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Design & Build Dornier Do 24

A bit of a challenge

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Robert Parker19/08/2018 18:34:28
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866 forum posts
1121 photos

Hi All,

The nacelles are now well underway and planking has begun

dsc04879.jpg

I had a light bulb moment this morning regarding the 2nd and 3rd formers to the nacelle. Instead of using different diameter discs I went for a single 3/8" piece and used a half round router bit in my dremel and formed the front radius took just a few minutes. I did not fancy using the router, too bit for such small pieces and fingers could get too close. The cutter worked very well in the dremel.

I also have glued in the wing mounting points

dsc04880.jpg

Planking started

dsc04881.jpg

A close up of the centre nacelle showing the hatch hopefully big enough to get at everything.

Next, to continue with the planking.

Regards

Robert

Robert Parker20/08/2018 22:02:30
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866 forum posts
1121 photos

Hi All,

I came across this earlier of a Dornier Do 24

dornier 24 crash.jpg

At first after watching a video I thought it was a crash but just before doing a 180 turn the pilot gave a boot full of rudder.

Both videos I have been unable to upload but they are worth seeing.

I also found another video on vimeo stating it was a stunt surprise I cannot believe the amount of stresses on both the crew and airframe, that one I'll give a miss.

Regards

Robert

 

Edited By Robert Parker on 20/08/2018 22:03:06

KiwiKid21/08/2018 06:41:49
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442 forum posts
444 photos

We did discuss this in another thread somewhere, but I can't remember where. What actually happened was that the Do was doing a touch and go and hit a submerged object at high speed on the starboard side which caused the a/c to momentarily swing to the right. The pilot instinctively feed in a heap of left rudder which, due to the twin rudders and the relatively high water speed, caused the violent swing to the left. Took on some water, but was able to limp in to shore.

do.jpg

do2.jpg

do3.jpg

do4.jpg

Robert Parker29/08/2018 20:51:21
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866 forum posts
1121 photos

Hi All,

The nacelles have proved a bit of a disappointment and I have decided to remove and remake the lower halve of the centre one as it just did not look right, although the other two undersides are passable at a push. The top sides are good. I'll post some photos when I'm happier with the out come.

However, the slow boat from China finally made it to the UK shores and my two packages have arrivedsmiley

dsc04988.jpg

My "3" way "Y" leads if you can call them that. I saw them on e-bay for a DJI Phamtom and I thought just what I need. Well that the ESC's power sorted.

That's all for now

Regards

Robert

Robert Parker06/09/2018 20:49:41
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866 forum posts
1121 photos

Hi All,

A little update on progress so far.

Centre nacelle has been re-made and I am a lot happier with the end result. I have placed the motors on the nacelles and fitted the wing to the fus. Sorry about the poor lighting, nights drawing in, winters coming along with another project looming.

dsc04990.jpg

Not a lot of clearance between the prop and the fus just 8mm, just a reminder the front underside of the hull is still un-sheeted just in case I need to gain access.

dsc04992.jpg

Actually I think the spot light gives a better look

dsc04996.jpg

Access hatches cut out, plenty of room for the ESC's

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Full flap.

I am now happy with the wing / fus connection and now ready to epoxy the rear fixing points.

The approximate weight is looking like 9lbs, a little more than I was hoping for, I have made an allowance of 1lb for paint and covering materials.

That's all for now.

Next apart from the fixing points being epoxied in position I'll solder all of the wiring connections

Regards

Robert

Robert Parker17/02/2019 15:19:44
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866 forum posts
1121 photos

Hi All,

It's been a while since I last worked on the Dornier having had a bit of a distraction and built myself a DB Bi Stormer.

I have spent some time today looking at the Dornier and trying to catch up on my train of thoughts back in September and having wired and installed the motors back then and am now a bit puzzled.

For some reason, which I cannot recall I have fitted 3530/14 motors with 30amp ESC's oops, these motors require a 50 Amp ESC.

I think I must have ordered the wrong size or had a senior moment again.

If I kept the motors and bought new ESC's they would be a tight fit in the outer nacelles and almost impossible in the centre one plus I am a little concerned about the heat / cooling

dsc05689.jpg

dsc05691.jpg

Central nacelle, a bit crowded without the ESC and the incoming power cables

Possibly a twin with freewheeling central prop?

That's all for now

Regards

Robert

Piers Bowlan17/02/2019 17:47:24
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1678 forum posts
41 photos

I am a little confused Robert. If these are the motors you have, they are rated at 22A max so a 30A ESCs should be fine. If you are planning to use a 4S lipo (nominal voltage 14.8v) and prop them to their max 22A (not advised generally) you will have 325W per motor or in the region of 975W for a 9lb model. Should be OK for a model of this type, I would have thought? Perhaps I am missing something?

McG 696917/02/2019 18:08:48
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2418 forum posts
976 photos

Hi Robert,

Apologies for not being able to give you any kind of advice here regarding your speed controllers, but at least I feel that you might have your mojo back for your Dornier. yes

Not that sure when following Piers's link that that particular J3 really needs an ESC... Never thought one would start a 3530 with an IC 'stick'... surprise

Well at least learning a bit every day, ain't it?

Cheers

Chris

Piers Bowlan17/02/2019 18:23:13
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1678 forum posts
41 photos

Ops, should have been this motor! Now everyone is confused!

Robert Parker17/02/2019 22:43:03
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866 forum posts
1121 photos

Hi Both,

As I said I'm trying to get back into this model and why I had got 30Amp ESC's, however, now this is possibly where I have confused myself, looking at the motor data sheet which is the same as Piers 2nd link and click on upload files then click on motor instructions it states 50Amp.

Though I must agree with a 30 Amp ESC should be OK with a max current draw of 22amp just puzzled why instructions call for a 50Amp.

Regards

Robert

Piers Bowlan18/02/2019 05:49:33
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1678 forum posts
41 photos

I think it is because you are dealing with Hobbyking instructions and something was 'lost in translation' on this occasion.

Robert, could you confirm that you are planning to use a 4s LiPo, as you are not going to get enough power on a 3s with this setup, I would have thought? Also, how did decide on the propellers you have fitted? The spec sheet for this motor suggests an 8 x 4in on 4s but that is for a two blade prop, so presumably you are using something like an 7 x 4in, three blade prop. ? Hopefully you have tested your setup with a watt meter in any event.

A great project Robert, thanks for sharing.

Robert Parker18/02/2019 06:30:35
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866 forum posts
1121 photos

Hi Piers,

I was hoping to use a 3s set up but I do have a 4s which I would need to make some slight adjustments to the battery box. As for prop sizes, I assumed i would be using a 3s setup and from the instructions prop size for 2s = 12 x 6 and 4s being 8 x 4, therefore, 3s would be 10 x 5 for a two blade and using a rule of thumb to down the diameter an inch for three blade, but a 9" prop would fowl the fuselage so by physical restraints I went for 8 x 4 x3.

Now that I have aired my thoughts I hopefully do some testing this week with different prop sizes.

Will keep all informed of the results.

Regards

Robert

Piers Bowlan18/02/2019 06:45:16
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1678 forum posts
41 photos

3s LiPo (nominally) 11.1v x 22A (max) = 244.2W per motor, x 3 = 732.6W total input. I thought that it could be a little marginal with a 9lb model but then again it has a good sized, highish aspect-ratio wing, so it could be fine. Might struggle a bit off water if that is your plan? With any luck the testing with different props will prove me wrong. Good luck.

Be interesting to hear what others think.

Edited By Piers Bowlan on 18/02/2019 06:47:20

Robert Parker18/02/2019 20:39:19
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866 forum posts
1121 photos

Hi All,

I have just carried out some prop tests this evening.

Here are the results,

Firstly, I just connected up a single motor. Not wanting a repeat of Saturday's disaster where after connecting a 4s battery to my TN Lancaster following some repairs and wanting to check out why she behaved so different from the previous flight to which I managed to burn out all 4 ESC's in a matter of seconds even though they were marked 2 - 4s, a smoking model in doors is not a good sight thank goodness the wife was out and the smell had gone by the time she returned. So new ESC's ordered along with new motors just in case.

So back to the Dornier, the props and batteries were what I had to available, the order of the test was 3 blades first as they were already fitted then the 7 x 5 and then the 8 x 5 props. The batteries were all freshly charged at the start of the testing period with each motor run lasting a few seconds.

single motor fitted with 8 x 4 x 3 blade

Battery 3s 4000 167Watts

3s 6000 172 Watts 13Amps

4s 5000 402 Watts

3 Motors running 7 x 5 2 blade APC props

Battery 3s 4000 333 Watts 29Amps

3s 6000 365 Watts 30Amps

4s 5000 723 Watts 46Amps

3 motors running 8 x 5 2 blade APC props

Battery 3s 4000 433 Watts 38Amps

3s 6000 472 Watts 40Amps

4s 5000 935 Watts 60Amps

3 Motors running 8 x 4 3 blade GWS props these do seem a little flimsy and may flex I think

Battery 3s 4000 434 Watts 38Amps

3s 6000 470 Watts 40Amps

4s 5000 950 Watts 62Amps

So it looks like I have to modify the fuselage to take the 4s, it is only just a bit too big to fit.

I have no intention flying off water with the exception when our field becomes water logged.

Any thoughts Piers or others on the above

Regards

Robert

Piers Bowlan19/02/2019 11:19:06
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1678 forum posts
41 photos

Well, as no one else has put their head above the parapet (!), I would be inclined to fit the 8x5 two blade prop and run it on the 4s LiPo. After all 935W is near enough 100W per lb as a ballpark figure and 60A is 20A per motor, so within the 22A max. Also a 7x5 three blade prop might be enough on 4s too, if you want scale fidelity.

On your earlier photo, showing just 8mm clearance between the prop tip and the Fuselage, presumably that was with the 8x4in three blade prop fitted? I just wondered, as if you want to stick with a 3s LiPo could you try a bigger prop (9x6) but if no room, the other options are a higher kv moto r- or bigger motor.

Robert Parker19/02/2019 19:53:40
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866 forum posts
1121 photos

Thank you Piers,

The 8mm gap is with the 8 x 4 props, the 8 x 5 is a contender but I might try some others later on.

I do think the 4s is the battery so I'll have to alter the battery compartment but not until I have done a trial balance as I was way off on my FW 200 Condor and had to move the battery back 8", though that is part of the fun of own designs.

Regards

Robert

Robert Parker02/03/2019 16:30:39
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866 forum posts
1121 photos

Hi All,

A bit more done today including re-calculating the CoG position as this has been on my mind since my terrible maiden attempt of my FW 200 Condor which had a major CoG error, the new position is 12mm forward of my original position possibly due to the weight gain.

Her she is just a few seconds after opening the throttles, yes that's right just a few seconds it all happened so quick I did not have time to react.

my condor 4.jpg

This remarkable Image taken by a fellow club mate, just before impact and the resulting damage helped put me off working on the Dornier and a lot of self doubt set in. All of the damage has been repaired and she is waiting to have another go, CoG moved a lot further forward after re-checking and confirmed by a fellow modeller.

So, back to the Dornier, I have modified the battery box to allow a 4s lipo to fit and drilled for the wing retaining bolts. Following that although there is still a lot to do I balanced the model and at least the battery box is in the right place and in it's present state the battery is at the rear end of it, so hopefully after finishing and painting I'll still have some room to play with for the battery position

dsc05718.jpg

dsc05719.jpg

The battery can move right up into the nose if needs be.

That's all for now

Regards

Robert

Robert Parker10/03/2019 17:22:35
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866 forum posts
1121 photos

Hi All,

Made a little progress, the biggest being what to covering type to use.

I had thought about using tissue and Poly C which is what I used on the Condor. After some thought and knowing that she will be belly landing on grass, I wanted something hard and durable and I was going to glass the bottom of the hull anyway, so I thought why stop at the hull. I know the shape of the fuselage will be challenging but I will do the same as when i built it and that is one side at a time, hopefully not ending up with a banana.

Never, glassed before so this will be the first for me, always willing to learn.

So I have now got all of the materials I need and made a start by giving the entire model a coat of sanding sealer.

That's all for now

Regards

Robert

Bucksboy10/03/2019 20:39:39
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552 forum posts
106 photos

Have a look at the Bucks Composites site, he gives advice on glassing using foam rollers. I’ve glassed four planes and it gives great results and very easy to do.

Robert Parker16/03/2019 19:24:52
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866 forum posts
1121 photos

Hi All,

I have made a start on the glassing on the wings, put it off for a bit, a process I've not done before, well not for around 30 years anyway and the products I used then were from Halfords and it was only a cowl, got good results though.

Back to the present day, well I must say the task i had been putting off was a real pleasure to do and as I was using Poly C I could use it in the kitchen with no hassle from anyone else in the household.

dsc05811.jpg

Underside done, now on the topside, this is even better than using tissue no bubbles no tears and so easy to work with........

dsc05812.jpg

I even covered the nacelles with the same piece as the wing just a single relief cut at the back of each nacelle and it was done, why have I not used this stuff before. I used Poly C and tissue on my FW 200 Condor.

dsc05813.jpg

On with the second coat to start filling the weave, by the time I was ordered out both sides of the wind and ailerons plus flap all had two coats not bad in three hours plus Wales won - perfect.

Next more coats to the wings to continue filling in the weave plus sanding sealer to the fuselage and continue making a new wing for my TN Lancaster just to keep me busy.

That's all for now

Regards

Robert

Edited By Robert Parker on 16/03/2019 19:27:41

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