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Aug 21, 2019, 07:09 PM
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Build Log

Foam board 1929 Dornier Do X

Hello all,

I am planning on building the 1929 Dornier Do X Sea plane. The plan is simple but I hope to add many scale details after the main build. I'm going to build it up the way the "Flight Test" foam board planes are built. In fact, I'm basing the design on one of FT Guinea Pig models. The idea is to download the plans and adapt them to the drawings of the Do X. Since foam board is inexpensive at Dollar Tree I can print and build a few until one glides nice.

This is where I need a little advice. I again find myself in competition with a good friend who is now going to build the Spruce Goose with the same methods above. ( I sent him a transmitter and some servos to get started.) The Do X has twelve engines above the wing, six facing forward and six facing rear. How can I accomplish all twelve motors?

The original plan was to have two motors like the Guinea Pig and the rest just free floating props. My friend is a big believer in "over kill is under rated" and I can see him having all the motors burning and turning on the Goose. We have no time limit really, other than bring it up with me next time I fly down. Were some what new to RC Flying but have been building/ making models of all sorts since collage.

I will be spending the next few months using Adobe Illustrator to come up with some plans and entertain all crazy ideas. There will be a prototype here and there. Photos for sure. So any help with the motors and props will be much appreciated.

I'm thinking 1/60-ish scale. Wing span: 796 mm Length: 667 mm Height: 170 mm ( similar to the Guinea Pig)

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Aug 21, 2019, 07:30 PM
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rajazo's Avatar
Ufff, difficult task!
The main problem I see is that the size you are planing to build implies a really smaller prop, and this could be an insurmountable problem!!
Reason the problem in reverse, what is the smaller motor propeller you can get and find how much thrust it produce, then scale the Do-X at that proportion.
Remember , you will need at least 50% of the AUW in static thrust to start flying.
Hi kv motors are necessary to work with smaller prop

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Aug 21, 2019, 07:53 PM
Foam is where the heart is
brett.c's Avatar
IMO, too small to carry all that extra weight.
I would go 1.2M or above.
To save weight and complexity consider brushed motors on a single ESC.

I built a Wal and it flew like an absolute dog.
I couldn't get the thrust lines right nor the counter/non counter rotating props. It would balloon or dive under power and had very poor directional stability, skidding and sliding all over the place. Cross winds were a nightmare. The DoX has a very small vertical stab area. IMO too small for a scale model.

But, there's nothing like a challenge, so good luck.
Aug 22, 2019, 01:16 AM
If it flies - I want one!
Petem's Avatar
Building on the replies so far, how about a herd of cheap brushed drone motors - perhaps the 8.5mm diameter ones driving 50mm or so drone props -
All driven by a single, say 30A brushed ESC?
Big advantage is that all the components are cheaply available, props in both directions - should result in a most impressive howl with them all going hard!
Have fun,
Aug 22, 2019, 11:10 AM
Registered User
I built an 8-motor with about 70 cm span using brushed 8mm motors connected as 4 series connected pairs in parallel on 2s. It worked quite well, but if (when) I do something similar again I'd scale it for 5 inch props and cheap brushless racing quad motors/escs.
Aug 22, 2019, 01:33 PM
An itch?. Scratch build.
eflightray's Avatar
From the 'Similar Threads' list below --

Maxford Dornier Do X

Aug 22, 2019, 01:39 PM
Retired CAD guy
birdofplay's Avatar
Simple would be two Good motors and 10 dummies free wheeling.
Aug 22, 2019, 07:03 PM
Registered User
Thread OP
Thank you to all who responded.

1. Need 50% of AUW in static thrust to start flying.
-I wanted a nice slow flight, should I aim for 60% or 75% of AUW in thrust ?
-What percentage do the slow flying B-17 models aim for?

2. Do X has small vertical Stab area.
-I'm willing to increase the Stab area to improve flight as long as it is not comically big.
-I don't think anyone would notice.

3. Cheap Drone motors with props in both directions.
-Love this idea, and plan on trying it.

4. Scale it for 5' props.
-I will look up some and play around with the dimensions in Illustrator.

5. Maxford Do X video.
-I saw the video and is the reason I posted for help to figure out if I could do it on smaller scale.

6. Simple two motor plane is the "sane choice".
-I'm in to deep, I said Howard Hughes mustache was stupid. My friend said Hughes mustache is an American Hero. I poked the beast and have to live with the consequences.

My brother hit on a good idea, order the Guinea Pig w/ motors and build it. Start building a
Do X model. Fly the Guinea Pig to make sure it can fly. Take the motors off and hot glue the twelve motor set up and see if it flys.

You all have given me a lot to think about. thank you again.
Aug 23, 2019, 02:15 AM
An itch?. Scratch build.
eflightray's Avatar
1. Slow flight has little to do with the amount of thrust. It's down to light weight and very low wing loading.
Big models will always look slower, small models will often appear faster.

Down at the 1M or less span, keeping the weight down will be a major problem.

Personally I think you have picked on a project that has a very low chance of success, even for an experienced modeler, unless you increase the size considerably.

I build using foam, Depron, and build multi-motor models, the Do-X is not a model I would want to take on.

Aug 23, 2019, 04:11 AM
Registered User
Yes, forget about 12 motors. Do 2 and have 10 dummies.
Scale to double the span you chose.
Use carbon fiber tube spar for wing and 2 mm carbon fiber rods for fuselage reinforcement (internal criss cross bracing). The wing and fuselage should be de-papered foam covered in very light packing tape
Increase vertical AND horizontal stab/elevator/rudder by 30% (only a very trained eye will notice the difference).

Now you'll have a very good chance of success.
Aug 23, 2019, 05:06 AM
Registered User
I would seriously recommend using small racing drone motors. For their weight they are currently the cheapest motors available. I would suggest using just 6 as tractors and skip free wheeling trailing props. You don't what any extra drag.
I do wonder if you will be able to make it light enough using 6mm foam board.
With 5 " props the span would be 1800 m and the chord 339 mm!
A racing drone motor with a 5" prop will give about 80 g of thrust so a target weight for a thrust to weight of 60% would be just 800 g (28 oz). Don'r worry, if you can achieve such a weight will fly slowly, very slowly!
It is a flying boat so no undercarriage (you can't afford the weight) and find a way to either hand launch or catapult and belly land (on grass).

A very ambitious project with many pitfalls to be overcome on the way, not least of which would be virtually no crash resistance or tolerance to wind, but it would look amazing flying at something like scale speed.
Aug 23, 2019, 11:09 AM
Registered User
Thread OP
Hello all,

The last three comments were like a kick in the balls.

Reality has come crashing down on me like a ton of bricks.
-Size, weight and strengths requirements
-Scale choice
- I may not be able to land and take off from water
-Those with way more experience see this project as overly difficult

I just started and I do believe I must already reconsider the constraints of the project. I most of all want a plane that looks good flying and can take off and land in water. I find it funny that many of the problems that plagued the full size version are causing me so many problems at the start. I foolishly thought at this size many of those problems go away and different ones become simple to solve due to the large base of knowledge in RC planes available on the internet. So lets try this one more time.

1. I want a scale look. (over sized Stab is OK for better flight characteristics)
2. I want to take off and land in water.
3. I would like to keep it on the smaller side for transport reasons.
4. Have a better looking, better flying plane than Mike.

So the plan is use the Flight Test twin motor sea plane as the base the way they set it up and add scale details to look good.

Thanks all for the advice, I will update when I have some drawings and some parts. It seems like a good idea to buy some motors and props and base the scale of the plane on that and see what I come up with.

Aug 23, 2019, 01:12 PM
An itch?. Scratch build.
eflightray's Avatar
Sorry for the 'low kick', but better to feel the pain now than when you are half way through a project with major problems, or worse, you build something and it crashing first flight.

Start simple and gain knowledge, especially the flying bit, then consider scale projects.

You will get there eventually.

Let us know how your friend gets on with the Spruce Goose.

Aug 23, 2019, 03:06 PM
Registered User
rajazo's Avatar
It is not my intention add more point to the mix, but caution with seaduck from flite test because it have a totally different fuselage.. you need to look a more similar plane like sea blue baby , it is a excellent flyer and fuselage has tail and all working bottom of a flyingboat , like the Dornier.

About motor, I canít recommend you the tractor pusher configuration because the pushers propeller take accelerated air from the tractor and produce less thrust... go to 6 or 3 or 2 tractor or pusher and the other dummies .
Aug 25, 2019, 12:14 AM
Registered User
Thread OP
Hello again,

No worries guys. I'm stubborn and eccentric, it rarely works in my favor.

I started using Illustrator again after a few years and it is just like when I get back from a work trip - none of the tools are where I left them. So the plans I'm working on are going to take a bit longer than I was hoping. I couldn't wait so I blew up the three view of the Do X and started to cut foam. A few Pictures below of the steep learning curve for building with foam board. It was an incredibly valuable few hours!

1. Foam Board if an amazing material. I will definitely be building my plane with it.

2. Hot glue is fast and strong, but it is heavy as S**T. Also a little messy and was difficult at times. Will not be using it for the build. I got half of the fuselage done and its as heavy as I thought the whole model would be. (I might have been working fast and heavy handed)

3.Hand cutting the foam sucks! I went through three or four blades. 100% it will need to be laser cut. (Of course I can hand cut some stuff if it comes up)

The whole point of trying to make a quick model was to help wrap my mind around this project and finalize some decisions about what the goals are. I didn't even have to finish the model to see the pit falls everyone was describing with my own eyes. I made a single sheet wing real fast to see it and the thought of two motors worried me, let alone twelve. I plan on spending a lot of time in Illustrator working on the plans so I can build a 700 or 800 mm Do X glider. Try a different glue, maybe CA w/ activator. Luckily I had the foam board and started the model before ordering the motors because I now know for sure I should wait till I build the glider.

I text my friend and told him about RC Groups and he plans on starting a build log of his plane as well.

Keep the advice coming, we all know I need it to slow down my impulses.


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