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Thread: Best 74DM pitch for short field operations?

  1. #1

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    Default Best 74DM pitch for short field operations?

    In looking through here I've seen everything from 52-58. I have a 58 and am left wanting more. How low do you go though? 52 is a bit extreme, I was thinking maybe 55 or 56 but what kind of speed loss will I have? Right now I get about 110mph indicated at 1000'MSL at 2400rpm.

    What say ye experts?

  2. #2
    Gilbert Pierce's Avatar
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    Default Re: Best 74DM pitch for short field operations?

    I had a 54". Awesome climb but burned a lot of fuel in cruise. 56" better cruise and almost as much climb as the 54".
    58" best for cruise and climb for me. Airborne in 1200' at 1800 lbs. on 80 degree day with density altitude of 2000'

    You would probably like the 54" on your short strip.

  3. #3

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    Default Re: Best 74DM pitch for short field operations?

    Gilbert, what kind of airspeed/fuel burn were you seeing?

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    Gilbert Pierce's Avatar
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    Default Re: Best 74DM pitch for short field operations?

    Quote Originally Posted by TxAgfisher View Post
    Gilbert, what kind of airspeed/fuel burn were you seeing?
    I was using the 54" on a trip to Alaska on 01 with a slicked up PA20-160 with a 61" prop, an unkown T-P and a PA28-160. My records got water damaged so I don't have the fuel burn at my finger tips. I can tell you I was using 76% power; 2450 at seal elevel and 25rpm per 1000 above sea level. We were flying 2 to 3 hour legs and I was using 2 to 3 gallons more at fill up than the PA20 and the PA28. We were probably cruising at 105 to 110 mph as the PA-20 was running about 2200 rpm and I ws typically turning 2500 to 2600 rpm. I was using considerably more fuel than they were.
    My records from that period got water damaged and can't read them. The Canadians required a flight log as I remember it so I had a note book with flight times and fuel usage. Unfortunately I cant read the data.

    With the 58". Prop and 75% power leaned, my fuel flow is 8.3 to 8.5 gph on the EI fuel flow gauge. I flight plan for 115 mph and in no wind or light wind conditions I hit that. Lycoming chart for the O-320 150 shows 9.0 gph at 75% power.
    Last edited by Gilbert Pierce; 09-18-2017 at 06:59 PM.

  5. #5

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    Default Re: Best 74DM pitch for short field operations?

    I see about 8gph perhaps a bit more with a 52" prop. I switched from a 56" prop earlier this year. Dropped my top speed by about 10mph. But it does make a difference on getting off the ground.

  6. #6

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    Default Re: Best 74DM pitch for short field operations?

    Flynfish, how significant was the the performance change in takeoff?

  7. #7

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    Default Re: Best 74DM pitch for short field operations?

    Quite noticeable actually. But I get to cheat being at sea level and having my density altitude below that much of the time. Using shortfield technique for landing and takeoff I practice on a 600ft gravel "strip" (just a chunk of the runway that I know the distances) at the home airport. I am not consistent enough when heavy to use that as the basis to go do a lot of exploring but I'm working on that. Prior to the prop change, the takeoff was considerably longer than my practice strip. One side benefit that I hadn't thought about really is since the spin-up time is shorter with the shallower prop it seems to help with precision of landings as it improves the "response time" to throttle changes. Could be my wishful imagination since I'm still learning this little beastie but was a change I noticed shortly after making the change.

  8. #8

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    Default Re: Best 74DM pitch for short field operations?

    I only have 4 inches of pitch left and I'm at 58... I'd hate to go all the way down and be stuck. Thinking about going to 55 or 56 so I could come up a tad worst case.

  9. #9

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    Default Re: Best 74DM pitch for short field operations?

    Here is a link to a video of me taking off from a 1000ft strip (several on here will recognize it) just a couple of weeks ago. Pardon the poor video quality after take-off, I obviously didn't have the mount clamped down enough so it turns to a bit of jello. But just to show T/O performance with this 52" prop. The 56" prop would be later and lower. This was with me, 3/4fuel and the normal Alaska survival kit in the back (sleeping bag, tent, camping stuff & shotgun). Measuring this on Google earth gives a bit over 500ft from where I power up to the wheels coming free. It should be finished uploading by AM, so if you click on it and it doesn't work, come back.

  10. #10
    Administrator Steve Pierce's Avatar
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    Default Re: Best 74DM pitch for short field operations?

    The Borer prop would be the best climb prop but will droop your cruise. Will also drop your fuel burn because of the lower manifold pressure. Some numbers to compare the Super 20 with a Sensenich and the McCauley Borer prop here. http://www.shortwingpipers.org/forum...20-Flies/page8

    Also remember your Type Certificate Data Sheet. It gives minimum and maximum static rpm. Each inch of pitch is worth about 50 rpm.

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