93" long PC-21 (Sebart PC-21XL) + Dualsky GA 6000.8 - RC Groups
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Sep 17, 2015, 02:14 AM
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93" long PC-21 (Sebart PC-21XL) + Dualsky GA 6000.8


The PC-21 is becoming a more well-known RC aircraft as of late. It's easy to see why. It looks great, it's different, it's a modern aerobatic design and it has essentially F3A pattern plane dimensions. In other words, it looks great but is proportioned to fly as great as it looks.

Sebart has a more compact .50 size PC-21 but as of this year they released an "XL" sized PC-21. It's essentially a 2.2M/83" wing airplane but wing span says little about this aircraft if one thinks general wing span amounts to a semi-equal comparison with a WWII warbird, or a more modern Tucano or Texan II for example. Really, on this plane, the largest dimension by far is the fuselage at 93" long. Not only is it 93" long, but it's quite massive in that it's nearly all cockpit (this is not a pencil thin sleek design).

While the scale basis of this plane is a great looking and great flying tactical training aircraft, I believe Sebart designed the PC-21XL as a precision flying F3A pattern plane that also passes for a scale aircraft. By this I mean the aircraft structure seems adequately strong (some strengthening mods may be required for personal tastes) yet the airframe is as light as a feather! The all balsa and plywood construction is of very high quality, light weight wood that I would have hand picked if I had the chance. The structure, while getting 95 percent of the scale lines correct, gets nearly all of the structure, flight controls and airfoils correct in a plane that is clearly set up to fly pattern precision aerobatics while looking very closely like the real PC-21.

Yes, the "scale police" will have some minor complaints and investigations to mount. The areas I don't particularly like are: The engine inlet is too big (probably to accommodate a gas engine is the builder wants one) and the nose is a bit "taller" than scale. I think this is to allow more lateral lift for knife edge flight and this also accommodates the larger engine inlet.

People like me will be making modifications to high profile areas like the cockpit and the propeller/spinner configurations. But all-in-all, the aircraft really does look the part, the flight videos show it flies the part, and it will be mostly will be left "as-is". I'll be having a fine time flying a thoroughbred of an aircraft that looks great.

Basic Specifications:
Length - 93" / 236cm (94" / 239CM with scale spinner)
Span - 83" / 210cm
Wing Area - 1395 Sq In / 90DM
Electric Power - Motor 50-60CC type of 3500-6000 watts / ESC 160A / 12S
Servos - High Torque JR8411 (Ail/Elev) and JR8911 (Rud/Flaps) Equivalent
Weight - 21 pounds / 9.5kg (less flight pack)
Est. Weight RTF F3A Pattern 180-230 watts/pound - 24 Pounds / 10.9kg (with 12s 5000mah flight pack)
Est. Weight RTF High Power 220-250 watts/pound Scale Setup - 26-28 pounds (12s 10,000mah flight pack)

EDIT
For those wanting to learn about the components I'm using in the build, skip to post #12 where I list out everything I'm using as far as motors, ESC's, servos, lipos, gear and brake valves, even pneumatic tubing, etc. This is by no means the ultimate choice in equipment for everyone - but these choices were settled on after some level of research and I am happy with the product components from previous builds.

My PC-21 XL Components are listed here:

Below is the standard Sebart video showing off how she flies...

Pilatus PC21 Sebart (4 min 22 sec)


And other videos I have cobbled together since this project aircraft began "flying" in 2016.

PC-21 XL Flight 3 (5 min 17 sec)


Ed (6 min 7 sec)


Sebart PC-21 XL, Lights and Sound introduction (4 min 41 sec)
Last edited by Eddie P; Apr 07, 2017 at 03:43 PM.
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Sep 17, 2015, 02:52 AM
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In my research before buying a kit, I realized while there may be several of these flying, unfortunately, there are no build threads to speak of that I'm aware of. Except one very simple thread at RC-Network.de

In fact the photo above showing the PC-21 with the Ramoser 5 bladed prop is from Michael R, via the above link.

When I took delivery of the kit I realized the level of build and pre-fabrication was quite high. There is not an incredible amount of work to do on this aircraft but none the less there is the basic task of neatly installing the equipment in a sensible and maintainable location that also works for CG, etc.

The recommended landing gear set Sebart sells with the PC-21 seems to be of reasonable quality and is perfectly suited for the models construction. Of note, the gear set offered by Sebart is not what I'd call cheap. The model does seem to be neatly designed around these units (these are the same gear from the 2+ Meter Avanti S jet). They are carbon brake pad equipped to give additional flexibility in runway landing performance. The tires are high quality and well suited for many landings at higher weights. The struts seem to be quality units with trailing link design and appear very stout for a 25 pound aircraft with lower landing speeds of this type. The gear units themselves are apparently designed to carry several pounds more than this aircraft will weigh at higher landing speeds too, so they should be durable.

The retractable operation is pneumatically operated. While I've been using nearly all electric powered landing gear in the past several years, I was happy to go back to "air power" for this aircraft. The gear are large and there have also been many nicely improved electrically controlled air actuating valves put on the market. And my favorite pneumatic brake system is still the best in the market. More on those components later when I show the installation. At the end of the day a simple landing gear and brake system is easy to set up on a simple model like this. I also suspect air powered actuators will be somewhat lighter on a large plane compared to electric gear with the larger motors for this size gear, and heavier electrical wire connectors.

Since we are talking about landing gear, if you get the recommended units it has been suggested to re-set all the screws carefully with blue locktite. It was a simple task but I do agree that the set screws in the struts and screws in the gear braces were not very tight. You would not want to skip this step. Notable point is to not set the axle screws too tightly (these are the screws the trunion rotates about the frame with). If you do this, the gear will not swing easily from extended to retracted if you set these two screw too tightly. Let the locktite do it's job to keep them in place at only a moderate torque to set them. All the other screws set as tight as you like.

EDIT

I've been told by Personal Message by one builder that his impression is the Sebart retractile gear rail mounts are a little soft and hard landings may bend the gear mounts. This experience is based on him using these gear in a slightly heavier Sebart Avanti S turbine jet model that is designed for the same gear. I will certainly report back in this thread if I encounter any issues in this area. For now I wanted to add this as a note for those looking to buy the Sebart landing gear set... to give some more information as has been passed on to me.
Last edited by Eddie P; Dec 02, 2015 at 08:31 PM.
Sep 17, 2015, 03:19 AM
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In case anyone was wondering what the flight controls look like - they are pretty basic but seem perfect for the job.

The trailing edges are blunted for better fine touch aerobatic control but do not look out of place due to the size of the airframe. I do however plan to seal the lower surface aileron gaps with gap seal tape to reduce required aileron throws.

The flaps are quite nice - at first since I did not have any detail photos on them so I assumed they might be simple flaps with no upper cusp or glove to partially fair the upper gap when extended. To my pleasant surprise they are actually simply hinged but slotted flaps with a curved leading edge to the flap panel. This allows high pressure air from under the wing to excite the upper flap panel and create more lift. These flaps are quite large and look to be effective. I imagine approach speeds should be a a few mph lower and they should add a large amount of drag. That will require a fair amount of approach power but when reduced in the flare the combination will greatly aid in spot landing capabilities (another plus for people flying from grass strips with obstacles along with the stout gear with super effective wheel brakes and quality tires to give adequate friction).

The flaps, ailerons, elevators and rudder are all simply hinged with Robart style large pin hinges drilled into the wood framing and balsa doubler blocks. You just add some oil carefully to the center pin area and secure the pins into the wood structure with 20 minute epoxy.

Of note, one balsa doubler block dislodged from one of the aileron hinge stations as well as one from the rudder. fortunately the rudder block was easy to re attach before hinging. The aileron problem required me to step drill an access hole in the lower outboard wing sheeting near the trailing edge, to re attach the block after I was able to shake it out of the wing (I had a feeling what it was and when I saw the block I was able to see where it came from by looking at the hinge holes carefully). The fix will just be a cosmetic one for the outboard wing panel and the rudder access hole was drilled into a non visible portion of the abutment. No repair required.

Upon looking at the wings and stabilizers I do realize this aircraft is really a large one and high power servos are in order. In fact, I am looking closely as some of the digital brushless servos Savox and HKS are offering these days for high voltage power. While the kit specs JR 8411's and JR 8911's, I can get just as much or more torque for the same servo case size and the same weight or less at high voltage (2s lipo) with higher precision, lower dead band and a lot less money.

The kit also specs a separate battery bus type setup. Obviously they are allowing for large, higher amp draw servos and heavy handed aggressive F3A flying. While I think a "sport scale" pilot could easily use a separate Castle Creations 20A BEC pro - to feed and pull from the receiver directly - I do have a spare "Smart Fly" setup I can use. This is a system where all high power servo channels run through the external power bus at full battery power (dual 7.2V lipo packs) while the receiver is regulated at a constant 5.5 volts to reduce voltage fluctuations during large servo operations. This way I know even if I get aggressive there is no way I'll over task the receiver and servo power supply.
Last edited by Eddie P; Sep 20, 2015 at 12:33 AM. Reason: added photo captions
Sep 17, 2015, 03:38 AM
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The landing gear, again, is really nice. It is supposed to be a snap to mount the gear into the pre-drilled gear rails but there are some typical, basic, ARF issues to deal with. None being show stoppers by any means, just things to look for and "nip-tuck" as required.

Upon initial inspection I found the gear wells to have some balsa issues where some of the wood work was splitting and some areas had gaps that were a little more than I was happy with. Since the instructions called for the builder to coat the wheel wells with epoxy I figured I'd do one better and use .6 oz cloth and water based polyurethane (WBPU). That way I get more strength, the same weight or less as epoxy and a better fix to the minor balsa issues I had. I started the task by using light spackle to fill some of the problem areas as well as add a nice radius to the edges of the wheel wells. After drying, those areas were sanded to a nice finish. The glass cloth was cut and applied with the WBPU and allowed to dry. I followed up with a light dressing of gray primer to finish the wheel wells and add some low level scale appearance effect.

Upon mounting the gear, and gear door hardware, I realized one of the gear rails was not really laminated well. This was going to be a problem maybe 10, maybe 50 flights down the road. I added some epoxy and a clamp to re laminate the rail. I removed some of the blind nuts that were not seated properly so I could have straight screws attaching the gear mounts vs mis-angled attachments. After that I had decently fitting gear with strong attach points in the wing.
Last edited by Eddie P; Sep 20, 2015 at 12:28 AM. Reason: added photo captions where needed
Sep 17, 2015, 03:49 AM
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Here are a couple photos... one of the plane with lights and one photo of the large fuselage interior. These are not mine, just images from online. It comes with a basic light package of LED's for taxi lights, landing lights, Nav and Position lights. The interior is so large there will be provisions for a slightly better, more scale cockpit environment.

I still need to get the Motor Package for the aircraft. At this point I'm planning on going with the Hacker Q80-8M motor and the Castle Creations Edge HV160 ESC. The Hacker is not readily available right now. I thought of buying used but I think I'll just wait for new stock to arrive. The kit comes with the standoffs already as specifically required by the Hacker and since I'll be running a Ramoser 5 blade prop, at least part time, I prefer to have the high efficiency (above 90) of the motor for the higher wattage I'll be running in the scale configuration.
Sep 19, 2015, 10:58 AM
Onward and upward.
Pilatuspc12's Avatar
Very nice, Eddie. I remember watching the first, all flat black, prototype fly at the Buochs airfield in Stans. It was quite a sight with incredible sound from the 5 bladed propeller. Thanks for letting us follow along.

Randy
Sep 19, 2015, 12:32 PM
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Randy that's really cool! Were you, by chance, working for Pilatus at the time? I like your avatar name!

First flight of a type is always special, I bet it was something to see in person.
Sep 19, 2015, 10:01 PM
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As I am waiting to decide what motor to go with (and since the Hacker Q80-8m is not available right now... on backorder... so I'm considering Suppo/Eflite/Etc in the meanwhile)...

This video should provide some level of entertainment and is a nice place to glean some aerobatic routine elements from

https://www.youtube.com/watch?t=208&v=dUyZJV7zpIU
Sep 19, 2015, 10:10 PM
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Tuning in for the Big Show Eddie! Impressive looking model! What are you thinking on using for a prop? How many cell count?

Love to see this one in the air!
Latest blog entry: 2017 Reno Air Races
Sep 19, 2015, 10:57 PM
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Oh man! I just laid out all the data I had on the motors and props. Something weird happened... got to typing too quick and I lost the post!

Anyhow, here is the gist of it:

I want to fly the model on 2 different setups depending on the mood.

Configuration 1: 2 blade props. 22x12 / 21x13 / 22x14 etc. This is essentially a 4000 watt setup or so on 12s and a 180kv motor like the Hacker Q80-8m or the Eflite 360 or similar Suppo. I can fly the plane with my existing 6s, 5000mah packs. It will fly F3A and "somewhat" scale aerobatic routines and precision aerobatics for about 7-9 minutes.

Configuration 2: Scale and Performance. Per the above video, "scale" is actually more performance oriented on this model. I will be buying Ramoser's 5 blade scale 104mm spinner and 5 bladed prop with hub (19 inch prop disk). This will essentially be a 130 amp setup, limiting flight times to about 5 minutes on my current battery packs or if I buy a new set of 8000mah packs I could have 8 or 9 minute flights with some throttle work.

The issue I have right now is availability and distribution of Hacker motors. You might have seen my thread on what motors favorable compare to the Hacker Q80-8m. I've been a long time Hacker fan but I have to be realistic, the Q80 is a lot of dough and the Hacker USA distributorship is a questionable one at best right now. That combination doesn't leave me super comfortable. I am going to wait to buy the scale Ramoser prop until I have ordered the motor. That way I know for sure what adapter for what motor shaft. Hopefully this will be resolved in a few weeks?!

In the meanwhile I still have servos to buy. Since we are talking JR8411 and 8911 equivalent they are standard case servos to fit in the supplied aluminum mounts (very nice by the way) but I need to be careful on what servos I get. I'm not going JR, I'll be likely getting Savox, HKS or Hitech high voltage so I can get the toque I need and the size and weight I need at a lower price than JR that I want to pay and the technology will be more advanced than the JR servos.

So the motor wait won't set me back on it's own, I have more work to do yet.
Sep 21, 2015, 12:21 PM
Onward and upward.
Pilatuspc12's Avatar
Quote:
Originally Posted by Eddie P
Randy that's really cool! Were you, by chance, working for Pilatus at the time? I like your avatar name!

First flight of a type is always special, I bet it was something to see in person.
Hi Eddie, yes, I was getting training at the factory for my Swiss ATP.
They wanted us to ferry the PC-12's over to the States. Instead, they gave me TDY to do airshows in Europe, that summer. Quite fun. Later, here at the Reno Air Races, they let me fly the pylons for quite a few laps for photos and some video, in 2000. It was a fun ride!
Last edited by Pilatuspc12; Nov 08, 2015 at 11:23 PM.
Sep 28, 2015, 11:19 PM
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I've effectively settled on a few pieces of hardware for the PC-21 in the past week or so. The motor will be a Hacker substitute. I could not get the Q80-8M when I was ready to buy it and this was actually a very fortunate accident - I've had a long hard look at the Dualsky GA6000.8M motor. It's got similar specs on it and a lot more affordable, plus it is a wonderful motor to own and operate (edit... still super happy with it after 2 seasons). I was hesitant about my unfamiliarity with the brand and the potential cheap components but none of that has borne out in my research and experience, in hind sight. Purchased from James at JB hobbies get's them in stock. I'll be using the Castle Edge HV160f ESC with the latest firmware that effectively runs the Hacker 28 pole motor well now so it should do well with the similar Dualsky motor (I hope).

I've got an older but in great shape (like new) Smart Fly dual battery bus "Power Expander Pro" that I'll be using with my receiver to deliver 7.2 volts via twin 2s lipo packs to the servos. The receiver get's filtered and regulated 5 volts. The servos get the whole whack. The Smart Fly board came out of a turbine jet I sold a few years back but since this plane is big it also has high voltage higher amp draw servos for the big flight controls. Plus, this plane is meant to be flown like a F3A pattern plane so I will be working it a little more than the typical scale warbird hence the redundant and high amp capable radio setup.

The retracts are air driven and so are the brakes. I'm using Jet Tronics digital retract and brake valves since I love using them so much on my other planes I use air for gear and brakes on. The nose gear doors are servo driven while the main gear have no movable doors just flush gear strut doors. The pneumatic manifold can be a simple affair of a one way check valve into the tanks with a "Tee" fitting back to the valves or a more complex manifold with air inlets and pressure gauges, this is not a requirement to go one way or another. In my case I'm using the all-in-one manifold filler and pressure gauge item that I've seen on some of the more recent jet builds. Instead of traditional "Tee" and "Wye" fittings for the air lines I'm using some Festo style plug in connectors since I bought my air tubing (Freelin Wade) and these fittings from McMaster Carr. (Parts 5648K22 for 3 colors of air line and Parts 5779K31 / 5779K41 for the Festo fittings) These are the highest quality parts and lines, much better than Robart lines and fittings available and they cost less from this commercial supplier.

The propeller will actually be two separate prop sets that I'll choose for the day or flight depending on what I'm after. I'll use the basic, kit provided 2 bladed spinner and a 22x14 prop for sport aerobatic flights using a basic 12s, 5000mah flight pack. Then I'll use the Ramoser, scale 5 bladed, high performance set for the fun of extra scale looks, performance and sound. Here is the Ramoser scale 5 blade 16D hub. The spinner is 104mm wide at the base and I'll use an 18.2" 5 blade set, and possible a 17.2" set to test. The scale spinner brings the aircraft total length to 94" in all. I will be able to interchange the scale, high performance 5 blade Ramoser prop and the 2 blade sport prop within a minute or so, as I will mount the motor and cowl to accept both with minimal setup.

The flight packs... I have several 6s, 5000mah packs capable of delivering 130 amps or so if pushed but I hesitate using them at more than 110 amps (They are advertised as 50c but to me means really more like "true" 25c). The 2 blade setup should not pull more than 110 amps in reality and more like 60-80 amps in flight. The 5 blade prop is a high draw performance item however. I think I'll be pulling 130-140 amps on the ground and maybe 100 in flight on average. At this point my feeling is to gang up 2s-2p on 6s 5000's, to get 12s, 10,000mah. (that's an extra 3.5 pounds on top of the light weight setup). I am still considering a single pair of 6s 8000mah packs but I hesitate as I don't have anything else to use those big pack on, other than this plane (I try not to design setups to use orphan packs, I like to share packs among several planes for flexibility and better usage). I'll probably make up a special harness to allow the 2s/2p packs and see if the extra pound and a half of weight is all that bad. If it's not, I'll run 2s-2p on the heavy duty scale prop and just 2s (2 in series 6s-5000mah) on the sport setup. The big pack purchase can wait or be deleted depending on how the 2s-2p flight test goes.

The servos are high voltage High Tech digital. I went with the modern yet economical Hitech HS-8330 SH for the ailerons and elevators and the HS-8335SH for the flaps and the rudder. The big slotted flaps need a lot of torque to hold those big surfaces flush (clean) during high G loading maneuvers and then again to hold them deflected for larger deflections for landings. The rudder is not huge, but then again it's a rudder. It's a non-loaded surface and if a surface is going to flutter from a weak servo it's the rudder that will play up first. In addition, these torque values are equivalent to the newer high voltage JR 8411 and 8911 at a fraction of the cost. Tower Hobbies is offering a huge sale right now for larger purchases so these servos can be had for a lot lower prices than even servo city lists them in those links I added.

NOTE: The servos listed are NOT programmable. If you want to reverse the elevator and flap servos so you do not need separate channels for the right and left sides get a programmable digital servo set for these features. I am using separate channels for each elevator and flap on my setup due to the servo layout / control linkage symmetry taking priority over servo positioning, and the servos not being programmable / reversible from each other on the single channel. Fortunately I have 14 channels available so I did not feel the pinch.

In the meanwhile here is a cool video of the real PC-21 in flight during airshows and exercises. It's got me scrambling for sound files for the sound system I'm putting in as well!!
(HD) Pilatus PC-21 Display at Axalp. "Axalp & More" Chapter 10 out of 12. (4 min 6 sec)
Last edited by Eddie P; Mar 07, 2017 at 01:14 PM. Reason: Notes about servos ~
Sep 29, 2015, 09:45 AM
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Really nice plane Ed! Love the flap details.
Sep 30, 2015, 02:49 PM
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Thanks Nick!

You flown your Valiant yet? Still doing BITW? I'll be there.. maybe as early as Thursday. Not sure yet.
Oct 14, 2015, 10:09 AM
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My 1/4 scale jet pilot found it's way into the shop.

Sizing looks to be right on the money. The Sebart PC-21XL is right about 1/4.8 scale and the pilot figure is too if you consider a 5' 9" inch pilot with the extra bulk of helmet and boots making him closer to 5'11" outfitted in gear. That's right in the 50th percentile (perfect average) of height in aircraft cockpit design.

I will be working on a scale, light weight cockpit for the pilot. So far it looks like the pilot will have no issue sitting in the fuselage in the scale position. The flight packs will be underneath him but there is a lot of room to spare.

The PC-21 was delivered with zero covering wrinkles - best I've seen. There have been a few very minor wrinkles that have found there way onto the model as it's been stored in an un air conditioned shed and the heat has been high int he later summer here. Still, they are super minor and easily removed after final assembly.
Last edited by Eddie P; Dec 01, 2015 at 12:23 AM.


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