Hatz Biplane Association

Here are the figures for NX1279 level using the lower wing l/e as the datum.
Right main 447 lbs @ -14.25"
Left main 457 lbs @ -14.25"
T/w 48 lbs @ 152.5"
Stagger 24"
L/E of MAC -13.2" (.55 x -24")
C/P limits of 18%-33% MAC = -4.2" to +3.3"
Arms:
Fuel -4.25"
Passenger -4.0"
Pilot 30.25"
Baggage 57.5"

Using these figures the Aircraft's EW C/G is at -5.84"
Normal loading gives C/G ranges from -1.29" fwd to 2.41" aft.
The airplane flies great, docile stall below 40 mph indicated, but plenty of elevator authority for flare.
Mark

Images of W/B form.

Thank you Mark!

Now I have confirmation that this aircraft is screwed up! Your fuselage length is 42.75" longer than mine...... Your stagger is 4.25" longer and I am assuming your gap is also greater than mine. In research I have done on biplanes I found that stagger and gap had a definite impact on lift and if too short a dimension, it was a detrimental impact! You made no mention of your chord or horizontal stabilizer dimensions, however I can see my problem!

The weight of your Hatz on the mains is similar, but the tail wheel weight on yours is 53# lighter! Just as I have said all along...... Too short and tail heavy! Also the pilot arm on my Hatz is + 41 compared to yours at + 30.25. My CG range (18% - 33%) is -0.8" to + 7.3"....... Far behind yours! Your LE of MAC is also further forward than mine by 2"...... AND, my EW CG is at station + 1.1 where yours is at sta. - 5.84! Nearly seven inches forward of mine!

Now at least I have confirmation that the bad flight characteristics are not in my head. I had calculated that increasing the size of the horizontal stab to 3300 sq." and adding three feet to the fuselage would just bring me to a tail volume ratio of 0.31. A J-3 Cub has a TVr of 0.34

Thank you again Mark!

J/C GTF

Now I'm confused........
Mark's data shows mains to tail wheel as 14.25" + 152.5" = 166.75".
Your plane measures 151".
How did you arrive at 42.75" ?

Jeff Moore

I'm with Jeff, I'm not seeing a 42" difference.
Your reduced stagger was probably an attempt to shift the MAC aft.
Also has the effect of increasing static tail weight
Have you checked your wing incidences. Might have gotten goofed up when the stagger was reduced.
Extra T/W weight is a concern. Where's your battery located?
Mark

Additional info.
My Gap is 54" (Very close)
Wing chord is 50" (This is an important difference)
114" from L/E of lower wing to L/E of horizontal.
Horizontal chord is 25" at root, 12 1/2" at last rib, 55" from root to tip. (Horizontals are almost identical)
My measurements are not exact. Just a tape measure and eyeball.....
Mark

Yes, I see I made a mistake in comparing our two sets of numbers. Interpolating from different sets of measurement points will do that. However, I don't see that as a point to pounce on in an attempt to marginalize my opinion of the problems with my Hatz. That is just petty criticism.

Mark, you are right. In all that I have read, a gap that is less than chord length is NOT desirable. Your gap exceeds your chord by 4". My gap is LESS than my chord length. Also the distance between all the leading edges on your aircraft are greater than mine. Much more balanced aerodynamically. The difference in arm between our aircraft for the pilot position is a HUGE deal.......

The battery went to the recycler years ago...... The entire electrical system including starter, alternator, cables, battery and box are gone. As well as the insane bell crank system to control the throttle and mixture. The lights, radio, unnecessary gauges and all the controls in the front cockpit are also gone. Removing that much weight off the nose is partially responsible for the W & B problem..... But it has always been a nagging feeling in the back of my head that weight was not the problem.

With the horizontal stabilizers off the aircraft and only the elevators left in place, the aircraft appears much more balanced from a side view. While it would be much easier to build a new motor mount and cowling, I fear only addressing the CG will not make this a safe aircraft. I feel I must address the aerodynamics and bring those numbers into compliance with commonly accepted knowledge. The center of pressure and the aerodynamic center of the aircraft must be fixed.

J/C GTF