Alterations to the Classic plans on the "Vintage Hatz"

[stearmoth]

Hi Hatzers,

While we are continuing our flight testing, I might tell you something about the modifikations we made to the Makelan Classic design:

I already wrote, that we lofted the fuselage lines and deck height in order to blend the Rotec R3600 with a collector shroud (like on a Stearman). The thrust line is set 6" below the center line of the top longeron. There is no down nor side thrust.
The tailplane design has been changed to elliptical (practical identical to Mehlin's Hatz planform). The tailplane is ground ajustable: previously set at 1.2° positive incidence, it has been lowered to the Classic plans set up, which is 0.6°. It even needs to be set some lower in order to have the trim tab neutral with two people on borad, half fuel and no baggage. Will see if necessary to change this again.
The fin is made separate to the fuse and set off as per plans. this seems to be abaou right. The cover between Stab and fin is aluminum (vintage style..)
The gear is as per plans, but with a plywood superstructure.
The wing tips are changed to Waco QCF design: the outmost plans rib is shifted a bit to the fuse and 2 ribs added.
The seats were bought as kits from Mark Marino and are aluminum.
A front door was added for easier access (highly recommanded).

As the beautiful Bendix wheels ( seen first on Mehlin's Hatz and last set bought from Dick Fischer) add a tremendous weight penalty (they weight about 60 lbs), we had to save weight where is has been possible in order to keep the MTO weight in the limits. Those wheels are just beautiful and the plane is easily steerable.

The following parts have been made lighter and different from the plans:

Light weight laminated spruze nose ribs
Special light weight tailplane steel ribs
Only 2 stringers on each fuse side, two on the bottom
All plywood birch, no mahagany
Aluminum compression struts (like on Mark's Bantam design) except the ones holding the aileron linkage in the bottom wings
Our own made square rolled tie rods (35% lighter than full 3/16" dia rods)
Built up aileron spars from spruce strips, uprights and plywebs

Carbon fiber center section tank: weights less than half the aluminum tank and has more capacity
Carbon fiber slave struts -> no vibration so far, weigh muss less than steel tubes!

Paint: Stits system with PPG top coat. not to much paint added!!! No wet look!

Weight and Balance:

Empty weight: 1056 lbs
Main wheels: 1000 lbs
Tail wheel: 45 lbs.
Center of gravity: just right

So far to tis theme. Please feel free to ask any questions!

Kind regards

Hans & Sam, H.C.#78, Switzerland

[dougm]

Great job you guys!

Regarding the gear, when you say it is built per plans, your gear is actually the original gear design for the O320 installation, correct? The plans were updated to include an engine mount and longer gear for the Rotec installation, but IIRC your gear was built before that change occurred so the gear you have is actually the shorter gear, is that right? If so, the shorter gear combined with the larger wheels ultimately gives you the ground clearance you need.

[stearmoth]

Hi Doug,

You are correct. We bought our plans in 2004 and they show the Classic's original lenght. This is perfect for us with the big wheels and Sam prouved that he easily can make 3-point landings!
Concerning the W&B, I will send you the required values and also the longitudinal pos. of the engine.

Hans

[Nick]

Hans & Sam, I am interested to know if you had to change your horiz stab angle. I am done my fuselage weldment and working on body formers which leads me to engine position. Unless I make the top deck 1" higher, I can't get the rotec thrust line to 6" below centre of top longeron. Did you raise the height of the top deck above original classic plans? (I also got my plans before the rotec variant)

Nick

hatz_fuze.png (196.29 KiB) Viewed 5633 times

[dougm]

FYI, if you contact Jeff Shoemake he will provide any missing plans pages (i.e. Rotec). FWIW the Rotec plans pages are for a different engine mount and longer landing gear. There's nothing in there about formers and such as it relates to the Rotec so the builder has to figure that out. Also, the updated plans specify the thrust line being 6" below the top longeron for the Rotec.

[Nick]

Thanks Doug. The drawing above has the engine at 6" as well, but I had to raise the upper deck by 1" so as not to get a bent looking fuselage.

Nick

[Bitshifter]

Doug, my classic plans shows the Rotec thrust line as 8.956 from the center of the top longeron not 6.

[dougm]

Thank you Ed for correcting me. Classic case of what I meant vs. what I said. What I meant was the thrust line was lowered about 6 inches (actually 6.956... just say 7"). The thrust line for the O320 is 2.000 below the centerline of the top longeron. The thrust line for the Rotec, as you correctly state, is 8.956 below the centerline of the top longeron.

Nick, this should address your problem. Your model has the thrustline 2.956" too high.

[stearmoth]

Hi all,

That clarifies a few uncertainities to me! I recall, that Jeff Shoemake told me that he set the thrust line about 9" below the centerline of the the top longeron, but never had the oportunity to see Jeff's plans update for the Rotec. When Doug wrote it is 6" I thought Jeff made it as low as we have it, but this is not correct.
As I wrote before, we are very happy with the engine's position in every aspect. We have the original gear lengt as per initial plans (I heard Jeff increased this as well later on), but we have the huge, large 25" dia Bedix wheels and therefore we don't have any problems with floor prop clearance (our prop dia is close to 80.7").
So,if you want to set the engine lower than we did, bee sure to have enough prop clearance for the prop you will install!
We have set our stab slightly at a negative angle (close to 0,1°) for neutral trim, however we are slightly nose heavy (which is much better than tail heavy, but in no way we could place the engine closer to the firewall!) I will measure the tail incidence and publish it here.
So, if you can lower the engine more than we did (and your prop clearance is o.k.), then it might have an effect to the tail incidence for neutral trim for cruising speed.
One thing you must consider when you are setting the vertical position of the radial engine: Visibility! The Classic fuselage lofting is made for a good streamlining for a cowled Lyc. engine. When installing a radial, then the thrust line must be set lower than for a Lyc., othervise it affects the forward visibility and looks strange in my objection! We raised the top decking that much, that it is almost as high as the pilot's back fuselage decking. We closely followed Mehlin's cockpit decking design. Of course, our forward visiblity is not as good as on John Kerr's Hatz (top decking is as per plans), but ours meets our taste for a bit a boplane fighter look...
I think you can do it eighter way, what suits you best. John Kerr's Hatz flies as well as ours and makes looooots of fuuuunnnn!

By the way: we have figured out a true cruising speed of 95 to 100 mph!

Kind regards
Hans & Sam, H.C.#78, Switzerland

[Bitshifter]

I am building with the longer gear as per the Rotec drawings and decided to lower the thrust line to 7 inches from the top longeron. This is about 2 inches above where the plans show it and like Hans and Sam have mentioned it does affect visibility. I have also lofted the fuselage and it gives more instrument panel which I like and a bigger feeling cockpit. I suspect that it will make it harder to enter the front pit so I will most likely add a door above the longeron.