More performance?

Group opinion recorded by the community.

Moderators: Rick, Lance Murray

Are you interested in higher performace in their AVGAS DA40?

Yes: Under $20,000 STC for a TA normalized IO360
23
30%
Yes: Small mods getting another 10 kts $10,000 or less
22
29%
Yes: IO390 (200hp) engine ($25,000)
16
21%
No: Love it the way it is
10
13%
No: I'd use another aircraft for that mission
5
7%
 
Total votes: 76
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Erik
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Re: More performance?

Post by Erik »

Charles wrote:
Erik wrote:But remember it is illegal and unsafe to run in opposite directions at the same altitude, so the assumption of one wind speed for the opposite bearing runs is incorrect if you do opposite runs at altitudes differing by 1000ft.
Just do it on a magnetic North-South track!
Ah - you are trying to trick me. Going due north or due south gives me the heeby-geebies since while I know the rule of where I am supposed to be, I get nervous that the next guy might not.

Anyway, technically FAR 91.179 - don't try to fool the flying mathematician - the rule is bearings 000 through 179 for the odds and 180 through 359 for the evens. By "through" this legal statement could be interpret as odds for 0<=angle<180 and evens for 180<=angle<000, but those half open intervals are beyond our measurement error. So I will give it to you.

Still gives me the heeby-geebies going north- south as I do when I go to Washington DC (south) to visit mom. Besides - Gary wanted a sheet full of math which I sent him. Didn't I Gary?
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Gary
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Re: More performance?

Post by Gary »

Erik wrote:
Charles wrote:
Erik wrote:But remember it is illegal and unsafe to run in opposite directions at the same altitude, so the assumption of one wind speed for the opposite bearing runs is incorrect if you do opposite runs at altitudes differing by 1000ft.
Just do it on a magnetic North-South track!
Ah - you are trying to trick me. Going due north or due south gives me the heeby-geebies since while I know the rule of where I am supposed to be, I get nervous that the next guy might not.

Anyway, technically FAR 91.179 - don't try to fool the flying mathematician - the rule is bearings 000 through 179 for the odds and 180 through 359 for the evens. By "through" this legal statement could be interpret as odds for 0<=angle<180 and evens for 180<=angle<000, but those half open intervals are beyond our measurement error. So I will give it to you.

Still gives me the heeby-geebies going north- south as I do when I go to Washington DC (south) to visit mom. Besides - Gary wanted a sheet full of math which I sent him. Didn't I Gary?
He did. It looks real but I still can't figure it out.
Gary
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Charles
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Re: More performance?

Post by Charles »

Gary wrote:
Charles wrote: I recently took my wheel pants off to prevent ice build up which invariably happens up here in the winter. I was expecting to notice a huge drop in airspeed and to look forward to next spring but even though I didn't take any accurate before-and-after measurements, I can't say I'm noticing any significant difference. That was a surprise to me.
I flew to Minneapolis in November and could not determine whay I was running 4 to 5 kts slower than usual until I remembered that the wheel fairings had been removed.
Interesting. Now I should mention that I've never flown in really warm weather without the fairings, and never in really cold weather with the fairings on, so my comparison may not be valid.
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Re: More performance?

Post by Antoine »

Just got an update from Brock's supercharger project.
They expect to testing fly in january, and the solution will be lightweight. Looks promising to me...
Antoine
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Re: More performance?

Post by Antoine »

Working on fairings for the main gear struts. I have started by calculating the drag of the current and ugly setup. it actually works out to 55 Watts. I reckon an airfoil shaped fairing would slash 60% off that.

Actually, the Cd decrease even more, but the fairing would have more frontal and wetted area. (dog owners who think that the wetted area of a wheel pant is a function of what their dogs do are WRONG!)

Even going up to 90%, the benefit is negligible ( compare 50 watts with the 100 kilowatts of engine power......) that would explain why Diamond didnt bother.

However, i believe that the draggy struts also disturb the airflow under the wing and around the main gear wheel pants, and that is not easily quantified

Also working on the horrible screws that hold the landing light assembly. these are a challenge as there is a good and obvious reason for the huge soft spacer that keeps the heads 2-3 mm above the wing surface.
And there are large gaps between the wing and cover... the cover isnt even watertight.

This lousy setup disturbs the airflow right at the leading edge, both above and below the wing and hurts at least 25 cm (10 ") of wingspan, plus the left aileron!
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Rick
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Re: More performance?

Post by Rick »

Antoine wrote:Also working on the horrible screws that hold the landing light assembly. these are a challenge as there is a good and obvious reason for the huge soft spacer that keeps the heads 2-3 mm above the wing surface.

And there are large gaps between the wing and cover... the cover isnt even watertight.

This lousy setup disturbs the airflow right at the leading edge, both above and below the wing and hurts at least 25 cm (10 ") of wingspan, plus the left aileron!
How much do you think would be gained by just covering the 'gaps' with clear tape? We just replaced our light cover (the old one was cracked), and I noticed what you mentioned - some significant space between the edge of the cover and the indentation in the wing where it sits.
Roanoke, VA (KROA)
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Kai
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Re: More performance?

Post by Kai »

Antoine wrote:Even going up to 90%, the benefit is negligible ( compare 50 watts with the 100 kilowatts of engine power......) that would explain why Diamond didnt bother.
That's exactly what I suspected.
Antoine wrote:However, i believe that the draggy struts also disturb the airflow under the wing and around the main gear wheel pants, and that is not easily quantified
There is an aerodynamic cover for the struts already. I believe it's on all XLS and at least on the new generation DA40s. Or was it only on the nose gear?
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Antoine
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Re: More performance?

Post by Antoine »

Kai wrote:
Antoine wrote:Even going up to 90%, the benefit is negligible ( compare 50 watts with the 100 kilowatts of engine power......) that would explain why Diamond didnt bother.
That's exactly what I suspected.
Antoine wrote:However, i believe that the draggy struts also disturb the airflow under the wing and around the main gear wheel pants, and that is not easily quantified
There is an aerodynamic cover for the struts already. I believe it's on all XLS and at least on the new generation DA40s. Or was it only on the nose gear?
Well I don't know. A friend of mine has an XLS, so I will check at the next occasion, but I think there is no fairing either.
The nose gear strut fairing was present on the first models (with the "fat" landing gear) but somehow disappeared on our models.
I think the nose wheel fairing is a bad job, compared to the Cirrus nose wheel (all of the fairings btw).

As to the question about how much gain by properly integrating the landing light, here my answer:

I think we should be careful NOT to seal this cavity completely. We must allow pressure compensation, because we dont know if this is provided for from the wing side. So I will leave a small gap on the lower side.
Bad flow at this point can have significant drag effects, but I don't know how much honestly.

I have bought some foam sealing tape that I will use to properly align the surface of the plexiglass cover with the underside of the wing (there is a 1 mm+ step now!). I will also remove the foam washers and make sure the screws sit very loosely. Then I will cover them with white tape, and cover the seams as well. This way the screws will not be putting too much crack strain on the plexiglass and they cannot fall off by going loose.

This will be a small gain gain, but its nice pleasant work!

If we want bigger gains we must look at the following:

Engine cooling drag and general design of the cowling (can't do)
Ugly finish of the plane at the wing root trailing adge. (can do)
Intersection drag of gear struts to wing. (can do)

In my plane, the stormscope installation and a couple of antennas are also not soooo nice...
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Jean
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Re: More performance?

Post by Jean »

Antoine,
You could also change your temp probe, remove the venturi vacuum backup and the second alternator on your aircraft.
For the cowling I have a suggestion (see pictures from contrailsfree.fr)
:lol:
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Rick
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Re: More performance?

Post by Rick »

Antoine wrote:As to the question about how much gain by properly integrating the landing light, I think we should be careful NOT to seal this cavity completely. We must allow pressure compensation, because we dont know if this is provided for from the wing side. So I will leave a small gap on the lower side.
I replaced our (awful) OEM landing and taxi lamps with the HID lamps last year, and I can tell you there is a 1/2" or more diameter hole from the lamp area, as well as a big channel between the front wing spar and the wing leading edge, both leading into the wing cavity. So completely sealing the light cover shouldn't be a problem.
Roanoke, VA (KROA)
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