Fastest Funjet Ultra 184MPH (296km/h)

Setup:
Motor: ARC 3655-1.5
Battery: 6S1P
ESC: 100A
Prop: 7x9

Category:

Sports

Tags:

• Worlds
• fastest
• Fast
• FunJet
• Ultra
• 184
• MPH
• Electric
• speed

[psionic001]

@panther3002, ps, be sure to check the rated top speed for your prop. I calculated somewhere about 27000rpm for the APC.

[psionic001]

@panther3002, all good info. All sounds approximately what I came up with within 5-10%. I think I came up with 30% loss in pitch speed vs actual speed and I use this to calculate my estimates. My next build should top about 205mph at best if it's built well.

[maynardr6]

Did you have to mix roll with throttle? Also, just flying around, does it do unpredictable things with throttle transitions. I had a 3648 turnigy in mine with a 7x6, and i just couldn't control it. Every time I gave it some stick, it would roll. Just wasn't fun to fly, so I went back to a lowered powered setup. So, what's the trick?

[psionic001]

@maynardr6 - No, I haven't mixed roll to throttle, but I intend to.

[1ArtisticSoul]

I'm sure you had to compensate for torque roll with that size prop at those RPM's. The last time I used a prop that size running those RPMs on my funjet I lost control of it and crashed. I actually think it ripped one of the ailerons off and I lost control of it. It happened so fast I couldn't tell, but I would have to have one aileron at least half way up to keep the plane level at wide open throttle. I don't run any bigger than 6X4 now. Enjoyed the video~

[psionic001]

@1ArtisticSoul - I trimmed for no roll at about 150MPH. When it got to 180+ I was fighting it.

I've since been 202MPH but when I cam off the throttle it rolled severely (due to trim), plus the servos were straining, and I crashed.

New build hopefully coming soon.

[francoishaha]

@panther3002 youtube.com/watch?v=DZZWtT32ym­Y

[panther3002]

@psionic001 Try putting a gyro on each of the elevons for roll stability. It will self-correct for torque roll. go to mycoolrc(dot)com and click on "How to use a Gyro to stabilize a control surface on an airplane" for installation guidance.

[panther3002]

@francoishaha Hey how do you do this exactly? I'm very curious. Do you have some special software, or are you just calculating the speed using the doppler effect it by hand somehow?

[MrJimneutron]

awse effort mate I have the orignal funjet and clocked it with a gps at 297km/h on 6 cells but at those speeds it locksout and has no control.. now that its bounced off the ground planing too beef up the servos and control surfaces and try more cells 320 any one????

[francoishaha]

the doppler theory is great, im using the wave specktrum to calculate the speed, and the result is the same as your radar gun, 184mph at 20 degre celcius.

[cluzeauu]

coz am a bit congused here due to all comments... what's the full setup of the ACTUAL funjet flying in this video mate? thanks..

[panther3002]

Some more nerdy info I've been curious about on your setup: A propeller is extremely inefficient if the tip speed reaches or exceeds the speed of sound (Mach 1). So, I calculated your tip speed (plane at rest) to be 551.0 mph. At sea level on a Standard Day, (speed of sound = 761.2 mph) this is a tip speed of Mach 0.72. However, at with a forward velocity of 180 mph, the total tip speed is 579.66 mph, or Mach 0.76. So you still have a little room to go until the prop no longer works right. =]

[panther3002]

Using the pitch calculation& solving for pitch, I calculate a needed pitch of 7.5, on a 7 in long prop.ie: a 7x7.5 prop.However, this assumes that this prop will still produce26460 rpm, which is wrong, since it should produce more with a smaller prop, & it assumes that drag increases linearly with airspeed, which is also wrong, since it's more of an exponential increase, so anyway, enough of that crap, I'll just try it until it works. Now we know u have a pitch speed of 225.5mph.Good enough! =]