|Aug 22, 2010, 07:07 PM|
Great Planes Cherokee 60 Post Build Report
It was all the great reviews that got me to buy in to this little gem. Here is my post build report with pictures on doing this plane with other than recommended gear.
Enjoy - Mark
I love how the ARF manufacturers always try and convince us we can get their plane in the air in just a "few" hours. I spent two hours with an iron just getting the covering acceptable. Then there were the little design issues (see text) which always take extra time not to mention the inspection and re-glue of many weak looking joints such as the cowl mount block that literally fell off in my hand. I'm pretty sure I have about 20 hours in the build and an additional 4 to 6 hours in development "re-dos". Of course, had I stuck to the manual using all the recommended gear, it would have gone a little faster.
I will say the manual was pretty good and had plenty of tips and pictures for the electric side although I didn't follow much of this. My plane ended up very light with the changes I made but these changes did not include modifying any structure with the idea to save weight. In fact the only cutting I did was to shorten the battery tray and cut out part of the servo tray. The rest was built per the manual with my equipment choices.
Please note: With regard to my listed weight savings, the comparative values shown came from both actual weight, which I measured, and catalog weight if the component wasn't available.
The fact they are suggesting Futaba 3003 & 9001 servos tells me it's all marketing and has very little to do with optimizing the performance. Here is what I used:
Rudder and Elevator - Hitech 225MG
Aileron - Hitech HS82MG
Flaps - Hitech HS65MG
Since I am using a switching BEC at 6v rather than a separate RX pack, I opted for a much smaller flap servo, the HS65MG, because a full size standard unit is simply un-needed given the requirement for torque and duty cycle. The other servos are also lighter, have higher torque and are considerably faster (2X!) than the recomended Futaba units.
All told this set up cost $58 more but I doubled the speed (halved the time) of full throw on the control surfaces. The Hitechs also produce more torque than the Futaba units when operated on 6v. An additional weight benifit of the Hitech set-up is the reduction in rotational inertia from using lighter servos out on the wings.
Total servo weight savings - 4.5oz (128gr).
The recommendation here is to use separate flight and reciever batteries. The flight battery is made up of one 3200 3S and one 3200 2S with a series connector.
The total battery weight of the recommended batteries including connectors, ESC and reciever pack is 24 Oz. Here is what I used:
Battery Pack - Zippy 6S1P, 20C, 3000mah, 16.5oz
BEC - Turnigy 6v Switching BEC, .64oz
SuperBrain 60A ESC, 1.8oz
Flight time - 9 - 11 minutes
Total weight of my set-up with connectors is 19.5oz, a savings of 4.5oz (128gr).
Motor & Prop
Motor - Turnigy SK4250-650
Prop - Turnigy Wood 12x8
The recommended motor is a Rimfire 42-50-800 which I like, however with the recomended Tower motor mount, it is pretty heavy. Additionally, because I wanted the efficiency of a higher voltage system, I decided to go with 6S and give the Turnigy SK4250-650 a try. It tested very well with the Zippy battery pack and Turnigy speed control and has, to date, about 25 flights without a hiccup. Also, given the way I constructed the motor mount, I ended up saving about three more ounces here.
The prop I have ended up with is the 12x7, Turnigy Light Electric Wood. The APC equivalent is fine but the efficiency difference cuts a couple of minutes off the flight time. I have also tried the 12x7 Top Flight Power Point and it falls somewhere between the APC and the Turnigy. I have ordered a Xoar to try as well.
Total motor weight savings - 3.2oz (91gr).
Total equipment weight savings - 12.2oz (346gr).
All up weight - 5.91Lb (2691gr)
This was a very pleasent surprise given that the manual states the weight as 6.75 - 7.25Lb (3060 - 3290gr).
The plane balances perfectly at the std 3-1/16" CG location without adding any weight or moving any components other than the main battery.
On the bench (static) numbers using a Medusa Research data acquisition unit:
At 100% throttle at a 10 second run point:
22.7 volts, 49.5 amps, 116oz thrust,1122 watts,11400 RPM,75mph pitch speed
My Bench Test
In flight data using the SuperBrain ESC data monitor:
20.8v min, 56.6A max, 1228W max, 11748RPM max, 145.9 deg F
The highest temp I have seen on the motor has been around 112F. The hottest day has been in the mid 80's.
The bench test results are real time at a given run point, the in flight values are minimum or maximum values stored during 5 minutes of flight time. The flight data includes both a 6 second vertical climb and a steady state, level flight run at 100%.
Spektrum DX6i TX
Spektrum AR6200 RX
I followed the manual on low rates but added some to the high rates.
I did make some changes here as well:
Minor Design Issues
Control Rod Tubes
The position of the rudder control rod tube exit (This may be a one time (my kit) deal) does not line up at all with the rudder control horn. This creates geometry problems caused by the angle of the control surface hinge centerline relative to the control rod, this was a challenge to make smooth and reliable.
Another design kluge is where the exit holes for the servo wires in the wing are placed. If you use these holes you risk having the sevo leads get tangled in the servo control horns of the elevator and rudder servos. The fix is to simply cut a new hole forward about an inch.
Would it be too much to ask the manufacturers to stop using #2 - #4 phillips head screws and just use socket head screws in these sizes? I am changing them all.
Maiden - In a word, wonderfully un-eventful. On take off the plane tracked solid and needed very little trim. Once trimmed it flies like a much larger plane. It is surprisingly fast, rolls are clean and inverted flight is a breeze. It is one of those rare planes that feels comfortable right away.
Landing this plane is easy and it looks fantastic. With flaps it slows right down and gentle three point landings are a piece of cake.
On low rates it flies scale like very nicely. It is rock solid and very easy to fly. On high rates, it is a bit of a different animal. I like the high rates but generally only fly with aileron and elevator on high with the rudder on low as it gets a litle snappy otherwise.
On another note I have tried using a 12x8 prop with a 4000mah, 20C battery and will say that this really brings the plane alive adding 10 - 15 mph to the top speed and making the verticle spectacular. The problem here is the Turnigy motor. The data logger shows I'm hitting 1630 watts on the verticle climbs and this motor is rated at 1150 max. I doubt it will last at this power so it's back to the 12x7 prop. The bigger battery adds 6.3oz to the AUW which wasn't really noticible and with the 12x7 prop, I can get 15 minutes of flight time.
I love it. It is a wonderful plane to build & fly and I would recommend it to anyone.
|Aug 22, 2010, 08:10 PM|
USA, KY, Lexington
Joined Dec 2007
That's a nice write up.
A quick question.
1.) Did the Turnigy motor's X mount line up with the blind nuts in the firewall? I'm curious because I hate redrilling firewalls.
2.) How long are your mounting spacers and where did you get them?
|Aug 23, 2010, 12:37 PM|
Cherokee Motor Mounting
To answer your first question, yes, the Turnigy X mount on the 4250-650 has the same bolt pattern as the original firewall. This was an added bonus for selecting this motor. One note here about these motors: If you haven't used Turnigy before, be prepared to do a thorough job of inspecting the motor for quality issues such as loose set screws and even loose magnets. They are inexpensive so you must believe they are lower quality in some respect. I have found some interesting things wrong but once found and corrected I have not had any issues at all with these motors.
On the second question, the spacer tubes were made from a piece of aluminum tube I bought at the local hobby store. A very close equivalent to the tube size shown in the pictures can be found here on the Tower Hobby site. The length of the tubes are all equal and that length is 2.300".
The length could have been 2.360" and this would eliminate the need for the small washers (X8) shown. I did it this way, with the washers, in the event I would want to adjust down & right thrust but this has proved unnecessary.
As far as the other hardware, I have this awesome local hardware store (here in the Seattle area) which has the biggest gadget freak fastener section I've ever seen. This is where I found the nylon "mystery" bushings, fender washers and very long 6-32 stainless screws. The purpose of the nylon bushing is to soften the mount in terms of electrical noise and help manage imperfections in the tube cut.
You could easily do this mount with just the tube and a single flat (fender) washer on the wood bulkhead. In this case the tube length would be 2.500". Keep in mind, the strength of this method is related to the quality of your tube cuts. That is, if the cuts are not square and the tube lengths vary much, you will loose strength. I used a mini lathe, but you could do this by hand with a bit of patience.
Please see the pictures for more info.
Cheers - Mark
|Aug 24, 2010, 10:55 AM|
Joined Oct 2008
1122 watts thats is alot of power.. Is speed the reason you choose your system? What made you go with the 6s lipo?
I have this set up on my Cherokee
Grayson GH2826-05 motor & 50A ESC
4S 5000 Lipo
APC 11X7 prop
625 + watts
It flys great, I love the flaps!
|Aug 24, 2010, 09:51 PM|
Yes, 1122 watts is a lot and was a little unexpected as I was shooting for around 950 watts with a little headroom. The 1630 watts I saw with the 4000mah battery and the 12x8 was a shock as well since I hadn't seen numbers anywhere near that on the bench tests I did so I re-ran the tests with the new 4000mah battery and found 1560 was the static top end with this new battery. The conclusion here is; batteries make a difference. The original testing was done with an older set of 4, 3S-2200's in a 6S2P config which apparently didn't have the punch that the new 6S-4000 has.
I chose 6S because higher voltages are more efficient and I wanted to limit the speed control to 60 Amps. So, if I had gone with 4S (15.8v midpoint) and was shooting for 950 watts then I would need a motor and speed control capable of 60+ amps continuous with no head room for props, etc. and I would need much more capacity (mah) to get decent flight times.
With 6S, the current need is around 40 amps for the same 950 watts so there is plenty of room for prop changes or using much smaller, lower capacity cells ($). I use a 3000mah Zippy as the regular pack which is lighter than any of the Zippy 4S-5000 packs and over an inch shorter. My flight times are fine with this and nothing ever comes down hot.
Yes the flaps are cool. This is the first plane I've had with flaps that actually make a very nice difference.
Thanks - Mark
|Aug 26, 2010, 07:51 PM|
Joined Apr 2008
I just stumbled upon this thread and I'm glad to see someone else enjoying this plane as much as I do. Mine logged flight #155 today and it has become my favorite all-around plane.
I've powered mine with three different electric motors (including the same Turnigy Mark uses) and am currently using the Rimfire 42-50-800 on 5cells and drawing about 950 watts. It's all up weight is 6.2 lbs - I also used lighter servos, but only for the flaps.
Mine had same issues - rudder pushrod needed to be angled about 1" ahead of control horn and the exit holes for the wing servo wires are in an awkward place. I just taped the wires down to the wing for a couple of inches.
I'm using aluminum motor standoffs supplied by Hobby-Lobby. The work great and weigh less than the recommended GP motor mount.
Mark's comment that "this is one of those rare planes that feels comfortable right away" nails my feelings exactly. I've got about a dozen operative electric planes right now but this one is my hands-down favorite!
|Sep 04, 2010, 10:42 AM|
To add just a little to this, I get asked a lot about the arming switch set up I use. I've included a simple wiring diagram here to help with the explanation.
This all started with my developing a fear of propellors in the 60's when I got bit by a Cox .049 on a Carl Goldberg Li'l Satan flying wing. While I have gotten over the nightmares, I do still respect this part of the airplane especially on the larger (500 watt+) ones.
To do this, I use a battery eliminator circuit (BEC) and then just simply put a switch between the signal and ground to the ESC. This effectively dis-ables the ESC and motor while keeping power to the reciever and servo circuit constant. So, providing there is no failure of the BEC itself, the only failure mode should be a motor shutdown if the switch fails. This would also work with a separate RX battery pack and some would say this is the most reliable method.
The switch I use is a double pole double throw as seen in almost all switch harnesses. On some planes with a programable controller, I add a separate servo plug to serve as a data port. This keeps me from having to continuously un-plug/re-plug this wire into the receiver.
Another little bonus for doing this is, I then can easily bump up the voltage to the RX to 6 volts which helps with downsizing servos (or speeding them up!).
Check out the picture! - Mark
|Oct 11, 2010, 01:57 AM|
My plane is on the way, have any of you used an ESC with a build in SBEC? I'm going to use Mark Q's setup, 6S, motor but I think I will use http://www.hobbyking.com/hobbyking/s...eed_Controller or something just like it.
|Oct 19, 2010, 01:21 PM|
Many ESC's BEC is only good to 4S. Make sure this one is usable at 6S. Additionally, check the forums and make sure the SBEC will actually provide 4A. You don't want a brown out with this beautiful plane!
Also, my setup consistently hits the hi 50 amp (max to date 72 Amps for less than a second) range on vertical outs and with a 60 amp speed control and good air circulation the ESC has run as high as 145 degrees F. The point here is if you are going with my setup, 6S, 650Kv and a 12x8 prop you'll likely flame a 40 amp speed control. If, on the other hand you are going to prop (way) down to maybe a 10x8, you might be OK. Test, Test, Test, etc...
Enjoy, it is a very cool plane! - Mark
|Oct 30, 2010, 10:32 PM|
Ok, I'll find one with a higher amp range, I just pulled 40 amps out of things I researched on the turnigy 42-650. I got my plane, all I am waiting for are my servo, motor, etc.
|Dec 05, 2010, 02:59 PM|
There is a big balsa block in the front-right hand side of the fuselage, What the heck is that used for? Is it just taking up space for this model, I assume that that use this fuselage for several models?
|Nov 05, 2011, 10:34 AM|
Very nice write up! I am glad that I found this thread but wish I had found it earlier. I have built my Cherokee ARF early this year. She flew very well in the maiden flight but the front wheel pan puncture the fuselage. I repaired the fuse, took off the front wheel pan and installed a larger (3" instead of 2.5") front wheel. We have a pretty rough grass run way. Larger wheels does help. I know, I know, it's a huge sacrifice to skip the wheel pan. I think I overdid the power plant, such as Turnigy 4060 instead of 4050 and the 40C batteries. I will try to lose some weight and see if I am comfortable to put the wheel pan back. I may make a plywood patch to protect the fuselage as well.
Maiden flight video:
Build and test video:
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