Replies to This Discussion

Permalink Reply by Daniel C Hall on April 29, 2014 at 9:56pm

We got one right on here.  Let me see if I can sort it out.  I made contact with him a while ago.   Here's a video posted here of his airplane.  Notice the very cool airshock suspension.   https://www.youtube.com/watch?v=ydyWihN9NcQ  

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Permalink Reply by Daniel C Hall on April 29, 2014 at 10:16pm

Here he is:      Landon Goudreau

For what it's worth, I would consider this route as well   http://www.recpower.com/3702%20-%203%20cylinder%20-%202%20cycle.htm

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Permalink Reply by Mikhail on March 31, 2017 at 9:24am

Hello,

Did you end up going with a rotax 670 in 701?   How is it performing?

I'm considering similar powerplant as well.

Thanks

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Permalink Reply by Brad Banitt on March 31, 2017 at 10:28am

Hello,

I did install and use a 670 for a period of time.  The climb and performance were ok.  I switched to a 912 ULS and the performance is better yet, and the 912 uses less fuel and the dependability is much better. At least I feel better!  I mainly switched to the 912 for the dependability of the 4 stroke.  Hope this helps.  For me, if I can afford the difference in price, the 912 is much better overall. 

Good luck in your Build!

Brad

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Permalink Reply by Mikhail on March 31, 2017 at 12:05pm

Brad, thanks for the reply!

While you had the rotax 670, did you take your plane on long flights?  Any "high altitude" operation? 

What were the biggest problems you encountered with that engine?  I'm planning on a Warp Drive 70" three blade + 3:1 reduction. What propeller and gear ratio did you use?

I've read threads with mixed opinions about 670, but not many that were specifically installed on a ch701.

I would love to get as many details as possible :)

Mikhail

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Permalink Reply by Brad Banitt on March 31, 2017 at 2:57pm

Hi Mikhail,

I will try to give as many details as I can recall for you to make a good decision. 

• I had Rotax Rick build the engine.  I had a 3:1 gearbox  You may hear mixed reviews on Rick.  My opinion is he is really a Guru on 2 strokes and will do anything to help people as long as  you don't blame him for the bugs that happen on installs that are not his fault.  I really like Rick.  I can't imagine building and engine and shipping it off to someone who claims to know how to install it.  Seems like a lot of risk.  I am glad there are guys like him out there still willing to do it for us.  Oh, the 3:1 gearbox was ok, but a little less gear may have got my RPM's down.  It took off as short as my 912uls almost.  It doesn't pull near as good as the 912.
• As said above, you will have bugs to work out.  The 670 goes in inverted on the 701.  Not a big deal, but it ahs to be set up to be used this way.  The crank oiling is easy.  The cooling system should be easy, but people mess this up all the time.  I have worked on motors in all types of things for 35 years and I understand cooling systems well. That  being said, I found out that making the cooling system work proper was a trick.  I blew a base gasket the first hour of flying from having the stat stick without a bleed hole.  When I got the cooling system figured out it ran cool from then on.
• I lost the stator on a flight.  It literally broke.  I have never saw this before or since.  I think that must have been some Karma payback for not tipping a waitress enough some time in my life. Anyway, I got some practice working on the back of the engine.
• EGT's were not an issue for me.  I moved the needle based on weather. 
• The upside down engine floods the plugs regularly.  This is kind of a pain.  Mine did it if it sat a few days.  It was fine when I flew it a lot.  I had the fuel shut off and it still did it.
• I used the same prop as you were looking at.  I used the taper blade.  Since then I have used the square blade.  No difference I can tell.  Great prop and wonderful guy to work with at Warp.
• I used Zeniths firewall forward engine mount for the 582. Worked good.  Zenith had to build one as they don't use that set up anymore.  Took 3 weeks.  Not to bad.  Roger at Zenith remembers the 582 Zeniths so he was a great help.
• The exhaust was a pain in the butt to fit in.  Remember you can't cut up the pipe unless you know what you are doing.  You will kill the power. I had made some pipes for motorcycles so I was able to take Rotax Rick's pipe for an Avid and modify it.  It still fit like a saddle on a camel, but it performed well.  You will also need to do some fiberglass work to make the cowling fit. In hindsight maybe I could have had Zenith let me know who made the pipes for their 582's and contacted them.
• The engine will do good fuel consumption if you can run it at low RPM.  I found flying it at any real speed required around 5500 rpm or more.  At this RPM is sucks fuel at a record pace.  Easily 7-8 GPH.
• I kept myself within 100 miles of home when I had this motor.   I had to mix fuel, which I did in the wing tanks, and my engine ran 40:1 mix.  100 miles was the farthest I wanted to fly.  A couple hours and it was fuel time.
• I live at 820 feet.  The highest I remember flying was 6000 feet.  It ran reasonably well.

I should mention I have had a Geo with a raven redrive in a 701 as well.  Really did not like it.  Heavy and poor performance in my experience. My opinion is that the 670 will work fine for scooting around and having fun.  If I was going any real distance on a regular basis I would put in a UL 582 if I wanted a 2 stroke or save up and buy a 912 ULS.  I also just installed a 912 that had the Zipper big bore kits installed.  That is really a fun motor.  It is super smooth and had a large noticeable power increase over even the ULS I had.  The 670 was fun to fly, but took more maintenance and messing with to keep going. 

Hopefully my opinions don't step on anyone's toes.  I dont' usually post to the forums as I don't want to get the feed back if I should create a fuss.  I hope this helps you with your project.  I don't want to discourage you if you want a 670. I did it and it just was not the right combination for me.

Good luck with your project!

Brad

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Permalink Reply by Lawrence Bird on April 1, 2017 at 11:42am

Thanks for this -- I've always wondered about a 670 in a 701 (I have a few parts of one mothballed -- for another day) and wondered what performance might be like on a light, truly stripped, utilitarian 701...

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Permalink Reply by Jim Cates on February 16, 2018 at 9:01am

Do you still have the engine mount for the 670 ? Would you like to sell ?

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Permalink Reply by Jim Cates on February 13, 2018 at 4:23pm

Please allow me to jump in here......Building a 701 an considering the 670 as my engine of choice. 

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Permalink Reply by Mikhail on December 28, 2020 at 8:17pm

A while ago I finished my ch701 with a Rotax 670 engine, but started actively flying it only recently.

https://youtu.be/jKggs0Qy-24

It takes off short and climbs pretty well.  Before it became windy and cloudy I managed to do a few one-hour trips.

I have not done much experimenting of STOL, but feels like ground roll is <100ft.  Landings can be quite short too.

Cruise is around 80mph at 5600rpm.

Rotax 670 is installed inverted, which means the oil collects at the spark plugs if I let it sit for 2+ weeks.  The engine will not start in this case, so I have to remove 1 spark plug and clean it out with towel/compressed air. 

I have a CHT probe and two EGT probes installed. CHT is pretty stable at 155F.  One time on a hot day during climb I've seen 160F. 

EGTs are the hottest at 5600rpm - 1150F (and give best efficiency).  When I reduce power to 5000 and point the nose down, EGTs creep up to 1200, and further decrease in power brings EGTs down again.

My ch701 has a belly radiator, which helps a lot I think.

I'm building a small monitor, so I'll be able to see fuel consumption, etc..

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Permalink Reply by Carl Geisser on May 16, 2021 at 8:13am

Mikhail,

Have you done much flying with your monitor setup?

If so, what have been your findings? 

I also have a 670 in a 107 and am very interested in what you find.

My experience (130 hrs so far) is very similar to what you posted, but i have not kept very accurate information on fuel burn, I guesstimate around 5-6 gal per hour burn on mine, may be as low as 4 in cruise but would be very interested in your findings.

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