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Re: re assemble wing and strut 52 170B
Posted: Tue May 27, 2014 5:00 pm
by c170b53
Good observation Bruce, but I'm not sure the results would change much from one lateral extreme to the other. Then again maybe some experimentation is in order!
Re: re assemble wing and strut 52 170B
Posted: Tue May 27, 2014 5:52 pm
by GAHorn
Bruce Fenstermacher wrote:I..., the wing sweeps back. It will be swept back the farthest with the eccentric adjusted outboard neutral....an extra knot of speed.
This is why
RED airplanes are usually adjusted with the eccentric outboard....(providing maximum swept-wing) ... in order to delay the onset of shock-waves due to their high Mach numbers.
Re: re assemble wing and strut 52 170B
Posted: Tue May 27, 2014 9:07 pm
by wingnut
Adjusting the eccentric bushings does change cable tension, and does "sweep" the wing tip fore and aft. Each bushing assy can have a maximum offset of .110", so it's possible to "sweep" each tip fore and aft .66" (this is why I always place them in neutral before doing a symetry check that measures from the wing tips to stabs or prop spinner), and also change distance between aileron bellcranks .220". Thats a significant amount of cable tension change.
I would always start neutral outboard (with the bushing rotated so the bolt is as far outboard as possible). On these 170's it is not possible to rotate to full neutral inboard without damaging the wing root rib. You can do it easily, but the fuselage carry-thru/fitting will put a gouge in the root rib
Re: re assemble wing and strut 52 170B
Posted: Tue May 27, 2014 9:27 pm
by bagarre
I wonder if you could get enough change of he eccentrics to compensate for the extra incidence in the horizontal stabilizer.
Rather, if the plane was balanced left to right with the eccentrics neutral inboard could you gain any speed by setting them both 90degrees up inboard.
This would assume the plane is so straight that it woudln't need the eccentrics in the first place.
OR set them 90 degrees up inboard and then adjust one down to compensate for the heavy wing.
That was about 30 seconds of thought on the topic so I may be quite simply wrong.
Re: re assemble wing and strut 52 170B
Posted: Tue May 27, 2014 10:15 pm
by wingnut
The maximum eccentric adjustment equates to 1/4 of one degree. I don't think that would be noticeable. That also involved approx 30 seconds of thought, so I may be wrong. But I'll bet if you put a case of beer in the baggage area, measured your airspeed on the way to my place. We drink the beer, and make the adjustment, then you measure your speed back home there will be a difference
Re: re assemble wing and strut 52 170B
Posted: Tue May 27, 2014 11:53 pm
by Bruce Fenstermacher
bagarre wrote:I wonder if you could get enough change of he eccentrics to compensate for the extra incidence in the horizontal stabilizer.
Rather, if the plane was balanced left to right with the eccentrics neutral inboard could you gain any speed by setting them both 90degrees up inboard.
I understand this in fact has been done by members in the past who were trying to ring every last 1/4 mile an hour out of their 170. John Pugliese, CA is one who comes to mine who may have adjusted the eccentrics for reduced drag and John was smart enough to paint his plane speed green.
Re: re assemble wing and strut 52 170B
Posted: Wed May 28, 2014 12:00 am
by bagarre
wingnut wrote:The maximum eccentric adjustment equates to 1/4 of one degree. I don't think that would be noticeable. That also involved approx 30 seconds of thought, so I may be wrong. But I'll bet if you put a case of beer in the baggage area, measured your airspeed on the way to my place. We drink the beer, and make the adjustment, then you measure your speed back home there will be a difference
I like the way you think but we should make it two cases to be sure
Re: re assemble wing and strut 52 170B
Posted: Wed May 28, 2014 12:06 am
by wingnut
Bruce,
FYI, all you need to do is paint the eccentric bushings green. It also helps to paint all the parasitic drag items green. Like the antennas, Venturi, and all the button head rivets.
Heck, after I left Paul's place, I painted his Venturi red just so it would stop whistling going down the road.
Re: re assemble wing and strut 52 170B
Posted: Wed May 28, 2014 12:26 am
by GAHorn
Bruce Fenstermacher wrote:[...
I understand this in fact has been done by members in the past who were trying to ring every last 1/4 mile an hour out of their 170. John Pugliese, CA is one who comes to mine who may have adjusted the eccentrics for reduced drag and John was smart enough to paint his plane speed green.
John has a problem. His
Green airplane performs so poorly he installed a bigger engine and constant speed propeller in an attempt to keep up with the rest of the fleet. His efforts with the eccentric bushings made so little difference as to be unnoticeable.
If he seriously wanted to speed things up he'd get a
RED paint job, and then he could reduce the throttle and save gas as well.
Re: re assemble wing and strut 52 170B
Posted: Wed May 28, 2014 1:29 am
by rollcloud
Well, quite a response. Thank you. I take it that the neutral position for the eccentric is to have the thickest part inboard. Such that if one were viewing the eccentric on the port side, looking aft,my he thick part would be at 270 degrees. The opposite would then be true on the starboard side.
Re: re assemble wing and strut 52 170B
Posted: Fri Feb 05, 2016 12:28 pm
by aviator
Bruce Fenstermacher wrote:I meant exactly what I said. With the eccentric adjusted neutral inboard the wing is swept forward as far as it can go. The wing might be perpendicular to the center line of the fuselage at this point, I don't know. Adjusting the eccentric up or down pulls the rear wing spar towards the fuselage and since you are not adjusting the front spar, the wing must swept backwards relative to its position with the eccentric adjusted neutral inboard. Does not matter if you adjust up or down, the wing sweeps back. It will be swept back the farthest with the eccentric adjusted outboard neutral.
Of course Cessna designed this system to adjust the trailing edge of the wing thus changing it's angle of attack in relationship to the other wing. But the sweeping action also occurs.
You should also be able to see how moving the eccentrics also can relax or stretch the aileron and flap control cables.
Eccentric relationship.jpg
I also believe, that when you are splitting hairs, the best course of adjustment is to adjust one wing eccentric up and the other down an equal amount as when necessary. This course keeps the angle of attack of both wings the same in relation to the horizontal stabilizer. Unless of course you were trying to change that relationship to gain an extra knot of speed.
I removed my wings for painting and used this visual on the cam system to help me understand the adjustment concept. However, the more I looked at it and compared it to the installed cams on the airplane, the more I became convinced that the diagram is actually backwards. Anyway, there is really no two ways it can work. As one of the other posters commented, putting the cams on backward will force the wing spar against the carry through spar, if is even possible. I adjusted both wing cams to neutral (not having marked them prior to disassembly) and the airplane flew perfectly with pilot and copilot seats occupied and slightly left wing heavy with only one person on board. Has anyone else ever noticed this?
Re: re assemble wing and strut 52 170B
Posted: Fri Feb 05, 2016 7:09 pm
by Bruce Fenstermacher
Theoretically an otherwise perfectly symmetrical aircraft would fly straight with two occupants of the same weight and turn left with just an occupant in the left.
There are a few aircraft that, in my flying career, I've flown enough to become intimate with their flying characteristics. I thought they turned left when I was solo and flew straight when better balanced. So I have no doubt you may be feeling and experiencing the same.
Re: re assemble wing and strut 52 170B
Posted: Sat Feb 06, 2016 12:24 am
by N2625U
Bruce Fenstermacher wrote:Theoretically an otherwise perfectly symmetrical aircraft would fly straight with two occupants of the same weight and turn left with just an occupant in the left.
There are a few aircraft that, in my flying career, I've flown enough to become intimate with their flying characteristics. I thought they turned left when I was solo and flew straight when better balanced. So I have no doubt you may be feeling and experiencing the same.
I've got a '63 172 that does that. If I'm alone it does like to turn left but park another fat bod in the right seat and it straightens up. If I fly solo from the right seat it has a tendency to turn right.