Multiplex FunJet - Page 52 - RC Groups
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Jul 26, 2006, 02:19 AM
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Bigplumbs's Avatar
Quote:
Originally Posted by casioppc
Hi Jurgen and any expert here

I flew the FunJet on mega 4T on APC 6x4 (drawing about 29A) and on warp4 3T on APC 5.5x4.5 & 5x5 (both props drawing about 40A) on same FlightPower 2150-3S pack and strangely the FunJet flies faster on mega 4T on 6.5x4. I thought my warp4 is spoilt so I borrowed my friend's warp4 3T and also encounter same slower speed as compared to mega4T.

Do you know why is it so?

Thanks in advance.
This is indeed confusing especially as I was about to buy a mega 16/15/3 to put in mine. I can only think that it is something to do with efficiency. At 40 amps compared to 29 amps you should have around 100 more watts of power. This could all be going in heat I surpose but it is confusing.

Also I run 3 mega 16/15/4 's on 3 cell lipos and only ever get around 22 amps.

The other thing of course is that you might be approaching the airframes max speed but with that thin wing I doubt it. Also if you look at Jurgens funjet on a fun 400/28 (similar to a mega 3 turn) it is certainly faster than mine on my 16/15/4.

Stupid question but is it possible the prop is slipping or even out of balance as this will effect efficiency ?

Not much help I am afraid but just some thoughts.

BTW Just flew mine on the 16/15/4 and APC 6 X 4 and I thought 'Do I rearly need quicker' ?

www.densplanes.co.uk
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Jul 26, 2006, 02:37 AM
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Bigplumbs's Avatar
Mega 16/15/3

I would quite like to see some video of a funjet flown on a Maga 16/15/3 on 3 cell lipo if anyone has any

Regards

Dennis
Jul 26, 2006, 04:35 AM
Registered User
ModelTony's Avatar
Quote:
Originally Posted by casioppc
Hi Jurgen and any expert here

I flew the FunJet on mega 4T on APC 6x4 (drawing about 29A) and on warp4 3T on APC 5.5x4.5 & 5x5 (both props drawing about 40A) on same FlightPower 2150-3S pack and strangely the FunJet flies faster on mega 4T on 6.5x4. I thought my warp4 is spoilt so I borrowed my friend's warp4 3T and also encounter same slower speed as compared to mega4T.

Do you know why is it so?

Thanks in advance.
Your figure for the Warp4-3 does seem rather high. I had about 31 amps running 5.5 X 4.5. I am using a Graupner 5.5x5.2 now and it gives a little increase in speed. To about 75 on the level using a speed gun.

For a given motor speed a 6 x 4 prop will probably give a greater static thrust than a 5 x 5, but as the airspeed increases the thrust from the 6 x 4 will reduce at a higher rate than the 5 x 5 until at a certain airspeed the thrusts will be the same (for example, say at 70 mph). If the airspeed increases above 70mph the 5 x 5 will have the greater thrust. As the aircraft flies faster the drag increases and when the drag equals the thrust the aircraft will stop accelerating. If this speed occurs before 70mph the 6 x 4 will have higher thrust and so the aircraft will fly faster with this prop, if above then the 5x5 prop will give the greater speed.

Tony
Jul 26, 2006, 11:39 AM
Senior User
Jeremy Z's Avatar
casioppc,

To know the full story, you'd need the RPM. I suspect that the lower kv motor is faster because it has enough torque to turn the slower prop faster. The higher kv 3T motor is probably slightly overloaded and cannot turn the prop fast enough to use the higher pitch speed.

It is either that, or your eyes are deceiving you, and it really IS faster.

To know for sure, buy or borrow a tachometer and measure the prop rpm. Then calculate the pitch speed based on the RPM and prop pitch. I think that things will "add up" then.
Jul 26, 2006, 11:41 AM
Registered User
Jurgen Heilig's Avatar
Quote:
Originally Posted by casioppc
Hi Jurgen and any expert here

I flew the FunJet on mega 4T on APC 6x4 (drawing about 29A) and on warp4 3T on APC 5.5x4.5 & 5x5 (both props drawing about 40A) on same FlightPower 2150-3S pack and strangely the FunJet flies faster on mega 4T on 6.5x4. I thought my warp4 is spoilt so I borrowed my friend's warp4 3T and also encounter same slower speed as compared to mega4T.

Do you know why is it so?

Thanks in advance.
The MEGA should not run at more than 25A, but even at 29A it should be much more efficient than a WARP 4 at 40A. The 6.5x4" prop should also be more effcient than a 5x5". For a direct comparison, you would need to run both motors with the same prop.

Jürgen
Jul 26, 2006, 11:44 AM
Registered User
Jurgen Heilig's Avatar
Quote:
Originally Posted by Bigplumbs
...
BTW Just flew mine on the 16/15/4 and APC 6 X 4 and I thought 'Do I rearly need quicker' ?
...
If it is too fast, you can always throttle back. If it is not fast enough at full power, there is not much you can do.

Jürgen
Jul 26, 2006, 12:45 PM
Keep building, buying,fly
Bigplumbs's Avatar

That was faster


Just put an APC 6 X 5.5e on mine with the Mega 16/15/4 with a flight power 1800 mah 20c 3 cell and she was considerably faster than with the APC 6x 4e and had very good climb/vertical. It was more windy though so perhaps not a fair test. My battery was hotter but not too much. I will test the amps to see where I am on the 6 x 5.5. Jergen is correct about the spec of the 16/15/4 being max 25 amps but I feel they can take more as has been proved in many other forums.

What fun we have especially with this little gem of a plane

www.densplanes.co.uk
Jul 26, 2006, 02:53 PM
Keep building, buying,fly
Bigplumbs's Avatar

Put my 6 x 4 Back


Tried the 6 x 5.5 prop with my Thunder Power 2100 13 C and it got rather hot. I have put my trusty 6 x 4 APC back on her and I think I will stick with that.

www.densplanes.co.uk
Jul 27, 2006, 08:01 AM
Part-Time Super Hero
MarkJayne's Avatar
Just got the new Multiplex Himax motor for the Funjet. I'tll be interesting to see what it throws out. Has anyone used one of these yet.

I would be trying it out right now considering I've got a couple of weeks of work, but er indoors decided she wants the decorating done. NOT FAIR.

Mark
www.rcflights.co.uk
Last edited by MarkJayne; Jul 27, 2006 at 10:39 AM.
Jul 27, 2006, 11:41 AM
Part-Time Super Hero
MarkJayne's Avatar
Ok, managed to check the Amp draw with the new motor.
She's pulling 31 Amps with a 2500 20C 3s1p and a 5.5x4.5 prop.

I may even get a quick flight later on.

Mark
Jul 27, 2006, 01:13 PM
Formerly of mcba fame
Matthew Allen's Avatar
So which Himax is that? 2815 or 2825? I'd like to hear how it does.

Matthew
Jul 27, 2006, 01:40 PM
Part-Time Super Hero
MarkJayne's Avatar
Quote:
Originally Posted by mcba
So which Himax is that? 2815 or 2825? I'd like to hear how it does.

Matthew
Its the HA2825-2700.

I flew it tonight. Very good. I had a few issues with my receiver as I had to move it behind the battery. Because this motor is quite a weight, the CG was to far back so a little rearranging was needed. I launched at full throttle and she flew straight with a nice gentle climb. Speed was also good with plenty of vertical performance.
Just need the RX sorting out as I did have a little interferance ( well she went down actually ).

Anyway I did get the flight on video, so I'll edit it up and let you guy's know when its up and running.

For now....

Mark
www.rcflights.co.uk
Jul 27, 2006, 03:04 PM
Part-Time Super Hero
MarkJayne's Avatar
Video is now up on running of the Funjet with the new Himax HA2825 BL Motor.

The link is on the home page and not in the video's section.

Mark
www.rcflights.co.uk
Jul 27, 2006, 03:38 PM
Registered User
That's cool Markjayne, mine is ready to fly with the same motor. How do you think using a 5x5 APC E ?
Jul 27, 2006, 04:48 PM
Registered User
Quote:
Originally Posted by MarkJayne
Video is now up on running of the Funjet with the new Himax HA2825 BL Motor.

The link is on the home page and not in the video's section.

Mark
www.rcflights.co.uk
Mark,

I could be wrong, but it looks like it is not as fast as your previous setup....

Other then that, awsome filming there as usual

Ron


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