SR Batteries Cutie Review

SR Batteries Cutie Review
Kit and Accessories Available from:
SR Batteries
Box 287
Bellport, NY 11713
Phone: 631.286.0079
Fax: 631.286.0901
http://www.srbatteries.com/

Review by Ken Myers
August 2001

Ken and his Cutie

     My kit arrived in its triangular US Postal Service packing box on Saturday, July 27, 2001. Iíd looked the prototype over at the April 2000 Toledo Show, and decided I just had to have one. My X-250 had turned itself into my favorite plane, so I knew the Cutie had to be added to my stable. I LOVE the way Larry designs.
     As usual, Iíd played around with the "numbers" to see how I might want to power this plane, but I felt it only fair to Larry to review it as a "stock" plane.
     The stock power system sets this plane up as a Park/School Yard type flier. That is EXACTLY what Larry designed it to be.
     I decided that I wanted a version to fall into what I call the "trainer/sport" category. To allow for the eventual change of power system, I had a few modifications to do before I started building. These modifications are ONLY necessary if you prefer to fly it in the "trainer/sport" category, rather than as a Park/School Yard type flier. Follow the modifications, found at the end of this review, ONLY if you want a plane that will be more at home on training night at a mixed field of glow and electric power.

Construction Notes:

     I started by covering the front of F1 that would not be under the cheek cowl area, the little tab on the top back of F2, the top of F3, the cheek cowl caps, and the inside of the wing hold downs with covering to match the fuselage. Iíve found it easier to do this BEFORE assembly. Of course, any of this covering that covered an area where glue would go was removed.
     The fuselage doublers were easily aligned and glued on with Larryís "special C clamp" method.

Fuselage under construction

     By the end of Day 1, Tuesday, at dinnertime, the fuselage was formed up except for the hatch and bottom sheeting.

     Day 2 started with the building of the unique hatch and sheeting the bottom. Here I "learned" to read ALL of the steps to a procedure before doing it. Iíve sheeted a "million" fuselage bottoms, so I just went merrily on my way, not noting that the landing gear holes needed transferring to and through the bottom sheeting. I was able to get the gear holes punched through from inside the fuselage, and then I used a pin to "find" the other holes for the landing gear mount hold down. I didnít put the holes in the rear mount provided for mounting floats.

Fuselage framed and ready to finish

     Sanding the fuselage went well, but took a while. Luckily, I was able to do it outside, as there is a lot to sand away to make the hatch. It would have been easier, had I had the Midwest sanding tools Larry mentions in the directions, but they were ordered after the kit arrived, and I was already in the building stage. They did arrive on Thursday, so they were used to finish up the work on Friday and Saturday.
     When attaching the landing gear, I was reminded how much I enjoy working with socket head screws. There is no slipping and gouging. Wonderful touch!
     At the end of Day 2, Wednesday, the fuselage was done and ready for final sanding before covering, the tail feathers were glued together and ready for sanding and the right wing panel ribs were glued to the spar and leading edge.
     The Cutie, in this construction stage, was taken to the Midwest R/C Society meeting, where it generated a lot of interest. Many folks found the construction of this plane unique and interesting. Day 2 also included the hour and a half round trip to the hobby shop for more thin CA.

     At the end of Day 3, the wings were framed up and the fuselage covered. The horizontal stab/elevator and vertical stab/rudder were hinged and covered. Scott Rellinger came over that evening and we worked on installing the power system for his Herr P-51. Itís looking good, and the Astro Flight 15 on 9 cells is performing as expected on the bench.

Framed up and ready to cover

     At the end of Day 4 all covering was completed. Hinging was done while covering using Monokote style hinges, as used on all my planes. To see how I do this, check my X-250 article online. The horizontal stab and elevator become an assembly, as well as the vertical stab and rudder. It is easier to add the control horns and tailwheel strap at this time. The hatch tab and lock were added.

Covered and ready for intalling of power system and 
radio

     Day 5 started with the gluing in of the cabanes, carefully adjusting and gluing on the horizontal stab/elevator unit and then gluing on the vertical stab and rudder unit. Finally the Monokote hinge, already installed on the bottom of the rudder, was ironed to the fuselage, under the horizontal stab.
     The radio was installed easily. I followed Larryís directions for the push rods, and the servo holes had already been enlarged for the HS-60 servos I used. The Hitec 555 was Velcroed in and the antenna run through inner Nyrod which comes out the side of the fuselage with the antenna being run to the horizontal stab. This is my preferred method, and I passed on Larryís loop around through the hole in F3 idea.
     Installing the SR Power system was a snap. It was super easy with only six screws to install. It only took about as long as readying this paragraph, if you donít count adding the VelcroTM to the Jeti JES 350 ESC to mount it on the side of the battery compartment, as well as the battery and battery floor.
     By 2:00 on Day 5, Saturday, everything was complete and she was ready to take to the air, after a range test. Unfortunately, the weather was sunny, windy and hot in the afternoon. I had planned to test fly it that evening, but my wife informed me that my father-in-lawís birthday party had been switched to Saturday evening from Sunday evening. Oh well.

     The "test flight" took place at the EFO flying meeting on Sunday, and proved to be a "non-event." The first light lasted about 10 minutes. The wind conditions were perfect - NONE! The temperature at 10:00 A.M. was about 80 degrees Fahrenheit. On flight 2, fellow EFO member Wally Brandel took the controls, as his Cutie is on back order from SR. Again, the plane generated a lot of interest. Several EFO members mentioned they have the kit, it is on order, or will purchase one soon. On flight 3, Gus Nuerenberg took the controls and flew it around for a while. EFO VP, Richard Utkan did all of flight 4, and this flight was timed at 8 minutes 30 seconds. Richard wasnít trying to see how long it would fly. He was just doing whatever he wanted. He discovered a very interesting flight characteristic. When the plane is throttled WAY back and full up elevator is applied, nothing happens. The plane just keeps flying straight-ahead, not even stalling or galloping, just flying slowly straight ahead with its nose pointed up. On flight 5, I did loops, stall turns, floated it around, and did several Richards, all the while talking about a lot of other things.

     This plane, in a very good way, is a no brainer. It is relaxing to fly, and can be flown "close in" and "far out." It is definitely a Park/School Yard flier, and Iím sure Iíll be able to fly it easily in the Oakland Yard golf dome this winter. If you are looking for this type of flying, with a plane not made from the "shipping container", this is it. It is easy to build, easy to fly and has real "personality."
     There was only one small disappointment, the gearbox is LOUD, LOUD, LOUD!!! It seems to run just fine, but it is noisy. One other small thing was that I missed the "addendum" sheet Larry included in the power system and didnít find it until "later." I also didnít know that the ESC uses a jumper to disable the brake, which Larry mentioned should be disabled. Luckily, there was a thread on the Eflight list that mentioned this, and I added the jumper to the ESC before flying it. It pays to read the instructions.

     Here are some hints that might help other builders of this plane.

Hint 1: To keep from building two right or left wing panels, carefully glue the rods on the W2 ribs. They are the tip ribs. Slide a couple of W1 ribs about half way down the tubes and spaced out a little from each other. Use the paperclip and rubber band "clamp" to hold things together. Set the assembly vertically over waxed paper with the W2 rib lying flat on the waxed paper and the tubes pointing toward the ceiling. Align the tubes with W2 being sure they are square using the square gauge provided by Larry.
     Obviously, the W2ís should be at opposite ends when the wing panels are laid together, so if you do one and then set it up next to the other while assembling the other, the leading edges should face each other. If you lay them out after assembling this way, youíll know right away if they are WRONG, and the only thing youíll have to change is ONE W2, not a lot of ribs, after you have glued them in. Please donít as why this tip is here! This also makes the beginning wing panel assembly a lot easier to handle and place in the jig. Yes, you have to slide the rest of the ribs on from only one end, but itís not hard, and it will save you grief, should you try and build two of the same panels.

Hint 2: While gluing on the horizontal stab, if you donít have two carpenter levels to level the horizontal tail using Larryís method, use a carpenter level to level the wing hold downs while a heavy weight rests on the saddle. I used a brick. I used a balsa shim under the fuselage near the wing saddle to level the wing saddle. Then I used the level to level the horizontal stab as per Larryís instructions. I moved the level back and forth to check things, but everything stayed in alignment just fine.

Using only one carpenter's level

Hint 3: Put the control horns on the elevator and rudder right after the covering is finished on those parts. Donít forget the control arm strap for the tailwheel.

Hint 4: Keep all of the small "punched out parts" and other small parts in a reusable lunch bag so that they donít "run away."

Hint 5: (Only applies if you are doing the modified version.) Remember to cut off the front tubes for the wing saddle if you are making a modified version like mine, so that the larger battery can slide through F2.

     The following lists what I used during the construction of the Cutie.

Tools:

single edged razor blades
electric drill and bits: 1/16Ē (the chuck end was used to poke small laser cut circles from the parts, 3/32Ē, 9/64Ē and 9/32Ē (actually I used a 5/16Ē because I had it)
Dremel tool (for relieving F2 - need only if modification is to occur)
brick (as a weight)
Monokote-type iron
heat gun
multi-size socket tool
sanding blocks (my own, and the Midwest ones that Larry sells)
small carpenterís level
wire cutter
razor saw
vice
needle-nose pliers
small plain end screwdriver
clothes pins
metric ball driver (1mm I believe for prop shaft adapter)
4 ft. metal rule
3 ft. metal rule

Adhesives:

2 oz. thin CA
less than 1/2 oz. thick CA
30-minute epoxy
baking soda

Covering:

1 roll red Econcote (because I had it)
1 roll yellow Towercote

Other:

masking tape
cellophane tape
recloseable plastic lunch bag (small parts storage so they donít get lost)
self-stick VelcroTM

Specifications:

Wing Area: 360 sq.in. (mfg.)

Weights:
Fuselage: uncovered but with wheels etc. 5.4 oz.
Wing: uncovered 3.8 oz.
Tail surfaces: uncovered 1 oz.

Fuselage: covered with wheels etc. 6 oz.
Wing: covered 5 oz.
Tail surfaces: covered 1.4 oz.

Total airframe weight inc. horns and all: 12.6 oz.

Motor/gearbox/speed control/switch/prop/spinner: 5.4 oz.
Battery: 6.8 oz.

All Up Weight (AUW): 27.6 oz. with 6 #64 rubber bands
Wing loading: 11 oz./sq.ft.
Initial Static Amp draw: 8.2 amps
Initial Static RPM: 7,260
Motor: Graupner Speed 400 7.2v
Gearbox: Graupner 2.33:1
Prop: Graupner 9x5 Slim
ESC: Jeti JES 350
Rx: Hitec 555
Servos: 2 Hitec HS-60
Battery: SR 10-cell 500 Max

A Closer Look at Whatís In the Kit

     When Larry ships the kit to you, this is what youíll find.
Rolled full-size plans
104 page construction and teaching manual
Laser cut balsa and plywood parts of the highest quality
All of the fittings including special jigs, Lexan parts, control horns, pre-bent landing gear wire, tailwheel assembly, main and tail wheels, push rods and more.
SR R/C Techniques, Volume R13, Basic Covering Techniques - learn the tips!
A packet with information on the Cutie, X250, SRís catalog and sample from other SR Techniques
Handy and very useful parts layout guide
A reminder that you can still purchase such things as the power system, radio etc. at a discount for up to 30-days after your order for the kit.

The Construction Manual

     While the manual consists of a lot of pages, it should really be thought of as a "learning guide." The expert can get by just concentrating on the parts with an exclamation point, but it is a whole lot of fun discovering where Larry, the expert, made mistakes so that you donít have to. The beginner can be guided through the first aircraft with the equivalent of an expert standing in the room helping and guiding. While it may seem "massive", the pages fly by in no time at all, and the outstanding photos are a perfect compliment to the simple, straightforward and many times amusing text. The manual is your friend. Read it! Enjoy it!

Modifications to Change the Power System

     First, I must state again, this power system change is in no way necessary if you want a Park/School Yard flier.
     The Trainer/Sport system Iíve chosen is the Kyosho Magnetic Mayhem direct drive motor using 6 1200SCR to RC2400 cells with an aero-naut 8x5Ē E-Prop #7228/24 and an appropriate ESC with BEC rated at 30 plus amps. I used the Jeti JES 350, since it was already part of the original system I purchased, and it met the power requirements.

The New System

     The modifications are listed below:
Mod 1: Remove 1/8" of the plywood from the inside of both sides of F2. This "widens" the hole through F2 to allow for the physically larger battery to slide through the former. Check to see that your pack will actually slide easily through the opening. Be sure to place the receiver almost totally under the servo tray, so that the battery can slide all the way back to the servo tray.

Before trimming After trimming

Mod 2: Make another battery support 3" long of 3/32" balsa. It can be made from fuselage side scrap. Be sure it is square and the grain is going across the fuselage. Cut the slot for this "new" battery floor in the sides of the fuselage doublers. Use the battery support slots already cut into the side doublers as a guide and extend the slots on the right and left doublers for 3" towards the tail from F2.

New slots and battery floor shown

Mod 3: Make new 1/8" thick slots for the bottom front wing mount closer to the top of the fuselage side doublers and aligned with the bottom of the top F2 tab. The photo illustrates where it goes.

Cross members shown in slots and new slots

Mod 4: Open the servo tray for larger servos. I used HS-60ís because I had them, but HS-81ís would be appropriate as well.
Mod 5: Chamfer the motor mounts at a 45-degree angle so that the angle goes with the motor that is hung under the mount.
Mod 6: Leave out one on the cheek fillers on each side of cheeks. This allows easier access when installing the larger motor.
Mod 7: Note so much a modification but a note. Only put VelcroTM on the "original" motor mount for mounting the 6-cell pack. I used two parallel strips, even though it is not needed to hold the stock pack in.
Mod 8: Drill 4 new mounting holes in the motor mount about ľ" in front of the original holes. Leave the original holes alone if you are going to be switching back and forth between power systems. Also open up between the two holes in F2.

Though fuzzy, the new holes can be seen, as well as the opening of the two holes in 
F2

The anti-spreader bar

Mod 9: Make the front cross anti-spreader piece from plywood. I used 3/32" plywood cut to ľ" wide and glued appropriate size pieces of plywood to just retain the top of the motor. The picture shows what it looks like. Be sure to mount the anti-spreader before using the Nyrod motor strap.

Motor holder-inner

Mod 10: Form a 4" piece of yellow inner Nyrod into a "U" shape by holding it between your thumb and middle finger while gently pressing together and heating with a heat gun. Do this slowly, with not too much pressure, and form a nice "U" shape. Let it cool before letting go. Cut a Ĺ" off of each side of the "U". Most likely it will have to be shortened a little more. Itís a try and fit kind of thing.

Mounting strap attached

Mod 11: Use the original power system screws, if you have them, or purchase some DU-BRO No. 2 x Ĺ" Socket Head Sheet Metal Screw Cat. No. 381. Use the screws to attach the "U" to the bottom of the original motor mounts and the anti-spreader bar to the top. Slide in the motor and snug them up so that the motor canít move, but do not over tighten the screws. Be sure that you donít have a lot of up thrust or down thrust in the motor.
Mod 12: Shims made of small pieces of brass tubing may be needed to adapt the prop to your prop adapter for the Magnetic Mayhem.
     With the modifications listed above and 6 RC2000 cells, the new All Up Weight is 37.6 oz. Thatís a 10 oz. weight increase. The new wing loading is 15 oz./sq.ft. The initial static amp draw is 26.4 amps and the initial static RPM is 9,900 using the aero-naut 8x5" and 6 Sanyo RC2000.
     Flight tests of this power system were completed in the evening of Monday, August 6. The temperature at the field was 93 degrees Fahrenheit at 7:30 P.M. The wind was 10+ MPH. Even with the less than ideal conditions, this system worked well, and as expected. The plane increased its top end speed with no changes in trim from the stock system. It easily took off of the not too neatly cut club grass. Loops, rolls and stall turns were extremely easy to do when the throttle was opened up. Full up elevator with the throttle pulled way back was still a non-event, with the plane just moving forward with its nose up and losing altitude, but not rolling off, even at the higher wing loading. Using throttle management, which is required to fly this plane like it is intended, flight times were l-o-n-g with the Sanyo 1200SCRC cells and super long using the RC2000 cells.
     With flight characteristics more like an old-timer, it seems that my prop selection is over-pitched. The next flight tests will be with an 8x4" prop.

Other Appropriate Motors for the Modified Power System

     While the Kyosho Magnetic Mayhem is an inexpensive and easily obtainable motor, there are a few other motors that will most likely be appropriate in this power/prop application. While it is impossible for me to actually test all of these motors, if you have one of these motors, you can mount an 8x4" prop, use 6 cells and see what RPM and amp draw you get. Remember that you are looking for a motor that will turn an 8x4" or 8x5" prop in the 20 to 25 amp range and between 9,000 and 10,000 RPM. The motor statistics indicate that these motors should work equally well in this application: Strontium 150, Graupner Speed 600 BB SP 8.4V #6309, Graupner Speed 500 SP 8.4V #6308, CEM-05 Cobalt, Astro Cobalt 05 7T#20 #605, and Goldberg Turbo 550.

The X250 and Cutie at August EFO Meeting

In Conclusion

     The Cutie builds into an attractive, easy to fly, Park/School Yard flier with the stock power system. With my power system modification recommendation, it is easily convertible to a trainer/sport plane, which is at home in a mixed field environment.
     While many people are under the impression that a R/C trainer should be made of ďbouncableĒ foam, because of the excellent flight characteristics, this is actually a much better trainer than an EPP foam plane. It flies slowly, is very stable, and if you donít steer it into the ground, wonít crash. Simply reducing the power, keeping the wings level and applying the elevator lands this plane very slowly and gently.
     Iím going to enjoy introducing non-fliers to R/C flight with this plane. It will also be my ďrelaxingĒ plane. I love its nostalgic look, ease of construction, and flight characteristics. Iíll use it with the stock system in my local park and at the dome. With the modified system, Iíll train folks at the mixed field. I highly recommend it for those who want to learn about building their own R/C planes, beginner through expert, as well as learning how to fly R/C.

     Unlike other sites, there is NO paid advertising on this site! When you see an ad link, Ken Myers uses and recommends the product(s), supplier or manufacturer. He uses the "stuff" or supplier himself!