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Old Mar 25, 2008, 08:29 PM
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Quote:
Originally Posted by Dr Kiwi
Reality check: 28-37-2.5 on 3s 2100:

Heck, a 6x4 might draw close 50A and 7x5 about 60A.
I don't assume everyone fly at WOT for the entirree flight. Funjet requires the biggest possible prop.

Is there something wrong in what I said ???
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Old Mar 25, 2008, 08:33 PM
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Make sure you lightly sand the Funjet with medium grit sand paper before you glass. Epoxy based resin will seep better into the tiny pores and adhere well. Don't ask me how I knew

Quote:
Originally Posted by JesseB
Numb Thumb?! You're that wacko that did 154 mph with an FJ! Nice work indeed - I've followed your thread. You set the bar a bit high for the rest of us though.

You actually have me interested in glassing, which I would've never considered previously.

Jesse
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Old Mar 25, 2008, 09:34 PM
Rochester, NY
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United States, NY, Monroe
Joined May 2004
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Quote:
Originally Posted by numb_thumb
Swap that ESC with a CC 80 and the apogee with a 5S 3300 and you will have some serious competition.

nice setup !!!
5S 3300 - I think 5S 2000 would be do-able on a big enough motor. I'll be starting with 3000 Kv 4S, then move to 2000 Kv 5S. 5S 3000 Kv is trying to get the motor to 55,500 RPM 44,400 on 4S, 33,300 on 3S - which is a little more sane. Your actual RPM WILL vary. I'll be doing 2000 Kv on 5S = 37000 RPM on a 6x4 is 140mph before removing all the drag and inefficiencies which will be lucky to hit 110. But a 5.5x5.5 Graupner speed prop will get me there. Know the math or be da man, for only a few flights before the fuel guys tell you you're running a little to rich.

Quote:
Originally Posted by numb_thumb
I don't assume everyone fly at WOT for the entirree flight.
There is variable throttle on these things ? Hook that beast up to a ON/OFF switch - one hand in pocket

Quote:
Originally Posted by morphs
I agree.. I think it is absolutely crazy to use a prop saver on anything over 100 watts.. Especially with that O-ring. At least replace it with a slice of surgical tubing
I used to do all Prop Savers upto 20,000 RPM - but lost alot of props and no longer use prop savers. We're all about learning in this Hobby - so no real risk in learning from mistakes. Hopefully the FunJet can glide well enough to a landing or just trust these guys and pull that prop saver. If you're breaking props and doing high RPM - go with a gas (sport) prop on a "proper" adapter.

Quote:
Originally Posted by AndrésMtnez
I´m thinking about changing the spar with a carbon one, do you think it´s necessary?
I put a CF Rod behind the foam upright stabilizer to make it rigid. Should be enough to keep it rigid at high speed. I also changed the spar with CF and you'd be surprised how much more rigid that wing is. Then glassed it with 3/4 oz fiberglass and another CF rod the length of the fuselage.

Quote:
Originally Posted by AndrésMtnez
I´d like to make some sort of removable wing fit my car´s trunk, but the vertical stabs goes just in the middle of the join fuse-wing, anyone has done something similar?
Check out Danny's Multiplex Microjet mods - with the removeable stabilizers.
http://www.rcgroups.com/forums/showthread.php?t=460889

Looking forward to maidening my FunJet once the weather breaks. For now we are enjoying weekends with Wine, No Women Allowed, and only singing allowed is after effects of Burrito and Beer.

Vinnie
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Last edited by JustGoFly; Mar 26, 2008 at 12:13 AM.
Old Mar 26, 2008, 12:13 PM
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Quite honestly I'm confused after reading this because I couldn't grasp what you are trying to say.

Why should I start with 3000 kv and then move to 2000 kv and use all different kind of batteries???

I think I have simplified the math for you.

http://www.rcgroups.com/forums/showp...2&postcount=68

2021 Peak Watts
100.88 Peak Amps
44117 RPM

Top Speed : 154 mph

Happy flying !!!



Quote:
Originally Posted by JustGoFly
5S 3300 - I think 5S 2000 would be do-able on a big enough motor. I'll be starting with 3000 Kv 4S, then move to 2000 Kv 5S. 5S 3000 Kv is trying to get the motor to 55,500 RPM 44,400 on 4S, 33,300 on 3S - which is a little more sane. Your actual RPM WILL vary. I'll be doing 2000 Kv on 5S = 37000 RPM on a 6x4 is 140mph before removing all the drag and inefficiencies which will be lucky to hit 110. But a 5.5x5.5 Graupner speed prop will get me there. Know the math or be da man, for only a few flights before the fuel guys tell you you're running a little to rich.Vinnie
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Old Mar 26, 2008, 12:22 PM
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It depends on the size of the motor you're using. Why not 12S ?

For my 2.5 oz motor - 5S on 2000 Kv is about the limit - for the size prop I'm using. I will be checking out 4S on 3000 Kv. I could load up a 13 oz motor and run 15S - it might work for one flight before the airframe came apart, and would be a flying brick.

Are you actually recommending a 2000 + Watt system for the FunJet ?

I'm thinking 130 mph on a 500-600 Watts setup would be more appropriately near the top end.

Vinnie
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Old Mar 26, 2008, 01:03 PM
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2000 Watts, that´s brutal!!!

I wonder what speed would you achieve with that setup in a pure F5D ship



One question,

You said the Funjet need the bigger prop possible, but that record was with a 4,1 inches prop (trimmed). I think the recommendation of a "big" prop is good because the fuse makes a shadow to the prop and the Funjet is not a pure speed ship, so it needs some thrust too, but if you´ve managed to achive 154mph with that small prop now I´m confused


Did you sand the trailing edge? This came to my mind just when I saw the 4mm they have, but I´m not sure if it´s worth it
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Old Mar 26, 2008, 01:19 PM
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JustGoFly, Don't confuse your motor with Arc 1.5 T.

I was commenting on Arc 1.5 Turn (long can) motor that Jesse B is using. I never recommended using your motor to anyone.

Also, I'm not recommending anyone to pump 2000 watts. That is why I said 5S 3300 to JesseB, NOT 6S 3300 that I used for my setup.

Quote:
Originally Posted by JesseB
Just finished this yesterday...

Motor – ARC 27-47-1.5
Quote:
Originally Posted by JustGoFly
It depends on the size of the motor you're using. Why not 12S ?

For my 2.5 oz motor -

Vinnie
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Old Mar 26, 2008, 01:37 PM
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It is brutal and I don't recommend anyone to go for that kinda of setup. I've scaled down my setup now.

In a F5D with that kind of power, I would have gone home without the plane

You nailed right on the point about the prop size.

Based on the RPM and prop pitch , the theorotical pitch speed comes close to 215 mph.

My actual speed was only 154 mph. So we can kinda guestimate that after accounting for efficiency and drag, 154 mph is still low compared to the theoritical speed. So this indicates that there was not enough thrust to efficiently consume/convert the pitch speed into actual air speed.

So 154 mph was not the efficient setup. It all brute power. In other words, had I put a 5.2 X 5.2 prop with a motor capable of running at 44+ K RPM without frying then I guess I would have hit close to 175 mph

twang explained it very nicely about the marriage between pitch and thrust

Quote:
twang ....As far as prop size goes, to produce speed you increase pitch which loads the motor, so changes are made to diameter to bring the load to an acceptable level. Unfortunately when you reduce diameter the prop becomes less efficient and these losses start to become important, that's why we can't use a 1 x 10 prop. You have to find a happy medium of speed vs "torque". It's a bit of a viscious circle, we want lots of pitch for speed and lots of diameter for power but can't carry the batteries to produce it, so a compromise is necessary.


Quote:
Originally Posted by AndrésMtnez
2000 Watts, that´s brutal!!!

I wonder what speed would you achieve with that setup in a pure F5D ship



One question,

You said the Funjet need the bigger prop possible, but that record was with a 4,1 inches prop (trimmed). I think the recommendation of a "big" prop is good because the fuse makes a shadow to the prop and the Funjet is not a pure speed ship, so it needs some thrust too, but if you´ve managed to achive 154mph with that small prop now I´m confused


Did you sand the trailing edge? This came to my mind just when I saw the 4mm they have, but I´m not sure if it´s worth it
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Old Mar 26, 2008, 01:41 PM
Rochester, NY
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Facts : Arc 28-47-1.5 is 4 oz's rated at 400 Watts.
Max recommended RPM is 23,400.

Running it at 2000 Watts is not a recommendation anyone should be making for this motor. You are not helping the distributors since I frequently get guys asking for Warranty replacement running my 1.5 oz motors over 1000 watts because they saw someone post their run online. They get about 10-50 runs and burn it up.

Vinnie
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Old Mar 26, 2008, 02:04 PM
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Probably you did not read my posts completely.

I never recommend anyone to pump 2000 watts. All I tried to demonstrate is that Arc motors can take the beating (with sufficient cooling and throttle control) and in the process I got my cheap thrill (yeah right ) of flying the fastest Funjet ever recorded on a Eagletree.

Watch my Projeti thread and you can see for yourself how durable these Arc motors are. The best is yet to come for the Projeti and I have run more than 50 sorties on the same Arc 1.5 T motor that pushed it to 154 mph on the Funjet. I'm waiting for a 80 amps ESC replacement from Castle before I break my own speed record on the projeti.

Again, pls understand I have nothing to do with your 1.5 oz motors. I was only commenting on my experience with Arc motors. Its sad to hear that some guys fry your motor at 1000 watts and that's why I always recommend sufficient cooling and throttle control along with my extreme setups. You can see "Sufficient cooling" and "throttle control" all over my threads. Without that, any motor will fail when pushed to the extreme.

Quote:
Originally Posted by JustGoFly
Facts : Arc 28-47-1.5 is 4 oz's rated at 400 Watts.
Max recommended RPM is 23,400.

Running it at 2000 Watts is not a recommendation anyone should be making for this motor. You are not helping the distributors since I frequently get guys asking for Warranty replacement running my 1.5 oz motors over 1000 watts because they saw someone post their run online. They get about 10-50 runs and burn it up.

Vinnie
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Old Mar 26, 2008, 04:01 PM
Rochester, NY
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Numb - how about a video ? We use doplar and radar to prove actual air speed. RPM does not tell you the airspeed of a plane and likely will never reach the calculated airspeed. Legitimate airspeed comparisons are a flat straight pass without letting off the throttle. Some will report speed in a dive - this says very little about the actual achievable speed. Go into a dive downwind on a 30 mph day to crank up your numbers, but pull level for 50 yards before measuring if you like - but measure level. It's still impressive as hell to fly that speed.

I think we'll agree to continue to misunderstand each other. I have nothing against ARC or any other setup.

I had a guy ask me how to get his Tiger moth to 100 mph. It's just degrees of insanity

Have fun and I hope to see your monster fly some day. We'll have to check in a few months whether you replaced that motor or not. Check the video I posted of the guy flying 129 mph (claimed 155) on 8S Mega 16/15/4. No person who knows about motors would say this is adviseable.

http://www.rcgroups.com/forums/showthread.php?t=784916

Keep an eye on those batteries - looks like you dropped below 3 volts per cell for a long duration after your sprint. This is likely what happened to the 8S setup as well. You're running more like a 5S setup and the 8S guy is likely dropping even lower or things would have cooked.

Enjoy,

Vinnie
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Old Mar 26, 2008, 04:23 PM
Annoying people since 1970 :)
United Kingdom, England, Taunton
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Wingtips hit 150mph with 6s and a Mega 16/25/3 well over a year ago see here
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Old Mar 26, 2008, 04:27 PM
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Okay, with all the +100mph FJs I've seen thusfar I wonder what kind of structural changes have been made? Obviously the pieces of foam that cause serious drag (i.e. wing tips and the fins) run the risk of being ripped off at these speeds?

Cheers,

Sander.
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Old Mar 26, 2008, 06:09 PM
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I don't intend to get into conflict with you as well. I'm just trying to defend what I did and said. If you keep on adding questions for me I will try to answer an much as I can .

Quote:
Originally Posted by JustGoFly
Numb - how about a video ?
Sure...I plan to add a video to my Funjet thread soon.

Quote:
Originally Posted by JustGoFly
RPM does not tell you the airspeed of a plane and likely will never reach the calculated airspeed
You misunderstood, I used Eagletree airspeed expander to calculate true air speed.

Quote:
Originally Posted by JustGoFly
We use doplar and radar to prove actual air speed.
Wrong, You cannot use radar or doppler to calculate actual air speed. You can only calculate actual ground speed.

Problem with Radar:
1. I don't think its brave/stupid to stand in the flight path holding the gun on a 154 mph Funjet. Any volunteers in bay area??

2. With a 20 mph downwind (which is not uncommon here) my Funjet would have shown 174 mph on Radar. Is this the Legitimate way?

Problem with Doppler:
1. All I need to skew doppler is to give a touch of up elevator after passing the sound recorder. Bingo, I get 10-30 mph more speed instantly.

2. With a 20 mph downwind my Funjet would have shown 174 mph on Radar. A slight touch of elevator tounch and my Funjet doppler will show 185mph +. Is this the Legitimate way?

Airspeed expander: Gives reliable air speed, not ground speed. Opinions may vary but out of above three options I would prefer a reliable option, that is the airspeed expander.

Quote:
Originally Posted by JustGoFly
Legitimate airspeed comparisons are a flat straight pass without letting off the throttle.
This is one of my favorite . I have explained my views few times before but allow me to do once more here.

My first question : Who defined what is legitimate airspeed comparision? Did they certify doppler and radar is the only way to measure speed? Did they certify doppler and radar cannot be cheated?

My second question :

100 mph = 44.7 mps = 146.6 fps
125 mph = 55.9 mps = 183.3 fps
140 mph = 62.6 mps = 205.2 fps
150 mph = 67.1 mps = 220 fps.

mph == miles per hour.
mps == meters per second.
fps == feet per second.

So 150 mph is 220 feet per second. I will let you do the math and see how far the plane will be from you in 5 seconds.

If you or anyone insist that I have to fly flat out straight and level at this speed, I would have to say you don't know what it takes to fly at 150 miles an hour and you have never flown a plane close to this speed.

Also, folks who haven't regularly flown high performance setups on a foamie pusher (not sleek pylon racers) often forget a flight characteristic called terminal velocity. This is the time it takes the plane and the power plant to overcome the drag and reach its full potential for speed.

Draggie foamie pushers like the Funjet takes a long time to reach its terminal velocity. At 150 mph, you fly for 5 seconds and the plance is aredy 1000 feet away from you. I don't know about you and others, but I prefer to take home the plane after a high speed sortie rather to try and fly level and lose the plane forever

However, that doesn't mean one can take the Funjet way high up and do a 90 degree death dive to calculate the max air speed. That is not right either.

RC flying is a hobby my friend, not a life and death game. I prefer to use Eagletree because it is reliable, safer and I like it. If you like only doppler or radar that is not my problem. It is not my duty to prove everything your way just because you are still old school.

You are more than welcome to come to my field see the Funjet / Projeti in action. This is the best fool proof way to verify whatever you want.

Happy flying !!!
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Old Mar 26, 2008, 07:18 PM
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This thread is starting to turn into the Phase 3 speed contest thread. This thread is not a contest but for offering options and help to those who have the FJ. Please lets not start fighting over speed issues. Numb Thumb did alot of research using on board sensors. Others choose to do the same with Doppler. Everyone is intitled to thier opinion and way of doing things. Lets just get back to the planes and stop the chest beating.

I am on no ones side but trying to get the thread back on topic.

Jason

*ducks and heads for cover*
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