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Jett FIRE 50 users.. what kind of rpms are you getting?

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Jett FIRE 50 users.. what kind of rpms are you getting?

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Old 09-24-2002, 10:59 PM
  #1  
Dustflyer
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Default Jett FIRE 50 users.. what kind of rpms are you getting?

I am getting ready to move my Jett FIRE 50 over to a Whiplash. Before I do, I am retuning the pipe for smaller props and higher revs. David at MACS said that the quiet tuned pipe I am running will give virtually the same rpm with small props as a nitro pipe, just much more quietly!

So far I've seen 18.5 with an APC 8.75 X 9.25 W cut down to about 8 1/4 inches diameter.

Should I go with less pitch and an 8 inch or less prop diameter? Anybody know the difference between the standard, the "W" series and "NN" series APC pylon props? Which is best?

Anybody tried one of those 7.5 X 8 carbon fiber props on a Jett FIRE 50? Is there enough thrust for a hand-launch?

Ultimately, what kind of rpm should I see with the Jett FIRE 50 with the optimum prop?

Thanks,

Gene
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Old 09-24-2002, 11:18 PM
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Noflyzone
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Default Jett Prop for Whiplash

Hi Gene,

For the first couple of flights on the Whiplash, give a standard 9-8 APC a go...Rick & I have tried the Whiplash with that combo and it is ballistic. We never figured that the 9" diamater would let the Jett 50 come onto the pipe, but we were sure wrong. Since the Whiplash is a little heavier than a DD, it needs a little more bite from the prop. After the initial runs with a 9-8, start cutting the diameter until you get the pull and rpm's where you want them. With the 9-8, then start moving up on pitch and down on the diameter. We didn't get a chance to tach the Jett 50, but it was turning some serious R's.....Good luck, and let us know what you think.
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Old 09-24-2002, 11:25 PM
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Default Dang...

If it's too heavy for an 8.8" diameter prop, that can't be good for the guys planning on running 46 sized DF engines or Q40 engines..

That sure puts a kink in any plans I had about getting one :stupid:

And Gene..if you would like to try a 7.4 X 8.25 CF APC without spending $7.50, send my your addy and I'll send ya one.
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Old 09-24-2002, 11:52 PM
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Default Not too heavy

Chuck,

I've corrected my post to clear up any misunderstanding that may have occured about the Whiplash. We cut down a 8.8-9.25 prop to around 7.75" diameter and found that the RPM's were great, but the prop simply cavitated at the unloaded rpm's. What I needed to say instead of what came out, was that the prop combo and the Whiplash simply weren't the right combo. The Jett 50 has brutal power and can turn a much larger prop in the air, even if the tach doesn't show it on the ground. The Whiplash has an extremely low drag coeficient and simply outruns the smaller props. Hope this explains what I really meant...
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Old 09-25-2002, 12:51 AM
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Default Props

Dan,

Hmm.. a standard APC 9X8, hadn't thought of that one. I was thinking more along the lines of getting up over 20K on the rpm's with something smaller.

Right now the 8" prop has plenty of pull to launch my Dust. It just seems to me the guys who are really doing the crazy high speeds are doing it with ducted fan motors turning ridiculous rpms.

I was running an APC sport 8X10 on my Dust turning 15.5K and that was plenty of thrust for a launch but the airplane is slow as anything now. I would think an 8 or even 7.5 inch diameter turning over 20K would have at least as much thrust and a lot more top speed.

I am having a lot of trouble getting my Dust flying fast again. When I first started out with the big long pipe and a 9X10 turning 15.5K or so it was incredibly fast. I cut the pipe down a bit and I think that was a big mistake, it never unloaded in the air any more and after that was quite a bit slower.

Figuring I ruined the pipe for the 9X10 I'm trying the high rpm route now.

I may be better off just throwing out my pipe and header and starting off with new long ones again. I may just do that but first I want to see what the engine can do with the smaller props.


Chuck,

Thanks, but do you think that 7.4 X 8.25 CF prop is really a viable choice for the Jett FIRE 50? Just wondering if you ever flew it successfully on your Dust and what kind of r's you got.

Gene
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Old 09-25-2002, 01:23 AM
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Default Yes..

Gene..the 7.4X8.25 ended up being the prop I ran exclusively. It performed very well on the Dust, turning about 22K at launch. I don't know what kind of R's you are looking for over 20K...

I really wish APC would make a few more sizes of the CF props available...this was the stoutest one I could get.
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Old 09-25-2002, 01:43 AM
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Default Prop

Chuck,

Wow, 22K with 8.25 pitch sounds like one heck of a fast airplane.

I'd love to try it out. My address is on the way!

Gene
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Old 09-25-2002, 02:14 AM
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Dave McDonald
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Default Jett FIRE 50 users.. what kind of rpms are you getting?

My buddy Joe has a DD with a piped Jett FIRE 50 that we tached at 18,500 on an APC 9x8. 15% Mach 7 fuel, K&B 1L plug. My ST GS45 with a homemade mousse can pipe (MCP) turned this same prop at 16,500.

For fun, we replaced the Macs pipe with the MCP on the Jett 50 and got the exact same 18,500 RPM. That blew us away! But we never tried flying the MCP on the DD.
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Old 09-25-2002, 02:54 AM
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Default Re: Prop

Originally posted by Dustflyer
Chuck,

Wow, 22K with 8.25 pitch sounds like one heck of a fast airplane.

I'd love to try it out. My address is on the way!

Gene
Well shoot..if you are that pumped I'll send the engine and pipe, too!

And these aren't really great numbers, FWIW..I'm running the pipe about 3/4" too long (see pics) and it's just a 46VRDF...

I would be stunned if the Jett 50 couldn't best it by 1K or so..

And I got the address..
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Old 09-25-2002, 05:50 PM
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Default thrust

I am running a 7 inch prop on my nelson/whiplash. If it does lauch like a rocket i will be very dissappointed.
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Old 09-25-2002, 07:54 PM
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Default Jett FIRE 50 users.. what kind of rpms are you getting?

7" props at high rpms on a Nelson will go very fast, but do not accelerate like rockets. They also develop alot of torque on take off, and will probably require a bit of right rudder on take off until it gets up and going.

I've not flown a whiplash, but have run 7" props on nelson engines for some time. Great engines, but not the fastest acceleration. My avatar uses 7" props on a Neslon Q40 engine.

If your talking a Nelson Quickee engine, I would stick with 8.8" props.
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Old 09-25-2002, 10:49 PM
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Default Props

I just ordered a bunch of new props from APC: an 8.75 X 9 NN, 8.75 X 8.5 NN, 8.75 X 8 NN, 8.5 X 7.5, and 7.8 X 7 Carbon Fiber.
The "APC man" said the NN props were the way to go for max speed.

What do you think of those props for the Jett FIRE 50?
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Old 09-27-2002, 05:13 PM
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Default NN props

I don't know if those would be good props for a Jett Fire, but I do know that the NN props don't seem to go as fast on my Nelson engines.

I would suggest the 8.8" apc props.

Pitches between 8 3/4 and 9 1/4.
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Old 09-27-2002, 05:34 PM
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Default Speed

Dave,

Thanks for that reply.

I'm going to play around with those props a bit. Based on what you are saying I probably shouldn't have bought those NN's but the guy at APC said they were the way to go.

My Dust will still launch nicely with an APC 8 X 10 sport prop turning around 16.5K. I flew it the other day with an APC 8.75 X 9.25W cut down to 8 1/8" and it still had enough thrust to launch fine turning 17.5 (peaked at 18.5) On that basis I am guessing an 8 pitch prop turning 20K or so ought to still launch fine.

The props I am most interested in trying are that 8.5 X 7.5 pylon and the 7.8 X 7 carbon fiber. That's probably pushing it for the 50 but it will interesting to see what happens.

You will find this interesting: The other day a gentleman was kind enough to go out of his way to take a radar reading on my Dust. The results were shocking. Turning the APX 8X10 at around 16.5K on the ground the best I could do was 139mph out of a dive! Could it be I didn't give the airplane enough time to accelerate?

Seems the airplane was much, much faster when I had the long pipe and I was turning a 9 X 10 at 15.5. If you've seen my video I think you will agree. I can e-mail it to you.

I'll keep you posted.

By the way, would you mind repeating the formula you pylon guys use for figuring speed?

Thanks,

Gene
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Old 09-27-2002, 06:53 PM
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Default Hi Gene

When I flew a highly modified YS 45 RE, I got the best luck from all of the N and NN props you just bought. They turned WAY better than the standard APC props.

I was getting about 17.7K on the ground with a 9X8.5 N on a patriot.

Anyway you bought the right props, just have to experiment now
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Old 09-27-2002, 07:49 PM
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Default Jett FIRE 50 users.. what kind of rpms are you getting?

Anyone got a OS 46 FX on a Whiplash dialed in. I am going to be running the mac's pretuned pipe on it. Has anyone figured out what is the best prop for this combo??

Thanks

Craig
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Old 09-27-2002, 07:51 PM
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Default N and NN props

You may want to contact Dub and ask what prop he would recommend for that specific engine. At least find out the power band range it is designed to run at. Once he gives you its optimal RPM band, find the prop that gets you there.

The 8.8" props are the newest APC pylon props, in in my opinion the best. Pitches are available from 8.5-9.25.

I am not aware of the speed calculation you are talking about. I just test my Nelsons before a race, and depending on the RPM readings, adjust the prop so I get in the proper RPM band that I want to fly at.

We also have a local guy with a high buck radar, so we have a pretty good idea of what goes, and what does not go.

I would try to stick to pylon props whatever you do, some of those sport props are not intended for the type of RPM readings you are getting.
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Old 09-27-2002, 09:54 PM
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Default Props

Dave and Matt,

Thanks.


Craig,

You want the APC 9X8 sport prop, in my opinion (hmm.. shouldn't have said that, we all know what it's worth!) the very best prop for that engine. It worked best for me when I was running the 46FX.


Gene
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Old 09-27-2002, 10:46 PM
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Default Earth to Gene...come in Gene..

Dang I wonder what a 7.8X 7 will turn..and here I was thinkin' the 7.4 X 8.25 might be a tad light...oh well...
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Old 09-27-2002, 11:06 PM
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Default RPM's

Chuck,

Yeah, I guess I'm kinda out there... but then again, when you're dumb enough to invest in the stock market and fool around with model jets, I guess you're dumb enough to try just about anything!

Gene
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Old 09-27-2002, 11:34 PM
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Default Well...

I won't get into jets..but I got in with some guys who did some awesome TA, chart gurus, and was able to pull a few rabbits out.. but that was a couple years ago..when it was easy!

Look back at Fannie Mae .... super predictable rise and fall..

KREM...who woulda thunk it?? This was a hit from a fishing trip to the DFW area..they opened one there and had lines around the block, cops controlled the traffic...yep, the chart shows it...

Couple of pennies..I like to shoot craps..

DNDN...rode that puppy up...did a few IPO's and quiet periods...

PWER...got bigger and bigger...and bigger!

But I been in cash the last year (save one penny..went .04~.31, got out at .24...ahhhh).

Not much investing..just gambling...stupid, stupid, stupid..but it worked for me...for the most part.

Of course I lost enough to buy a house..but the winners were sweet!

Anyway, tell me how that prop works for you!
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Old 09-28-2002, 12:04 AM
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Default Genius?

Chuck,

Wow, almost sounds like my biography. Been studying charts all my life. I made a pile on Veritas but quickly thereafter confused personal genius with a bull market. When it was over I was right back where I started!

I guess you could say the Diamond Dust is a lot like an options contract... maximum excitement with a small and fixed downside risk!

Gene
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Old 09-28-2002, 02:23 AM
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Default Whiplash

Hey Gene,

When you gonna put up that Whiplash? I noticed that you said your DD with an 8-10 sport prop would only go 139mph out of a dive. We have a guy here in Lafayette with an os 46 turning the same rpm 16,200 with a 9-7 APC going 146 mph. Imagine what that Piped Jett 50 is going to do on your Whiplash. Scarry HUH???
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Old 09-28-2002, 11:07 AM
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Default Whiplash

Dan,

I want to find a good prop/pipe combo on the Dust and get another radar reading. Then I'll switch everything over to the Whiplash and clock it with the same engine and prop. My guess is it will be faster than the Dust.

Gene
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Old 09-29-2002, 01:19 AM
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Default Jett FIRE 50 users.. what kind of rpms are you getting?

my rear exhaust OS 40 and tuned pipe does well with a 9x7 apc on a dd
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