Hi Allan

Glad to see some one else is building a 750 over here how far are you into  your build ,finally got my tail kit last week and have started building .

Would like to talk more about the rotec it is an engine of choice for me but it is about 40lbs heavier than lycoming 233 and a bit more on contential o200 still have to do more sums to see if I can make it work.

Chris Hoare

Denmark WA

Hi Chris.

i am looking at installing a rotec radial on my 750. i have done lots of research with Rotec directly and many drawings discussed with caleb at Zenith. The weight is not a real big issue. It's very close to the O-200. You certainly loose on the useful load but that's a personal choice. In all my research i've drawn many possibilities in terms of CG and thrustline position. i really like the simplicity of a radial engine, the sound, and the challenge of building a round aluminum cowling. The diameter of the engine will make the cowling a real challenge to build from scratch.

I'm not yet at that stage of installing the enfine but getting closer with every part i make -:)

i made a wood mock-up to see how it would look on the 750 and then the photoshop rendition to really have a good idea before I invest too much time and $$$$. But if you want to stick to the safest and easiest road to flying.....use a Rotax 912. They are popular, reliable and no brainer to install with all the support and videos around on this site.

Quite a different story with a Radial....LOL  we are OFF the beaten path with that one. that's what amateur building is all about !!

The reason i will use the radial is becasue i will be on floats and not on wheels. The prop clearance is or could be an issue. Rotec assures me that the 3 blade prop works just fine on the rotec radial. So with a 3 blade prop on floats the clearance is perfect.  The engine will be installed pretty close to the firewall. Those engines have a great deal of thrust, it should be great on floats. The aerodynamic will suffer becasue of the drag but i don't care.....I will fly maybe 50-75 hrs a year -:)  it's for the fun of it...otherwise i would build an RV. I initially thought of a full glass panel but i finally decided to keep it simple and more bush like looking...  a six pack instrument panel with a good GPS that's it.

Andre

hello Allen,

All I have done so far is theoretical research. i don't have the engine yet. All I'm doing is verifying the viability of installing a Radial on my 750 under construction(scratch build).

My work keeps getting in the way of building....LOL

From my research, questions and correspondence with Zenith's engineering (Caleb gerhart), it's possible to install the radial on the 750. The CG will not be an issue because the engine is placed closer to the firewall with about 8" of clearance to the back of the FW.The wight is similar to a continental O-200. 

The real problem is  the prop clearance when on wheels and the visibility forward. That is why I would not install a radial on wheels unless you are willing to extend the front fork by a FEW inches and the main landing gear or using large tires. 

For my configuration on floats...there is no real problem because of the float height installation is under my control. 

Also a point to consider is the location of the OIL tank...that remains to be worked out in my case. I haven't looked into that yet but I'm not real concerned. i will design my own oil tank to fit where I have space. 

That's the reason most people use  proven FWF available engines like the Rotax, ULpower, O-200 etc.  It's all figured out in advance by the Kit manufacturer and the operating parameter pretty much defined. POH

When using new never tried engines on the specific aircraft like the 750....there are so many variables that can make the build MUCH longer let alone flying the plane -:)

I enjoy building, fabricating  and figuring things out as much as flying...-:) 

There are multiple ways to get there:

1) Rent a plane and fly (immediate)

2) Buy a plane (faster but costly)

3) Build a kit ( 1 yr and less money)

4) Build from scratch ( x yrs, less money, flying when ? ) 

As for the CS prop?  My opinion is that's it's not required for a a Zenith 750, quite heavy and not much advantage on the cruise speed with such  a draggy aircraft.

The Radial has PLENTY of torque, i don't see an issue for take-off on floats.

If I manage to install a 2 blade on the radial...that would be awesome...the performance of the radial Rotec is at it's optimum on a 2 blade prop 76", 55" of pitch

Interesting project and i don't know of any 750 using a radial engine yet.

Andre