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Old Nov 29, 2014, 06:22 PM
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Originally Posted by ruppwf View Post
Hi Jeff,

the 9x6 prop is no problem because the prop will be always behind the fuselage or the tails.
But the 4S 3000 mAh lipo is too heavvy. And the suggesed motor is heavvy. I have calculated the weight of your setup and total flight weight will be 775 g.
With this weight the RJ800 will have a very fast landing speed. With normal landing speed of a normal RJ 800 (weight 415 g) the elevator cannot hold the RJ800 in the air and will fall down like a stone if you have not very high landing speed. You can test landing speed adding weight (lead) to a normal RJ800 up to 775 g and try the landing. Than you will see the landing behavior of the RJ800 with your proposed setup.

A better setup, very powerfull and fast (210 kmh) is:
NTM Prop Drive 28-36 3000kv/755W
TGS Sport 6x4 E
4S 1800 mAh 25C nano-tech
Current is 38 A (measured)
Flight weight is 635 g
With this setup you must reinforce the wing with carbon fibre tubes and the landing weight also is high and the landing speed fast but still good to control. With even higher landing weight, resulting in higher speed you risk damage of the RJ800.

Rupp

Rupp....great info, thx. So am I reading this right? Your power setup above only draws 38A??
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Old Nov 29, 2014, 06:45 PM
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Rupp, how about this:

NTM Prop Drive 28-36 3000kv/755W = 87g
*5*S 1800 mAh 25C nano-tech = 255g
My own 80A esc = 56g
TGS Sport 4.75x4.75E

So all-up, the powertrain (less rx, prop & collett) would be 4oz/400g...per HK, they list the RJ800 "flying weight" as 400g (which I assume means foam + motor, nothing else?)

Therefore including 2 servos, I get an all-up/ in-the-air weight of what? 850g or so (on 5s)

Can you provide your analysis?

Finally...My esc can take the amps; but can the motor, in dives, in short bursts (3-8 sec)?
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Old Nov 29, 2014, 06:50 PM
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Whoops!! Nevermind the post; you already indicated that my setup weight was 775g

But the only variable is the 5S (255g), vs 4S (205g), and the additional 50gr?

Maybe I have something added up wrong here...

Final note: I am used to, and have experience with, flying hi-speed models...including, but not limited to, hot landings (on cut grass)
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Old Nov 30, 2014, 05:28 AM
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Quote:
Originally Posted by poiyt View Post
Rupp....great info, thx. So am I reading this right? Your power setup above only draws 38A??
Yes, measured 38 A WOT
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Old Nov 30, 2014, 06:31 AM
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Quote:
Originally Posted by poiyt View Post
Rupp, how about this:

NTM Prop Drive 28-36 3000kv/755W = 87g
*5*S 1800 mAh 25C nano-tech = 255g
My own 80A esc = 56g
TGS Sport 4.75x4.75E

So all-up, the powertrain (less rx, prop & collett) would be 4oz/400g...per HK, they list the RJ800 "flying weight" as 400g (which I assume means foam + motor, nothing else?)

Therefore including 2 servos, I get an all-up/ in-the-air weight of what? 850g or so (on 5s)

Can you provide your analysis?

Finally...My esc can take the amps; but can the motor, in dives, in short bursts (3-8 sec)?
Hi Jeff,

f irst the flight weight of Radjet Kit is not 400 g. The motor weights only 39 g.
Second your proposed setup should have 685 g
The empty weight of the RJ800 is only 254 g. This is calculated from my flight weight of 637g minus the weight of motor, controller, lipo, receiver and prop of
383 g.
Sorry! The weight of empty RJ800 is not 254g but 222g (minus 30 g of 2 servois).
Your first setup would have not 775g as i wrote before but 814g.

Using a 5 S lipo is not recommended because the motor will be too hot at WOT
and you will have not necessary 50 g weight more than 4S .
I have not tried the TGS Sport prop 4.75x4.75. But with 6x4 I got 210 kmh (measured with GPS Data Logger). Trying a 4.75x4.75 APC-E prop I got not such speed.

Rupp
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Last edited by ruppwf; Nov 30, 2014 at 08:37 AM.
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Old Nov 30, 2014, 06:54 AM
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Quote:
Originally Posted by poiyt View Post
Whoops!! Nevermind the post; you already indicated that my setup weight was 775g

But the only variable is the 5S (255g), vs 4S (205g), and the additional 50gr?

Maybe I have something added up wrong here...

Final note: I am used to, and have experience with, flying hi-speed models...including, but not limited to, hot landings (on cut grass)
Hi Jeff,
as I wrote before not 775 but 814g should be the weight of your first setup.
Your first setup contained
130 g for the motor
337 g for the lipo
63g for the 60A controller
30g for prop/adapter/receiver

Landing: The faster and heavvier a model is landed on grass the risk of damage is greater. In my opinion it makes no sense to make a flight model heavvier than necassary. If you try a new speed record the weight is not important. But if you enjoy flying around you should have as little as possible weight for better flight characteristics.
But before building a heavvy model you should add the foreseen weight in form of lead and look at the flying properties.
Rupp
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Old Dec 02, 2014, 11:45 AM
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Rupp....great stuff...thx. I sent you a pm.

Jeff
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Old Dec 03, 2014, 05:55 PM
Reap the wild wind
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Bristol,UK
Joined Feb 2007
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For anyone with a beat up but still airworthy RJ you could do worse than have a go at slope soaring. We all know that HK copied the planform of the Funjet and my much mended FJ does slope quite well
Andy
Funjet slope maiden,Westbury White Horse,Mob fw 2 25 and #16 2Dec14 (1 min 26 sec)
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Old Dec 19, 2014, 02:25 AM
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Finally ordered another radjet and a new motor NTM Prop Drive 28-36 3000kv/755W ... Never used this motor before which has 200Kv more and rated around 200 watts more then my last 28-36 2800kv ntm motor which was lost months ago... I am thinking 40c 2200 3s packs, 50 amp esc and a apc 6x4 sports prop should get me 100mph WOT....Anyone use this motor and have any suggestions? thax
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Old Dec 19, 2014, 02:34 AM
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Also I am building my zeta blaze which is same airframe as New larger Version of radjet anyone have it and Know COG location ?...I also think it needs Up elevator reflex more than the regular radjet thanks
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Old Dec 19, 2014, 05:41 AM
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United Kingdom, England, Worcester
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Originally Posted by hate2crash View Post
Finally ordered another radjet and a new motor NTM Prop Drive 28-36 3000kv/755W ... Never used this motor before which has 200Kv more and rated around 200 watts more then my last 28-36 2800kv ntm motor which was lost months ago... I am thinking 40c 2200 3s packs, 50 amp esc and a apc 6x4 sports prop should get me 100mph WOT....Anyone use this motor and have any suggestions? thax
I used that motor on 4s, maiden flight one of the magnets decided to come unstuck and totalled my Skyfun .
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Old Dec 19, 2014, 05:44 PM
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Originally Posted by Add1ct3dd View Post
I used that motor on 4s, maiden flight one of the magnets decided to come unstuck and totalled my Skyfun .
Never had problems with my 2800kv ntp... Maybe you over propped and motor got over heated... I am thinking anything over 4,5x4,5 on 4s with 3000kv on radjet might be over propping
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Old Dec 20, 2014, 10:04 AM
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Nope it wasn't overpropped, I ran the 2800kv all day long, switched to the 3000kv and downsized the prop, first pass it exploded mid flight I guess I was just unlucky with the motor. Runs a Dr Madthrust now and had no issues .
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Old Dec 20, 2014, 03:59 PM
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Originally Posted by Add1ct3dd View Post
Nope it wasn't overpropped, I ran the 2800kv all day long, switched to the 3000kv and downsized the prop, first pass it exploded mid flight I guess I was just unlucky with the motor. Runs a Dr Madthrust now and had no issues .
Yeah sounds like a defective motor,,,,what prop you use on your 2800kv with 4s? thax
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