Another impossible dream. Maybe not.

[Deskpilot]

You can also have each engine pointing outwards, a bit. At the correct angle there will be no assymetric effect with a big fin, You need contra rotating engines. Nev

Hi Nev. Interesting theory. Know of any designs that have used the concept? Can't say that I've ever heard of it before.

 

 

[Deskpilot]

Following Arthur's advice, here's my new tail-plane. No fillets, brackets or control horns are shown for clarity. The gap between the fin vertical and the rudder will be more or less completely covered with alloy strips riveted to the vertical post.

 

 

 

[Deskpilot]

Am I dreaming or is this a real possibility?

 

 

 

 

[Pilot Pete]

The view from the pilots seat would be awsome. Prop position looks a lot safer. Looks to be quite a do-able project.

 

 

[Deskpilot]

Having pondered the problem of wing strength and construction method (wire braces v cantilevered), I'm playing with main spar design. Obviously the spars will have to be light as there are 4 of them required.

 

 

My idea is that the opposite wing will have the 'C' section facing the opposite way so that the 2 webs can be bolted together, back to back so to speak. The top and bottom caps will have cut outs to allow this to happen. I want the ribs to be recessed into the caps but level with the surface so that the skin can be firmly attached in an 'unscalloped' fashion. I would also like to have some form of support in the rib nose area, again to prevent scalloped L.E.'s.

 

Note, I have decided to go for the more normal flat bottomed wing profile for ease of construction. To me it looks and sounds good but I really need some knowledgeable guidance before I go any further.

 

 

[pylon500]

This is starting to look more 'doable' as we go..

 

With a small enough span, simple cantilever spars should work.

 

The aluminium tubes for ribs will work, although there is a bit of excess material there, but at this scale, probably OK.

 

You will need to do a bit of bracing within to hold their shape.

 

For your leading edge I would just use thin alloy, 0.016" 6061-T6 should do, but do away with the wood packers and just fold a back lip down and rivet to the spar.

 

This will give a sort of 'D' tube, albeit with gaps at the ribs.

 

The folded spar can stay reasonably thin, say about 0.032", just add laminations of angles from the centre outwards, probably more 0.032" about 1"x1", the first going two thirds the length, the second going one third, and maybe one just going a quarter of the spar length.

 

All riveted to the web section.

 

The back to back idea is used a lot, but remember, the joining of the two spars doesn't need to be done through the caps.

 

A couple of good verticals, say 1" square tube with at least 1/8"walls bolted to the caps (inside the 'C' at the join point) and having just one bolt, say 5/16th 'Ø, or 3/8th if your nervous, through the middle of the square tubes.

 

Wish I was better, and quicker, with a graphics package:smash pc:

 

Your trailing edge need only be 0.016", probably around 2" wide with a small lip top and bottom.

 

I like the tailwheel arrangement drawings but think you may need to brace the square shape joining the four trailing edges.

 

The shape is also starting to look a little familiar, have a look at;

 

 

And check the articles here;

 

http://en.wikipedia.org/wiki/PDQ_Aircraft_Products_PDQ-2

 

And,

 

http://forums.bmaa.org/default.aspx?f=17&m=93273

 

Arthur.

 

 

[Deskpilot]

Thanks for reply and help Arthur, only problem is, it's opened a whole lot more queries from me. I hope you can find the time and patience to answer them for me.

 

This is starting to look more 'doable' as we go..With a small enough span, simple cantilever spars should work.

The aluminium tubes for ribs will work, although there is a bit of excess material there, but at this scale, probably OK. How so? Also, I assume that the spar will have to fill the rib top to bottom, which means that there must be a flat section on the upper surface?

 

You will need to do a bit of bracing within to hold their shape. Yes, just didn't want to clutter the image. Would simple verticals suffice or do I have to fiddle with angles pieces?

 

For your leading edge I would just use thin alloy, 0.016" 6061-T6 should do, but do away with the wood packers and just fold a back lip down and rivet to the spar. This will give a sort of 'D' tube, albeit with gaps at the ribs. OK, I understand what you're saying but I was thinking of fabric skins. Ally, not only can it get dented easily, is a lot more expensive, isn't it?

 

The folded spar can stay reasonably thin, say about 0.032", GULP, you sure? That's only 0.8mm. I was thinking more in terms of 2.5/3mm just add laminations of angles from the centre outwards, probably more 0.032" about 1"x1", the first going two thirds the length, the second going one third, and maybe one just going a quarter of the spar length. Would lightening/stiffening holes still be required?

 

All riveted to the web section. No rivets on the outward arm?(perpendicular to web).

 

The back to back idea is used a lot, but remember, the joining of the two spars doesn't need to be done through the caps.

 

A couple of good verticals, say 1" square tube with at least 1/8"walls bolted to the caps (inside the 'C' at the join point) and having just one bolt, say 5/16th 'Ø, or 3/8th if your nervous, through the middle of the square tubes. Sorry, don't understand this at all.

 

Wish I was better, and quicker, with a graphics package:smash pc: I'll accept a clear pencil sketch mate..............gotta pencil? lol

 

Your trailing edge need only be 0.016", probably around 2" wide with a small lip top and bottom.

 

I like the tail wheel arrangement drawings but think you may need to brace the square shape joining the four trailing edges. Still a lot of work in this area Arthur. All in good time.

 

The shape is also starting to look a little familiar, have a look at;

 

[ATTACH=full]17544[/ATTACH]

 

And check the articles here;

 

http://en.wikipedia.org/wiki/PDQ_Aircraft_Products_PDQ-2

 

And,

 

http://forums.bmaa.org/default.aspx?f=17&m=93273

 

Arthur.

I'm not aiming at a minimalist plane, more on the line of something that many semi skilled builders could manage to complete and fly safely. At the same time, something that is not just a clone of everything else out there.

 

So far, I have used 1, 1.5 and 2inch tubes in the design. This has all been pure guess work and mainly for convenience. What sort of sizes should I be looking at and what wall thicknesses.

 

Thanks again Arthur. I'm sure your insight and knowledge is also beneficial to other forum members.

 

 

[Deskpilot]

As it's been cold and miserable outside, I've spent a couple of hours interpreting Arthur's suggestions as I understand them. No rivets are shown but I did do some research on sizes, spacings and patterns. For those who have never looked into it, it a bloddy big subject.

 

Anyway, peruse my images, click to expand. All comments welcome, especially from you Arthur.

 

 

Note that I decided to take the skin down onto the web and not the cap as Arthur suggested. One less bend and, when 2 halves are bolted together, the fold lines will align with each other. To take them down to the cap would create a difference off about 1 inch side to side. As I didn't understand the bolting of vertical 1inch square tubes to the cap, I've left that for an explanation. It makes sense to me only if the tubes are horizontal.

 

 

 

 

 

 

 

[pylon500]

G'Day Doug,

 

Just looked at you latest renderings and where you have understood me, you have depicted well.

 

Now for the bits I obviously didn't describe well enough;

 

In the first picture, the 2' overlap is correct (this gives you a 22' span), the depiction of the laminated angles is incorrect in two ways, the longest angle (light green) should be around two thirds of the length of the C spar (8'), the second angle (dark green) should be around one third the length (4~5'), and the smallest angle (blue/grey) should probably be around one quarter of the spar length (3').

 

In both the first and second picture you should depict two sets of angle doublers.

 

The ones shown should be sitting in the bottom of the channel, and a second set should be up inside the top of the channel.

 

In hindsight (and looking at your graphics) I can see it would be easier to rivet these angles to the C channel spar through the top and bottom flanges (caps) to avoid confusion when riveting the wrapped leading edge flanges onto the vertical (web) part of the spar,as depicted in picture 4.

 

You also need to do these drawings for the other wing, showing the C spar the other way so they overlap.

 

This may show up some other possible problems.......

 

The folded trailing edge is pretty much as I described, the details would be in the diameter of the rib tubes to dictate the width of the trailing edge.

 

The diameter of the rib tubes then needs to be decided via the compromise of how much unsupported rib can be carried, versus the amount of bracing required, versus the weight penalty taken by using bigger tubes?

 

Smaller diameter tubes will need more bracing (ie 1/4"Ø) whereas larger diameter (3/8"Ø)would need less, but would be more bulky and heavier?

 

If building a constant chord wing, then the ribs are all the same, why not knock them up out of sheet alloy as per normal procedure?

 

Have a look at my 'mass produced' ribs in my Stearman project;

 

https://picasaweb.google.com/113292981019876413104/MurphyRenegadeStearmanProject

 

They are not really that hard to do.

 

Back to the spar web, yes, use lightening holes, flanged as depicted.

 

They could be a little closer together than drawn above (what pitch did you use?)

 

These would run from the tip to about the one third from the centre, try to avoid having a hole line up with the end of a doubler angle.

 

OK, the wing joining bit...

 

Forget about the 1" square tubes, I've had a netter idea..

 

You have the two spars overlapping back to back for about 2' in the middle, you need to figure out how wide the fuselage is at this point and determine what the wing is going to attach to on the fuse.

 

You will probably need to double up the vertical tubes behind the seat to four, so you end up with tubes in front of, and behind the two spars.

 

These tubes need to go up to about the horizontal centre line of the spars.

 

This is where the spars and the fuse all join, via two bolts, one through each set of vertical fuse tubes and the back to back spars between them.

 

These bolts should NOT go through the spar web doubler angles, they should go through the web area at probably about one third of the spar depth, from the bottom.

 

Because this is just two pieces of spar web (trust me 0.032" spar webs should be plenty) it needs to be reinforced to give a bearing surface for the bolts, heres how...

 

Between the spar angles, we need to build up some vertical plates about 2" wide (three lots of the same thickness as the angles, 0.032"x3) PLUS, two more plates that are long enough to fit in between the caps.

 

Riveted with two rows of rivets, and room for the actual wing joining bolt.

 

This got really hard to explain, so I've had to spend an hour or so knocking up this drawing;

 

 

The next thing I notice is that we are going to need a rear spar, but as it's getting late, I'll come back to that later...

 

Arthur.

 

 

[Old Koreelah]

Hello Deskpilot, have you considered using klegecell where stiffening is required? Very light and strong, easy to shape.

 

 

[Louis Moore]

Would an approach like this not work?

 

http://www.airdromeaeroplanes.com/images/fantasy-01a.JPG

 

 

[Deskpilot]

Would an approach like this not work?http://www.airdromeaeroplanes.com/images/fantasy-01a.JPG

Not for what I'm after. Waaay too many fly wires = lotsa drag

 

Half skinned wing = very slow flight.

 

Don't like the idea of an engine over my head.

 

My forward view will be far better.

 

 

[Deskpilot]

Hello Deskpilot, have you considered using klegecell where stiffening is required? Very light and strong, easy to shape.

Hi OK, My original idea was to use very cheap ally tube for the ribs because I can get it. Also, my thinking was that, with the right formers, it would be dead easy to get them all the same. I realise the same applies to foam but at the cost of a lots of mess and debris.

 

As for using foam to shape the 'D' cell, doable but again, bloddy messy.

 

 

[Louis Moore]

Deskpilot, I did not mean that exact design outlay, just the wing spar set up.

 

 

[Old Koreelah]

Hi OK, My original idea was to use very cheap ally tube for the ribs because I can get it. Also, my thinking was that, with the right formers, it would be dead easy to get them all the same. I realise the same applies to foam but at the cost of a lots of mess and debris.As for using foam to shape the 'D' cell, doable but again, bloddy messy.

What's messy about cutting A D-section profile out of a klegecell sheet?

 

 

[Deskpilot]

What's messy about cutting A D-section profile out of a klegecell sheet?

Had to look it up yesterday OK and probably came to the wrong conclusion that cutting and sanding any sort of foam would be messy. If accurately hot-wired, I guess the mess is limited. BTW, were you thinking just rib noses or a full, solid D section?

 

 

[Old Koreelah]

Had to look it up yesterday OK and probably came to the wrong conclusion that cutting and sanding any sort of foam would be messy. If accurately hot-wired, I guess the mess is limited. BTW, were you thinking just rib noses or a full, solid D section?

Whatever rigid structure you like. it's a PVC foam sheet and can be bent and formed after gentle heating to 60C.

 

A hot wire won't cut it but normal knives and saws will. It's usually used as part of a fibreglass laminate, but I found it excellent for giving plywood structures great rigidity. I plan to redesign my wing leading edge with klegecell Profiles, then bend and glue plywood over them.

 

 

[Deskpilot]

I've been playing with ways to mount my wings and found that I really ought the set the airfoil once and for all. Now I know that this is a slightly unconventional configuration, but what profile would you use? I don't mind if it's flat or convex on the underside, but not interested in concave. I'd like to keep the thickness between 10 and 12%if possible to reduce drag.

 

Just a thought, is it possible to have a different profile on the lower wing to the upper and if so, what would the benefits be? Review my configuration before answering, please.

 

 

[cscotthendry]

There will also be a simple brake block that can be pressed down onto the front wheel tyre, not meant for emergencies but might prevent one from ramming a hangar wall.

Doug:

 

It might add a bit of weight, but brakes on the mains rather than the nosewheel would be way safer. For a start you have more traction on the ground and secondly, the brake drag force will be behind the CofG which will help keep you straight under braking. Billy cart steering with a rudder will be a bit confusing during the transition from flying to landing. If you don't cross the rudder cables, you'll have unconventional steering in the air, but at least it will be consistent with the ground handling.

 

Re wing profile: A concave bottom will only add drag. A flat bottom would probably be best. If you have a convex bottom, there will be some amount of negative lift generated with it's attendant drag. Unless you're planning aerobatics, that negative lift will do nothing for you.

 

 

[Deskpilot]

Hi Scott

 

Doug:It might add a bit of weight, but brakes on the mains rather than the nosewheel would be way safer. For a start you have more traction on the ground and secondly, the brake drag force will be behind the CofG which will help keep you straight under braking. Billy cart steering with a rudder will be a bit confusing during the transition from flying to landing. If you don't cross the rudder cables, you'll have unconventional steering in the air, but at least it will be consistent with the ground handling.

See my post #28, gone to tail-dragger, much easier and lighter. No brakes as yet.

 

Re wing profile: A concave bottom will only add drag. A flat bottom would probably be best. If you have a convex bottom, there will be some amount of negative lift generated with it's attendant drag. Unless you're planning aerobatics, that negative lift will do nothing for you.

 

Thanks for that insight. Like I said, concave was definitely out of the question anyway.

[cscotthendry]

...

See my post #28 ...

 

...

Oops, My Bad. That's what I get for not reading all the way through before posting.

 

 

[Deskpilot]

Found a nice Rotax 912s for my plane. Not real, unfortunately, but fits my model quite nicely.

 

 

 

Still modifying things. I've decided to lower my wings so the upper wing support has to be reworked. New undercarriage but no springs, doughnuts, bungies shown so far. One wheel will be an inch or so in front of the other but I don't think that will be a problem. Might also have to put a spreader bar in there as well.

 

 

[Deskpilot]

As per usual, I think I've over done it a bit with my design. However, FWIW, here's my idea for towing to the airfield and hangar storage space saving.

 

Repeat on the other side then remove lower wing. Folded wing could lie flat but the second one would damage the first so.............

 

On the trailer, a tail enf support under the rear end to stop any tendency to fly off. Staps obviously hold the wings in place.

 

And in the Hangar....

 

 

 

Perhaps I should concentrate on making this thing lighter.

 

Comments always welcome.