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Oct 08, 2005, 05:31 PM
Park Jet Guru
jetset44's Avatar
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Fokker DR1 Parkflyer

Here’s my latest project to share with the forum, an all-foam Fokker DR1. The design goal of this model was to be a nearly scale parkflyer that also had good 3D aerobatics capability. This was a challenging goal and a few design compromises had to be made to achieve a model that could do both things well, but the end result met all my expectations. When throttled back and flown slowly, this model looks remarkably scale in the air and is a nice-flying parkflyer. But when you throttle up and put the sticks in the corners, in can also do some wild gyrations and great aerobatics. When I fly this bird at my local park, I like to surprise onlookers by flying really slow and scale-like for the first minute or two, and then let loose all of a sudden with wild aerobatics. That gets a funny reaction!

Here are the specs:

Wing area: 575 sq in
Span: 36.5 in (upper wing, not including aileron horns)
Length: 30.1 in
Weight RTF: 21.0 oz
Wing loading: 5 oz/ft2
Motor: Himax 2015-4100 with 6.6 gearing
Battery: Thunder Power 11.1V 1320 mAh Lipo
Prop: APC 12x6 SF
Current draw: 12.0 amps static
Power input: 110 watts
Power loading: 84 watts/lb
Radio equipment: GWS R6 receiver, GWS Pico servos, Phoenix 25 speed control

This design started with a true scale outline, traced from an accurate three-view. But I made several deviations from scale to improve flying qualities, including:

* Flat foam airfoil – This makes construction MUCH easier and provides great aerobatic capabilities.

* Ailerons on all 3 wings – The original Triplane had ailerons only on the upper wing, but I installed full-span ailerons on all 3 wings. This was done for three reasons: 1) It provides an insane roll rate, 2) It puts ailerons in the prop blast, which allows roll control while hovering, and 3) When set up as flaperons, this allows adding camber to all 3 wings for much improved slow flight capability. The flaperons can also be used for landing flaps and for elevator-to-flap mixing, but I’ve found both of those to be of limited use with this model.

* Enlarged vertical tail about 20% - This was done to improve flying qualities, since the original Triplane had a very small tail and very low directional stability. The larger tail also allows better snap rolls and spins.

* Increased elevator chord – The horizontal tail planform is still scale, but I increased the percentage chord of the elevator to provide more control power for better aerobatics, especially for hovering, snaps, and waterfalls.

* Lengthened nose – The original Triplane was a lightweight airplane with a very heavy rotary engine, hence it had a very short nose. This has always made flying models of the Triplane notoriously hard to balance. To counter this, I sacrificed the scale lines a little and added 1” to the length of the nose. I also designed a battery compartment that allows placing the battery right up next to the firewall. But even with this, I STILL had to add 1.0 oz of lead to the nose to balance this bird! I would hesitate to lengthen the nose any further, though, since it would lose that famous Triplane snub-nosed look.

* Sized for high-power motor setup – The recommend Himax geared motor provides 26 oz static thrust, which provides a better than 1:1 thrust-to-weight ratio and easily allows hovering.

Here are some pics of the model, which I painted to match Ltn August Raben’s DRI from Jasta 18 (I’ve included a picture of the full-scale replica below). The reason I chose this paint scheme was balance, since the white tail doesn’t require painting. Note that because the moment arm from the CG to the tail is 4 times greater than the moment arm to the nose, if I added 1/4 oz of paint to the tail it would require an additional 1.0 oz of lead in the nose to maintain balance. Thus, there was a strong incentive to not paint the tail! The Jasta 18 white-tailed scheme works perfect for this.

Here's a flight video:

(3 min 2 sec)
Last edited by jetset44; Jun 25, 2009 at 01:24 AM. Reason: Added flight video
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Oct 08, 2005, 05:38 PM
Park Jet Guru
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Flight Characteristics

How does it fly? Well, keeping in mind that the original Fokker Triplane was never considered a great-flying airplane, I’d say this model handles really well—but it's not perfect. Like the original Triplane, it's very maneuverable but has low stability in pitch and yaw and can be challenging to fly at times. Even with the enlarged vertical tail, the model has low directional stability and requires constant attention to the rudder. In fact, the smoothest turns use mostly rudder and just a slight bit of aileron. There is LOTS of roll and pitch coupling with yaw, which makes knife-edge flight very challenging. Pitch stability is also low, even though I moved the CG well forward of where I originally thought it should be. The location shown on the plans will provide slightly positive pitch stability, but it took a lot of lead in the nose to get the CG that far forward and even still this model might feel “pitchy” to some.

But on the good side, this model is extremely responsive and if you stay ahead of it it’s quite fun to fly. It can turn on a dime and roll in the blink of an eye. Loops, aileron rolls, point rolls, spins, snaps, and hammerheads are all easy to do, and inverted flight requires almost no forward stick. While I wouldn’t call this a true 3D airplane, it can do several 3D maneuvers fairly well including hovers, harriers, walls, and waterfalls. Nothing gets a reaction from onlookers more than watching a scale Fokker Triplane harrier right up to where I’m standing and then begin hovering a few feet away!

I’ve had a blast flying this model, but I would not recommend it for low-time pilots. It is a challenging airplane to fly that requires especially good rudder coordination, but for more advanced pilots it really is rewarding to fly.

The flaperons add a new dimension to this model. Because they run full-span on all three wings, they can be used to effectively change the camber of the whole wing—which provides a very nice effect. Adding 5 to 10 degrees of flaps provides about the same amount of camber as typical slow parkflyers (and roughly similar to the real DR1), and makes a significant difference in how the model flies--it floats much better and slow-speed handling is much improved, plus the model becomes more stable in pitch. Thus, this setup really lets you have your cake and eat it, too. You can drop the flaps and switch to low dual rates to enjoy a gentle slow-flying (and very scale-looking) parkflyer, or raise the flaps and kick up the dual rates for some wild 3D aerobatics. I’m very happy with this setup.

Here are a few more pictures of the finished model.
Last edited by jetset44; Oct 09, 2005 at 04:14 PM.
Oct 08, 2005, 05:49 PM
Park Jet Guru
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Here are some photos showing the construction details of this model.
Last edited by jetset44; Oct 09, 2005 at 04:04 PM.
Oct 08, 2005, 05:52 PM
Park Jet Guru
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Here are the plans for the Fokker DR1 parkflyer. These plans consist of two files—a scaled assembly drawing that shows how everything fits together and a drawing with full-scale parts templates. The parts template is posted in both tiled and non-tiled formats. Previews are posted below to show how the plans should look when assembled.

Enjoy, and post pictures if you build one!


EDIT (4-18-11): For those that wish to send me a contribution for this model, please note my PayPal address has changed from what I originally put on these plans. My new PayPal address is [email protected]. Thanks!
Last edited by jetset44; Apr 18, 2011 at 10:22 PM. Reason: Changed PayPal address
Oct 08, 2005, 06:20 PM
JohnVH's Avatar
Looks cool Steve!! Nice job.
Latest blog entry: Will DRACO hover nose down?
Oct 08, 2005, 08:01 PM
Registered User
ExtremeSkyes's Avatar
Tks for posting Steve...Looking good. Can you give estimates for depron required?? Similar quantities to other park jets?

Oct 08, 2005, 08:40 PM
Park Jet Guru
jetset44's Avatar
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You're welcome, Ex. I'm not sure how much Depron it requires since I always end up using lots of scraps and spare pieces. But I'd guess it's similar to the park jets, which is almost 2 full sheets.
Oct 08, 2005, 09:31 PM
Design > Build > Fly
Qrome's Avatar
Steve, this is great! I have always wanted to do a Dr 1, but the smaller ones just don't seem to do it for me. This one looks just about right. I have bluecore, but I think I will need to try and get some depron for this project. Thanks.
Oct 08, 2005, 09:31 PM
Use the Force!
LBMiller5's Avatar

Quite the opposite end of the Flight Spectrum!

Hi Steve,

The plane looks great! Quite a departure from the Jets, but a welcome plane none-the-less.

What program do you use to create your plans? They always look so great!

Keep up the good work, and don't forget to spend time with the little one. She will be borrowing your car before you know it.

Oct 09, 2005, 12:24 AM
Vintauri's Avatar
Looks great Steve. I hope to work on this one soon but I'm getting too many ideas and projects going I really need to finish some of them.

Soon enough though.

Oct 09, 2005, 12:26 AM
Park Jet Guru
jetset44's Avatar
Thread OP
Howdy Lucien,
Yes, I needed to do something different after cranking out 5 jet fighter designs. The Triplane was just the ticket. I create all of my plans in TurboCAD, which I highly recommend. It's ideal for this kind of work.

Borrowing the car seems like it's an eon away--what I'm waiting (and hoping) to hear before too many years is "Dad, can I fly the Triplane now?"

Oct 09, 2005, 12:40 AM
sensitive artsy type
Treetop's Avatar
Superb! Excellent work.
Oct 09, 2005, 09:30 AM
Beautiful job !!! , absolutely unreal , would love to see it in the air , thats a lovely bird
Last edited by re3626; Nov 29, 2009 at 04:25 AM.
Oct 09, 2005, 03:09 PM
Registered User
Steve, Buddy! What an awesome Canadian Thanksgiving present. No turkey for me, I am cutting out depron! Cant wait to see the videos
From the Rock in the great white north
Oct 09, 2005, 03:53 PM
Park Jet Guru
jetset44's Avatar
Thread OP
Great! I can't wait to see how your Triplanes turn out if you build them. I hope you enjoy it as much as I like mine.

I'm hoping to get some flight video soon. That's difficult to do this time of year since it gets dark so early and I can only fly on weekends. Plus, my main video shooter (my wife) has to watch the baby now... I'll work on it.


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