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Feb 24, 2013, 09:05 PM
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Mazzepa1's Avatar
Build Log

Project PZL P11c

Greetings all. During my budding career(?) as an rc aviation enthusiast, I've noticed that the most usable help to me has come largely from actual build logs. I always thought, "Man, what a time consuming PITA doing a build log must be."

So, time for some payback. What follows is a recounting of what is in great part applications of lessons learned as applied to the building of an EPP kit of the Polish PZL P11c by Marek Rokowski.
I've had my eyes peeled for a kit of this plane for a while, so I jumped at this one when I became aware of it in spite of the fact that my EPP building skills were virtually nil. Marek told me that the P11c may not be the best choice for me due to the complexity of the wing. Oh well this is not the first time I carried on in spite of wise advice.

Yes, it's all in Polish, but Marek is functional in English. This is a doable thing as you will see........

First off is getting the kit. Marek is setup for purchase via Paypal. Cost was 34 Euro + 5.50 Euro shipping which equaled $51.35 when I placed my order. Kit arrived 9 days after it was shipped, box was a little roughed up but the contents were in good shape.

Photo of kit contents is borrowed from a Polish rc forum: The link was provided as part of Marek's sales info, so I'm assuming it's cool to use as reference. Scroll through the photos, they were very helpful to me in filling the gaps left by the manual (pretty generic) and the plan (specific to the P11c, but I always want more info from plans).

Looks a bit sparse for $50+, but what's there is gold. Not shown is the plan and manual as depicted in Marek' website. As can be seen on the vinyl sticker sheet, none of the numbers are duplicated. I asked Marek to include a second sheet, and he did so for no charge.
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Feb 24, 2013, 10:44 PM
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Mazzepa1's Avatar

Wing work

Well alrighty then, time to get to it. I started with the wing, 'cuz it's the most interesting part, I guess.

So how in the heck should a guy cut in the spars for a double dihedral (gull) wing anyway? I chose to cut the slits before assembly so a straight edge could be used to guide the blade. I laid out the wing pieces flat with the leading edge trued to a piece of angle aluminum, then taped them together. Marked cut depth with tape on my scalpel, marked the end points, and cut the slits along a straight edge.

This is the underside of the wing, top has only the one long spar. Procedure for it was the same.
Feb 24, 2013, 10:49 PM
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Mazzepa1's Avatar
Uuurrrgh! Would someone tell me how to add text after a photo is attached in a post? I'm not seeing how to alternate text and photos.

My attempts to do so result in all the text being stacked at the top, and all photos being placed at the bottom.
Feb 25, 2013, 10:02 PM
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Mazzepa1's Avatar
Carrying on as best I can.

Photo #1 - The real deal, this plane is at Poland's National Air Museum.

Photos #2, #3 - After the spar slits were cut, I glued the wings together on the angles as they came. Did very minor foam material to get max contact at the glue joints. Efforts to jig, or pin the pieces together for alignment/true checks were largely futile. Too many pieces going too many ways. Decided to trust the cuts and go for it. Result was a wing that is very nicely symmetrical from side to side. Whew! thanks for a good job cutting the angles, Marek.
CF rod spars were held in the slits well enough by friction fit to hold them while CA was applied. Excepting the spars, adhesive used exclusively throughout build was Welder Glue, magic stuff for joining EPP. Elevator spar was a piece of cf strip, just cut a slit and glue (also CA) it in, piece is flat. No stiffener in vertical.

Photo #4 - Front view of wing. Gull shape is "flatter" than I hoped to see, but still looks good.

Photo #5 - End view of wingtip showing the symmetrical shape of the airfoil. Dotted lines are for reference so I don't get lost cutting/sanding the rounded wingtip taper. Using the "facet cuts" technique to achieved desired shape. I found that with EPP almost all shaping is done by cutting. Sanding doesn't so much remove material as shred it, to be smoothed w/a hot iron. More on that later.

Photos #6 & #7 - Used tape to mark top & bottom inboard edges of wingtip taper. Learned quickly that Sharpie marks on EPP are nearly impossible to remove w/out taking material. I used pins and tape for almost all my marking anywhere marking would be seen on the finished product.

BTW, this is my second EPP build. First was a Western Michigan Parkflyers Yak (great airplane), which is all flat pieces. Line and square everything up and glue away. The P11c is a large step up for me, especially trying to get a true airframe working with all the curves. I never did perfect a good methodology for alignment and wound up using a whole lot of the ol' "TLAR, glue it".
Feb 26, 2013, 01:14 AM
Registered User
robertus's Avatar
I am glad that you build this beautiful plane.
You made too small angle in the wings. Try to correct this if you have a possibility now after assembling.
Feb 26, 2013, 01:18 AM
Hobby King Hater
Kimber's Avatar
Uuurrrgh! Would someone tell me how to add text after a photo is attached in a post? I'm not seeing how to alternate text and photos.

My attempts to do so result in all the text being stacked at the top, and all photos being placed at the bottom.
To add text below the image you have to load your pics on a server
and use the url.

The images loaded here will always be at the bottom of the post.
Feb 26, 2013, 04:35 AM
bruno28's Avatar

fighting squadron

The good work done with a kit Marek is not the easiest, I envy your workspace, clear and clean, this is how you will work correctly, congratulations for your construction step by step to help all the guys build these kits in EPP.

Following quickly ... Nono28
Feb 26, 2013, 05:33 AM
Registered User
marek rokowski's Avatar
Hi Mazzepa1
very good build log.
you taked the most dificulte from my kits, but results i see really good
how say Robertus, you made too small angle in the wings

all the best
Feb 27, 2013, 10:30 PM
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Mazzepa1's Avatar
Agreed, angles are too shallow. By the time I noticed, the spars were in and I decided against trying corrective measures as it would take some very skilled knife work to rectify. I'm not yet that confident. I figured if it was an insurmountable mistake, I'd just get another kit and try again. I'm a novice builder and figure mistakes will be made, just be sure to learn from them.

Thanks for the tip. I'm going to press on as I'm doing for this log, then get that URL deal figured out. Nice to have royalty looking in.

What technique do y'all use when installing the spars in these double dihedral wings?
Last edited by Mazzepa1; Feb 27, 2013 at 10:35 PM. Reason: Correct typo.
Mar 01, 2013, 05:47 AM
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Mazzepa1's Avatar
So let's talk a litle about the power and electronics.

Recommended motor is a Tower Pro 2408-21 black which is a 50g, 1400KV motor. I have an eRC BL300, a 36g, 1400 KV unit. Surely it'll be adequate for a plane that comes in around 380g AUW w/recommended motor & battery.

Battery range is 1000mah-1350mah, 3S. I'll go with the 1000mah to keep the weight down.

Servos will 3 of the good 'ol HXT-900s. Rudder hinge is cut, but an option I will forego. Plane is reported to fly well in A/E/T configuration so, A/E/T/ it is.

Here's the list:
Motor eRC BL300
Prop 7x6 APC electric or 8040 GWS DD
ESC Thunderbird 18A
Receiver OrangeRX (Plastic case replaced by heat shrink)
Battery 1000mah, 3S Turnigy NanoTech 25c-50c

A word about the transmitter as well. I recently purchased a used Spektrum
DX6i. This is my first programmable radio, so I'll be learning that rigamarole.
All I've used up to now is a DX5e.

Guys at the club have been ragging me pretty hard to let go of a few bucks and move up, so I caved in and sprang for it. I was claiming to be a "purist" and not wanting to sully the experience of vicarious flight with electronic aids. They said I was just cheap.By all accounts this "expo" is very helpful, we'll see.
Mar 04, 2013, 05:54 PM
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Wing tipping

Where'd the photos go?
Last edited by Mazzepa1; Mar 04, 2013 at 06:05 PM. Reason: Photos didn't appear on 1rst attempt.
Mar 04, 2013, 06:02 PM
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Wing tipping

Wingtips are precut fore to aft, but lacking that nice, curved taper from inside to out.

Almost convinced myself to leave them alone, "May need the extra strength for damage protection in case of a ground loop." and "I've never tried doing this before, I'd hate to mess up such a pretty plane." All to no avail as my heart told me this plane deserved the best I could give it, so I'm going in.

Photo #1 - End view before the knife begins its work on the top side of the right wingtip. I did all 4 "shapings" the same way.

Photo #2 - Weapon of choice is a fresh, goot-n-sharp replacement blade for those knives you break off at a score line every so often as it dulls. Saw these being used over and over on the Polish forum. 1rst cut is @ 45 deg to the corner (1rst facet), starting at the LE tape mark increasing depth quickly to a cut that is about 4mm wide at the base of the material being removed. Hold this cut depth to approx. 2/3 of chord excluding the aileron tip, then decreasing depth gradually so that almost no material is removed from the aileron tip.

The hardest part has been done. This is kinda like shingling a roof, all subsequent work is referenced from the 1rst one down, get it right and all you have to do is stack all the rest on from there.

Ok, the 1rst cut provides us with 2 facets as we're working from the center reference marking and up. 2nd cut is on the facet between the 1rst cut and center. This cut is much shallower and at a much greater angle than the 1rst cut. Cut depth/width ratio is varied as on the 1rst cut.
Now get the calibrated eyeball on it. You'll see that you're already surprisingly close to a rounded shape here. Time for some very minimal shaping cuts (shaving really) of the facets you just created. The less you have to cut at a time the more important it is to have a very sharp blade as the EPP will roll away from the edge very easily, causing you to want to increase the angle more than is needful to get a "bite" so you're cutting instead of rubbing. You will screw up if you do this.

Photos #3 & #4 - Working the top facet of the 1rst cut and up. The angle of cut is much shallower. Notice that the curve of the wingtip is generally followed for width of the cut. Depth & width increase more dramatically, but again fairly quickly from the LE starting point and decreasing more gradually towards the aileron tip. Very little material was removed from the aileron tip, mostly by sanding to blend our wingtip taper to the aileron TE height. Again, the calibrated eyeball is utilized to shave off the resulting facets at ever shallower angles until we are very close to our final, desired rounded taper.

A word about sanding EPP. You don't remove material so much as shred it. I have a photo coming of the horizontal that shows this pretty well. This ugly, fuzzy look is dealt with by ironing it. My initial exposure to this technique is here:
Got to report #28 for some video instruction. Very helpful. I used my Hangar 9 covering iron.

Photos #5 & #6 - End and top views of finished product. Doesn't look like much has happened, does it? My photos are not of the highest quality, and there is no contrast to show depth with the foam in white. The payoff comes when you paint it, the wing looks so much better, more finished if you will. I'm sure it will fly better, too.
Mar 11, 2013, 12:40 AM
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Rounded edges for the horizontal

Photo #1 - Variation of facet cutting/shaving/sanding to round the edges of the horizontal/elevator. Sanding was done using an 80 grit drywall sanding block which is abrasive bonded to a foam block.
As can be seen, if this was as good as it gets, one would be better off to leave the edges square.

Photo #2 - In spite of the photo being out of focus, it's plain to see what an improvement in appearance can be gained by ironing down the fuzzies. I got the best results by rolling the iron over the surface rather than wiping it. The fuzzies lie at various angles, so when you roll the iron, it just lays them down. If you wipe with the iron, as you're getting some down, you're raising others back up.
Mar 11, 2013, 06:00 AM
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On to the fuze

Fuselage consists of two halves. Everything but the landing gear happens in the top half. The bottom being a cap glued on after the internal components are installed in the upper half.

View is up into the upper fuze half.

Starting with the hor/elev, the CR stiffener, music wire joiner and control horn are seen. It's just taped on, to aid in locating the pushrod and its guide tube.

In the fuze note the full length CR stiffeners and bulkheads, which were cut from extra material that came witht the kit.

Elevator servo was cut through from the top, in the wing saddle area.

Diagonal line across the stiffener marks the path of the guide rod to exit the fuze.
Mar 28, 2013, 05:59 PM
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Staying with it

Photo #1 - Hor/elev taped on loosely to locate terminus of pushrod. Held the pushrod guide tube in line with desired path and marked. Removed the pushrod from the guide tube and pushed it through EPP along the desired path. Left it in place to use as a guide for drilling to allow installation of guide tube.

Photo #2 - Found a length of brass tubing almost the same dimensions of the guide tube. Sharpened one end with the trusty x-acto, slipped it on the pushrod and drilled out EPP for a guide tube channel. Did the aft, angled opening from the rear. Openings through bulkheads from the front.

Photo #3 - The supplied guide tube wasn't quite long enough, so I cut it into 2 segments with the gap as seen here. Slipped it in over the pushrod (wire, really) a dab of glue here & there to keep the tube in place, and done. The HXT 900 has no problem moving the elevator with authority. Push-wire showed no tendency to kink or bow.

Photo #4 - The manual/plans make small mention of electronics placement. I decided to install a tray for the ESC under (looking up in this view) the servo to keep leads to the ESC from fouling the Elev servo arm. Scalpel was used to cut through one side of the fuze and just deep enough in the opposite side to seat that end of the tray (cut from a piece of 1/16" ply)

Photo # 5 - Sliding the tray through.

Photo # 6 - Tray installed. Glue the through cut shut (great attribute of EPP, a cut glued back together is virtually undetectable), then a dab or two of glue on the tray to keep it in place. Access to electronics after assembly is minimal to none. Bear in mind that this design is for combat flying and a fairly short life span. I'm using it as a semi-scale sport flyer. Should the need arise, I'll just cut out a plug of EPP, do my thing and glue it back in. Of course, one should check out equipment before installation.
Last edited by Mazzepa1; Mar 28, 2013 at 06:01 PM. Reason: correct typo

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