View Full Version : Fokker DR1 quarter scale scratch

12-07-2009, 09:26 PM

Started a quarter scale DR1 to try out some techniques. The Rudderpost will feature scale hinges like you see on the pics and will probably be made with a foam skin over a brass structure.

Plans are made in 3D Cad based on the full scale drawings of Ron Sands and corrected to metric measuring up a German museum Bird.


12-08-2009, 03:18 AM
looking forward to seeing it as you progress...I still build with balsa, so watching how you do it with foam will be interesting

12-08-2009, 08:21 PM
not too much change but still... one step further!

12-08-2009, 10:58 PM
Subscribed! Pm DCFlyer if you need any tips, he made a great DH-1 and even though you are making a different plane he maybe able to help you.

Looking forward to this!


12-11-2009, 09:23 PM
First parts for tailskid are "basically" finished


Not moving fast but I simultaniously alter the Cad plans to get an as-build plan.

12-11-2009, 10:15 PM
Kool, very nice.

12-12-2009, 10:14 PM


brass structure is ready to be glued in between two Depron sheets.

started on the seat too


12-14-2009, 08:27 PM
Fixing the frame with one side panel

The next panel too:

Close the seam with CA glue

And that's it for today... not much again but still happy with the progress!

12-14-2009, 08:48 PM
Not being picky here, but I have a question ....when you install the elevators and the horizontal stab, and the rudder.....I didn't notice a provision for elevator movement, or space above the top hinge for the elevators...you are going to need approximately one inch.....only reason I noticed this is i am just getting ready to start covering a 1/3 scale scratch build, and almost forgot the space myself...luckily it was the third model off these plans, and I noted the omission when I built the first model and changed the plans. :o

12-14-2009, 09:14 PM

this shows a close-to-the-real-one replica. Does this answer your question Ron?

Are you building a DR-I too? is there a thread here on the forum please?


12-14-2009, 09:32 PM
Not questioning your ability...just wanted to make sure that you knew about the required clearance..I want this to be successful as much as you do.....the DR1 makes a wonderful flying model, and if you build the tail light, requires almost no ballast to balance it...my last one had the batteries directly on the C of G...I did need to add lead to make it balance, but it was 1/4 ounce on the tail...
This is the third 1/3 scale DR 1 off these plans which I drew up in 2008....the other two models are still flying, I sold the original a few years back, and decided that I need another, so I am in the process of building it now. I didn't start a thread on the build, no one's really too interested in a basic balsa/basswood/solartex build.... but once a week or so I post in the WW1 planes forum with progress...if you have the time or inclination to look back, there are several posts there from me including a kinda tutorial on hand painting lozenge camo....I am watching this with interest because it is a totally different type/method of build, and I think, will work just fine..we have lots of ways to save weight, and reading other people's build threads are a good way of learning...like how to build wheels that are 1/3 the weight of commercially available wheels, how to build decent looking motors,/ engines/ how to build guns/carve pilots etc... if you read these threads long enough, you will find good information, no matter if you been building for a hundred years...there's always someone with a newer/better idea out there..........that's one of the things that draws me to this hobby. OH another question...have you picked a colour scheme yet?

12-15-2009, 09:48 PM
Made some kind of jig to make rib stitching patterns.


Gave the seat cushon a leather look coat too


and started a 3D model assembly to start checking weight distributions...


and that's it for today ;)

12-16-2009, 03:32 AM
lookin pretty sophisticated there Dirky.........are you going to make all three wings independant of each other ? or make the top two stay together?

12-16-2009, 07:23 AM
Thanks for the interest Ron…
Not sophisticated at all. It’s part of my daily job to search for alternatives on how to build systems. Making them better, cheaper, smaller, quicker… Value engineering they call it!
And that is what I’m trying to do with this DR-I.
- Although I love the Balsa/wood structures that still look a lot like the ones I was building 40 years ago, I want to experiment with this “all different materials technique” to see where I will end up! Main goal is saving construction time. Compared to the wood method I hope to reduce building time to 50%.
- Reason number 2 on my list is cost. This bird will be build using almost nothing else than leftovers. Stopped at a building site about a year ago and asked the contractor if I could have the insulation foam leftovers. Ever since he keeps the bigger parts aside for me. A beer once in a while is the price I pay. The hinges on the pictures are made out of old brass PCB spacers… and there is so much out there that one can give a second life to… J
- Number 3 is not clear yet but is weight saving. Whatever we do, it is hard to beat the all balsa constructions. But I will do my utmost best to build as light as possible! Getting the weight down means a smaller motor, smaller batteries…
- Number 4 is for me personally the most important one. Experience! Next projects on my list are a scale Fieseler Storch and a scale Bf109, designed/build on original blueprints.

Let’s talk disadvantages too:
- fragile: E.g. When my Fokker will flip over during landing the rudder will be damaged much more than the balsa rudder. In general, foam breaks easily so damage is more likely to occur when doing stupid things… (Please do not compare this with the classic foamies that mostly use thick blocks to shape parts.)
- … and more? We’ll see!

colour scheme:
- not decided yet. Want something moderate, not too flashy!

And regarding the wings, I’m still thinking about how to separate parts for transportation. I really want to stick close to scale so the (maybe fake) aileron command cables will somehow make it more difficult to separate the upper wing. On the other hand, at scale, this 1.8m span aircraft can still be transported one piece if needed…


12-16-2009, 06:01 PM
sounds like you have a very interesting job...
Making the model lighter not only will mean less power, it will mean it flies closer to scale speed..your model needs to fly at approximately 26 miles per hour( 40 km/h) and take off at roughly 12Km/h looks aside, this is one of the things I look for at a scale meet..I don't pay so much attention to all the details on the model, as the flying characteristics.
( I have judged at scale events)
A 1/4 scale WW1 model that flies at 40 or 50 mph in real time is NOT scale....also lighter means less damage in the event of an "event" :rolleyes:
AND you will find that if you build this particular model very light, there's almost no chance of it going on it's back.....in 6 or 7 years I flew my original, it was I don't think ever over upside down. ( on the runway)
mine comes apart all three wings independant of each other, so it's not perfectly scale where the rear cabane struts are, but in the 10 or so years this model has been going to scale meets not one person has noticed it ( oops my secret's out) ::o I moved the rear cabane struts about 1.5cm rearward...and lengthened the distance between wings by 1cm this allows room for the aileron cables to be place in a very near to scale position, and also allows you to tip the center wing on edge to feed it through the cabane struts in order to assemble the model...
I will always make deviations from "scale" in order to make the model perform better, and here we are allowed to deviate from "exact" scale by a certain percentage..so i have learned that if you modify the rudder to make it larger, and you don't want it to look larger, then you modify the rear of the fuselage to suit..ie: either lengthen, or make a little deeper, or whatever you need to do to make it "look" right..and the bonus part of this is it allows you to modify more than the rules allow,and since the judges cannot touch your model, get closer than 9 feet, or actually use a tape measure on anything, it works because because it "looks" right. Possibly my approach to scale is a little wierd, but it's fun, and that's why I'm so interested in your thread here...it's different, and i am going to learn something from it...and as an added bonus, I am convinced it will work. looking forward to more progress.

12-16-2009, 07:24 PM
Thanks for the comments!
I have no problem with deviations from real scale. Like you state, if it looks like the real thing, it's OK!
This DR-I was originally drawn in AutoCad with the intention to build it full size using the techniques of the (by the way based in Chiliwack) Murphy Aircraft Renegades I build before. Medical problems made me loose my pilot's lisense so RC is the only thing I will be able to fly for now. The plans were based on the Ron Sands replica plans.
I simply scaled those plans to get the 1/4 size and started improvising the different techniques on that drawing.

I really hope this works out well and hope that this thread will end with pictures of a flying DR-I...


12-17-2009, 06:29 PM
I'm sure it will work..it's a very interesting project, and i'm interested in how you approach the different little problems that come up during the build i have my own ways, and often there are better solutions which we learn by watching others.
BTW...Murphy is just down the way a bit from my place...good place to pick up aluminum scraps :-) Keep us updated on the build.

12-18-2009, 09:07 AM
Got a question... Hope the more experienced flyers can get me the right answer :-)

The original DR1 was heavy on the tail. This is clear when you see the tailplane's angle of incidence (4 deg). Many models are modified and have less angle for the tailplane or more for the wings...
Is it wise to fly a tail heavy RC aircraft or should I also modify it? Or simply use the trim to correct in flight and balance the weight correct around the CG?


12-18-2009, 01:34 PM
In general, tail-heavy airplanes are treacherous to fly. They usually have poor to no pitch stability. I'd be very concerned.

You might want to take your question to the guys at www.rcscalebuilder.com (http://www.rcscalebuilder.com). Those folks are SERIOUS about scale and many are involved in WWI era projects. I wouldn't be at all surprised if this question has been discussed there.

12-18-2009, 06:06 PM
Dirky...just use the positive incidence of the horizontal stab ( I used 5 degrees) ...I think you will find that the model even when properly balanced flies with the tail up..my last one did, and both the others off my plan do..they are not difficult to fly...likely one of the easiest ..similar to a PUP..but more aerobatic....one of the other points i forgot to mention, is that all three wings are set at 0 degrees to the datum line..don't fall into this make the top wing more to stall quicker trap...with this model it doesn't work...if you are concerned about tail heavy, you can "cheat" on the nose between the after cabane strut and the cowl, and no one will be able to see it....but it shouldn't be necessary....

12-18-2009, 09:43 PM
Do you also use the original Goettingen airfoil Ron?


12-18-2009, 11:33 PM
Actually used a slightly modified Eppler 195..I have found that for especially electric models, it seems to work well...and to make it "look" under cambered, the wing tips are curved...from a couple feet away, you would never know the airfoil is not original...this is one of the mods I made in the interest of making the model fly pleasantly..it has absolutely no bad habits with this airfoil...be sure to build in a little washout at the tips too..I used about 1/4 inch

12-20-2009, 08:49 PM
Rudder starts looking good:

Fuselage assembly test1:

Had to make a special tool to make thinner fus-sides:

Started the stabiliser too but no pics yet.


12-20-2009, 09:04 PM
nother, so I am in the process of building it now. I didn't start a thread on the build, no one's really too interested in a basic balsa/basswood/solartex build.... but on

I have to disagree... the balsa builds are the most interesting in my book :D

not that big on foam, as you might could tell...


12-20-2009, 09:22 PM
By the way, the 3D model has the counter on 1.2kg but still many parts are missing:


12-20-2009, 10:49 PM
Very unusual and interesting build method.. I've got to say i's have never considered brass as a main structural materail as it's rather heavy and not very strong, compared to say, aircraft grade aluminium alloy (duralumin) but it does have the advantage of being easy top work and solder, and I guess if used sparingly weight will be ok... The finished result certainly looks nice anyway.

I'm curious about your wing main spar design.. It looks like you have put lots of holes in the top and bottom flanges. The flanges are the elements that carry most of the tensile and compressive stresses putting holes in them will drastically weaken the spars in bending...
The more common practice would be to put the holes in the webs (the vertical elements), like a castallated beam (http://www.archpaper.com/uploads/IMG_0376.jpg). Possibly worth thinking about changing the design?


12-21-2009, 08:33 AM
Thanks for the input Steve,

my intention is to make the upper and the lower flanges with 6061T6 aircraft grade aluminum. The webs are intented to be hard balsa.
The plan is to finish the fuselage more or less before making the spars. So I can calculate perfectly, using the correct weight, how strong the flanges need to be.
Main goal is really to make a very light aircraft!

Regarding the brass, it is indeed correct that brass is too heavy. For the stabilizer and the elevator I will change tecnique a little and replace some of the brass tubes by probably carbon tubes. If that works out well, I might even consider rebuilding part of the rudder later on.

I consider this built as a test, so some rework will probably be necessary...

12-21-2009, 02:24 PM
Watching this build with interest.
To be correct the "flanges" to which you refer were on the full size just sheets of ply joining together the top and bottom of the two closely spaced box spars to provide drag resistance and additional torsional stiffness.
This contemporary sketch shows the construction.

As the properties of aluminium and even the hardest balsa are so different you might find it difficult to achieve a spar with an efficient strength to weight ratio.

12-21-2009, 09:04 PM
thanks for the sketch!

The model is based on Ron Sands plans which come very close to the real DR-I. The box spar I will use is exactly 1/4 scale of the real thing outside dims. Where the top and bottom sheets are meant to take + and - loads, the webs are mainly there to keep top and bottom connected and the box itself adds strenght regarding torsion. Now that torsion thing is very interesting when 3 wing spars are connected by struts. That really adds anti-torsion-strenght. Therefor my guess is that using balsa for the webs will be strong enough.

Any hints on lighter but stronger spars is welcome!


12-21-2009, 09:15 PM
Any hints on lighter but stronger spars is welcome!

Spruce top and bottom flange caps (I’m guessing about 1/8" thick) with 1/32" or 1/16" ply vertical webs... This is how it's generally done on full size planes.

You could substitute carbon for the top and bottom flange caps and use solid balsa, grain vertical for the fill then bind the assembly with Kevlar thread.. This is ultimately about as strong as you can get but probably excessive for a short winged triplane.. the spruce and ply option is what I'd go for.

PS.. and don’t make any lightening holes on the spruce, that would be very bad...


12-21-2009, 09:22 PM
Attached is a calculator for working out spar strength.. for an unbraced triplane i'd guess you should allow about 50% of the plane weight when calculating the spar size for one wing..


12-22-2009, 03:55 AM
My spar on the top wing is a 3/32 one piece on edge from top to bottom...think like a 2X6 board on edge the ribs are all cut so that a 4" piece of 1/16 balsa will cover the portion from the leading edge to the spar...so the wing is sheeted from the leading edge to the spar top and bottom...this makes a D tube......more than adequate for a 1/3 sized model of this type.... I know it isn't exactly scale, but firstly no one will know because it can't be seen once the model is covered.....secondly I know this is more than adequate for strength through experience..I have several models between 1/4 and 1/3 scale that are getting pretty old now, and I have never had a wing failure. and thirdly it is about the lightest way I have found to make a very strong wing.

12-22-2009, 08:31 PM
The next pictures show the progress on the fuselage. Not really spectacular but it shows how I will build up the fus, especially the zones that will carry the loads. Up front 4 alu corners will be glued on the top and bottom panels. Those on top will hold the spar of the middle wing and the struts for the top wing… and the lower will carry the lower wing spar and the landing gear. A round bulkhead will hold the 4 corners together and carry the motor…

Made some tools to easily cut out corners in the foam board. The tighter the parts fit, the lesser glue I’ll need.


Still satisfied about the light weight!

12-23-2009, 10:21 AM
Thanks for the calculator Steve!

I asked one of the nerds here at work to calculate something and faster than his shadow the MatLab logo appeared on his screen J

The idea I had about a box with upper and lower 50x0.4mm 6061T6 sheet connected with two 25x6mm hard balsa webs should do the job up to 6kg @ +6G. However, Lightening holes in the alu sheet should get smaller towards the fus. Anyway, it beats the weight (not the strength) of any spruce/ply combination so it seams. At least for what I will need because I’m pretty sure I’ll never reach 6kg.

Thanks for helping me think!

12-23-2009, 02:49 PM
The idea I had about a box with upper and lower 50x0.4mm 6061T6 sheet connected with two 25x6mm hard balsa webs should do the job up to 6kg @ +6G. However, Lightening holes in the alu sheet should get smaller towards the fus. Anyway, it beats the weight (not the strength) of any spruce/ply

Sounds like you have thought it through, but I'd still callenge the idea of lightenning holes, It's much more effective to simply taper the spar. The spar is only as strong as it's weakest part and if it's got holes then the weakest part is where the hole is.. The 'solid bits' between the holes are just a waste of material, they add only weight.

I also think you will find a well designed spruce spar is just as strong. T6 aluminium is at least 3.5 x stronger than spruce granted, but it's also 6 x heavier. Probably the biggest issue if using metal/wood composite spars is making a good enough joint between wood and metal to transfer the load.. If the glue joint is the weakest point then that's where any failure will occur.

Having said all of this i'm sure your design will work okand it will be a bit different to the norm...


12-23-2009, 04:02 PM
I really appreciate your input Steve (and others) and I do not want to say it's not right what you state. There are so many different factors that are influencing my silly brain that points me to the alu/balsa try-out first. One of them being the immense pile of leftovers of 6061-T6 sheet I have from the time I was building 2-seater experimental aircraft.
Another very important factor is that I want to try different methods that (could) allow faster building.

Anyway, please keep on adding any remarks. It sure helps me and I'm grateful for that!

12-23-2009, 05:52 PM
dirky.building is a personal thing...we all build in a particular fashion for a particular reason..either it works, or it's something new we heard about that we wish to try.., or we're trying to make use of someone else's castoffs, or use a new material...or we're trying an experiment...and we all learn from following threads like yours...

12-23-2009, 06:07 PM
On the Dr1 the inter plane struts were only there for torsional rigidity. As the sketch shows they were pin jointed at the spar and as there was no rigging all the bending loads were carried by the spars.
How are you planning to glue the ally to the balsa?
In view of the rather novel construction I suggest you make a test a spar to find out how and at what load it fails. Fokker did this with sand bags on the full size although for a publicity photo he got about 20 people to stand on one.

12-24-2009, 10:45 AM
Sure I will make a test spar first, no doubt about that.

The struts will be like the originals and also attached with scaled pins. Their function will also be “torsion” rigidity!

As for the glue, I will also test something different:
- the balsa will be varnished with PU and the contact surfaces sanded with grain 800 to get a smooth edge. Next I will use acrylic double sided tape to get the parts together. I want to trust this because I hung a water bin in my dog’s house with this tape two years ago and it still holds up to 3 liter every day… J
- If this would not work, I’ll try with acrylic 2K glue but spray the aluminum with etching primer first
- Last but not least I can use Pro-seal 2K glue, and that will do the job 100% sure (it’s used to glue BD-5 and BD-10 kits and Murphy aircraft uses it to glue – and seal – Aluminum fuel tanks… but that would be too expensive because I would need to buy a quart and once opened the shelf life would be something like 3 months…

And a Merry Xmas to all of you too!

Edit: PS, must say this is the only forum where people are giving hints and/or asking questions! So I'm really glad to be here!!!

12-24-2009, 11:04 PM
I'm really curious to see this plane finished. It is very interesting!!! I have 4 RC Fokker DR1s and they are very tricky on the ground but great in the air!!!! Steve

12-26-2009, 08:12 PM
Steve (and others of course),

I would appreciate some kind of overview regarding scale and weight of some flying DR-I's. That will give me a better idea what weights to be satisfied with during construction...


12-26-2009, 09:25 PM
I've got nothing of similar size to compare it with but I'd expect a 25% scale DR1 to come out around 7-8kg..... lighter is better of course!

12-26-2009, 09:33 PM
Well, I have a 40"ws one that has a wing area of 495 sq.inches, has a wing loading of 7.9 oz. an inch, and weighs about 30 ounces ready to fly. You can see that the wing area is huge so they fly rather "light". You really shouldn't have a wing loading problem. Depending on how scale you want it you can move the wheels forward a little and help with nose overs on landings. Steve

12-27-2009, 06:04 PM
Mine is 1/3 scale ready to cover with no motor or batteries, it weighs 8 lbs.

12-29-2009, 08:31 PM
1 lbs so far:


12-29-2009, 11:37 PM
Thats cool Dirky!!!! Let us see more of this build!!! Steve

01-01-2010, 08:14 PM

Made a cowling mold on January 1st :-)

Happy New Year to you all...

01-02-2010, 02:34 PM
That cowl looks really good!!! A true artist at work!!! Steve

01-02-2010, 08:05 PM
are you going to use fibreglass for the cowl? or some other method? .I used fibreglass over a male mold like you have there.

01-10-2010, 06:56 PM
sorry for the delay. Temperatures are too low to warm up the workshop in the evening... Need to put some insulation panels first.
Regarding the cowling I want to try epoxy coat over a nylon hose first.

(In the meantime I'm designing (in 3D) the Messerschmitt 109 at the same scale using similar weird building methods... )

01-11-2010, 11:49 PM
Post pics of your process please! Steve

01-12-2010, 08:32 PM
Ruined my cowling mold a few minutes ago! Going to make a new one using MDF (Medium density fibreboard)... Unless another idea pops up!

01-12-2010, 08:53 PM
Ruined my cowling mold a few minutes ago! Going to make a new one using MDF (Medium density fibreboard)... Unless another idea pops up!

What is the dia of a 1/4 scale cowl? Look for an alum pot that size.

01-12-2010, 09:14 PM
265mm... little less than 10 1/2"!

01-13-2010, 05:35 PM
Actually a foam mold works well for fibreglassing over..but you need to cover it with monokote first..... then wax it....I did that with mine, and made 2 cowls from it...one for the model, and a "spare" for just in case..and it's still useable....

02-03-2010, 06:30 PM
Been close to a month now and no progress report?? we're all dying of curiosity here,
What's happening with your DR1? Any progress lately?

02-03-2010, 06:39 PM
sorry for the "no news" but the weather here is too bad to warm up the workshop for short periods... But no panic, it will continue!
thanks for asking!

Ryan Flyer
02-03-2010, 07:24 PM
Nice Build!

03-11-2010, 09:34 PM
my apologies to those interested but I had a visitor the other day and the project was immediately sold... perhaps up to a next one!

03-11-2010, 11:22 PM
Noooooooooooooo!!!!!!!!!!!! You can't be serious!!!! Steve

03-12-2010, 03:38 AM
RATZ ! ! !

Ryan Flyer
03-12-2010, 03:57 AM
What????!!! :eek::mad::(

03-12-2010, 08:16 AM
thanks for the + reactions:
I can hardly say no to a little money if I can spend it on tooling in the workshop.

There will be another DR-I (or something else) soon after the CNC mill is functional.

thx again....

Ryan Flyer
03-12-2010, 07:30 PM
Cant wait for updates on the new plane!

05-17-2011, 01:19 AM