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CARF Joker build thread

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CARF Joker build thread

Old 01-25-2021, 06:44 AM
  #876  
jvaliensi
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I have the airplane completely assembled. I have the air trap and 2 batteries at the front, in the nose cone.
I found that without any fuel the airplane is nose heavy. About 100g (3.5oz) needs to be removed from the front. When I add fuel, this will get worse.
Moving the air trap is not an option I want to undertake, because then I'm ripping it all apart and starting over.
I found the batteries fit on either side of the turbine. But I'm not sure this is the safest spot to put them. I don't think heat will be an issue because the batteries are about 50mm (2") away from the turbine.
The other option is a lead in the tail. I'm guessing it will need about 200g(7oz)
A third option is to use one battery. My electrical system is two 9.9V batteries connected in parallel. This 4400 MAH and should give 6-8 flights between recharge. My wiring is simple and there is not a redundant circuit if the one battery fails. I consider the LiFE's to be stable power sources and I'm not overly concerned.
Empty weight was 7.44kg (16.4-lbs). With trim weight it would still be under 17-lbs.

Any thoughts?
Old 01-25-2021, 06:55 AM
  #877  
Dave Wilshere
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What is your total battery weight? I had three batteries in the nose cone 1x 2700 1x 2200 Rx and retracts plus 1x 1600 all 2s Li-Po.
It does go nose heavy full of fuel, but if you balance with 1/4 main tank it stays in a good range through the flight.
Old 01-25-2021, 07:17 AM
  #878  
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Hey Dave,

Just a note of thank you for always being checking and helping on the Joker, I am one of those who read but not comment, and you have help me a lot!

Mine is ready but the CG, as I canīt find fields close to be able to go fly as they do not alow jets (Madrid), hopefully soon as I have a prospect.

Thanks again for keep taking care of the thread
Old 01-25-2021, 07:28 AM
  #879  
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My two batteries weigh 370g for the pair, or about 185g each.
Old 01-25-2021, 10:51 AM
  #880  
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So it will be nose heavy if they are in the nose area
Old 01-25-2021, 11:38 AM
  #881  
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Yer killin' me, Dave!
Old 01-25-2021, 12:53 PM
  #882  
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If I pull the batteries out of the nose the airplane will not rest on the front wheel.
Old 01-25-2021, 12:54 PM
  #883  
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Originally Posted by apereira View Post
Hey Dave,

Just a note of thank you for always being checking and helping on the Joker, I am one of those who read but not comment, and you have help me a lot!

Mine is ready but the CG, as I canīt find fields close to be able to go fly as they do not alow jets (Madrid), hopefully soon as I have a prospect.

Thanks again for keep taking care of the thread
Thank you, itís a pleasure, hopefully you can enjoy your Joker soon.

Dave
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Old 01-25-2021, 12:57 PM
  #884  
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Originally Posted by jvaliensi View Post
If I pull the batteries out of the nose the airplane will not rest on the front wheel.
Where is the ECU battery again? At the end of the day, it does not matter where the batteries need to go as long as you achieve the balance position.
There are so many variables, like servo weight in the tail that can influence the balance.
The Joker is quite light on the nose when there is only 1/4 of a tank left.

Dave.

Last edited by Dave Wilshere; 01-25-2021 at 01:00 PM.
Old 01-26-2021, 12:41 PM
  #885  
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HI,
Has anyone found the stall speed of the Joker, with and without flaps deployed?
Old 01-26-2021, 12:44 PM
  #886  
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The Joker manual calls for the CG at 175mm w/ an empty tank, but full UAT. I may be close to this. Probably better off using this as a starting point.
If I have to add tail weight, then I think replacing my K70 w/ a K85 is in order.

Originally Posted by Dave Wilshere View Post
Where is the ECU battery again? At the end of the day, it does not matter where the batteries need to go as long as you achieve the balance position.
There are so many variables, like servo weight in the tail that can influence the balance.
The Joker is quite light on the nose when there is only 1/4 of a tank left.

Dave.
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Old 01-26-2021, 01:03 PM
  #887  
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175mm with an empty tank is definitely nose heavy!
180mm with a 1/4 tank is where I would start.

You cannot focus on a stall speed with a model and so many variations of weight, balance and flap set up. Into a 15-20 knot wind it will ‘hover’ onto the ground.
Old 01-26-2021, 02:14 PM
  #888  
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I ad few flam out and this model glide " off course with keeping the nose down " its a very docile jet , very gentle stall no surprise.
Old 01-26-2021, 02:17 PM
  #889  
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It would be nice to have a few ball park numbers for stall speed to start with.
Old 01-26-2021, 02:19 PM
  #890  
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fly and lift the nose up at high altitude, then you will have an idea ...like DAVE said you start nose heavy and finish with CG spot on
Old 01-28-2021, 02:31 PM
  #891  
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I balanced mine at about 180 with about 20% of fuel in the tank. After a few flights like that I even moved my 2100 ecu battery from inside the nosecone to the tray under the canopy. That is how I fly it to this day. In my link you can see mine landing pretty slowly even with a k100. I was surprised at how slow it could fly during my initial testing but it is no Havoc or Tomahawk Sabre


Originally Posted by jvaliensi View Post
The Joker manual calls for the CG at 175mm w/ an empty tank, but full UAT. I may be close to this. Probably better off using this as a starting point.
If I have to add tail weight, then I think replacing my K70 w/ a K85 is in order......It would be nice to have a few ball park numbers for stall speed to start with.
Old 01-28-2021, 03:06 PM
  #892  
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I ended up with 7oz of lead in the tail to get the CG at 180 w/ 1/4 tank of fuel.
Waiting for good weather for the 1st flight.
Old 01-28-2021, 05:08 PM
  #893  
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Originally Posted by jvaliensi View Post
I ended up with 7oz of lead in the tail to get the CG at 180 w/ 1/4 tank of fuel.
Waiting for good weather for the 1st flight.
Thatís a lot of weight to be adding. Canít you reduce the size of the radio batteries?

Danny
Old 01-28-2021, 06:00 PM
  #894  
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Well it increases the aircraft weight by 2-1/2%. I could take out 1 of the 2 2200MAH batteries. But it does not seem worth it.
Old 01-28-2021, 10:05 PM
  #895  
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Are you balancing on an electronic scale setup? 7oz of tail weight just does not sound right. It still sits on its wheels without full fuel?

Dave
Old 01-28-2021, 11:12 PM
  #896  
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Jim... It seems like you have the same retracts as I do (Electron 30).. I will bring my Joker to fly this Saturday. I have a Xicoy balancer and we can weigh the nose wheel and then you know how to add weight..

The nose weigh with electron retracts is different than with stock retracts due to the bend of the main struts...

David

PS .. Joker with X120 is amazing 🤩

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Old 01-29-2021, 06:14 AM
  #897  
jvaliensi
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Hi,
I have the Xicoy balancer. I did copy LA Jet Guy's set up. Which has the Electron retracts and the batteries and UAT under the nose cone. However, I used a K70G4 which is lighter than a JetMunts 100. There is about a 300g weight difference and I added 200g all the back.
So, thats why I needed tail weight. Now that the CG is set, even with a full UAT and a 1/4 tank the nose gear is very light on the ground. If I pick the nose up the tail will stay on the ground. My CG is at 180mm.

Last edited by jvaliensi; 01-29-2021 at 06:19 AM.
Old 01-29-2021, 10:45 PM
  #898  
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Originally Posted by jvaliensi View Post
Hi,
I have the Xicoy balancer. I did copy LA Jet Guy's set up. Which has the Electron retracts and the batteries and UAT under the nose cone. However, I used a K70G4 which is lighter than a JetMunts 100. There is about a 300g weight difference and I added 200g all the back.
So, thats why I needed tail weight. Now that the CG is set, even with a full UAT and a 1/4 tank the nose gear is very light on the ground. If I pick the nose up the tail will stay on the ground. My CG is at 180mm.
Jim... thatís correct .. with electron retracts if you take the nose cone off it will tip on its tail... itís due to the main wheels struts geometry.. also note that steering will be slightly difficult since there is not much weight on the nose wheel.

On takeoff all will be well since there will be some down pressure till you rotate..

David
Old 01-30-2021, 12:16 AM
  #899  
Dave Wilshere
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All Joker set ups do that if you take the nose off...he seems to be saying that just lifting the nose (on a completed model) it stays tail down. That ( and all his weight) does not sound correct.
Throw the Balance scales in the bin and check the balance manually at 180mm to make sure there is no miscalculation...

Dave
Old 01-30-2021, 02:10 AM
  #900  
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Do as Dave says, balance manually at 180mm from wing center leading edge, that’s exactly what I did, flew great since first flight, never have had a CG issue, I’m at about 70 flights on my airframe, and I’m using a 3 liter fuel tank

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