Irvine .53 / Ugly Stik

[Scruffmeister]

Hi All,

I'd be interested to get some thoughts on this please. I'm planning on taking the classic Ugly Stik design and adapting it to suit an Irvine .53 engine. By adapting I really mean scaling although I will probably redraw the plans to hone my CAD skills.

I'd like the model to be fully aerobatic to a minimum of the BMFA 'B' (Loops, Rolls, Spins, Stall-Turn) but not overpowered.

My initial thoughts are to aim for around 55" wingspan, maybe 12x5" prop.

What would be your ideal wingspan / prop combo for for Irvine 53 on this model?

Cheers!

[Jonathan W]

I don't know the exact answer to your question, but I have a 72" Ugly and it's about right with an OS91FX (2 stroke) on a 14x7. It will go vertical not unlimited, but a long way, such that to do stall turns you need to throttle back. Therefore your proposed 55" and engine/prop sounds in the right ball park.

I would advise that the fuselage has very little side area (hence "Stick" and this does limit the aerobatic range. Also, it has a wide chord "barn door" type wing and I find that mine does not spin very well, tends to end up in a slow spiral dive despite the CG being a little to the rear.

That said, it's a good tough hack model that you don't need to be too proud of. It floats in on landings really nicely and is very forgiving.

PS the smiley was accidental, but happens to be about right!

Edited By Jonathan W on 13/09/2019 22:30:27

[Denis Watkins]

SM, that Irvine could pull 6 - 7lb

So look to guestimate around 66" span

Or use a smaller motor

[Former Member]

[This posting has been removed]

[Jonathan W]

Posted by Denis Watkins on 13/09/2019 23:00:06:

SM, that Irvine could pull 6 - 7lb

So look to guestimate around 66" span

Or use a smaller motor

 

I have to disagree with this. If my 72" version is good with a 91 engine, I don't see how a 66" version will be adequately powered by a 53. No doubt it would get off the ground, but remember that this particular model has a large wing area (low aspect ratio wing), thick wing section and is very draggy. I would expect 55 to 60" tops to be suitable for the Irvine. But in the end, we all have an opinion, so take your pick!

For another point of reference, another club member powered his 72" Ugly with a 91 4 stroke and said it flew like a trainer, very sedate.

Edit to say...

Looking at the various plans on Outerzone, the original Phil Kraft design was 60" and he typically used an Enya 60, which was a old crossflow engine, although the model would also fly more sedately on a 45. Therefore I would say, go with the original 60" design by Phil Kraft and the Irvine 53 will be spot on. Why mess about scaling up or down when you have a proven plan just the right size?

Edited By Jonathan W on 14/09/2019 00:06:43

[Denis Watkins]

Right lads, the OP stated " not overpowered "

So an Irvine 53 on a 55" wing seemed excessive to me, if not to overpower

A 60 would fly the 72"

The extra 30 + 60 of the 90, is used up carrying the motor

The OP, has in this case mentioned power

The Seagull Stick weighs 3.5kg as a guide

Edited By Denis Watkins on 14/09/2019 07:52:05

[SIMON CRAGG]

I would say a .53 would be ideal on this particular model at 55".

It could either be dumbed down with a larger prop, or a pipe added if more power needed.

Good to see ic is alive and well anyway!.

[Scruffmeister]

I only have an Irvine .53 engine available for this so changing engine not an option. I like the description that you would "need to throttle back for a stall-turn", but that the model would not have unlimited vertical.

Ultimately this model is intended to allow me to hone my drafting/(limited) building skills and provide my kids with a hack they can use as they move beyond their BMFA A-test to hone their skills. It needs enough power to get out of trouble if I'm on the buddy box with them though!

Perhaps 60" is about right? I've used this Irvine .53 on a Wot4 (ARTF, 53" and it goes like a rocket - quite a bit more powerful than I envisage for this model. I know the original Kraft design was 60" on a 60-size engine but I imagine the Irvine .53 is fairly powerful compared to a .60 of the time the plan was drawn.

[Doug Campbell]

I have a 60" stick with a Super Tigre 51 in the nose with a 12x6 prop. Ample power for any acrobatics, not unlimited vertical but more than enough for sport flying. So 60 inch span is my recommendation.

Doug

[Nigel R]

My take

60" is a good size for that .53

I would make two main modifications to the model:

Remove all dihedral. It will work against you if you want it aerobatic.

Use a proper wing section not the blunt nose thick thing shown in the plan. NACA 0012 or very similar. RAF30. E168. They will spin and snap roll better.

Structurally the design is ok. But I would make the wing of a d box type and forget the half ribs. it will be stronger.

I would probably convert to dowel and bolt for the wing as well, I'm not a big fan of elastic bands to hold wings on with.

Or you could just build a Mike Delacole Rival which is essentially a stik design with a better engineered structure and it is sized right for your engine. It is on outerzone.

[Jonathan W]

That's a good point from Nigel R on the wing section and reflects my experience of reluctance to spin. Also, I would agree that no dihedral is necessary.

On the engine front, the Enya 60 was a good engine of its time and will only be a little short of power compared to the Irvine 53. The silencers in those days were less restrictive, so that tends to boost the Enya relatively.

The Rival looks good and you could stretch that towards 60" if you wanted to play around with CAD.

Ref the weight of the OS91FX in my 72" Ugly, it's a light engine for its size and weighs 550g, exactly the same weight as the OS61FX (quoted from the OS owners manual). The 72" Ugly has 1000 sq.in wing area and is draggy, so it needs the power. I was flying it only yesterday!

[Scruffmeister]

The Rival, and its big brother Big Easy both look great - many thanks for pointing me toward those.

The Rival is 55" designed for 0.46

The Big Easy is essentially a scale-up, 66" and designed for 0.60-0.90

So, with that in mind maybe 58" is the correct scaling for a .53 !?

In a more general sense, is there a rule of thumb for IC of HP to wingspan for various styles of flying - e.g. the equivalent of the Watt/Kg rule used in electric flying?

[Nigel R]

A .40 makes a 4lb model go pretty good.

And a .60 for a 6lb model.

I've never paid that much attention to wingspan when thinking about power.

Other opinions are available

[kc]

If you really want to resize a model and draw it in CAD there are so many desgns you could start with - but is it realy worth the time if plans such as the Rival are so readily available?

However one design that might be worth drawing to a larger size is New Era 3( the revisited version) - if you read the article on Outerzone you might consider the design is worthy of being larger by maybe a third at 55 to 60 inch. ( note it's only the New Era 3 that has such a good reputation and the Revisited version is slightly modernised )

[brian sylvester 1]

I have 60ins wingspan das ugly stick built from an old jenson kits plan it flies very well on a 1980s hp61 so i would think a modern irvine53 would power it nicely.