xcellrc
Nov 10, 2004, 02:00 AM
!Introduction
| spec2
| @911334
|> <b>Model:</b> |< <a href="http://www.cermark.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=C&Product_Code=CER-A107B&Category_Code=AAA">Cermark Graduate</a>
|> <b>Wingspan:</b> |< 58"
|> <b>Wing Area:</b> |< 624 sq. in.
|> <b>Weight:</b> |< 4lbs. 15oz.
|> <b>Length:</b> |< 46"
|> <b>Wing Loading:</b> |< 18.2 oz/sq. ft.
|> <b>Servos:</b> |< 4 standard size
|> <b>Transmitter:</b> |< JR 10X
|> <b>Receiver:</b> |< Hitec 555
|> <b>Battery:</b> |< 4.8volt 720mah NiMh
|> <b>Engine:</b> |< O.S. 46FX
|> <b>Propeller:</b> |< APC 11 x 6
|> <b>Fuel Capacity:</B> |< 8.8 fluid ounces
|> <b>Manufacturer:</b> |< <a href="http://www.cermark.com">Cermark</a>
|> <b>Available from:</b> |< <a href="http://www.cermark.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=C&Product_Code=CER-A107B&Category_Code=AAA">Your favorite local Cermark Dealer, or Cermark Direct if no dealer is available in your area.</a>
The Cermark Graduate is a low wing, sport airplane designed for intermediate pilots. It is very well built; 90% pre-built from balsa, light plywood and covered in Ultracote. The lightweight airframe worked very well with the semi-symmetrical airfoil and tricycle landing gear to provide excellent take off and landing performance for intermediate pilots. The Graduate makes an excellent aerobatic trainer for the pilot that has progressed beyond high wing sport models. Experienced fliers will enjoy its versatility, and pattern plane like performance.
* <b>Required Equipment</b>
* Four channel radio system with four servos
* Two stroke .40-.47 or four stroke .52 size engine
* Basic hand tools (knife, screwdriver, pliers)
* Thick and thin CA glues
* Five and thirty minute epoxy
!Kit Contents
The kit came in a very sturdy cardboard box, very well packaged. Even the gorillas that work for the shipping company couldn’t damage the contents. The quality of the parts in this ARF were quite impressive. It was great to find the canopy already tinted, trimmed, and mounted to the fuselage. I was also very happy to find a fiberglass cowl painted to match the orange, white, and gray Ultracote covering scheme. The covering was tight and wrinkle free.
@911335:The kit contents were all individually bagged, including a complete hardware set.
!Assembly
I started by reading the instruction manual before beginning assembly. This didn’t take long, as the instruction manual was only four pages long. There were a few areas where a picture would have made assembly easier. A builder with a little experience should have no problems with the instructions.
It took me four easy evenings to assemble the Graduate. I spent half of that time taking pictures and writing notes. An experienced builder could have easily finished building it in two evenings.
!!Wing
Though not specifically spelled out in the instructions, I removed the covering overlapping the root ribs, and epoxied them together, in addition to gluing in the pine (not plywood as the manual indicates) dihedral brace.
The main landing gear attached to the wing panels. Because I fly from a grass runway that can be rough at times, I felt that fiberglassing the center section of the wing would be a good idea. To do this, I peeled the Ultracote covering back about 1-1/2" from the center joint. Using twenty minute finishing resin, and a two inch wide strip of two ounce fiberglass cloth, I fiberglassed the center section of the wing.
@911336:Several clamps were used to hold the wing halves in alignment while the epoxy dried.
@911337:Center section of the wing showing covering peeled back and fiberglass cloth reinforcement applied.
@911338:Center of the wing after the fiberglass was sanded and the covering has been ironed down.
Step 5 in the instructions was aligning the wing and drilling the wing bolt holes. I found this step was already completed for me. All that was left was to attach the light plywood wing hold down plate with CA glue. That was a great time saver. The hinge slots were pre-cut for the supplied CA type hinges, so installing the ailerons was easy. Mounting the gear was equally simple.
@911339:Radiusing the indicated area allowed the landing gear struts to mount properly.
@911340:Proper orientation of the nose gear hardware so the steering arm aligned with the pre-cut pushrod slot.
!!Fuselage & Engine
I chose to mount the engine inverted instead of upright as the instructions outlined. The pre-drilled holes in the firewall allowed the engine mount to be installed upright or inverted. The engine aligned with the cowl either way. The only modification I had to make was to drill a new 3/16" hole for the throttle pushrod. The inverted engine provided a cleaner installation, and a more streamlined appearance. The cowl required minimal trimming to provide clearance for the muffler, needle valve, and cooling air exit. I added an exhaust diverter to the muffler to help keep some of the oily exhaust residue away from the plane.
@911341:Inverted engine mounting provides a sleek appearance.
@911342:Rulers were used to measure the distance from the tip of the stab to the tip of the wing on both sides to ensure proper alignment.
@911343:I used a square to make sure the fin was perpendicular to the stab.
@911344:T pins were used to hold the stabilizer in alignment.
@911345:Masking tape was used to hold the fin perpendicular to the stab while the epoxy dried.
!!Radio Installation
Now that the majority of the assembly was done, all that was left was to install the control horns, pushrods, and radio equipment.
The instructions indicated that the rudder and elevator pushrods were pre-built. In my kit they were not, but hardwood dowels, and 2-56 threaded rods were supplied to build them. I followed the diagrams in the instructions, and used the supplied hardware to install the servos.
The recommended control throws are given in degrees in the manual. Though not clearly indicated, the degrees given are meant to be for each side of the neutral position. I couldn't find my deflection meter to measure the degrees of movement, so I converted the degrees into inches measured at the widest point of the control surface. I used these figures as a starting value:
|
| Elevator: | 7/16th inch up | 7/16th inch down
| Rudder: | 1½ inches right | 1½ inches left
| Ailerons: | 3/4th inch up | 3/4th inch down
After installing the aileron linkage as instructed, the ailerons would move only about 3/8" up and 1"down. This arrangement provided the opposite differential movement of what should be available. I used an offset servo arm to help bring the up and down movements closer to the same measurement.
@911346:The balsa used for the elevators and rudder was lightweight, so before bolting down the control horn, I perforated the area under the control horn, and saturate with thin CA.
@911347:Black heat shrink tubing was used to keep the clevis' closed securely.
!!CG
Even though I am a slow builder, I had the Graduate finished in less than ten hours. All that remained was to apply the supplied vinyl graphics and check the center of gravity. Transfer tape was supplied to apply the lettering. The recommended center of gravity is 3" from the leading edge of the wing. With a relatively light weight .46 sized two stroke engine, I didn’t expect to need any tail weight. Initial tests showed the Graduate was slightly nose heavy. I used a very thin 720mAh 4.8V NiMH receiver battery pack wrapped in foam, and slid it under the servos. This helped bring the airplane closer to the suggested CG. With all the radio components moved as far back as possible, I only had to add ½ ounce of lead at the tail to obtain the recommended center of gravity. Using an engine larger than suggested would have made balancing the model difficult.
@911348:The first picture of the completed airplane!
!Flying
!!Basics
Once I had finished assembling the Graduate, I couldn’t wait to take it out for the first flights. I headed out to the local club field in the middle of the week, so I could avoid the weekend crowds. That seemed like a great idea...I found that a friend and I had the field to ourselves. The only problem was that the runway hadn’t been mowed. I had tall grass and weeds to contend with. I wasn’t so sure I would be able to get the Graduate in the air. Not to be deterred, I decided to go ahead and start the engine and get it tuned. Mounting the engine inverted does have a few negative points. Fueling becomes a little more complicated, and engine tuning is a bit more critical. These were minor concerns. My trusty O.S. 46 FX started up easily, and ran well, as expected.
@911349:The Graduate...
@911350:...ready for flight
I range checked the radio equipment both with the engine running and with it off and everything was fine. The JR transmitter and Hitec receiver were working perfectly. A double check of control throws and directions, and everything was ready to go. I carried the Graduate to the runway to attempt a high-speed taxi test. I found that even in the tall grass and weeds, it easily accelerated. With tricycle landing gear, the Graduate handled on the ground much like a radio controlled car. It was very responsive. I made a mental note to decrease the nose gear throw, as it didn’t need much throw at all to turn quickly on the ground. The Graduate turned slightly to the right while rolling on the ground. I corrected this using the rudder trim on the transmitter so that it now rolled straight, and then adjusted the clevis on the rudder control horn so that it was centered again.
!!Taking Off
Now, with the airplane tracking straight down the runway and no rudder correction needed, it was time to fly. The Graduate accelerated quickly, and with a little up elevator added, it was in the air. I made a couple of passes to trim the airplane for straight and level flight. I only needed a few minor adjustments in elevator and aileron trim to have it flying straight and level.
@911351:Picking up speed and rotating for take off.
@911352:The color scheme shows up very well.
!!Aerobatics
There had been no surprises so far. The Graduate was flying very well. The orange and white color scheme shows up very well in the air and provides good orientation. To get a better feel for the range of speed the plane is capable of I circled the field several times. At full throttle, the graduate is surprisingly fast. I don’t mean pylon racer fast, but definitely more exciting than a typical high wing trainer. While flying at full throttle, I pulled up into a full elevator deflection loop. I didn’t have any problems with high-speed stalls, and it stayed on heading. I let the Graduate climb higher to test the low speed handling characteristics. I pulled the throttle back to idle, and gradually added more up elevator. The Graduate slowed down very nicely before it gently stalled straight ahead. It showed no tendency to drop a wingtip and fall off into a spin.
In the air, the Graduate has the look and feel of a small pattern plane. It feels very solid, and responsive. Aileron rolls were easy to do. It was apparent after several consecutive rolls that the deflections give in the instructions were slightly conservative for my tastes. I prefer to fly on a fairly high rate, with enough exponential used to keep it from being too sensitive around neutral. While inverted in a roll, only a slight amount of down elevator was required to maintain altitude. The roll rate with the initial settings was around one roll every two seconds. The Graduate easily looped from horizontal flight at anything above 1/3 throttle. At full throttle large consecutive loops were possible. Vertical performance was good. The graduate would hold speed very well when pulled into a vertical climb, eventually slowing down, but still climbing. In later flights I tried an 11x5 APC propeller, and the vertical performance was slightly better. It was possible to hover the Graduate for a short length of time even though it was never intended for this type of flying. Overall, I liked the performance better with the 11x6 APC propeller.
@911353:Rolling to inverted flight.
@911354:Vertical performace is very good, short length hovers are even possible.
The Graduate has generous side area, and a large canopy right at the CG of the plane. These features really help knife-edge performance. At full throttle, the Graduate would hold knife-edge using approximately half rudder. With full rudder deflection, it would climb slowly, or I could throttle back for a slower pass maintaining altitude. The big surprise with knife-edge flight was the lack of roll or pitch coupling with yaw input. It did push slightly to the gear with full rudder input, and required a slight amount of opposite aileron control to keep it from rolling upright. This could be mixed out in the transmitter, but the coupling was so barely noticeable that it wasn’t needed. It would have required mixing values of 5% or less. Next I tried a knife-edge snap roll back to knife-edge flight. The first attempts I overrotated in the snap roll and exited the maneuver upright. With a little practice, I was able to anticipate where to release the controls to exit in knife-edge flight. This was very impressive for an intermediate level airplane. Sustained knife-edge circles, and figure eights were all possible. Knife-edge flight with the Graduate is definitely a strong point.
@911355:Low and slow knife-edge is stable
@911356:Cross controlled slips look great
At a nice high altitude I tried to get the plane into a flat spin. It is such a stable airplane that it generally tried to fly out of most spins. Once I got into the flat spin however, it began to rotate faster and drop quickly. To really speed up the rotation once the spin had flattened out, I reversed the elevator input. Releasing the control inputs did not instantly stop the spin. After one or two additional turns, the nose dropped and the Graduate flew out. That was a good reminder to keep the flat spins up high! By keeping full throttle in the spin, and reversing the rudder input, the Graduate would stop rotating within 1/2 turn.
With a semi-symmetrical airfoil, I expected the Graduate to need a lot of down elevator to hold altitude in inverted flight. Slight forward pressure on the stick was all that was required. By moving the CG slightly back from the recommended 3" starting position, it could be easily made to fly hands off inverted if that is your preference. I preferred the more stable arrangement with the CG at the indicated starting value. The airplane was very stable inverted, and did not try to roll upright on its own. The one down side to mounting the engine inverted was that in inverted flight the engine tended to lean out because of the fuel tank's location relative to the carburetor. It was not at all unmanageable. I had to leave the mixture slightly rich upright, to ensure consistent operation.
@911357:Inverted flight requires only slight down elevator input.
@911358:Did I hear someone say "lower"?
!!Landings
Landings were very easy. The graduate slowed down well, but it liked to keep flying, so a low rpm idle was important. As I made my initial landing approach I pulled the throttle back to idle, and held the nose about level to lose airspeed and altitude. The controls remained effective at the lower airspeed. Once over the runway, it settled in nicely and I held the nose up to bleed off more airspeed before it touched down on the main landing gear. The landing gear was fairly stiff so landing with too much speed could result in a small bounce. I kept the nose gear slightly lower than the main gear so that it sits at a negative angle of attack on the runway to help prevent those bounces. In other landings I tried side slipping to really shorten the approach. The Graduate did this very well. While trying to land in a side slip on one wheel, I landed a little “firmer” than I had planned. The landing gear arrangement was very solid and was able to hold up to the bad landing, with only one gear strut bent slightly. The Graduate landed faster than a high wing trainer, but similarly. A pilot that is comfortable with landing a trainer will not find landing the Graduate much more of a challenge.
@911359:A smooth, nose high landing on the mains
!! Adjusting to My Tastes
I experimented with several propellers, and found that the APC 11x6 was the best for my style of flying. Using an 11x5 helped it to slow down on landings. It also provided slightly better vertical performance, but it didn’t seem to track as well through aerobatics. I moved the CG forward and aft of the starting point, and found the recommended value to be good for all around flying. After several weekends of flying and experimenting, I ended up using these values for control throws:
|
| <b>Surface | <b>High Rate* | <b>Low Rate*</b>
| Elevator: | 5/8" with 35% exponential | 1/2" with 30% exponential
| Rudder: | 1-3/4" with 35% exponential | 1-1/2" with 30%exponential
| Aileron: | 7/8" with 35% exponential | 1/2" with 25% exponential
* <center><i>(Rates are each direction)</i></center>
!!Conclusion
I have really enjoyed assembling and flying the Graduate. It far exceeded my performance expectations. I have given several other modelers a chance to fly it...experts liked the solid feel, and its aerobatic capabilities; intermediates liked its low speed stability great for learning new aerobatic maneuvers. All loved it. It is a stable, yet aerobatic airplane and has plenty of power with the recommended engine size. It is lightweight, (my plane's completed weight is less than the advertised flying weight by 7 ounces) and generous wing area make it a versatile airframe.
!!Flight Video
+911363:The Graduate's early flights reveal great possibilities.
+911364:Just a glimpse of things to come!
A big thank you to Phil Barber for the great flight photos and video!
!Coming Soon!!
!!What's next for the Graduate?
I live in North Carolina, about 5 miles from Lake Norman. With a surface area of 32,510 acres it is the largest man made lake in the state. Over 32,000 acres of flat water, with no trees in the way, sounds like an ideal flying field to me. I had been float flying with some friends this summer and had a great time. I finally got around to converting my original 19-year-old trainer into a floatplane. The results weren’t impressive. The plane was old and heavy, the floats weren’t very well proportioned, but it did float and fly. I had learned a lot from the experience and I was ready to get to work on a new plane. The Graduate's excellent flying qualities made it a natural choice for my next floatplane conversion. Check back for a complete article on converting the Cermark Graduate into an awesome floatplane, including scratch building your own floats!
@911360:Great picture catches the Graduate and its reflection as it takes off.
@911361:Check out the scratch built floats covered to match the airframe.
@911362:Splashdown, another fun touch and go on the water.
| spec2
| @911334
|> <b>Model:</b> |< <a href="http://www.cermark.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=C&Product_Code=CER-A107B&Category_Code=AAA">Cermark Graduate</a>
|> <b>Wingspan:</b> |< 58"
|> <b>Wing Area:</b> |< 624 sq. in.
|> <b>Weight:</b> |< 4lbs. 15oz.
|> <b>Length:</b> |< 46"
|> <b>Wing Loading:</b> |< 18.2 oz/sq. ft.
|> <b>Servos:</b> |< 4 standard size
|> <b>Transmitter:</b> |< JR 10X
|> <b>Receiver:</b> |< Hitec 555
|> <b>Battery:</b> |< 4.8volt 720mah NiMh
|> <b>Engine:</b> |< O.S. 46FX
|> <b>Propeller:</b> |< APC 11 x 6
|> <b>Fuel Capacity:</B> |< 8.8 fluid ounces
|> <b>Manufacturer:</b> |< <a href="http://www.cermark.com">Cermark</a>
|> <b>Available from:</b> |< <a href="http://www.cermark.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=C&Product_Code=CER-A107B&Category_Code=AAA">Your favorite local Cermark Dealer, or Cermark Direct if no dealer is available in your area.</a>
The Cermark Graduate is a low wing, sport airplane designed for intermediate pilots. It is very well built; 90% pre-built from balsa, light plywood and covered in Ultracote. The lightweight airframe worked very well with the semi-symmetrical airfoil and tricycle landing gear to provide excellent take off and landing performance for intermediate pilots. The Graduate makes an excellent aerobatic trainer for the pilot that has progressed beyond high wing sport models. Experienced fliers will enjoy its versatility, and pattern plane like performance.
* <b>Required Equipment</b>
* Four channel radio system with four servos
* Two stroke .40-.47 or four stroke .52 size engine
* Basic hand tools (knife, screwdriver, pliers)
* Thick and thin CA glues
* Five and thirty minute epoxy
!Kit Contents
The kit came in a very sturdy cardboard box, very well packaged. Even the gorillas that work for the shipping company couldn’t damage the contents. The quality of the parts in this ARF were quite impressive. It was great to find the canopy already tinted, trimmed, and mounted to the fuselage. I was also very happy to find a fiberglass cowl painted to match the orange, white, and gray Ultracote covering scheme. The covering was tight and wrinkle free.
@911335:The kit contents were all individually bagged, including a complete hardware set.
!Assembly
I started by reading the instruction manual before beginning assembly. This didn’t take long, as the instruction manual was only four pages long. There were a few areas where a picture would have made assembly easier. A builder with a little experience should have no problems with the instructions.
It took me four easy evenings to assemble the Graduate. I spent half of that time taking pictures and writing notes. An experienced builder could have easily finished building it in two evenings.
!!Wing
Though not specifically spelled out in the instructions, I removed the covering overlapping the root ribs, and epoxied them together, in addition to gluing in the pine (not plywood as the manual indicates) dihedral brace.
The main landing gear attached to the wing panels. Because I fly from a grass runway that can be rough at times, I felt that fiberglassing the center section of the wing would be a good idea. To do this, I peeled the Ultracote covering back about 1-1/2" from the center joint. Using twenty minute finishing resin, and a two inch wide strip of two ounce fiberglass cloth, I fiberglassed the center section of the wing.
@911336:Several clamps were used to hold the wing halves in alignment while the epoxy dried.
@911337:Center section of the wing showing covering peeled back and fiberglass cloth reinforcement applied.
@911338:Center of the wing after the fiberglass was sanded and the covering has been ironed down.
Step 5 in the instructions was aligning the wing and drilling the wing bolt holes. I found this step was already completed for me. All that was left was to attach the light plywood wing hold down plate with CA glue. That was a great time saver. The hinge slots were pre-cut for the supplied CA type hinges, so installing the ailerons was easy. Mounting the gear was equally simple.
@911339:Radiusing the indicated area allowed the landing gear struts to mount properly.
@911340:Proper orientation of the nose gear hardware so the steering arm aligned with the pre-cut pushrod slot.
!!Fuselage & Engine
I chose to mount the engine inverted instead of upright as the instructions outlined. The pre-drilled holes in the firewall allowed the engine mount to be installed upright or inverted. The engine aligned with the cowl either way. The only modification I had to make was to drill a new 3/16" hole for the throttle pushrod. The inverted engine provided a cleaner installation, and a more streamlined appearance. The cowl required minimal trimming to provide clearance for the muffler, needle valve, and cooling air exit. I added an exhaust diverter to the muffler to help keep some of the oily exhaust residue away from the plane.
@911341:Inverted engine mounting provides a sleek appearance.
@911342:Rulers were used to measure the distance from the tip of the stab to the tip of the wing on both sides to ensure proper alignment.
@911343:I used a square to make sure the fin was perpendicular to the stab.
@911344:T pins were used to hold the stabilizer in alignment.
@911345:Masking tape was used to hold the fin perpendicular to the stab while the epoxy dried.
!!Radio Installation
Now that the majority of the assembly was done, all that was left was to install the control horns, pushrods, and radio equipment.
The instructions indicated that the rudder and elevator pushrods were pre-built. In my kit they were not, but hardwood dowels, and 2-56 threaded rods were supplied to build them. I followed the diagrams in the instructions, and used the supplied hardware to install the servos.
The recommended control throws are given in degrees in the manual. Though not clearly indicated, the degrees given are meant to be for each side of the neutral position. I couldn't find my deflection meter to measure the degrees of movement, so I converted the degrees into inches measured at the widest point of the control surface. I used these figures as a starting value:
|
| Elevator: | 7/16th inch up | 7/16th inch down
| Rudder: | 1½ inches right | 1½ inches left
| Ailerons: | 3/4th inch up | 3/4th inch down
After installing the aileron linkage as instructed, the ailerons would move only about 3/8" up and 1"down. This arrangement provided the opposite differential movement of what should be available. I used an offset servo arm to help bring the up and down movements closer to the same measurement.
@911346:The balsa used for the elevators and rudder was lightweight, so before bolting down the control horn, I perforated the area under the control horn, and saturate with thin CA.
@911347:Black heat shrink tubing was used to keep the clevis' closed securely.
!!CG
Even though I am a slow builder, I had the Graduate finished in less than ten hours. All that remained was to apply the supplied vinyl graphics and check the center of gravity. Transfer tape was supplied to apply the lettering. The recommended center of gravity is 3" from the leading edge of the wing. With a relatively light weight .46 sized two stroke engine, I didn’t expect to need any tail weight. Initial tests showed the Graduate was slightly nose heavy. I used a very thin 720mAh 4.8V NiMH receiver battery pack wrapped in foam, and slid it under the servos. This helped bring the airplane closer to the suggested CG. With all the radio components moved as far back as possible, I only had to add ½ ounce of lead at the tail to obtain the recommended center of gravity. Using an engine larger than suggested would have made balancing the model difficult.
@911348:The first picture of the completed airplane!
!Flying
!!Basics
Once I had finished assembling the Graduate, I couldn’t wait to take it out for the first flights. I headed out to the local club field in the middle of the week, so I could avoid the weekend crowds. That seemed like a great idea...I found that a friend and I had the field to ourselves. The only problem was that the runway hadn’t been mowed. I had tall grass and weeds to contend with. I wasn’t so sure I would be able to get the Graduate in the air. Not to be deterred, I decided to go ahead and start the engine and get it tuned. Mounting the engine inverted does have a few negative points. Fueling becomes a little more complicated, and engine tuning is a bit more critical. These were minor concerns. My trusty O.S. 46 FX started up easily, and ran well, as expected.
@911349:The Graduate...
@911350:...ready for flight
I range checked the radio equipment both with the engine running and with it off and everything was fine. The JR transmitter and Hitec receiver were working perfectly. A double check of control throws and directions, and everything was ready to go. I carried the Graduate to the runway to attempt a high-speed taxi test. I found that even in the tall grass and weeds, it easily accelerated. With tricycle landing gear, the Graduate handled on the ground much like a radio controlled car. It was very responsive. I made a mental note to decrease the nose gear throw, as it didn’t need much throw at all to turn quickly on the ground. The Graduate turned slightly to the right while rolling on the ground. I corrected this using the rudder trim on the transmitter so that it now rolled straight, and then adjusted the clevis on the rudder control horn so that it was centered again.
!!Taking Off
Now, with the airplane tracking straight down the runway and no rudder correction needed, it was time to fly. The Graduate accelerated quickly, and with a little up elevator added, it was in the air. I made a couple of passes to trim the airplane for straight and level flight. I only needed a few minor adjustments in elevator and aileron trim to have it flying straight and level.
@911351:Picking up speed and rotating for take off.
@911352:The color scheme shows up very well.
!!Aerobatics
There had been no surprises so far. The Graduate was flying very well. The orange and white color scheme shows up very well in the air and provides good orientation. To get a better feel for the range of speed the plane is capable of I circled the field several times. At full throttle, the graduate is surprisingly fast. I don’t mean pylon racer fast, but definitely more exciting than a typical high wing trainer. While flying at full throttle, I pulled up into a full elevator deflection loop. I didn’t have any problems with high-speed stalls, and it stayed on heading. I let the Graduate climb higher to test the low speed handling characteristics. I pulled the throttle back to idle, and gradually added more up elevator. The Graduate slowed down very nicely before it gently stalled straight ahead. It showed no tendency to drop a wingtip and fall off into a spin.
In the air, the Graduate has the look and feel of a small pattern plane. It feels very solid, and responsive. Aileron rolls were easy to do. It was apparent after several consecutive rolls that the deflections give in the instructions were slightly conservative for my tastes. I prefer to fly on a fairly high rate, with enough exponential used to keep it from being too sensitive around neutral. While inverted in a roll, only a slight amount of down elevator was required to maintain altitude. The roll rate with the initial settings was around one roll every two seconds. The Graduate easily looped from horizontal flight at anything above 1/3 throttle. At full throttle large consecutive loops were possible. Vertical performance was good. The graduate would hold speed very well when pulled into a vertical climb, eventually slowing down, but still climbing. In later flights I tried an 11x5 APC propeller, and the vertical performance was slightly better. It was possible to hover the Graduate for a short length of time even though it was never intended for this type of flying. Overall, I liked the performance better with the 11x6 APC propeller.
@911353:Rolling to inverted flight.
@911354:Vertical performace is very good, short length hovers are even possible.
The Graduate has generous side area, and a large canopy right at the CG of the plane. These features really help knife-edge performance. At full throttle, the Graduate would hold knife-edge using approximately half rudder. With full rudder deflection, it would climb slowly, or I could throttle back for a slower pass maintaining altitude. The big surprise with knife-edge flight was the lack of roll or pitch coupling with yaw input. It did push slightly to the gear with full rudder input, and required a slight amount of opposite aileron control to keep it from rolling upright. This could be mixed out in the transmitter, but the coupling was so barely noticeable that it wasn’t needed. It would have required mixing values of 5% or less. Next I tried a knife-edge snap roll back to knife-edge flight. The first attempts I overrotated in the snap roll and exited the maneuver upright. With a little practice, I was able to anticipate where to release the controls to exit in knife-edge flight. This was very impressive for an intermediate level airplane. Sustained knife-edge circles, and figure eights were all possible. Knife-edge flight with the Graduate is definitely a strong point.
@911355:Low and slow knife-edge is stable
@911356:Cross controlled slips look great
At a nice high altitude I tried to get the plane into a flat spin. It is such a stable airplane that it generally tried to fly out of most spins. Once I got into the flat spin however, it began to rotate faster and drop quickly. To really speed up the rotation once the spin had flattened out, I reversed the elevator input. Releasing the control inputs did not instantly stop the spin. After one or two additional turns, the nose dropped and the Graduate flew out. That was a good reminder to keep the flat spins up high! By keeping full throttle in the spin, and reversing the rudder input, the Graduate would stop rotating within 1/2 turn.
With a semi-symmetrical airfoil, I expected the Graduate to need a lot of down elevator to hold altitude in inverted flight. Slight forward pressure on the stick was all that was required. By moving the CG slightly back from the recommended 3" starting position, it could be easily made to fly hands off inverted if that is your preference. I preferred the more stable arrangement with the CG at the indicated starting value. The airplane was very stable inverted, and did not try to roll upright on its own. The one down side to mounting the engine inverted was that in inverted flight the engine tended to lean out because of the fuel tank's location relative to the carburetor. It was not at all unmanageable. I had to leave the mixture slightly rich upright, to ensure consistent operation.
@911357:Inverted flight requires only slight down elevator input.
@911358:Did I hear someone say "lower"?
!!Landings
Landings were very easy. The graduate slowed down well, but it liked to keep flying, so a low rpm idle was important. As I made my initial landing approach I pulled the throttle back to idle, and held the nose about level to lose airspeed and altitude. The controls remained effective at the lower airspeed. Once over the runway, it settled in nicely and I held the nose up to bleed off more airspeed before it touched down on the main landing gear. The landing gear was fairly stiff so landing with too much speed could result in a small bounce. I kept the nose gear slightly lower than the main gear so that it sits at a negative angle of attack on the runway to help prevent those bounces. In other landings I tried side slipping to really shorten the approach. The Graduate did this very well. While trying to land in a side slip on one wheel, I landed a little “firmer” than I had planned. The landing gear arrangement was very solid and was able to hold up to the bad landing, with only one gear strut bent slightly. The Graduate landed faster than a high wing trainer, but similarly. A pilot that is comfortable with landing a trainer will not find landing the Graduate much more of a challenge.
@911359:A smooth, nose high landing on the mains
!! Adjusting to My Tastes
I experimented with several propellers, and found that the APC 11x6 was the best for my style of flying. Using an 11x5 helped it to slow down on landings. It also provided slightly better vertical performance, but it didn’t seem to track as well through aerobatics. I moved the CG forward and aft of the starting point, and found the recommended value to be good for all around flying. After several weekends of flying and experimenting, I ended up using these values for control throws:
|
| <b>Surface | <b>High Rate* | <b>Low Rate*</b>
| Elevator: | 5/8" with 35% exponential | 1/2" with 30% exponential
| Rudder: | 1-3/4" with 35% exponential | 1-1/2" with 30%exponential
| Aileron: | 7/8" with 35% exponential | 1/2" with 25% exponential
* <center><i>(Rates are each direction)</i></center>
!!Conclusion
I have really enjoyed assembling and flying the Graduate. It far exceeded my performance expectations. I have given several other modelers a chance to fly it...experts liked the solid feel, and its aerobatic capabilities; intermediates liked its low speed stability great for learning new aerobatic maneuvers. All loved it. It is a stable, yet aerobatic airplane and has plenty of power with the recommended engine size. It is lightweight, (my plane's completed weight is less than the advertised flying weight by 7 ounces) and generous wing area make it a versatile airframe.
!!Flight Video
+911363:The Graduate's early flights reveal great possibilities.
+911364:Just a glimpse of things to come!
A big thank you to Phil Barber for the great flight photos and video!
!Coming Soon!!
!!What's next for the Graduate?
I live in North Carolina, about 5 miles from Lake Norman. With a surface area of 32,510 acres it is the largest man made lake in the state. Over 32,000 acres of flat water, with no trees in the way, sounds like an ideal flying field to me. I had been float flying with some friends this summer and had a great time. I finally got around to converting my original 19-year-old trainer into a floatplane. The results weren’t impressive. The plane was old and heavy, the floats weren’t very well proportioned, but it did float and fly. I had learned a lot from the experience and I was ready to get to work on a new plane. The Graduate's excellent flying qualities made it a natural choice for my next floatplane conversion. Check back for a complete article on converting the Cermark Graduate into an awesome floatplane, including scratch building your own floats!
@911360:Great picture catches the Graduate and its reflection as it takes off.
@911361:Check out the scratch built floats covered to match the airframe.
@911362:Splashdown, another fun touch and go on the water.