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zfehr

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

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Guest andrewluck

>>The Chieftan was a stretched Navajo. It was stretched 24". That's something I hadn't realised.I can't understand why TRI decided to calculate CG as they did. One thing I did try was moving the "Model Centre - Design CG" distance from 1.7 to 1.0. With my regular loadout I ended up with the nosewheel off the ground :-) A value of about 1.2 seems to work better but I haven't looked to closely yet.Andrew Luck18 miles SW EGSH

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Guest Dean

>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.I actually tried Jet fuel B something or another, I can't remember the actual name. It fired right off and performed about the same. Makes me think the fuel grade function isn't implemented in Fly II although I haven't tried the automobile grade to see if it would knock. :)

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Guest spenik

Really? I tried all the fules with all the planes and found some interesting results. Only the pistons can run on 100LL to automobile fule. as it gets progressively higher in grade so does the idle RPM. Only the Turbines can run Jet fule, I unfortunetly did not knowtice a difference between Jet A, Jet A1, Jet B, Jet B plus and so forth.

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Guest Dean

Your right. I just check this again and I now realize I have had the "use fuel grade" setting's effect on the sim backwards.

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Guest andrewluck

Found the following on Usenet:"There are really only two types of Jet fuel used worldwide, "narrow cut " Jet-A1 which is used for almost all civilian aircraft, and Jet-B, the "wide-cut" ( includes some of the gasoline fraction as well as the kerosine fraction ) fuel used by the military. Most engines are designed to handle both, and the varying specification names are mainly historical, however ( AFAIK ), all civilain passenger aircraft use Jet-A1 worldwide. During the last two decades the only divergence has been in the changes of freezing point, as the original -50C maximum specification was really only required for a few high ltitude long-distance routes ( eg over Himalayas ), and that a elaxation to -47C would be acceptable, with the ocassional need to modify flight plans to avoid cold air. That reduction was estimated to increase the global availablity of Jet-A1 by almost 10%, thus keeping the prices down. There is now also provision in the Jet-A1 specification for carriers and suppliers to negotiate the freezing point. Jet A is similar to Jet A-1 except that the maximum freezing point is -40C, and so it is not commonly used internationally.There are a large number of specification that are variants of Jet-A1, with anti-icing additives, static dissipators, and ( more recently ) differing freezing points for some regional products, but they are all essentially Jet-A1 and are compatible with each other. The military also have special versions of kerosine, the widecut specification was originally designed to maximise yield of jet from crude oil ( up to 40% ) which could be in short supply during wars, and also to have excellent low temperature properties ( - 60C maximum freezing point ) for global operational use.There are other military kerosines, eg for safety reasons, aircraft carriers use a high flash point fuel, minimum FP=60C, versus 38C for Jet-A1. There is no flash point limit for Jet-B, but it will be much lower.Essentially today there are only two common types, Jet-A1 and Jet-B, each of which is covered by multiple specifications.Jet-A1 = AVTUR = NATO F-35, and ( with slightly differing static dissipating additive related specifications ), = AVTUR/FSII, Nato F-34, US JP-8. Jet A is identical to Jet A1, except for freezing point specification.Jet-B = AVTAG/FSII = Nato F-40 = US JP-4The less common high flash aircraft carrier fuel is AVCAT/FSII = Nato F-44 = US JP-5. Bruce Hamilton"Andrew Luck18 miles SW EGSH

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Guest

I wonder what he means by civilian passenger aircraft. When I was working at Cessna 4+ years ago, we had to do some analysis on some of the Citations using Jet-B because our potential customer required it. I forget where it was, but I think it was in what was formerly the USSR. I remember going through the initial planning for those studies because Jet-B was widely used in that area of the world because of the constant cold temperatures. Maybe it has changed over the past four years, though.US fighter jets don't use JP-4 or JP-5 anymore. They stopped several years ago. JP-4 was so volatile that refueling was always dangerous, and I know the mass properties engineers at Vought hated having to do pump-down weighings on the F-8's over there. And for anyone interested, the SR-71 ran a modified JP-5/8...I think it was dubbed JP-7, but I'd have to check on that again. It just had an additive to raise the flashpoint, and they would run with it mixed with straight JP-8 if they needed to. The fuel situation used to be so complex, but now it's just JP-8 (for the military).The fuel requirements for the aircraft in FlyII are defined in the engine files. Here is the section from flyhawk.ngn: -- Fuel Grade Performance Data -- -- Fuel Grade Data -- -- Grade Name -- AVGAS_100LL -- Power Factor -- 1.0 -- Damage Factor -- 1.0 -- Fuel Grade Data -- -- Grade Name -- AVGAS_100 -- Power Factor -- 0.99 -- Damage Factor -- 1.01 -- Fuel Grade Data -- -- Grade Name -- AVGAS_80 -- Power Factor -- 0.85 -- Damage Factor -- 2.0 -- Fuel Grade Data -- -- Grade Name -- AUTOMOTIVE -- Power Factor -- 0.80 -- Damage Factor -- 2.0 nick

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Guest spenik

Interesting! So what about The PC-12? What is the Power and damedge factor diference between Jet A and the other Jets?

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Guest

Well, I've got to get to bed, so I'm not going to look tonight. You can open the PC-12 pod file with the podviewer and extract the .ngn file for it. Then just open it in a text view and you should see something similar to what I posted above.nick

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Nick,The visual model for the Kodiak is definitely a Navajo B model with the Panther conversion (wingtip extensions and flat engine nacelles). If the flight model matches up with the visual model this would only have the 310 horsepower turbocharged lycomings. The engines in the visual model are not counter-rotating either. Piper made a C/R version of the Navajo with counter-rotating propellers, 325 horsepower lycomings and baggage compartments behind the engines. The Chieftan was a longer aircraft (I can't recall if it was 24" or 36"), my father owned the first one delivered to the west coast. This model had an extra window compared to the regular bodied Navajo, the baggage behind the engines, counter-rotating propellers and 350 horsepower lycomings. I recall that when he bought it his pilot Larry Perkins and he re-wrote the POH, with higher rotation speeds, no flaps on take-off, for safer engine out performance. I'm going to try to look into some of the files for this aircraft to see if I can up the horsepower, cause it doesn't fly anywhere near what I remember.Zane


Dr Zane Gard

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Sr Staff Reviewer AVSIM

Private Pilot ASEL since 1986 IFR 2010

AOPA 00915027

American Mensa 100314888

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