Zenith CH-701. What engine to use?

[FormerHangie]

The other issue with the VW is the heads can't cool well enough to support a lot of output. The later Type 1 1600s sold in the US put out a thumping 46 SAE net horsepower. You can bore and stroke the engine all you want, the Achilles heel in an air cooled engine is heat dissipation in the cylinder heads. When Porsche first started going down the the liquid cooled route, they started with the heads, just like Rotax has done with its engines. Those VW cylinder heads just don't cool well enough to get a lot of output out of that engine. Sure, you can get more than the stock car engine produces, you've got more airflow to work with, but I still don't think you can get enough to get your two place STOLplane to perform as you'd like it.

The 80 hp Rotax is about $2500 less than is the 100. Still, when those trees at the end of the runway start getting close, you'll be wishing you spent the money for the 100 hp. As the saying goes, buy quality, and only cry once. Plus, you'll get most of it back when you sell.

 

[FormerHangie]

Here's another option, the four cylinder Jabiru:

 

[docmirror]

The other issue with the VW is the heads can't cool well enough to support a lot of output.

This isn't nearly as fatal as it is in VW hi perf cars. The cooling effect of all that air in a plane rammed into the cowl at 80MPH or better really makes a heck of a difference. Also overheated heads are rarely catastrophic. They will crack, lose comp, maybe shoot a spark plug out the cowl but it'll still run on 3!

I think if I limit take off power on a VW to max RPM for 2 min it will last ok. But I just don't trust the casting/forging of materials from China. And when that shaft breaks, you are well and truly shafted.

 

[FormerHangie]

This isn't nearly as fatal as it is in VW hi perf cars. The cooling effect of all that air in a plane rammed into the cowl at 80MPH or better really makes a heck of a difference. Also overheated heads are rarely catastrophic. They will crack, lose comp, maybe shoot a spark plug out the cowl but it'll still run on 3!

I think if I limit take off power on a VW to max RPM for 2 min it will last ok. But I just don't trust the casting/forging of materials from China. And when that shaft breaks, you are well and truly shafted.

Revmaster lists a forged crankshaft on their site, you may want to ask them where it comes from. They seem to do a lot of custom stuff.

 

[Henning]

Revmaster lists a forged crankshaft on their site, you may want to ask them where it comes from. They seem to do a lot of custom stuff.

Crower will build you an ultralight billet crank for a couple grand that will take nitromethane type forces, and there are people that will machine you a set of aluminum billet cases and all the other parts for racing and you can get them to handle hundreds of horsepower, but by then, you could buy a 914.

 

[docmirror]

Revmaster lists a forged crankshaft on their site, you may want to ask them where it comes from. They seem to do a lot of custom stuff.

It comes from China. They all do. The last US stroker crank for the VW was about 2004 or so. After that, all from China. Revmaster can say all they want about the crank, but they won't say where it comes from. I know.

 

[yakdriver]

UL Power 260iL 100hp, aircooled, direct drive, electronic fuel injection, 159lbs with all accessories, $20,850mand Zenith has firewall forward packages. I'm flying a 350iS in a 750STOL and it is a great smooth running engine. Don

 

[docmirror]

OK, lets all go back and read the first post. This is not an effort in writing big checks. I was hoping for something under $10k, and so far we're flirting with $15-20k.

If it can't be done, then it can't be done.

 

[Henning]

OK, lets all go back and read the first post. This is not an effort in writing big checks. I was hoping for something under $10k, and so far we're flirting with $15-20k.

If it can't be done, then it can't be done.

You can buy a mid time O-235 on that budget.

 

[warthog1984]

OK, lets all go back and read the first post. This is not an effort in writing big checks. I was hoping for something under $10k, and so far we're flirting with $15-20k.

If it can't be done, then it can't be done.

Find a wrecked snowmobile of 900cc+. Yank the engine and pop on a reduction unit. 7500 otd.

 

[Jim Logajan]

No offense, but after seeing who's behind the Viking aircraft engines, I"m gonna pass. Hope it works out well.

Specifics are always important. I've often seen this sentiment, but when I went to read the information that was claimed to back it up, there wasn't much there that backed up their specific claims, such that they existed.

With respect to personality clashes: I don't really give a tick. Is the engineering OK or not for the engine being evaluated?

By the way, there are some others who are using the Honda Fit engine block as a base for an aircraft engine. Such as:
http://www.raven-rotor.com

 

[Henning]

There are also people using the Suzuki 3 cylinder, check with the Highlander boards. One of the former members here has on in one, but it's really been a a huge PITA.

 

[FormerHangie]

You can buy a mid time O-235 on that budget.

It's too heavy for that airframe.

OK, lets all go back and read the first post. This is not an effort in writing big checks. I was hoping for something under $10k, and so far we're flirting with $15-20k.

If it can't be done, then it can't be done.

Suitable engines for that airframe, according to the designer, are 65 to 100 hp, < 185 lbs installed weight. That gives you any of the 80 or 100 hp Rotax, Jabiru, or UL Power engines. It also includes the VW conversions, but you've eliminated them because of the crankshaft issue. A Corvair is too heavy, as is an O-190, O-200, or any Lycoming. The Rotax 582 has been installed in that airplane, but you're looking at high density altitude flying, and that's not probably not enough power.

If you're looking for a new engine, only the VW conversions fit your price range. Unless you can find a used Rotax or Jabiru, I don't think there's anything out in the marketplace for you.

 

[yakdriver]

This is where a lot of homebuilders reach a brick wall and end up quitting on the project. Remember cheap is not necessarily the least expensive way in the end. If you go with something other than what Zenith has engineered you will have to fabricate an engine mount, exhaust system, cowling and figure out baffling/cooling systems etc. It will take you a lot longer to fabricate all these systems than it takes to build the airframe. Then when you are finished will you have a reliable powerplant that actually performs as advertised? In my experience there are very few auto engine conversions that perform as advertised. Most end up heavier and put out less horsepower. Rotax 912 is a well proven performer on the 701 and there are some on the used market since they are so popular. Added to that Zenith has a firewall forward package that makes installation a breeze. I have been building and restoring airplanes for over 30 years and have built a RV7 and a Backcountry Supercub from start to finish along with several other homebuilts and restorations. Just finished a Zenith 750STOL that I did about 80% of the work on and just beginning a Supercub rebuild. I have flown auto conversions, two stroke Rotaxs and several 912 and 914 aircraft so I know what is involved. Good luck on your project and I hope you will post down the road showing us you flying it. Don