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

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Guest Allan Jones

Fire up the Navajo, and select Weigh & Balance with CG info showing. It's much too nose-heavy with the default loadout, reading about -7 (an impossible (?) value).I removed the front luggage, the co-pilot and the first row of passengers, added 200-pound passengers to each of the rear seats and 200 pounds to the rear cargo. The resulting CG reading was 35 -- more reasonable. The plane took off better and, when at cruise at 186TAS, the "jiggles" never showed up when I engaged autopilot.Prehaps with an unrealistic weight/balance condition, the AP is fighting to do the impossible. Try using loadout to correct the CG issue and see if the Navajo is better behaved.

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Guest Allan Jones

Steve,Did another test late yesterday, and the CG numbers were different (?) under the same loadout conditions. The modified loadout produced a CG value of 54 instead of 35 as I previously noted. Still, shifting the CG toward the tail seems to help. I can't help wondering if there is something wrong "deep down" in this aircraft's definition files.In Fly! 1/2K, the Navajo (speciifically, Rob Young's v88 version) was my favorite twin. Now they seem like completely different planes! In the II version, the Nav needs every bit of KLWSs 6512 feet of runway 26. and then just barely clears with lots of protests from the stall horn. I'm not a "real pilot," so I don't know if the real plane is so sluggish close to the ground.

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Allen,The Navajo isn't even close - this plane needs to be worked over big-time by someone with the skills of a Rob Young. The rest of the Fly! II aircraft are really pretty good, and the Rob Young corrections for the 'Flyhawk' and the Pilatus are a big help.I've found the initial loadout on the Navajo to be improper, so your approach certainly helps. I can verify that the aircraft is way underpowered (the v88 version was spot-on) and takes some special handling, but I have been able to get it off a 3000' runway. What flap setting are you using and when are you rotating? I can also verify that you'll need to "clean up" shortly after takeoff, level off for acceleration, then continue your climb-out.

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Guest Dean

Alan,Interesting discovery. I'll check it out and see if helps the autopilot problem.

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Guest Allan Jones

Randall,Thanks. Your procedure is quite close to what I do on take-off, including the low-angel initial climb. I set one click of flaps at power-up. I've tried getting to ~70 knots and then deploying the flaps, but it doesn't make much difference. Unless I tweak the W/B, the plane never seems to want to fly itself off the ground. I have to yank it up and that usually overcorrects and I hear that lovely stall horn.I found yesterday that the odd CG numbers are caused by the CG window needing to be re-opened to update. It doesn't update automatically when I change loadout. The -7 number is with stock loadout, inboard tanks full, outboard empty. I still get the best "feel" when the front-back CG number is about 35.I'm raising the gear as soon as I can, often with only a few feet of air between me and oblivion. I'm also going wing-smooth as soon as I feel I have control. Still makes for a slow climbout compared to the excellent v88.I, too, wish that someone could overhaul this model.

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Guest Bart

Just open the svh file and kick the CG back some, under the (CofG) tag, the last number is the front to back setting, a negative setting will move the cg toward the tail...or open the loadout file (.vld) and set what you are setting for loadout as the default, save you having to adjust it everytime.If it has a forward CG it'll take a lot to get the nose up on the takeoff run, if it'll come up at all.c ya :-waveBart flyhelp@zoomtown.comhttp://bartsflyplace.tripod.com/pics/ryans...ight/flight.gif http://bartsflyplace.tripod.com/bart_logo3.jpg

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Guest Allan Jones

Thanks Bart!I wasn't sure where those settings were hiding.As for getting the nose up, I was thinking a couple of bricks of C4.....

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>In Fly! 1/2K, the Navajo (speciifically, Rob Young's v88>version) was my favorite twin. Now they seem like completely>different planes! In the II version, the Nav needs every bit>of KLWSs 6512 feet of runway 26. and then just barely clears>with lots of protests from the stall horn. I'm not a "real>pilot," so I don't know if the real plane is so sluggish close>to the ground.Five days late with the reply, but yes, this model is sluggish and underpowered. Needs far too much attention to climb..... when even possible. About 10 years ago, I flew multi-lessons in a Piper Seminol which doesn't have the power of a real Navajo. Even a takeoff out of Afton, Wyoming with three adults & a child at over 6000' with the Seminol had much more power & climb than the FLYII Navajo/Kodiak.Like everyone else, I agree that the V88 model was far superior. It was my favorite for FLY1.

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Guest Dean

I must be the only one without issues with the Fly II Navajo, other than the autopilot jiggles. Since I don't have the real world experience of Larry or Randall, ignorance must be bliss! I have never heard the stall horn on climb-out with the Fly II Navajo and when I check the A/C specs, 1200 fpm rate of climb at 101 knots, I can hit them exactly all the way to 24,000 ft with the default loadout.

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Guest Dean

Just to add to my confusion, here is a shot of my default loadout information with C/G showing. It's the same everytime.

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Guest Colins2

RandallMany years ago when I did my multi rating in a Seneca 11, we had to carry some weight in the aft baggage compartment to get the cg within limits. I seem to recall that with just 2 front seat passengers it was outside the envelope.This was something the FAA examiner was really keen on.No surprise, as he was in the front with me!Maybe the (real) Navajo is similar? I'm not sure.Colin

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>Randall>>Many years ago when I did my multi rating in a Seneca 11, we>had to carry some weight in the aft baggage compartment to get>the cg within limits. I seem to recall that with just 2 front>seat passengers it was outside the envelope.>It's interesting to note the different flight characteristics regarding passenger weight, that you might not normally think about. For instance, in a RV6A experimental like mine, which is side by side seating in which your legs overlap the main spar (CG), but your body is slightly behind the CG...........................If flown solo with a heavier C/S prop & depending on pilot weight, you might have to carry or add some slight power during the final moment of touchdown to keep the nose from dropping to quickly. With a passenger & more weight behind the CG to compensate, you might not even have to think of it.L.Adamson

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Are you starting the flight at sea-level or something. :)Beginning at 4200'msl and engines leaned, my Kodiak/Navajo tries to fly like a "one legged dog". Just never seems to have enough power & un-normal stick forces are required to even rotate. I'm using the default loadout --- same as yours. I'd never use this bird out of Bountiful, Skypark which is just north of KSLC. Too many oil refinery towers less than a mile from the runway, for a plane that can't climb!! :)L.Adamson

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Guest Dean

>Are you starting the flight at sea-level or something. :)I never really thought about it but now that you mention it, yes. Most of my Kodiak flights have been out of sfo, dal, iad or phl. All under 700'msl. I also use auto mixture and auto fuel grade so I don't know if that would make a difference. It doesn't climb nearly as quickly as the Pilatus which I've been flying lately, but I can hit the above numbers in it. This may be the dumb question of the week but, are you guys retracting the cowl flaps on climb out? Once I'm trimmed for a steady climb I close them to the first notch.

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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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Guest

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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