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Guest Ted_Thompson

HU-16 Trim vs. DC3

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I was thinking that they should behave more alike then not, but this HU16 likes to throw it's nose up...I put the DC3 trim gauge in the HU16 cockpit, just to be sure that the readings would be from the same source.I found that when at 8900' with a MAP of 46" and RPM of 2500 that both planes did about 160-170 Kias. However, to maintain level flight the DC3 settled in with about -3.7deg of pitch trim, but the HU16 came in at around -13.0deg of pitch trim.Being a layman, it looks way off kilter, but do any of you seasoned pilots (virtual or otherwise) see it that way?

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>I found that when at 8900' with a MAP of 46" and RPM of 2500>that both planes did about 160-170 Kias. However, to maintain>level flight the DC3 settled in with about -3.7deg of pitch>trim, but the HU16 came in at around -13.0deg of pitch trim.Hi,I can't speak about the HU16 (never flown it), but the DC-3 would definitely need nose down trim if you're trying to fly straight and level at almost maximum power (MAP 46", RPM 2500).Normal cruise power for the DC-3 is more along the lines of 30" MAP and 2050 RPM.Good thing those are virtual engines or they'd be wrecked :).Hope this helps.Eric

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The HU-16 has a high wing with corresponding high engine location. This will cause more nose-down pitch, requiring more negative trim.Regards,JerryH

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>The HU-16 has a high wing with corresponding high engine>location. This will cause more nose-down pitch, requiring more>negative trim.>>Regards,>JerryHhmmmm, wait I'm confused, doesn't "This will cause more nose-down pitch" mean it would make the nose drop down? Wouldn't negative trim make that worse? Or do I have something back-assward in my mind? <-quite likely.Under the above conditions, if I were to set the trim to 0 degress, the nose shoots up and the plane tries to do almost a tail stand in mid air. It pitches up until it stalls, then the nose drops and you pick up speed, then it starts all over again...With trim this can be controlled, but I was wondering if it's correct or not - to me it seems like something is goofed up in the model.

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I've been away from this stuff too long to remember all the normal sign conventions. All I was saying previously is that you need more negative lift on the tail to counteract the nose-down pitching moment caused by the engine placement. To get more negative lift on the tail, pull back on the stick and/or dial in more negative trim.If I'm right, the model is probably okay - if I'm wrong it's goofed up.JerryH

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As for excessive nose-down attitude, this results from using (way too much) power. You're fighting a tremendous amount of drag and, to the degree that this matters to you in flight simulation, burning enormous amounts of fuel and wearing out the engines. The problem therefore results not from imperfections in the flight model, but from trying to operate the aircraft in a way it wasn't designed to be operated (and wouldn't be operated in real life).For a thorough explanation of how such aircraft were/are operated, see the tutorial by "FS Aviator" at Tom Gibson's California Classic Propliners site (a certain amount of time and brainpower needed to take it all in!)http://www.calclassic.com/files/Propliner_Tutorial.zipHappy Fourth of July!Ed_Garr

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I got it from the other thread, but to clarify, the nose doesn't want to go DOWN it wants to go UP... WAAAAAYY up as in "goes up until it stalls" up.None of the "stock" planes do this, at least not the props.

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/SNIP/>straight and level at almost maximum power (MAP 46", RPM>2500).>>Normal cruise power for the DC-3 is more along the lines of>30" MAP and 2050 RPM.>>Good thing those are virtual engines or they'd be wrecked :).>>Hope this helps.>>EricNot the R-1820-82's in the HU16, for them that's exactly the max sustained ratings, well at 3500' anyway. I finally found the reference again where I got those numbers, a 1983 FAA certificate data sheet No. E-259 (like I know what THAT means...) I found it on the net when I was looking for the specs on the Wright R-1820-82 engines.

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Hi,Just for reference, you almost never fly a piston powered plane at max sustained power (METO, maximum except takeoff) unless you have an engine failure or similar. The overhaul guys would be on your case!Cruise power for *all* R-1820's is closer to the 30" MAP and 2050 RPM described above. At higher powers you will be nose down when trimmed level (i.e. the nose will want to rise).Is this aircraft designed for FS2004? If using flight dynamics designed for FS2002 you will have trim problems.Hope this helps,--Tom GibsonCal Classic Propliner Page: http://www.calclassic.comFreeflight Design Shop: http://www.freeflightdesign.comDrop by! ___x_x_(")_x_x___

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I think it started out as a 2002 model.... I don't know.I've gotten a copy of airwrench, and corrected all the geometry of the aircraft and so on.I set the power and lift scalar to 1.2 each and she seems to fly fairly well now. I think in the case of lift I'm correcting for the fact the FS9 ignores incidence, or so I've read... Power I'm not so sure. She lands well, flys well, and climbs almost exactly as described in a first hand account I found on the net. She'll now cruise around 150k at like 34" and 2000RPM, 0 pitch, and only slight negative trim.Problem now is getting up to speed... even though the thrust seems right in the air, getting from 0 to 80-90knts is a MAJOR chore... Dunno what's up with that.

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