Spar-Fusalage Attach Drawings

[Hank Jarrett]

Re: Spar-Fusalage Attach Drawings

The trick is to check your scales close to the weight they will be measuring. Having them go back to zero when the load is off is pretty useless. If you can weigh at each wheel and then get a static weight to check the scale with at that weight you can find the Tare at the weight you are measuring. You want as much accuracy as you can get at the weight you are measuring.
When i have done W&Bs in the past the biggest problem I have seen is folks not getting the plane level. Had one guy who argued with me that you could do it without leveling the plane! That WILL let you find the CG, but not the CG with the plane in the flight attitude you need to know for comparison with the limitations. It IS kind of fun to do it with the tail up and down so you can find how high up the CG is. Of course for record and legal purposes it means nothing, just fun to find.

Hank

[Joe cooper]

Re: Spar-Fusalage Attach Drawings

If your t -craft is in basically the same condition as it was when Russ Hardy flew it, it should be just fine in every respect. A person nearby you that is a t craft expert and knew Russ well, is al Zoltish in Lancaster, n.y. Who rebuilt a trophy winning t craft that I owned. You might want to contact him. He flys out of Akron n.y.

[Joe cooper]

Re: Spar-Fusalage Attach Drawings

Hank, as a new Tcraft owner I love learning from your knowledge. Probably a dumb question, but to at least get an idea if my W & B paperwork is close to accurate can I use just regular scales that people use? I know it would not be official, but maybe give an indication. My 1946 seems to fly pretty close to book numbers, granted it's a C85 and I wouldn't call the pitch force light or heavy, but I don't have any other Tcraft to compare to.

Thanks

please see my message.

[Hank Jarrett]

Re: Spar-Fusalage Attach Drawings

Your timing is "pretty good". I am going to be giving a talk to our local EAA chapter on compass swings first of the year and was thinking of doing one on W&B after that. I need to write up a Power Point presentation on W&B to dispel some common misunderstandings about W&B. Are you interested in being my Guinea Pig for the process? I can give you a "short version" followed by a "why do we do it that way" version. It is really pretty simple once you understand the physics. People get all wrapped up in things like using the right datum point and where to level when they really don't matter at all. I can do an accurate W&B on any plane with the reference point 10' in front or behind the plane and still find an accurate CG. We do it from a standardized point (the Leading Edge of the wing on a Taylorcraft) because it makes it easier for the IA to check your work. The problem with the LE of the wing is you have to worry about the sign of the moments and that is where most people make math mistakes.
To start with you need to take your scales out and put one under each tire. Don't worry about leveling or anything else, you are just weighing the plane EMPTY (from what I can find that means NOTHING in the plane that isn't attached permanently including fuel and oil). Just take all your junk out, drain the fuel and put a scale under each wheel and add up the weights. Since you won't be draining the oil unless you are changing it, just make sure you have the engine filed and know how many quarts that is. Subtract the weight of the oil and that is your empty weight. That is NOT the weights you use to check your CG!!!!
Next step is to go to a local feed and seed or meat market with certified scaled and ask them to let you put a weight within five pounds of what you measured on the scale you used on each wheel. If your tail wheel weighed at 16# test it again at 15# and make sure it is accurate. DON'T MIX UP THE SCALES! You might get away with it on the mains, but NOT the tail wheel! If your mains showed around400# each, check them with a known weight of around 400#. you DO NOT CARE if the weight is off around zero, ONLY around the weight you will be measuring! If the scales are accurate around the weights you are using, go back and level the plane (horizontal stab level with a bubble level with the tail scale on top of the magazines you use to get the tail perfect and the mains on the other two. The total weight should add up to what it was when you weighed it last time, but the individual weights WILL NOT BE THE SAME since the plane is LEVEL now.

Next you tape a plumb bob over the leading edge close to the side of the fuselage on each side and let it hang down so you can mark a point right under the leading edge on the floor on both sides. You do the same to a point under the center of the axle of each wheel (the center of the axle will be directly over the center of the contact point of the tire, which is a little hard to locate with any accuracy). You now drop a mark directly under the center of the spinner and chalk mark the center line fore and aft of the rear tire.

You DID record the weights while level, right? Now roll the plane off the scales and move it away. Snap a chalk line down the center of the planes fuselage on the floor (spinner mark to center of the tail tire mark) and between the two mains marks. Next snap a line between the two leading edge points.

The line between the leading edge points and the line between the mains should both be parallel to each other and perpendicular to the center line. If they aren't, you have a crooked plane and we have a lot more to talk about!

Measure the distance from the Center Line and the tail wheel point and the center line and mains and the Center Line and the tail wheel point and the leading edge and the center line. These two measurements are your moment arms. The weights WHEN THE FUSELAGE WAS LEVEL are your weights to apply for calculating the CG.

When you have the two lengths and the three weights it just takes a few minutes to get the CG. If anything wasn't square or perpendicular, or the scales didn't add to the same weight the second time, let me know. It can all be fixed, but don't bother going any further if something isn't right. You will be wasting your time.

It REALLY IS FUN once you have done it a few times and I have done DOZENS of W&B measurements and calculation on everything from model planes to Navy attack jets. Our planes are really easy once you understand what you are doing. Where most people get in trouble is trying to do it from a set of instructions where they just do as told and miss that there is a mistake. A quick check is that teh CG should end up about 1/4 to 1/3 back from the leading edge of the wing. I have seen guys get a calculated CG a foot in front of the LE and can't figure out what happened. Had one guy get one where the CG wasn't even IN THE PLANE!

[FAT KID]

Re: Spar-Fusalage Attach Drawings

Sorry no engineering drawings that I know of for the fuselage wing attach fittings. Were the spars ever replace during a wing recover job? It is possible that someone was trying to change the angle of incidence by repositioning the rear wing spar fitting. Not sure how long you or your plane been in Alaska but people up here will try about anything to get their plane climb faster and land slower. Cub guys up here are always screwing angle of incidence of their wings.

Ben

[smmilke]

Re: Spar-Fusalage Attach Drawings

I'd like to get this thread back on track and focused on the issue of angle of incidence. I'm in the field doing some work so I can't reply that frequently or take a look at my airplane right now. I can answer a few questions that have been posed and have some of my own as well.

Hank,
I understand what you are saying about measuring angle of incidence of the wing airfoil, first at the root then along the span, relative to the horizontal stab. I can do this when I get back, but I would like to see a picture or drawing of the incidence angle measuring setup you were talking about (the simplified method if possible). Also, I would like to get some idea of what results would confirm that the problem is in fact the rear spar attach fitting location. I can take measurements of a million things, but without criteria for conclusively identifying the problem I will not be able to fix the problem.

Dave, to address your last post,
I have not done the rigging process myself as the plane flies level. The ailerons droop slightly when the plane is parked but are up just slightly when in flight. From everything I have read this is the safest and most appropriate way of rigging the ailerons. Since the ailerons are rigged identically on each wing and each wing is washed out opposite the other I can't imagine that redoing the rigging of the wings or ailerons would be of any benefit. It may speed the plane up but at the cost of having one wing significantly heavy. This is part of the reason I suspect something needs to be rebuilt and then rerigged.
I will measure the angle of the root ribs as Hank suggested.
I will also check the bolt to bolt distances on the front struts. I'm assuming you are trying to say that one strut could effectively be longer than the other?

Ben,
Before I bought the plane I spoke to the guy that did the major rebuild (new spars, gross weight increase, recover, etc.). He made no mention of trying to adjust the angle of incidence and I am sure if he was trying to do this he would have done it on each wing. The repair tag welded to the frame tube next to this area seems like a more reasonable explanation for the discrepancy than this guy trying to change the angle of incidence of one of the wings.

Thanks for all the input so far!
Shaun

[Guest]

Re: Spar-Fusalage Attach Drawings

I'd like to get this thread back on track and focused on the issue of angle of incidence. I'm in the field doing some work so I can't reply that frequently or take a look at my airplane right now. I can answer a few questions that have been posed and have some of my own as well.

Hank,
I understand what you are saying about measuring angle of incidence of the wing airfoil, first at the root then along the span, relative to the horizontal stab. I can do this when I get back, but I would like to see a picture or drawing of the incidence angle measuring setup you were talking about (the simplified method if possible). Also, I would like to get some idea of what results would confirm that the problem is in fact the rear spar attach fitting location. I can take measurements of a million things, but without criteria for conclusively identifying the problem I will not be able to fix the problem.

Dave, to address your last post,
I have not done the rigging process myself as the plane flies level. The ailerons droop slightly when the plane is parked but are up just slightly when in flight. From everything I have read this is the safest and most appropriate way of rigging the ailerons. Since the ailerons are rigged identically on each wing and each wing is washed out opposite the other I can't imagine that redoing the rigging of the wings or ailerons would be of any benefit. It may speed the plane up but at the cost of having one wing significantly heavy. This is part of the reason I suspect something needs to be rebuilt and then rerigged.
I will measure the angle of the root ribs as Hank suggested.
I will also check the bolt to bolt distances on the front struts. I'm assuming you are trying to say that one strut could effectively be longer than the other?

Ben,
Before I bought the plane I spoke to the guy that did the major rebuild (new spars, gross weight increase, recover, etc.). He made no mention of trying to adjust the angle of incidence and I am sure if he was trying to do this he would have done it on each wing. The repair tag welded to the frame tube next to this area seems like a more reasonable explanation for the discrepancy than this guy trying to change the angle of incidence of one of the wings.

Thanks for all the input so far!
Shaun

yes

[Scott]

Re: Spar-Fusalage Attach Drawings

I have the drawing package from essco aircraft and there is nothing in there that would give you the detail you're looking for.

Having said this a degree and a half at the root, in my view, will not make a hill of beans difference to the speed, if the aircraft is otherwise rigged correctly. What the "air" is interested in is the effective angle of incidence over the entire span. So a degree and a half at the root can easily be compensated for in the remaining 16' out to the tip. Angle decreases toward the tips, this results in less wing tip losses (probably not a big concern of Taylor's) and also makes the stall more manageable.

I would first use a gps to check to see if your airspeed indicator is in the ballpark. While flying, I would stall the aircraft a couple of times to see if it has any tendency to drop a wing or any other bad habits. A properly rigged Tcraft has a completely uneventful stall, in fact if you reduce airspeed very gradually, the inboard portion of the wings will stall with the outboard portion still flying (ailerons still have authority). Anyway a stall or 3 can tell you a lot about how straight and rigged the ac really is.

Just because the aircraft flies hands off, does not mean it's flying straight. Check your slip indicator to ensure its mounted level in the aircraft ie with the aircraft exactly level laterally the ball should be in the middle. If it isn't your "straight" and level flight is actually a side slip (good way slow the airplane down).

Other things to check is your tach and everything else that might result in the engine not operating at rated power and thrust.

If all of the above checks out, follow Hanks instructions. It's not difficult to check the wing rigging, but if you need to make adjustments sometimes the adjusters in the lift and jury struts can be hard to move (maybe start spraying them with release oil now!)

My advice would be don't go anywhere near that fuselage attach point, we;ll probably never know, but I'm willing to bet it's within the factory "tolerance." No dis to Tcraft, I don't think any of the other manufacturers of this class of aircraft were much better in the day, but the bar apparently was not set particularly high when it comes to engineering/aircraft standards.

[astjp2]

Re: Spar-Fusalage Attach Drawings

Measure your wing root to the top of the fuselage and compare them. My prewar is flush, the post war airplanes are down on the side of the fuselage about an inch to make sure the angle of incidence is correct, then put a string with the fuselage level between the fwd spars and put a level on it. then do the same to the rear spars, if they are both level, then you need to see if there is a difference in the wing angles for each wing. A few numbers to compare will tell you a lot. You need to make sure your fuselage is absolutely level when you do this. While you are at it, check your gear for being aligned. I try to get 1/8" toe in at 18" forward of the axle in both taxi and flight attitudes. Good rigging really makes these airplanes fly well. Tim

[Mark Julicher]

Re: Spar-Fusalage Attach Drawings

Good stuff Hank.

I am lazier than that. It costs $60 to send my electric scales to the OEM for annual certification. BTW, if you go on line and buy scales from a race car parts dealer it costs less for 4 scales than buying 3 scales from an aircraft vendor - same brand name.

-- Rolling a big plane onto scales is trickier. With your experience you must have a some techniques for that.
-- Closing hangar door is essential if there is any breeze.
-- It sounds like perhaps you don't trust the moment arms listed in the TCDS?

[3Dreaming]

Re: Spar-Fusalage Attach Drawings

The only way to truly measure if there is a difference in the angle of the fittings on the fuselage is to place a rod through the holes in both the front and rear fittings and measure the angle. The hole is what counts, not the top of the fitting.

When you say each wing is washed out opposite the other do you mean one wing is washed in and the other washed out, or the one strut is adjusted in and the other is out? If you are truly washing a wing in to make it fly straight then you have a problem.

One thing you can do and I know it sounds simplistic, put the tail up on a barrel and stand directly behind the airplane and look at the wings. You should be able to see how the wings a twisted and if one has a different angle at the root.

[Hank Jarrett]

Re: Spar-Fusalage Attach Drawings

Shaun,

I just put a saw notch into the TE block of the "stick" to keep it in position. That way the stick doesn't rock back and forth from the airfoil curve. The piece on the front really just kept me from needing to hold it up against the wing and you really don't need it if you have some help. The manual measures from the SKIN just under the spar (NOT THE SPAR, THE SKIN!). It really doesn't matter what the incidence angle is as long as it is the same on both sides (Yes, before all the aerodynamicists jump in, I know incidence DOES matter, but not for this discussion).
When the plane is LEVEL at the stab, slip the stick up against the TE and the front cross stick will be against the lower skin under the main spar (I glued a stick perpendicular to the long one and 1 5/16" thick at the front spar wide enough to bridge two ribs). The stick should be level on both sides of the fuselage at the root. If it isn't there is a problem. I use a Harbor freight weighted protractor and just went from one side to the other at each rib making sure the measurement was the same. It wasn't, but it was pretty close and strut length trimming makes the plane fly straight. If the incidence is way off form one side to the other you will need a lot more aileron deflection to stay straight and that is a lot of drag. In a "perfect" plane the angles would be exactly the same from side to side at each rib with a smooth change of angle from root to tip. YOU ARE NOT GOING TO GET THAT but you should be within a couple of degrees. The only wings I have seen that looked PERFECT were on sailplanes. The wing angle should also be slightly more leading edge down as you move towards the tip, NEVER up!

The trailing edge of the wing DOES NOT need to be aligned with the upper longerons. Nice when it does (looks better) but there is a wood piece there that can throw it off too. To get a well rigged plane what is important is to get the sing angles right, not the alignment between the TE and Longeron.

The rigging of the ailerons slightly down on the ground and slightly up in flight is normal. The slack is what keeps the controls from being too stiff. Mine droop about 1/4" and rise to about 1/4" up in flight.

I HAVE seen struts with different lengths and that can make a real mess to rig.

I tried several ways to roll my plane onto the scales and shallow ramps worked best for rolling. Since I was working alone most of the time rolling itself was the problem and I ended up making a lever that fit into the main wheel pant brackets to just lift up one gear and slide the scale under (great for changing tires too). Mark is also right that you need the hangar doors SHUT! Just a tiny wind will change the numbers.
I also DO NOT trust the TCDS distances. They were way off on each plane I did W&B on (and there was a lot of variance between planes!) Make sure the tail leaf spring is not sticking either. If it is not curved all the way it changes the distance and if is slips while you are measuring you will have to remeasure. If your spring is sticking you need to address that too! I put some Teflon tape between the springs and mine flexes really nice now.

Hank

[N96290]

Re: Spar-Fusalage Attach Drawings

When I removed the struts to have the three that were unsealed sealed one side was adjusted all the way in and the other was way out. When I reinstalled them I started with them about centered and to get the wash out right I was back to the same one strut in and the other out. It flew good and when my IA looked at it before autographing the log he just shrugged and said looks ok to him. Now I am curious and will try to remember to measure the struts and see if I can figure out where the difference is. Mine had one strut replaced with a Univair strut by a previous owner and the other three are as far as I know original. There must have been a lot of that going around back in the 40's, TLAR engineering.

[smmilke]

Re: Spar-Fusalage Attach Drawings

I finally have time to start devoting towards the plane for the next couple weeks. I just got the plane in a hangar and have started the annual. I would like to get some airfoil angle measurements relative to the horizontal stab this weekend.
Hank, I am a little unclear on a couple parts of your measuring tool.
How long should the tool be from the TE notch to the end of the cross piece?
How wide should the cross piece be? It sounds like I should be measuring at the skin in the middle of the ribs where the fabric comes closest to the front spar. Wouldn't a cross piece (parallel to the spars and between ribs if I understand you correctly) bring the tip of the inclined stick down due to the curved nature of the fabric between ribs?
If the inclined stick runs all the way from the front spar to the TE, doesn't it push the skin under the rear spar up as there is still some slight camber between rear spar and TE?

Sorry it has taken so long for me to get back on this project!
Shaun

[Hank Jarrett]

Re: Spar-Fusalage Attach Drawings

The measuring tool goes from the TE to just ahead of the main spar. The cross piece is long enough to span at least two ribs so you are NOT measuring on the "starved horse" between the ribs (small as it usually is). My cross stick spans three ribs, the one being measured as well as one on each side. I screwed the cross stick at one end of the cross when I used it next to the fuselage, but don't think it is really necessary to measure right next to the fuselage on most planes (I think I WOULD on yours to see if the wing attach is off). The cross piece is screwed on the stick at the front spar location.
When I first did it I saw that the fore and aft stick did hit the rib, which is why the notch piece at the TE. It holds the stick down below the airfoil and teh notch is the same height as the cross stick.

Hank