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Old 10-22-2013, 10:08 PM   #1
FreeSparrow
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Default Acroduster II Tail Heavy

Folks, I have a question.
I have an Acroduster II with AIO360.
It is tail heavy and requires nose down trimming (see picture).
My mechanic increased the elevator incidence by 3.5 deg. but this is still not enough. There still is a 4 deg angle between the elevator and the horizontal tail. Any ideas? should I replace the bolt (We are the last 2 threads there)?

Thank you,
Avi (FreeSparrow)


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Old 10-22-2013, 10:16 PM   #2
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The operative questions is where is your CG with pilot and fuel on board?

The weight of the pilot moves the CG aft. The weight of the fuel moves the CG forward.

And what was the airspeed when that photo was taken? Level flight?

Best of luck,

Wes


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Old 10-22-2013, 11:04 PM   #3
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If you are within c.g. limits, then you need to increase the incidence in the horizontal stabilizer. I believe there to be a front mount that you can add washers under between the stabilizer and the fuselage cross-member, then adjust the brace wires and struts.

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Old 10-22-2013, 11:36 PM   #4
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My two questions are;

Where is the CG and how confident are you that the last W&B was done correctly?

What does the elevator look like at the same speed inverted?
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Old 10-22-2013, 11:44 PM   #5
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The front of the Horiz. Stab is fixed but the rear attach is where the adjustment is made, should be a stack of washers that can be added/subtracted to get the incidence you need. If you are lucky the bolt was installed to where it is easy to remove, most now will weld a nut plate to the cross member so that the bolt can be removed.
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Old 10-23-2013, 01:47 AM   #6
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You say the stabilizer incidence was increased by 3.5 degrees. Where was it relative to the top longeron before the move? What is the wing incidence? And like others have asked, where is the CG? How much does the airplane weigh and how heavy is the tail in the level attitude?

Most biplanes seem to need some positive incidence in the tail. Usually zero to about 1.5 degrees leading edge up is considered a starting point.

Dave Baxter can probably give you the best answers but he will need good weight and balance numbers from some known datum points like a wing spar attachment.
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Old 10-23-2013, 01:53 AM   #7
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Is the stick unusually light or sensitive in pitch?
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Old 10-23-2013, 03:06 AM   #8
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Default Acroduster Too C.G

Avi There are several more questions that need to be asked, some already have.

Current weight and balance weighed in level flight?

Empty weight ?

Was this with just you and full or half fuel main tank?


Most biplanes require some positive incidence as Neil has suggested, in relation to the upper longeron, for me 3.5 would be the extreme if this was indeed measured at the upper longeron.

The published empty weight for the Acroduster Too is 1050 lbs. I am going to guess that your empty weight is a bit higher than this?

The G.G. limits for the Acroduster Too is from 20.5 to 26.6 inches aft of the Datum and that being the firewall.

The published aerobatic weight is 1630 lbs and if you are flying the airplane with, IE: Two heavy pilots and chutes and full fuel you would be right at that weight. If you are flying above these weights then a new limit load factor would need to be calculated which would result in a lower G load rating.

Your airplane originally had a hartzell C/S aerobatic propeller, does it still have that or has it been changed to a lighter Hoffman or MT?

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Old 10-23-2013, 03:59 AM   #9
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The W&B was done three times (when it was built by Ray's Aviation in Santa Paula), before I bought it and last December. All the times the results were similar:
Empty Weight: 1223 Arm: 16.511 Moment: 20192.95
With one pilot and 24 gal. of fuel in the main tank I get 22.45 (max CG: 26.5 in.),
well within the envelope. Luckily I weigh only 165lb. and I never do A/B with over 1600lb.
So it doesn't seem to be a CG issue. I have ample elevator authority (both up and down). ON Friday I will take more pics while flying inverted and also will take some pics from the elevator assembly.
In the meantime, thank you all for input and stand by for news.
Avi.
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Old 10-23-2013, 04:04 AM   #10
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the pics were taken while flying straight and level.
with 24 /24 I get around 155 kts indicated.

See CG and Weight info in my other reply.
Thank you,
Avi.
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Old 10-23-2013, 04:08 AM   #11
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More info: the Prop is the original aerobatic Hartzel. All seems to by by the book.
My assumption is that when trimmed in straight and level, the elevator must be in line with the horizontal stabilizer and the trim. Is this correct?
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Old 10-23-2013, 05:32 AM   #12
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Take pictures at different speeds. See if there is a speed that it flattens out. Measuring the stab in relation to the fuselage is assuming that the front wings are where they are suppose to be angle and stagger. You may need to get the plans out and check everything. Figure out what the wings to stab angle really is.
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Old 10-23-2013, 07:01 AM   #13
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Default C.g. Issues

My Starduster too elevator/ stab is about the same configuration when I fly. I am sure I have an aft c.g. Issue. I reweighed my plane and am sure my numbers are accurate. After looking at your numbers it seems that you are taking for granted that the W.B on your plane is correct. It seems the the basic planes c.g. is a little farther forward than I would have guessed. What are the individual weights for each wheel? And the tail wheel in horizontal ? I think you might find that it is not what you think it is. I have deduced from my own issue that taking 5 lbs off of the tail wheel will move my c.g. Forward exactly 1/2 inch. So it doesn't take much

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Old 10-23-2013, 07:17 AM   #14
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Was the picture at beginning of thread taken with the one 165 lb pilot 20.45 CG out of 20.5/26.6 limits, and 24 gallons at 24/24 prop/manifold at 155 kias? t

That seems fast.

If fast and light wouldn't it normally need a bit more nose down trim?
i.e. with the trailing edge of the elevator pointed down and stick fwd?

Maybe the angle of incidence on the wings are higher i.e. more nose leading edge up than it should be? Seems that would make it easier to land on the opposite end of the spectrum at least.

Wing incidence boards needed?


Just uninvited musings. The picture looked like fun though.
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Old 10-23-2013, 01:24 PM   #15
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Quote:
Originally Posted by FreeSparrow View Post
......
My assumption is that when trimmed in straight and level, the elevator must be in line with the horizontal stabilizer and the trim. Is this correct?
It depends on how you use the airplane. If it's a X-country machine, then yes, you would want the elevator faired at cruise speed with an average load. If its primary mission is akro then you might want the elevator to fair at zero G/zero AOA, especially if you're doing a lot of vertical maneuvers. Or you may choose to set it up to fair at WOT while upright to lower the drag between maneuvers in a sequence.
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Old 10-23-2013, 03:56 PM   #16
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The stick is sensitive in pitch, but this is typical for Acroduster.
It is definitely is not light at all.
The flying characteristics feel balanced (I also had some of my friends that fly Pitts, to fly it. It felt OK to them).
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Old 10-23-2013, 04:01 PM   #17
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The pic is "almost" as fun as actually flying it
I will try to make multiple pics with different airspeeds.
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Old 10-24-2013, 04:48 AM   #18
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Avi one other thing you might check it the thrust of the engine mount? Most all of these mounts were made by Starduser, and as such may have some up thrust built in. So please check the thrust line of the engine it should be Zero Zero with the upper longeron level. IE: no down thrust or right thrust. The front flying wire link is suppose to go under the lower engine mount spools, and some mounts were made that were not shimmed up to compensate for the 090 or 100 thou thickness of the link, and if so would result in up thrust! Does this make sense? Dave
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Old 10-25-2013, 12:33 AM   #19
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Avi, with your trim tab neutral, how does that affect the tail force, does it lighten up the stick force any? Does it require more elevator, more that the 4 deg, to hold strait and level.
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Old 10-25-2013, 05:01 PM   #20
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Chris,
Weather permitting, I am planning to take it foe a "test" flight and take pictures of all the attitudes and configurations.

Thanks for the input,
Avi.
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Old 10-26-2013, 01:43 PM   #21
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I think that you should try this: set the trim neutral, fly at a speed hands off level. See if the elevator is faired. I would guess that the IAS will be around 115. I think that you are asking the airplane to fly much faster than what is "aerodynamically neutral" (my term) for it. Yes, it can go much faster, but the controls neutral speed is far less.
It may be interesting for us all to try it and compare our "neutral hands off speeds".
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Old 10-27-2013, 02:07 PM   #22
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An IO540 would solve all your problems, especially that heavy wallet that is weighing the tail down.
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Old 10-27-2013, 05:42 PM   #23
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RE: IO540
I was very successful at making a small fortune in the General Aviation business.
Ask My ex-wife...
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Old 10-27-2013, 11:14 PM   #24
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Quote:
Originally Posted by FreeSparrow View Post
RE: IO540
I was very successful at making a small fortune in the General Aviation business.
Ask My ex-wife...
Most of the people I know that made a small fortune in Aviation started with a large fortune.
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Old 11-06-2013, 03:43 AM   #25
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Larry,
thank you for the input.
I took a few pics right side up, up side down and vertical and with controls neutral.
Indeed the IAS with controls neutral (24 x 24 ) is around 115kts.
25 x 25 give me 120 kts IAS.
The only time it flies straight and level with neutral trim and controls is at 90 kts (24 x 17 inch.)

Next week I will verify the W&B. But I have a feeling that I need to increase the incidence by another 5 deg. Otherwise the plane flies like a violin.


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