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zfehr

Navajo ("Kodiak" Shakes and Jiggles: Maybe found the pr...

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With cowl flaps closed, engines leaned, and gear retracted, I can only hold around 900 fpm at 80 knots ---- constantly. I'll send the engines in for an overhaul...L.Adamson

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Guest Dean

>I'll send the engines in for an overhaul...Maybe their due.... ;)

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Guest Allan Jones

Larry,Those are close to the climbout numbers I get after adjusting the load to lighten the nose. Trying to hold 1200 fpm was a excercise in falling.Do you think a 600-pound gorilla would fit in the rear baggage compartment? I bent the throttle levers trying to add power that isn't there!

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Guest Dean

There might be an altitude issue at work here. I tried a flight from Denver to Albuquerque in the Kodiak last night and could barely hold 800 fpm at 90 knots. ATC expected me at 19,000' 10 minutes after departure and it took me over 17 minutes to get there. Unless it is a Mac issue, I don't understand why your loadout varies. Mine is consistantly 3% default loadout and adding 50lbs. to the front bagage area balances the A/C at 0%.

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Guest Dean

Well I can confirm it is definitely an altitude problem. Apparently the lack of oxygen causes the pilot to THINK he is climbling at 1,200 fpm at 100 knots. The best I could do from SFO was 800 fpm at 100 knots. I give, the Kodiak is an underpowered slug.

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Guest Allan Jones

Dean, thanks,Runway 26 at KLWS is 1430' elev--same thing. Need a bigger rubber band!It turns out my numbers are the same as yours. I was checking after topping off tanks, plus noticed that the CG window doesn't auto-update after a change. Taking these into account, we are seeing the same thing.

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Guest andrewluck

Whilst looking for CG data on the Navajo I came upon this document which contains the Standard Operations, checklists etc for the Seneca and Navajo:http://www.vif.at/docs/OMB.pdfVery useful stuff.If anyone has any ideas about how TRI chose to calculate theat CG % value then I'd be grateful for any leads.Sans cluesAndrew Luck18 miles SW EGSH

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>Well I can confirm it is definitely an altitude problem.>Apparently the lack of oxygen causes the pilot to THINK he is>climbling at 1,200 fpm at 100 knots.That must be the problem & all our engines need an overhaul.. :)L.Adamson

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Guest spenik

Mine included! I wonder why? Can't just use the old Navajo 88 can we? :-)

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I haven't checked the engine files, but the aircraft characteristics, variable load items, fule, and wing files in the Kodiak are all identical to the Navajo 88 (except for a tiny CG shift aft in the Kodiak). I've been wanting to get into the flight models in FlyII, and this thread has pushed me. ;-)As noted above in this thread, the Navajo is a nose-heavy airplane. It has to be when you are putting 6 people and baggage in the rear. The CG range is pretty wide, too. From what I have found searching the web, the most forward limit is 120" and the aft limit is 135". Unfortunately I could not find what the datum is on the Navajo, but the above data tells you the allowable CG can vary 15". Based on my rough calculations performed against a poor 3-vied drawing I found, that's a little less than 25% of the MAC. That's a pretty big range compared to, say, an F-16 which can only vary about 15% of the MAC (but in reality it stays in the aft 10% of that).I haven't had much trouble with the Kodiak, but I haven't done much higher altitude takeoffs. I'll have to try that out. From what I've found so far, I'm inclined to think it is engine related rather than CG related.That being said, I think the the fuel CG locations and some of the wing AC locations could use some work. I examined several aircraft .wng files last night, and I can't make sense of where the outer wing ACs are coming from. On all of the aircraft, I think they are too far inboard. That would explain some of the reduced roll rate people have been talking about. I'd love to discuss this with an experienced aircraft modeler offline. :-) nick@nik2.com I'll attach a picture here of a CG and AC chart based on the Kodiak files. I wish I had a real flight manual so we could reall fix them up. (The .pdf below does not give the fuel tank CGs.) I'd also like to know if there is any way to find out what the model center is for each FlyII aircraft. Anybody know how to find that info?One more thing... ;-) The CG indicator in FlyII is next to useless. It doesn't show anything really. What I think I've found out so far is that 0% on the indicator means you are at the empty aircraft CG. So the indicator gives you and idea that you are ahead or behind the empty CG, but that's really useless information without knowing the actual CG limits of the aircraft. I also don't know how percent is being calculated. Percent of what??? Normally, this would be %MAC, but I have never seen any conventionally configured aircraft with an empty weight CG (or any CG for that matter) of 0%mac. lol With all that in mind, you can easily get a negative % on this indicator. Heck, if you modeled a Citation VII the FlyII-represented CG would always be negative as soon as you add any passengers or fuel. That aircraft is at its most aft when it is completely empty. Same holds for the single-seat F-16.The attached chart I made in excel shows that the outboard tanks are aft of the inboard tanks. Based on the shape of the Navajo wing I find that hard to believe, but then again I don't know where one tank stops and the other starts laterally. Also note that the outboard wing/aileron ACs are inboard of the outboard fuel tank CGs. This is true on all the aircraft that I checked last night, and I find that hard to believe as well. I would think that the CG of the wing fuel and the lateral distance to the AC of that wing section (with a typical trapazoidal wing) would be very close.I'll keep looking into this and try to "correct" these issues (if they are off as I think they are) with the little data I can find. I will also look into the engine files and compare to the v88. Anyone have a Navajo flight manual to answer some questions? I found one online for about $20, but I don't want to have to buy it just for this. ;-)nicknick@ nik2.comhttp://forums.avsim.com/user_files/8221.gif

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Guest andrewluck

Take a look at the pdf file mentioned a bit further down the thread. It has fuel tank CGs as well as limit graphs for different weights.From these figures, I guess the real world datum is near the tip of the nose as Forward baggage is 43" aft of datum. One thing that puzzled me is that rear baggage is 178.7" aft whilst the rear passengers are at 229" i.e. behind the rear baggage. I always though the stowage was behind the back seats.There was a CG discussion on the PMDG forum a while back. Search for CG and you'll find it.Andrew Luck18 miles SW EGSH

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Guest Dean

>I haven't checked the engine files, but the aircraft>characteristics, variable load items, fule, and wing files in>the Kodiak are all identical to the Navajo 88 (except for a>tiny CG shift aft in the Kodiak). I'm not surprised by this since Rob Young did most of the flight model work for Fly II. After my last post above I couldn't understand why I thought the Kodiak had a better climb rate than it did so I deleted the .hst file and tried a take-off from SFO with a zero flap setting. I was definitely able to maintain 1100-1200 fpm at 100 knots up to about 14,000' than it was a slow decay of climb rate at that speed. I realized then I never fly the Kodiak above that altitude. Good luck figuring out what is going on here.

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lol I must have looked at that pdf too many times last night. I completely missed the fuel CGs. Thanks. It's interesting that the outboard fuel is more aft than the inboard fuel. I guess at least the landing gear bays must eat into the front of the inboard tanks. I'm sure the datum is near the tip. I'd just like to know exactly what it is, that's all. That and knowing the model center would make this a breeze. :-)EDIT:I just got done reading through the CG thread in the PMDG forum and confirmed that indicator in Fly is basically useless unless you know the empty CG in %mac. It's a shame really. The real %mac could have been indicated if the aircraft definition files simply included an entry for the LEMAC vector from the model center. :-(100*(LEMAC - CG)/MAC would do it.nick

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Up and down like a rollercoaster! ;-) I found the problem with that pdf again tonight. The pdf refers to a "regular" Navajo, whereas the Fly aircraft is a Chieftain. The Chieftan was a stretched Navajo. It was stretched 24". It looks like they just put a plug in right behind the pilot's seat, so it should be pretty easy to adjust to the pdf. That explains why I was coming out about 2 feet off in my wing calculations last night. I guess my drawing is alright after all. :-)nick

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Guest andrewluck

Those .hst files have a lot to answer for. Deleting them is the same as getting a major done on the aircraft :-)What I haven't tried yet is automobile fuel to see if makes a difference. Usually I stick to 100LL, power with auto gas should be about 80% of the higher octane good stuff.Andrew Luck18 miles SW EGSH

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