Searching Z8RC.com for the best match.........

Wednesday, September 22, 2010

Scam Alert: RCGroups.com

Scam alert.  After posting a few of actual reviews on RCGroups.com, I was met with this message:

Critical of a paying sponsor, your post has been edited.

I know, who cares that RCGroups is just another commercial internet scam; hardly a great revelation.   Just realize that any information you read on RCGroups.com has been content filtered to help their paying sponsors rip off the general public.  Of course, some of their sponsors make good products, but if that were always the case their moderators wouldn't need to edit-away what their user base really thinks.  The site is loaded with intentionally-inaccurate information, as long as it is favorable to their paying sponsors and/or unfavorable to their sponsors' perceived competition.

Sunday, September 5, 2010

Quick Take: Blade SR, MSR, or 400?

The Blade SR's twitchy tail takes getting used to, but the errors generally offset in a hover.  The SR is a  Collective Pitch lead-in trainer to a more expensive, aerobatic copter like the Blade 400.  Despite re-branding efforts, the SR offers fliers little more than a repackaged CP experience.  The CP was not, and the SR is still not, a solid flying helicopter.

The Fixed Pitch MSR is not a realistic trainer for a Collective Pitch helicopter, which is why I did not rate the MSR "Highly Recommended."  The SR is more difficult to hover and fly than an MSR, and it is much easier to damage (first timers will benefit from training gear), so it demands more care.  While some think the MSR is tricky to fly, it is actually too stable to provide a useful lead-into a larger CP heli.  In RTF form, the SR only costs about $40 more than an MSR and it comes with a real heli radio and the same adjustable gyro as the Blade 400, making it a better deal.  And unlike the MSR, the SR develops a relevant Collective Pitch skill set and is a genuine stepping stone to larger CP helicopters. The MSR is fun to learn, but it flies in a too-easy, single rotor Fixed Pitch skills niche, mostly by itself.


For the more daring and possibly more wealthy, it is ok to go from an MCX or CX to a Blade 400.  The 400 is a hotter flier than the SR, but when tamed with low response rates, it can be a more docile flier than an SR and without the tail twitch.  It's larger scale is a little more forgiving of wind.  Without a lot of simulator time and someone to set up your low rates (buying the RTF version then dialing down the preset DX6i rates to 50% is also fine), you'll probably crash either the SR or the 400 in a jump from coaxial, so the daring + dumb should stick to an SR.

Saturday, September 4, 2010

Balsa or Foam?

With the latest surge in foam plane popularity, most serious hobbyists own at least one.  The beauty of foam is the speed at which a decent looking model can be stamped out.  But that's where the beauty ends.

Even the toughest foam is delicate and difficult to keep looking crisp.  It is especially weak in a crash where foam cracks with light to moderate force.  While it is relatively easy to repair with foaming gorilla glue, epoxy, or if you are really in a hurry, hot glue, the fragility of foam means it needs to be repaired more often.

A high quality balsa and ply frame covered using a name-brand plastic film can last for a decade or more without looking worn.  Balsa and ply is about five times stronger than foam, making it more resilient in a crash.  If you manage to break a balsa and ply frame, the damage is usually substantial because of the force required to do serious harm.  However, it is possible to reconstruct a wooden structure from scratch with very little cash outlay, unlike foam planes where spare parts are rare and too often, pricey.  It isn't uncommon for foam plane manufacturers to gouge customers $20 or even $30 for a foam replacement part that only costs pennys to mint.

Laser cut wood kits, assembled en mass, have brought the price of balsa and ply kits down to the foam level, or even less.  Since wooden kits are generally aimed at a more sophisticated crowd, pre-builts are usually sold as ARFs.  The great thing about purchasing a film covered-wood ARF is that base kit is relatively inexpensive, so you might buy two for the price of a similar scale foam RTF--one to build, and one to keep for quick-replacement parts.

Finally, balsa and ply models fly straight and true long after foamies are twisted, scratched, bent and broken.  Foam deforms and bends under aerodynamic force making the plane a lot less predictable during maneuver, especially at high speeds and G forces, and also in gusty winds.The additional strength of quality wood kit lets the plane cut the air with greater speed and agility at a similar power level. 

Hands down, if you have a choice, go wood. 

Quick Take: Super Tigre .10

Update: These photos added to support the comments, below:
 
 
 
Original post follows:

-----
Electrifly Edge 540 hangs at the ready with an 11x7 prop. 
Background:  Art Tech Pitts Special with 10x5, Parkzone T-28 Trojan to 
F-8F Bearcat conversion w/E-Flite 10-15 size retracts and a 10x7x3. 
All are S/T .10 powered.
The Super Tigre .10 is a unique 10-size motor that uses steel instead aluminum construction.  It out performance the next best motor in its class (the E-flite Power 10) by about 2:1.  The result of S/T's light weight construction is a 2.2 ounce feather with monster thrust.  Installed thrust with a GWS 11x7HD in front of a sleek cowl is a bit above 50 ounces at 30C. 


One reason the 10 class motor is so small at 62g that S/T has cleverly used the mount as the heat sink, instead of adding a huge, heavy, empty motor case behind the coils like most manufactures' approach to heat diffusion.  This means the required infrastructure to hold the S/T in place does double duty, mount + heatsink = even less weight.

In my Electrifly Edge 540 vs. Parkzone Extra 300 head-to-head showdown (it wasn't much of a contest), I discovered the S/T .10 slightly outperforms the PZ 15 size motor in raw thrust, and completely demolishes it in Thrust:Weight ratio.  PZ stock motors have always had spotty reputations, like the absurdly cheap, heavy but plastic 480 included Parkzone's popular T-28 Trojan), but at only $19.99 the S/T motor remains unmatched in both price and performance.  Packaging the motor with a plane, can qualify for a 20% discount on regularly discounted site's like towerhobby.com (no affliation) puts the street price of the S/T 10 motor in the $15 range.

Wednesday, September 1, 2010

Parkzone Extra 300 PnP vs. Electrifly Edge 540 ARF


Parkzone Extra 300 PnP
41" wingspan
$185

VS

Electrifly Edge 540 ARF

41" Wingspan
$105 + (4 servos @ $40) + (ST .10 @ $20) + ($30 ESC) - ($5 GP rebate) = $190

(subtract 20% from the Edge +ST price for Tower Hobbies standing member  discount.  Unfortunately they do not carry Parkzone stock.)


The balsa and ply Edge takes some effort to assemble, will the performance be worth the build time?




Construction Time and Ease
First things first, how do these planes compare from box to flight? Well, that's an easy answer: they don't. There is no comparison!

The PZ Extra 300 (why didn't they call it a 330?) is really an RTF packaged in PnP form. Setup is very straight forward and quick. You insert the carbon tube, slide the wings into place over the tube, then install two screws inside the fuse tack each wing-half in place. The tail section is classic PZ slide and tape, then you clip the elevator clevis to the control horn. Lastly, wire landing gear is popped into a slot on the bottom, then flimsy orange fairings are snapped on and screwed into the under body. The 4 landing gear fairing screws are fussy to install, other than that, assembly is a breeze. Let's say, 30 minutes to read through the directions as you go.
The Great Planes Edge 540 (why not call it the 580, because it doesn't have a real AEIO 580 under the hood?) is a completely different kind of build. The Edge is a balsa and ply ARF pre-covered in Monokote. It is essentially a scratch build with the heavy lifting already done for you. It is beautifully assembled and covered, to a higher quality than most could probably hope to achieve even if you wanted to spend excess time. After that, the minor construction details are unfinished and the guts need to be conceived and added. For example, you have to hinge all the control surfaces and fashion a suitable engine mount. Unlike the Xtra, as I assembled the Edge I kept thinking to myself, I hope I never crash this thing because it is a mini work of art. There is a lot of time and glue required, and even more that has already been accomplished. Drilling a few holes is also required to complete the model. Resultant model breakdown and setup is similar: half-wings slide onto a carbon rod, each tacked inside the fuse with a small screw. The box says ARF with 4-6 hours assembly time required; I say, no way. Let's say, one very full day from box to runway. If you don't like working from morning to evening without pause, two days is more like it. No small difference. In the end, you have a beautiful model with a finish that will last a long time with care.

Extra 300 construction time and ease (1-10): 10
Edge 540 construction time and ease (1-10): 5


Kit and Component Quality
The non-comparison doesn't end with time to build, there is a major quality dichotomy. The Xtra 300 is typical PZ. The foam is tough, generally attractive at a distance. The plane's clean "newness" will deteriorate over time as the foam creases and ages. The Edge 540 is a gorgeous model in every sense, the perfect paint, the glossy metallic plastic covering, the classy color scheme, the impressive laser-cut craftsmanship.

Instruction manuals are also different. The Xtra manual is basically a legal disclaimer with a page or two describing assembly that you could figure out on your own. The Edge manual requires full featured assembly instructions, as it is an advanced stage model kit, plus it has several pages of nicely detailed 3D aerobatic flying instructions.

The Xtra comes with a 15-sized motor and a minimal 30A ESC. Initial engine runs are rough and out of balance, hopefully it is only the prop. Servos seem adequate but PZ's record providing quality servos is rather poor. Every PZ foamy I've owned (let's just say, many) has developed a chattering or erratic servo, or two. These are entry level components at best.

The Edge comes without guts, but the kit price of $105 is low enough to equip it at the same or higher quality level. I chose a Super Tigre .10 engine due to the low price, superior workmanship, and extreme thrust to weight ratio of about 22:1 with a 10x5 in front of a good cowling. Seems like the perfect match for this light weight model. I expect an aircraft T:W of about 1.5:1.

Extra 300 kit and component quality (1-10): 6
Edge 540 kit and component quality (1-10): 10


Appearance and Overall Design
These two models are virtually identical in scale. The wingspans match within 1 centimeter, the Edge is has a 70 millimeter length advantage, or about 2.75". Within those parameters, the Edge has much larger control surfaces all around, and potential throws are a lot more extreme. Eyeballing it, I would say the Edge possesses roughly double the control surface area and triple the limits of travel. The following video clip shows the two planes bound to a single transmitter, with the control horns set to one hole from maximum throw in both planes:

Parkzone Extra 300 and GP Edge 540 Control Surfaces (0 min 27 sec)
http://www.youtube.com/watch?v=UwCh6bgCDqA
Click the link above for video.
Even though the planes have the same wingspan, it's clear in a side-by-side comparison that the Edge has a significant wing area advantage. The Edge lists 353 square inches of wing area, the Extra specs are missing that stat. At 13.6 oz per square foot, the Edge 540's wing loading is medium to slightly heavy in this class, so the Extra's wing loading has to be rather high.

The Edge looks scale. The trademark Edge straight leading-edge with trailing-edge sweep, combined with the lines of the enormous rudder and hefty elevator look almost outrageous to the trained eye. The high gloss metallic blue and bright yellow color scheme make the plane seem classy, even a little conservative. The edge is pilot and phony flight instrument free, which I prefer. I figured out that there aren't little toy people who fly these things. Right?? The access hatch is located on the bottom between the gear, and it also uses a dowel and magnet system. The painted fiberglass cowling pops on/off using 8 strong rare earth magnets, a nice touch.

The Xtra doesn't look quite scale. The mid-wing is a bit high for a full scale 300 match, and the fuselage has a slightly hunched appearance. PZ fixed their usual weak magnet problem on the electronics hatch with a much longer and stronger magnet. The 300 cowl is cheap orange plastic with quite a few small screws to remove. PZ's availability of spare parts makes the cheap plastic less of an issue. There is a red helmet ninja-looking pilot, for effect.

In fairness, the Xtra is marketed as an "In-between" that sits between trainer and 3D, so I guess we shouldn't expect the same kind of absurd control surfaces and insane throws. Those are plain dangerous to expert and novice alike. The Edge looks like a purpose-built unlimited-class all-out aerobatic performer. Flight tests will reveal the effectiveness of the obvious visual differences in model accuracy and execution.

More practically, both planes sport a high-vis color scheme. The Edge chooses the scientific best base color for aircraft clarity in the sky, yellow. The Xtra goes with an extreme look, wearing a mildly fluorescing orange suit. From the bottom, Great Planes choose a high-contrast blue and white checker board, great contrast though not at all in-sync with the overall look of the plane. PZ stuck with orange for their large checkered bottom, it could more easily be mistaken for the top wing's sweeping orange diagonals. Functionally, the Edge should be easier to see and orient.

Extra 300 appearance and overall design (1-10): 7
Edge 540 appearance and overall design(1-10): 9


Static, Installed Thrust to Weight Ratio
Static Thrust-to-Weight ratio is perhaps the most important power metric of an aerobat. Thrust to weight ratio is a little more slippery than some might think. Like a car with a broken manual transmission, most aircraft with fixed pitch propellers are perpetually stuck in one gear. The prop you select is the one gear you get to use. To continue the car analogy, you can chose a low gear like 1st if you want to go up steep hills, but you won't have a high top speed. If you want to gear for top speed it's best to chose 5th gear, but you'll have trouble getting off the line.

To make matters a little more complicated, aircraft propellers are wings that commonly list two key aspects of their "gearing," diameter (wing span) and pitch (Angle of Attack). The astute reader might recognize some unaccounted-for terms from the Lift Equation, namely wing area and speed. Wing area, or in this case propeller blade area, is obviously known but not listed. Most people assume it away as a non-factor though it is linearly important. More important still is speed because the term is squared. With props, speed translates into achieved RPM where the prop tip is moving faster by a factor of PI than the prop hub, or wing root. To compensate for the speed difference, prop designers usually taper the blade area toward the tip to distribute the generation of thrust more or less evenly as a function of radius. To make calculations even more squirrelly, speed, or RPM, is limited by drag which is primarily a function of lift, and lift is the equation result we are trying to determine!


But wait, there is more, much more. Isaac Newton told us when you get hit with a moving apple, it hurts. The impact of Newtons Second Law on aircraft propellers is that a lot of thrust is lost. When moving air, pushed by the propeller, deflects off of a part of the airplane behind the prop, which is in turn connected to the prop via the engine shaft, it creates a force than tugs back on the prop. This force substantially reduces achieved thrust. A quick thought experiment reveals why: imagine an engine mounted to a flat board that prevents 100% of the air from shooting behind the engine--this engine generates no thrust--even though it may be spinning at the same RPM as an engine that isn't installed on a flat plate. This is called installation error. Any amount of thrust left over after installation error can propel an plane forward, so this is called Installed Thrust.

You'll often see thrust measurements from RC enthusiasts who mount engines on test stands. Ignore these tests and chuckle kindly at those who perform them. They are off by around 50%, depending on a given airplane's drag contour as it sits behind the motor. Since every aircraft's drag profile is completely different, there is no value whatsoever to this type of test. The results are useless for any given engine installation, and most people need to install motors to use them. It is tempting to think you might gain some general sense of engine/prop performance from test stand results, but you can't. The prop's lift contour will align to any given aircraft's drag profile completely differently for every prop and engine selected. Also, the mass of the engine will massively influence flight characteristics, and will not be reflected in the result. Like car manufactures trying to sell cheaper cars, they crash-test into "infinite mass" barriers. This hides the effect of mass when a cheaply built car is utterly obliterated in a crash by a heavier, well built car. Mass matters.

For my thrust tests, I was careful to use a useful, but certainly not perfect methodology. There is only one perfect methodology, flying the airplane, feeling it, and recording empirical data. Since I can't strap on these planes, I chose to measure and compare "Static, Installed Thrust-to-Weight Ratio." "Static" because the test is conducted at 0 airspeed. "Installed" because the engine and prop is tested as installed in the airplane that will eventually be flying behind it. To conduct the test, I simply tie each aircraft to a scale and put the pedal to the metal, firewall it, drop the hammer, give'r the gas, go max dinosaurs, WOT, put the screws to her, whichever you prefer.

For an initial test, I felt compelled to go with Parkzone's factory prop on the Xtra 300, which is a PKZ 5101 spec'd at 10.5 x 9. Later on, I might switch up the prop to generate more data. This prop is a pretty interesting choice. The diameter is small for a 15-sized motor and the pitch is very steep for an aerobat. The small diameter will lower overall drag to juice the RPM, mitigating some of the drag from the steep pitch and allowing the engine to turn in very solid static thrust. The steep pitch will achieve a very high top speed, once the prop engine is unloaded in the air and the RPM goes even higher. PZ's choice favors speed. To go back to the car analogy, it's kind of like choosing 4th gear.

I'm guessing PZ picked this prop for a few key reasons, in order of guesstimated importance: (1) high airspeed will likely be perceived as high performance from PZ's target demographic, who may not be not the most aviation savvy consumers in Toy Land. (2) it probably keeps max amps relatively low so the included ESC can stay cheap. (3) the airplane has a tapered wing with relatively high wing loading, so they probably wanted to keep it moving to avoid novice pilots tip-stalling, snap rolling, and spinning it into a dirt pancake. Ironically, if this does happen, the prop's steep gearing will make it harder to recover since low speed thrust is limited, resulting in slower acceleration out of square corners and lots of induced torque per oz of pull.

The Xtra uses the ParkZone 15BL Outrunner 950Kv, with a list price of $70. I couldn't find a weight listed for it, or any decent specs or power limits. For a rough idea, these are engine specs for E-Flite's Power 15. I'll add the correct specs here if I can find them:

Power 15
* Recommended Prop Range: 10x6�13x6.5
* Voltage: 7.4 - 14.4V
* RPM/Volt (Kv): 950
* Idle Current (Io): 2A @10V
* Continuous Current: 34A
* Maximum Burst Current: 42A (15 sec)
* Speed Control: 40-45A Brushless
* Weight: 152g (5.4 oz) without mount

The Edge is an ARF, so I got to choose both the engine and the prop. I picked the Super Tigre .10 for its light weight, strong pull, and low list price of $19.99. I chose an 11 x 5.5 prop for my one gear. The wider diameter prop and lower pitch should help generate huge low end grunt and extreme acceleration. The low pitch should allow plenty of RPM for a brisk top speed, but this Edge won't set any speed records from NY to London. Basically, I reversed PZ's priorities.

Super Tigre .10
* Recommended Prop Range: 10x7e - 11x7e
* Voltage: 7.4 - 11.1V
* RPM/Volt (Kv): 1250
* Idle Current (Io): 1.2A
* Continuous Current: 29A
* Maximum Surge Current: 33A
* Max Constant Watts: 320W
* Max Surge Watts: 370W
* Speed Control: 30A Brushless
* Weight: 63g (2.2 oz) without mount

Here are some initial results:

Extra 300 RTF weight, no battery: 28.3 oz
Edge 540 RTF weight, no battery: 26.7 oz


Extra 300 RTF weight including NRG 2200 mah 35C battery (6.8 oz): 35.1 oz
Edge 540 RTF weight including NRG 2200 mah 35C battery (6.8 oz): 33.5 oz


Interestingly, the weight difference is almost exactly the difference in engine weight if you use the Edge's stock plastic spinner (I added a solid aluminum spinner), so, sans engine, these airframes are virtually identical in both size and weight.

Extra 300 Static, Installed Thrust: 43.6 oz
Edge 540 Static, Installed Thrust: 48.9 oz


Extra 300 Static, Installed Thrust to Weight Ratio: 1.24
Edge 540 Static, Installed Thrust to Weight Ratio: 1.46


For more detailed results, please see the attached chart. Again, it is somewhat amazing how close these two are on paper. The main power difference boils down to an arbitrary selection of prop gearing. I geared the Edge for optimum static thrust, while PZ geared the Xtra for high airspeed. As such, two differences jump right out: Aircraft T:W which heavily favors of the Edge, and Pitch Speed which heavily favors the Xtra. It would probably be pretty easy to swap the results by swapping the props.

One clear loser is the 30A ESC. 30A is no where near sufficient for these motors/props and battery. My guess is that PZ will be forced to raise the ESC rating to 40A, much like they've done on other models. PZ's decision to include a weak ESC more than negates the Edge's $15 higher price tag, since the Edge is an ARF instead of a PnP, you can buy one 40A ESC instead of buying a packaged 30A with the need for a 40A.

It is worth noting again that the PZ 15BL motor is not the exact model of the stats I have quoted. Chances are, the bundled motor is of lower quality than the Power 15, placing both motors slightly in the red zone. That said, the performance of both planes is outstanding, so a lesser performing battery could easily bring everything a little closer to the green arc.

First Flight Impressions
The wind was blowing at only 10 knots for about an hour this morning, so I took the chance to put a battery through each plane. I only had two batteries, so making adjustments then re-flying wasn't a possibility.

On low rates, the Xtra went first. On takeoff roll, the plane was definitely poorly propped and under powered. The engine wailed, but not a whole lot of acceleration was evident. Liftoff took a fair amount of road/rwy in contrast to a loud motor whir. As soon as the plane broke ground, high torque, fairly low speed, and a lack of sufficient pull wanted to roll it over. I was able to counter the plane's initial move but almost immediately, the plane was calling the shots and not me. Once the plane was farther airborne, it became evident that, most likely, the CG was too far aft as the plane was only about 75% controllable. At high speed, control was vague but more like 90% predictable. It was all I could do to get the plane reasonably in trim, onto a base leg, and back down on the ground for a high speed, head-first slide into home plate. Between the moderate winds and the aft CG (I think) issue, my first Xtra 300 flight was simply a terrible flail.

I checked the CG 3" back with with a finger balance before take off, but clearly this plane needs a more precise calibration, or perhaps I just missed it. It's odd that the Edge calls for a 2.5" CG with the same proportions. Since I know the CG was reasonably close, I have to admit, I'm not sure about this plane. Next time it'll have the right prop on it and the battery pushed farther forward. I've seen enough to recommend not even trying the factory prop. Maybe a 12x6 will give more low end muscle while still preserving enough RPM to get some speed against the wing loading? Or maybe this plane would be a good candidate for the Bf-109 3-blade. The third blade should give more static thrust and the 8 pitch should keep the plane moving? I sense testing in the future.

Determined to get some decent flying in while the winds were still in check, the Edge was up next. I checked the CG by balancing 2.5" back, at the main spar, using my fingers, again. I've balanced every RC plane I've ever flown this way and I guess I'm too stubborn to believe it doesn't work. The Edge taxied forward making quite a well amplified scraping sound. The plane has no tail wheel, and the balsa and ply frame turn the plane into an amplified Monokote drum. The manual recommends inserting a metal washer in the tail skid for durability, which I did. As long as the throttle is above 20% or so, the plane actually taxis fine. I got it pointed it down the runway and eased the power in about halfway. The nose initially tracked left under torque, and without a tail wheel, any input of right rudder had to fight the tail skid's new orientation. Within a few feet, the tail picked up and the plane was easy to correct back to center line. The Edge popped skyward.

Trimming the plane in the bouncy air took a few passes, but soon it was tracking well. Elevator trim was more difficult to nail than roll and yaw. On low rates, I had too much elevator travel. I found my DX6i's trim function was lacking enough resolution, the plane either wanted to dive or climb, there wasn't a correct trim level available. I settled for a bit of climb. The plane flew beautifully considering the unstable air. Low speed flight was controllable down an airspeed that seemed like the plane should stall and falling off to a side, but no bad behavior was evident. High speed flight got a bit exciting in the pitch axis, as the plane had a tendency to "dig in" and dart up or down. I think it's a simple matter of too much throw, and possibly a CG that is a tad aft considering the lack of flight control testing and dial-in. I flew the Edge in "sport mode" for the rest of the sortie and found the plane to be a very enjoyable sportster.

Approaching to land, the plane was pretty good in the cross wind especially for its size. A little wing low and opposite rudder put it down in the middle of the road. I decided to forgo flap testing on the first flight, as the winds were not favorable for a floating approach. As the plane lowered to about 3 feet above ground, I noticed the left wheel pant had reversed in flight and was in fact upside down. Since there was no was to fix it in flight, I continued to land. Touchdown was uneventful. The left pant scrapped on its top with little friction and the plane's huge rudder wasn't about to let the plane get far off track. The Edge half-rolled, half-skidded to a nice strait stop. A minor white scrap on top of the pant was the only battle scar.

For the next flight, I'll need to reduce the elevator throw either physically or digitally. The wheel pants need to be epoxied against the flat metal gear strut, sandwiching it between the double nut on the wheel bolt doesn't seem to grab enough pant to keep them in place. I think the 11x5.5 prop is about perfect, providing tons of low end grunt of plenty of top speed. The first flight was a lot of fun, minus a few issues that I think I can iron out. I think we are going to get along just fine.

Extra 300 Static, First Flight Impression (1-10): 1
Edge 540, First Flight Impression (1-10): 8


...two week update...

Update and Conclusion
Like so many others, my Extra 300 has a serious product defect, the airfoil is semi-symmetrical instead of symmetrical , and the flatter side is installed on the top. Please do not attempt to fly this airplane until Parkzone recalls all existing stock and fixes the defect.

I rate the Parkzone Extra 300 a 0 and give it an "Avoid at all costs" recommendation.  The Extra $300 has the honor of being rated the suckiest RC plane ever. F

The Great Planes Edge 540 ARF has exceeded both my kit quality and flying expectations by a wide margin. It is an outstanding flyer. A+

Parkzone T-28 Motor Upgrade Comparo


The T-28 is a great trainer, but let’s face it, after a few weeks some might find it a little wanting in the Thrust:Weight category. The stock plane comes with a peppy, but fairly hefty Parkzone 480 motor that generates about 23 oz of installed thrust using the stock prop. That’s about 0.74 T:W in a stock 30 oz plane, ok, but not always enough to reliably yank beginning pilots out of a square corner. Another problem is the weight of the 480. It causes pretty fast glides and touchdowns and slow pattern turns require a careful balance between stall speed and approach speed.

For this discussion, I’ve considered three upgrade motors--the E-Flite Power 10, the Turnigy 35-36C, and the Super Tigre .10. I also provide some numbers and commentary on the stock Parkzone 480. I graded each motor in commonly desired areas for improvement, and provided some commentary on how easy they are to install and how they change the T-28’s flight characteristics. Brand loyalty seems to tug on emotion for a few people who are married to brand XYZ for some reason, so I made certain to eliminate subjectivity in my scoring method. Personally, I don’t care at all about any of the brands, but I do want a smart choice that works. As you will see, any of these engines will thoroughly transform your T-28, so if you are glued to a certain brand, by all means, choose that one.

My scoring system was simple: each engine received the exact number of points as a percentage of the maximum score for each category. For example, if the maximum category performance was a 9, and another engine managed only 8, the high score received 100% of the available points the lower performer received 89%. This removed guess work from scoring. I was careful to standardize the trial conditions, and I have documented each test with live video, already available on YouTube.

My weighting system is 25% price, 75% performance. I under-weighted price from my personal viewpoint to cater to performance-oriented hobbyists, I think it might be more like 50/50. To determine the engine’s price, I tried to pick the lowest total outlay. In my case, that meant picking two engines up locally, with representative sales tax applied, and internationally mail ordering the other. Two of the motors required new ESCs and other required equipment. I added accessories to the price only if they were absolutely required.

The battery used in the test is a mid-price, very high performance NRG 35C 2200 mAh that delivers more than 12V under load. Since it was the same for each motor, I didn't count the cost, but it could make an outstanding upgrade in its own right, as you will see shortly. Since I had a couple of new APC 10x7 props, and this is a great all around size for the T-28, that's what I decided to use. Testing lots of props wasn't the point of this test, we all know a 10x10 won't give any sustained vertical on any of these engines, in exchange for higher top speed, etc.

Two quick notes before we dive in: first, my E-Flite EFLC3115 charger tends to pack a little more juice into batteries than most, though not enough to trip the battery overcharge PCB at 12.90. Others charging to 12.6 or lower might see an oz or two less thrust, but will get more battery cycles in exchange. I also taped-over my Firewall Louvers Mod for the ground tests--note the red tape on the firewall--this sacrifices 2 to 3 oz thrust at these power levels, but results reflect a stock setup.

These findings probably surprised me the most. Since I am results-oriented, I put the conclusion first and added my subjective flight impressions, none of which were scored, in the text that follows.

Conclusion:

All three engine upgrades feel virtually identical in the air, under full power. I challenge anyone to tell the difference in a blind test; it would be extremely difficult for me after 30 years of flying everything from recreational to high performance gliders, to vintage and aerobatic biplanes, to unlimited competition aerobats, to prop and jet military trainers, to the greatest fighters the world has ever known (all those 1:1 scale) to quite a bit of RC stuff. The only really remarkable difference between all of these T-28 upgrades occurs once the throttle comes back. I found that surprising.

Another big surprise was how well the stock motor performed once connected to an top-end battery and a prop better matched to the T-28’s 5.25” wide radial cowling. Plug the PZ 480 + 35C + 10x7E numbers into my Final Standings spreadsheet, and the stock motor actually places 2nd with a score of 85% (giving it 100’s on price and ease of installation and a 55 mph pitch speed). Upgrading to a 35C battery and adding a 10x7 or 11x7 (lower top speed, more vertical) is an excellent upgrade path and should be given very strong consideration by those looking to spend basically nothing, assuming you’d buy these things anyway, to achieve a greater than 1:1 T:W with their T-28.


#1 Super Tigre .10--“Cheap thrills; fewer spills.”

If you value low cost and easy, this little motor has the added appeal of not requiring a new ESC when conservatively propped with high rate battery. $25 and done. To illustrate better, my first Trojan’s 30A stock ESC and 15C 1800 mAh battery now live in an Art Tech Pitts S2-B with an ST .10 turning a 10x5 prop. The 30A is almost 10A's too conservative for this setup but the Special really screams (easier to fly than the T-28, btw).

The real beauty of this engine upgrade is a significantly lighter nose which produces airy glides and more docile pattern turns. Greasing a slow landing with high AoA, makes me wonder if the T-28 wasn’t designed from the ground up with a lighter engine in mind. Watch out for puffs of wind when you are out of airspeed and ideas, before a tire-dancing touchdown.

After the light nose, I think the next best attribute of an ST upgrade is acceleration. The motor is noticeably more abrupt than the higher mass options, and in a different class all together than PZ's stock package. Trainers should be easy to fly, but when you get into trouble you want the airplane to stand on its tail and haul skyward. Less inertia, lower moments, and very high T:W wrenches the plane up out and away from square corners.

This T-28 has an unnatural nose rate, you'll definitely want to dogfight single-circle. If it turned a little tighter, you might shoot yourself down. So eager is the T-28 nose that I dialed-in maximum elevator deflection just to see what would happen. With up-elevator forced against the T-28’s physical limit (set by the rudder pass through), the plane loops in what is best described as a reverse Lomcevok, or inside tumble, in separated rather than laminar fashion. The second tumble becomes much more interesting, as it breaks any which way but loose.

Spins with the gear up are a continuous blur without much dumbbell effect to fight the wrap, and the plane exits immediately upon neutralizing the controls. Perfect. Continuous aileron rolls stay mostly uncoupled, spinning off four to six from 10 degrees nose high through 10 degrees nose low. With the CG set reasonably aft, this T-28 is nicely aerobatic, but not loosey goosey and is easier to land than stock. Take off procedure is Elevator- Full Up, Throttle - Max. The tail scrapes hard every time, but it sure is fun to see a takeoff roll of 6-18 inches on a hot day.

One odd flight characteristic of this upgrade is the lack of required trim. Unlike some planes, the T-28’s thrust line pulls hard downward, and with a lighter hood the amount of compensation under power is about nailed. This T-28 is as close to trim-free as any airplane I’ve flown, full scale or RC, with the exception of the F-16 which auto-trims for 1g. A joy to fly.

Parkzone T-28 Super Tigre .10 35C (1 min 28 sec)

#2 E-Flite Power 10--“When Money is No Object and Landings are Into a Headwind”

Depending on how you weight price, the Power 10 can fall to a more distant second, or even third place. This engine pumps out the highest T:W, but it takes longer to lift off than the ST, then after a brief period of déjà vu its eagerness to rip toward blue trails off as the heavy nose begins to teeter.

Flying is pure fun as long as the engine is pumping. My retractable gear, “Streak Trojan” dropped like a rock without the Power 10 on high. Aerobatics are effortless and lines are smooth. As heavy as this engine is, the first two aileron rolls track better than stock before drooping toward mother Earth. Gear-up speed is impressive, but not noticeably different than the other two. That probably has something to do with attempting to pull a heavier tree stump through the right boundary of the VN Diagram.

When power rolls to half at the perch and the gear comes down, so does the airplane, demanding a lot of up trim and the re-application of power to arrest the sink rate. Flatter, power-on approaches are probably easier for beginning hobbyists than trying to judge a steep fast glide, but this engine almost forces a loud final followed by a “chop-the-power” method of spot landing. Experienced pilots might feel vulnerable flying power-on finals, aside from begging to get shot down, any engine hiccup and you are walking the rest of the way home, or in the case of RC flying, swinging roles to CSAR on foot.

Unfortunately, I only had the opportunity for one T&G before the carefree ease of substituting this engine for the PZ 480 turned sour. A brash clanking noise made itself known as the gear fell and locked, making me wonder if the nose gear had pushed the cowling forward into the prop. Given the expense of this T-28, I thought I better get it down quick with min power, though I needed some power to make the runway and the engine delivered. Landing was uneventful. As I taxied back, I realized that keeping the power low was a rare moment of good judgment. Looks like a giant aluminum motor housing isn’t such a great heatsink after all. The heat of the Power 10 absorbing a 35C dump melted the T-28’s nylon motor mount like a BLU-97 through a T-72. The mishap occurred about 5 minutes into an aggressive flight, despite enhanced airflow from a cylinder-less cowling and a louvered firewall. See attached photos for your scare of the day.

The Power 10 runs way too hot on this battery for a simple PZ 480 style installation—bummer.

Parkzone T-28 Power 10 35C (0 min 58 sec)


#3 Turnigy 35-36C--“A Big Steed That Doesn’t Want to Be Mounted”

I like to build stuff, I’m a born tinkerer. But sometimes projects fight back too hard. The thing I’ll remember most about this engine after it is gone to ebay isn’t the strong thrust, the upgrade price, waiting on shipping, the amp drain or even the lead nose, rather, the ordeal of mounting it.

This engine has a pretty weird design. The prop mounts directly to the outrunner bell using an interesting adapter that mounts a second shaft via 4 bolts into the engine casing. You don’t mount the prop directly on the steel shaft like most motors. It works fine if (a) you have a hole in the firewall to stash the main shaft which sticks out the back (and the T-28 does), and (b) if the cowling mouth is a very short distance from the firewall. It is (b) that creates a T-28 installation dilemma: you can either reverse the Turnigy shaft by application of lethal force, void your brand new engine’s warranty and possibly bend it before you have a chance to turn it on, or, you can fashion a very unique firewall spacer.

I waited long enough for international shipping, so I chose the second method, but only because I underestimated the difficulty of the task. The engine doesn’t come with sufficient mounting hardware to tackle a T-28 installation. The ST .10 doesn’t come with T-28 spacers either, but the Turnigy problem is much more complex because the engine casing itself is drilled and tapped very close to the shaft. That means you must use the inner holes of the included “X” bracket to screw into the engine, and the outer holes to link the engine to the firewall. The front circle of the T-28’s nylon engine mount isn’t large enough to attach the Turnigy spacers. Fortunately, my Power 10 came with a small bonanza of extra mounting hardware, so I borrowed its aluminum X bracket to match up with the Turnigy X bracket’s outer holes and spacers, then I drilled inner holes to match it back to the T-28 mount, again, by stealing some extra Power 10 nuts and bolts. Assembly order is tricky—Turnigy mount to engine, Power 10 bracket to T-28 mount, bolt through Turnigy bracket, slide on spacer, slide on washer, then loosely attach to Power 10 bracket, then the nut. The bolts had to be long enough to stay loose while assembling all four spacers, but short enough to end between the two circles of T-28 nylon mount, and only after completely assembled: tightened down. After tightening, I snipped off the extra bolt length to save weight, though I know I’ll never be able to reassemble this mount without new bolts. If that sounds like an ordeal, it was nothing compared to fitting it up by trial and error. I think reversing the shaft would also require a custom spacer arrangement.

When all was done, 3.74 oz had ballooned to 5.1 oz, with two X brackets, a redundant steel motor shaft, 12 bolts (4 to mount the second shaft, 8 to build the spacer), plus 4 engine mounting screws to attach the engine. Worst of all, the T-28’s nylon engine mount couldn’t handle the heavy hanging weight, there is a loud clacking resonance at around half throttle. I’ve read that this is common with Turnigy installations, so 35-36C users should probably invest in an aluminum T-28-Turnigy motor mount (ebay). The big chunk of aluminum will be heavier still, but certainly safer. With a solid metal mount, a new problem becomes how to air-cool the higher-amp ESC, so I recommend doing my Firewall Louver mod when using this engine for better ESC cooling and to squeeze out more installed thrust to counter the heavy weight of the motor and mount.

In the air, the Turnigy T-28 had good initial vertical climb, but the nose wanted to side off at lower altitude than the others. Aerobatics have plenty of punch, and the looping maneuvers are easier to make symmetrical with sweeping back halves. The plane dives like a P-40 separating from a Zero. Flat top speed seems exponentially drag limited, and feels exactly the same as the other two.

In Aero 101 we teach that that L/D)max, or the single airspeed that yields min airframe drag, max excess thrust, best climb angle, best glide range, and maximum flight time, occurs at a faster airspeed as weight increases, but max glide distance doesn’t change. In theory, all else equal, the airplane that takes on weight (airfoil constant) will glide faster but reach the same point on the ground. This engine proves without doubt that rule of thumb doesn’t hold up when you double the weight of only the nose, requiring double down elevator force to hold down the far end of the CG seesaw as you glide. That adds even more effective weight, dropping altitude quickly in a glide without as much forward travel.

Pattern turns are best carved at a steady clip, not engine-off floaters to keep control authority above significantly increased stall speed. Landings are fast, but the good news is that wind is a little less of a factor at the higher speed and the engine weight still allows the nose gear to rise a bit above the mains as the plane scoots along. Flaps might be in order, but also become self justifying as they add a couple more ounces.

This engine nicely illustrates the basic aeronautical engineering case for obsessive weight reduction. Every ounce saved, saves up to six (rule of thumb) more ounces as less lift is required, thus creating less drag, thus requiring less thrust, less fuel, reduced complexity, and even reducing scale of the airframe itself. While every ounce added demands several more ounces to scale everything up similarly.

On a side note, since I was paying for international shipping of my Quanum telemetry system (died on second use), Pitts S2B, and the 35-36, I decided to throw in a Turnigy 3000 mAh 40C LiPo. I hooked that big momma up to my 35-36 to see if it made any difference. Bang! 46 oz of thrust, not a bad boost. Interestingly, when I plugged the 3000’s 40C numbers into my xls, T:W actually dropped. This big battery tips my postal scale at a whopping 10.1 oz, about a third of the T-28’s total weight with the stock battery installed. It adds more than 40% of the weight of the aircraft, pre-battery. I guess I could have checked that before ordering—so I have another fabulous paperweight for the time being.

Parkzone T-28 Turnigy 35-36C 35C (0 min 54 sec)
If anyone is interested in a single-flight Turnigy 35-36 and/or Power 10, PM me. Realize the Turnigy run was overstressed with a 10x7 prop pulling 36.1A and 419Ws, above its maximum allowable burst of 35A and 400W. I do not recommend using a prop this aggressive on the Turnigy 35-36C with a strong battery.

Casualties are always higher in training than combat. During this test:
1 E-Flite 40A ESC smoked by their own Power 10 on first use—don’t know why
1 battery charger out of commission after charging Turnigy 3000 mAh LiPo ...and charging ...and charging.
1 T-28 engine mount melted by the Power 10, lucky I didn’t lose the plane
1 Quanum Telemetry system, unexplained failure after two uses—bummer, I liked it



The following image is in support of comment:  http://z8rc.blogspot.com/2010/09/parkzone-t-28-motor-upgrade-comparo.html?showComment=1346011089154#c5103177794726256278

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