Info needed to scratch build an alloy plane

[Timm427]

I am looking at scratch building a plane that I designed. I originally designed it as a plastic composite but now considering a pop rivet alloy clad job.

 

Can anyone tell me a good place to research alloy A/C building techniques and typical materials used etc.

 

I started looking into aircraft alum alloys and I thought there would be a couple, but with the variations of coating and tempering there are dozens.

 

See initial concept drawing below - some of the lines have since been straightened to allow for it to be built in sheet alloy and the wing position moved backwards

 

 

 

[vk3auu]

Unless you have had considerable experience building, I would seriously suggest that scratch building a self designed aeroplane will be fraught with many difficulties. If you want to build something from scratch, you would be better off spending $500 on a set of plans for something like the Zenair CH650 which has just been released.

 

It sounds from your post that you don't have the necessary expertise. If I am wrong, forgive me.

 

Over to the group.

 

David

 

 

[Timm427]

David

 

Thanks David, I have already considered building something like a Sonex and haven't ruled that out. And as mentioned in the forum talking about AeroVees, I still haven't ruled out building a STOL like a Savannah although I have that 100knot figure I would like to achieve.

 

My real interest though is to design and build something myself and not really interested in scratch building an existing design. You are right in saying I don't have the expertise to commence this project hence the questions I was asking. Since posting this topic I have come across a designer by the name of Bill Whitney and have sought some advice there.

 

In the meanwhile I am hoping to gain as much knowledge as possible, so if you have any expertise in A/C construction especially alloy's I'd love to hear it.

 

Actually I think I already picked up something from you (ie only use rivets in shear applications for high stress / critical areas such as brackets supporting control surfaces)

 

Regards Tim

 

 

[Guest gosk8ing]

Also remember that rivets are designed to shear before structural failure. ie. you'll have to find out the shear loading of both the rivet and sheetmetal and use the correct rivet so the shear loading for the rivet is a little bit less than the sheetmetal.

 

Heres some other info on rivets. All this info is for solid rivets. You probably already know this information, but ill say it anyway.

 

The only rivets you would be using is AD and maybe A.

 

The diameter is normally 3 times the thickness of the thickest sheet being joined.

 

Edge distance should be min 2D, max 4D.

 

Pitch between rivets in a row should be min 3D, max 12D.

 

Gauge (Transverse pitch) distance between rows in a multi-row layout is usally 75% pitch, min 2 1/2D.

 

One thing you have to watch out for are stress raisers. Also try and maintain load path continuity.

 

By the way, I dont have any scratch building experience.

 

I cant think of any books, but there should be plenty out there. Im just getting the info of some notes I have.

 

 

[Timm427]

Thanks Gosk8ing and I didn't know any of that (except for rivet type) I take it all distances are measured from the centers and that spacing along the joint would be determined by the direction and magnitude of the maximum forces (+ safety factor) to be applied.

 

I know it is possible to design the rivet layout based on gut feel and others examples, but it would be good to know the formula for calculating this as well.

 

Regards Tim

 

 

[Guest gosk8ing]

Im not to sure about the safety factors. I know when they tested a B777 wing, it broke at 154%.

 

https://www.youtube.com/watch?v=pe9PVaFGl3o"

 

They have to achieve 150% by the regs.

 

Also when they tested the A380 wing, it failed below 150% so airbus had to put a big doubler somewhere near the wing root on the first 10 or so aircraft so it would achieve 150%+. Then they had to go back to the drawing board to fix it.

 

Australian standard design loads are as follows:(CAO 101)

 

Normal: +3.8g -1.5g

 

Utility: +4.4g -1.75g

 

Aerobatic : +6g -3g

 

I would assume you would design your plane for those stress +150%.

 

SO..

 

Normal: +5.7g -2.25g

 

Utility: +6.6g -2.6g

 

Aerobatic : +9g -4.5g

 

If I was designing my own plane I would build it to aerobatic design loads even if its not an aerobatic plane.

 

But thats just me...I like it a bit stronger.

 

Also because I wouldnt want to kill myself in my own designed plane, I would seriously think about breaking apart my first plane to see how strong it is.

 

 

[Guest gosk8ing]

I would consider redesigning the wing so the chord and thickness is the same all the way along. You will lose some performance but manufacturing will be a fair bit easier.

 

Say you have 10 ribs for one wing. Your going to have to make 20 form blocks (10 nose ribs and 10 main ribs). If the wing had the same chord and thickness, you only need 2 form blocks.

 

But if you dont mind making that many form blocks, go with the tapered wing. Looks and performance is better.

 

Im not to sure because I havent done it before, but I think forming the leading edge on a tapered thickness wing will add some difficulty.

 

 

[old man emu]

Have you considered making a scale model of your design to see if there are any aerodynamic faults i your design?

 

Old Man Emu

 

 

[Yenn]

Timm427.

 

If the leading edge is straight there should be no problem bending it, and a lot of people say that the time to make forms is a small price to pay for the wing taper.

 

As far as making a scale model to see if there are any aerodynamic faults, it may not work, as the Reynolds number would be very different.

 

Can you give us some more info about the design, such as dimensions, weight, speed and engine?

 

 

[Timm427]

Gosk8ing

 

As you mentioned I did consider redesigning to a straight wing but thought that would detract as you say from the performance and the look. I also assume that tapering the wing relieves some stress on the spar(s) at the wing root as the mean distance of lift along the length of the wing moves closer to the fuse i.e reduced leverage (I have just assumed this so far and not done any calcs)

 

The other thing I have been investigating (and I have a mate who has done this) is to build a CNC Router for Making Form blocks and also machining some of the alloy parts (I know you can use woodworking tools on normal aluminium not sure about 2024 and 6061). This would mean that making the various form blocks for the different size ribs would be a matter of outputting the Autocad file to the CNC machine (there is a step in between but I won’t bore you with that)

 

For making form blocks that taper in the Z direction I would CNC these at 5mm deep per pass, stepping out with each one to allow for the taper and clean the mould with a file (if you can picture that)

 

Hopefully the leading edge can be accurately designed in cad as it is a consequence of the distance top of spar to bottom at the root and tip (apex of the curve at the ends of the leading edge, when drawn flat, being the forward most point of the leading edge) joind by straight lines along the wing length.

 

Regards Tim

 

 

[Timm427]

Have you considered making a scale model of your design to see if there are any aerodynamic faults i your design?Old Man Emu

Yes Old Man Emu I plan on building a 1/4 scale flying model to test the basic aerodynamic layout and also get an idea of the "look" of the finished design.

 

I know that it is not a terribly accurate way to test the final design because (as Yenn has pointed out) Reynolds numbers along with air density, weight(mass) and power do not scale accurately. However if the design has an inherent flaw hopefully it would start to show.

 

Regards Tim

 

 

[Timm427]

Can you give us some more info about the design, such as dimensions, weight, speed and engine?

Yenn

 

My wish list

 

cruise Max 120 knots

 

Vne 140-150

 

Stall Vso 42-45 Vse1 47-49

 

Power 80H/P to 100H/P (80 preferred for endurance fuel consumption/weight)

 

Gs +5 -3 (may have to reduce for weight)

 

Controls

 

Aileron Elevator Control -Dual Stick

 

Brakes Stick mounted brake levers (toe brakes would be nice but add complexity and weight)

 

Control System Push Pull control cables (as used in Jabiru)

 

Electric Flaps

 

Trims - (My concept {havn't seen B4}) Electric Trims on rudder elevator and aileron using "1/4 scale size" model servos mounted in the control surface, with optional interface for autopilot and levelers etc.

 

Flap control - Electric

 

Undercarrige - Rear individual legs clamped to steel subframe within the fuse. Nose - rubber dampend suspension direct connected to pedals

 

Spar - Sonex/Soneri type spar system held within the fuse by a chrome molly subframe that supports the wing rear undercarriage and possibly forward bars that bolt through the firewall to the engine mount. (last item depends on weight and design issues)

 

Dimensions to come

 

 

[Timm427]

Dimensions (metric) as Drawn

 

Fuse.

 

Length - 6380

 

Cockpit width 1075 (allowing for 20mm thick top rail on fuse side, should be about 1100 at shoulder)

 

Cockpit height 1170 (Floor to canopy)

 

Wing

 

Airfoil - Not selected NACA 64-415?

 

Wing Span - 8460

 

Root Chord - 1447

 

Tip Cord - 1095

 

Mean Chord - 1266

 

Wing Length (Root - Tip) 3776

 

Wing Area - 9.56

 

Aspect Ratio - 6.68

 

Tail

 

Ground to tail height - 2222

 

Horizontal Stab. width - 3118

 

Weight to be calculated

 

 

[Yenn]

Tim427.

 

I had a quick look at your wish list and it looks OK.

 

I havn't looked at the 64-415 wing details.

 

It looks as if you will need to go to the 100hp engine to achieve 120kts, That is according to Raymers info. Weight / hp = 215 multiplied by (V (fps) to the power of .61) which gives about 11.59 lbs/hp.

 

If the above is correct you will then have a weight of about 1159 lbs.

 

Working back from your wing area and a stall speed of 45kts or 76f.p.s. you will need a Coefficient of lift of 1.4 at stall, which I would think is achievable.I have converted your metric figures to imperial, because that is what the Yanky textbooks use, not because I like imperial.

 

Keep up the work.

 

 

[Timm427]

Thanks for the info Yen. Work on this project is slow at present because business is getting busy. I'll have to work on my priorities. I acquired Bill Whitney's DVDs on AC design and watch all of them the day they arrived. Now I have to sit down with a notebook and pen and watch them again.

 

I picked up a lot of good "rules of thumb" watching these DVD's and with these in mind have been looking at existing designs to see how they stand up. It is interesting how many models have ignored good design principles, like taking a 60deg angle from the leading and trailing edge of the horizontal stab and verifying that there is still enough rudder exposed for spin recovery. I will be making some design changes based on these videos.