right hand.  Props rotating in the opposite direction are left hand, not pusher.  Boats are the same.  I have a boat with one RH and one LH, both by definition are "pushers".  Most boats are not pulled through the water unless they're being pulled by another boat.

If I'm all wet I would like to get it straight.

well Mike, if you dont fall out of the boat, you wont be all wet,,

[Tim Wescott]

Thanks guys, since I intend to convert this plane from glow to electric and will be using a pusher prop turning clockwise rotation I will install the bell crank per the instructions.

If my in-the-head calculations are correct, that's not what you want to do with a reverse-rotation prop.  Mike can jump on me if I'm wrong.

[Mike Haverly]

Tim,that's kinda what I'm implying.  By my definition and he does what he says, the airplane will go backwards!  Maybe it's just semantics or political correctness.  Where I come from, pushers push things.

[Tim Wescott]

Tim,that's kinda what I'm implying.  By my definition and he does what he says, the airplane will go backwards!  Maybe it's just semantics or political correctness.  Where I come from, pushers push things.

I was using "reverse rotation" to get back to his original question about bellcrank placement -- on which topic I'd like to get confirmation or objection.

In this case, since we seem to be in a sea of semantic confusion, I'm using "reverse rotation" to mean that if you waltz into a hobby shop there'll be a wall full of "normal" props, and no, or maybe one or two "pusher" props (except for the quad-copter prop sets).

"Normal" is clockwise from the cockpit, yes?  Blows air toward the headstock if you mount it in a "normal" lathe and turn the thing on in the "normal" direction (I don't think I've ever seen a lathe with the headstock on the right as it's designed to be used)?  Or am I backwards?

[Mike Haverly]

Tim, I think you are correct, forward that is.

My electric profile has the bellcrank mounted with the up line forward.  With a LH prop it was tough to get it to do what I wanted.  Every time I would get the lead outs moved back to where they needed to be it would just about pull me over on my face on the bottom of outsides, never mind some wind with that!  Like I said, I got straightened out on that problem by you know who and it does much better now.  Again, lesson learned.

[andy borgogna]

Mike you might want to vent your frustration on the naming of left vs. right handed props on the people who make the props.  APC marks every clockwise prop with a "P" indicating pusher.  How do I know this, well I work in a hobby shop and sell them all the time.  Understand I do not argue with your logic but you might try to understand that the term "Pusher" goes back many, many decades, it's clearly not something I invented or misused.  Anyway thank you for your input.

[Howard Rush]

Are you sure that's the direction you want the prop to turn?  Many folks tried backwards props and have reverted to traditional props. 

[Mike Haverly]

Andy, OK I'll just say they are wrong.  There I said it.  Really it doesn't matter to me what you use.  A right hand prop just works better.  What I said about cockpit reference is correct, APC or not.  I have some of those APC's marked with a "P", and they spend their time on a shelf.  The question about the bellcrank is what I said.  Down line in back will increase line tension on outsides.  I think that's why everyone fell in love with the CCW props to make line tension at the top of the hourglass when in fact that should have just finished trimming the airplane.  These things flew for years with IC engines turning the normal way.  The carrier guys were different and started using engines with CC rotating crankshafts. 

[Tim Wescott]

The carrier guys were different and started using engines with CC rotating crankshafts. 

The carrier guys have different aims (as you know).  The motor tends to torque the plane over when they goose the throttle, and when you goose the throttle it's usually because the thing is slack on the lines and you're eskeert.  The last thing you want happening at that point in time is for the plane to torque in towards you (I know, I've been playing with carrier with a CW engine).

Carrier guys do not worry about the line tension in the hourglass at all, for some reason.

[Steve Thompson]

Full size light aircraft engines typically turn clockwise when seen from the cockpit - same as our typical model engines.  I believe this is referred to as Right rotation.

Right hand rule can be used:  Extend an imaginary line out from prop shaft axis, wrap fingers around axis (like you are hitch hiking) with fingers wrapping around in direction of rotation.  If it is right hand rotation, your thumb should point forward.

[Howard Rush]

...wrap fingers around axis (like you are hitch hiking)...

Another analogy may be more pertinent here.  

One could unambiguously describe traditional prop rotation as a positive rotation about the X axis.  You'd need to define the X axis, but once you start talking about airplanes and directions, you really need to settle on some definitions, and I think it's helpful to use those common to the rest of aeronautics.  

[Target]

Maybe I missed the entire theory, but doesn't up or down line forward favor insides or outsides equally since the pattern is full of both?
I get that the plane is sort of hanging from one line when a sustained pull on either line is given, but without the lines for and aft adjustable with them one above the other, how is one way better than the other, since maneuvers are being flown both pitch up or pitch down?
I'm guessing that it has something to do with "P-factor", but I guess I don't fully understand.

Thanks,
Chris
PS. what about using a vertical with area above and below the thrust line?

[Tim Wescott]

Maybe I missed the entire theory, but doesn't up or down line forward favor insides or outsides equally since the pattern is full of both?
I get that the plane is sort of hanging from one line when a sustained pull on either line is given, but without the lines for and aft adjustable with them one above the other, how is one way better than the other, since maneuvers are being flown both pitch up or pitch down?
I'm guessing that it has something to do with "P-factor", but I guess I don't fully understand.

Thanks,
Chris
PS. what about using a vertical with area above and below the thrust line?

The pattern has roughly an equal number of inside and outside rounds and 90-degree corners, but it has 8 inside 120 degree corners and only two outside ones.  Moreover, the final corner of the triangle is it's own special beast.

[Howard Rush]

PS. what about using a vertical with area above and below the thrust line?

Like this?  Can't work

[Target]

Hmm, yeah, like that....
Strange that I never noticed that. I haven't looked at the Max Bee too much.
Thanks, Howard.
And Tim.

R,
Chris

[Roy DeCamara]

I guess by some individuals definitions,  P-38's flew with a tractor propeller and a pusher propeller.   

[Paul Smith]

Full size light aircraft engines typically turn clockwise when seen from the cockpit - same as our typical model engines.  I believe this is referred to as Right rotation.

Right hand rule can be used:  Extend an imaginary line out from prop shaft axis, wrap fingers around axis (like you are hitch hiking) with fingers wrapping around in direction of rotation.  If it is right hand rotation, your thumb should point forward.

Right hand rotation means rotating the right way.  
As in right-handed is correct, vs left-handed which is wrong-handed.

[Dennis Adamisin]

Hi Andy.  Back to your question, if your are going to use an righty/tractor/CCW prop then install the bellcrank backwards with the front line up.  If you are going to use a lefty/pusher/CW prop then install the bellcrank with the up line in back.

If anyone asks which way your prop rotates answer, "To everything, turn, turn, turn..." Its safer that way.

[Trostle]

I guess by some individuals definitions,  P-38's flew with a tractor propeller and a pusher propeller.   

When I get my library out of storage, I will check on the story of the P-38 development.  Yes, it had counter rotating props, but the first one did not turn well.  The propeller rotation was reversed and it worked fine.  Same story on the DeHavilland Hornet/Sea Hornet.

Keith

[Tim Wescott]

When I get my library out of storage, I will check on the story of the P-38 development.  Yes, it had counter rotating props, but the first one did not turn well.  The propeller rotation was reversed and it worked fine.  Same story on the DeHavilland Hornet/Sea Hornet.

In the case of the P-38, they started with the rotation set to minimize torque issues with one engine out.  That turned out to cause nasty turbulence over the stabilizer, so they swapped the engines.

[Roy DeCamara]

Well, I don't know what the problems were with the P-38.  I recently read a book about the F-82 Twin Mustang.  The first flight of the prototype would not lift off.  They tried several things.  I don't remember if they ever got it to fly as originally setup.  What they did discover was that with the engines setup with the left prop turning clockwise and the right prop turning counter-clockwise resulted in the prop blades moving downward as they passed in front of the center wing section.  This resulted in taking the air away from the center section resulting in a great loss of lift.  The solution was to switching the engines with the prop blades lifting the air to the center section and producing the required lift.  Perhaps the P-38 had a similar problem.