Negative pitch for level flight?

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shortspecialbus
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Negative pitch for level flight?

Post by shortspecialbus »

Hi all,

I decided to take the cherokee out for a spin last night for the first time in quite a while, definitely the first time since P3Dv4. I noticed during my flight that the aircraft had what I'd consider a negative pitch in order to maintain level flight. I was flying from NZWR to NZTT (via AA, if anyone cares) with real world weather from ASP4, just below the yellow line on the airspeed indicator, so around 125kts or so at 3500ft MSL. Winds were a slight tailwind from the right, 6kts. The attitude indicator indicated that I was flying with about 3-5 degrees pitch down, and the view out the front window seemed to confirm it.

I don't recall flying around level with a negative pitch before with flaps retracted. However, it might be normal in the Cherokee due to a very efficient wing or perhaps the wing chord is angled upwards more than I'd have expected or something, and I'm just not remembering it. Is this typical for the Cherokee? Plane was loaded with 1 pilot, 1 passenger, (180#, 120# respectively), no baggage, and full wing tanks.

Apologies if I'm using incorrect terminology here or grossly misunderstanding something. I really need to get around to reading Stick and Rudder.

Thanks,

-stefan

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Nick - A2A
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Re: Negative pitch for level flight?

Post by Nick - A2A »

Hi Stefan - sounds like something a bit fishy is going on if you're pitched down by up to 5 degrees for level cruise. I'd say that with my (P3Dv4) Cherokee installation, there might be a slight nose down attitude in cruise, but probably not more than a degree or so unless I'm carrying very little fuel. I certainly don't think the Hershey Bar wing can be described as "very efficient" at any rate. (The Cherokee glides rather like the proverbial housebrick! :mrgreen: )

You mention ASP4, so one possibility might be that's it's modelling some vertical (upward) movement of air that's creating the effect.

Cheers,
Nick

shortspecialbus
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Re: Negative pitch for level flight?

Post by shortspecialbus »

Nick M wrote:Hi Stefan - sounds like something a bit fishy is going on if you're pitched down by up to 5 degrees for level cruise. I'd say that with my (P3Dv4) Cherokee installation, there might be a slight nose down attitude in cruise, but probably not more than a degree or so unless I'm carrying very little fuel. I certainly don't think the Hershey Bar wing can be described as "very efficient" at any rate. (The Cherokee glides rather like the proverbial housebrick! :mrgreen: )

You mention ASP4, so one possibility might be that's it's modelling some vertical (upward) movement of air that's creating the effect.

Cheers,
Nick
It seemed excessive to me as well, hence the post. I'll try another flight and see if I can get some screenshots and maybe shed light on it. It's possible that it's ASP4, however it maintained it for the entire cruise, and usually weather stuff is a bit more localized than that. Certainly can't rule it out, though! I'll try to get an update in here later today.

Thanks,

-stefan

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Nick - A2A
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Re: Negative pitch for level flight?

Post by Nick - A2A »

An excuse for a little flight in the Cherokee is always good Stefan, so I did a quick test of my own. Here's the result with much the same weight and balance and airspeed that you describe. As you'll see, the aircraft is pitched down by rather less than a degree. (You can actually read the AoA at top left: it's -0.3°.)

This was without wheel fairings and so on fitted I should add. With all the speed mods bolted, on the AoA was closer to -1°.

Image
(Click on image for full size version.)

Cheers,
Nick

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DHenriques_
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Re: Negative pitch for level flight?

Post by DHenriques_ »

shortspecialbus wrote:Hi all,

I decided to take the cherokee out for a spin last night for the first time in quite a while, definitely the first time since P3Dv4. I noticed during my flight that the aircraft had what I'd consider a negative pitch in order to maintain level flight. I was flying from NZWR to NZTT (via AA, if anyone cares) with real world weather from ASP4, just below the yellow line on the airspeed indicator, so around 125kts or so at 3500ft MSL. Winds were a slight tailwind from the right, 6kts. The attitude indicator indicated that I was flying with about 3-5 degrees pitch down, and the view out the front window seemed to confirm it.

I don't recall flying around level with a negative pitch before with flaps retracted. However, it might be normal in the Cherokee due to a very efficient wing or perhaps the wing chord is angled upwards more than I'd have expected or something, and I'm just not remembering it. Is this typical for the Cherokee? Plane was loaded with 1 pilot, 1 passenger, (180#, 120# respectively), no baggage, and full wing tanks.

Apologies if I'm using incorrect terminology here or grossly misunderstanding something. I really need to get around to reading Stick and Rudder.

Thanks,

-stefan

Normal nose attitude for the Cherokee in level flight should be with the nose below the horizon. The angle of incidence coupled with the angle of attack are the two main components in this equation. Naturally the aircraft gross weight is a factor as well and that will act to fine tune the exact angle of attack the wing will seek at any given time.
You can easily check for your nose attitude being correct by cross checking with your instruments. Pin the altimeter then check your ADI. Pin the altimeter and that will show you the nose attitude for level flight at your present gross weight.
I fly our A2A Cherokee all the time and from experience instructing in and flying the real one I've found no problem with the level flight attitudes if that helps in any way.

Dudley Henriques

shortspecialbus
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Re: Negative pitch for level flight?

Post by shortspecialbus »

I'm loading up the plane right now to do some testing, but one thing in your screenshot that stands out is your RPM. Mine was between 2300-2400 depending on the precise moment in order to hold that airspeed. Yours is considerably more. I'm wondering if something mucked up my aircraft.cfg. I do have a couple different gauges, for an older-style attitude indicator as well as airspeed in knots. I wonder if I managed to screw something up when I set that up.

At any rate, loading now for some testing.

-stefan

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Nick - A2A
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Re: Negative pitch for level flight?

Post by Nick - A2A »

shortspecialbus wrote:(...) but one thing in your screenshot that stands out is your RPM. Mine was between 2300-2400 depending on the precise moment in order to hold that airspeed.
If you've got various additions such as the wheel fairings fitted Stefan, I imagine that could explain some of the discrepancy in RPM. Of course, any 'unauthorised' mods to the aircraft.cfg could be an explanation too, but simple gauge replacements shouldn't be an issue as far as I'm aware.

Definitely worth testing without real world weather connected though.

Cheers,
Nick

shortspecialbus
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Re: Negative pitch for level flight?

Post by shortspecialbus »

Ok - I cannot reproduce this. I stuffed the AoA into the TextInfo so I could see exactly, and it's floating right around -1, which is where I'd expect it to be. Attitude Indicator also looks fine, as does the view out the window.

I think we can chalk it up to a weather program anomaly, pending any evidence to the contrary. I still have a considerably lower power setting than you, but that doesn't necessarily mean anything. (Edit: makes sense, re: speed fittings.)

-stefan

Edit, for fun:
Image

Seems fine now. (another edit, since imgur's compression munged it - here's the original size: https://i.imgur.com/iaTbeom.png

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Nick - A2A
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Re: Negative pitch for level flight?

Post by Nick - A2A »

shortspecialbus wrote:I think we can chalk it up to a weather program anomaly, pending any evidence to the contrary.
Yeah, I'd suspect some sort of large scale updraft effect in the weather engine or something along those lines.

Cheers,
Nick

shortspecialbus
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Location: C29

Re: Negative pitch for level flight?

Post by shortspecialbus »

Thanks guys!

-stefan

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