SoarNeck
Mar 24, 2004, 08:00 PM
!Introduction
| spec2
| @906133
|> <b>Wingspan:</b> |< 124"
|> <b>Wing Area:</b> |< 1054 square inches
|> <b>Weight:</b> |< 111.8 ounces
|> <b>Wing Loading:</b> |< 15.5 oz/sq ft
|> <b>Tail Servos:</b> |< <a href=http://www.multiplexusa.com/">MPX MCV2s</a>
|> <b>Wing Servos:</b> |< Volz MicromaxxHP/WingMaxxHP
|> <b>Transmitter:</b> |< <a href="http://www.multiplexusa.com/">Multiplex 3030</a>
|> <b>Receiver:</b> |< <a href="http://www.multiplexusa.com/">Multiplex IPD7</a>
|> <b>Battery:</b> |< 12 GP3300 cells
|> <b>Motor:</b> |< <a href="http://www.icare-rc.com/plettenberg.htm">Plettenberg Ergo</a>
|> <b>ESC:</b> |< <a href="http://www.icare-rc.com/motor-controls.htm">Hacker Master 70 Opto</a>
|> <b>Available From:</b> |< <a href="http://www.icare-rc.com">Icare Sailplanes</a>
Since starting in model airplanes, there has been more than one occasion where I've sworn that I'd never get involved with a new class of airplane. First I said that I could never justify a molded airplane, next that I would never bother with brushless motors, and most recently I claimed that electric-powered open-class (wingspan >100") models were far too expensive for me. On average, these excuses seem to have lasted for about six months before they get broken!
My latest about-face came last year when I watched a friend fly his Heinrich Stork with a new electric fuselage. While that particular model was underpowered and heavy, I started dreaming about how nice it would be to be able to pop down to the field for a quick flight after work, without a winch. Additionally, an electric drive would allow me to fly my open-class models in the winter, when snow and ice made it difficult to use ground-based launch equipment.
When I found out that Lubos Pazderka was releasing an electric fuselage for his Eraser line of models, I knew that my fate was sealed. When I requested more information on the new model, I was told that the new fuselage was designed to be used with existing Eraser wings, or it would also be available as a complete package with the lighter Eraser Xtreme wing; the new electric model combination is called <a href="http://icare-rc.com/eraser.htm">the Eraser XE.</a>
I had been flying the sailplane version of the Eraser F3B for about three years and already had complete models, so I decided to order just the fuselage and horizontal stabilizers (my models were v-tails, and the XE is a cross-tail). Since Lubos was still in the design phase when I ordered the new model, it took about 9 months for my fuselage to arrive. It was worth the wait!
To power the model, Etienne at <a href="http://www.icare-rc.com">Icare Sailplanes</a> provided a Plettenberg Ergo motor and Hacker Master 70 Opto speed control. This is a nice sport setup for the model, and provides long run times on a reasonable number of cells. The Ergo is a very versatile motor, given that it can power a wide variety of models by simply changing the prop and cell combinations.
For those that are interested, I <a href="http://www.rcgroups.com/links/index.php?id=4139"> reviewed the F3B sailplane version of the Eraser early last year</a>. Since I was planning on using a wing from one of the models mentioned in that review, I won't repeat the details of assembling the Eraser wing here - the procedure will be identical for someone purchasing an Eraser XE wing. <a href="http://www.rcgroups.com/links/index.php?id=4139">If you are interested in the wing assembly information, please click here to read the sailplane review</a>.
!Kit Contents
@906134:The box contents after the packing peanuts were cleared away. Note that the stabs also came wrapped in bubble wrap.
@906135:The bag of hardware included with the model.
The box I received in the mail from ICARE was very well packaged, with all the components nicely supported by a combination of bubble wrap and foam packing peanuts. After spending 10 minutes cleaning the peanuts off the floor of my shop (they're effective, but they sure are messy), I unpacked everything and checked that nothing was damaged.
My first impression of the fuselage was that it was very nicely molded, and the fit and finish seemed very good. The fuselage is primarily fibreglass with appropriate carbon reinforcement, which was a nice improvement over the F3B sailplane's fashionable, but structurally questionable, hybrid carbon/kevlar weave construction.
All the required hardware is included with the fuselage, and it is all of very high quality. No instructions were included with the fuselage, but the assembly looked fairly straightforward. iCARE confirmed that instructions are included with the Eraser XE, if ordered as a complete unit.
The hardware list included a couple of the largest carbon stab joiner rods that I've ever seen on an open-class model, which left no doubt that this model was designed with excesses of strength in mind. Also included was a handy molded fibreglass servo tray, which is left uncut in order to accommodate a wide range of possible equipment. A full set of computer connectors is included, though only one half will be used since a companion plug is already mounted in the wing. A full set of wing bolts was also included even though I only ordered the fuselage on its own, which was a thoughtful and appreciated touch.
@906136:Included with the model was a Hacker Master 70 Opto speed control, and a Graupner folding prop spinner.
As I mentioned before, the drive system that was provided with the model is a Plettenberg Ergo motor, mated with a Hacker Master 70 Opto speed control. This motor is intended for use with 12-16 cells, and is an extremely impressive unit. I noticed that the Ergo was a little lighter than a Hacker LMR motor that I had, and that the front bearing housing was a little longer than the Hacker. I chose to use 12 GP3300 cells in the model, built by myself into a pack of 2 sticks of 6. (Details below.)
The propeller that was included was an Aeronaut 18x11 carbon folder, which came with a Graupner 40mm precision folding prop spinner (collet-based).
!Assembly
The Eraser XE fuselage is nicely designed, with a separate molded nose tray that converts the battery and motor into a "power cartridge" arrangement. Hookups are very easy, and the wiring length between the speed control and battery are kept as short as possible. The only downside to a cartridge is that it becomes rather difficult to get current measurements with a clamp meter, since holding onto the separated nose piece could be quite dangerous if a powerful motor is used.
The nose of the XE is held on by a single countersunk metric Allen bolt. Since metric fasteners are still relatively rare in the North American modeling world, the fact that a matching Allen key was included is a thoughtful touch (one is also provided for the wing bolts). Placing a tab of tape over the bolt when flying would be a good idea, although vibration isn't much of a problem with a well-balanced drive system.
@906137:An Allen key is provided to remove the nose-retention bolt.
@906138:The full length of the power cartridge is enough to accommodate up to 16 sub-c cells with no balance problems.
The firewall of the XE is perfectly designed to mount a geared Hacker B50 or equivalent motor, and comes pre-installed with generous carbon reinforcement. The front bearing housing on the Plettenberg motor is a little longer than a Hacker, however, so a spacer is required so that the propeller sits closer to the front of the fuselage.
@906139:The firewall spacer was made from 3/16" aircraft-grade plywood.
My 3/16" ply spacer backed the motor off just enough so that the spinner fit as nicely as possible. I was sent a 40mm spinner to use with this model, but it was quite a bit undersized for the job. Having a 42mm spinner on hand as well, I tried that one, but it was a little bit oversized. I'd say that the nose requires a 41mm spinner...and good luck finding one!
@906140:Here the speed control is soldered to the motor.
@906141:A hammerhead-tipped iron is being used to add 2 more cells to an existing (but unused) 10 cell pack.
The next step was to solder the motor to the speed control, which is reasonably straightforward if you use a good iron. I left all the wires at their supplied length, added 4mm gold-pin connectors to the battery side of the speed control, and used heat shrink tubing to protect all the joints.
Having an unused 10 cell pack of 3300's on hand, I added another 2 cells to the pack before it was cycled 3 times. Twelve cells in concert with the 18x11 Aeronaut prop will draw about 45 amps, so consider 14-16 cells if you're looking for LMR-type performance. For a sport setup, the 12 cell pack provides over four minutes of run-time, which is more than enough to almost guarantee hour-long flights.
Kapton wrapping is not strictly required for 50A currents, but it is recommended. A $20 (cdn) roll of tape will do 50-75 packs, which actually means that it is much cheaper than the average hobby-store shrink wrap. On top of this, the kapton won't melt even if touched by an iron, and it allows much more heat to exit the cells. Just beware of the tenacious wrapping that comes on the latest run of GP3300 cells...removing the wrappers from 12 cells will take about an hour and a half!
Once the motor was installed, I secured the battery pack into the nose piece at its rearmost position with a few bands of kapton tape. I then added leads to the battery pack that were long enough to mate with the wires coming off the speed control. Final balance would be addressed after the rest of the electronics were installed, and the pack wires shortened at that time to suit the final balance point.
@906142:The stock fuselage opening showing lines that were draw for the enlarged area.
@906143:The finished cutout. Note that the corners are radius-ed to the diameter of the Dremel sanding band.
Next in line for installation were the fuselage servos, which went in the rearmost bay underneath the wing. While the fuselage comes with cutouts done at the factory, I found the servo bay to be a little bit too small for my servos. Therefore, I enlarged the bay with a Dremel tool, using a combination of a cutoff wheel and band sander. Make sure to keep the corners of the cutout radius-ed when you do this, or cracks may develop. Also, make sure not to grind into the bands of carbon that run just under the wing saddle. I didn't realize that they were there until I was done, and I ended up nicking the carbon on both sides.
Next, I cut openings in the servo tray (see the photo of the bag of hardware) to accept the servos I planned to use. I had a pair of Multiplex Micro MCV2's on hand and chose to use them, but I would really recommend slightly smaller servos like the Volz MicroMaxx HP. The MPX servos fit, but there is only microscopic clearance on all sides of the servos. I actually had to grind the bottom of the servos slightly to allow them to fit properly, since otherwise the servo horn screw touched the bottom of the wing.
@906144:Here are the two lengths of wire that I removed from the existing pushrods. Solder clevises were used to link the pushrods to the servo horns.
@906145:The servo wires are shortened to save space in the fuselage. Note the position of the servo arms...there is less than 1mm of clearance between the servo arm retention screw and the bottom of the fuse!
When the tray was dry-fit in place, I checked to see if the pushrods needed to be altered in any fashion. Because of the clearances I mentioned before, I needed to cut the pushrod wires quite a bit to mate to the servo arms properly. Since I ended up removing the entire threaded section of the wire, I substituted <a href="http://www.shopatron.com/product/product_id=DUB112/101.0">Dubro metal solderable clevises</a> in place of the plastic/brass clevises that are supplied. I tend not to use plastic hardware very often anyway, since it doesn't always agree with the cold temperatures of a Canadian winter.
Finally, I shortened the servo leads so that there wouldn't be much excess floating around in the fuselage. This step isn't strictly required, but it makes the installation a little cleaner.
<div class="dashed">
<br> <center><b>NOTE:</b> Do not glue the servo tray in place until you have installed the receiver battery.<p></center>
</div>
@906146:The cells were assembled in two sticks of two, unlike the single stick shown here.
@906147:The same building jig and iron was used to do the main motor pack. The final switchjack and switch plug.
After deciding to use KAN1050 nimh cells for my receiver pack, I assembled the pack. While the MPX servos might have benefited from going to 5 cells, the Volz wing servos neither require nor tolerate operation on 5 cells (I found this out last year, having melted a MicroMaxx after 3 years of operation on 5 cells).
I chose to use a switchjack to replace a traditional switch and charging jack, since the battery pack will be mounted behind the servos. These are available from <a href="http://www.shredair.com/chps.html"> Shredair as CHiPS</a>, or you can make up your own much less expensively from <a href="http://www.hollyday.com/rich/hd/sailplanes/switchjacks.htm">Hollyday Designs.</a>
Next, I drilled a hole in the rear fuselage behind the wing that would clear the switchjack. I mounted the receiver pack behind the servos using velcro, with a small dab of Goop adhesive for security and vibration resistance (call me paranoid).
Finally, I fished the connector from the pack underneath the servos, and secured the tray in place with some thin C/A. Friction alone would have held the tray in place (it is almost geometrically impossible to move), but I wanted to make sure. Removal of the RX pack at this point is possible, but rather difficult.
@906148:Completed gear installation.
The receiver was installed in the middle bay, with the connectors pointing upward. This is one of the few times where a receiver with top plugs is more helpful. I chose to use a <a href="http://www.multiplexusa.com/">Multiplex IPD7 receiver</a>, since, in my opinion, this line of receivers is by far the best on the market right now.
@906149:Making up the fuselage wiring harness using four male plugs and a computer connector.
@906150:The finished propeller.
You'll need to make up a harness using four male plugs and the computer plug. I copied the harness from my sailplane version, making sure to keep the correct wiring code. I also tied the plugs into their sockets by first running a piece of Spiderwire (spectra) line between the signal and and positive wires leading into the black male plug, and then tying the line around the back of the receiver. That way, you'll never inadvertently pull a plug out of the receiver.
Next was to assemble the propeller. Since Aeronaut blades will bind slightly in a standard Graupner spinner, I had to lightly sand the blade mounts to gain a clearance fit. The screws were secured with medium c/a and kicker to prevent them from vibrating loose.
The final step in the build was to balance the model. Please consult the table at the end of the flying section for the final balance point and control throws.
While I had no real idea about what the decalage angle was supposed to be, I hoped that the neutral setting for the stab would be about in the center of the travel cutout in the fin. Rather than just guess, I decided to measure the decalage angle on my v-tail version of the Eraser, and use the same angle. Using a Robart incidence meter, I measured a 1 degree difference between the stab and wing on the Eraser F3B sailplane version. Using that same amount proved to be almost exactly correct, as the model flew out of my hand straight and level on the trim flight.
!Flying
I finished the Eraser XE right in time for a wonderful break in the weather. We had a couple of well-timed sunny days to break up a string of really cold ones! Although nobody was available to do the first toss for me, I thought that since I was used to throwing my friend's F3F hotliner, I was probably fine to do the test flights on my own.
The low pitched prop (relative to an F3F 16x16 RFM version) meant that the model had plenty of static thrust to make launching easy. I actually had to resist the subconscious urge to grab onto the fuselage as it roared out of my hand. The 12 cell setup developed more than enough power to comfortably bring the model to winch altitude in about 10-15 seconds, and it would do this many times over (motor run time is about 4 mins on GP3300 cells; 45A). The power produced isn't at the level of an open-class F5J model, but the Plettenberg Ergo is a far more versatile motor choice than would be required for the F5J event. As is was, the Ergo allowed the model to maintain a comfortable 20 degree climb-out, with camber slowing the model's speed slightly but helping the overall climb quite noticeably.
Having an electric drive system on board meant that the traditionally tedious task of setting the c/g became very easy, since balancing weights could be added or removed and the model quickly relaunched without spending time hunting down a winch 'chute. I had initially balanced the model quite nose heavy to try to compensate for not really knowing what the neutral stab setting was, so the XE had a noticeable tendency to pitch up with increasing airspeed. In later flights, I slowly taped more and more weight to the tail until I had the balance point where I wanted it, at which point I moved the battery pack backward and removed the added weight. The tendency to pitch up with airspeed was gone;the thrust angle in general seems to be very close to perfect.
@906151:The Eraser XE at the field just before its maiden flight.
@906152:While I generally prefer the look of a v-tail, the lines on this model aren't bad at all!
While the added weight of the electric drive system is noticeable in flight (112 oz vs 81 oz), all in all, the model performs very similarly to the <a href="http://www.rcgroups.com/links/index.php?id=4139">sailplane version</a>. It won't fly quite as slowly as the glider version due to the higher wing loading, and as a result the XE seems to be most comfortable flying a bit faster than the sailplane and carrying more trailing edge camber while thermalling.
The honest handling characteristics of the sailplane version are all preserved in the XE, with only a slight dampening of pitch responses. That said, it seems to respond to the slightest hint of lift, and can still circle tightly enough to work all but the smallest bubbles of lift. The model shows no tendency to spin at my ending c/g location. Wingtip thermal cues and roll rate are the same as as for the sailplane version, unsurprising since no extra weight has been added to the wingtips.
Rudder response seems to be even better with the XE than the v-tailed sailplane (which is excellent to start with), which I initially chalked up to a larger tail. When I sat down and ran the numbers, I was surprised to find that the tail volume is actually shorter on the XE. The tail boom length is shorter on the electric model, which is presumably an attempt to allow the model to balance more easily. This probably wasn't a good idea in the end, however, since I would imagine that the model would be very hard to balance with more than 14 sub-c cells on board without moving the RX battery pack a long way down the tail boom (possibly interfering with the pushrods there). The tail volumes are shown in the table, for those that are interested. I would guess that the increased rudder authority likely comes from the broad rudder chord, as opposed to any difference in tail area. The rudder on the XE is an extremely effective control surface, with plenty of power to command rudder-only thermal turns, or to correct for errant gusts of wind on landing approaches.
|
|< <b>Eraser</b>|< <b>Horizontal</b>|< <b>Vertical</b>
|< <b>Version|< <b>Tail Volume</b>|< <b>Tail Volume</b>
|< F3B v-tailed Sailplane|< 0.520 (w/ vtail compensation)|< 0.024
|< XE Cross-tailed Electric|< 0.447 |< 0.020
High speed flight is rock-solid, with only minimal pushrod flex apparent. No hint of flutter was ever detected, and at the final c/g location there is minimal elevator input required to maintain course at high speeds.
I plan to fly my XE extensively this summer, since it will allow me to put in a couple of quick flights after work, or after the winch batteries run flat. It will be interesting to see how the model performs on the F3B Speed & Distance course, since it seems to offer an easy way to get some solid practice flying laps. But first, I'm looking forward to not having to fly under 4 layers of clothing!
|
| <center><b>Control Throws and C/G Location</b></center>
|> <b>Balance Point from TE:</b> |< 150mm at root(easier to measure)
|> <b>Balance Point at LE:</b> |< 87mm at root
|> <b> Aileron Throw:</b> |< "+16mm, -11mm"
|> <b> Aileron Exponential:</b> |< 40%
|> <b> Elevator Throw:</b> |< "+8mm, -10mm"
|> <b> Elevator Exponential:</b> |< 10%
|> <b> Rudder Throw:</b> |< "+9mm,-13mm"
|> <b> Rudder Exponential:</b> |< 0%
|> <b> Thermal Camber (average):</b> |< "-4mm ailerons & -6mm flaps"
|> <b> Reflex (average):</b> |< "+1mm, ailerons & flaps"
|> <b> Elevator/Flap compensation:</b> |< 70% flap = -3mm elevator
|> <b> Aileron/Rudder Mixing:</b> |< 35% rudder with full aileron
!!Quick video clips of the Eraser XE in flight:
+906153:Hand Launcing the XE.
+906154:Surprisingly tight thermal turns!
+906155:A clean roll.
+906156:A nice, smooth touchdown.
!Conclusion
All things considered, I am extremely pleased with this model. The Eraser XE manages to preserve most of the flight characteristics that make the sailplane versions so appealing, while adding the independence that comes from electric flight. Whether you are considering a model for F5J competition or just one that will allow you to experience the efficiency of a larger model for sport flying, seriously consider the XE.
After having so much fun with this model, I can't wait to find out what my next failed promise will be!
| spec2
| @906133
|> <b>Wingspan:</b> |< 124"
|> <b>Wing Area:</b> |< 1054 square inches
|> <b>Weight:</b> |< 111.8 ounces
|> <b>Wing Loading:</b> |< 15.5 oz/sq ft
|> <b>Tail Servos:</b> |< <a href=http://www.multiplexusa.com/">MPX MCV2s</a>
|> <b>Wing Servos:</b> |< Volz MicromaxxHP/WingMaxxHP
|> <b>Transmitter:</b> |< <a href="http://www.multiplexusa.com/">Multiplex 3030</a>
|> <b>Receiver:</b> |< <a href="http://www.multiplexusa.com/">Multiplex IPD7</a>
|> <b>Battery:</b> |< 12 GP3300 cells
|> <b>Motor:</b> |< <a href="http://www.icare-rc.com/plettenberg.htm">Plettenberg Ergo</a>
|> <b>ESC:</b> |< <a href="http://www.icare-rc.com/motor-controls.htm">Hacker Master 70 Opto</a>
|> <b>Available From:</b> |< <a href="http://www.icare-rc.com">Icare Sailplanes</a>
Since starting in model airplanes, there has been more than one occasion where I've sworn that I'd never get involved with a new class of airplane. First I said that I could never justify a molded airplane, next that I would never bother with brushless motors, and most recently I claimed that electric-powered open-class (wingspan >100") models were far too expensive for me. On average, these excuses seem to have lasted for about six months before they get broken!
My latest about-face came last year when I watched a friend fly his Heinrich Stork with a new electric fuselage. While that particular model was underpowered and heavy, I started dreaming about how nice it would be to be able to pop down to the field for a quick flight after work, without a winch. Additionally, an electric drive would allow me to fly my open-class models in the winter, when snow and ice made it difficult to use ground-based launch equipment.
When I found out that Lubos Pazderka was releasing an electric fuselage for his Eraser line of models, I knew that my fate was sealed. When I requested more information on the new model, I was told that the new fuselage was designed to be used with existing Eraser wings, or it would also be available as a complete package with the lighter Eraser Xtreme wing; the new electric model combination is called <a href="http://icare-rc.com/eraser.htm">the Eraser XE.</a>
I had been flying the sailplane version of the Eraser F3B for about three years and already had complete models, so I decided to order just the fuselage and horizontal stabilizers (my models were v-tails, and the XE is a cross-tail). Since Lubos was still in the design phase when I ordered the new model, it took about 9 months for my fuselage to arrive. It was worth the wait!
To power the model, Etienne at <a href="http://www.icare-rc.com">Icare Sailplanes</a> provided a Plettenberg Ergo motor and Hacker Master 70 Opto speed control. This is a nice sport setup for the model, and provides long run times on a reasonable number of cells. The Ergo is a very versatile motor, given that it can power a wide variety of models by simply changing the prop and cell combinations.
For those that are interested, I <a href="http://www.rcgroups.com/links/index.php?id=4139"> reviewed the F3B sailplane version of the Eraser early last year</a>. Since I was planning on using a wing from one of the models mentioned in that review, I won't repeat the details of assembling the Eraser wing here - the procedure will be identical for someone purchasing an Eraser XE wing. <a href="http://www.rcgroups.com/links/index.php?id=4139">If you are interested in the wing assembly information, please click here to read the sailplane review</a>.
!Kit Contents
@906134:The box contents after the packing peanuts were cleared away. Note that the stabs also came wrapped in bubble wrap.
@906135:The bag of hardware included with the model.
The box I received in the mail from ICARE was very well packaged, with all the components nicely supported by a combination of bubble wrap and foam packing peanuts. After spending 10 minutes cleaning the peanuts off the floor of my shop (they're effective, but they sure are messy), I unpacked everything and checked that nothing was damaged.
My first impression of the fuselage was that it was very nicely molded, and the fit and finish seemed very good. The fuselage is primarily fibreglass with appropriate carbon reinforcement, which was a nice improvement over the F3B sailplane's fashionable, but structurally questionable, hybrid carbon/kevlar weave construction.
All the required hardware is included with the fuselage, and it is all of very high quality. No instructions were included with the fuselage, but the assembly looked fairly straightforward. iCARE confirmed that instructions are included with the Eraser XE, if ordered as a complete unit.
The hardware list included a couple of the largest carbon stab joiner rods that I've ever seen on an open-class model, which left no doubt that this model was designed with excesses of strength in mind. Also included was a handy molded fibreglass servo tray, which is left uncut in order to accommodate a wide range of possible equipment. A full set of computer connectors is included, though only one half will be used since a companion plug is already mounted in the wing. A full set of wing bolts was also included even though I only ordered the fuselage on its own, which was a thoughtful and appreciated touch.
@906136:Included with the model was a Hacker Master 70 Opto speed control, and a Graupner folding prop spinner.
As I mentioned before, the drive system that was provided with the model is a Plettenberg Ergo motor, mated with a Hacker Master 70 Opto speed control. This motor is intended for use with 12-16 cells, and is an extremely impressive unit. I noticed that the Ergo was a little lighter than a Hacker LMR motor that I had, and that the front bearing housing was a little longer than the Hacker. I chose to use 12 GP3300 cells in the model, built by myself into a pack of 2 sticks of 6. (Details below.)
The propeller that was included was an Aeronaut 18x11 carbon folder, which came with a Graupner 40mm precision folding prop spinner (collet-based).
!Assembly
The Eraser XE fuselage is nicely designed, with a separate molded nose tray that converts the battery and motor into a "power cartridge" arrangement. Hookups are very easy, and the wiring length between the speed control and battery are kept as short as possible. The only downside to a cartridge is that it becomes rather difficult to get current measurements with a clamp meter, since holding onto the separated nose piece could be quite dangerous if a powerful motor is used.
The nose of the XE is held on by a single countersunk metric Allen bolt. Since metric fasteners are still relatively rare in the North American modeling world, the fact that a matching Allen key was included is a thoughtful touch (one is also provided for the wing bolts). Placing a tab of tape over the bolt when flying would be a good idea, although vibration isn't much of a problem with a well-balanced drive system.
@906137:An Allen key is provided to remove the nose-retention bolt.
@906138:The full length of the power cartridge is enough to accommodate up to 16 sub-c cells with no balance problems.
The firewall of the XE is perfectly designed to mount a geared Hacker B50 or equivalent motor, and comes pre-installed with generous carbon reinforcement. The front bearing housing on the Plettenberg motor is a little longer than a Hacker, however, so a spacer is required so that the propeller sits closer to the front of the fuselage.
@906139:The firewall spacer was made from 3/16" aircraft-grade plywood.
My 3/16" ply spacer backed the motor off just enough so that the spinner fit as nicely as possible. I was sent a 40mm spinner to use with this model, but it was quite a bit undersized for the job. Having a 42mm spinner on hand as well, I tried that one, but it was a little bit oversized. I'd say that the nose requires a 41mm spinner...and good luck finding one!
@906140:Here the speed control is soldered to the motor.
@906141:A hammerhead-tipped iron is being used to add 2 more cells to an existing (but unused) 10 cell pack.
The next step was to solder the motor to the speed control, which is reasonably straightforward if you use a good iron. I left all the wires at their supplied length, added 4mm gold-pin connectors to the battery side of the speed control, and used heat shrink tubing to protect all the joints.
Having an unused 10 cell pack of 3300's on hand, I added another 2 cells to the pack before it was cycled 3 times. Twelve cells in concert with the 18x11 Aeronaut prop will draw about 45 amps, so consider 14-16 cells if you're looking for LMR-type performance. For a sport setup, the 12 cell pack provides over four minutes of run-time, which is more than enough to almost guarantee hour-long flights.
Kapton wrapping is not strictly required for 50A currents, but it is recommended. A $20 (cdn) roll of tape will do 50-75 packs, which actually means that it is much cheaper than the average hobby-store shrink wrap. On top of this, the kapton won't melt even if touched by an iron, and it allows much more heat to exit the cells. Just beware of the tenacious wrapping that comes on the latest run of GP3300 cells...removing the wrappers from 12 cells will take about an hour and a half!
Once the motor was installed, I secured the battery pack into the nose piece at its rearmost position with a few bands of kapton tape. I then added leads to the battery pack that were long enough to mate with the wires coming off the speed control. Final balance would be addressed after the rest of the electronics were installed, and the pack wires shortened at that time to suit the final balance point.
@906142:The stock fuselage opening showing lines that were draw for the enlarged area.
@906143:The finished cutout. Note that the corners are radius-ed to the diameter of the Dremel sanding band.
Next in line for installation were the fuselage servos, which went in the rearmost bay underneath the wing. While the fuselage comes with cutouts done at the factory, I found the servo bay to be a little bit too small for my servos. Therefore, I enlarged the bay with a Dremel tool, using a combination of a cutoff wheel and band sander. Make sure to keep the corners of the cutout radius-ed when you do this, or cracks may develop. Also, make sure not to grind into the bands of carbon that run just under the wing saddle. I didn't realize that they were there until I was done, and I ended up nicking the carbon on both sides.
Next, I cut openings in the servo tray (see the photo of the bag of hardware) to accept the servos I planned to use. I had a pair of Multiplex Micro MCV2's on hand and chose to use them, but I would really recommend slightly smaller servos like the Volz MicroMaxx HP. The MPX servos fit, but there is only microscopic clearance on all sides of the servos. I actually had to grind the bottom of the servos slightly to allow them to fit properly, since otherwise the servo horn screw touched the bottom of the wing.
@906144:Here are the two lengths of wire that I removed from the existing pushrods. Solder clevises were used to link the pushrods to the servo horns.
@906145:The servo wires are shortened to save space in the fuselage. Note the position of the servo arms...there is less than 1mm of clearance between the servo arm retention screw and the bottom of the fuse!
When the tray was dry-fit in place, I checked to see if the pushrods needed to be altered in any fashion. Because of the clearances I mentioned before, I needed to cut the pushrod wires quite a bit to mate to the servo arms properly. Since I ended up removing the entire threaded section of the wire, I substituted <a href="http://www.shopatron.com/product/product_id=DUB112/101.0">Dubro metal solderable clevises</a> in place of the plastic/brass clevises that are supplied. I tend not to use plastic hardware very often anyway, since it doesn't always agree with the cold temperatures of a Canadian winter.
Finally, I shortened the servo leads so that there wouldn't be much excess floating around in the fuselage. This step isn't strictly required, but it makes the installation a little cleaner.
<div class="dashed">
<br> <center><b>NOTE:</b> Do not glue the servo tray in place until you have installed the receiver battery.<p></center>
</div>
@906146:The cells were assembled in two sticks of two, unlike the single stick shown here.
@906147:The same building jig and iron was used to do the main motor pack. The final switchjack and switch plug.
After deciding to use KAN1050 nimh cells for my receiver pack, I assembled the pack. While the MPX servos might have benefited from going to 5 cells, the Volz wing servos neither require nor tolerate operation on 5 cells (I found this out last year, having melted a MicroMaxx after 3 years of operation on 5 cells).
I chose to use a switchjack to replace a traditional switch and charging jack, since the battery pack will be mounted behind the servos. These are available from <a href="http://www.shredair.com/chps.html"> Shredair as CHiPS</a>, or you can make up your own much less expensively from <a href="http://www.hollyday.com/rich/hd/sailplanes/switchjacks.htm">Hollyday Designs.</a>
Next, I drilled a hole in the rear fuselage behind the wing that would clear the switchjack. I mounted the receiver pack behind the servos using velcro, with a small dab of Goop adhesive for security and vibration resistance (call me paranoid).
Finally, I fished the connector from the pack underneath the servos, and secured the tray in place with some thin C/A. Friction alone would have held the tray in place (it is almost geometrically impossible to move), but I wanted to make sure. Removal of the RX pack at this point is possible, but rather difficult.
@906148:Completed gear installation.
The receiver was installed in the middle bay, with the connectors pointing upward. This is one of the few times where a receiver with top plugs is more helpful. I chose to use a <a href="http://www.multiplexusa.com/">Multiplex IPD7 receiver</a>, since, in my opinion, this line of receivers is by far the best on the market right now.
@906149:Making up the fuselage wiring harness using four male plugs and a computer connector.
@906150:The finished propeller.
You'll need to make up a harness using four male plugs and the computer plug. I copied the harness from my sailplane version, making sure to keep the correct wiring code. I also tied the plugs into their sockets by first running a piece of Spiderwire (spectra) line between the signal and and positive wires leading into the black male plug, and then tying the line around the back of the receiver. That way, you'll never inadvertently pull a plug out of the receiver.
Next was to assemble the propeller. Since Aeronaut blades will bind slightly in a standard Graupner spinner, I had to lightly sand the blade mounts to gain a clearance fit. The screws were secured with medium c/a and kicker to prevent them from vibrating loose.
The final step in the build was to balance the model. Please consult the table at the end of the flying section for the final balance point and control throws.
While I had no real idea about what the decalage angle was supposed to be, I hoped that the neutral setting for the stab would be about in the center of the travel cutout in the fin. Rather than just guess, I decided to measure the decalage angle on my v-tail version of the Eraser, and use the same angle. Using a Robart incidence meter, I measured a 1 degree difference between the stab and wing on the Eraser F3B sailplane version. Using that same amount proved to be almost exactly correct, as the model flew out of my hand straight and level on the trim flight.
!Flying
I finished the Eraser XE right in time for a wonderful break in the weather. We had a couple of well-timed sunny days to break up a string of really cold ones! Although nobody was available to do the first toss for me, I thought that since I was used to throwing my friend's F3F hotliner, I was probably fine to do the test flights on my own.
The low pitched prop (relative to an F3F 16x16 RFM version) meant that the model had plenty of static thrust to make launching easy. I actually had to resist the subconscious urge to grab onto the fuselage as it roared out of my hand. The 12 cell setup developed more than enough power to comfortably bring the model to winch altitude in about 10-15 seconds, and it would do this many times over (motor run time is about 4 mins on GP3300 cells; 45A). The power produced isn't at the level of an open-class F5J model, but the Plettenberg Ergo is a far more versatile motor choice than would be required for the F5J event. As is was, the Ergo allowed the model to maintain a comfortable 20 degree climb-out, with camber slowing the model's speed slightly but helping the overall climb quite noticeably.
Having an electric drive system on board meant that the traditionally tedious task of setting the c/g became very easy, since balancing weights could be added or removed and the model quickly relaunched without spending time hunting down a winch 'chute. I had initially balanced the model quite nose heavy to try to compensate for not really knowing what the neutral stab setting was, so the XE had a noticeable tendency to pitch up with increasing airspeed. In later flights, I slowly taped more and more weight to the tail until I had the balance point where I wanted it, at which point I moved the battery pack backward and removed the added weight. The tendency to pitch up with airspeed was gone;the thrust angle in general seems to be very close to perfect.
@906151:The Eraser XE at the field just before its maiden flight.
@906152:While I generally prefer the look of a v-tail, the lines on this model aren't bad at all!
While the added weight of the electric drive system is noticeable in flight (112 oz vs 81 oz), all in all, the model performs very similarly to the <a href="http://www.rcgroups.com/links/index.php?id=4139">sailplane version</a>. It won't fly quite as slowly as the glider version due to the higher wing loading, and as a result the XE seems to be most comfortable flying a bit faster than the sailplane and carrying more trailing edge camber while thermalling.
The honest handling characteristics of the sailplane version are all preserved in the XE, with only a slight dampening of pitch responses. That said, it seems to respond to the slightest hint of lift, and can still circle tightly enough to work all but the smallest bubbles of lift. The model shows no tendency to spin at my ending c/g location. Wingtip thermal cues and roll rate are the same as as for the sailplane version, unsurprising since no extra weight has been added to the wingtips.
Rudder response seems to be even better with the XE than the v-tailed sailplane (which is excellent to start with), which I initially chalked up to a larger tail. When I sat down and ran the numbers, I was surprised to find that the tail volume is actually shorter on the XE. The tail boom length is shorter on the electric model, which is presumably an attempt to allow the model to balance more easily. This probably wasn't a good idea in the end, however, since I would imagine that the model would be very hard to balance with more than 14 sub-c cells on board without moving the RX battery pack a long way down the tail boom (possibly interfering with the pushrods there). The tail volumes are shown in the table, for those that are interested. I would guess that the increased rudder authority likely comes from the broad rudder chord, as opposed to any difference in tail area. The rudder on the XE is an extremely effective control surface, with plenty of power to command rudder-only thermal turns, or to correct for errant gusts of wind on landing approaches.
|
|< <b>Eraser</b>|< <b>Horizontal</b>|< <b>Vertical</b>
|< <b>Version|< <b>Tail Volume</b>|< <b>Tail Volume</b>
|< F3B v-tailed Sailplane|< 0.520 (w/ vtail compensation)|< 0.024
|< XE Cross-tailed Electric|< 0.447 |< 0.020
High speed flight is rock-solid, with only minimal pushrod flex apparent. No hint of flutter was ever detected, and at the final c/g location there is minimal elevator input required to maintain course at high speeds.
I plan to fly my XE extensively this summer, since it will allow me to put in a couple of quick flights after work, or after the winch batteries run flat. It will be interesting to see how the model performs on the F3B Speed & Distance course, since it seems to offer an easy way to get some solid practice flying laps. But first, I'm looking forward to not having to fly under 4 layers of clothing!
|
| <center><b>Control Throws and C/G Location</b></center>
|> <b>Balance Point from TE:</b> |< 150mm at root(easier to measure)
|> <b>Balance Point at LE:</b> |< 87mm at root
|> <b> Aileron Throw:</b> |< "+16mm, -11mm"
|> <b> Aileron Exponential:</b> |< 40%
|> <b> Elevator Throw:</b> |< "+8mm, -10mm"
|> <b> Elevator Exponential:</b> |< 10%
|> <b> Rudder Throw:</b> |< "+9mm,-13mm"
|> <b> Rudder Exponential:</b> |< 0%
|> <b> Thermal Camber (average):</b> |< "-4mm ailerons & -6mm flaps"
|> <b> Reflex (average):</b> |< "+1mm, ailerons & flaps"
|> <b> Elevator/Flap compensation:</b> |< 70% flap = -3mm elevator
|> <b> Aileron/Rudder Mixing:</b> |< 35% rudder with full aileron
!!Quick video clips of the Eraser XE in flight:
+906153:Hand Launcing the XE.
+906154:Surprisingly tight thermal turns!
+906155:A clean roll.
+906156:A nice, smooth touchdown.
!Conclusion
All things considered, I am extremely pleased with this model. The Eraser XE manages to preserve most of the flight characteristics that make the sailplane versions so appealing, while adding the independence that comes from electric flight. Whether you are considering a model for F5J competition or just one that will allow you to experience the efficiency of a larger model for sport flying, seriously consider the XE.
After having so much fun with this model, I can't wait to find out what my next failed promise will be!