John Alber & Gary Schulze (A&P IA) Hatz CB-1 Project:

John's email of 14th March 2005 Summarise the reasons in selecting a R2800.

John Writes: We are closer to deciding on a Rotec. Because of weight considerations, we think the 2800 will be best. To summarize where we are:

I bought a Hatz with a LOM 332 engine that had experienced a prop strike. Rather than tear it down, I decided to replace it. Photos of the Hatz and engine installation attached. The LOM gives the aircraft quite a long nose and hence quite a long forward moment arm. My preference is to use an engine with a shorter profile. A radial is perfect. The LOM's dry weight with accessories is 249 pounds. Its nominal horsepower is 140. It flies fine with that.

Both cost and weight push me towards the 2800.

So, some questions:

1. Drawings. Can you email a little higher res drawings of the 2800, with CG shown?

reply: CG can be viewed by clicking here. As can be seen its 5" forward of the rear edge of the mounting plate.

2. Thinking about reconfiguring. I will attach drawings of the 332. CG is at the "T" near the generator. Given the LOM's weight and CG, how might you suggest we mount the 2800? Can you use any of our existing mount?

reply: None of your existing mount can be utilised but with a custom built mount the job is easily done...

3. Mount. What is the cost of a mount from you?

reply: $950USD

4. Prop. What prop do you recommend and what is its cost? My gear has been extended 3", so I can swing a long prop.

reply: A good starting point prop, for cruise and climb is one of 76" diameter and 50" pitch. This is a wood laminated prop superbly finished and costs $950USD. With this 76" prop in place here are some interesting figures:

• Take off performance is at 110hp at 2466 prop rpm (max recommended)
• b) Cruising performance is estimate at approx. 85hp and at 2000 - 2250 prop
• max. torque 245ft lbs at the prop hub at 2250 prop rpm
  

5. Performance. With a long prop, can you give me any sense of performance? E.g. like an O-320, like something else? Hatz's work well with either O-290s or O-320s

reply: We've found the best way to answer the specific question about performance is to draw on the various discussions we've had with builders and pilots who all feel the HP is understated. Here is a distillation of these discussions:

...HP is really not a guiding factor. Lets use a comparison with a Rotax 912S and our R2800.

Can the Rotax swing a 76" prop at 2400 rpm. The answer is no it can't. But the R2800 at the same HP rating can with ease. Why? Because HP is not the guiding factor. Torque is the factor that needs to be looked at.

So what 'size flat' engine will produce the 2400rpm using a 76" prop? Answer 140 to 150 HP making the R2800's performance indicator as being significantly greater than an O290 but slightly less than an O320.

Will the R2800 fly a Hatz, Rebel, DR1 Sopwith, Luscombe.... yes it will for the same reasons that the R2800 flies the Storch (and boy that's a craft with real weight and drag!) back again to 76" prop spinning at 2400 rpm.

The other thing we need to look at is thrust - this is what we found:
In a recent static thrust test we achieved 500lbs thrust the next best was the Rotax at 260lbs (As for the 0200, Rotax and direct drive engines up to and including the O290 we out perform them all).

Making a direct comparison the R2800's performance is above an O290 and not quite that of an O320 (but not too far off from the O320)

Again its a function of torque and utilising/translating the HP available to best advantage.

...

Thanks. - John Alber - Illinois - USA

There is a definite air of excitement at Rotec with this Hatz project... This aircraft is going to be nothing short of awesome!

We're hanging out for for the after pics...