Chilli Breeze 48" Build (IC)

[Jonathan M]

I'm finally about to make a start - my first plan build - with foam wings from Cloud Models.

 

Will keep as close to the plan/article as possible, but take advantage of modern RC gear to help keep the weight down, and reckon a 2/3AA 800mAh NiMh will be ample for a normal flying session.  Power will be a new OS35AX with standard silencer.  Servos will be HS85MG in each of the wings (original design had a single central standard and torque rods).  Thinking of  fitting the same for the tails , or perhaps the beefier HS225MG for these?

 

My main opening question is what density balsa should I be selecting for the main fuselage components?  The sides are 3/32" (with a 1/32" ply doubler, a 3/32" wing-seat doubler and 1/8" x 1/4" spruce longerons), while top decking is 1/16", etc.

 

The 3/32" sheets I have range in weight from 8 to 16lbs/cubic ft (i.e. from fairly light to really quite heavy), but I have several in the medium range.

 

I simply don't know what the norm is - not just for the fuselage but for the various major components (different built-up wing parts, tail parts, etc) across a whole traditional power model.  The old website had an article by one of the regular columnists, but I cannot find this anymore.  Any suggestions?

 

Edited January 9, 2022 by Jonathan M

[Nigel R]

My take;

 

Medium for all the fuselage sides and top deck and underside. 

 

I'd not put spruce longerons in - bit overkill, just do them from more medium balsa. 

 

Anything else in the fuse is of small area so use whatever you have. Foamboard formers work well. Might want to find light sheet for the cowl if you can but again if it's medium, no big deal. 

 

Tail, light Sheet. Or build it up from 1/8 framework and light 1/16 sheet. 

 

Wings, sheeting is light, its the highest volume wood part there so this one is important to keep light. Light for leading edge and trailng edge if possible but medium works fine. Ailerons, I go medium, as they are stronger. Some will say light. Jury's out. But, flutter is a thing on strip controls, and stringer/stiffer is better at resisting. Ribs, medium, but they're not a significant component.

 

Hope that helps

 

Ps definitely the 225 inside the fuselage for rudder and elevator. 

Edited January 9, 2022 by Nigel R

[Jonathan M]

Thanks Nigel, very helpful!

 

I found the article I'd seen before, it was by Peter Miller https://www.modelflying.co.uk/woodnt-you-know which complements your advice above.

 

Thanks also for the heads-up on tail servos ?

 

[Andy Stephenson]

I used light sheet for the tail on my Breeze and half of it broke off in flight. The only thing that saved it was the half that was left had the working elevator half. Had it been the side with the control horn that was lost it would have re-kitted in an instant.

Mine required so much lead on the tail to balance it before the incident, I rebuilt it with the hardest wood I could find and lost the lead.

 

[Jonathan M]

Andy, that sounds alarming!  Did the tailplane half just fold at the root?

[Nigel R]

You could run a 1/2" wide strip of harder wood along the hinge line of the tailplane if you wanted some reinforcement, or you could use a strip of very light glass to cover the centre section of the tail.

 

Andy, it sounds as if you had a flaw in the wood itself?

 

[Guest]

Mine had the same problem as Andy S.  Tailplane broke in half and it was a bin job,methinks a design fault "!!!!!

I'm with Andy,use the hardest wood you can find.

I'm sure someone else has had this problem on this model.

 

Jim

[Andy Stephenson]

5 hours ago, Jonathan M said:

Andy, that sounds alarming!  Did the tailplane half just fold at the root?

Yes it was alarming, and it came off not at but right near the root. I had put it through quite a lot of high G manoeuvres but it was supposed to be designed for this. My fault, my choice of wood.

[Jonathan M]

Sounds like a classic stress riser situation, especially as the fuselage itself is well beefed up with vertical grain 3/32" doublers in the tail area.

 

My 1/4" stock is medium.  Will have a think about recessing in a couple of lengths of carbon strip in effect to create a full-span spar about half way down the chord-ish.

[RedBaron]

Is it possible that the cause of failure could be related to power train vibration?

 

My C-B is at the stage of most structure built and control systems being installed.

I have chosen to do a built up tail plane. Would that be worse or better than a solid t/p? It is not too late to install carbon rod into the t/p structure.

 

Any comments would be appreciated 

[Jonathan M]

Given the two reports so far of tailplane failure, I'd be inclined to slip in a carbon rod.  What's up front?

[RedBaron]

Thanks for the comment Jonathon. Up front is electricals - a 4-Max PO-3541-1070 with a 50A ESC to be specific.

[MikeQ]

Hello Jonathan

 

how’s your Chilli Breeze coming along?

re wood sizes and density, you’ll find you can get away with way lighter than you think.

 

I would classify 4Ib as very light and 12Ib as heavy/hard.  Most RC building would be around 6lb to 8lb for me.  Spars etc maybe a little heavier.  All depends.  Above 12Ib and your into table legs.  Lots of chaps seem to build the model to ‘feel strong in the hands’.  Thing is, the model isn’t subject to loads like massive grabbing hands once in flight.  As long as the model is stiff and straight.  That’s what you want.  Trouble is getting the wood these days.

 

Hope you are making progress.

 

Cheers

 

Mike

 

PS. One thing to take into account alongside wood density is grain type.  That’s a whole other topic.

 

 

 

Edited May 2, 2022 by MikeQ

[Jonathan M]

Hi Mike - just seen this.

 

The CB is on hold for building this coming autumn/winter.  (Since finishing the Gangster, I've been focussed on building a couple of trad FF diesel models - a Veron Cardinal and Gordon Whitehead's all-sheet Nieuport Baby - as well as flying RC thermal and indoor FF scale.)

 

Your observations about wood densities and model stiffness are spot on.

 

Jon

[Jeffrey Cottrell 2]

Hi Guys

Contemplating a Chilli Breeze build, but I'm a bit concerned by reports of tailplane failure. What's the best solution?

Wondered about a built up structure with 1/8" inner frame with 1/16" skin each side. Means I could put in diagonal struts which would resist any twisting force, but not sure if this would be sufficient.

Your thoughts?

Jeff

[Nigel R]

I've never had a failure in a tailplane built as you suggest, from 1/8 and 1/16, right up to 60 powered aerobatic jobs. Nor have I ever reinforced with struts or wires or anything. I have always felt that structure to be more than enough for flight loads.

 

If you're concerned, make the core thicker, 3/16 or 1/4. It won't add any weight. Obviously the control needs to be thickened up to match.

 

Your mileage may vary.

 

Edited May 20, 2022 by Nigel R

[kc]

The alleged tailplane faiure might have been excessive vibration possibly made worse by a very narrow fuselage at the very tail end.   It might be better not to pull the fuselage in at the tail quite as much which could give more support. 

The comment about tailplane failure was passed on to the designer Mike Delacole ( Delks on this forum ) and he may have commented somewhere on the forum if you look.

Edited May 20, 2022 by kc

[Andy Stephenson]

Just do what I did and use hard solid 1/4" balsa for the tailplane, this fixed the problem. With an Irvine 36 and tuned pipe, the CG was too far forward as originally built so lead was added to the rear of the Fuz which may have contributed to some sort of resonance. But having fitted a heavier tailplane I lost the lead and all was good after that.

[kc]

1/4 solid balsa is of course the material shown on the plan.

That's the same construction as many .40 size and some larger models. 

 

The only time I have seen a 1/4 balsa tailplane break in half was on a Wot4 which broke in mid air - fortunately the instructor grabbed the Tx from the trainee and amazingly landed the model OK with half a tailplane and the elevator hanging off .    Great bit of flying from that instructor -the last time I saw him he was flying full size. 

  

However the post flight inspection of the Wot4 revealed that the intact half of the balsa tailplane had just a trace of an indentation where a scalpel seems to have just lightly scored the balsa whilst trimming the Solarfilm!    The other broken half was probably the same or perhaps even more scored.  A very important point to remember when trimming film - never let the scalpel touch the balsa anywhere critical like  a tailplane, fin or wing to fuselage joint.   Material usually fails at the point where its slightly different -even just a scratch or a score line on some materials.

[Andy Stephenson]

Always slide a piece of thin card or plastic under the film when scalpel cutting it against balsa.

[Ian Dewar 2]

I had two of these with Irvine 36s. Lovely to fly but I lost both (!) due to elevator flutter which immediately broke the linkage. I think I had used nylon clevises on the first and,stupidly, on the second. The first was spread across a nice tarmac RAF runway, the second repairable. Might be worth making sure your linkage is nice and robust. So tempting to make another, but my Irvine 36 is a bit tired now, shame they aren't around still.

[Andy Stephenson]

If I build another one I have an Irvine 39 for it but with that much power I will probably glass it for rigidity.

[Jeffrey Cottrell 2]

Hi All

Looks like the Breeze and the Wind are as popular as ever.

Just a reminder:

Some time ago I was looking at a way to get intermediate rib shapes for a built up wing. Posted a question on here and also RCGroups.

The question led me a contact from a guy called Harry D in Canada. Turns out to be a bit of a whizz with rib plotting software, and in very short order he was able to produce not only the intermediate rib shapes, but even cutting templates incorporating spar cut outs etc.

These he sent to me as Acrobat files so I could download over here.

He also gave me permission to share these files, so for anyone contemplating a Chilli Wind or Chilli Breeze build PM me with your e-mail address and they're yours.

Jeff

[Andy Stephenson]

PM sent.

[Ace]

Please - PM sent