Piper Pawnee Progress

[Mike S]

Well been busy over the last few months putting the blade 400 in the to airwolf fuse and sorting out engine troubles with the wot trainer.  So finally got round to finishing the Pawnee after having to put it on hold for a month or two.



Decided to follow suit with the Wot trainer and this being a large aircraft go with a separate bec & lipo for the rx setup. Just have to sort out the wiring runs



Power is a JP EnerG IC60 50-20 with a HImodel professional 80A esu turning a 13x8 apc prop.
Using a 5S pack amps are approx around 56amps at wot, yet to run the static test to confirm this and work out the flight times. Have two 5s lipos one is a 3000 30c and the other a 5000 20c. Auw is 8lb or 8.5lb depending on the lipo used. 



According to the manual it suggests that the c/g should be 2 7/8– 3 3/8 inches (73mm–85mm) from the le mid wing or 6 3/4 inches (171mm) behind the cuff of the wing against the fuselage, with a range of 6 1/2– 7 inches (165mm–178mm).

Hanger 9 have now released a bulletin which reads:

We have determined from further flight testing that the CG range of the Piper Pawnee can be 2 ½ inches (63mm)  to 3 3/8 inches (85mm) from the leading edge of the wing. With the CG at 2 ½ inches it will be easier for you to balance and not need as much tail weight.

So for its maiden would it better to setup the c/g a little nose heavy until the correct position can be found and should I aim for around the mid position of the c/g range?.

[Russ]

So for its maiden would it better to setup the c/g a little nose heavy until the correct position can be found and should I aim for around the mid position of the c/g range?.

I'd go with the forward CofG (63mm from LE) and dial it in from there.

Will be interesting to see how this one flies. At 8 - 8.5lbs its should be pretty good in the wind.

[Sheraz]

I would agree,

Talking from experience, a tad nose heave is easier to deal with


sheraz.

[Mike S]

Ok I will have at a look at the CofG tomorrow and try and do a static test and work out the amps and see if they match whats on paper. All being well I would like to get this maidened in the next few weeks. Hmm just had a thought the wing span when fitted is 6.8ft and the fuse is near 5ft long and I have a small car. lol

[Gareth]

Looking good Mike, She is going to have a nice weight to her and because of the large wings she should slow down nicely as well.

I would start off at the forward position and bring some stick on weights for the first flight (easy way to adjust).

With the small car issue, tip the passenger seat back and put it in that way, you will have loads of room.

Gareth

[Mike S]

The car seats do lay down well in the suv . Ahem  should fit the plane ok.

[Mike S]

Right well been a while since I had a look at the Pawnee but now I have flown my Pulse it has given me the push to get this sorted.

Ran the motor up with my watt as follows:

5s 3000 30c lipo,
80amp Hi-power esc 
JP EnerG IC60 50-20
13x8 prop.

Paperwork suggest 56amps, watt meter read out 36amps at wot, hmmm
Half throttle read out 18amps??

The esc may have start up setting that allows the esc to detect the thottle movment on the tx like the Jp EnErG esc as motor responds at around 1/4 throttle. I will have a re-read.


CofG with the 5s 3000 is dead on 63mm from LE at 74 its nose heavy with 85 unable to balance.
I will have to rethink this as my other lipo is a 5s 5000 20c and of course upsets the CofG at 63mm putting to nose heavy.

Options 1:

Add weight to the 3000 to match up lipo weight of the 5000 and move the flight lipo and rx futher back to help achive balane at 63mm.

Option 2:

Fly it with the 3000 to see how the CofG is and work from there.
Hole is cut in the rear underside of the fuse for the air to get out.

[Gareth]

The esc may have start up setting that allows the esc to detect the thottle movment on the tx like the Jp EnErG esc as motor responds at around 1/4 throttle. I will have a re-read.

Mike,

I have heard about some ESC's doing this. IIRC its to do the with pulse frequency of the low and high settings of the TX (Futaba and Jr are different). The way to get round this is to have the model on and move the end points of the throttle. you will have to make the low end about 80% and the high end about 120% but have a play and see what works. I will try and find a link and confirm what i think.

Gareth

[Gareth]

I do remember correctly and i have found the link.

http://www.highalpha.org/forum/viewtopic.php?f=7&t=8828

If you can use a program card that might be an option or just change the end points on the TX to match the expected pulse of the ESC. it sounds like you are missing on 1/4 of your power in the top end. lots more fun to be had with that.

Gareth

[Mike S]

Intresting. Thanks Gareth.

I do not have the programming card but can get one if needed. I will have a read of the instructions and have a go at these end points on the tx..

[Gareth]

what is the ESC, i have a load of different cards that might work. I have one from hongkong, one from robot birds, one form hacker and a jeti one.

Let me know if they would help and i will dig them out.

Gareth

[Mike S]

Right found the instructions. You can set the throttle range the same way you can on the Jp esc's. I will do this over the next few days and comfirm all is ok.

Gareth the model is:

Hi-Model 80a Professional

80amp (burst to 100amp>10secs)
User programmable yes

http://www.himodel.com/electric/HiModel_Professional_Series_60A_80A_Electric_Brushless_Speed_Control_Type_Professional-60A.html

[Gareth]

Hi-Model rings a bell, i will have a look i think that was the ESC that was in the P38, not sure if the program board went to Phil with the model or not. Would also be worth asking Phil as i think i would have passed it on (those being the only Hi-Model ESC's i had). Phil changed the ESC's and motors out before selling the model on so might still have the bits needed.

Gareth

[phild]

I cant remember having any cards with the model sorry.
Mike just as a matter of interest what weight did the aircraft work out at and how many watts did you get when you  ran  the motor up? If I remember correctly I used a six s set up in my pawnee, and still did'nt get sparkling performance from it.
You should be looking for a minimum of about 700w preferably 800+ I don't know what KV your motor is but you may be better off looking at a larger prop maybe something like a 15X8 which should bring the power up and give you more static thrust than you are getting from the setup you currently have.
As for the CofG I placed a 3s5000ma battery either side of the servo tray which worked out just fine for the stated Cof G at that time, but I have hear from others who were looking to stick huge amounts of lead into the tail to balance with a battery in the nose.

I will be interested to see how you get on with the Pawnee, once you have got all the teathing problems sorted you should have no problems flying the thing as it is really a huge pussy.
Best of luck with it

Phil

[Mike S]

Phil lowest weight come out as follows but I need to confirm this as it was a while I go checked the weight but:

5s 3000 auw = 8lb 2oz
5s 5000 auw = 8lb 10oz

From the manual APC (13x8)   Amps 58.0 Thrust 2320g Watts 854 Rpm 8900 Vts 18.5V

Once I have sorted the throttle range on the  esc I will re check the amps with watt meter.