Sterling Fokker DVII build - RC Groups
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Jan 09, 2017, 06:37 PM
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Sterling Fokker DVII build


Well, I've decided to attempt a vintage Sterling DVII, 1/6 scale 58 inch span, first released in about June 1968 when pictured on that month's cover of Flying Models. The ad in that issue offered the kit for $39.95.

To quote the ad, "Finest quality balsa sanded to micrometer tolerance and density graded. Accurate and cleanly die cut balsa and plywood parts..... 58 1/2" of Scale Magnificence!"

My kit must not have seen that ad. Given what I've read about Sterling wood, my kit balsa was actually better than expected. Only one piece missed the micrometer sanding and was left with rough saw cuts on one side. The plywood is pretty awful, being some coarse luan-like 3 ply. To be determined how much I'll use.

When I bought the kit a while back (being sucked into paying collector prices, by the way) I immediately destroyed any collector value by removing all the parts from the die cut sheets. The balsa parts separated with minimal prodding. The ply was another issue; the die cutting went about half way through the sheets. I had to cut almost all the ply parts out with my scroll saw, using masking tape on the back to minimize the tearing of the soft luan.

I bought some wheels and some guns and a used Enya 90 four stroke. It takes me forever to finish anything, but right now I'm excited about building it. The Wisconsin winters are long, so it is a good time to start.

Jim
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Jan 10, 2017, 08:17 AM
Brighto?
Mike Denest's Avatar
Brace yourself for a thrill ride and welcome to Sterling quality Do what you can to keep the weight out of the tail as you will still need to add a substantial amount of nose weight to achieve balance. Trace your parts and replace the crappy ply with good grade aircraft ply. The landing gear is too springy and will only nose over the airplane when you touch down. The fix is to add a second wire axle that attaches to the bottom wing which will make the gear nice and stiff.

It flies like a pattern ship and has the glide ratio of a brick but other than that, it is an easy airplane to fly. Good luck and post photos.

https://www.rcgroups.com/forums/show...DVII-1-6-scale
Jan 10, 2017, 10:01 AM
Registered User
Mike, thanks for posting the link. It contains some good tips. I see I actually posted a picture of my fuselage plan in that thread - in 2012. I've had the kit since January 2011; it's been a long time sitting.

First order of business is to see what room the Enya 90 needs. I'm thinking the firewall will need to be moved back. The rear gear leg mount system has to go. I'll extend the fuse bottom back so it accepts the rear leg. The lower wing leading edge at the fuse will be notched to clear the gear. Probably will need a short sub-spar. A more scale tail skid is planned. I'll draw all this out before gluing anything.

The gear will get rebuilt at the bottom as well with some scale-like up and down movement at the axle. I'll see if I can steal something from one of the 1/4 scale DVII plans.

I'll cut away as much excess wood as possible in the rear fuse. It's an odd construction method, basically a balsa box with stringers on the outside to replicate scale structure. Sticks would have been just as easy and lighter.

Jim
Jan 10, 2017, 10:49 AM
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John Cole's Avatar
Jim,
Thanks for posting this thread, I will be following your build. This model is on my 'someday list'.

John
Jan 10, 2017, 09:20 PM
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I've started the fuselage. The second former will end up as the new firewall, so no major changes there. Sides are are an odd mix of pieced together 3/32 sides with sandwiched doublers added to the front. I enlarged the rear cutouts, but the total weight saving was only one ounce. When the doublers are on, 3/16 square longerons are added to simulate the fuselage tubing. Lots of parts, messy, fit wasn't great.

More problematic for me is the method for mounting the gear and cabanes. The wires are essentially "sewn" (bolted, actually) to the structure during construction. That puts them in the way for finishing and painting and impossible to fix if damaged. The plan is to scrap the kit method and install brass tubing to accept remade gear and cabane wires.

Jim
Jan 11, 2017, 08:04 AM
Brighto?
Mike Denest's Avatar
Quote:
Originally Posted by jjscott
First order of business is to see what room the Enya 90 needs. I'm thinking the firewall will need to be moved back.
Jim
I have one my uncle built years ago that is now retired. After building several of these kits, he got tired of putting all that lead in the nose to get it to the Cg so he lengthened the nose 1 inch. He still had to put lead in it but not as much. Looking at the airplane you would never notice it.
Jan 11, 2017, 11:22 AM
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The PIPE's Avatar

Were you thinking of scale AIRFOIL wings for the Sterling D.VII kit?


Dear jjscott:

The PIPE Here...I've had one of the Sterling D.VII kits myself that was acquired from the late Hank Iltzsch decades ago, and was quite seriously disappointed with the completely NON-scale airfoil that kit used...

...which led me to use the plans alone to start scratchbuilding a 1/6th scale D.VII around 1980, with fully SCALE, undercambered airfoils throughout.

I was just wondering...IF you had some access to good scale drawings for the D.VII, would you consider doing the same thing for your D.VII, as it looks like you've not even started the wings as yet?

I've included JPEG copies with this reply of the four-sheet Nicholas Karstens Fokker D.VII scale drawing set. These are said to be one of the best "sets" of scale drawings ever done for Reinhold Platz's famous design for his employer, Anthony Fokker.

The RCG "Scale Drawings" forum does have THIS thread going for Fokker D.VII scale info, but as the Karstens drawings just arrived there, too, you DO have the first chance to get them from the attachments included with this forum thread reply.

I've also got scale "gear-wing" documents that you seem to be looking for as well...

Quote:
Originally Posted by jjscott
...The gear will get rebuilt at the bottom as well with some scale-like up and down movement at the axle. I'll see if I can steal something from one of the 1/4 scale DVII plans.
...

...please check out the attached Karstens drawings of the D.VII, and if you like those, I'll send along the "gear-wing" docs as well in this thread...

...as well as a photo or two of my 30% completed 1/6th scale D.VII, which uses 3/16" OD birch dowels for its fuselage (entirely an open-structure scale design, with sheet material in the nose). It has a bit-smaller Enya 60-4C four-stroke mill in its nose, which if I needed it, would also easily accommodate an Enya 80-4C instead, IF I had one!

Hope this quartet of scale drawings can help you out...and a scale-airfoiled wing set would quite likely make a hugely beneficial difference in how your 1/6th scale D.VII would fly.

Yours Sincerely,

The PIPE....!!
Last edited by The PIPE; Jan 11, 2017 at 11:53 AM.
Jan 11, 2017, 11:22 AM
Registered User
Mike, what kind of access is there to the interior of the nose behind the engine? Is it possible to put the receiver battery and servos up there and still get at them?

I haven't gotten far enough to know if there is a removable top hatch.
Jan 11, 2017, 11:41 AM
Registered User
Thanks for the drawings Pipe. Helpful.

I've not yet thought much about the wings. Mike noted the Sterling DVII flies like a pattern plane. The pointy symmetrical airfoil is probably the reason why. There's always the dilemma about what to do about things that are wrong. That fat wing is what identifies the DVII. It's not there on the Sterling kit.

That said the object is to build the Sterling kit using as much of the kit as possible. So, the kit ribs will be used. I am thinking about changing the leading edge to blunt it up a bit. We'll see when I get there.

There's also no top fuselage view on the plans. I need to draw one so I can see how those front bulkheads go together with the larger engine and wider mounts.

Jim
Jan 11, 2017, 12:09 PM
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The PIPE's Avatar

You COULD always do a scale-airfoil D.VII wing set "later"...!


Dear jjscott:

The PIPE Here again-as I'm not the sort that can comfortably "stay ahead" of a too-fast RC aircraft, both my 30% finished 1/6th scale D.VII, as well as a quite-likely quarter scale RC Giant D.VII from a yet-to-be-started set of CAD plans by yours truly, meant to use one of the huge Saito FA-220 four-strokers converted to CH spark-ignition methanol running (check my blog concerning my need to AVOID using gasoline for anything in Giant Scale!) for its power needs someday, would definitely get the scale-airfoiled wings.

If you ever find that the Sterling kit's symmetric-airfoiled wings do make your D.VII a "too-fast-flyer", the Karstens drawings give you the info for building a scale-airfoil set of wings for your airframe someday. One thing to remember, though, is that the "tapering airfoil" design for either set really should be built with the upper forward spar being as "board-FLAT" as possible, for both the upper and lower wing sets, to be fully "scale-looking" as possible...you'll find that out from examining the Karstens drawing no.2's upper left "nose-on" depiction of the D.VII, both wing panels are "board flat" as shown for the upper forward wingspar in each set of wings, and that's achievable with either the Sterling symmetrical ribs, or the scale undercambered ones.

So, now you've got the info to someday, if you'd like (and as I'd do from the start), to build the scale airfoil wings, should you ever choose to. Also, as you stated the Sterling plans don't give you the top view of the fuselage structure, I've included the Charles Cash scale D.VII fuse structure drawing with THIS reply, if it's of any help for that sort of situation.

Thanks for the reply, and Yours Sincerely,

The PIPE....!!
Last edited by The PIPE; Jan 11, 2017 at 02:19 PM.
Jan 12, 2017, 07:46 AM
Brighto?
Mike Denest's Avatar
I think a better scale D-VII would be Proctor's (1/4 scale) or if you can find them, Bob Holman's design based on the drawings included on the plans.

jj, I will look at mine tonight and report back on the hatch.
Jan 15, 2017, 02:21 PM
Registered User
I puzzled for about half a day about what to do about the engine and radio installation. Reading through the old posts on the Sterling kit and the Balsa USA 1/4 scale DVII disclosed that downthrust, positive stab incidence and a really light tail were necessary.

I redrew the fuselage formers to get 2 degrees of down and 2 degrees of right. The hardwood mounts were spaced out for the Enya 90 and the tank installation was incorporated. I needed to draw a fuse top view to get the layout.

To lighten the tail I discarded the die cut outlines and laminated 5 layers of 1/16 balsa. The stab mount was shaved in the back a bit to give some positive incidence.

The rudder and elevator servos will fit between the front and rear gear legs, keeping them forward of the c.g. I'll need a bottom hatch for access and will use pull-pull.

Sounds good on paper. We'll see. Jim
Jan 15, 2017, 04:03 PM
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The PIPE's Avatar

Actually, the FULL SCALE D.VII had both of "those" in there from the start...


Dear jjscott:

The PIPE Here...just read your most recent post, and some things you noted...

Quote:
Originally Posted by jjscott
...Reading through the old posts on the Sterling kit and the Balsa USA 1/4 scale DVII disclosed that downthrust, positive stab incidence and a really light tail were necessary.

I redrew the fuselage formers to get 2 degrees of down and 2 degrees of right (thrust). The hardwood mounts were spaced out for the Enya 90 and the tank installation was incorporated. I needed to draw a fuse top view to get the layout.

To lighten the tail I discarded the die cut outlines and laminated 5 layers of 1/16 balsa (also doable, solely with aluminum tubing for the "outline"...no kidding!). The stab mount was shaved in the back a bit to give some positive incidence...Sounds good on paper. We'll see. Jim
The Karstens drawings actually SHOW an offset-mounted vertical fin on the plans in a 2 angle to port at its forward corner...



...and in checking the Charles Cash drawings of the "bare fuselage members", the stabilizer mount member along the upper rear surface of the fuselage has a 3.25 positive incidence angle in reference to the full scale thrustline of the Mercedes D.IIIa or BMW IIIa straight-six mill of the original D.VII.

I just thought I'd let you know about the already-existing, historic "allowances" that Herr Platz at Fokker Flugzeugbau had already done on the D.VII airframes, that resulted in the offset left fin front corner placement to "build-in right thrust", and the 3-1/4 degree positive incidence on the stabilizer mount to help provide some down thrust...all without doing anything to the full-scale engine's mounting angles in respect to the fuselage structure.

As to using ALUMINUM tubing in place of "laminated wood strips" for tail surface and wingtip outlines (specifically, the aileron tip "elephant-eared balance area") on a D.VII, be advised that an old buddy of mine, the late Hank Iltzsch, used aluminum tubing on more than one example of his RC Giant Scale Bristol Scout D model construction article that appeared over a generation ago in the pages of the AMA magazine...Hank's Bristol Scout D two-part article is in the March & April 1981 dated issues of the AMA magazine, to be precise - it's plan no.328, still available from the AMA for $24.00. The beautiful Hank Clark-drawn "isometric bare-bones" drawing of the Scout D's framework from that article actually calls out for 1/8" inch OD aluminum tubing as Hank used it for its tail surface outlines, and a scan of it is attached at the "footer" of this reply.

Hope this helped, even a small bit...

Yours Sincerely,

The PIPE....!!
Last edited by The PIPE; Jan 15, 2017 at 04:13 PM.
Jan 15, 2017, 05:55 PM
Registered User
Thanks again Pipe for the good information. I am only guessing about the changes to thrust and incidence angles. Remember the Sterling DVII has a symmetrical rib which shouldn't cause the exact problems encountered by 1/4 or full scale versions. It's also possible I should have left everything as designed. Only flying will tell.

Aluminum tube outlines are a good idea - maybe for the next one.

I have now glued the front formers to to the fuselage sides. The engine mounts were then slid in and glued. That front former had to be opened up on top for the engine to fit. I thought the engine should be in place while the glue set up.

Jim
Jan 17, 2017, 05:56 PM
Registered User
I've pulled the tail together, will let it set up a bit before installing the rest of the cross braces. Bellcranks for the rudder and elevator pull-pull cables end up just forward of the cockpit and above the lower wing center section. They will be easy to get to for installation of the cables and adjustment.

Jim


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