Finished my streamlined strut covers yesterday.  Didn't really see much top end performance increase, maybe 1 MPH.  Slow speed handling is much happier though.  Stall speed is down and the plane happily climbs at 30 MPH now where before it got a little mushy at about 40 before.


I have the 80 HP Rotax 912 UL, 70 inch Warp Drive 3 blade with nickle leading edges set to about 8 deg.  This combination gives me 78 MPH cruising at 5200, 5400 RPM on full power climbout and a top end 5800 RPM straight and level.


Any suggestions (besides removing the slats)?


Doug M

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Comment by Shafid Khan on May 24, 2011 at 1:58am
Removing the slats adds around 12% to cruising speed and climbing performance is better also. I had to put my slats back on to keep the aircraft legal.
Comment by Doug MacDonald on May 16, 2011 at 8:31pm
Yes Nelson, plans deviations add time and often weight to the plane.  Zenith does make an aluminum strut kit for the 701 now.  As I understand it, it is essentially the same setup as the 750 but sized for the smaller plane.  They are supposed to be a bit pricey though.
Comment by nelson D on May 16, 2011 at 6:03pm
good point ,this is the reason why i won"t be installing any streamline strut covers on mine,i saw some people using aluminum struts taht come streamline ready,however they also advice not to deviated from the original plans
Comment by Doug MacDonald on May 16, 2011 at 8:12am

Yes Chris, I love my little 701.  It is performing better than I wanted except that I'd like to get just a little better cruise.  Don't we all.  Basically, if I don't get anything more out of it I'm far from disappointed.  Climb, takeoff roll, and landing are all well above my expectations.  I'm going to try and load up the engine just a bit more and see if that illusive five MPH with strut covers can be found.  I don't want to trade too much climb performance though.  The improvement from the strut covers was very noticible and I want to keep that.



Comment by Chris Aysen on May 16, 2011 at 7:55am

Doug - I think there may be something to say about airframe integrity. If you noticed Bob's post, Stu Duncan's plane does 90 mph cruise. My cruise on the same set-up (912S) is about 80 and I have about 3/4 degrees more pitch in the prop. My theory is not all airframes are the same and yes I mean 701s comparatively and 750s comparatively. I believe this may be affecting our cruise speed. A slight twist here and a little more incidence there is playing havoc on cruise speeds. I have about an average 1/8 inch twist in my horiz. stab. that may be affecting my cruise. Of course I have not mounted the strut fairings yet so that's probably not helping. I love my plane, I know it has limitations and I'm not going to build another stab. unless absolutely necessary. If I had wanted 100 mph cruise I would have chosen another plane. I think your enjoying your plane has much as I enjoy mine!!! Safe flying.


Comment by Doug MacDonald on May 15, 2011 at 9:44pm

Joe, I made my own strut covers.  I used a couple of angles boards screwed to my worktable making a wide "V", an inch and a quarter dowel (closet rod I think), and a huge "C" clamp to bend my covers.  It took a little experimenting but after trashing a couple I came up with a process that worked.  I have no shortage of scraps of 016 laying around after scratch building the plane.



Comment by Doug MacDonald on May 15, 2011 at 9:40pm

As Bob McDonald says, "You can only psh ugly so fast."  I'm thinking I might add a little pitch back into the prop to see what that does.  The 70 inch prop on the 80 hp does require a little less pitch than the 68 people normally run.  But really, if 78 is all I get, so be it, the plane flys amazingly otherwise.  I'm not really in that much of rush anyway.  Just wondering if I'd missed anything.


Oh, and I had the VGs on the bottom of the elevator before first flight.



Comment by Joseph F. Truncale on May 15, 2011 at 7:18pm

No suggestions, Doug, but I'm interested in the streamlined struts myself. Did you make your own, or buy from Raven Aviation, or....?



Comment by Bob McDonald on May 15, 2011 at 2:48pm
"You can only push ugly through the air so fast". It is what it is, and no other aircraft does STOL better on a budget. I flew Stu Duncan's CH701 with Rotax 912S / WARP prop at Can-Zac and his cruise numbers were up closer to 90 mph with the prop at 9.5 degrees.Stu's CH701 will out climb & out STOL take-off my CH750 (lighter airframe ...same HP). If you throttle back to 5000 rpm and accept a slightly lower cruise airspeed your economy fuel consumption will be around 15 liters / hr and your range increased to the maximum of your fuel tank capacity. The Rotax 912 80 hp is giving you 1 mph / hp in a high drag airframe cruise with miserly fuel consumption and 2500+ hr TBO engine. The Rotax 912 80 hp cruises my CH601HD (another high drag airframe) at 100 - 105 mph...same WARP prop & pitch. What you are up against is the airframe "terminal velocity"...."the aerodynamic wall"... the point at which the return in increased airspeed for increase fuel ceases. My CH750 hits this point at 95 mph.... it will hit 100 - 105 mph full throttle "BUT" the fuel consumption climbs from 18 litres/hr to 20 - 22 litres/hr making more wind noise in the cockpit but really yeilding very little in airspeed for the effort. There are really only 2 performance enhancments that work on either the CH701 or CH750 airframe...steamlined struts and VG's on the under side of the elevator. Enjoy flying your ugly bird !  ;>)
Comment by Jonathan Porter on May 15, 2011 at 2:31pm
Keep the slats.  Add VGs to the elevator and enjoy the best low and slow handling you can get!

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