Hatz Biplane Association

Page 8 shows the lower stab wire lug but gives little info about it, such as its material. I assumed it was welded to the lower longeron.

Looking at page 24 I would assume it is made of the same material as the other wire lugs (.090 4130) and is also 5/8" wide. Does it actually go all the way across the bottom of the fuselage and if so is it welded anywhere at all or is it just held on by the bolt for the tail spring??? It seems it would be pretty weak where the bolt hole is drilled. If this were the case I would think it would be shown in the lower left corner of page 24 between the tail spring and fuselage.

I was thinking welding a small lug to the longeron may be inadequate as it could simply "pull out" a piece of the longeron wall and break off, but a bracket similar to the attachment for the cabanes (except only one piece instead of 3) should work if welded to a section of the longeron and cross tube at this location. These could be kept short enough that they don't interfere with the tail spring or it could go all the way across and provide a pad for the tail spring to rest on.

I'd just do it "per plans" in other words "make it look like the picture" but I'm not sure what that is in this case.

Jackal,

Mine has been in place 'per plans' for 25 years. Remember that in normal flight there is down force on the stab. In both the upper and lower attachments there kind of a 'carry through' load bearing. Incidently, I added a second set of tail wires after a few years, as under certain loads I got a little shake in the leading edge of the stab.

Steve G

Don't have mine nearby to look at at the moment, but, IMHO, you would want a strap instead of a tab. The strap carries the load from the tail wire on one side to the tail wire on the other which in turn carries the loads to the top attach points on the vertical stabilizer, making a complete circle. A tab would break the circle, so to speak. One less thing to worry about as you are tightening the wires at assembly.
If you consider adding forward wires, consider a streamlined strut from the lower longeron instead of a set of wires...less drag, less expensive than streamlined wires, less visible.

MST

I intend to build "per plans" I'm just not sure from the drawing what that is.

This doesn't seem like it should be overly complicated, but somehow I'm still confused.
The "strap" that goes across to "complete the circle", does it not cross the fuselage at the same place the bolt goes through to hold on the tail spring - page 8 notes it is on c/l with that AN-6 bolt. So this strap has a large hole in it right?? It seems like there would not be much margin left after the hole was drilled. Does this strap come off when the tail spring bolt is removed, or is it welded on also. If it is welded on would not the cross tube that the tail spring bolt goes through "complete the circle? Somehow I think I must be visualizing this all wrong and making it harder than it is..... Or am I wrong about the lower stab flying wire lugs being in line with the tail spring bolt. If it is put in line with the tail spring bolt it makes a nice straight line (keeping all 4 wires "in plane" - which is good when tensioning them) when viewed from the side, from the upper wire attach on the vertical fin, down and forward through the stab spar (where the wires attach), and further down and forward to the point in line with the tailspring bolt.

Since you mentioned additional struts on the stab, I've heard about the tail moving around a bit in flight, but had also heard that the fix for that was using 3/4 x .049 longerons all the way to the tailpost and not reducing them in size as shown on the plans (at least some copies of the plans). Is there more to keeping your tail in place than that? Even with "full size" longerons, are additional stab struts still considered the Hatz way?

Sorry for being so dense, anyone got a picture???

-Jackal

Sorry no picture. I think there is a bushing welded in place where the bolt goes through the strap, so its plenty strong.

Steve G

NOTE

If you are building from the Hatz Classic planes. The 2.25" lug length is not long enough to clear the fabric when you install the wood formers, stringers and fabric. You should add at least 3/4' of an inch. This is a bad "FIX" after the fabric is on.

Michael
N838MM

The tail wheel spring attach bolt is forward of the tail post by about 6" (best guess from memory). The tail spring rides across the area where the strap would be, so the strap is actually creates a hard point at the bottom of the tail post for the tail spring to ride on. That hard point is a pivot point when the tail spring to flexes. Yes, the line up of the tail wires has to be vertical and is inline with the vertical and horizontal stab spars so that when you tension the wires, it doesn't pull the stabilizer spars forward or rearward.

Flexing of the horizontal stab leading edge has nothing to do with the longerons, other than the longerons are where we brace the stabilizer to. It is the leading edge of the stabilizer that we are trying to immobilize.
Hope this helps.

MST

Very informative and thanks for your input. As always, good information leads to more questions: Since the Vertical Fin Spar (Tailpost) is aft of the Stabilizer rear spar (at least it is on mine and I did my best to follow plans exactly) the upper flying wires on the spar slope back as they go up to the tailpost. This seems like it would cause tightening these wires to pull the stab spars back. Page 8 of the plans shows the lower flying wire lugs to be on centerline with the forward mounting bolt for the tailspring. This point is somewhat foreward of the stab spars. Actually it is at the exact distance forward that a flying wire from this point up and back to the stab spar is perfectly in line with the upper wire which runs up and back further to the tailpost. I thought this was probably on purpose so there is no "net" pull on the stab spars. It seems if the lower flying wire were attached to the lower longerons directly beneath the stab spars (which would be at a point between the forward and aft tailspring attach bolts, and also at a point on the fuselage where there were no cross tube between the lower longerons) then the lower flying wire would pull straight down on the stab spars, but the upper ones would pull up and back and this would create some "net assymetrical force".

Attaching the lower flying wire lugs at the point on the longerons adjacent the forward tailspring attach bolt keeps all 4 flying wires in the same plane (geometrical plane, not airplane). Also there is a cross tube there which originally lead to my confusion about the cross-strap shown on page 24 which would seem redundant. I don't have any intention to deviate from the plan design, but still seem unable to nail down just what that is. Should the lower flying wires attach to the longerons at a point beneath the stab spar, or at the point adjacent the forward tail spring bolt, which is forward of directly below the stab spar????

I take it also that it is your suggestion to add the lower struts braces from the forward stab spar (if its called that) down to the lower longerons? Much easier now than later. Any pointers on a good dimension (wall thickness, etc) of this material?

Thanks for your input,

-Jackal

Jackal, I had the same question, and like you found many different answers and methods. When I get a chance I'll take a picture of what I've done. I have it fabricated but not yet welded on. Basically I"ve run a strap across where the spring bolt goes. I am running the back most edge of my strap along the bottom of the bolt tube (tanget) to get a weld all the way across (I used a round tube on my bolt location per plans). In doing so I had to cut a half circle out around where the bolt busing sticks out. This accomplises several things. One it does make a strap all the way across, it also gives a weld all the way across, lastly, it gives a forward tailspring pad. It looks good sitting on my fuselage, I just have not had a chance to weld it. I'll get a pic.

Dave,

Glad to hear I'm not the only one that interpreted/mis-interpreted (still not sure) this matter the same way. It also makes sense out of the confusion of answers that there seems to be no one right answer, at least as far as what exists on Hatz's

What you describe is just like mine, round tube for a cross tube and all (per plan in other words). Since I put the tube in I've seen numerous pictures that have used a square tubing. I can see a couple advantages to that - It makes a nice flat place for the fwd tail spring pad (although its load would be pulling away from the fuselage so not sure a "solid pad" is required on the front mount) and it gives more room for the tail spring attach bolt to go through and not interfere with the brace in the middle on top of that cross tube, but making a simple cluster there and extending the tube with the bolt goes through up a bit easily solves that. Anyway, If I were doing it again I'd likely use square like many others have.

It seems to me a better place to attach the flying wires is at that fwd tail spring bolt (as seems to be clearly indicated on page 8) since it keeps all the wires "pulling in the same plane" but I've come to learn in this that many have not attached them here. I guess that's the "E" in EAA - freedom is great.