Page 1 of 2 12 LastLast
Results 1 to 10 of 13

Thread: Faster with a Climb Prop and Cowl Flaps?

  1. #1
    Senior Member turbopilot's Avatar
    Join Date
    Feb 2010
    Location
    La Quinta, CA
    Posts
    536

    Default Faster with a Climb Prop and Cowl Flaps?

    My CC was delivered with a 55 pitch cruise prop. Over the winter I added the new cowl flaps and changed to the new metal edge prop at the same time moving from a 55 pitch cruise prop to a 54 pitch.

    Before these changes I documented my POH max power cruise speeds. I am now flying with the new prop and the new cowl flaps in the full open position (most drag). My CC is now flying 4 mph faster. Before the prop and cowl flap changes I would nominally see 88 mph on an ISA day at 1,000' MSL burning 5.1 gph. Same conditions I am seeing 92/93 mph now.

    Makes no sense. Both the prop change and cowl flap change should yield slower speeds. Wonder if there is some special stuff on these metal edge Cato props?

    BTW, I have calibrated my TAS against GPS per this procedure. My TAS is only 1 mph slower than actual based on this calibration. So this speed increase is real, not measurement error.
    Bob Anderson, CC11-00435, N94RA

  2. #2
    Senior Member RanRan's Avatar
    Join Date
    Jul 2010
    Location
    St. Clair Shores, MI
    Posts
    232

    Default Re: Faster with a Climb Prop and Cowl Flaps?

    Quote Originally Posted by turbopilot View Post
    My CC was delivered with a 55 pitch cruise prop. Over the winter I added the new cowl flaps and changed to the new metal edge prop at the same time moving from a 55 pitch cruise prop to a 54 pitch.

    Before these changes I documented my POH max power cruise speeds. I am now flying with the new prop and the new cowl flaps in the full open position (most drag). My CC is now flying 4 mph faster. Before the prop and cowl flap changes I would nominally see 88 mph on an ISA day at 1,000' MSL burning 5.1 gph. Same conditions I am seeing 92/93 mph now.

    Makes no sense. Both the prop change and cowl flap change should yield slower speeds. Wonder if there is some special stuff on these metal edge Cato props?
    What's the difference in the weight between the propellers? There has to be some variable to account for the magic.

    It's a big flywheel turning out there - between weight, pitch and torque...maybe you hit the magic number.
    Last edited by RanRan; 05-11-2011 at 02:16 PM.

  3. #3
    Administrator Pete D's Avatar
    Join Date
    Jan 2010
    Location
    Yakima, WA
    Posts
    1,158

    Default Re: Faster with a Climb Prop and Cowl Flaps?

    Did you dynamically balance the new prop installation? Tho tends to speed up the aircraft....

    Pete D

  4. #4
    Senior Member turbopilot's Avatar
    Join Date
    Feb 2010
    Location
    La Quinta, CA
    Posts
    536

    Default Re: Faster with a Climb Prop and Cowl Flaps?

    Quote Originally Posted by Pete D View Post
    Did you dynamically balance the new prop installation? Tho tends to speed up the aircraft....

    Pete D
    Not yet. Need to do it. Subjectively it is smoother than the original prop which was not balanced.

    Have you noticed any speed difference in new airplanes coming off the line with latest version of Cato props?
    Bob Anderson, CC11-00435, N94RA

  5. #5
    Senior Member Centmont's Avatar
    Join Date
    Jan 2010
    Location
    Winifred, Montana
    Posts
    257

    Default Re: Faster with a Climb Prop and Cowl Flaps?

    Theoretically with 100% efficiency, the difference in a 54 and 55 pitch inch prop is only 2 mph at 2200 rpm. Need to look elsewhere for explanations.... There is very little difference in those two props. Ralph

  6. #6
    Senior Member JohnM's Avatar
    Join Date
    Feb 2010
    Location
    The Villages, FL (06FD, Grass Roots Airpark)
    Posts
    202

    Default Re: Faster with a Climb Prop and Cowl Flaps?

    How about this thought - with the cowl flaps full open at our cruise speed, I would expect a very minor drag increase - certainly nothing on the order magnitude from the installation of tundra tires. We are just not moving fast enough.

    However, with the cowl flaps full open, I would expect the cooling drag through the cowling to be a lot less. The resulting reduction in drage will more than offset the negligable increase in drag from the open cowl flaps. Hence more speed for the expenditure of the same energy.

    Fly safe.

    john

  7. #7
    Senior Member turbopilot's Avatar
    Join Date
    Feb 2010
    Location
    La Quinta, CA
    Posts
    536

    Default Re: Faster with a Climb Prop and Cowl Flaps?

    Quote Originally Posted by JohnM View Post
    How about this thought - with the cowl flaps full open at our cruise speed, I would expect a very minor drag increase - certainly nothing on the order magnitude from the installation of tundra tires. We are just not moving fast enough.

    However, with the cowl flaps full open, I would expect the cooling drag through the cowling to be a lot less. The resulting reduction in drage will more than offset the negligable increase in drag from the open cowl flaps. Hence more speed for the expenditure of the same energy.

    Fly safe.

    john
    Something to consider. I recall Randy posting last Fall that the new cowl flaps resulted in the loss of speed based on testing at the factory.

    Of interest we are in the middle of a heavy bug season with all the rains in California. It is interesting to watch the distribution of bug hits on the cowling to see how air is moving. With the big cowl flaps in the full open position most bugs are hitting the flange portion of the cowl flaps at the edge. Looks to be very little air passing over the cowl flaps within a few inches of the cowling itself.
    Bob Anderson, CC11-00435, N94RA

  8. #8
    Senior Member RanRan's Avatar
    Join Date
    Jul 2010
    Location
    St. Clair Shores, MI
    Posts
    232

    Default Re: Faster with a Climb Prop and Cowl Flaps?

    Quote Originally Posted by JohnM View Post
    However, with the cowl flaps full open, I would expect the cooling drag through the cowling to be a lot less. The resulting reduction in drage will more than offset the negligable increase in drag from the open cowl flaps. Hence more speed for the expenditure of the same energy.
    There would be some drag improvement. But 10 square inches of reduced drag at the intakes can't be enough to add 4-5 mph in speed. Especially when you consider that the intakes were not full-draggy to begin with - they were allowing a lot of air through before the flaps were installed.
    Last edited by RanRan; 05-12-2011 at 08:14 PM.

  9. #9
    Senior Member
    Join Date
    Jan 2010
    Location
    Palm Beach, FL
    Posts
    205

    Default Re: Faster with a Climb Prop and Cowl Flaps?

    For what its worth there IS some magic in Craig's 54 stock prop that comes with our CCs. I tested for Craig last year a redesigned prop that his computer analysis said would offer 25% more thrust and not lose any speed, NOT! We lost 14 mph and the thrust and performance apeared pretty much the same. My plane #107 came with the orginal 54 without a nickle edge and I was the first to go to the Nickle Edge as our water ops when on the Amphibs was casuing the prop to erode. The Nickle edge solved the erosion problem with no difference in performance. I will also pass on that I fly with 26 Bushwheels in the Winter and the Bauman 1500s in the Summer ( also have the cowls flaps in the mid psotion all year long in Florida) and do not change the prop as it performs magnificently for both operations and we do not see ANY change in airpseed on same power setting. ( now thats not what anyone would have expected) Truly an amazing prop design and I told Carig in my humble opinion hes got it just right. He is also a delight to work with and totally stands behind his work. Best Gary

  10. #10
    Senior Member JohnM's Avatar
    Join Date
    Feb 2010
    Location
    The Villages, FL (06FD, Grass Roots Airpark)
    Posts
    202

    Default Re: Faster with a Climb Prop and Cowl Flaps?

    Quote Originally Posted by RanRan View Post
    There would be some drag improvement. But 10 square inches of reduced drag at the intakes can't be enough to add 4-5 mph in speed. Especially when you consider that the intakes were not full-draggy to begin with - they were allowing a lot of air through before the flaps were installed.
    I believe that since cowl flap users are seeing a significant oil temp drop, the airflow through the cowling is significantly improved hence less cooling drag. Since we cannot actually see how much air is going through the cowling, we have to rely on secondary indicators such as oil temp or CHT.

    If memory serves me, the original post detailed changes in 2 parameters so it will be difficult to attribute how much of a speed change came from what adjustment.

    JM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •