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Stuka aerodynamics - 1/17/2013 4:48 AM   
davidhand



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Status: offline 		I was considering modeling a Stuka, but I saw that Martin Simons in his book on model aerodynamics says the aggressively tapered wing is very poor aerodynamically.
Does anyone have an further information on this? The same thing would probably be true of the DH Mosquito.



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RE: Stuka aerodynamics - 1/17/2013 5:40 AM   
combatpigg



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Status: offline 		If you build the plane light enough, you can "get away with" any scale wing design...even radical super sonic designs can make decent RC flyers.
You can also "cheat" a little bit and give the wing a little more area near the tips, or even more area in span as well....if you aren't worried about scale judging.
It is possible to scratch build a reasonable facsimile to the original design and come away with a decent handling model plane, but obviously some designs lend themselves to more challenges and tweaks than others. It takes more work and know how [it seems] to build light..or shall we say, just heavy enough for flight and not TOO heavy.
Anybody can build too heavy...that's easy....



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RE: Stuka aerodynamics - 1/17/2013 6:10 AM   
wellss


 

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Status: offline 		I flew the Great Planes Stuka several times. It was very gentle, nothing to worry about at all. You can use high taper with forward sweep. So, airplanes like the Mosquito, Stuka or Hampden should be no trouble.

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RE: Stuka aerodynamics - 1/17/2013 1:28 PM   
sensei



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quote:

ORIGINAL: combatpigg

If you build the plane light enough, you can ''get away with'' any scale wing design...even radical super sonic designs can make decent RC flyers.
You can also ''cheat'' a little bit and give the wing a little more area near the tips, or even more area in span as well....if you aren't worried about scale judging.
It is possible to scratch build a reasonable facsimile to the original design and come away with a decent handling model plane, but obviously some designs lend themselves to more challenges and tweaks than others. It takes more work and know how [it seems] to build light..or shall we say, just heavy enough for flight and not TOO heavy.
Anybody can build too heavy...that's easy....


+1

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RE: Stuka aerodynamics - 1/17/2013 3:37 PM   
rmh



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Status: offline 		The airfoil experts would have you believe the theory they know applies to these smaller examples (models)
It has a relationship but that's about it
Getting structure and weight correct ,is far more important for our models
It's all about compromise on the full scale stuff and they fly in pretty tight envelopes !
On out models -we can change the speed, weight, structural materials, much more easily

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RE: Stuka aerodynamics - 1/17/2013 4:49 PM   
da Rock



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Status: offline 		Good thing about tiny outboar wing areas is they have tiny effects.

Yeah, there should be more chance Reynolds effects will have some effect. How much, however, is the key.

What size are you worried about? The tip chord is the telling measurement.

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RE: Stuka aerodynamics - 1/17/2013 7:12 PM   
vertical grimmace



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Status: offline 		Stuka's are generally known as very good, stable fliers. I thought the same way about the Stuka, as I read the Simmons book early in my modeling career. I think there are many things at play with the Stuka. The ailerons and flaps being seperated from the trailing edge has to have some effect. I'm sure an expert will chime in here. As always, washout would be a good idea. Scale models such as these are pretty easy to make "flyable" as a model anyway, as they will just do circuits of the field. Try designing a scale Stuca to fly IMAC though, then you will be tested. When designing scale models for 2610 combat, that was a real task. High wing loadings, but needing the ability to out maneuver the competition.
Your biggest concern with these scale models is not having a high stall speed when landing. Hence the need for light wing loading, and washout.
Look up some Ziroli Stuka threads. The owners rave about how easy they fly. Almost like trainers. Probably one of the best candidates for a first warbird.

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RE: Stuka aerodynamics - 1/29/2013 7:08 AM   
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Status: offline 		If its a true Stutka then its ailerons will be offset below the wing in a Junkers configuration. Why Stutkas were so stable. Shocking I know that they are called Junkers and guess who, dun-dudda-dun invented them... Junkers aircraft company and placed them on their Stutka dive bomber! For a modern example look no further than a Zenith Air 180 and its smaller cousins(Best real small aircraft you could possibly build/fly). The reason that even if you do "stall" your wing, your ailerons, being the 'Junkers' style will be below the wing and in free stream, meaning they will still have clean air flow and therefore Aileron power. Yea, a bit of extra drag, but wonderful for high angle of attack and likewise slow flying conditions.

RC airplanes unless made out of bricks, lead, and concrete will fly just fine as their wing loadings is absurdly low and wing shape makes zilcho difference. If you want to argue a UAV wing where efficiency is key, ok, otherwise ...

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RE: Stuka aerodynamics - 2/22/2013 8:04 PM   
Mattokun


 

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Status: offline 		If you're in doubt, you could also twist the outer wing a bit (like, -1 degree or so maybe, at the tip). That reduces local lift at the tips, and should help to make it more "calm".


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RE: Stuka aerodynamics - 2/23/2013 1:54 AM   
Lnewqban



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quote:

ORIGINAL: davidhand
.......Martin Simons in his book on model aerodynamics says the aggressively tapered wing is very poor aerodynamically.....


If I remember correctly, he referred to a slender wing ending in a point, belonging to a sailplane.

That is different to the case of the Stuka, IMHO.

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RE: Stuka aerodynamics - 2/24/2013 2:46 PM  1 votes
Villa



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Status: online 		Hi davidhand
The following has nothing to do with your subject, but I thought I would still offer it since the Stuka is a favorite plane for me. During WW-II the Germans used the Stuka as a dive bomber to hit things as small as a war tank. Well, statistics started to show that many pilots were so concentrated on hitting the target that they forgot to use UP elevator after releasing their bomb, and crashed into the ground, due to what is called "mission focused". So the engineers added a control connected to the bomb release that would input UP elevator upon bomb release. Problem solved.

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RE: Stuka aerodynamics - 2/25/2013 9:04 PM   
da Rock



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quote:

ORIGINAL: Lnewqban


quote:

ORIGINAL: davidhand
.......Martin Simons in his book on model aerodynamics says the aggressively tapered wing is very poor aerodynamically.....


If I remember correctly, he referred to a slender wing ending in a point, belonging to a sailplane.

That is different to the case of the Stuka, IMHO.



Simons definitely has some wing planform views that include one with a zero chord tip. The view is accompanied by a warning of the bad results that planform gives.

There seems to be more than one aerodynamics writer who provides slightly more practical advice on tiny tip chord designs. Simons book includes the same advice, thank goodness. The formula you see more than one place is that the tip chord should be > RC/3. I believe Simons says to avoid TC < RC/3.

I've not got the numbers for the full scale Stuka, but wouldn't be surprised if it's TC was just about 1/3 the RC. edit: after seeing the 3-views, the TC for most Stukas is definitely closer to .0RC than .3RC

< Message edited by da Rock -- 2/25/2013 11:08 PM >

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RE: Stuka aerodynamics - 2/25/2013 10:05 PM   
UStik


 

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Correct, but mind the G model (tankbuster)...

(And it's a triple-tapered wing, maybe to approximate elliptical planform.)

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RE: Stuka aerodynamics - 2/26/2013 6:12 PM   
BMatthews



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Status: offline 		Full size designs such as the DH Comet, Mosquito and others do have a reputation for surprising the pilots during slow flying or during high G turns where the highly tapered tips can stall before the root and cause a tip drop or even a snap roll. The classic method to control this is to incorporate more washout in wings with a high taper ratio than what is normally used.

But if you read around a goodly number of folks think that these designs are totally unflyable. That's not the case as models of them have flown just fine. But there's no doubt that a wing with a high taper ratio will require some care on the part of both the builder and the pilot compared to a constant chord style of wing.

On something like a Comet, Mosquito or Stuka I'd probably look at building in 3 degrees of washout. It might be a little more than what is needed but it's better to use a LITTLE too much than not enough and get surprised later on. On the other hand only 1 degree would simply not be enough to really help.

Part of the solution also resides in the pilot. When flying slow with any model it's wise to use the ailerons with a gentle touch and avoid using more than a smidge to perhaps a 1/4 of the total travel. Smaller aileron inputs and being patient while the model slowly rolls will greatly aid in avoiding the sort of problems folks get with higher taper ratios.

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RE: Stuka aerodynamics - 2/26/2013 9:03 PM   
da Rock



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Status: offline 		Remember that the Stuka has those separate ailerons.........

The combination of unique things about the airplane certainly would suggest that not much should be assumed about how it's going to act. Just think about the usual problem of low speed tip stall on approach we all know and love. The usual warning is to steer the plane in with rudder because the wingtip on the side with the aileron going down assumes an increased camber and the AOA also is altered when the aileron deflection makes a new airfoil out there at the tip. Since the Stuka's aileron deflection doesn't change anything about the wing tip other than by influencing the airflow, all those reasons vanish.

There doesn't seem to be any history of the plane snapping on pull out. Lord knows that sucker pulled serious Gs coming out of almost vertical dives. Of course there wouldn't have been a lot of aileron used if you remember most times the pilot was close to being blacked out. But the plane was very near the end of the envelope on AOA.... But no record of it being nasty at anything.

It'd be interesting to know the design history too.

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RE: Stuka aerodynamics - 2/27/2013 3:17 AM   
Lnewqban



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quote:

ORIGINAL: da Rock
It'd be interesting to know the design history too.


"The wing was the most unusual feature. It consisted of a single center section and two outer sections installed using four universal joints."

http://en.wikipedia.org/wiki/Junkers_Ju_87

Those tips couldn't lift much; hence, couldn't induce any snap.

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RE: Stuka aerodynamics - 2/27/2013 11:09 AM   
UStik


 

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quote:

ORIGINAL: da Rock
edit: after seeing the 3-views, the TC for most Stukas is definitely closer to .0RC than .3RC

OK, let's agree on .25C, actually it's 0.27C if you count the Doppelflügel (ailerons, flaps) in (see Abbott/Doenhoff p. 215 and 217, fig. 122).

AFAIK they didn't use flaps during hold-off but the Doppelflügel actually made for a slotted wing airfoil in any case. Besides, the outer wing panels are swept forward what may delay the stall by leading the "foul" boundary layer to the slots. The picture shows the slots, even if that is a Ju 87 towing a paraglider, hence flaps deflected.

The mentioned automat released the bombs automatically in sequence and then set up-trim for hold off. One of my books says 3.5 Gs were normal, that's not nearly black-out. Edit: And if you consider the high dive speed, the wing should be not at all near stall during hold-off but near its G-load capacity.

Never heard or read the 87 being vicious, but did hear and read that some 88 pilots had a love-hate relationship to their airplanes for some of their traits probably coming from high wingloading and nearly elliptical wing. The He 111 with its bigger wing was seen as a contrast.



This time I had not an instructor who flew the 87, my only connection to the 87 is that my father worked in an internship in a Ju 87 repair shop. Because he was slim and agile, he had to crawl into the tail cone and hold up for riveting. That told only for amusement, even if not his...

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