What sports aerobatic for an OS 30FS...?

[Jonathan M]

Having recently moved close to a club which permits IC but is in public space (where keeping the noise down is basic good manners) and has a much smaller mown patch than my old one, I'm looking to build a sports aerobatic to be powered by my never-yet run OS 30FS.

 

 

The sort of power flying I normally prefer is closer to the more traditional Gangster 63 Lite type of classic aerobatics (but not super-fast) rather than the antics of fun-fly etc.

 

My first thoughts were for a low-wing tail-dragger design circa 47-50" span but not yet found a plan that I really like or ticks all the boxes.  However I have been studying Peter Miller's original Peggy Sue 50" plan and article which is certainly very attractive (curvy but not over-complicated to build) and I'm sure perfectly aerobatic, and the high-wing (constant chord, no dihedral) format has its advantages.

 

But before I take the plunge, I'd really welcome any other suggestions.

 

Could be plan, kit or short kit.  Would be happy with tapering wing construction if necessary.  Tail-dragger more practical for the new patch.  Enclosed cockput preferred, but not essential.  Etc.

 

[Martin Harris - Moderator]

Several people have put 30s in Peter Miller’s Ohmens - designed for electric power but easily modified and quite aerobatic. I reduced the plan to 40” span and it flies very well on an OS 20FS

[Denis Watkins]

Have always had small 4 strokes on the go since starting out with I/C and a 30 size, On a good day, with the wind behind it, new plug and fresh fuel develops about 370W, which leccy flyers find useful in decision making.

Best plan is to expect 300 watts at this stage so weight is as always your enemy.

Build light and strong, and enjoy these wonderful small motors.

Build around a 4oz tank, as a 30 will run economically quite a while, I land at the 12 minute buzzer.

Carry 9 x 5 - 10 x 6 props

[john stones 1 - Moderator]

Boddingtons Excellence.

[Jonathan M]

59 minutes ago, Martin Harris - Moderator said:

Several people have put 30s in Peter Miller’s Ohmens - designed for electric power but easily modified and quite aerobatic. I reduced the plan to 40” span and it flies very well on an OS 20FS

 

Gosh, that's a good suggestion... here's how Didier flies his on a 26FS... more than astonishing!

 

[Peter Jenkins]

Chilli Breeze?

Edited October 28, 2023 by Peter Jenkins

[Jonathan M]

Yes, CB lovely, have the plan etc - but looking here for an airframe for the 30FS.

[David Davis 2]

Mini Jazz by Malcolm Corbin. I have seen them fly well on an OS 10 and 15.

[Frank Skilbeck]

How about a Mini Astro Hog, plan available Here

[Jonathan M]

Mini Astro Hog is really lovely thanks Frank.  Pretty close to the thing I'm looking for in terms of aesthetics etc, and I do fancy the inset ailerons, but I think its much too small for the 30FS (article says don't go above a 15).  Something closer to 50" span should have a lower wing-loading and be easier to see.

 

One could I suppose scale up slightly (or scale down a design that's a bit too big to start with), but I'd lack the knowledge to know which primary structure components would need to go up (or down) in thickness or section.  It seems easier for me at this stage to work off a plan that's fully resolved, and only tweak minor things to suit (e.g. separate wing servos rather than bell-cranks or torque-rods).

[David Davis 2]

14 minutes ago, Jonathan M said:

Mini Astro Hog is really lovely thanks Frank.  Pretty close to the thing I'm looking for in terms of aesthetics etc, and I do fancy the inset ailerons, but I think its much too small for the 30FS (article says don't go above a 15).  Something closer to 50" span should have a lower wing-loading and be easier to see.

 

One could I suppose scale up slightly (or scale down a design that's a bit too big to start with), but I'd lack the knowledge to know which primary structure components would need to go up (or down) in thickness or section.  It seems easier for me at this stage to work off a plan that's fully resolved, and only tweak minor things to suit (e.g. separate wing servos rather than bell-cranks or torque-rods).

 

Jazz 20 here: https://www.sarikhobbies.com/product/rc1771-jazz-twenty/. It has a 47" wingspan.

[Jon H]

1 hour ago, Jonathan M said:

Something closer to 50" span

 

I had a galaxy models twin scorpion and it needed two 30fs's to haul itself into the air. I am sure they were 52 inch span so you might find a single 3o struggles a bit with a model that size. It depends on the weight mind you. I had a 52 inch JP tiger moth and it was lovely with a 30fs fitted. Equally, it wouldnt be enough for my 52 inch Nieuport. 

 

I did have a mini jazz once upon a time and used it to test an ASP 30fs. flew ok but the airframe was rather bent which didnt help. 

 

 

 

 

[Engine Doctor]

Forget all i said just been corrected its ann OS  . Nice little engines.

Edited October 29, 2023 by Engine Doctor

[GrumpyGnome]

Thought it was an OS engine.......

[Engine Doctor]

Weĺl said GN i blame it on the clocks going back 😉

[Jonathan M]

On 28/10/2023 at 22:42, Denis Watkins said:

Have always had small 4 strokes on the go since starting out with I/C and a 30 size, On a good day, with the wind behind it, new plug and fresh fuel develops about 370W, which leccy flyers find useful in decision making.

Best plan is to expect 300 watts at this stage so weight is as always your enemy.

Build light and strong, and enjoy these wonderful small motors.

Build around a 4oz tank, as a 30 will run economically quite a while, I land at the 12 minute buzzer.

Carry 9 x 5 - 10 x 6 props

 

Very helpful advice, thanks Denis.

 

One design that I really rather fancy is Dereck Woodward's 47" Amelia originally for 20-25 four-strokes, so maybe the 30 Surpass would be too much power or too heavy in the nose?  I could get the plan printed at say 111% to bring it up to 52" which would also helpfully reduce the wing-loading a bit?  Or shorten the nose moment by half an inch?  Other things are easy to tweak to give a slightly less cartoony look, e.g. give the canopy front a bit more slope and make the tail outlines a bit less pointy without reducing their surface areas.

 

The wing is apparently weak as it employs hard balsa spars instead of spruce and has neither sheeting on the underside to make a full D-box nor sheer webs, but these things are easy to alter at the plan stage.  I'd fit separate servos in each wing half, and possibly consider inset ailerons instead of strip ones.  The undercarriage wire can be made to bind to the former in front of the wing LE instead of clamped to the wing?  So plenty of scope for minor changes to suit without radically changing the basic format - much easier than designing something from scratch!

 

 

[Antony R]

Derek Woodwards Amelia is a lovely little sport model, I built one about 25 years ago and fitted an os25fx as I didn't have a small fourstroke available at the time, your 30fs will be just right at the design span of 47", built it light don't overengineer it, the model is plenty strong enough as it is except for the balsa spars which I substituted with spruce, I've always planned on building another as it was so nice to fly.

[Graham Davies 3]

+1 for the excellence. I had several of these powered by anything from an Irvine 20 to an Enya 40. They fly really well.

 

Also +1 for the Ohmen. Didier's flying is fabulous, and really shows what this model can do.

 

You might also want to look at Peter Miller's Ballerina. It's the size you are looking for, but you'll need to build it very light for it to sparkle with the 30FS

 

Peggy Sue is also a good choice. I have Peter's model and it's a great airplane. I think Peggy Sue 2 is the smaller one and would probably suit the 30FS better.

 

Graham

[Jonathan M]

Antony, thanks so much for the positive feedback on the Amelia.

 

I'd be happy to build it as designed and at 47", except for the fact that on another thread it was reported by someone who flew one that it seemed very 'nose-heavy', although who knows where the builder put his CG (the plan shows it at 28% from the LE)?  The 30FS isn't really any heavier than the 26 but, as the CG almost certainly needs moving back a bit, shortening the nose a tad (in the fuel bay between F1 and F2) might avoid adding weight at the tail?  Also the wing is seated at 0° incidence which would mean up elevator trim all the time for S&L flight, so I'd tweak that to give a clear 0.5° positive.

 

Although mindful of not adding excessive extra weight, I'm still inclined to sheet the forward wing underside as well as spruce spars.

 

There's no reason why the wing cannot be bolted on with nylon, and I'd prefer a neater wire undercarriage solution that fixes to the fuselage at F2 instead of hinging on the wing and flopping about with oily rubber bands.

 

All these musings are happening because the Amelia has somehow caught my eye... one can't spend ages building a model one doesn't completely fancy, can one!?

[Jonathan M]

Graham (just seen your post which came through just as I was posting mine above), that's really helpful, thanks.

 

I actually ordered the Peggy Sue plan the other day, so its still in the running... and even if not now perhaps as an airframe for a second 30FS model some time!?

[Nigel R]

You could go for anything that used to use one of the plain bearing 0.25FP engine (Dereck Woodward used them everywhere). The 30FS is very nearly equal in both weight and power. Little Special might be my choice from his output.

 

 

[Martin McIntosh]

My Ohmen has an OS 26FS which fitted easily and the model flies much better than on electric; I believe that the 30 has the same dimensions. Plenty of info on the build blog.

[Piers Bowlan]

The Ohmen is a very nice electric model but if you are going to put a 30FS in it why not build one of Peter’s IC designs like his Alley Cat? The wing is identical to his Ohmen incidentally. I started building one years ago…I must finish it some time!

Edited October 31, 2023 by Piers Bowlan

[Antony R]

22 hours ago, Jonathan M said:

Antony, thanks so much for the positive feedback on the Amelia.

 

I'd be happy to build it as designed and at 47", except for the fact that on another thread it was reported by someone who flew one that it seemed very 'nose-heavy', although who knows where the builder put his CG (the plan shows it at 28% from the LE)?  The 30FS isn't really any heavier than the 26 but, as the CG almost certainly needs moving back a bit, shortening the nose a tad (in the fuel bay between F1 and F2) might avoid adding weight at the tail?  Also the wing is seated at 0° incidence which would mean up elevator trim all the time for S&L flight, so I'd tweak that to give a clear 0.5° positive.

 

Although mindful of not adding excessive extra weight, I'm still inclined to sheet the forward wing underside as well as spruce spars.

 

There's no reason why the wing cannot be bolted on with nylon, and I'd prefer a neater wire undercarriage solution that fixes to the fuselage at F2 instead of hinging on the wing and flopping about with oily rubber bands.

 

All these musings are happening because the Amelia has somehow caught my eye... one can't spend ages building a model one doesn't completely fancy, can one!?

I don't remember an issue with CG but it was a long time ago now, its a light structure and was very adequately powered by the 25fx, I didn't install the forward tank hatch but made f2 open and got to the tank that way, maybe saved some nose weight there?

Be mindful of adding weight here and there, it soon adds up, it is a vintage style sport model not an extra. 

[Jonathan M]

Piers, good point about an IC-specific design, although a conversion from electric isn't a real impediment if it comes to that.

 

I saw the tiny photo of the Alley Cat on Sarik's website a bit ago but couldn't find any more images or information on it anywhere, nothing as far as I could see anywhere on here.  In the end I assumed stubby nose, little or no dihedral and general Miller-ness of approach, which is fine but too little to go on.

 

Maybe you'll finish your's sometime...?  What wee beastie would you put in it?