RC India

test flew the catalina yesterday,but cant able to take off  from the water.as you can see in the video the plane is always turning to the left even at minimum throttle.is there anything to be corrected with the lateral balance?suggestions from all are welcome





http://www.youtube.com/watch?v=ULsSToaCRrM

The biggest issue with twin engine/Motor design is to maintain Exactly equal thrust on both the motors. I feel you starboard (right) motor is somehow producing slightly more thrust, maybe due to high RPM or slight difference in Prop dimension. Even slight offset in the thrust angle can cause similar issue.

Use both the Ailerons and Rudder to trim this action, if you can.

I believe ujjwaana is correct. you can check the rpm of both the motors using the following type Multi-Blade Micro Tachometer.
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=10783
While take off, you can try to keep a little extra Rudder to counter the tendency to turn. But I sujjest you check the rpm first. If you have spare props try mixing changing them until you get a uniform rpm in both motors.

Please also check the direction of the WATER RUDDER

Please read this link.
http://www.rcgroups.com/forums/showthread.php?t=674400
It says how to correct it, and a good guidance how to takeoff

tnx manoj.lot of information on the rcgroups site,will try to correct the lateral balance first and see how it performs. both the motors and props are the original one comes with the kit

santhosh

Then I believe the only problem is with the Lateral Balance and careful rudder correction while takeoff. :)

Dear Santhosh,
Since you have test flown it already, all the diffrentila thrust issues are not likely to be there, unless some thing has changed after the test flight.
in my opinion, after checking things as per manoj and ujjwana, u can try once agin hand launching the model and correcting  few things in flight and triming  it out. After this is done it will be easier to take of from water.
" Evite yanu parappikkunnathu?"

 i had made the Polaris plane and had tried taking of from Water. But this is a single motor pusher and rudder  for water steering.

http://www.youtube.com/watch?v=zJySfjs0a6Y

Santhosh Gi, Correct me if I am wrong, Did you manage to takeoff ??  I only saw the video of aborted takeoff attempts. ???

dear Manoj,
in the first post he said that "test flew the catalina yesterday"
thats why i wrote...

sorry for confusing you ashta,manoj. in fact i am not able to fly it yet. tested on the water but its always looping on water. tghe place is near to  my home in irinjalkuda

Hi Mr.Ashta, I noticed the following.. " Evite yanu parappikkunnathu?"  Are you from kerala ?? :) I never knew that.

if you have not flown it yet, then my suggestion may be more relevent. pl try hand launching after correcting the issues as stated by Manoj and Ujjwaana

yesterday again after adding some weight to correct the lateral balance tried it on our paddy fields,still no luck it's always looping.seems to be the rpm of the left motor is low,watch the video


http://www.youtube.com/watch?v=A2zFOTwJWBk

on the third attempt we forgot to put the rubber fuselage plug  :banghead: :banghead: and here is the final result


http://www.youtube.com/watch?v=UZpkNqsvEYs

Woah :(  Up for some major work on it.

It seems like the looping can be handled by applying rudder correction, which I can't see in the video. Remember how I was flying Prakkat's Twinstar with different thrusts on the two motors just by holding a significant amount of rudder to one side ?  The same should work here too !

Another option is to use radio mix programming to adjust the inputs to both the motors, connected on two separate channels.  Prop surgery (trimming one prop slightly, a small bit at a time) may be another less desirable option.

 i tried with rudder correction ( which is not in the edited video).also the water rudder touches water only wen the plane gains speed

Santa,
It has nothing to do with the aeroplane, it is do with your control inputs, take off technique for a sea plane is completely different from surface borne  aeroplane, the reason is simple, rudder application will aggravate, water looping tendency, do the following :-

1. Open power very slowly, try not to apply rudder, even if you do, it should be very little.

2. What you should apply the most is opposite aileron, your aim is to pick up the dropped wing. remember as the ailerons are effective dropped wing will come up suddenly (due to sudden release of surface tension of the water) and you may touch the opposite wing,

3. during take off you need to keep wings level, unlike ground, water is a flexible surface and unlike ground aeroplane which has larger track , seaplanes have a smaller track. therefore, direction maintenance on water is by maintaining wings level by moving aileron continuously, sounds funny but true.

4. taxying in water is also mostly with the help of aileron.

Bottom Line

Open power slowly , pick up the dropped wing, when it comes upright, adjust and keep wings level, continue to slowly increase power, DO NOT pull back on the stick, let her fly off the water on her own.AILERON is the key.

Carefully watch this video, you will see hardly any rudder , he aims to get the dropped wing up first, then he looks to take of, somewhere in between you can see he is concentrating on keeping wings level by constantly moving aileron during take off. also in the end see the taxy, is with aileron and very little rudder. for landing you need to come on a power on shallow approach.

http://www.rcgroups.com/forums/showatt.php?attachmentid=1412810

while I am not an expert in any sense, leave alone for water takeoffs, but I did notice that the left wing is in contact with water while right one is not. Now, when in contact with water, that portion is putting in little bit of more resistance to forward motion than the other and hence could be the reason for left spin. It also could mean that your 2 halves of the wings are not of equal weight

thanks gusty, really valuable information  after a long time, i tried to correct the direction with rudder only, but on the initial
stages of take off it has no effect as the rudder is not touching the water , and if we increase the throttle the loop starts, next time will play with the ailerons but have to wait at least one month for the monsoon to come

It thought it had same behavior on the ground too ?

wheel base and wheel track are very big factors in designing an aircraft, in fact this determines the undercarriage , wheel well, and fuel that it can carry due reduced fuel due to wheel well(When the undercarriage retracts) it is a very big topic,

in water however it is the fuse which is the hull, footprint of which is small , left/right dragging force that a port /stbd wheel can create on ground is absent on a hull, on the contrary some hull will produce reverse effect , (If you apply left rudder, it will turn to the right) that is why it is important to get wings level as quickly as one can, without applying too much of power till you get wings level. thereafter it is  a piece of cake

It would be interesting to do some ground tests on a long piece of smoothly tiled floor (I guess after putting a bit of tape on the parts that would hit the ground).

Make sure that both ESC are of same brand and same rating.

Santhosh's electronics are always perfect, that's why i didn't question his build.

Not the build... I suspected differential thrust.

everything is as per the manual, used the suggested rimfire motors,esc's props etc.for my  mpx twinstar  i cut the centre lead of one of the esc's and conected it through  a y cable to the rx,for the catalina i didn't. connected the two esc's to a y cable and to the rx as the manual says so, not sure that make a big difference  :banghead: