Gained 5 knots, not sure why?

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Charles
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Gained 5 knots, not sure why?

Post by Charles »

My plane is coming out of its annual. Before, I would cruise at 138ktas at 8000ft WOT at peak EGT, giving about 8.5gph (2002 model). This morning, I saw 143ktas consistently in the same conditions. My engine has 1960 SNEW.

The only significant thing that I can think of that changed at the annual is an adjustment to the nose wheel tension, which was way too low before. It is now near the top end of the spec. Coincidently, and possibly unrelated to the nose wheel tension change, I had to reduce the bend in the rudder trim tab in order to achieve coordinated straight flight.

Could it be that this simple nose wheel adjustment has resulted in less rudder correction and gave me 5 kts?
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CFIDave
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Re: Gained 5 knots, not sure why?

Post by CFIDave »

Yes.

If you previously flew with the ball out to one side because of a crooked nose gear off to one side (even when correcting with the rudder), but now are able to fly in cruise with the ball centered (without touching the rudder pedals because the nose gear is straight), you'll gain up to 5 knots.
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Charles
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Re: Gained 5 knots, not sure why?

Post by Charles »

Thanks Dave. To be clear, the ball was centered without rudder input before, but the trim tab was bent quite a bit more than now.
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MarkA
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Re: Gained 5 knots, not sure why?

Post by MarkA »

I also has to adjust the rudder trim tab (it is basically flat now) after installing a "Bret fin" on the front wheel faring and saw a 3 - 5 knot increase in speed with typical cruise settings.
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briankelly327
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Re: Gained 5 knots, not sure why?

Post by briankelly327 »

Fixing the nosewheel will definitely add 5kts.

If the nosewheel is angled to one side, then you either have to fly in a slip with one wing low, or in a skid with offset rudder to keep the plane from turning. Either way the effect is the same - the plane mashes the 140kt slipstream from the side instead of head on, causing a lot of drag. The plane naturally requires no rudder trim when the nosewheel isnt canted to a side.

I used to tighten nosewheel tension, which fixed the problem on 80% of flights. But the fin fixed it so the nosewheel is aligned 100% of the time.
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Charles
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Re: Gained 5 knots, not sure why?

Post by Charles »

So I guess I still have a few knots to gain with the Bret fin. Will look into that. Thanks for all the answers.
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Rich
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Re: Gained 5 knots, not sure why?

Post by Rich »

Charles wrote: Tue May 10, 2022 10:34 pm So I guess I still have a few knots to gain with the Bret fin. Will look into that. Thanks for all the answers.
No, but the fin is a more reliable solution to the problem. Mine has been on for years and requires no fine-tuning of the friction setting.

One of the things I've put on my plate as part of the new Diamond communication (and possibly a type club) is to either get Diamond to provide a better fairing or somehow get a long-term provider of the fin. Bret is no longer active here on DAN. I recall he no longer has a DA40 and it's unrealistic to expect him to provide these things on demand. Plus it appears that the different models of nose wheel fairings required a couple of different variants for mounting.
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Re: Gained 5 knots, not sure why?

Post by Boatguy »

Charles wrote: Tue May 10, 2022 1:26 pm My plane is coming out of its annual. Before, I would cruise at 138ktas at 8000ft WOT at peak EGT, giving about 8.5gph (2002 model). This morning, I saw 143ktas consistently in the same conditions. My engine has 1960 SNEW.
Great annual! :D
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Pilot55
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Re: Gained 5 knots, not sure why?

Post by Pilot55 »

I still have the fins and help diamond pilots. I did sale my da40 a few years back and move to a lancair for cross country flying, but I still think diamond products are one of the best flying aircraft made.
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Pilot55
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Re: Gained 5 knots, not sure why?

Post by Pilot55 »

Also, If I could get a stc on a wheel pant I would make them for DA40 pilots, but the cost to get the STC would make the wheel pant way too expensive.
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