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Spruce Goose Foamie scratch build

Old 09-11-2014, 01:15 AM
  #1  
MononkBen
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Default Spruce Goose Foamie scratch build

OK... This is a crazy idea from a 54 years old RC newbie... Building a 60 inches wingspan RC Spruce Goose foamie from insulation foam purchased at Home-Depot...

I have zero experience in RC building, but I am am a professional electrical engineer... So this is just an engineering mid-life crisis... I should survive this without a divorce...

Somebody suggested that I start a build post, and I think this can be fun... So I will share my learning curve and discoveries, good and bad...

This will be a long project. The model should be almost scale (as much as technically possible), but it may not be a display chef-d'oeuvre.. We shall see...

Right now, I have watched a lot of youtube videos, I read a lot on RC, I have a pair of nice hot wire cut wings, ready to cover with paper, and I am figuring out the motor KVH/Prop/voltage/amp/watt/trust... more to come shortly!

I foresee a long journey... :-)

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Old 09-11-2014, 01:36 AM
  #2  
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Brace the wing with a good strong Spar, wood, CF, or it wont be strong enough, a Tapered I Beam made with bass wood will be good and strong, epoxy it in place, a slow stick fuselage will work too, or a square piece of square aluminum tube at least 40" long.

http://www.ebay.com/itm/NEW-GWS-Slow...p2054897.l4275
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Old 09-11-2014, 02:53 AM
  #3  
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Subscribed.....good luck with your build...please keep us posted and don't be afraid to ask questions.....
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Old 09-11-2014, 02:56 AM
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here we go... first, the plan I am using is one everybody interested in the Spruce Goose have seen... I expanded this to the right size using a "photo to poster" web application... Print and put pieces together to have a scale size template.

I used some base wood to cut the airfoil templates, based on a bomber airfoil picture found on the net.

I did some hot wire cutting experimentation and ended up with a 3 phase hot wire cutting procedure (Front and back: parallel wire cutting, middle of the wing: angle wire cutting. I used a home made half inch PVC bow, a nichrome wire, a 48V power supply with 8 x 4Ohm 10W resistors in serie. I use jumpers on the resistors to modulate the current, and temperature of the wire. After a few unsuccessful attempts, a snapped nichrome wire, and a little bit of sanding, I ended up with this pair of decent wings, 60 inches wingspan.

These wings are surprisingly solid. I used an unsuccessful wing experiment to check its resistance to bending, and it snapped at 90 degrees angle. Once covered with craft paper and glue (as seen on youtube), they will be even stronger.

Before I pursue this project into cutting the floating body, I need to figure out the motors and propeller. My scale plan has 4 inches between motors...

After a lot of google search I think I figured it out... I will explain in the next post.
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Old 09-11-2014, 03:09 AM
  #5  
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you will need to space the motors out farther apart, 4" wont be enough room for the props, at least 5 1/2" is needed. or you could stager the motors forwards and back and have the props overlap.
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Old 09-11-2014, 03:18 AM
  #6  
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Chellie,

You are miles ahead of me here... I will certainly consider reinforcement on the wings, but I am not there yet...

I was certainly thinking to install the 4 motors on each wings using a single base plate, and use it as reinforcement at the same time. I still need to figure out how I will do this, and I am saving this challenge for later.

I am planning to do this slowly and one step at a time, reading a lot, and using my engineering background to integrate everything I learn with my knowledge of physics principles, materials properties, electrical's, and the rest. I do not expect this to be perfect, but the fun is into figuring it out...
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Old 09-11-2014, 03:22 AM
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Originally Posted by MononkBen View Post
Chellie,

You are miles ahead of me here... I will certainly consider reinforcement on the wings, but I am not there yet...

I was certainly thinking to install the 4 motors on each wings using a single base plate, and use it as reinforcement at the same time. I still need to figure out how I will do this, and I am saving this challenge for later.

I am planning to do this slowly and one step at a time, reading a lot, and using my engineering background to integrate everything I learn with my knowledge of physics principles, materials properties, electrical's, and the rest. I do not expect this to be perfect, but the fun is into figuring it out...
We are all here to help if we can there are a lot of Brilliant Minds here on Wattflyer, I have learned from them all
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Old 09-11-2014, 03:24 AM
  #8  
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nice looking wing

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Old 09-11-2014, 04:06 AM
  #9  
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Default KVH/prop/voltage/amp/watt/rpm/trust/efficiency for the NULL

Before I move on, I need to select the motor and propeller that I will use.

I have learned that I must have a 1:1 trust/weight ratio in order to have an RC flying machine. This is not 3D... I just want it to fly!

I have done extensive search for a way to figure this out, and have found many motors, many forums with experts advice, many motor specs, and many calculators. However, most of the expertise is focused on propellers that are much larger than what I need, as I have only 4 inches between my motors, and 8 of them. And the calculators or formulas are not so straightforward for a newbie.

A visit at the hobby store in Laval, QC, revealed that I had quite a challenge... The store expert could not tell me anything but "You really have a huge challenge figuring this out... you need to do some trial and error and maybe you can have something that works...". In other words: you are on your own!

I need a small prop, a low weight motor, moderate consumption (because I have 8 of them and more watts = more battery = more weight) and a reasonable price (cost x 8!!).

Then I found this link: http://www.rctoys.com/pdf/prop_data.xls
It is an excel document with 13440 characterization of motor/KVH/prop/voltage/amp/watt/rpm/trust data.
The information seems reliable, as I validate some of the data with some DR Kiwi analysis available on the wed, and they matched exactly.

I added 2 columns to the worksheet: trust/weight and trust/watt.
Using filters, I selected the prop sizes that are applicable to my project.
Additional filtering allowed me quickly figure out the motors that had the best weight/watt/trust compromise for my spruce goose. ( it is no use to have more trust if there is too much added weight and amps...).

So I identified many comparable (probably identical makes) 17 grams 2230 KVH motors that provides 260 grams of trust with 6 AMP at 10.9 Volts with a 4.5x4 prop. Multiply by 8 and I have a 2KG trust capacity. I think I can match this in the plane weight.

Now that I have some good references, I will keep searching for the best solution. Ideally I would like to have a 4 x 5 prop, hoping it can give me the equivalent trust efficiency, without the need to increase the space between my motors, but this seems to be a hard find...

Next, I will order my motor and prop selection, along with everything needed to perform some trust test on my own and ensure that I get what I expect... this may take some time though...

Hours of big big fun!
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Old 09-11-2014, 04:20 AM
  #10  
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Chellie,

The props overlapping is technically possible (the wing is angled), but I didn't like the idea of overlapping.
That being said, this made me realize that I can overlap safely by alternating the spinning direction (CW - ACW - CW - ACW) to ensure that they don't hit at 18000 rmp in opposite direction...

I think I can manage with 4 inches between motors with this 4.5x4 prop 260 gram trust and alternate spinning. I will keep searching for a 4x5 propeller and compare the trust and watts if I can find one. I will make a final choice once I am in a position to do these trust tests later this fall.

Cheers!

MononkBen
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Old 09-11-2014, 04:23 AM
  #11  
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get the 1800kv version of this micro motor from Hobby King, they are out of stock on the 1800kv motors, i think I might have bought them Out with my last order I love this little power house, you can push this motor to 20 amps and 200 Watts,the motor has thick windings, i do it all the time and they love it, with a 7x6 APC prop, I cut the motor shaft at where the threads start towards the bell, and use a collet prop adapter, use at least a 25 AMP ESC and soak them in corrosion x for a few days in a Jar to water proof them, use a 3 cell lipo.


http://www.hobbyking.com/hobbyking/s...arehouse_.html

http://www.hobbyking.com/hobbyking/s...arehouse_.html

Just a little example of the power these 1800kv micro motor produce.

my friend Kosh with just one 1800kv motor on his plane with a 3 cell lipo and a 7x6 APC prop

[media]http://www.youtube.com/watch?v=MgV17GlLMlI[/media]here is a 84" W/S lancaster with 4 of the micro 1800KV motors with 7x6 props on 3 cells.

[media]http://vimeo.com/61730176[/media]and here is a 64" W/S Wellington with 2 of the 1800kv micro motors on 3 cells with 7x6 Apc props

[media]http://vimeo.com/22757213[/media]
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Old 09-11-2014, 04:25 AM
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I think you will need at least a 5" prop to get any thrust, and better to use a 6" x 6 pitch prop to give you the thrust to get off the water

http://www.hobbyking.com/hobbyking/s...ller_2pc_.html

the 1800kv micro motor with a 7x6 prop produces about 22 oz of thrust, with a 6x6 prop, the thrust may be around 20 oz, X 8 about 160 oz of thrust or about 10Lbs of thrust, that should get you off the water ok and at about $7.00 per motor, that wont hurt your wallet to bad

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Old 09-11-2014, 04:40 AM
  #13  
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Hi Chellie,

Nice and affordable motor. The 2000KVH above looks good to me.
It is 37 grams, but is said to have a higher trust with reasonable watt..
I might order one of these too and test it to see if the gain is higher than the extra weight.

I need to keep my KVH high, because lower KVH consumes too much current with smaller prop and this causes the watt/weight efficiency to drop significantly.

Cool video and picture!

Cheers!
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Old 09-11-2014, 05:05 AM
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Originally Posted by MononkBen View Post
Hi Chellie,

Nice and affordable motor. The 2000KVH above looks good to me.
It is 37 grams, but is said to have a higher trust with reasonable watt..
I might order one of these too and test it to see if the gain is higher than the extra weight.

I need to keep my KVH high, because lower KVH consumes too much current with smaller prop and this causes the watt/weight efficiency to drop significantly.

Cool video and picture!

Cheers!
Hi the 2000 kv motor should work well for you, not that much different from the 1800kv motor, I use these motors all the time, and i love them just put a little epoxy where the motor wires come out of the windings, that keeps them from vibrating and breaking and put a little epoxy on the motor mount to motor, to keep the motor from ever wanting to spin in the mount, just some cheap insurance, and it makes these motor almost bullet proof I turned on Barry to these motors a while back for his wellington and lancaster builds and he loves them, its all he used now for his builds, Take care and have fun, Chellie
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Old 09-11-2014, 05:32 AM
  #15  
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Default Diy Thrust Stand

http://www.wattflyer.com/forums/show...t=thrust+stand
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Old 09-12-2014, 04:30 AM
  #16  
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Default Propeller considerations

Hi Chellie,

The prop size is a delicate matter... a 6x6 prop would indeed be an easy solution, but unfortunately it is not an option.. this is a flying boat, and the distance between the water line and the engine is very limited here... I have only 4 inches between the center of the engine and the bottom of the body, which will be in water... Even with a 5x3 prop, I will need to cheat and raise the wings, and/or the engine nacelles, to ensure the blades are not hitting the water at 18000 RPM... Ouch!

Although my motor/prop selection produces a limited trust of 4.5 pounds (8x260g) with a 4.5x4 blade, I think it can take off, as the body will gain sufficient speed to raise out of the water and allow the aircraft to increase speed enough to take off and fly. I admit that this may not be a quick take off, but the spruce goose was heavy monster after all... The 17 grams motors and low power requirement (6 Amp) will also contribute to reduce the aircraft weight. I may order one AX 2306N 2000kv for test purpose, and I will compare the weight/trust/watt efficiency that I can gain, and make my final choice then.

The 4.5x4 prop is really the largest I can afford, and I am OK with the blades overlap, since the wing is not straight. For sure, I will alternate the spinning direction between motors, just in case...

I will put the ESC's in the engine nacelles (I have 4 inches x 1.25 inches diameter), so I will only need a power bus to the ESC, and a thin parallel wire bus for the ESC controls. The batteries will be in the body and I will use them to balance the plane. The key here is to minimize weight so I can have a near 1:1 trust/weight ratio. So I am optimizing everything, including the wire weight in my design...

Cheers!
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Old 09-12-2014, 04:32 AM
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Default Propeller overlap and alternate spinning directions

Illustration...
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Old 09-12-2014, 08:18 AM
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Originally Posted by MononkBen View Post
Hi Chellie,

The prop size is a delicate matter... a 6x6 prop would indeed be an easy solution, but unfortunately it is not an option.. this is a flying boat, and the distance between the water line and the engine is very limited here... I have only 4 inches between the center of the engine and the bottom of the body, which will be in water... Even with a 5x3 prop, I will need to cheat and raise the wings, and/or the engine nacelles, to ensure the blades are not hitting the water at 18000 RPM... Ouch!

Although my motor/prop selection produces a limited trust of 4.5 pounds (8x260g) with a 4.5x4 blade, I think it can take off, as the body will gain sufficient speed to raise out of the water and allow the aircraft to increase speed enough to take off and fly. I admit that this may not be a quick take off, but the spruce goose was heavy monster after all... The 17 grams motors and low power requirement (6 Amp) will also contribute to reduce the aircraft weight. I may order one AX 2306N 2000kv for test purpose, and I will compare the weight/trust/watt efficiency that I can gain, and make my final choice then.

The 4.5x4 prop is really the largest I can afford, and I am OK with the blades overlap, since the wing is not straight. For sure, I will alternate the spinning direction between motors, just in case...

I will put the ESC's in the engine nacelles (I have 4 inches x 1.25 inches diameter), so I will only need a power bus to the ESC, and a thin parallel wire bus for the ESC controls. The batteries will be in the body and I will use them to balance the plane. The key here is to minimize weight so I can have a near 1:1 trust/weight ratio. So I am optimizing everything, including the wire weight in my design...

Cheers!
Hi Build the Fuselage taller at the hull, about 1 to 1-1/2" taller, it wont be noticeable, but it will give you a little more prop to water line clearance, have the wing sit at a positive incidence when the craft is sitting in the water, you will need about a 5 degree pos wing incidence sitting on the water, because the pull of the motors will want to pull the front of the hull down, and you will need a pos incidence on the main wing to break free from the water.the single hull will go down into the water a little, you will loose about 3 degrees of incidence under power, but you will still have 2 degrees of pos incidence on the wing to help to lift you off the water, thats why i say 5 degrees of pos wing incidence floating still on the water.

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Old 09-12-2014, 08:41 AM
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look at the video, at 0:14 seconds, the main wing has about 5 degrees of pos incidence sitting on the water, also look at the Stabilizer assy, it looks to be sitting a 5 degrees also for a reference, even though the plane is built with a 0 - 0 wing incidence, the way it sits in the water is very important, with a single hull, its going to get pulled down more when taking off as opposed to a twin float assy. at 0:19 seconds, you will see the nose go down under power, but they still had enough pos wing incidence to get off the water.


https://www.youtube.com/watch?v=E9C-uMBcZcs

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Old 09-12-2014, 09:34 AM
  #20  
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Originally Posted by MononkBen View Post
Illustration...
IMHO, its best to have all the motors on one side of the wing to turn in the same direction, the top of the prop to turn towards the fuselage, and to have the motors, angled about 1/2 degree into the fuselage. rather than straight forwards.
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Old 09-13-2014, 07:04 AM
  #21  
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Hi Chellie,

Why is it that we can't alternate the spinning direction? Especially if the blades are overlapping?

If I use larger prop and overlap the blades, and if they spin in the same direction, there is a risk of high velocity collision... Also, the blade overlap area will be subject to significant turbulence caused by opposite blade velocity, and this will reduce the trust efficiency accordingly, and spoil the purpose of using larger blades to get a stronger trust...

Alternate spining direction will not only reduce turbulence and preserve the trust, but it will compensate for the moment of rotational inertia. I don't see anything wrong with it, apart from being an unusual concept that reduces flight maneuverability issues...

I know a former acrobatic jet fighter pilot who explained me once how the moment of inertia of his powerful single jet engine would impact the way he would maneuver his aircraft... Doing a right acrobatic turn was straight forward for him, as he would compensate the moment of inertia by pulling up the stick... But turning left was nearly an impossible task (in an acrobatic figure perspective), as he would need to tilt down to compensate the moment of inertia of his engine, and this was not the most efficient way to control his aircraft with precision... so all the complex acrobatic figures they would do were based on right turns... (re: Belgium Red Devils, 1960's and 1970's). As far as I am aware, this is still true.

I like the idea of using a 5 degree tilt though... I was planning to use a "flapperon" configuration for takeoff... by using a 5 degree tilt on the wing and the elevator, I might not need flaperons after all. I will consider it when comes the time to build the body. Still, I like the concept of using "ground effect" for take off as being part of the Spruce Goose original concept.

The Spruce Goose in this video is way larger than mine... Maybe I should reconsider the 60 inches wingspan and make it a 90 inches wingspan... but then, why would I make it easier and prevent me from having all these challenges and the fun that comes with them... Nah! I will keep it 60 inches, and this will be my creation, a one of a kind, 60 inches, 8 motors, newbie, scale Spruce Goose RC aircraft... I don't care if it fails... the fun is in the engineering of something that is not easy!

Howard Hughes wouldn't have gone the easy path... He created a flying boat with a larger wingspan than any modern aircraft, and he did that in the 1940's, without a computer, and using a slide rule for his calculations... see 1943 scale model flap deflection test at https://www.youtube.com/watch?v=8indPzIoH_U... mmmhhh... I could build a similar test rig on my backyard pool for next spring maybe... Honey! Would you mind? .... mmmhhh... maybe not!

Cheers!
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Old 09-13-2014, 09:18 AM
  #22  
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Hi Ben IMHO having alternating rotating props will interfere with a Vortex thats being created by the props, imagine the props under water rotating in different directions and being overlapped, thats just the way i see it in my minds eye, give it a try both ways, it wont cost much, just a few extra props to buy
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Old 09-13-2014, 09:34 AM
  #23  
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Here is some interesting reading on 4 alternating counter rotating props

http://diydrones.com/forum/topics/ov...1360970&page=3


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Old 09-13-2014, 10:08 AM
  #24  
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You should be able to use 4" props, just use a quite high KV motor to spin them fast. And you don't need 1:1 thrust:weight ratio... As you correctly pointed out, this is a scale model, the ability to climb vertically is not required
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Old 09-13-2014, 09:20 PM
  #25  
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Default 5 x3 vs 4x4, no overlap

Thank you Chellie and JetPlaneFlyer.

I will try to avoid overlap then...

I am considering the Turnigy SK3 2118-2250 (~2340Kv) or an equivalent.
It is only 17 grams and the price is reasonnable.

The 5x3 prop without overlap doesn't look good with the 64 inches wingspan (see picture.. I cheated the position of the body..)

A 4x4 prop gives me 3.5 pounds of trust at 10.8 V / 7x8 Amps.
It looks right, although I need to cheat just a little bit on the motor position (see picture - not really noticeable).

A 4.5x3 prop gives me 4.4 pounds of trust at 10.8 V / 6.7x8 Amps.
But there will be a small overlap, or else I have to displace the motor position, which I would like to avoid.

I have a question: what would be my maximum weight with a 3.5 pound of trust for it to take off and fly?

Cheers!
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