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Author Topic: wing sections for lock down power models  (Read 948 times)
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I hate trees
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« on: May 31, 2013, 04:34:52 PM »

Hi,
I'm thinking about a new SLOP model and am pondering different wing sections.
The Dixielander seems to go ok with NACA 6409 and I think that was the same section on the Super Zeus.
I've seen some recommend NACA 4409, but does it have that much effect on the climb compared to the 6per cent camber?
What about going thinner? say NACA 6407 1/2, if the structure can take it?
I'm planning on a diesel model so it will have a 12 second run.
I'm interested to know what everyone thinks or recommends NACA or any others.
Cheers,
Adam
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RobinB
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« Reply #1 on: May 31, 2013, 05:19:21 PM »

Adam, what size is the plane to be ?
How highly-powered?
Most relevant - where's the CG?

Robin
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glidermaster
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« Reply #2 on: May 31, 2013, 06:38:51 PM »

Adam,
I am firmly of the belief that we use too much camber generally on f/f models, especially where over the years, aspect ratio has risen markedly - i.e. FAI type models.

However, I think the same holds true for more classic-type classes, inc SLOP, just maybe to a lesser degree. My own OS15FP model (which has its own thread here on HPA) uses a section of about 4% camber, not that I have any creditable resume of success with it by way of validation. I would, however, stand by the wing structure which has stood up to 2 full speed D/Ts (my mistake - both times!), and is not heavy. It is basically an all-wood fully closed torsion tube or D box.

Anyway, as Robin said, there are other design elements to consider, and on a locked down model, as pitching moment increases with the square of speed, and is a function of camber, higher camber might well be useful - which, of course, contradicts what I just said!

To answer one of your questions directly, you will certainly notice the difference if you build a NACA 4409 Dixielander, and compare it to a NACA 6409 (Standard) Dixielander - climb-wise, that is.

John
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Ployd
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« Reply #3 on: May 31, 2013, 08:07:09 PM »

Hi Adam

All things being equal the 4409 section while having less camber will be (in fact is) faster in the climb than the 6409 section. I have used the 4409 section on all my Dixielanders with out any noticeable degradation of the glide (which is also a little faster) and rides through turbulence better.

I would tempted to suggest that their are better airfoils around including the Connover section as used on the Lucky Lindy so I would recommend a little more research and don't rule out the LDA section being used in F1C.

Ployd in OZ
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lincoln
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« Reply #4 on: May 31, 2013, 09:29:31 PM »

I have looked at some wind tunnel data on the 6409 recently. In the glide, i.e. at high lift, it's good for models that are LARGE, i.e. high Reynolds number.  Say, 150k. Probably good at moderately high aspect ratios, since it develops so much lift. Not so good for small models.  Not the greatest at low lift either. By not so good I mean lots of drag.

Can't say about other airfoils. I don't do power ff so I may be missing some points
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Yak 52
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« Reply #5 on: June 01, 2013, 04:02:41 AM »

If you want thinner and lower camber have a look at BE50 (7% thick, 4% camber) it's an older F1C profile. Compared to Naca 6409 it has less drag in the climb and is a lot better at low Re in the glide.

http://airfoiltools.com/airfoil/details?airfoil=n6409-il
http://airfoiltools.com/airfoil/details?airfoil=be50sm-il
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« Reply #6 on: June 01, 2013, 04:31:15 AM »

Thanks for all the replies so far.
The model I have in mind is to be PAW19 CT3 powered and about 480sq inches (60x8).  The diesel powered model gets 12 secs run compared to 10 for a glow.  My Heatwave has a CT3 and cuts very clean so I can get very close to the whole length of run.  With a glow with suction and strangler rather than flood off you always seem to have some burble to count from your 10 secs, so you probably have to go for a nine second run.

Looking at various successful SLOP models in the UK the options seem to be:
NACA 6409 as on SuperZeus (renowned for good glide)
BE50 (or similar) on Phil Balls models (carbon d box).  I think the Verbitsky sections were based around Benedek 8% sections (as used by Mike Gaster, Vic Jays etc)
NACA4409 Dave Limbert recommends
I haven't seen an LDA section specifically for power models and there was talk of pitch sensitivity on some of these in windier conditions.
If I go for a thinner section then presumably I should thin the stab to be approx. 2% thinner than the wing.
My Heatwave weighs 21.5oz and has approx. 465 sq inches of wing area.  I'm going to aim for 18.5oz for the new model, which is not easy since nearly 8oz is engine, tank, timer,prop etc!
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applehoney
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« Reply #7 on: June 01, 2013, 09:19:44 AM »

> you always seem to have some burble to count from your 10 secs,

Not in North America - the 'rundown' is not taken as part of the engine run time.

A similar sensible rule proposal in the UK  was turned down by the FF Tech. Committee, in its wisdom
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glidermaster
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« Reply #8 on: June 01, 2013, 05:35:51 PM »

Some interesting opinion here.
In my opinion the LDA work which is so much to the fore at present can be boiled down to simple essential characteristics. These are principally the semi-symmetrical nose shape, tied to high camber but which is centred well aft - giving a very curved rear aerofoil.

BE50 doesn't really fit with this description, but was (I think) developed very empirically over many many models, most successfully, too.

Ployd mentions the Conover which is completely different; thick, very sharp leading edge, flat bottom, camber centred well forward. I think that if you're trying to pep the climb up, you might want to avoid this one.

Ployd's NACA 4409 Dixielanders are intriguing (I guess 4408 would also work with a better wing structure that classic Dixielander).
I've been looking at Drela aerofoils for some future projects (of an undisclosed nature!!).

Are you designing from scratch, Adam?

John
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lincoln
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« Reply #9 on: June 02, 2013, 07:05:51 PM »

Not sure what Cl a model like this climbs at, but if it's 0.05 or greater, have you considered the AG35?
polar is here:
http://www.charlesriverrc.org/articles/drela-airfoilshop/ag35_polars.pdf
I calculate that at a Cl of 1, your model's wing will have an average Reynolds number of 73k. That's probably higher than a lot of other ff models. Note that if your wing is tapered, the AG36, 37, and 38 are meant for somewhat smaller chords. You can find them here:   http://www.charlesriverrc.org/articles/drela-airfoilshop/markdrela-ag-ht-airfoils.htm

The AG38 is a fast airfoil, but it slows down reasonably well. I've flown a couple of gliders that had the AG35 transitioning to AG38.

Hypothetically, one might design an airfoil that was a bit better at the high and low end by sacrificing some performance in the middle, since this is a ff model. RC gliders spend a lot of time in that middle area, at least when they're not in lift.

Once again, I am not a power ff flyer, so I don't know the balance needed between climb and glide.
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b.spooner
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« Reply #10 on: June 03, 2013, 02:55:16 PM »

Hello Adam,

I have built 3 SLOP models (all about 540sq. in area, 21 oz) using a Verbitsky wing section and have no complaints about climb or glide speed.  A fourth 'rounds' model (based on a Dave Clarkson design) uses a Wortmann M2 section but sometimes this shows an inconsistent climb pattern - why I don't know!  Hence a very strong recommendation to try the Verbitsky section.  All my SLOPs use either a OS 20 FP MAX or K&B 20.

Cheers,

Bryan
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danberry
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« Reply #11 on: June 04, 2013, 05:32:19 PM »

Build a 9% flat-bottom 'foil and don't look back.
10/13 secs should yield a model good for 7-8 minutes to the ground.
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FF Bruce
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« Reply #12 on: June 04, 2013, 09:06:33 PM »

I'll add my two cents,I'm with Dan but I'd go with 8% flat bottom wing and 6% stab.They are easy to build go fast and also trim quickly.Up untill Alum.wings,in F1C we all used flat bottom wings for those reasons.
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gossie
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« Reply #13 on: June 04, 2013, 10:48:44 PM »

Generally speaking thin flat bottom for me too.   But girls need to be different.
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