I noticed on the BV138 that the center motor had a four blade prop and the outboard pair had three blade props with wider blades. Any theorys about that? It must have had some practical significance because it required manufacturing another part.

Was the center motor for take off and then feathered? The outboard ones look like they may have been more effective at higher altitudes, but I've read with the diesel motors it only got to about 16,000 feet.

Len

Len the book i have on the BV-138 says this about the engines

3 205 Junkers D liquid cooled six cylinder opposing piston diesel inline engines.. Each with 700 Horse power.. Outer engines fitted with VDM 3 blade metal Variable pitch propellers 3.30 diameter ..Center engine with a 4 blade Airscrew

The BV138 is in the queue, but the DO24 is going on the building table.

I scaled a three view of the DO24 up by 6x and got a 44 inch span. At that size I could use 5.75" diameter props. The wing area comes out to 306 sqin or 2.14 sq ft.

I had a mustang with a 42" span that had an 11 ounce per sq foot loading and it was a real floater with the power off, but fairly fast.

Here I could use some of your collective wisdom. What do you think of shooting for plane that weighs around 20 ounces? That would give it a 9.5 ounce per sq foot loading.

As it will be quite a bit slower, how much lighter does it need to be?

How light can a 44" span DO24 be?

It looks like the DO24V had the same motors as the BV138. It looks a bit different, but maybe...

Len

This weekend was spent generating cross sections for the hull. I may have enough now to start work although I am still undecided what construction technique to use. After more thought it was shrunk to 34". Here is what is there so far in case it may be of use to someone else.

Len

edit: I found a picture of a drawing that shows cross sections. I have not angled the sides in enough at the top for the front. I have enough material to sand it in pretty much. Here is a link to the drawing.

http://www.dornier24.com/images/pages/Do-24_d035.html

and here is one to a cutaway drawing:

http://www.dornier24.com/images/pages/Do-24_d021.html

The motors I want to use arrived today along with the GWS4530 props. Each weighed 5 grams, the mount another gram. First test showed 9700 rpm at 1.7 amps and 7 volts. Rod Badcocks calculator says 66 grams of thrust.

I don't know what I was thinking, but 10 ounces should be a high side target. For a few days the plans were at a 40" span, but now they are back to 34". Cute motors.

Len

What's your wing loading with AUW? Nice PDF plans and cross sections... I'd love to see this plane at 60"-80" using cheap BP18 outrunners and MA 8x4x3blade props. Too bad nobody makes 5-blade props... though they'd probably be so inefficient that you'd never get it off the ground...

At a 34" span I calculate the wing area to be 1.37 square feet so if I hit a target weight of 10 ounces it would be a wing loading of 7.3 ounces per square foot. I think it would look real scale in flight.

The first attempt at the fuselage was of mixed results. A piece of carbon tube was used to support the formers, which were of 1mm zepron, at the rear of the fuselage. I thought this worked well.

When the sides went on the "foam safe" CA and kicker melted the foam to the point of weakness and actual separation in a few spots. I smeared on some gorilla glue to see if I could save it, but I don't have real high hopes. Now I am thinking of putting a slab of blue foam on the rear bottom and shaping it then working my way around the fuselage with slabs of blue foam.

It will probably be started again once I get a feel for working with this stuff.

The fuselage weighed 17 grams at this point.

Len 1mm is a bit thin in my opinion .. if your going to work with the depron/zepron then i would go with 3mm for the formers ..

I think you are right Ron, I am getting a feel for how to approach cutting the sides, a couple more runs that come up dry and maybe something will pan out.

Thanks for the goodies, they will come in real handy on the next project.

Len

http://www.rc-fliegerfilme.de/flash/rcw3.htm

i hope you don`t regret going for the 24 if you see those pics

Great looking so far !

Great video.

I hope to get to the BV-138 after the DO 24. They are both great subjects.

Cleveland Model & Supply Company is having a 30% off sale and I picked up plans for the Martin 130 China Clipper at 48" span and PBY-5A Catalina at 39".

that was an awesome Video ..

That was a really cool video. The camera in the turret actually moved.. wow
Justin

I may have gone overboard in the other direction, but the formers are 3mm and the sides are 6mm. I cut about 5mm from the sides, bottom, top and (at the back of the plane behind the step) at an angle so it could be sanded into the needed shape. I used 5 minute epoxy. My reasoning is that if the basic supporting frame is strong it should have the right shape on the sides and should go together warp free. Hopefully it will not weigh too much. With this approach the carbon rod isn't needed to keep it straight.