rmh

Well - ALL airfoils are compromises
They can't be the "best" at all speeds -can they?
As far as the ability of the experienced SWAG over the text book approach for models - Iwill take the guy who loves his work and has experience -every time -It ain't even a choice. I do prefer a Dr who knows where to cut -but some don't. Trust me on this one
I am missing one leg because a team of Dr's didn't get it right 25 years ago - who could have done better back then?
I'll never know except today- the guys who "fixed" the job said the other guys just didn't have the right answers back then.
So trust in the infallability of the textbook if you will -I don't
It's all a calculated approach/risk.
I also spent ten years debunking personal injury claims/lawsuits- the experts who wrote those usually had a sheepskin as long as your arm. I loved that job. Snapping the sheepskin out from under em was lovely.
Nope I won't buy the aerodynamics comes first apprach - the real world says you setup the ideal goal then compromise till you get the best you can under the circumstances .
Solch Ist

topspeed

Dick Hanson,


Is SWAG = Scientific Wild Ass Guess ? I am a finn dunno all english words...106 meanings in the dictionary for SWAG.

I recently got a remark that something flies well when it is beautiful. That is hard to define too, but I know the meaning.


rgds,

Juke

rmh

Da!
The beautiful description is much the same as
"if it looks right it fllies right"
many words have more than one meaning allowing for many word games.
Acronyms are a national and government passtime in the USA
A POSSLQ is an obscure tax form acronym from years back.
" People of Opposite Sex Sharing Living Quarters"
This was to describe unmarried people living together .
A new generation of shorthand via text messaging -is a blend of acronyms and teen age jargon.
I am lost
IDK I am just AOF
It must be the sme the world over.

Ben Lanterman

Dick wouldn't my experience in the F-15 design count as real world? We did it just the way I outlined earlier. Aero did come first because it determined if the airplane would pull the maneuvering load factor at all angles of attack. The structure guys come later and do indeed get yelled at if the airplane is too heavy, but, aero came first. I am sure you have seen the design of an airplane cartoons where it is seen from each different technologies viewpoint. In the case of the F-15 the aero always came first.....

If you are making a model of a CAP or whatever, the aero has already been decided, you copy it or it isn't a CAP. Model and full size are close enough that model can use full scale airfoils nicely. All that is left is to put in a light structure. In that case it would seem that aero comes first also.


Ben

sir crashallot

the thing is ben i have only got the stock and balsa and ply and money to do this once, i cant afford to gamble on an aerofoil which mixed in with the model could cause it to be a total handful and even worse have to fight to keep it in the air, dont get me wrong iv flown some nasty planes that others wouldnt and couldnt keep control of for more than a few minutes. im am a capable pilot but the current situation leaves me unable to afford a kit thats tried and tested so in order for me to get satisfaction im having to do my own from scratch, i dont mind either because it will be a great learning curve but when it comes to flying i can afford to have a bad aerofoil in the wing which could render all the work iv done and put into it useless and a watse of time and stock.

soi think the best advice for me is to look at the top flite wing sections as there have been thousand of kits of the mustang sold in both small and giant sizes, now common sense would be to search for the reputation of there wing which i have and never come accross one complaint of its wing and design, so in theory i have 2 options go solo and draw up my own wing and risk it or be safe and just build a wing using the tried and tested top flite wing aerofoils which to me makes more sense, im not enetering compatitions i just like and love the mustang just as much as the spit and the hurricane, but if i can get away with using the top flite wing sections then it opens up a new collection of warbirds for me, hope this hasnt offended you but it puts you in the picture of the stuation im in and what circumstances im in, i can barely aford this hobby and i have to be very carefull on how i organize my spending on it, i really cant afford to risk losing a plane and then my radio and engine iontop.

rmh

The arguments could go on an on ad absurdium
The selection of present TopFlite airfoils are as good as any
Caveat: As long as you get the wing loading in a reasonable range
Top Flight did in a past , some kits which made the planes very heavy for their size and the most infamous was the "snappin Cap" which many blamed on the shape (CAp20) of the model
nothing could be further from the truth.
The problem was that those kits were overweight
At the time we spoke with them about it before it was released I think it was 1983 or therabouts . They sent us the plans before the model was released and our comment was that it was going to be heavy
Their comment in reply was that it was intended as a sport model not a competition model and the target market really required the beefy construction
For years the Cap - all Caps-in the USA got the moniker "snappin Cap " and this was -in my opinion- largely based on the great number of these kits which were built and in the hands of novice fliers turned out to be a handful
the airfoil could have been razor tuned by the entire NASA group and the results would have remained the same - it was simply heavy - both sizes of the kit.
Our CAP 20 at the time was a different size -much larger -but weighed less than their kit . It was done as a competition kit ( see 1984 NATS Dec 1984) The model flew well even at low speeds and could do violent maneuvers on command - all because it had a far lighter wing loading - it was scale by the way ,except for wing airfoil.
subsequent Top Flights have proven to sell well and are very nice - we all learn thru experience.
I stand by my comment that selecting an airfoil before establishing weight and structure is pure folly.
NO ONE is that good.

Ben Lanterman

Sir Crashallot - You are mis-understanding me - I am saying that you SHOULD use the Top Flight sections as noted by BAX in the first several posts of this forum. They are the airfoils developed by Dr. Selig for scale RC use. They were developed especially for that use.

That is what I have been arguing with Dick about. He would have you pick out something that is a SWAG and use it, saying that if the airplane is light enough that it doesn't matter that much. I prefer to use the approach that is based in aerodynamic science - which the Top Flight sections are, and then try to keep the airplane light.

Ben

da Rock

There is a repeatedly expressed opinion that if you base ANYTHING on published, scientifically derived information, it's not as good as basing WHATEVER you're doing on the word of an experienced modeler. Guess which one.

Poppycock

Aeronautical doctrine is based on ideas that have been changed and refined over the years. And what's so ironic, is that most of them are simple and intended as starting points, not final solutions with absolute guarantees.

Does anyone know of ANY recently designed a/c that wasn't tested in a windtunnel to see if it'd stay upright? And didn't get modified if the sucker reacted differently with real air blowing over the model than the formulas predicted? Aeronautical doctrine almost demands the formulas aren't good enough, that testing has the final word. In fact, what happens after the windtunnel suggested modifications? They strap some egotistical lump into the sucker and see if he's still alive after the test flights. OK, actually, they test the crap out of the plane to see what it ACTUALLY does, and sometimes change some more stuff.

Don't get your knickers in a twist over SWAGs from BMEs nor expect the few aerodynamic references you can find to be magic. There ain't no magic, and there ain't no magicians.

rmh

use what ever you like but if you go with the TopFlite just because " Selig did it ".....
you must accept that unless your finished weight falls within the decent loading parameters -the airfoil won't save the plane.
A peepee contest about whether or not my choice of shape would be as good or better is a baseless argument.
Most of my airfoils were developed from Florsheim Imperial shoes and they have a very good track record.

sir crashallot

the build method will be very light and i openly admit thats its main strength will be in the glass skin, it will withstand nose overs and stuff but a heavy crash will right it off, but a model of such standards and size should not be alowed to crash so it will be very light

da Rock

Choice of airfoils for models has been proven over and over to be non-critical for models that don't have to lift the most weight or turn the fastest time or hang longer in light lift.

Bottom line on the "anything works as long as the wingloading allows"........ the fullscale airfoil falls into the "anything" category, doesn't it.

Selig, Eppler, Wortman, (any others?) did some model specific airfoil work. Their stuff does what they say their stuff should do. And competition modelers proved it and are still proving it.

But if all you want to do is fly aerobatics (which doesn't need a magic airfoil for an extra 4mph around the pylons) you won't go wrong following the advice of an expert in that kind of modeling. You might want to update the Florsheim WingTip sole curve a bit however and maybe use your air-spring soled, velcro strapped, glow-in-the-dark trimmed basketball shoe sole however. After all, anything works for that stuff. right?

sir crashallot

haha yeah, right another question pops into my head regarding the wings, i belive washout or wash in is introduced to models that duffer from servere tip stalling, can you or anyone tell me if i should encorperate any into the model i plan to build. i want to be able to jump into the build and not have to break off incase i run into any problems i didnt think about, if i can get everything all ireoned out smooth then im laughing in the face of confusion, so there will be no suprises when the build starts

Chad Veich

My Feedback: (60)

No need to reinvent the wheel here. Lots of good flying Mustang models have been built so the ground work has already been layed for you. The real question is what is most important to you, ease of flying or scale fidelity? Brian Taylor's 69" span P-51 design has proven to be very successful and it is as scale as anything available, including the laminar airfoil. Is it as easy to fly as an old Dynaflite Mustang with a flat bottom airfoil? Probably not. But it actually looks like a Mustang and not the box that the kit comes in! I'm not an aeronautical engineer, have not studied airfoil design endlessly, and will not claim to be an expert. However, 20 years of model flying and lots of warbird stick time leads me side with Dick Hanson on this one, light weight and accurate construction will pay much higher dividends than will airfoil selection. My .02 cents anyway.

Chad Veich

da Rock

The Mustang as a model doesn't really have a reputation for tip stalling. That is, if the model isn't overweight. At an average weight, and certainly as a light weight, it won't be nasty.

Most times, washout can be done after-the-fact. If your wing is glassed, or a sheeted foam wing, washout can't be done later. But with the usual style of construction, you twist and iron it in when you decide you need it.

One thing about models is they usually don't need lots of lift. Washout actually reduces the ability of the wing to carry the load, so building some in isn't going to be a mistake unless you also build in a lot of weight too.

sir crashallot

it wont be heavy thats for sure, the heavy part of it will be the 25cc lump of engine and the glassed skin, il be doing the glass skin to make sure its solid as i will bebuilding it not weak but very light,

da Rock

The glassed skin requires you to make the decision before flying.

So to be safe, put in a degree or two of washout. If the model has a cambered airfoil, it will have far more lift than required for flying around in a scale like manner. So giving away a bit of maximum lift won't matter at all.

HighPlains

My Feedback: (1)

I build mostly "D" tube wing structures. Any wash-out with this type of construction better have it built in.

rmh

Jeeze does anyone remeber D tubes ?
my first exposure was a Testors Senior in about 1951. that sucker got stuffed straight into a lawn like a dart and the wing had no damage.

sir crashallot

haha never heard of a d tube,
with the sounds of it im too young to know what these are as im only 22, heard of taking the tube and derailed and G strings but never d tube

rmh

Now I gotta ask one
if the wing area is the same - how can a camber give more lift than a non cambered wing when each has identical area
You are looking at the cambered shape being more efficient than a thin symmetrical shape?
again this is a model.in the size discussed.
Not sharp shooting just asking why this should be.

sir crashallot

right weve been going over aerofoil sections, now i keep hearing the words light and heavy so i thought id do some calculations,
the wing area of the wing is going to be 1680 inch, wing span is 70 and 16.5 inch root 7.5 inch at the tip excluding the very tip which is rounded, unfortunatly i cant provide a weight but i will be targeting the 10lb limit, engine radio and airframe, heck i may even go to a 9lb limit if the build goes as light as i think it could. will 1680 inch of area be enough lift for this bird and is the weight limits iv set ok or too heavy still.

topspeed

Michael Luvara had a similar task when he made a model of Tsunami with laminar foil.

http://members.tripod.com/~tsunam/

The Hergett Mustang gives 9 pages in google ( The eppler 203 foiled Mustang)...so it is pretty popular.

You are more after the scale effect and thus search for the "right" foil may give you extra credits for appearance as well.

You have some good comments here of modelists and real AC engineer...I think you will find the answer soon ( use the "force" or go for a stroll and it all clears for you I am sure ).

Good luck !

da Rock

You're kidding right?

da Rock

You're kidding right?

da Rock

You're kidding right?