Replies to This Discussion

Permalink Reply by Richard Unwin on June 14, 2012 at 7:46pm

Welcome to the challenge that making your own plane is...

I will add my ideas for your answers below.

1. max out this space which will allow for changes to prop sizes if needed, but its a trade off between keeping the booms rigid and also how high the undercarriage is to allow the max prop size to be run. Also depending on where the undercarriage is can change what happens on take-off as the front wheel leaves the ground and the planes attitude changes the prop can strike the ground.

2. My original wing design was 2500mm long and 300mm wide (and was going to be a Clark Y but the foam cutter changed it to a different shape with a curved bottom) It flies well and just mushes out when trying to stall and doesn't drop a wing which is great. I will ask the cutter what the shape is. 

3. I used 12mm Carbon rods with a 1.2mm wall section and mating 14mm carbon rods that allowed me to make sockets to plug the tail section on and off.

4, I used a general rule of thumb of %15 of main wing area for Elevator surface and %7 for the rudders, as for the boom length I could only buy the rods in 750mm sections but with the tail joined on its almost 900mm long, my main idea was to get the tail back as far as possible while still be rigid, the further back it goes the more stable the plane will be and the less pitch sensitive the elevator control will be, give a nice stable flight platform.

5. I built a H tail as I believe that the APM units still dont like controlling a V tail, ( if I am wrong on this someone let me know)

I have posted a few pictures on my blog let me know if you have any other questions.

richie

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Permalink Reply by Richard on June 15, 2012 at 1:16am

Hi Richie, your answers have been extremely helpful, and enough for me to go on, Your blog is an excellent reference. A friend of mine has already started on the fuselage, As we knew the approximate size for this. I am going to try and build to the rough weights you have spec'd out in your blog if that okay, as they are quite similar to mine. My fuse is a bit taller than yours. 

A friend has already starting vacuuming the fuse mold - some pics... 

One more question if possible, 

I was thinking of using two thick Carbon fibre tubes in the front and back of the wing to strength. And noticed you have thin spa's top and bottom, Is there any reason you went for that strengthening method?

Your build looks really good by the way!

Rich

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Permalink Reply by Richard Unwin on June 16, 2012 at 6:13am

The wings only use a internal dual tube and spar set up that only runs about 1/3 of each wings length, if you look closely At the first picture from my "Uav build update" you can see some filler ontop of the wing and this is where the inner wing tubes finished. The rest of the wing is just reinforced with the upper and lower flat carbon piece, which when vacuum bagged the whole wing in a light weight fibreglass really stiffened up the whole wing. I also used the slots cut into the wings for the top and bottom flat carbon to run wires out to the ends of the wings for lights and servos, so give some thought to that now as its a real bitch when you forget a particular wire run,(dont ask me how I know).

Keep the questions coming as i am more than happy to pass on anything that i have done if it helps.

Richie.

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Permalink Reply by Richard on June 16, 2012 at 2:47pm

Richard, Cheers for the advice, I think I have enough info to continue with the build. I guess it is just going to be trial and error whether I get it right first hit. I guess it's lighter to use thin spas to reinforce the majority of the wing as opposed to running 2 hollow booms the entire wing length. 

I will keep this thread updated with progress...

Cheers for the help, Its very useful!

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Permalink Reply by R. D. Starwalt on June 16, 2012 at 6:59am

Richard, Several of your questions might be addressed by an old publication - Model Glider Design by Frank Zaic

I recently finished it and in it he discussed (pre 1938) tail boom materials/sizes, wing aspect ratios, rudder sizes, elevator sizes, and even tail planforms.

Most of your questions, except the fact that we now have carbon fiber materials, are discussed from the perspective of gliders.

As you are starting with a somewhat clean sheet of paper, perhaps patterning your new bird after some other twin boom designs might be useful? Listed below are some online plans to inspect and perhaps get an 'average' value from.

Netopyr  Pushaire  SIPA Mini jet  XP-3

I would also average in dimesions from the OV-10 Bronco, P-38 Lightning, Cessna Skymaster, and maybe others listed HERE.

Perhaps some dihedral is also appropriate because you need some built-in stability for photography?

I see a white paper on this subject... oh to have more time in a day. This website stimulates so many ideas.

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Permalink Reply by Richard on June 16, 2012 at 2:49pm

Hi R.D. Starwalt, thanks for the info, the plans youve listed are useful to me and I have observed surface area ratios, and feel i have enough info to continue the build. I am going to make the entire frame modular, so if the booms are initially to long/short, i can change it easily. 

Cheers

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Permalink Reply by Richard on June 18, 2012 at 3:01pm

Update, I have been doing some research, and taking in all your advice, and have refined my measurements and sizing's accordingly. The below is an accurate scale drawing of the measurements. Here are the important details...

Fuselage

120mm x 120mm square box section 600mm long, with cowls on each end.

Tail booms will be 12mm outer dia with 1mm wall thickness

Wing

Chord - 300mm

Wingspan - 2400mm

Aspect Ratio - 1:8

Profile - Clark-Y

Wing area Calculation = 2400mm (span) x 300mm (chord) = 720000mm sq. Subtract Fuselage area = 36000 

Total wing area = 684000mm sq.

Elevator

Elevator needs to be 15% of wing area so 15% of 684000mm sq (total wing area) = 102600mm sq (elev surface area)

The elevator does look a bit large, but I guess this thing needs to be stable.

Vertical Fins

I am going to make this aircraft a T tail as i have heard APM doesnt like inverted V tails just yet, but the tail will be removable anyway so when it is more supported, I can just change it over.

Power System

Eflite power 60 with 14 x 8 Prop. It says it is good for models upto 4kg weight. A bit expensive though. And ideally i would like to run this on 3s, but it seems 4s is the minimum. Best get saving for some new packs! If anyone has any recommendations for motors that would be great.

And now onto the visual.....! My trial of AutoCAD 3d studio max has expired, so 2d visuals from now on! 

As always - if anyone has any positive or constructive feedback, please let me know! 

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Permalink Reply by Veikko Vierola on March 21, 2013 at 3:16pm

Hi, it looks good. I planned pretty similar design once with two engines. http://diydrones.com/xn/detail/705844:BlogPost:897647. Let me know how it flies when your plane is ready.

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Permalink Reply by Wanabigaplane on June 18, 2012 at 4:07pm

Hi, we have some experience with Hugins and our Mugin.

For booms look at ex carbon fibre golf sticks. (In Aus they are a common item at the dump recycler.)

For V tail we used a Vtail mixer we use the normal rudder / elevator APM arrangements. The rudder output goes to to the nosewheel, then the rudder and elevator go to a V-tail mixer. Neither the pilot or the APM notices the difference.

With T tail or H tail you have a problem with rigidity. I think you are much better off with the horizontal stabiliser between the booms. With two rudders you will either need an extra servo, or a boom between the rudders.

With a V tail, the join of the two elevon halves is a weak point that needs consideration in the design phase. You may even consider a strut between the booms to make the tail end a strong triangle.

With the long flat sides of the fuselage out front, you need good tail volume. However, the weight in the nose to counterbalance this becomes a problem which wth electric is solved with placement of the batteries.

Think how you are going to transport and assemble this bird at the field during the design phase. Having put up with our arrangement, I long for the alternative where the tail, booms, and mid wing all stay in one piece for transport and assembly.

Plan your nosewheel undercarriage carefully. It is going to be long, and with the need to steer it, becomes a bit difficult and vulnerable to a bad landing.  You need either crash resistance or easy in field replacement.

Jack.

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Permalink Reply by Richard on June 19, 2012 at 6:21am

Hi Jack,

Cheers for the Info on the Golf sticks, I have found 1000mm x 12mm outer dia (1mm wall) Carbon fiber tubes for £11 each. Which should work, not quite sure if 1mm is going to be strong enough, as i cant seem to find carbon fiber golf clubs anywhere.

I hadn't thought of using a v tail mixer, wouldthis one be okay? I would definitely like to do a V tail if possible as opposed to H or T tail. If building an inverted V tail, I would probably join the 2 elevon halves with 30 minutes epoxy, I am thinking of building up the tail with balsa, then covering with Fiberglass, that should give it plenty of rigidity.

I am planning on making the outer wing panels removable, and also the booms removable, and also the tail removable. For clarification, is your bird built in one complete piece?

If the fuse, center wing section, booms and tail will fit in the car, I will make them removable/modular, but keep them assembled for quick setup times.

I have already purchased this rear landing gear, it is the CCU14 from this website in the UK, about 1/3 down the page. 190mm high. I have looked around for decent nose wheels, but think i may need to get something machined. Something similar to the one on the Mugin maybe. I have had quite bad luck with the undercarriage on my URSUS 2200mm twin boom airframe, I initially used aluminium rear gear, but then upgraded to sprung steel, but was too heavy, the front strut was quite nice, but kept bending. Here is a picture from that build thread...

I am not sure about making the nose wheel steerable, at 190mm high excl wheel, its going to be a challenge!

Any advice on nose wheel and inverted V tail construction greatly appreciated!

Rich

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Permalink Reply by Wanabigaplane on June 19, 2012 at 7:21am

I guess any v-tail mixer would do. I don't know anything about that one.  Don't forget to test it on fresh batteries as well as low batteries.

I am suggesting the midwing/booms/tailpiece stays together as one structure. The midwing is attached   to the fuselage at the field just like a normal model aircraft - for example, two dowels in the leading edge and two nylon bolts at the trailing edge. Minimum assembly at the field, no feeding of cables through the structure, or attachment or clevices. It's just an idea I have - let anyone, who has tried it, chime in and tell us if its not a good idea.

Jack.

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Permalink Reply by Jake Stew on June 18, 2012 at 4:11pm

Not a twin boom, but you might find this video interesting as far as durability goes...

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