[NSRCA-discussion] YS Questions+more - Rolls
george w. kennie
geobet at gis.net
Fri Mar 7 17:07:35 AKST 2008
Jim,
Your logic seems very sound to me.
G.
----- Original Message -----
From: J N Hiller
To: NSRCA Mailing List
Sent: Friday, March 07, 2008 7:30 PM
Subject: Re: [NSRCA-discussion] YS Questions+more - Rolls
Matt you have been doing this longer than I have and I value your suggestions. I tend to work with the CG and wing incidence first because it is quick and easy. I readjust the wing incidence every time a CG change is made to reacquire neutral elevator. I am not yet ready to mess with a cambered stab airfoil. I found that down thrust changes influence the pitch more as the airplane slows and very important in controlling pitch approaching a power on stall turn, which may be different than coasting to a stop. The main reason I go the easy route first is that the down line and knife-edge are also being affected and if the change is detrimental it is easy to undo and try something else.
The first Option-120 I built had an adjustable motor mount and stab as well as the wing so I could set and try several different combinations. I was able to get an acceptable pitch trim from 1/2 to 2 degrees of down thrust by tweaking the CG and wing incidence except for a power on vertical stop where more down thrust would pull the nose to the belly and the prop-wash on the stab would pitch it to the canopy if the down-thrust was insufficient. Once I obtained an acceptable balance I resisted further tweaking of the down-thrust angle. I found that trusting the airplane to hold vertical while approaching a stall turn was quite important. It is difficult to see a flop inducing off vertical pitch and little time to correct it.
I should also state that if the wing was changed very much by either cambering the stab or moving the CG the down thrust needed to be reset to maintain stall turn entry pitch.
The adjustable stab appeared to be of value only when the effective vertical wing to stab separation was to be changed. Correct me if I am wrong but it has been my understanding that the vertical separation has a significant influence in knife-edge trim.
In most proven designs without adjustable stabs have been pretty well tweaked for stab location / incidence and down thrust leaving weight, wing incidence and CG to pilot preference tweaking. It seams we are trying to trim to the most acceptable compromise that supports several flight attitudes found in the schedule to be flown and pilot compatibility.
I have probably said too much but the subject interests me greatly. It’s an unending learning by doing experience that I can indulge in outside, all summer. I have the #4 Option (small stab revision) airframe ready to cover. The snow pile beside the driveway is under 4 feet now and the lawn is emerging from under the trees.
Jim Hiller
-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of rcmaster199 at aol.com
Sent: Friday, March 07, 2008 11:23 AM
To: nsrca-discussion at lists.nsrca.org
Subject: Re: [NSRCA-discussion] YS Questions+more - Rolls
If the model pulls to canopy on a FULL POWER vertical upline and you reduce downthrust, the problem will worsen. You need to add downthrust (about 1 degree initially, and more if needed). I would not mess with CG, at least not yet.
Horizontal flight places quite a load on the wing....the wing must lift the load accordingly. Vertical flight removes the load therefore whatever trim was found in horizontal flight will affect the vertical flight. The simplest fix is downthrust addition for the condition Mike references, but assumes that the model is close to begin with.
Downline flight (NO POWER) is a totally different trim scenario and may indeed require wing/stab inc adjustment and CG adjustment.
It should be understood that it is an iterative process to get "perfect" trim.
MattK
-----Original Message-----
From: J N Hiller <jnhiller at earthlink.net>
To: NSRCA Mailing List <nsrca-discussion at lists.nsrca.org>
Sent: Fri, 7 Mar 2008 11:33 am
Subject: Re: [NSRCA-discussion] YS Questions+more - Rolls
The airplane may be flying with positive trim. Try reducing the down thrust or move the CG back.
If it doesn’t help put it back.
Jim Hiller
-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of Michael Wickizer
Sent: Friday, March 07, 2008 8:19 AM
To: NSRCA Mailing List
Subject: Re: [NSRCA-discussion] YS Questions+more - Rolls
Bryan:
I agree that the plane doesn't know which direction it's flying, but then why will a plane fly straight and level then pull to the canopy in uplines? This has been driving Brett and me crazy for over a year. Admittedly, it a much shorter drive for me:)
Mike
------------------------------------------------------------------------------
> Date: Thu, 6 Mar 2008 23:13:48 -0500
> From: shinden1 at cox.net
> To: nsrca-discussion at lists.nsrca.org
> Subject: Re: [NSRCA-discussion] YS Questions+more - Rolls
>
> Chris ,, the airplane does not know it`s flying horizontal or vertical
> the wings are still lifting whether up or down that s why we can use the vertical up or down to test this problem ,
> Bryan
> ---- krishlan fitzsimmons <homeremodeling2003 at yahoo.com> wrote:
> > Lance,
> >
> > Just a thought though, if going straight up, up straight down, aren't the up and down ailerons both inducing equal drag, no lift? I've often wondered if our straight up test is actually a perfect test for this. It is for our up and down lines, but what about our 45's or horizontals where we do indeed have lift on the low aileron and drag on the other? This would create a different condition I'm guessing.. Probably small, but still a little different because as I mention, both create drag on the up or downline.. Still, it's the best test we have I guess..
> >
> > Chris
> >
> > Lance Van Nostrand <patterndude at tx.rr.com> wrote:
> > This thread is timely because I've been experimenting with differential
> > recently on a new design that seems to need it. Never needed it before on a
> > pattern plane but now I might. My test is to fly very high, point the nose
> > directly at the ground and roll pure aileron. Plane should be axial, but
> > remember that axial is along the vertical CG, which may not be a line that
> > pierces the wing LE/TE. You need to do it a few times to be sure that their
> > is an axis that everything rotates around and that line is straight. If it
> > wobbles, then we have an issue. Another way to determine this is to do
> > unlimited rolls while flying straight up. If the airplane consistently arcs
> > off its vertical line, you have a problem.
> >
> > Aerodynamics suggests two contributors. One is that the lowered aileron
> > increases the lift of the airfoil and lift creates drag so this wing may
> > pull the plane off axis. the other is that the spiral slipstream of the prop
> > is pushing down on the right wing and up on the left so up/right aileron is
> > more effective than up/left and down/left is more effective than down/right.
> >
> > The overall effect for most pattern planes is minimal and usually ignorable,
> > but on IMAC style planes these factors can be significant and the resulting
> > differential corrections may need to be adjusted with something as simple as
> > a prop change (from 3 blade to 2 for example).
> >
> > the correction of course is to start playing with aileron differential.
> > Given the contributors I've suggested, its not a given which way you go with
> > the differential to correct the problem and the answer might not even be
> > symmetrical.
> >
> > Note that contributor #1 above will change if you are flying upright or
> > inverted, so it would seem that a correction for upright flight would simply
> > exacerbate inverted flight, but contributor #2 is the same for any flight
> > mode but is throttle dependent.
> >
> > --Lance
> >
> > ----- Original Message -----
> > From: "Koenig, Tom"
> > To: "NSRCA Mailing List"
> > Sent: Thursday, March 06, 2008 4:45 PM
> > Subject: Re: [NSRCA-discussion] YS Questions+more - Rolls
> >
> >
> > > My head is spinning!!! The more I think about this, the more questions I
> > > have.........rather than answers!
> > >
> > > Maybe the contra rotating prop set up on a Voodoo X( Nat??) maybe the
> > > answer??
> > >
> > > I still 'feel', that the best rolls I get are with a 0 differential set
> > > up-BUT- somehow I 'drive' that wing to 0 ( or should that be some sort
> > > of equilibrium??) during the rolls. Certainly in my case, it seems to be
> > > Pilot dependant!!!
> > > I'm starting to think that my rudder control has turned to the
> > > proverbial trying to micro analyse what's happening!
> > >
> > > Tom
> > >
> > > -----Original Message-----
> > > From: nsrca-discussion-bounces at lists.nsrca.org
> > > [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of
> > > shinden1 at cox.net
> > > Sent: Friday, 7 March 2008 9:15 AM
> > > To: NSRCA Mailing List
> > > Subject: Re: [NSRCA-discussion] YS Questions+more - Rolls
> > >
> > > what happens on a 4piont?
> > > Bryan
> > > ---- Del Rykert wrote:
> > >> The general consensus has been that the faster moving molecules over
> > > the top surface don't require as big as a deflection as the aileron that
> > > deflects towards the bottom of the plane. What one tries to achieve is
> > > the plane tracks as purely straight on a string as possible while one
> > > rolls both directions without introducing any yaw.
> > >>
> > >> Del
> > >>
> > >> ----- Original Message -----
> > >> From:
> > >> To: "NSRCA Mailing List"
> > >> Sent: Thursday, March 06, 2008 2:49 PM
> > >> Subject: Re: [NSRCA-discussion] YS Questions+more - Rolls
> > >>
> > >>
> > >> > Nat and all you other aerodynamicists,
> > >> >
> > >> > I thought that the rational for "aileron differential" was that
> > > upward deflection causes more drag than downward deflection so to
> > > equalize drag and prevent yaw with aileron deflection, aileron
> > > differential is needed. It seems that you guys are now saying that
> > > ain't so. Please elaborate.
> > >> >
> > >> > George
> > >> >
> > >> > ---- Nat Penton wrote:
> > >> >
> > >> > =============
> > >> > IMO center hinged or top hinged is OK. With top hinge, to achieve
> > > equal vertical travel of the trailing edge requires different angular
> > > travel, up vs down. The objective is zero aerodynamic differential.
> > >> >
> > >> > Ron I don't think a fairing would prevent separation but, how are
> > > you able to fair the gap using the top hinge ? Nat
> > >> > ----- Original Message -----
> > >> > From: ronlock at comcast.net
> > >> > To: NSRCA Mailing List
> > >> > Sent: Thursday, March 06, 2008 7:20 AM
> > >> > Subject: Re: [NSRCA-discussion] YS Questions+more - Rolls
> > >> >
> > >> >
> > >> > And while your at it, I'd appreciate some discussion of the impact
> > > of the top hinge system as seen on Viavat, and Prestige birds - (top
> > > hinged, with fairing that eliminates the gap at deflection)
> > >> >
> > >> > Thanks, Ron Lockhart
> > >> >
> > >> > -------------- Original message --------------
> > >> > From: vicenterc at comcast.net
> > >> >
> > >> > Nat,
> > >> >
> > >> > Could you explain why the differential should be different for
> > > non-center hinged? I understand that the mechanical configuration of
> > > non-center hinged requires differential to obtain same travel in both
> > > directions. However, the travel up and down should be close to equal.
> > >> >
> > >> > Thanks,
> > >> >
> > >> > --
> > >> > Vicente "Vince" Bortone
> > >> >
> > >> > -------------- Original message --------------
> > >> > From: "Nat Penton"
> > >> >
> > >> > Tom
> > >> > It's just something that is peculiar to the Southern
> > > Hemisphere.
> > >> >
> > >> > Changing wing incidence will not help. Unless things are really
> > > screwed up , at our roll rates, centrifugal forces are too low to
> > > cause a problem. You want zero differential, aero speaking ( same
> > > up/down if center hinged ).
> > >> >
> > >> > I find the best check is the fast half-roll in the vertical up.
> > > Regards Nat
> > >> > ----- Original Message -----
> > >> > From: Koenig, Tom
> > >> > To: NSRCA Mailing List
> > >> > Sent: Wednesday, March 05, 2008 7:24 PM
> > >> > Subject: Re: [NSRCA-discussion] YS Questions+more
> > >> >
> > >> >
> > >> > Hi Troy!
> > >> >
> > >> > Thanks for the info. I thought you would be toiling away on
> > > the next developmental stage of these engines!!
> > >> >
> > >> > Hopefully soon, I can find the time to get flying again. I am
> > > looking forward to running this little beast. I am still a little
> > > concerned in keeping it quiet though.
> > >> >
> > >> > Four blade props? I have some of the 18.1 x 12 two bladers
> > > but I just cant see how I'll shut the thing up with these paint
> > > stirrers??
> > >> >
> > >> > Also-one more question to any of you out there in pattern
> > > land.
> > >> >
> > >> > I have struggled with aileron differential for years. I am
> > > just not happy with the rolls. I have tried various design fixes-but
> > > about the only one that seems to work is to get the wing back to 0-0 (
> > > which can be achieved by a few ways, design, mix or thumbs) Differential
> > > itself does not seem to work if the wing is POA ( well...it works for
> > > half the roll !)
> > >> > Another black magic fix appears to be to run parallel
> > > ailerons-but this only 'sorta' seems to fix it. I like the feel of
> > > equal% chord ailerons however.
> > >> >
> > >> > I am frustrated with it-I like my planes to roll as if they
> > > had a string up its ...........well you know!
> > >> >
> > >> > OK-any 'secrets' I need to know??? Very good elevator work
> > >> > fixes it ( hence my 0-0 comment)
> > >> >
> > >> > Tom
> > >> >
> > >> >
> > >> > --------------------------------------------------------------------
> > >> > ----
> > >> >
> > >> >
> > >> > _______________________________________________
> > >> > NSRCA-discussion mailing list
> > >> > NSRCA-discussion at lists.nsrca.org
> > >> > http://lists.nsrca.org/mailman/listinfo/nsrca-discussion
> > >> >
> > >> >
> > >> > --------------------------------------------------------------------
> > >> > ----------
> > >> >
> > >> >
> > >> > _______________________________________________
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> > >> > NSRCA-discussion at lists.nsrca.org
> > >> > http://lists.nsrca.org/mailman/listinfo/nsrca-discussion
> > >> > _______________________________________________
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> > >> >
> > >
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> >
> >
> >
> > Chris
> >
> >
> >
> >
> >
> > ---------------------------------
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