Ontario- Canada

Hatz Classic
(Kurtis Arnold)

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(Rotec-Radial home page for Krtis Arnolds Hatz Clasic)

Kurtis Arnold's Hatz Classic Project: (RotecRadial home page for Krtis Arnolds Hatz Clasic)


I have wanted to build my own aircraft since I was 16. I spent years reading and researching trying to decide what kind of aircraft best met my wants (I mean needs). I decided that if I was going to toil for several thousand hours over 5 years, I wanted to end up with a unique aircraft. As in so many other aspects of my life, I didn't want to follow the herd. I wasn't interested in an aircraft that could get lost at Oshkosh amidst several hundred of the same type. I also admired a bygone era of grass fields and biplanes.

I started seeking a biplane with classic lines. I was interested in the traditional construction methods of metal tube, wood, and fabric. I was just about ready to order a set of Acro-sport plans, when I saw the cover of Sport Aviation with Mike Footes Hatz Classic. The Hatz Classic is cosmetic redesign of the veritable Hatz CB-1. Billy Dawson, of Texas, took the Hatz (which is rumoured to be modelled after a WACO) and rounded it off, stretched out the fuselage and gear to make it more reminiscent of a classic WACO. The result won Grand-Champion at Oshkosh and a company named Makelan Corp began marketing plans and components for the aircraft. The WACO of course is powered with a radial engine, but the Hatz Classic employed the use of a Lycoming 0-320

I had been aware of ROTEC's R-2800 since it was first mentioned in Sport Aviation, and followed an online discussion on its suitability for the Hatz. One other change to the Hatz Classic is both a gross and empty weight increase. I felt that the CB-1 was perfectly suited to the R-2800, but was sceptical that it had the punch to pull my "rounder" Hatz about. I inquired to ROTEC about the possibility of a 150 hp Variation. At the time there were no plans…

I spent the last 2 years fabricating the major assemblies from the plans, and travelled to Oshkosh last year in search of an engine. Since I began the project, most everyone that's wandered through my shop had commented on how wonderful my creation would look with a radial. I agreed, but couldn't bring myself to put a 50 year old radial on a brand new airplane that will hopefully propel me around the sky 50 years from now while in my 70's. I wandered across the ROTEC website one day and was ecstatic to find that they were looking for initial commitments for a 150 hp Radial. After a few exchanges with Jim, I took a deep breath and forwarded the deposit. For the price of a new Lycoming knock-off, I'm going to get a brand new, modern technology 9 cylinder radial, that is the perfect size, weight, and look for my Hatz Classic.

Hatz Classic

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Kurtis working on the wing assembly...


Watch out for more to come...


All of us at Rotec are excited by the prospect of seeing Kutis's Hatz project progressing towards completion.

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Upper Wings

Lower Wings


Fuselage Head On


March 2006 Kurtis Writes:

Progress on the Hatz has been slow and steady. I have completed the wings, and the structural parts of the fuselage. I'm happy that the fuse turned out to be quite straight. It's a funny thing how progress seems to be in fits & spurts. You spend a few weeks making fittings, tabs, pieces etc. and then all of a sudden they appear on the fuselage.

The version of the Hatz we're building is a "Hatz Classic" which is more rounded off than a CB-1. In addition there are some other changes, like longer landing gear, different wing tips, corrugated aluminium ailerons, and a slightly larger cockpit. Billy Dawson made these modifications to help the Hatz appear more like an F-2 WACO. With the ROTEC 3600 we're working harder to make it resemble a WACO even more. I have designed a variable incidence stabilizer trim system for two reasons; one, to take any worry about the trim effects of the lower thrust line off my mind, and two to more resemble an F-2. Also, we ordered 8.50 X 6 tires. This additional size will look good in large bubbleous wheel pants and provide the additional clearance required for the Prop.

The remaining major components to fabricate are the interplanes, fuel tank, horizontal stab, elevators, and the seats. Once those are finished the project shifts gears to the cosmetic stage. I'm looking forward to that part.

My intention at this point is to use a stock firewall from the plans and then make a "dish pan" for the engine from that. At this point we're not planning on putting a speed ring over the engine. In this way, it should show off the shiny aluminium of the engine pretty well.

The project has been constructed entirely from plans, and I have very much enjoyed the process. Unfortunately I can't seem to find any tubes right now for the 8.50 X 6 tires - otherwise the fuse would be on the gear. It seems that the tubes are back ordered every where in Canada and the US. I guess we'll be forced to be patient until April when they are expected to be back in stock. (It's not we don't have anything else to work on :)

Attached are some pictures of our progress so far. In the background of the bottom wings you can see some of the other plane I'm fortunate enough to have the chance to fly. So, with the warm weather coming, I'll have plenty to do while I'm waiting for glue to dry.

My e-mail address is below, and any prospective Hatz builders should feel free to drop me a line with any questions. Hopefully, in a few months I'll be able to submit a photograph with the wings hung the tail on, and the engine proudly displayed out front.

Blue Skies - Kurtis Arnold - HC 040 tigermoths@rogers.com


9th March 2006: Engine Arrives - "The engine is simply art. The prop is beautiful as well. ... Progress is good, and I’m so happy to have the engine here. Hopefully we’ll have it hung soon." - Kurtis Arnold

Wed 3/05/2006 - Kutis Writes: Hi Jim

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Sitting in the Hatz Cockpit areaWell, in the last month a few significant hurdles have been safely cleared.

I managed to get the landing gear finished aligned and welded on. It looks straight – I guess we’ll soon see. The tail-wheel and seats have also been constructed and installed. There’s a lot more room in the front cockpit that I expected. I have attached a picture of the first time I got to sit in our new plane. It only took 3 years to get here.

Trial MountThe tires you see installed are 8.50 X 6 as purchased from McCreary. I decided to use the larger tires for two reasons. First, this gives me the prop clearance I needed without modifying the gear. Second, old airplanes had big tires, so I think they look good. We had little problem installing the gear, and I purchased Die springs to use for the shock absorbers. We built a little squeeze press so that we could pre-load them to about 500 lbs for the empty weight of the aircraft.

R3600 Engine MountBeing as I embarked specifically on a scratch built aircraft – I decided to construct the engine mount myself. I think I spent as much time building the jug as I did fabricating the mount, but I’m happy with how it turned out. For those that are curious, I have set the thrust line 6 inches below the top longeron. In so doing the bottom of the engine is just above the bottom of the firewall on the plans, and the top of the engine lines up with the top of the aluminium cockpit top.

So, I had a goal, and managed to meet my deadline. I hung the engine on the last day of April. It was quite effortless and we were elated that everything lined up and slipped on effortlessly. I will be heading out tomorrow with the accessories to trial fit everything and verify the clearance.

The engine looks great on the fuse and has been attracting lots of attention. There were more than 10 people around when we put it on, and the next two days were consumed as visitors stopped by to inspect the installation. I measured the prop clearance with the longerons level. We have 53 3/8” from the prop hub to the floor. With the 82” prop the ROTEC furnished, that leaves me the 12” of prop clearance I was looking for. I’m intending to use a stock Hatz Classic firewall. We’ll see soon, but it would appear that a tire change, a new engine mount and cowl and an existing classic could fly with this engine. (I’ll keep you all posted)

The next job on the list is constructing the trim system. I am constructing a variable incidence stab similar to the cub’s design. So once that is constructed I can install the tail feathers.

Every day it looks a little more like an airplane!

Kurtis Arnold - Toronto, Ontario Canada

March & April 2008 Updates:

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Well time sure does fly…

Over the last 18 months my responsibilities at work have been growing. Associated with the increased responsibility seems to be a more demanding travel schedule. So, I've been working hard to fit in some building where I can.

In Canada, our homebuilts have to be inspected before they can be covered. I'm just about ready for that. I've set a personal goal to run the engine before the pre-cover inspection. In that way, I'll be ready to actually start covering when the inspection is complete.

Clear view of oil tank and air intakeThere has been some considerable progress since I last provided an update for ROTEC. The engine is mounted, the oil tank is complete. I made the decision to mount the oil tank on the engine mount. I made this decision to minimize the number of times I had to route hoses through the firewall, and to avoid the potential danger of hot oil over my passenger's knees. This decision generated some work, where a plain old square tank would have worked well behind the firewall, a more complicated tank was required to both fit under the cowling, and meet the volume requirements. I have constructed the tank from .040 5052 aluminum. Since the attached pictures were taken, the hoses have been installed, and the installation worked quite well. I happened upon a business in US called the Chassis Shop ( www.chassisshop.com ). They specialize in parts required to make race cars, and stock a number of CNC machined fitting that have been quite useful. For the oil tank, I purchased male AN nipples what were designed to be welded onto the tank. In this way, I saved having to install female welding bungs (more work) and the space required for the adapter. They sell a number of other useful things such as threaded bungs for installing rod ends in the ends of tubes, and tabs that are ready to weld on.

The engine has a dual electronic ignition system. Not wanting any single failure to turn my Hatz into a glider, I set out to design a redundant electrical system. It took some time, the design is complete and I'm about the start on its installation. It's largely based on guidance from the "Aeroelectric Connection". The system makes use of the supplied alternator, but has two batteries, an endurance bus, and a contactor bypass for the ignition. Based on my calculations, if I was to loose an alternator I would be able to operate my endurance bus for at least as long as I have gas in the tank.

3/4 view of craft.I have just finished (Friday night) the construction of the fuel tank. That was quite a job. A few years ago at Oshkosh, Billy Dawson (Hatz Classic Designer) talked about the tank, and how Jeff (the kit builder) didn't much care for building the tanks. I can see why. I welding it together myself, and while I have a nice accurate tank now, it was a LOT more work than I thought. The tank I built was designed on Billy's advice to maximize the fuel capacity. To achieve this I made the tank so that it tapered in where the doublers and wing attach fitting are, and went up and around the compression tubes in the center section. In short, the tank is within ¼" of interference to everything between the spars on the center section. Also, I welded in my fuel filler neck not in the middle, but to the side of the tank (more about that below). I have two un-vented filler necks, one in each front corner. In the middle of the tank, I will be welding a fitting on to attach a single ¼" vent.

This past fall at Brodhead Wisconsin, I found a Hatz that was powered by a 145 hp Warner radial. I spent considerable time talking with the builder, Maylan's a great guy! Anyway, after I took him for a ride in the Tigermoth, he offered me a chance to fly his Hatz. Up to this point, I'd had a total of about 6 minutes in the air in hatz, a single circuit. I spent 45 minutes enjoying his airplane. If I needed any more motivation get on with my project, this was it! Anyway, when I was finished, I put some fuel in. This is where I discovered how hard it is to get to the filler neck as designed. After consulting the internet and looking at other WACO pictures, I discovered that they too have moved the filler necks to the corner of the tanks, while leaving the vents in the center.

Engine mounted front onI have put the prop on, and I'm happy to report that my measuring worked out. With the upper longerons level, my prop is 12 ¼" from the floor. I did not extend the gear, but instead purchased 8.50X6.00 tires. I have 12" with the tires inflated, and will have 6" with a flat tire. It's worth noting that my gear is constructed from Hatz Classic plans, and I believe the CB-1 plans have shorter gear.

The engine itself is mounted so its thrust line is 5.8" below the upper longeron. My prop (purchased with the engine) is 82.25 inches in diameter. With help from Jim and Paul I measured out the CG of the Lycoming on the plans, and the Rotec. I have installed my engine as close to the firewall as I could to try to keep the CG the same. In so doing I made a little work for myself. For those fabricating your own engine mounts; pay particular attention to the location of the diagonal bracing. I ended up interfering with my fuel pump. To rectify the situation I ended up purchasing a similar pump, but one from a car with air conditioning. In this way it's tipped ahead and misses the bracing diagonals. Also, with the limited clearance from the firewall it was necessary to fabricate a rather elaborate air box. My air box is welded from 0.040 5052 and I have mounted two K&N air filters designed for a 1986 Kawasaki motorcycle. I don't have provisions for carb heat (a Canadian requirement) in the air box, and have instead purchased an electric carb heat system fro Jabiru in the UK. They have a little bock, with two electric heating elements. It is mounted to the carb, and the premise is if the carb never gets below freezing, the water can't stick. I haven't tried it yet myself, but I figure if it's passable in England, it's got to work here. :

From The RearYou may also have noticed the variable incidence trim system. Because of the realigned thrust line, and my inability to determine if this would create a substantial pitch trim change, I elected to install this system. It took quite a while to fabricate, but I'm happy with the result. I have the ability to move my horizontal stab through 7º of travel. If you're curious about the process, it was detailed in a recent Hatz Club newsletter. The most difficult part was finding someone to weave the continuous cable. Finally, I found Ty Daniels in Wisconsin who was able to rescue me, and weave the required cable (Thanks Ty). The trim system is operable from both cockpits by pulling or pushing the cable forward of back, much like an E-2 cub, or Fleet Finch.

So since these pictures where taken, I have finished the oil plumbing, and fuel tank. The horizontal stabilizer is complete with all the little details required to mount it looked after. I have most all of the components I need to start wiring now, and that's where I'm at. Once the wiring is complete I will be pushing it out into the adjacent hangar (hopefully it'll be warmer around here by then) to put the centre section on and hang the wings. I also have to form the skins and get my ailerons ready for inspection as well.

I'll try to do a better job of keeping you all up to date…

Kurtis Arnold
ROTEC powered Hatz Classic

It's amazing what a little aluminum will do to make something look like an airplane.

Turtledeck . Turtledeck

Wiring starts this weekend.

Talk with you soonrotec+Radial=R3600 Hope So! GREAT WORK!