Looking for best way to level airplane.

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Eugene

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Reality is you have to know when to stop.
Well, this is exactly what I'm trying to learn from you guys. I'm trying to get a feel for how critical all these dimensions in real life. This is only 100 MPH airplane.

I heard somewhere, that if you don't give those engineers deadline, they will be playing with this project forever and nothing will get ever accomplished!
 

poormansairforce

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Just an Ohioan
Knowing the designers of your plane and how they seem to think I wonder if they did it that way thinking they would help take care of any torque roll from the prop.....
 

Eugene

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Knowing the designers of your plane and how they seem to think I wonder if they did it that way thinking they would help take care of any torque roll from the prop.....
I talked to designer many times. His mission was to build 50 hp ultralight for a German market. Airplane was designed 100% symmetrical including engine installation. Production rates were purchased by somebody else. So different company was trying to install 100 HP engines and 4412 wing for American market. From what we know today they did played with engine angle an elevator ballasts, but didn't change tail or tail boom.

Vertical tail is too small and some guys reported 45° departure with abrupt power change despite full right rudder.

Did they actually twist the wings on purpose to compensate for a bigger engine? I hope not!
 

wsimpso1

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My water levels are great tools. I have had one each between root leading edges, between tip leading edges, between root leading edge and trailing edge, between tip leading edge and trailing edges.

Way better than my laser level. Now
Does it make any difference what diameter water tube will I use? I have miles and miles of 3/8 clear tubing .
It has to be same on voth ends so it has same miniscus and large enough to both pass bubbles and not have a lot of capillary action. I think mine are 3/8".
 

wsimpso1

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Well, let's remember that each design has its characteristics.

First things first. The dihedral may seem important, and you keep talking about it, but let's get realism in here. The wings fly and the fuselage goes along for the ride. That is so primary to every airplane. So our primary effort is to get the two wings to fly the same. What does that mean? Well, if one wing is 1 degree and the other is 2 degrees, and there are no other errors, the wings will try to fly at 1.5 degrees and the fuselage will have 0.5 degrees of roll angle that it will try to correct, putting in a small rolling moment. Would it be better if it were perfect? Yes, but if you are less than 0.25 in error on each, I would bet that you could never see it and other trim errors in roll will be much bigger. And if you can see it, fix it, but it won't change the way the airplane flies very much.

What would I worry over? If one wing is at different AOA than the other, one will always stall first and they will always make a rolling moment one way that you will have to correct. Ideally they will fly the same and neither wing will want to drop as you stall it. Yeah, right, but let's approach that ideal. I would worry first over having AOA IDENTICAL at the root. If you have an adjustment at the root for AOA, by all means make the AOA IDENTICAL at the root. Next I would get dihedral pretty close left to right at the forward spar - which is also the main strut. How? Water level between the roots at 0.25c, another between the tips at 0.25c, then another from one root to one tip for angle. Get the roots at the same height, then the tips at the same height, then fool with the dihedral until they are both close to your desired number, but more importantly, close to each other. Settle the bolted joints to take the clearance out of the bolts in holes and use water levels to make the side to side good. Once you have the fuselage level and the dihedral in, then you adjust the drag struts to get the same AOA at the tips. Measure this using water level from drag spar tip to tip, and I would try to make this perfect, but let's remember that your wings are flexible - a wing that consistently drops in stall can be adjusted with a little tweak of the drag strut to reduce tip AOA on that side, and a wing that shows no preference for wing drop in stall but always rolls to one side in normal flight can be fixed with a fixed tab on an aileron.

Now what features to look at? The wing is tough to grab hard points for so a lot of folks, me included, like the idea of upper surface templates. I saw and sand mine out of MDF with pin holes to hold the right and left together for shaping - goal is identical and good fit on the top of the wing. One each for root and tip on each wing. This gives you flat surfaces at the top that you can sight along for water level readings and for checking side to side.

The order in which you do all this stuff is important. Once the root is set, it is should be good. Once the dihderal is set using the main struts, it should need little fuss. Then you can play with the Tip AOA. Yeah, that might interact with the Root AOA and dihedral, so you iterate. But if you are trying to set things in a different order, it will be a long process. If there is a lot of slop in the pin joints, you might look into fixing that. And the airplane might take re-rigging after tightening the bolts and again after it is flown because stuff will settle some.

Summarizing:
  1. Make and install fittings that ride the top skins of the wings;
  2. Level the fuselage left and right, fore and aft by getting the root heights the same at 0.25c and at the drag fitting if you have an adjustment for that - that gets Root AOA trued up;
  3. Get the tip heights close at 0.25c for dihedral - this is so it looks right on the ground as much as anything else;
  4. Adjust Tip AOA to match factory setting for washout and make them IDENTICAL side to side;
  5. Revisit all readings and repeat the sequence until it stops getting better;
Remember that with a torsionally soft wing (you do have drag struts) you tune the washout to give a symmetric and predictable stall and then tune the ailerons and flaps to null out roll in cruise.

Billski
 

proppastie

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NJ
as to accuracy of the bubble in my protractor ....1/2 bubble out (bubble split by one of the lines) was 1/2 a degree on the protractor scale (line middle of 2 lines) ....I have an accurate one probably as good as todays Starret ( it is a Union out of business)....not sure about the Horror Freight one.....way to check is to set it level and rotate 180 degree. ....again the level of the bubble vs the scale on the protractor is subject to manufacturing tolerances.
 

Eugene

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May 26, 2017
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1,675
Location
Merrill, Wisconsin, USA
Well, let's remember that each design has its characteristics.

First things first. The dihedral may seem important, and you keep talking about it, but let's get realism in here. The wings fly and the fuselage goes along for the ride. That is so primary to every airplane. So our primary effort is to get the two wings to fly the same. What does that mean? Well, if one wing is 1 degree and the other is 2 degrees, and there are no other errors, the wings will try to fly at 1.5 degrees and the fuselage will have 0.5 degrees of roll angle that it will try to correct, putting in a small rolling moment. Would it be better if it were perfect? Yes, but if you are less than 0.25 in error on each, I would bet that you could never see it and other trim errors in roll will be much bigger. And if you can see it, fix it, but it won't change the way the airplane flies very much.

What would I worry over? If one wing is at different AOA than the other, one will always stall first and they will always make a rolling moment one way that you will have to correct. Ideally they will fly the same and neither wing will want to drop as you stall it. Yeah, right, but let's approach that ideal. I would worry first over having AOA IDENTICAL at the root. If you have an adjustment at the root for AOA, by all means make the AOA IDENTICAL at the root. Next I would get dihedral pretty close left to right at the forward spar - which is also the main strut. How? Water level between the roots at 0.25c, another between the tips at 0.25c, then another from one root to one tip for angle. Get the roots at the same height, then the tips at the same height, then fool with the dihedral until they are both close to your desired number, but more importantly, close to each other. Settle the bolted joints to take the clearance out of the bolts in holes and use water levels to make the side to side good. Once you have the fuselage level and the dihedral in, then you adjust the drag struts to get the same AOA at the tips. Measure this using water level from drag spar tip to tip, and I would try to make this perfect, but let's remember that your wings are flexible - a wing that consistently drops in stall can be adjusted with a little tweak of the drag strut to reduce tip AOA on that side, and a wing that shows no preference for wing drop in stall but always rolls to one side in normal flight can be fixed with a fixed tab on an aileron.

Now what features to look at? The wing is tough to grab hard points for so a lot of folks, me included, like the idea of upper surface templates. I saw and sand mine out of MDF with pin holes to hold the right and left together for shaping - goal is identical and good fit on the top of the wing. One each for root and tip on each wing. This gives you flat surfaces at the top that you can sight along for water level readings and for checking side to side.

The order in which you do all this stuff is important. Once the root is set, it is should be good. Once the dihderal is set using the main struts, it should need little fuss. Then you can play with the Tip AOA. Yeah, that might interact with the Root AOA and dihedral, so you iterate. But if you are trying to set things in a different order, it will be a long process. If there is a lot of slop in the pin joints, you might look into fixing that. And the airplane might take re-rigging after tightening the bolts and again after it is flown because stuff will settle some.

Summarizing:
  1. Make and install fittings that ride the top skins of the wings;
  2. Level the fuselage left and right, fore and aft by getting the root heights the same at 0.25c and at the drag fitting if you have an adjustment for that - that gets Root AOA trued up;
  3. Get the tip heights close at 0.25c for dihedral - this is so it looks right on the ground as much as anything else;
  4. Adjust Tip AOA to match factory setting for washout and make them IDENTICAL side to side;
  5. Revisit all readings and repeat the sequence until it stops getting better;
Remember that with a torsionally soft wing (you do have drag struts) you tune the washout to give a symmetric and predictable stall and then tune the ailerons and flaps to null out roll in cruise.

Billski
Thank you! It is unbelievable how much I did not yesterday! This will give me a lot to do and think about.
 

blane.c

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capital district NY
So, I am making conclusion that $400 laser is good enough for building houses but not really good enough to build in airplanes.
Often levels get left on their tripods in the sun with the leveling screws tightened, When the sun heats the plate the screws keep it from expanding equally and the plate warps. The level is never as accurate after that.
 

Appowner

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Mar 30, 2021
Messages
43
What Bill Ski said. Wing incidence first and foremost. Then dial the rest in as best you can and see what you have.

There are so many things that can account for a 3mm difference on a full size. Is the fuselage sitting square on the floor and is it held firmly in that position? Did you check and compare all strut fittings side to side to make sure all holes were drilled exactly the same? Or how about the mounting points on the wings and fuselage for those fittings? How easy could it be to have some measurement 1/16 inch different from side to side? And what might that do to the rest of things?
 

Eugene

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How easy could it be to have some measurement 1/16 inch different from side to side? And what might that do to the rest of things?
I did some thinking over the weekend, like I always do. But this time it was actualy productive.

Aircraft was built at the factory in Europe with 1° negative wind swept. I was the one who removed negative swept and made wings straight. I did all kinds of diagonal measurements to make sure that wing is still square two diffusers, but because I really don't know what I'm doing it's possible that I am a little bit off. It is possible that wings not exactly square to the tail boom.

I will need to do some measuring next time I am at the airport
 

Eugene

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Merrill, Wisconsin, USA
What Bill Ski said. Wing incidence first and foremost. Then dial the rest in as best you can and see what you have.
Wing incidents from left to right wing is the same and cannot be changed. Wings click into center beam that is pretty straight and square. So, I don't need to worry about that part. Fuselage incidence was changed by me by 5° in comparison to original design.
IMG_5440.jpegIMG_5758.jpegScreen Shot 2021-02-18 at 20.17.25.pngIMG_5696.jpeg
 

Heliano

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Dec 24, 2015
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Location
Campinas, SP, Brazil
Be careful when using laser or any type of lever: differences between one wing tip and the other (for a 33-feet wing span) to be within 1/4" requires an angular precision of 0.035 degrees. Does your lever have that kind of precision?
Water tube works great building bridges, houses, sailboats and aircraft.
Dihedral should not be the main concern. It is not critical. Concentrate on making the incidence angle strictly symmetrical at all wing butt lines.
 

TFF

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Apr 28, 2010
Messages
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Location
Memphis, TN
People have measured Piper Cub tail posts from center and they can be 3-4 inches right or left of center. Production tolerance. I doubt your plane is that bad, but don’t confuse production tolerance of an Eastern European homebuilt with what perfect is. Tweak for sure, but you are going down the road of making new parts for everything if you don’t set a cap on it.
 

Pops

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Built 400' tall coal fired electric power plants with everything set with a water levels. Building steel has punch marks for different elevations and everything set from that with the water levels. Little alcohol in the water helps to have less water tension for more flat reading. Also helps from the water freezing when working in the winter time.
The 3/8" ID tubing is good.
 

Aerowerx

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Marion, Ohio
Your in HVAC IIRC so you should have a vac pump? Or add a little Dawn dishwasher detergent to eliminate the surface tension to help the bubbles migrate out.
Why are bubbles a problem?

The water will level itself out if there are bubbles or not. In a water level, just compare the top surface of the water at each end of the tube?
 

BJC

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Why are bubbles a problem?

The water will level itself out if there are bubbles or not. In a water level, just compare the top surface of the water at each end of the tube?
An air bubble weighs less that the same volume of water.


BJC
 
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