Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

jett 40 qm engine

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Old 07-20-2007, 12:29 PM
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izzy
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Default jett 40 qm engine

can anyone shed light on this before i go fly tommorow

can the qm40 jett engine take a apc 8.8 prop x 7.0 ( the ines used on q500 planes

reason is i am deciding tonight wether to put a rossi40 with tuned pipe or the qm40 engine on a lanier predator 2 ARF

open for all suggestions

thanks
izzy
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Old 07-20-2007, 12:37 PM
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Ed Smith
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Default RE: jett 40 qm engine

In the interests of safety do not use that prop on that engine. The Jett Q40 engine is meant for use in Q40 Pylon Racing. AMA rules set 422. In that rules set there is a specific set of rules for the allowable propellor. Basically the only prop allowed is the APC Carbon Prop. Read the rule for full details. The reason is that the grey props may not stand up to the power of any Q40 engine.

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Old 07-20-2007, 12:54 PM
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izzy
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Default RE: jett 40 qm engine

will the qm40 prop pull the q500 decently ,that is my actual question, will i get good top end speed ?
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Old 07-20-2007, 01:52 PM
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Mike Connor
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Default RE: jett 40 qm engine

I do not have actual experience with what you are doing but I do not think the Q-500 airframe is clean enough for the small CF props. I also doubt the engine would pull the load of the larger props to the engines designed rpm range.

But I think you should do it so we all would know.
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Old 07-20-2007, 02:20 PM
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daven
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Default RE: jett 40 qm engine

I personally wouldn't run a gray APC prop over 21,000, I am not sure what RPM you would get with the 8.8" x 7 prop, but I would think it would be a bit more than 21,000.

These props were just not designed for that type of RPM, and I would definately not suggest trying one.

I would suggest trying a 8x6 Zinger wood prop, or take a 9x6 Zinger and sand about an 1/8" off the TE of the prop (narrow the blade). Then coat with thin CA, light sand and polish, and then balance.
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Old 07-20-2007, 03:26 PM
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Default RE: jett 40 qm engine

Daven

I see Dave is not overly bussy at todays practice (assume he is in Min.) to keep up with the gang. Good timming here. Now obviously I'm not going t make it to this weekends race, don't even have a Q-500 in flying condition or decent Q-500 engine in the cabinet. Lets thnik a little about Tuson 08, and your second place thought process public embraceemt. Am thinking seriously of putting something togeather just to harass the gang a little in the inturm and respond to your sly challange. O wish you to to take a few things into consideration regarding giving a REASONABLE HANDICAP giving the following as a basis. 1. Have not flown a triangle cource in almost 40 years. 6'-4" against poor little shriveled 5'-8". Theory based on havilng 8" of flight advantage on each 3 directions. Something like 8X3=24 X laps add 24" time handicap. (I do the math) Aged senior of 73 against youthfull 40's. Home made thingy complying with the rules against a full out composit airframe. Any used older Jett or Nelson engine I am able to buy at auction, cheep, against new LS Nelson. Rapidly diminishing eyesight from developing cataracts from eye exam 7-16-07. As we begin negociations, I estimate that a reasonable handicap of 10 seconds at the finish line would be sporting on your part. You will also avoid the reputation of beating up on a poor old defenceless man who probably wont even be able to get it up (the airplane). Lozer buys dinner. Think about it after the weekend. If you won, overall, I give now, maby.
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Old 07-20-2007, 06:49 PM
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Default RE: jett 40 qm engine

IIRC, APC says their competition series [$3.95] gray props are safe up to 190,000 divided by the diameter. This means that a 8 inch prop is OK up to 23,750 rpm.
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Old 07-21-2007, 02:13 AM
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Default RE: jett 40 qm engine

see this thread post #939

http://www.rcuniverse.com/forum/m_30...47/key_/tm.htm
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Old 07-21-2007, 07:31 AM
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Default RE: jett 40 qm engine

Combattpigg,

That is correct, but you are not factoring in the unload off the pipe in the air.

21000 (slightly rich) on the ground will unload approximately 2,000 more in the air getting you very close to the max rpm of that prop.

Stick with Wood, it is safer.
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Old 07-21-2007, 08:57 AM
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Default RE: jett 40 qm engine

question is if the 8.8x7 or 8.8x8 will even reach these rpms on this engine considering it is much more load than 7.xx7.8 prop used in qm40 on the Short stroke engines
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Old 07-21-2007, 11:06 AM
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Default RE: jett 40 qm engine

The safest bet of all is to work around real speed set ups like the control line speed guys do...by working from behind the engine 100% of the time, uncluding pressing the spinner into the starter cone to get the engine started.
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Old 07-23-2007, 01:04 AM
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rmenke
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Default RE: jett 40 qm engine

vasek:

Just trying to understand what I am seeing in your pic.. I see a jett red carb with a jett remote needle and a engine I don't recognize. What?
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Old 07-23-2007, 10:08 AM
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Default RE: jett 40 qm engine

ORIGINAL: izzy

will the qm40 prop pull the q500 decently ,that is my actual question, will i get good top end speed ?
Short answer - no

The big prop will not permit the engine to unload in flight, and it will not needle properly on the ground.

The QM40 engine has to turn up over 22K rpm to run properly. It should best launch around 22.5K rpm (and that is about 800 rpm down from ground peak rpm)

And, as Ed noted, the only commercial props suitable for the engine are the APC carbom QM40 props, or a carefully prepared wood prop.
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