HobbyKing.com New Products Flash Sale

Graupner Cub

The Graupner Cub has great presence in the air and has no problems flying on windy days due to its larger size. With the Jeti motor setup, you can also use larger props that a typical glow .40 would use as well. Subsequently the Cub has made a great electric conversion, as the plane assembles very quickly, converts easy, and flies great.

Splash



Wingspan 72" (1.83m)
Length 40" (1m)
Wing area 690 sq. in. (45 dm2)
Motor Jeti 45-3 Brushless
Speed controller Jeti 70-3P Opto
Batteries 16 CP-2400
Servos Futaba 3003 (Ailerons), Airtronics 9410 (Elevator, Rudder)
Prop APC 11x7E
Weight 6.1 lbs (2.77 Kg)
Wing loading 20.4 oz./sq. foot (64gm/sq. dm)
Available from Hobby Lobby International Inc.

The Path To Cubness

I must admit, when I was first offered to do a review of a Piper Cub model, I wasn't too excited about it. Nothing against the ubiquitous Cub, a common sight in any club field, it was that I was more interested in something more, "heavy metal" and imposing. Maybe like a 30-cell P-38 model. (one can wish...)However, after a bit of thought, I realized a big .40 sized Piper Cub is a great model to have. Equally applicable to fun-flys, scale meets, and weekend flying. It is also a great candidate for float flying. Plus, every modeler should have a Cub, right?

The Kit

It's fertig bespannt! The plane came in a semi-large box that's also great for practicing your German. As you can see, there aren't many pieces to assemble.
The Graupner Cub arrived in a rather large box with all the equally large pieces neatly packed inside. Unpacking the parts revealed a rather large fuselage with even larger wing halves. (Did I mention that this model is pretty big?)All of the airframe parts were very nicely covered with a low temperature (Oracover?) iron on covering in the typical Cub yellow color. The only wrinkles found were on an aileron, which was fixed with a heat gun blast. Construction is of mixed balsa and light ply with plenty of lightening holes. The wood work and construction is very well done and not excessively overbuilt. I doubt much more could be done to lighten it up if one were to build it as a kit specifically for electric. Another nice feature is that all the control surfaces are pre-hinged and even pinned for security. The kit also included vacuum formed dummy engine cylinders, a pre-painted fiberglass cowl, and nice pre-made (and nearly scale) landing gear struts. The main manual is in German, but includes many photos of the construction steps. If your German in not up to speed, there are no worries, as an English instruction supplement in included.

Wings

Aileron servos are mounted into pre-made, screw-on servo plates.
Construction starts with the wings (if you are a by the book type of person), which come in two halves. Since the aileron servos reside in the outer wing panels, you must install the aileron extension wires into the two wing halves. (I used 24" extension wires.) Graupner was very thoughtful and provided pre-installed threads for pulling the servo leads through the wing, which was quite useful. Once the servo leads are pulled through, then the wings are joined together with epoxy and work can then be started on the ailerons.
The wings included strings to pull the servo leads through the inside. A dihedral brace is glued into place before joining the wings with epoxy.
The aileron servos are mounted into servo mount plates that are subsequently screwed into the wing. These plates made setting up the ailerons very easy, as they are designed for standard size servos. (I used Futaba 3003s for the ailerons.) Mounting the control horn and linkage after the servo plate is bolted into place completes the direct control setup. I must admit that I spent more time admiring the wings than it actually took to assemble them!
Wing halves being glued together Aileron servos mounted and connected

Fuselage

Fuselage construction is a little more involving, due mainly to the electric conversion changes and extra detailing. Equally of superb construction, the fuselage assembles quite quickly. It even includes cockpit gauges and a painted deck. In addition, the tail pushrods come even pre-installed. I noticed that some of the wood window frames weren't glued completely, but some medium CA quickly solved the issue.
The fuselage as it comes out of the box Inside the fuselage, note the control panel
First, the tail parts are glued into their respective places. Interestingly, the manual shows the use of a soldering iron to remove the extra covering from the fin slots. However, my trusty hobby knife did the job just as well. The kit includes a rather nice tail wheel assembly that comes pre-bent with a spring dampener.
Trim the covering from the tail slots Tail pieces after trimming some covering away for gluing


Tail parts glued into place Included tail wheel assembly looked and worked very good
Once the tail surfaces were mounted and connected, I did find it necessary to bend the elevator rods a little for more free movement. The rods are attached to the servos with nice E-Z type connectors (also included). Wood elevator and rudder servo mounts are also pre-installed along with a receiver switch mount. Again, standard sized servos (Airtronics this time) were used and fit perfectly.
Jeti 45-3 motor and 70-3P controller setup Two 8-cell packs of Sanyo CP2400mAh cells, from Eflightpacks.com, are wired in series to make 16 cells
The motor Hobby Lobby recommends for the Cub conversion is the Jeti 45-3 brushless. It is a big hunk of a motor (just under 11 ounces) designed for swinging larger props direct drive style. Hobby Lobby's website recommends 10x7 to 11x7 props for 12 to 16 cells. For my setup, I decided on 16 cells (two eight cell packs wired in series) and an APC 11x7E electric prop to start at the higher power levels. Controlling all this is the Jeti 70-3P (70 amp) opto-coupled speed controller. This is a pretty powerful controller that only weighs 1.4 ounces. (40g) and is rated for up to 16 cells.
Graupner clamp-on motor mount is used to attach the motor to the standard glow motor mounts.


x
The motor is held in place with four screws. Note the cooling hole in the bottom of the cowl. The batteries needed to be poked through the firewall to get the balance correct.
To mount the 45-3 motor, I decided to use a very simple product that uses the stock engine mounts that are included in the kit. Graupner part #1153 is a simple clamp-style motor mount that works for many motors of around 35mm in diameter. The included mounts were the perfect spacing for using this style of motor mount, which uses four screws to keep everything in place. In addition, the motor mount firewall includes a few degrees of right thrust built in. To get the C.G. correct (70mm from the leading edge), it was necessary to cut a hole in the firewall to let about an inch of the battery packs poke out. I first drilled a bunch of pilot holes then cut out the section with a small handsaw. The rest of the battery pack fits in where the fuel tank would go. It was also prudent to cut out a small section of the fuselage former just behind the firewall (normally used to hold the fuel tank).
Vacuum formed cylinders were cut out, sanded, and then painted before gluing to the cowl.
Once the motor was mounted, the cowl was then mounted into place using four wood screws. The cowl does have a rather large hole cut into the bottom of it (for the glow engine's cylinder to poke out of), but it is not really noticeable, even in flight, and it makes for great motor cooling. The dummy cylinders are vacuumed formed from sheet styrene, which I cut out and painted with regular plastic model paint (gunmetal and steel colors) before gluing into place with CA.
Graupner has done all the hard work for the landing gear. Foam wheels and "Cub" hubcaps Here are the mounted landing gear and wing strut support plate. Note that the gear fairings are held on with tie wraps.
One of the real gems of the Cub kit is the landing gear, which comes out of the box just as the picture shows. It has nicely done solder and truss work and even has simulated shock absorbers. The landing gear fits into slots on the bottom of the fuselage, and it is held on with straps and screws. Wood landing gear strut fairings are held on with tie wraps, which must have the slots cut out for them. This was the only part of the kit that I thought wasn't so elegant, but it does work well. The wheels are of the lightweight foamy kind with plastic wheel hubs that have raised "CUB" lettering, which I eventually painted with black plastic model paint to accentuate the letters.
Wing struts Wing strut mounts in the wing are screwed into blind nuts
The final assembly process involves setting up the functional wing struts. Yes, the struts are actually load supporting and are not just for looks. A lower wing strut bracket is mounted just behind the landing gear, and metal eyelets are screwed into threaded mounts in the wings. I needed to trim the eyelet holes in the wings a bit with a hobby knife to prevent the covering from getting into the threads. The struts themselves are made of pre-painted metal (aluminum, it seems) with adjustable length clevises on one end and a screw hole on the other. The screw-hole ends must be bent to about 45 degrees with pliers to match the fuselage bracket and bolt hole. With the wing bolted (two wing bolts) in place and the struts connected, I suddenly had a model with presence.

Flight Setup

The radio electronics are installed and ready for flight. Velcro holds some parts to the side of the fuselage. A UBEC from Koolflight (white part on the right of the fuselage) is used instead of a receiver battery.
The final steps were to apply the large set of decals and setup the control surface throws. When I say large decals, I mean large decals as the wing letters are huge. They are the "cut out, peel, and stick" type so it doesn't take long to apply them. The numbers are apparently of a relatively well-known plane, as I've seen the same registration in a picture of a real Cub. Interestingly enough, the fuselage came with the black stripes already in place.
The huge decals look really good once in place.
A computer radio is highly recommended, as the manual recommends setting up the ailerons with control differential (20mm up and 7mm down), but a standard radio could be used with a "Y" connector for the ailerons. The rudder and elevator throws were also setup as stated in the manual. I did put the recommended settings on the radio's low rate and more aggressive throws on high rate, just in case they weren't enough. (This later proved to be unnecessary.)
The ready to fly weight, with batteries installed, came to just under 98 ounces (6.1 lbs or 2.8 Kg) for a nice wing loading of 20.4 oz./sq. foot (64gm/sq. dm). This is actually a touch lower than the published weight in the manual of 6.4 lbs (2.9 Kg). A bench test of the motor setup showed that the 11x7E prop spun at 9,400 rpm and caused the motor to draw 32 amps for about 500 watts, which comes to 78 watts/lb.

Day Of Reckoning

Look Ma, a Cub! Takeoffs are quick and powerful.
The maiden flight took place on a bright and sunny day, if a bit breezy. Following a successful a range-check, I taxied out to the end of the runway with a pause for calming the nerves a bit; I slowly advanced the throttle to full. The Cub tracked down the runway quite well, just needing a bit of right rudder to keep going straight. After about 50 feet or so, she was up in the air and climbing very well. In fact, it will sustain a near 45-degree climb with no problems. However, the first flight was done with the CG a little too far back (before I cut the hole in the firewall for the batteries) and it showed. I had to keep the speed up or it would tend to stall a wing easily. It certainly made for an exciting first flight. Sanity prevailed and I decided to end the flight early to correct the balance problem.
Whether low or high, the Cub makes great looking scale-like passes. Is it real, or Memorex?
The next flight was with the CG in the correct position and it, of course, behaved much better. The control setups per the instructions were just fine. Even though the ailerons didn't look like they moved much, the roll rate was quite good. The same goes for the elevator and rudder. One thing I immediately noticed was that it liked a bit of rudder to make the turns more coordinated. You don't have to use rudder in the turns, but if you didn't, it would noticeably slip in the turns, which looked kind of funny (this would be a good model to learn rudder control).
The Jeti 45-3 motor provided plenty of power to pull the model through all sorts of non-scale maneuvers like large loops, slow rolls, and even sustained inverted with no problem. Level flight can be easily maintained at partial power. Power off stalls simply caused the model to mush forward wings level at a nice slow speed. Power on stalls did show a tendency to drop the left wing, probably due to the torque of the prop. Landings are pretty easy as the glide is quite flat and it retains speed longer than I would have expected, which is kind of surprising as one would think the struts would cause allot of drag. A typical flight of mixed aerobatics on the CP2400 cells lasts about 7 min. I'm sure that using the newer high capacity nickel metal hydride cells, 10-minute scale-like flights would be easily achievable. Since the motor is only pulling 32 amps full throttle, there is still room to go to an even larger/more pitched prop if I ever decide to add floats to the model.

Conclusion

Flying the Cub has been really neat. It has great presence in the air and has no problems keeping up with other glow planes. (In fact, some of my fellow club members chided me for flying a bit too fast for scale at times.) Another nice thing is that the model has no problems flying on windy days due to its larger size. With the Jeti motor setup, you can also use larger props that a typical glow .40 would use as well. Subsequently the Cub has made a great electric conversion, as the plane assembles very quickly, converts easy, and flies great. Now I just need a Flying Farmer pilot figure.

Discussion

Reply
Thread Tools
Old Jan 05, 2005, 02:56 AM
Registered User
Joined Jan 2005
22 Posts
I want to purchase the piper cub by Graupner. I have doubts about the electric set-up with the Jeti 45 3 motor and 70-3p apto controller. Can anyone suggest a motor that would work real well, and probably a gearbox? Thanks and Maholo... [We fly in alot of wind here on Maui most of the time, but year-round]... Trooper...
ttrroopprr is offline Find More Posts by ttrroopprr
Reply With Quote
Old Jan 05, 2005, 03:12 AM
Registered User
Joined Jan 2005
22 Posts
I want to purchase the piper cub by Graupner. I have doubts about the electric set-up with the Jeti 45 3 motor and 70-3p apto controller. Can anyone suggest a motor that would work real well, and probably a gearbox? Aloha and Mahalo-... [We fly in alot of wind here on Maui most of the time, but we can fly year-round]... Trooper...
ttrroopprr is offline Find More Posts by ttrroopprr
Reply With Quote
Old Oct 27, 2005, 11:08 AM
Registered User
Zephyrhills, FL
Joined Oct 2003
144 Posts
I've been looking for a Cub ARF to electrify and this one appeals to me rather than several others I've looked at. However, the wheels look funny. Are they the correct scale diameter??
Eplane65 is offline Find More Posts by Eplane65
Reply With Quote
Old Jul 08, 2006, 01:55 AM
know it all
Miami, Fl
Joined Nov 2003
2,949 Posts
oh well, Hobby Lobby put it on sale.. this size cub would use 3" wheels.

Herm
hermperez is offline Find More Posts by hermperez
Reply With Quote
Old Jul 27, 2006, 07:01 AM
Live to Fly, Fly to Live
Tweek's Avatar
Youngsville, NC
Joined May 2006
175 Posts
Since this is 72" wingspan, does it qualify as 1/4 scale? I don't know what the full size Cub is...

Thanks,
Dave Hockaday, AMA 119484
www.2vulcans.net
www.rd-rc.org
Tweek is offline Find More Posts by Tweek
Reply With Quote
Old Jul 27, 2006, 07:28 AM
know it all
Miami, Fl
Joined Nov 2003
2,949 Posts
nope, 1/6 scale I think.. 104" is 1/4 scale.

Herm
hermperez is offline Find More Posts by hermperez
Reply With Quote
Old Oct 13, 2006, 10:49 PM
Flying is FUN
Joined Apr 2005
153 Posts
What no video come on
layback2 is offline Find More Posts by layback2
Reply With Quote
Old Oct 29, 2006, 05:38 PM
Fred
United States, FL, Bradenton
Joined Oct 2006
87 Posts
Hi I just built this Piper Cub and had 4 flights...all crashes. I have moved the center of gravity from 100mmm to 70 mm and the effect is the same..as soon as the aircraft leaves the ground the left wing veers down and the plane goes down violently. I used an AXI 4330/20 motor(outrunner reverse mounted) and 24 volts generated by 2- 3 cell LIPo's in series with a 13x8 prop and also with a 14X 10 prop. In every case the plane crashed. I sure would appreciate any comments.
Fred
fredsgr is offline Find More Posts by fredsgr
Reply With Quote
Old Nov 14, 2006, 10:00 PM
Flying is FUN
Joined Apr 2005
153 Posts
just maybe you need help on the ballance i use to persons one holds the prop and one holds the bottom back of the plane and both lift at the same time if the left or right wing drops then you need to add weight to that wing maybe just maybe that will help you hope so it help me on larger wing planes were the CG was not right and try the 100 mm again the try the ballance like i do good luck
layback2 is offline Find More Posts by layback2
Reply With Quote
Old Nov 29, 2006, 07:55 PM
Eye Drather Beef Lying
ElectRick's Avatar
Jacksonville, FL
Joined Aug 2002
2,696 Posts
Esprit Models website says the CG in the book is wrong. It should be 70mm from the LE, or right on the main spar. If you tried it at 100mm, no wonder it snap rolled on takeoff.

http://www.espritmodel.com/index.asp...OD&ProdID=2099

Regardless of what Hobby Lobby's motor recommendations are, an AXI 4120 is too much motor for the plane. There are bigger 81" Cub conversions on Ezone that fly great on the AXI 2826. The added torque from too large a motor can aggravate the tendency to snap roll on takeoff if you don't roll on power slowly.


Rick
ElectRick is offline Find More Posts by ElectRick
Reply With Quote
Old Dec 10, 2006, 08:47 PM
Fred
United States, FL, Bradenton
Joined Oct 2006
87 Posts
Crashing Cub

Thank you both for replying to my query regarding my crashing cub. The cub is in tiny pieces now. I am thinking of building the same model again to get to the borttom of the problem. When I submitted my comments I saw no comments for a while and decided no one was reading this link. So I stopped looking. I see I was wrong. The correct motor is a AXI 4130/20.
I will try a slower take off and maybe a smaller prop to reduce my thrust. The 4130/20 is a slow turning motor.
I had some advice today regarding mixing some rudder with the airleron.
Thanks again.
Fred
fredsgr is offline Find More Posts by fredsgr
Reply With Quote
Old Dec 10, 2006, 09:32 PM
Registered User
Zephyrhills, FL
Joined Oct 2003
144 Posts
I have a Hangar 9 Cub; 80 inch wingspan which computes to roughly 1/5 scale. It weighs 8.5 lbs. I use an AXI 4120/18 motor and a 5 cell 5000 mah lipo battery and a 13X10 Zinger prop. It has PLENTY of power.
Eplane65 is offline Find More Posts by Eplane65
Reply With Quote
Old Dec 10, 2006, 10:17 PM
Fred
United States, FL, Bradenton
Joined Oct 2006
87 Posts
How does it fly? Any tendency to loop to the left on take off?
fredsgr is offline Find More Posts by fredsgr
Reply With Quote
Old Dec 11, 2006, 11:37 AM
Eye Drather Beef Lying
ElectRick's Avatar
Jacksonville, FL
Joined Aug 2002
2,696 Posts
AXI 4130-20 is the correct motor--for this little plane?

People use the AXI 4130 for some slow flying quarter scale planes! That is waaaaay overkill for power on this airframe IMHO. That's a motor for at least a .60 sized glow plane, if not larger. This airplane would fly fine on a .25-.40 glow engine.

I have this plane myself, and I plan to use a motor that's equivalent of the AXI 2826-10 on it. Motocalc says it'll be plenty.

Putting too much motor on a slow-flying plane--that can't handle the torque and power--is as bad as using too small a motor.

Do what you like, but I'm betting you are staring at a lot of the problem already, in your motor choice.

Rick
ElectRick is offline Find More Posts by ElectRick
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Graupner Cub as first gas plane? 800mZero Fuel Plane Talk 6 Jul 26, 2005 08:18 AM
Graupner cub? hoverboy Scale Kit/Scratch Built 0 Mar 30, 2005 09:37 PM
Graupner Cub dave_lilley Site Chat 0 Feb 17, 2003 09:52 PM
Graupner Cub dave_lilley Scale Kit/Scratch Built 0 Feb 17, 2003 09:52 PM