72 lanc motor prop question

[Djay]

I have just built the 72 inch TN lanc and fitted it with the recommended purple power motors and 8x4 3 blade props, all up weight aprox 7 1/2 pounds.

Each inner and outer pair of motors is fed by one 4500 3 cell Lipo, ( 2 batteries total).

On its first flight the left aileron servo failed after takeoff and when I used rudder to turn it spun, I cut the motors and it levelled out just before crashing and sustained minor damage.

After repairs It flew again but problems with the retracts meant I had to fly gear down.

After gear repairs I flew again the following week, but it struggled for power on take off, even though the batteries were fully charged.

The plane struggled to fly at full power and dragged its tail all the time, even though it is balanced slightly nose heavy.

The plane would not turn due to lack of power and spun into the ground.

Damage was limited to broken side skins on the nacelles and nose stoved in.

I made a new nose and grafted it on, and spliced new wood into the nacelles.

It is ready to fly again but I am reluctant to use this power train set up.

Does any one else fly their Lanc with this set up?

On the purple power site they recommend 8x6 two blade props, but supply the 8x4 three bladers.

Will switching to the 2 bladers make any difference to the power delivered by the engines in flight? I have a set of APC electric props I can use.

Any suggestions to prop sizes will be appreciated.

Failing that I will have to upgrade the motors to the next size up from Purple power.

 

Darryl

 

Edited By Djay on 29/08/2011 12:28:50

[Tim Mackey]

These motors ( which are just turnigy units in a different colour ) will poroduce maximum power ( circa 200watts ) on a 3s with an 8 x 6 two blader.

When I calc the equivalent 3 blader, I usually just reduce the diameter by an inch, so giving in your case a 7x 6 3 blade. I wouldnt have thought that there was a ton of difference between the 8x4 against the 7x6, except of course the pitch speed will be higher on 6" pitch.

Have you checked the power of each motor with a wattmeter? Its not the first time I have experienced wildly different actual results from those specified by P/Power themselves.

 

4 motors @200watt each should be ample for an 8lb warbird - not particualrly powerful, but ample.

[Djay]

Hello Tim.

Thanks for the reply.

 

I have contacted 4 max, who supplied the set for this lanc and he says I should be using the 8x4 two blade on this motor.

So why supply 8x4 three blade?

 

I will try thr 8x6 two blade as I have 4 of them available, and will have to send of for the 8x4 two bladers if you think they will work ok?

Each pair of motors are wired in parrallel with one battery of 4500, 3 cell lipo.

 

 

Darryl

[Tim Mackey]

I didnt mean to give the impression that I recommended the 8 x 4 as I personally reckon the pitch is too low for the model - I'd stick with the 8 x 6 two blader, and check the power readings on the wattmeter - you have got a wattmeter - right

 

Remember of course, the current will drop a bit in the air as the props unload.

 

When you say each pair of motors is wired in parallel, I assume you mean that each pair of ESCs is wired in parallel at the battery connections.

[Djay]

Hello Tim.

Yes I do have a watt meter, not checked the motors yet.

Correct each pair of ESCs is wired to one battery, inners to one battery, and outers to the other..

4 max recommended the 8x4's saying the 8x6 will be to much for the 1300kv motors, but then I told him we fly in 45+c temps and high humidity, so he recommended try the 8x6 props.

Funny really as on his web site for that particular motor he recommends 8x6 two blade.

 

Will be test crashing it with the 8x6 APC electric props on Friday if winds are not to high.

 

Darryl

[Tim Mackey]

Yet again, evidence that recommendations for props on certain motors is "unreliable".

The motor specs ( on that very site ) recommends 8 x 6 two bladers on a 3s battery - so why now tell you to fit 8 x 4s

Now Ive mentioned it before, but I had a similar issue with this vendor myself some time back - using a motor and prop combo supplied by him, the claimed current draw on a 3s lipo would be 35A. In fact, it was over 50 !

When I mentioned this, I was told it was probably my meter ( an expensive Astro Flight wattmeter which had given sterling service for 3 years prior ).

So I checked the data again with an eagle tree logger, and got 50A +/- 2A

I borrowed 3 more wattmeters of differing makes off friends, and got figures ranging from 47A to 51A. I relayed this to the vendor, and was "fobbed off" with claims that he had checked these motors himself, and was satisfied that his data was correct. Ho Hum.

As our American cousins say...go figure

I vote with my feet, and have never used them again.

 

PS: USE THE METER before you fly - thats what its for

[Keith Simmons]

I also brought some motors from 4 max using their recommendations, but as I am still building, have not tested the set up with a Watt meter. .

 

Can I ask which brands you have found to be reliable recommendations and not so reliable as it is expensive if the motor is found to be weak or current to be too high for the chosen prop to fly the model. (I can use the motor for a different smaller model for the future but first will experiment with different powertrains and props using a watt meter.)

[martyn sharp]

Hi keith I am thinking of using these for my lanc i have used EMAX befor and found them to be realy good also there is alot of data in the forum on GC

 

what do you think Tim

 

Martyn

[Tim Mackey]

I am not saying the actual motors are not good - they are simply re-badged Turnigy ones, and at the price point, they represent good VFM.

Some of the tower pro range are fine, others not so.

Mega motors are excellent, as are MVVS - at a price of course.

Scorpion are good mid range.

E Flite are excellent, and I have had good results with a couple of EnErGy motors I have.

TBH, I have always been pretty pleased with the Turnigy stuff.

[Tim Mackey]

EMax - only ever had one, and it was fine, but I soon sold the model on, so cant comment on its long term performance.

[Djay]

Well, finally got round to test flying the Lanc with 8x6 APC props.

What a difference, the plane was transformed, as soon as I opened the throttle it raced off and lifted in no time at all.

I flew around at just above half throttle, and occasionally went to full throttle.

The props have made it into a nice flying aircraft, not a wallowing pig.

 

So i would recommend the Purple Power set up, with inner motors and outer motors wired to individual batteries, size as recommended for the set on the web site, and use the APC props.

ESC's and batteries were not even luke warm after 5 minutes of flying.

 

I believe that the 3 bladers supplied are so thin and flimsy that they were flattening out in flight and loosing their pitch.

they are only thin flexi things more for a slow light park flyer.

 

Now I can concentrate on trimming and getting used to the model, so I can enjoy it.

 

Darryl

[Tim Mackey]

Excellent news