Spacewalker half scale 168" electric

[Mike Booth]

Andy, thats all good, and I for one always look for the positive in any situation.
I am sure you have all the right qualifications.
I have worked in composite design , stressing and engineering in motoracing.
Standards are what it is all about.
One of several good things about your project is the resourcing of some hard to find items which are clearly bulletproof.
What we are looking for in the LMA is a upward curve on the 'how to' graph so we can all learn from new projects.
When you get allocated an inspector, thats it really.
Its a bit like building a house , a continuous liason with the inspector to improve the general layout and raise standards.
Its only my opinion, but given my own working experience, I would say Phil is in the top league of commecial model makers in the country.
Any advice will only be there to maintain or improve a standard.
We are'nt here to retard model aviation, just carry out the requirements laid down by the CAA.
Think how good it would be if your 1/2 scale ends up setting the standard.
The one thing to bear in mind all the time is that at your scale the Spacewalker is no longer a model.
It might even be bigger than a real Cri Cri.
With every connection, link, preparation and display, one has to think like the full size.
Best of luck, I will look forward to seeing the paint go on when the time is right.

Regards M.

[Andy Boylett]

Some more building......

I have altered the design of the tailwheel a little...

IMG_2864.JPG (37 KiB) Viewed 13176 times

I was unhappy with the pivot bolt and have upped it in size now. It is now a 5mm bolt running through a thinwall ss tube set into the carbon/glass composite.

However, I am still not sure it is ok. What sort of thump do you think this could get? This really is an unknown to me. Another way of thinking about this maybe to ask what thickness of aluminium have people been able to bend on a tail-wheel? Any thoughts?

Here are some more pictures...

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Will that ally bracket be strong enough?

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IMG_2866.JPG (29.41 KiB) Viewed 13176 times

ps, the wheel is temporary as I have not made a scale one yet

[Dave Collis 2296]

Andy:
I wish I knew how to post a photo on here, however.....

On my 1/2 scale S/Walker, the hard points for the tail braces are lengths of 1/2" dia. hardwood dowel, let into the tail surface, full thickness. There is a hole in the centre, to which I used "Du-Bro" metal straps, bent to the req'd angle and bolted with a 4/40 bolt and L/nut. Tha cable I used is sold as "Down-rigger"stranded fishing cable, stainless, 150lb. breaking strength. The cable is terminated and crimped, (using crimps for that particular cable), at a "Sullivan" 4/40 eye-bolt (with the end of the "eye" soldered shut. The eye bolt is good because it is a round smooth surface as opposed to a sharp-edged hole in a piece of flat stock. The eye-bolt screws into a "Du-Bro forked clevis, which in turn is through-bolted to the steel strap.

My plane weighs 70lbs, has been flying since 2004, and once the "initial stretch" of the cable was adjusted out, the set-up has remained tight and completely trouble free...no re-adjustment required. Having said that, the plane is flown in a very conservative manner, has never been "thrown around" and never will be.

All I can offer is," it's worked well for me", Phil, as your inspector, has, of course, the final say as to what he wants to see.

Just a friendly comment. Looking forward to seeing the S/Walker in the air...video, hopefully

Cheers,
Dave.

[Andy Boylett]

Andy:
I wish I knew how to post a photo on here, however.....
On my 1/2 scale S/Walker, the hard points for the tail braces are lengths of 1/2" dia. hardwood dowel, let into the tail surface, full thickness. There is a hole in the centre, to which I used "Du-Bro" metal straps, bent to the req'd angle and bolted with a 4/40 bolt and L/nut. Tha cable I used is sold as "Down-rigger"stranded fishing cable, stainless, 150lb. breaking strength. The cable is terminated and crimped, (using crimps for that particular cable), at a "Sullivan" 4/40 eye-bolt (with the end of the "eye" soldered shut. The eye bolt is good because it is a round smooth surface as opposed to a sharp-edged hole in a piece of flat stock. The eye-bolt screws into a "Du-Bro forked clevis, which in turn is through-bolted to the steel strap.
Cheers,
Dave.

Thanks again Dave. Interesting to see you use a cable that is very close to the one I propose. Yours is 68kg and the one I have looked at is 54kg.
Cheers, Andy

[Tony Collins 1073]

Dave, If you care to E-mail your pics to me I'll happily edit and post them for you.

hangar4ATtalktalk.net

Tony.

[Dave Collis 2296]

Thanks, Tony.

I am able to download my photos to my "reply". but they are too big..(way too big!!) If I knew how to reduce them to the req'd 0x0x600 pixels, I should be able to post them. The photos are in my own picture file.

Cheers,
Dave.

(I will try to send you a picture for the Spacewalker thread.)

[Tony Collins 1073]

Hi Dave,

Have answered your PM. I have posted a couple of times on how to put your piccys on the forum but they seem to get lost with time ,so here is guidance from a previous post.

Max Dimensions for our forum are 600 wide and 400 high. Good luck

http://www.imageoptimizer.net/Pages/Home.aspx

PS To Dave Parry. Dave, should I start a new thread on posting images and you make it a sticky as so many guys seem to need help on the subject?

[Dave Parry]

Hi Dave,

Have answered your PM. I have posted a couple of times on how to put your piccys on the forum but they seem to get lost with time ,so here is guidance from a previous post.

Max Dimensions for our forum are 600 wide and 400 high. Good luck

http://www.imageoptimizer.net/Pages/Home.aspx

PS To Dave Parry. Dave, should I start a new thread on posting images and you make it a sticky as so many guys seem to need help on the subject?

sounds good to me Tony

[Andy Boylett]

Not very well at present and my back is stopping me get around again All I managed to do today was test out charging of my receiver batteries in situ. I didn't bothe to use long extension wires, just sat the charger inside the fus....

IMG_2853.JPG (56.06 KiB) Viewed 13285 times

This charger can charge all 4 of the receiver LiPos at the same time. The LiPos are fixed in situ inside the fireproof bag to the left of the photo.

[Andy Boylett]

I have just calculated the load on the stabiliser if the plane were travelling at 80mph and suddenly turned through 90degrees in a downward dive, putting the wings and the stab flat on to the air flow at 80mph. For an instant this would likely be the maximum load the surfaces could ever see. I have not used the servo force program, I have done this from scratch.

Using this scenario:
The load on each half of the stab would be 25.362 Kg.........which is less than the approximate method I used earlier.

The wings of course would likely snap off as the load on each would be 200kg

If I reduce the speed to 40mph:
Stab load is 6.3Kg
Wing load is 51Kg, which is survivable!

The drastic difference is because the air pressure force is proportional to Velocity squared.

[Tony Collins 1073]

This picture posted on behalf of Dave Collis.

Waco Build 041

Waco Build 041.jpg (133.42 KiB) Viewed 13254 times

Andy, here is a picture of my t/brace on my 1/2 S/Walker.

Dave.

[Andy Boylett]

This picture posted on behalf of Dave Collis.

Waco Build 041

Waco Build 041.jpg

Andy, here is a picture of my t/brace on my 1/2 S/Walker.

Dave.

Thanks Tony,
Dave, those look like Dubro fittings? I used a couple of them with solder ends under my stab for the Bradford show!
And the 'ring' ends are just like the ones I have been showing Phil, as the ones I like. I like them because they drastically reduce the strain and pressure point on rigging wires that you get on the turnbuckle fittings that have machined ends - those only have a very small radius on the edge of the hole.
Nice to see the picture,
Cheers, Andy

[Andy Boylett]

This picture posted on behalf of Dave Collis.

Waco Build 041

Waco Build 041.jpg

Andy, here is a picture of my t/brace on my 1/2 S/Walker.

Dave.

Dave,
I think the threads in those fittings are 4/40, is that right? If so, do you know where I could source the eyes to suit?
Cheers, Andy

[Dave Collis 2296]

Sullivan products have the eye bolts in both 2/56 and 4/40 size. Any decent hobby shop should be able to supply. If you can't obtain them, let me know and I can send some over to you.

Cheers,
Dave.

[Andy Boylett]

Stabiliser loadings

Calculation of stab loadings based on calculated elevator torque:

Elevator torque: Using shareware calculator from Phil
Assuming 100mph air speed
The calculated elevator torque is 20kg/cm

Elevator pressure loading – what is the load pressing down on the elevator?
Torque is 20kg/cm
Elevator chord is 12cm
Shape approximately gives centre of pressure at the centre of the chord
Therefore elevator Load is 20/6 = 3.3kg
ie a 3.3kg load at a distance of 6cm gives a torque of 20kg/cm

Stab loadings Assume all direct load from the elevator is taken at stab trailing edge
ie. no transfer of load to stab leading edge (assume structure is flimsy)
Load on stab trailing edge is 3.3kg
This load is taken by the fus, the strength of the stab and the wire support
Assume strength of stab is zero, therefore load split between fus and wire.
Fus will take 40% due to location of wire
Therefore load at wire point is 3.3*0.6= 1.98Kg
Wire is at 35deg, therefore tension is 1.98*1/sin35 = 3.45Kg

The rear stab wire Wire proposed has 54kg breaking strain, 1mm diameter (d).
Assume wire ends are through eyelets with a minimum radius of 3d, 3mm
(note, a tighter radius will considerably increase the stress on the wire
and decrease its strength ie a chamfer is a very small radius of often less
than 0.5mm)
Apply full size aircraft safety factor of 2 for an eyelet
Apply wire manufacturers recommended safety factor of 2
Required wire strength is 2*2*3.45 = 13.8Kg

The front stab wire The calc above assumed no load transferred from the elevator
Therefore the only load is due to aerofoil effect, when elevator is deflected.

This aerofoil effect is because, say as the elevator moves down, the rear edge of the stab is driven upwards by the load from the elevator, but the leading edge of the stab does not drive upwards as quickly because it is only being moved by the fus, thus causing a twist in the surface. This ‘twist’ causes an aerofoil effect loading the leading edge of the stab in a downwards direction in this case.

The stab on this plane is both flat and extremely stiff. Any difference in movement between the leading edge and the trailing edge would likely be in tenths of a millimetre, with the resultant load miniscule. The sums are very complicated and require measurement of the stiffness of the surface and its second moment of area. There is no point doing this as it is too small to be an issue.

I have not had time to check these sums so they may alter when I do ...but at the moment I think it shows proposed wire is "well strong enough".

[stewart clifford]

hey man just too much maths just build the plane, fly it be happy.

[Dave Parry]

hey man just too much maths just build the plane, fly it be happy.

Well said, that man.

[Denis Brown]

Seagull do an almost ready to fly one

[stuart knowles 1611]

Ok, things have got a bit warm, I hope that those involved see that it is all being done with the best intentions, and speaking for I, it is good to hear the detail of why things must be. Challenge and debate is all part of hammering out the best ways forward.

I saw this model at Bradford and have watched and learned from Phil for a long time on other forums. I am full of admiration for both of them.

I look forward to seeing this build continue.
stu knowles 1611

[Andy Boylett]

Back to finishing off the fus now.....

I have modifed the wing centre section such that there is a ply plate extending forward, that can take the fron undercarriage mounts. This meanas that I can now remove the centre section without removing the undercarriage...

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You can see under the ply plate it is tied back to the main centre section wing ribs.

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Now, having done that mod I have completed the fus underside, just like its full size counterpart. Here is the framework in place ready for sheeting.

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