Hatz Biplane Association

Al,
Thanks for the reply about the Stearman tail. I think I'm beginning to understand the back end of the airplane. Check out this description and let me know If I understand correctly. First off any conventional aircraft with the elevator behind the wing is configured so that the center of lift or pressure of the wing is behind the center of gravity. To keep the AC stable the stabilizer/elevator pulls opposite of wing lift (down in straight and level flight) The better streamlined the Stab/elevator are in straight and level flight the less induced drag, more speed etc. a reason for having an adjustable stabilizer instead of a trim tab on the elevator, or another way of getting a wider CG range. The lifting airfoil shape of the stabilizer on the Stearman works in the same way but in this case instead pulls less down than it would if the airfoil was symmetrical, or another way of saying it, is that as the speed of the aircraft increases, the lift as the same angle of attack increases so the nose must be trimmed more nose down to maintain level flight, reducing the angle of attack. The lifting stab. means less nose down trim in this situation.

Regarding the length of the Hatz, back of the wing, the longer it is the more leverage the tail would have, the less trim force necessary to stabilize the airplane, the smaller the tail surfaces could be and the wider the CG range. I don't know how much change in length, tail surface area or shape would do to trim force or CG range. Do you agree with this line of reasoning?

My two cents.

I have collected a number of drawing sheets of the rev's prior to the current set. Why, because I'm just interested. In terms of fuselage length: You'll note on the current set of plans that Dudley changed some of the length numbers between the bays, and included the letters N.T.S (not to scale). He did this to keep from having to redraw bays, while indicating a lengthened fuselage. I have not measured the actual graphic, but I think it retains the original scale of the shorter fuselage. Or at least one version of the shorter fuselage, or.....

That fuselage drawing has given many builders some grief. The drawing is actually a projection of the fuselage frame, but some have interpreted it as a drawing that can be used to create a jig for the fuselage weldment as drawn. They weld up the fuselage with flat sides, to those dimensions, then bend in the sides, and low and behold, the fuselage gets shorter to the tailpost. Now all the cable runs to the elevator and rudder take slightly different paths, and some have reported interference with cross tubes. All these variables create a fleet of slightly different aircraft. Lauzon made some interesting mods to the baseline aircraft; I got copies of some of them a couple of years back to study.

It might be fun to have a contest at Broadhead to give an award to the most "stock" Hatz on the field. The arguements over what represents "stock" (which version of plans should be used???), and then how well they were followed, would be very informative to the current set of builders... and to the historians (me?) We'd better be prepared to award "Most Stock" to every A/C in attendence...... We might also need to have someone standing by to breakup the fist-fights....

Caasi

Good Morning fellow Hatzers…… My name is J. C. Kantorowicz. I own Hatz #3 and have spent many hours working to make my Hatz flyable. There were numerous problems including wings out of rig, a weak engine, wrong prop and insanely heavy construction. There are no plans for this Hatz, no weight and balance, basically no paperwork of any kind accompanied my purchase. All the while I have felt that the aircraft was tail heavy. Of course at first that had a lot to do with a worn out engine.

Now with a fresh O-320, wings rigged correctly and all the unnecessary weight removed……. It is really tail heavy……. Too the point I feel (and yes, I have thousands of hours of tail wheel time) it is dangerous to fly in this state. This aircraft always was in attendance at the Montana Antique Aircraft fly in at Three Forks, Mt. each year…….. But no one can recall having seen it fly in or out……. When I bought the Hatz it had @ 350 hours TTAF in @ 40 years. Proof I guess that it didn't fly well.

In calculating the Aerodynamic Center and Center of Pressure of this aircraft I find that the tail is too small and the fuselage is too short to provide any static margin. Regardless of weight and balance, it is impossible to bring this design into a commonly accepted range of gravity. Rebuilding the engine mount and moving the engine forward 7 ½ inches would solve the problem and move the CG ahead of the CP. As would rebuilding the horizontal stabilizer to a larger dimension and adding THREE FEET to the fuselage. This would barely bring the Hatz to the flying characteristics of a J3 Cub.

As I read posts on this web site I see discussion of length of fuselage and size of the horizontal stabilizer discussed…… All without any real reference to actual dimensions. I have tried to view the photographs of as many Hatz as possible in an attempt to see what others have built and are in flyable condition. Most photos however, don't give me the "square on" views I feel necessary to visually determine the problem. My EAA advisor is convinced my research is flawed, but will not give me any real help. Everywhere he has pointed me to look for answers, I find the same results……. The tail is too small and the fuselage is too short.

Help ???

J. C. Kantorowicz
Great Falls, Mt.
406-788-0483

J. C. Kantorowicz

Is it N25104 built by Rich VanDerGeest? If it is I can assure you there's nothing wrong with the fuselage length, engine mount length or tail size. This airplane was flown by numerous pilots back in the eighties with John Hatz doing most the test flying. There is there's nothing wrong with it dimensionally. I flown it myself many hours and it was a fine flying airplane.
If I were you I'd start with weighing it and run the numbers yourself, then I'd check the entire elevator control system and trim system. That has a Cub jackscrew, make sure it's going to it's limits and working in flight.

Al

Yes Al, it is that airplane. It may have flown fine before coming here to Montana where it was wrecked on its first landing at Helena in 1983 (?). I absolutely guarantee you it is not a "fine flying airplane".

I have weighed it...... twice. I have carefully measured it. I have calculated it's flying ability both aerodynamically and by weight. All of the controls work perfectly..... NOW..... They did not when I purchased it. I forgot to mention in my first post that the ailerons were also very screwed up.

When I first bought this Hatz, if I let go of the stick and had my feet off the rudder pedals..... The airplane would IMMEDIATELY roll to the left and go into a dive. It took FULL right rudder to fly straight at cruise...... Which by the way was very nose high. Initially, the trim had to be set full forward to fly at cruise. After all my work it is closer to the middle of it's operating range. I also lowered the empty weight by 230#. But lowering the empty weight has no aerodynamic effect on the AC, CP or CG range. Lowering the EW would have an effect on where within the CG range the gross weight of the aircraft falls. Sadly, as the Hatz is now, the CG range is barely three inches long when it should be eight inches long.

The tail volume ratio of this Hatz is 0.15. The minimum for a safe, statically balanced airplane is 0.3. The average aircraft range is between 0.3 and 0.6. The tail is too small and/or the fuselage is too short.

Telling me that it is a "fine flying airplane" will not help. I need to know how long a Hatz should be from the leading edge of the bottom wing to the leading edge of the horiz stab. How wide and deep the dimensions are, or the square inches of the horiz stab. It would also be helpful to know what the distance is from the firewall or leading edge of the lower wing to the prop flange. That will give me a starting point.

J/C GTF

J. C. Kantorowicz

Send me your numbers and let me look at them.
ajhatz@hotmail.com

Al

P.M. on the way.

J/C GTF

HuskyandHatz@gmail.com

I apologize for not having patience. Actually, I believe that patience is a character flaw However, I have been at this project for years now with little to no results. I sent all the numbers on this Hatz some days ago and there has been no response. I realize that people's lives do not revolve around their hobbies, but posting a question to the Aviat Husky (my real airplane) web site or discussion group receives a reply within hours. If I don't see a reply within a day, it is because I have not checked the site or my e-mail. Again, I'm sorry, but I am used to actual, ongoing discussion…….

Here are the numbers on Hatz #3. I would greatly appreciate some advice and help to get this aircraft flying safely…….

Top wing 304" long, 16,416 sq." Bottom wings 123" long each, 13,284 sq."

Chord, all wings 54"

Stagger 19.75" Gap 52.5"

Tail chord - root, 25" tip, 13.5" (last measurable point before taper to point) ½ span, 56" = 2002 sq."

Leading Edge, bottom wing to LE tail 109.5"

Mains to tail wheel, 151" Mains are 14" ahead of lower wing LE

Mains to prop flange, 47"

Weights, no fuel, no oil - L. Main, 454# R. Main, 453# Tail wheel, 101#

Total empty weight of a/c = 1008#

Weight of a/c with everything firewall forward off -
L. Main, 285# R. Main, 286# Tail, 151# = 722# airframe only

How do these numbers compare with other Hatz currently flying?

Thanks…… J/C GTF

Please verify that all the dimensions were taken with the aircraft in a level position.
I'll be able to compare to NX1279 later today.
Mark

Yes……. Dead level…… fore and aft, side to side. Plumb bob, square and long straight edge used to mark the concrete floor beneath. Measured directly off marks on the floor. Weighed with digital aircraft scales…….

J/C GTF