Hi Dave,
My current wings (Midrex) are 10% at the root and 8% at the tip ,with chords of 345mm at the root and 190mm at the tip. (bottom wing - top one is slightly smaller)
I'm increasing the root chord to 375mm and reducing the tip to 165mm with thickness at 10.5% and 7.5% respectively. I'm going from a straight TE to a 50mm rear sweep of the tips. Span increasing from 1.75m to 1.775m. I may put some fencing on this ,but if I do it will be mostly on top of the top wing and on the bottom of the bottom wing - this will mostly be to enhance stability on spin entries by preventing top side span-wise flow on the high wing. I may develop the strut mounts into fences also - they lend themselves to this development I think - but this depends on weight.
Generally, while trying to get lighter wings, I'm trying to enhance yaw stability and to 'centre' the drag and mass some more. This should also be a little more sprightly while being better in the wind. I started out ,in my thinking, with an elliptical wing but there is no rib cutting service here. I could have sent off for them but was afriad of where the weight would go and time and money are limited.
Anyway I was going to do this for performance but I'm not too keen on the look.
I decided on a straight taper and this is something that I can do myself in foam. The increased taper, once done properly, should help with overall stiffness and in particular give stiffer tips.
If there is any movement in the tips ,due to play or flex, the model will misbehave in pulls,pushes and snaps with wind complicating this further. I have been there !!
Thin sections work well once they are not too highly loaded and the loading is way down on these bipes.

Brian

Bryan, from my experience increase the wing thickness specially on the tip, 7,5% is too little.

TUNY

Tuny,
Why ?

Brian

Thanks Brian.

Dave

Thinner airfoils require more speed to work properly and stall easily, not a good quality on the tips

Tuny,
Ok thanks.

Brian

Brian, BTW, I tend to agree with TUNY on wing section at the tips. Not necessarily for the same reasons as TUNY. Tip stall is likely a minor concern on these very lightly loaded bipes.

In my latest design, Delta, I went to some extreme in reducing tip thickness percent. My chord was very small already at 7" (thickness of around 0.55") so my LE radius became very small. That small radius (1/16") I believe is causing unwanted inconsistency in snap and spin exits. It's just too small a radius and is not allowing as smooth a flow over the tips as I am accustomed to.

My best wing design to date was on my Temptress which has a tip chord of 7 1/4" and thickness percent of 10. The LE radius at the tip seems perfect to me at 1/8". It's a very wide flight envelope with the best snaps and spins I've ever seen. Very controllable and minimal control surface throw of around 12 degrees for ele and ail. If I want faster, I simply crank in throw and if I want slower, reduce that.

Point is, if the tip actual thickness is around 0.7" for a chord of around 7" it appears to be a very good set of dimensions. A little thinner is probably okay for a bipe, but I wouldn't go overboard.

I've seen much thicker tips work okay too but the required throws go way up..... not necessary. One such set of wings is on my Aesthesis (14% based on local hotshot input) and I absolutely hate the wing response. Resorted to stall strips on the tip LEs to get some reasonable response

Hi Matt,

Thanks. There is a lot in play here.
Not least amongst them is the totality of the wing inc,, relative chords etc.
I'm trying to get the wing centre to do the heavy lifting so to speak.
My LE will go from blunt-ish to sharp.
The only snap on my horizon for the next two years is one on top of a loop - avalanche.
Here one can slow the model right down,pop the nose and ,,,,, .
A really honest snap is the aim here.
I can cheat the LE a little at the tip if I think it's needed - I will see just how stiff this wing is first.
You are correct re needing large throws - I have some of that going on at present.
A problem with this is that the rate of rotation builds through the manoeuvre if high inputs are required to initiate.
So I'm trying to progress from a known reference. I'm experimenting as well.

Brian

Tip stall is a big problem when trying to land a snap, or a spin, or a sharp pull or push with tail wind

Hi Tuny,
I think it will be fine.
Actually the worst model (pattern) I've ever had for this was a PL Partner.
On a set of spins, properly stalled, it would do 3/4's of a rotation after release. It needed a pile of opposite to get any sort of accuracy.
I may have had a slightly rearward (can't remember) cg but nothing excessive.That had a chunky tip section and a blunt LE.

Matt,
' In my latest design, Delta, I went to some extreme in reducing tip thickness percent. My chord was very small already at 7" (thickness of around 0.55") so my LE radius became very small. That small radius (1/16") I believe is causing unwanted inconsistency in snap and spin exits. It's just too small a radius and is not allowing as smooth a flow over the tips as I am accustomed to.'

That is almost exactly the size as mine are but obviously there are two each side on a bipe.
Hope I have not over done this.
I will dull the LE a little just in case but for the single snap on top in the new FAI 'P' I'm looking for an instant bite.
I think , assuming my weight calculations are correct, that the loading will be the key. This is the plan at least.
I also think that weight distribution is very much in play here. Again , assuming I get it right, the outboard weight will be extremely low and coupled with that close to zero flex I'm expecting it should be fine.

Brian

I think your path is good Brian and I agree, it will be fine. Did I understand correctly? Tip chord around 7" and root chord around 15"?

The root will lift fine and will avert any tip stall, anywhere in the flight envelope. IF the tip stalls, you would never know it.

The mono wing in myDelta has a 22 1/2" root. Tip stalls are not in her repertoire even with the current CG location of 38%. Of course, I exchanged a DLE55 for an OS33 which removed about 10 ounces from the nose, so I am in process of a building a new, rear sweep wing. Not working hard at it tho. I have a set of panels cut from 1/2 pound density foam (each core is 530 squares and weighs 2 ounces!.............. too bad I can't find foam like that every day)

Matt,
' I have a set of panels cut from 1/2 pound density foam (each core is 530 squares and weighs 2 ounces!.............. too bad I can't find foam like that every day) '

They don't make that here anymore. I used that in my Typhoon wings and I cored it out also - 1/16 light balsa and wrinkle cote - it was plenty strong.
If you core out the outer 40 to 50% of the span with a geodetic pattern and go with your inside veil method you ,even with the same sections , will get better snaps.
Initiating will be a lot easier due to the much reduced 'inertia' - it is reduced by a MULTIPLE of the 'missing' weight.
Stopping them is a similar story but this time momentum is in play as well as inertia - again a multiple of the weights in play.
We all too often forget about some of the fundamentals of the physics involved because we get our minds buried in other detail.

Yes 7" and 15" at the root - @ 10.5% - ( D Snow; please note - I had said 11% earlier)
Also it will be quite blunt at the root.
I am not putting enough chord in the LE capping strip to get a 'true' section at the root - we cut the cores this way - it will be rounded off some as a result.
I expect the slow flying characteristics to be quite good.

Brian

Hi,
Have finally made a start.
The actual cores are coming out at 32.5g.
Also have the skins down to 22.5g before applying the inside carbon veil. There will be a little more sanding to do after the skins are applied.
Also have decided to seal them by spraying the first coats of dope - I got a new toy - a HVLP gun which works good for this - hard to believe how little air this needs to spray well.

Looks good Brian! Only comment I would make is that last time I honeycombed wings (on a Summit 120) I left the lands much thinner than you have done and the result was entirely satisfactory finish and strength wise over the couple of hundred flights I had with the model before I sold it. That was with filmed covered wings and a YS120 up front!

Oh and I used hairspray to seal the cores.

Malcolm

Hi Malcolm,
I think the camera angle is tricking the view a little.
The lands are 10mm on the template giving a 9mm land on top and 8 to 9mm on bottom (due to pull/push on the wire - one template only).
My scale is not good enough to measure the weight of two sealing coats of dope - it seems to have added nothing at all ??

Brian

Edit ; I no longer have any use for hair spray

Hi Brian,

That width sounds about right.

Ditto re the hairspray!

M

The coats of dope indeed add very little. A couple grams each sheet is probably all you add. But this step really helps when laying down the veil or other sheer fabric. Let me suggest that you also lay the veil down with dope. I use nitrate for that, two coats, and rub the veil in with a finger during the second coat making certain every square mm is laid down. Then lightly sand with 320-400 paper. You will add around 10-12 grams each sheet and will be quite stout. Pesky veil may be laid down with a MK iron

BTW- I decided not to build a new wing for Delta afterall. I took a closer look and decided to move the existing wing back instead. It calculated to 0.95" so I moved it 1 1/8" to give me some margin. I'm in process of making a mold of the 20.5 x 10 PN APC so I should be able to remove another 3 ounces from the prop up front.

I'm saving the wing cores I discussed above for my next project "Convergence".

Hi Matt,
Thanks.
Following your veil method closely with this effort, except for spraying the sealing coats.
Is there anything that I can add to colour the dope a little for spraying.

MK iron ??

Brian

Oh sure, any colored dope can be added to give some contrast. I use orange nitrate. If you have butyrate colors, just add a little bit to the nitrate. White, yellow etc, will contrast well.......If you use butyrate in the nitrate don't use more than about 10%. Butyrate is easier to find at the LHS but is no where near as stable as nitrate in the short term. The less the better... Best is finding some dry pigment and admixing dry. Maybe a local Art Supply store....

MonoKote iron. You'd have to play with amount of heat. You want to melt the dope a bit so that the veil sticks. But if you use your finger to rub the dope into the veil, you shouldn't have much trouble with iltfing. I brush a small area and then rub, and so forth until the sheet is set. I often use a paper towel as I rub to accelerate the drying and setting. It's just a technique of course; other techniques work also.

I assume that you will not spread the adhesive over the whole sheet, just the areas that bond. All the more reason to make sure the veil is well stuck to the sheet.

Matt,
Thanks again.
Yes glue only on the core walls.

Brian

Hi,
Just a little more detail.
Top and bottom wing core weights were 65g and 70g prior to honeycombing.
They are now at 27.5g and 32.5g respectively.
The wing skins were 30g prior to sanding and they are now at 26g with 0.2oz carbon veil applied - to the inside.

Brian

Brian, the panel weights are about what I thought you'd get. So 2 skins plus the core you are at just about 75 to 80 grams each panel. Expect about 20-25 grams of glue and these should come in at around 100 grams each panel. Each wing most likely will weigh about 200 to 230 grams plus center reinforcement. I think these are plenty light enough to this stage. Depending on type of finish, I believe they shouldn't be much heavier than 330-350 grams, ready for servo and linkage. Fine job!

Let me suggest that you go over the veil carefully and glue down any bubbles.

Hi Matt,
Will do.
I have worked out a glueing method, using PU, that will use 5g to 7 g per skin.
It's just that I have not done it this way before with veil between the wood and the core.
I will do some testing today and examine the results.

On honeycombed large mono wings I used thinned PVA put on the wall caps in a bead with a syringe. The PVA was thinned by 30% and a little food dye added.
10cc was more than enough per skin but when dry this left only 2g to 3g of dried PVA. So I was skinning a large mono wing panel for way less than 10g.
This required that the foam cores be pre sanded to a fine surface finish and the panels had to be put in a cold dark room for a few days to dry out when they were removed from the press.
More later.

Brian

Hi,
Got the tails cut and honeycombed.
Cores now at 9g each.

Brian

Brian, I used to honeycomb my cores but went away from it a few years ago. You've got me thinking about going back to honeycombing on the other surfaces besides the rudder. The weight savings is there making it worthwhile.

Since I prefer finishing the balsa in esaki tissue or silkspan and dope, strength is a non-issue. The only thing I didn't care for was the dimples which are visible after the finish is applied...... but functionally, its a non-issue. Maybe smaller openings might help the dimple appearance; just thinking out loud.