Hi Guys,
Just started building a 2m DS ship and got as far as the lost foam fuz.So i've put all the details into XFLR5 to try and understand how it will perform, but i must admit that i'm struggling to get to grips with it and i need to get her built while the weathers warm for doing the composite stuff.

So if there's anyone who's familiar with XFLR5 who could take a look and give some improvement pointers,that would be a great help.

What i'm trying to get from this plane is....
target speed of 150mph or more
A.u.w more on the heavier side,say 1.5kg + as it's a homebrew.
Circuits would probably be about 100m diameter.

Also need to know best sizes for flaps,ailerons and elevator.

Thanks for any help

Tim

I think it looks good! Build it and it'll do what you want for sure...

I took a brief look and figured that at 100m circuits you're only pulling a Cl=.14 and that XFLR5 says you need to have Cl between 0.3 and 0.5 for optimum Cl/Cd. 150mph / 100M diameter is also a pretty lazy circuit at 4.7sec...Ideally, you'd need to fly circuits about half that size (150ft dia is 2.1 seconds at 150mph) to get Cl=.3. I'd plan on building heavier if your slope will allow and fly about 3-3.5second circuits. For instance, 85oz (2.4kg) at 70m diameter (3.3 second) circuits would get Cl up to 0.3 for a speed of 150mph...

If you don't want to build heavier and can't manage the tighter circuits, you could use a couple degrees of reflex to drop the optimum Cl range.

If I were you, I'd start cutting foam and build (2) at the same timeso you're ready to go when the wind blows!

If you want the Vtail to be more durable, you could probably go thicker like 8% without any significant penalty.

DISCLAIMER: This advice is given by a plumber not an aerodynamicist ;o) take it FWIW

Thank for your imput sll914,shouldn't be a problem to do smaller circuits on the site where we fly.

Does anyone know what % of the DS19 wing chord should be used for the flaps and ailerons.Also on this 2m wing,how long should each of these be,50/50 ?

Cheers

Tim

In the past I used +/-20% chord for the surfaces on DS-19 planes. As far as the length of the surfaces is concerned, I'd use somewhere around 55/45 with more aileron than flap so that you have enough roll control with full butterfly for landings.

Spencer

if it's not too late I would, if you haven't already, consider an X-Tail or T-Tail as they seem much more stable for ds...

chris

Originally Posted by daboz

if it's not too late I would, if you haven't already, consider an X-Tail or T-Tail as they seem much more stable for ds...

chris

Hi Chris,
I had thought about doing both of those ideas, but thought that a v-tail would be the easy option.

Anyone got any links on how to build these type of tails or rather how they're fixed into the fin?

Cheers

Tim

Agree with Spencer and Chris. I think your operating CL is way too low even allowing for the G loading of a 100m dia path, which at 150mph on a 100m dia is around 10g.

I would suggest raising your AR to around 12:1 which would allow you to carry less ballast which together with a path dia of closer to 75m would help to load the aerofoil.

My rough calcs would indicate you would still need something like another 0.4kg- so total weight would be around 1.9kg which together with the lower wing area and tighter path would get you close to a operating CL of 0.35.

Your stalling speed at 1.9kg would then be around 24mph at a CL of 0.9 and no flaps. This is still slow - you will be flying in winds close to this speed - so maybe even more ballast.

I'm also a fan of T and cross tails as I believe they are far more effecient particularly in yaw for DS.

I'm not an Aero Engineer either - it just happens to be a passion. You need to keep trading off compromises to get close to the final result which you will still need to fine tune by flying.

hope this helps and doesn't confuse.

Cheers
John

Hi Guys,
I've changed the A/R to 12 by skimming 10mm off the overall width of the wing as recommended,But i could do with some more advice if you don't mind.

If i were to do a T-tail,how do you work out how much area you need for the fin?

I'm also looking at the wing joiner at the moment and i'm going to do it out of C/F at a size of 30mm x 10mm,But what i'm not sure about is how far to extend it into the wing for DS.

Cheers

Tim

Avago, I couldn't open your file, but for what its worth - here's my 2c.
Although there are some guides to sizing Vert. Stabs similar to Tail Volume calcs -I would advise a minimum Vert Stab of 6% of the wing area.
This with say a tail moment based on a tail volume of around 0.4, and a tail area of around 10%, should give good yaw control.
The old eyeball comes into play as well to adjust in size(larger) if it still doesn't look right. i wouldn't go much below 6% unless you have a very long moment like a current F5E model.

John

Thanks for the advice John.

I might turn this thread into a build log when i get back off holiday.I've got the fuse done and i've just made a c/f wing joiner which is post curing at 60* in the oven while the Mrs is sleeping,hopefully she'll never know.

Cheers

Tim

Hi Guys,
Just thought i'd post a few pics of how my DS ship is coming along.I'm not going to turn this into a full blown build thread,but thought that those of you that have offered me advice might be interested and i'll post odd pics as i get other stuff done.

Cheers

Tim

Tim, that looks really nice. Where did you get that great looking carbon joiner assembly?

BTW I have designed a built X-tail models and something I have noticed is that the thicker foiled fins stabilise in yaw much quicker and tend to track better.

Tony.

Thats neat work Avago, and i don't think you will have many problems with the strength of the joiner. i would not have worried too much about cranking the last bit of the spar but it wil not hurt and possibly helps a little with span loading.

Good luck and here's to a maiden before your summer finishes.
John

Hi Tim, did you mould the spar and joiner box yourself? Nice work if so... (any pics of the mould?)

If not too late, one thing I would do different is tapering the cap spar to spread loads and reduce risk of a stress riser at the end of the joiner box. i.e. full width cap spar at the root and joiner box, tapering out to the tip...

Hi Guys,
I've taken a few pics of the mould i made for making the wing joiner.It's not perfect but does have some advantages as it can be broken down to release the joiner with a few lite taps with a rubber mallet and also the polyurethane bars and sheet that i used to make it doesn't really need waxing as the resin won't bond to it.

The joiner did need a little finishing just to true it up and i've posted a pic of the setup i used on my pillar drill useing a straight edge and drum sanding bit.

I think if i have to make another joiner,i'll get a proper mould machined at work useing the polyurethane material and it should be a lot more accurate.

I made the joiner tube by waxing/PVA/wax on the joiner,then wetted out 2 layers of 125g uni-carbon and wrapped this around the joiner twice,followed by a layer of 200g twill weave CF.I just put it in a poly bag and placed a piece of rope around the outside of the joiner to act as a breather, No mylars or anything fancy.

Cheers

Tim

Also forgot to mention that this is the method i'm useing for making my I beam spar,but will be bagging both surfaces together after spars are complete.

http://www.favonius.com/soaring/bagging/bagging.htm