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Old Aug 08, 2012, 08:31 AM
186mph Funjet Ultra
E-speed buff's Avatar
nieuw vennep, the netherlands
Joined Feb 2010
483 Posts
Hi mopar

For high speed you need thin air and high temperature (high speed of sound), so you have to fly at high altitude and high temperature.
The high desert in Nevada is perfect for this, this is why Rare Bear could fly its world rercord speed of 528Mph with a piston engine and propellor there.
If the temperature is slightly lower you will run into the "Soft Wall", your prop tips are going to approach sonic speed and lose efficiency.
Downside is that your minimum speed also goes up, so launching and landing will be more difficult.

Grtz Rene
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Old Aug 08, 2012, 08:33 AM
Why the dirt on the wings?
moparmyway's Avatar
New York
Joined Jan 2009
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Quote:
Originally Posted by E-speed buff View Post
Hi mopar

For high speed you need thin air and high temperature (high speed of sound), so you have to fly at high altitude and high temperature.
The high desert in Nevada is perfect for this, this is why Rare Bear could fly its world rercord speed of 528Mph with a piston engine and propellor there.
If the temperature is slightly lower you will run into the "Soft Wall", your prop tips are going to approach sonic speed and lose efficiency.

Grtz Rene
Ahh ...........
Thin air
High temp

not higher density .
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Old Aug 08, 2012, 08:50 AM
"The Judge"
sebbe's Avatar
Sweden
Joined Feb 2006
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Dont matter where that funjet with that motor and prop and that 2200mah 6s 40C HC lipo is flying, you will never reach +230mph level no wind..

Maybee 195mph..
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Old Aug 08, 2012, 08:54 AM
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United States, NC, Jacksonville
Joined Jan 2010
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Quote:
Originally Posted by moparmyway View Post

1900 x (3.4 x 6)=38760 rpm
Lets say the 6.5x6.5 prop was on there with 100% efficiency
(38760 x 6.5) / 1056 = 238.58 mph
Where did the 1056 number come from?
What is more realistic prop efficiency?
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Old Aug 08, 2012, 09:09 AM
"The Judge"
sebbe's Avatar
Sweden
Joined Feb 2006
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The faster it goes, specially for a "thick" airframe like funjet, the higher numbers you need to get that speed... therefore flying a funjet level speed over 200mph with NO wind, is hard..

It can bee done, but need much higher numbers
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Old Aug 08, 2012, 09:18 AM
Why the dirt on the wings?
moparmyway's Avatar
New York
Joined Jan 2009
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Quote:
Originally Posted by dmaaero View Post
Where did the 1056 number come from?
What is more realistic prop efficiency?
The formula for pitch speed is what I wrote in my previous post, thats where 1056 comes from.

The 100% I referred to was; if there wasnt a prop on the shaft of that incredible motor, it would spin at 38760 with 3.4 volts per cell on a 6 cell battery.

NO RC motor in the world will spin a prop the same rpm as it would spin its shaft under no load
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Old Aug 08, 2012, 09:26 AM
Why the dirt on the wings?
moparmyway's Avatar
New York
Joined Jan 2009
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Another interesting note,
You know those on line prop power calculators ?
Here is one where they state that in order for a 6.5x6.5 prop (graupner) to spin at 38,760 RPM, you would need a minimum of 3660 watts @ 20 deg C.

Figure one heck of a strong 6 cell battery @ 3.4 volts per cell and you need about 180 amps to do it without drag or losses..................... the MAX of his batts MAX burst rating

http://www.badcock.net/cgi-bin/power...+++0&Temp=20.0
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Old Aug 08, 2012, 10:08 AM
"The Judge"
sebbe's Avatar
Sweden
Joined Feb 2006
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Its really funny when someone shows a speed that is off like this, so many + (me including) makes eveything to prove its wrong, when allmost everyone reading this dont care as they still know its wrong numbers

next time I will be more quite, to much energy trying prove the opposite
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Old Aug 08, 2012, 10:51 AM
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Denver, CO
Joined Nov 2007
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--For $50, swap out the motor you already got in there and try it then take video and let us know
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Old Aug 08, 2012, 12:07 PM
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Pilotnx211's Avatar
Joined Jan 2011
61 Posts
Quote:
Originally Posted by E-speed buff View Post
Hi mopar

For high speed you need thin air and high temperature (high speed of sound), so you have to fly at high altitude and high temperature.
The high desert in Nevada is perfect for this, this is why Rare Bear could fly its world rercord speed of 528Mph with a piston engine and propellor there.
If the temperature is slightly lower you will run into the "Soft Wall", your prop tips are going to approach sonic speed and lose efficiency.
Downside is that your minimum speed also goes up, so launching and landing will be more difficult.

Grtz Rene
Grtz, thank you, as your very right! Yesterday, we had a kick in speed over sea level of 18 + mph alone. The launch on the bungie came within several inches of the wing tip hitting the ground. The landings all had much higher speeds.

On the battery. All are not created equal, we all know this and why this one gave so much? Maybe it was"mislabled". But the "balance charge" did take alot longer then my other batterys.

On this "magjic" HK motor, maybe its also a freak of nature and different from the specs that are on the box. You Tube does have a test of the motor pulling over 2400 watts. Maybe its best to not lock in numbers which might be wrong to begin with. Remember, their was a 6 sec barrier in drag racing, then 5 secs, then 4 secs and all of them have been broken. Its called "thinking outside the box"!

I also stated that covering was used. Some have posted it turns into "insulation" above 165 mph, well, not so in this case! I hinted the wing was "very smooth". Also, everyone of you will agree, drag reduction, is very important! Hint, airfoil shapes can be reshaped! Seems "a few" overlooked some areas which might give improvements. A bunch of small improvements does add up!

Remember, their was and still is a "flat world society", so spinning your calulators, showing all your math, will not change what these pictures show. Also, most importantly, its been shown by several with this combo that the FJ will go fast. Maybe best "to think" what improvements can be done to make it go faster!

Regards, Tom.
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Old Aug 08, 2012, 12:22 PM
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Raleigh, NC
Joined Sep 2004
2,530 Posts
Umm... yeah.

To be honest I don't really trust that RCSpeedo App. I had that app and found it a bit finicky. You could easily fake out high speed numbers with it. I found that just making a turn would cause it to spit out numbers sometimes ridiculously high numbers because the sound wave of going away and turning back looked like a high speed pass.

Later I uninstalled that app and went back to using doppler software on my PC because it was just much more consistent and reliable - plus I got to choose the wave sample so I could make sure it was a wav sample of the actual pass.

So if you really want us to believe you - just post a video of your passes. Let us be the judge.

I'm seeing a trend of self appointed record breakers. Sorry - that's just doesn't "fly" with this crowd...
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Old Aug 08, 2012, 01:21 PM
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"I'm seeing a trend of self appointed record breakers."

he did post:
"NO RECORDS CLAIMED NOR WANTED"

I think record attempts do need straight and level, multiple documentation, etc BUT

I think its GREAT to just go out and go fast! If it came going straight down, so what. You get the sensation of speed and knowing you were at the controls. A lot of planes have been flown faster than their official speed records. As far as the numbers matching the result...there are a lot of variables that aren't accounted for. If its remotely possible, and its unofficial, then why not give it a definite maybe rather than rain down negativity ?

One thing is for sure..it wasn't slow and the numbers are in the same arena as other flights with the same setup.

Good Job Pilotnx211 ! (no, you may not quote me on this )

Mike
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Old Aug 08, 2012, 01:30 PM
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Pilotnx211's Avatar
Joined Jan 2011
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""To be honest I don't really trust that RCSpeedo App. I had that app and found it a bit finicky. You could easily fake out high speed numbers with it. I found that just making a turn would cause it to spit out numbers sometimes ridiculously high numbers because the sound wave of going away and turning back looked like a high speed pass.""

Well, glad your being "honest" now!

""Later I uninstalled that app and went back to using doppler software on my PC because it was just much more consistent and reliable - plus I got to choose the wave sample so I could make sure it was a wav sample of the actual pass.""

You "choose" which wave sample to use, hmmmm..........I choose to make another choice!

""So if you really want us to believe you - just post a video of your passes. Let us be the judge.""

No Unction judges for me! Nope, not wanted or even asked for!

""I'm seeing a trend of self appointed record breakers. Sorry - that's just doesn't "fly" with this crowd...""

No need to be "sorry", just reread my post #6636, it has a BIG disclaimer!

Thanks,
regards Tom.
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Old Aug 08, 2012, 01:46 PM
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Raleigh, NC
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Ok, then. Let the copy cats begin. Now that you've posted a speed like that lots will try to follow you. If they don't succeed - guess who they will blame?

Sorry but as much as everyone says - "It's just for fun!!" It's not - you will create a wave of disappointment in this thread as lots try to copy you and fail.
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Old Aug 08, 2012, 02:03 PM
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Quote:
Originally Posted by cjbucher View Post
Ok, then. Let the copy cats begin. Now that you've posted a speed like that lots will try to follow you. If they don't succeed - guess who they will blame?

Sorry but as much as everyone says - "It's just for fun!!" It's not - you will create a wave of disappointment in this thread as lots try to copy you and fail.
Their will be no disappointment at all, as their are others using this setup! Their are You Tube videos with this setup! I am not the first, I copied and did just a "clean up" and other ""changes"" to get the FJ to go faster! Also, check my post #6636 of my android picture....it has only 35 views at this time. HINT!!!

My setup will change shortly, going to a 5S and be using a 7 X 10. If the motor holds up, will then go to a new 6S and bigger C battery. Its going to smoke for sure, but its fun and thats what its being done for! We also tried a HET 1W40, but the motor spun up so fast, it bent the collet on the shaft which spun the rear bearing.

Regards, Tom.
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Last edited by Pilotnx211; Aug 08, 2012 at 02:15 PM.
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