HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Jan 24, 2012, 01:27 PM
Registered User
andrecillo76's Avatar
Heidelberg
Joined Oct 2009
379 Posts
Beta Version available

Hi,

Lothar was so kind to make plans for a quick and easy built Manatee. His idea was to keep the system simple:
  • two wings separated at the center
  • a central rib for quick change into glider or motorized version
  • two flaps added as a landing aid

I like that we have two branches for one and the same design. Lothar's is the quick and easy branch, while Kent's is more elaborate with a great looking skid, spoilers and a smaller transporting size.

Lothar's plans are now available at the SourceFroge repository (Release 0.2):

https://sourceforge.net/projects/hortenmanatee/

The plans are found inside the file "MANATEE_Lothar.DXF". In principle anyone with access to CAD and to a thread milling machine could build a prototype. The ribs and jigs have to be organized for thread milling. The file contains notes on the materials used. I think Lothar suggests 0.6mm Plywood for the D-Tube.

So, anyone in for a prototype?

Regards,

Andrés


@Kent: I hope it does not tumble In german Tümmler is also a race of pigeons, which tend to fly continuously in circles...
andrecillo76 is offline Find More Posts by andrecillo76
Reply With Quote
Sign up now
to remove ads between posts
Old Jan 24, 2012, 02:26 PM
less is more
Knoll53's Avatar
United States, CA, Marina
Joined Sep 2006
2,851 Posts
Beta Version??? It looks like a complete short kit.

Nice going Lothar. You DO have a quick system. I'm still modeling all the little parts. I see what you mean by a center rib. Your "cabin" is just a Rib. That will work fine and it reduces the length needed for CF joiner.

Question: I see that you are using an all wood spar design with plywood shear webs. Do expect to limit the speed of the glider version based on the spar design or is it ready for 100 mph pull out?

Andres: If anyone can get it to tumble, it is me.

Kent
Knoll53 is offline Find More Posts by Knoll53
RCG Plus Member
Last edited by Knoll53; Jan 24, 2012 at 02:33 PM.
Reply With Quote
Old Jan 24, 2012, 03:02 PM
Registered User
Tijgerhaai's Avatar
Germany
Joined Nov 2005
339 Posts
Hey Kent,

the drawing I made, is for a nice "sail and soar around". I am sure, it's able to make some loops. But not for 100 mph catapultstarts with a Megarubber. There should be more wood in the main spars or CF......

My goal was to make an easy to build wooden plane, which looks nice in the air. The design of the rocket pushed plane is somebodyelse's job. This You find there was the job of 3 evenings at the computer. Very easy.

May be I will build this plane for summer in Denmark. They have great dunes there and lots of wind. A little bit like Your pacific coastsite in Ca.

Lothar
Tijgerhaai is offline Find More Posts by Tijgerhaai
Last edited by Tijgerhaai; Jan 24, 2012 at 03:03 PM. Reason: something forgotten
Reply With Quote
Old Jan 24, 2012, 03:31 PM
less is more
Knoll53's Avatar
United States, CA, Marina
Joined Sep 2006
2,851 Posts
Lothar: The reason I ask about your spar cap is because I have not had much luck when pushing the limits of wood. Your laminated spar cap solves some of the problems I had with wood due to slope of grain. See photo. Multiple pieces of small sticks act like plywood when laminated to solve the problem of one piece with bad slope of grain. From the looks of Andres's Beluga video, that wood spar may be stronger than you think.

So do you produce your drawings with 2D CAD tools only?

I know at some point I will pull out from a terminal speed dive so I am throwing lots of 50K carbon tow at this one. Specifically, 8 layers at the root out to 2 layers at the tip per spar cap. Maybe 30% more on top. The 50K tow is surprisingly cheap and I like it's versatility. I may also add a central ballast box for the big wind days we get around here.

Kent
Knoll53 is offline Find More Posts by Knoll53
RCG Plus Member
Last edited by Knoll53; Jan 24, 2012 at 03:41 PM.
Reply With Quote
Old Jan 24, 2012, 03:46 PM
Registered User
Tijgerhaai's Avatar
Germany
Joined Nov 2005
339 Posts
Well Kent,

main reason for me not to use so much epoxy things is my health. Untill 5 years ago I worked a lot with this and my health wasn't the best. Problems with skin and bones. Since I am working with wood at the planes and boats, I save a lot of medicine......

I am sure it's also possible to make strong planes by using only wood. Just today I went to our airfield and tried again the big Lady HXII with 6 kg and 2,66m Span. She rolls and loops much better, since I changed the 6s A123 to 6s Lipo. It was a lot of fun to fly at full speed over the place and the loops got to LOOOOPS Only wood...

If I would be able to work with CF more, I am sure I would do it

Yes, I use only 2D tools. For me it works better, because I am used to. If You understand the geometry behind the design, it's as fst as 3D tools.

Regards

Lothar
Tijgerhaai is offline Find More Posts by Tijgerhaai
Reply With Quote
Old Jan 24, 2012, 03:58 PM
Registered User
andrecillo76's Avatar
Heidelberg
Joined Oct 2009
379 Posts
Kent,

the box Lothar draw should withstand the bending moment. I just made a test with the same 3mm birch ply proposed. It withstanded a bending tension of Sigma=80 N/mm², which lies well in the published range for plywood (30-120 N/mm²).

If I did not make a mistake this late, the joiner box should be stronger than needed. The bending moment at the joint is 90 Nm for a 100 MPH pull. The box should have a section modulus of about Wy=5900 mm³. Hence sigma=90000Nmm / 5900 mm³ = 15 N/mm², which is well below the 80 N/mm² measured. This means a security factor of over five. Taking a factor of two, the box should withstand a full pull at 150 MPH. If Lothar's design does not withstand such a dive, then due to the spars or the spar caps. But these look quiet strong to me (I'll check them tomorrow).

I guess a 100 MPH full pull should be fine. Your's will withstand for sure a terminal dive, and I hope you share a video with us

Andrés
andrecillo76 is offline Find More Posts by andrecillo76
Reply With Quote
Old Jan 24, 2012, 04:44 PM
less is more
Knoll53's Avatar
United States, CA, Marina
Joined Sep 2006
2,851 Posts
Lothar: Sorry to hear about the epoxy sensitivity. It's is very common. So far I am fine, but I should increase my safety measures with epoxy. Just one pair of nitrile gloves is not enough.

One thing is clear, if you understand the geometry in your head, 2D is faster than fully modeled 3D. 3D modeling is not quick, but it allows even a dummie to create complex parts because you can check your work visually. I have atleast 10 evenings into my project so far and have lots left to do. I'll admit that I am intentionally looking for difficult things to model in 3D just to test my limits without concern for how long it takes. I started life in 2D drafting and I admire what you are able to do with it. (Maybe I should return to 2D...)

Andrés: I'm not sure what 3mm birch plywood "box" you are analyzing, but I'm sure you know what you are doing. I think a terminal speed dive would be less than 150mph so Lothar is ready for anything.

I guarantee that you'll see the dive video. It is a "given" with me. I can't help myself. I used to snap wings quite often, until I finally started building stronger spars.

Kent
Knoll53 is offline Find More Posts by Knoll53
RCG Plus Member
Old Jan 25, 2012, 10:48 AM
Registered User
andrecillo76's Avatar
Heidelberg
Joined Oct 2009
379 Posts
Hi Kent,

I meant the battery box, used also as a joiner. I measured the dimensions of the spars proposed by Lothar and came to the graph shown below. Essentially, it means that considering only the bending tension, the spars should be able to withstand a 100 MPH full pull.

I took a piece of spruce, a leftover from a spar, and conducted a "measurement". I found a max. bending tension of about 40 N/mm². The spar proposed by Lothar has a security factor of 1.6, which is more than required by FAR part 23 for real planes (factor 1.5). If one does not make a full pull, higher speeds could be flown.

There are other factors that determine the stength of the wing, such as shearing forces on the D-Box and shearing forces at the spar caps and shear webs. And then we have the non-static effects, such as flutter... It's a matter of testing the limits

Regards,

Andrés
andrecillo76 is offline Find More Posts by andrecillo76
Last edited by andrecillo76; Jan 27, 2012 at 01:41 AM.
Reply With Quote
Old Jan 25, 2012, 11:59 AM
less is more
Knoll53's Avatar
United States, CA, Marina
Joined Sep 2006
2,851 Posts
Thanks Andres, I see the birch plywood joiner/battery box now. It crosses the main spar in the first bay. This crossed connection between a joiner and main spar has always concerned me. Shear webs cannot full transfer forces because they do not align, which leaves the ribs to do the work. This is, no doubt, why those ribs are 3mm birch plywood. Again, I'm sure you know what you are doing.

I see that you have checked Lothar's main spar in bending. Good graph. I trust that the steps in the graph are located at the steps in the spar cap laminations.

I wonder if a true stressed skin design with ,8mm plywood could work. Fully skinned wings with just ribs. If a complete tube were to be created from the LE to TE sub spar, with a truss type rib, it should be a rigid complete structure. No joiners.

Kent
Knoll53 is offline Find More Posts by Knoll53
RCG Plus Member
Old Jan 25, 2012, 12:03 PM
Deniable plausibility
Shedofdread's Avatar
Derbyshire, UK
Joined Aug 2008
2,316 Posts
Make a mould for just the D-box? Web to close the tube and then ribs back to the TE. Just a thought.

Regards,

S
Shedofdread is offline Find More Posts by Shedofdread
Reply With Quote
Old Jan 25, 2012, 12:19 PM
less is more
Knoll53's Avatar
United States, CA, Marina
Joined Sep 2006
2,851 Posts
With a mould you could lay up most any spar cap and web combination. This would certainly work. Aligning the ribs and the D-tube would be a challenge for me....

I was wondering just how light and simple it could get with the stressed skin approach using just plywood and ribs. It is a big flat squashed tube.

Kent
Knoll53 is offline Find More Posts by Knoll53
RCG Plus Member
Old Jan 25, 2012, 12:42 PM
Deniable plausibility
Shedofdread's Avatar
Derbyshire, UK
Joined Aug 2008
2,316 Posts
Quote:
Originally Posted by Knoll53 View Post
With a mould you could lay up most any spar cap and web combination. This would certainly work. Aligning the ribs and the D-tube would be a challenge for me....

I was wondering just how light and simple it could get with the stressed skin approach using just plywood and ribs. It is a big flat squashed tube.

Kent
Here's a thought - A male mould (made from wooden ribs / structure) over which steamed plywood (to render it flexible) is pulled and clamped. Maybe from 1/32 ply and multiple layers? Say 3 or 4 layers at the root tapering down toward the tip. If the layers were bonded together on this mould / jig, it would be very stiff and [hopefully ] not too heavy.

Oh, also said mould could be used as a router jig for trimming.
Shedofdread is offline Find More Posts by Shedofdread
Reply With Quote
Old Jan 25, 2012, 01:23 PM
less is more
Knoll53's Avatar
United States, CA, Marina
Joined Sep 2006
2,851 Posts
Inasmuch as plywood is available in 4' x 4' sheets from Aircraft Spruce, this formed plywood technique sounds do-able. One sheet of plywood for the entire wing panel. A mass production technique for plywood wings. Who knew.

I still wonder if structural principle of stress skin plywood wing with nothing but ribs is sound. I suspect that by the time you fully tested and fixed problems, you'd be at a conventional design.

Kent
Knoll53 is offline Find More Posts by Knoll53
RCG Plus Member
Old Jan 25, 2012, 02:07 PM
Deniable plausibility
Shedofdread's Avatar
Derbyshire, UK
Joined Aug 2008
2,316 Posts
And if you put some end grain balsa between the plywood, what've you got? The De Havilland Mosquito, Vampire, Venom..

S
(currently unable to invent anything )
Shedofdread is offline Find More Posts by Shedofdread
Reply With Quote
Old Jan 25, 2012, 02:20 PM
Registered User
andrecillo76's Avatar
Heidelberg
Joined Oct 2009
379 Posts
Quote:
One sheet of plywood for the entire wing panel.
I hope not in one piece. The surface of a Horten is Gaussian curved and cannot be covered with one sheet of plywood. Some time ago somebody tried it, although we said he shouldn't. The result was a catastrophic wing. It flew, but it looked like a golf ball full of (irregular) dimples . Unless the whole wing is done in a mould with glass or carbon fabric, I would always use some sort of spar. The weigt of the spar is negligible compared to the rest. Even a shell wing needs at least some sort of shear webs...


@Kent: You are right, the steps in the graph are due to the quantization of spar caps.

Andrés
andrecillo76 is offline Find More Posts by andrecillo76
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Build Log My First Ever Build code name "NABS" diymuppet Flying Wings 11 Dec 24, 2011 07:33 AM
Build Log Code Name: BRT18 70" Flat wing foamy Photon Foamies (Scratchbuilt) 27 Sep 13, 2007 03:05 AM
Sukhoi Su-32FN Platypus (NATO Code name FULLBACK) Sluf7 Electric Ducted Fan Jet Talk 44 Aug 10, 2006 01:25 AM
Idea Frankenstein Bio-Tech (project code name required) DuncanRigby Ornithopters 8 Apr 25, 2004 10:35 AM