[NSRCA-discussion] pitch

[Rcmaster199 at aol.com]

One of the better knife-edging models and pretty fair all-around  sport 
fliers in recent past was.... of all things, a Stuka Divebomber with slats  fully 
deployed. It was an ARF (which annoyed me to no end....).
 
It had this tiny fin with all rudder area above the stab, and a wing that  
was mounted to the very bottom of the fuse and with a bunch of dihedral. It  
showed virtually no roll couple and no pitch couple with either top rudder. It  
would slow roll and point roll from horizon to horizon. Designer was either 
very  lucky or had pattern design experience in spades. Only faults I found was 
its  inability to do clean snaps and easy stalls.... rudder was possibly too 
small  and stab too large for its wing
 
Point is there are many ways to skin the kitty.
 
But I must admit, trying to make an UStik knife edge and make it perform  
like a pattern model is a little like putting lip-stick on a pig. No offense  
intended to owners of UStiks; these model types have their place. 
 
The designer of the original UStik for those new to the sport, Phil Kraft,  
pattern competitor extraordinaire, intended the model for testing equipment and 
 not much else.
 
regards,
MattK
 
In a message dated 2/1/2006 11:58:29 AM Eastern Standard Time,  
jivey61 at bellsouth.net writes:

Well  Georgi I think you did a good job of starting some hackles,hehe.
Jim  Ivey
----- Original Message ----- 
From: "George Kennie"  <geobet at gis.net>
To:  <nsrca-discussion at lists.nsrca.org>
Sent: Wednesday, February 01, 2006  11:45 AM
Subject: [NSRCA-discussion] pitch


> I'm having some  problems with this one. Nothing serious, mind you,
> but just a little  confusion.
> If we take this stab/fuse joint pressure build up to be  causative,
> then it should logically follow that in order to  achieve
> equilibrium, the rudder area above and below the stab should  be
> equal.
> Then if we take the Stick, everything (area) is  above the stab,
> which lends credence to the hypothesis, but if we go  back to the
> Cap, the area is now closer to equal, but probably  weighted slightly
> in one direction or the other, but closer to the  equality that we
> are seeking, and yet the reaction is just as violent  except in the
> opposing direction.
> Therefore, we must assume  that the point of equilibrium is at some
> point between the two  locations.
> With our thoeretical airplane with it's adjustable stab, we  end up
> determining that indeed the point of equilibrium appears to be  at a
> much lower point (relative to the rudder area) than we would  have
> originally anticipated. So we, at this point find ourselves  doing
> some serious head scratchin'.
> On the other hand, if we  take the two airframes together and analize
> the force arrangements we  find that they are basically inverted
> mirror images of one  another,i.e., Stick, ........wing on top, stab
> on bottom. Cap, wing on  bottom, stab on top. And yet the rudder area
> intersect points are  definitely not mirror images.For that to be the
> case, the Cap would  have to be a T-Tail. Something doesn't jibe!
> Here we have the Cap with  close to a balanced area scenario and yet
> we have the dreaded pitch to  the belly. If we now turn the Cap
> upside down and cut off the canopy  and glue it to the belly
> pretending that the belly is now the top and  fly the airplane it now
> pitches to the canopy( new top, but still  really to the belly). The
> problem with this scenario is that, in this  inverted position the
> Cap's fin and rudder become equivalent to the  biggest sub-fin,
> ventral, strake, whatever you want to call it and yet  it doesn't
> correct the pitching problem.
> I have strong  feelings that the dynamics are located in a different
> area and would  contend that a poorly designed force arrangement
> cannot be corrected  with a band-aid approach.
> This is not intended to raise anybody's  hackles, just my two cents.
> G.
> 
> 
> 
>  
> 
> Since were still guessing at cause of pull to top in knife  edge,
> Here is my Suspect -
> Stab is on bottom of fuse- true  with this design?
> When rudder is applied, air pressure builds at  intersection of fuse
> & Fin,
> with the top of the  stab.  Pressure on top of stab creates a nose up
>  condition.   There is no equivalent pressure on bottom, cause  there
> is little or no fuse and fin.
> 
> If that is the  cause, adding a strake to bottom might improve it.
> 
> Later, Ron  Lockhart


 
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