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why small prop sizing on the cermark f-16's?

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Old 11-01-2007, 05:03 PM
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cottp51
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Default why small prop sizing on the cermark f-16's?

1st off guys and gals what a kick ***** web site i really enjoy it!!!!! here we go, i was all geared up to purchase the "new" cermark f-16 prop jet unfortunatley the ones cermark have in stock are missing the canopy's and landing gear and there next shipment is not due for another 60 day's or so,i did however go ahead and order the f-18 which is due around the 10th of november, anyways in my reasearch of these two birds i kept noticing guys running small prop sizes (example .91's .90's .100 running anything from 10x8 to 12x8's) that to me would be an engine killer, will these bigger engines take this kind of rpm's?, i'd also like to know why they are doing it is it because of ground clearance? i will be flying mine off a grass air field and any input will be greatly appreciated, and remember, bore holes in the sky not the ground
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Old 11-01-2007, 05:40 PM
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Default RE: why small prop sizing on the cermark f-16's?

OK, get a Jett .90LX... they LIKE those kind of rpm's > believe you me

what you get in a small prop& higher pitch is speeeeeeeeeeeeed (once it the air) but it takes longer runway

think of DF's.... LOTS rpm's & a small "prop" = speed = long smooth runways & lots of noise

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Old 11-01-2007, 07:43 PM
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Default RE: why small prop sizing on the cermark f-16's?

cottp51:

Vasek has it right on. There are Jett Sport engines, and the rest simply follow, way behind. Yes, you can mount a OS 91VRDF (ducted fan) engine and go a little faster, for a while, but the complications of installing this type of ducted fan engine are a pain. They are rear exhaust and rear carb and offer a lot of install challanges and costs. The Jett is a overall winner right out of the box, and something that will be around for a long long time of hard use. They are well worth the money in performance and long life. You will buy a number of other engines before you ware out a Jett. Wish I had found them years ago, have been running them for more than 6 years now and still a rabid fan, and a large pain to Dub Jett and Bobs 27, both are great people who understand nuts like ourselves. Stay with the LX version and black pipe where available with the 50, or 60. LX will give you more rpm with no real decline in idle or transition. ENJOY
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Old 11-01-2007, 08:08 PM
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Default RE: why small prop sizing on the cermark f-16's?

The jets are great motors i bought my first and on the test stand i was amazed by its idle (and great high rpm of course:P) also dub and bob27 are very patient and very willing to answerer all your Q's no matter how dumb they maybe. If i had the need for another one of these engiens for a speed applications i would go back to jett no question im a student and it took me 2/3 of my summer to save up for it and it was worth every penny.
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Old 11-01-2007, 11:18 PM
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Default RE: why small prop sizing on the cermark f-16's?


ORIGINAL: cottp51

1st off guys and gals what a kick ***** web site i really enjoy it!!!!! here we go, i was all geared up to purchase the "new" cermark f-16 prop jet unfortunatley the ones cermark have in stock are missing the canopy's and landing gear and there next shipment is not due for another 60 day's or so,i did however go ahead and order the f-18 which is due around the 10th of november, anyways in my reasearch of these two birds i kept noticing guys running small prop sizes (example .91's .90's .100 running anything from 10x8 to 12x8's) that to me would be an engine killer, will these bigger engines take this kind of rpm's?, i'd also like to know why they are doing it is it because of ground clearance? i will be flying mine off a grass air field and any input will be greatly appreciated, and remember, bore holes in the sky not the ground

Theres a running thread here somewhere on the F-18 which your welcome to find to help you out. Speed needs pitch 12/6,7,8's seem tobe the prop of choice on these planes with any form of a .90
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Old 11-02-2007, 09:27 AM
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Default RE: why small prop sizing on the cermark f-16's?

To more directly answer the question on prop size.....

Prop selection is all about matching the engine/aircraft/exhaust system and performance desirements.
It is not something that you can pull out of a spec sheet or find a standard for. Key is understanding the rpm an engine performs best at, what rpm band it is capable of, and then using that information to make your aircraft perform its best.

Todays typical "90" size engines can run with anything from 11x8 props up to 14x6 props all depending on how you set them up, and more importantly depending on what aircraft you are flying.

1) No, you are not going to hurt most engines allowing it to turn fast. The way to hurt an engine is a lean run, run it hot, use garbage for fuel/lubrication, or overload it so it struggles to perform. More folks kill the engines by using TOO much prop.

(yes, some engine are designed for lower rpm use... those will not usually be hurt by a smaller prop, but there will be no real return in performance trying to find the extra rpm because the engine simply will not deliver more rpm due to port timing or flowpath restrictions - in which case... prop selection is again the key - prop for the correct rpm - lots of choices)

2) Most of the 90-91 "60 size block" engines are simply over-grown "60" engines. You want to prop them similarly. So 11" and 12" props are perfect. For example, the OS 91FX runs fantastic at 13,000 rpm ground peak rpm. Stock muffler or tuned muffler... does not matter. You select a prop to hit that ground peak number. Then back off 500 rpm for flight. That engine also performs well anywhere between 11K and 14K ground peak rpm. Nice engine..... well behaved when set up properly. Worst thing people can do to it is lug it down to (example.. 9500 rpm) with a big prop... then you will hear folks complain about fuel draw, throttle response, getting hot, air bubbles.. and resort to pumps and such.

3) The F-16 and F-18 discussed here do have ground clearance limits. Turns out the 12" prop is about as big as you want to run.

4) The two aircraft come in at over 9lbs finished weight. Some closer to 10 lbs. You need a serious powerplant out front with the "right" prop.

5) Lots of experience with both airframes for speed, take off performance, and over-all flight balance to be found here. I can provide the following summary if it is helpful

OS91FX - stock muffler - APC 12x7 prop
OS91FX - Jett or ultra-thrust - 12x8 prop Alternate potentially a 11x9 or 11x10.
Magnum 91 - needs Jett-stream or ultra-thrust to perform for this application - 12x7 or 12x8 prop
Evo 100 ---- only one example I know of flying - apparently ran quite well on a 12x8 or 12x9 with stock muffler.
ST90 - stock - 12x6 or 12x7 prop (have to get rpm up)
ST90 - jett or ultrathrust muffler - 12x8 - similar in performance to the OS91, perhaps a bit lower ground rpm.
Jett 90L - 12x6 prop (14,000 + rpm)
Jett 90LX - 11x8 prop (15,000 + rpm)

Grass is generally not a problem for the aircraft. Many folks flying off of turf.

I hope this is helpful.
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Old 11-02-2007, 09:49 AM
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Default RE: why small prop sizing on the cermark f-16's?

thanks for the reply bob good info,the engine i will be using is the evo 100,i have one in my 60size p-51 and it is one heck of an engine, needless to say my mustang has endless vertical performance yet flys as docile as i want it to.
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Old 11-02-2007, 09:52 AM
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Default RE: why small prop sizing on the cermark f-16's?

man... cant find it....

someone built either an AK mig-29 or su-27 with Evo power in here...... might have been in the kit building forum.
If i recall the performance was pretty good there.
Any my experience with the Evo engines - good products, and they run very well.
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