Wing differences

[AV8nvrtd]

I'm supposed to fly a Christian Eagle down to Tucsons Ryan today to give a demo flight to a prospective buyer (weather permiting, it doesn't look real good right now). This is a great aircraft to fly. Just about as quick in roll as a Pitts and quite a bit more stable on landing with a little wider stance. Still a hand full though.

My question to you is (OK Larry, Ernie and others, let the students have at it!!!!!) what makes this plane and others such as the Pitts, Extra, Lazer and others like these fly so well inverted? What makes the wing so special for this mission? Is there a name for this type of wing? What are the drawbacks in trading aerobatic performance for ease of flight?

Hopefully, I won't see the answers that you give until I get back from RYN (I'm looking out the window and praying to the plane Gods).
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[lnuss]

You could also ask what helps the very quick roll rate on some of them. A Pitts is a delight to fly and, from what I've seen of it, the Christen Eagle should be as delightful. Sure would love to get my hands on one.

[HR]
Larry N.

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[AV8nvrtd]

There you have it! That is a very good addition to what I asked previously. Have at it guys and gals.
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[ChristopherT]

>You could also ask what helps the very quick roll rate
>on some of them. A Pitts is a delight to fly and, from what >I've seen of it, the Christen Eagle should be as delightful.
>Sure would love to get my hands on one.
>Larry N.

Well, the Pitts and Christen Eagle probably both have
a symmetical airfoil on the wings. These provide good lift
when inverted or right side up, but I have no knowledge what
thier bad points would be.

I do know the ailerons are deeper, in relation to the wing's chord, than standard aircraft. If the chord of a Cessna 182 wing is 5 ft and the aileron is cut into the trailing edge 6 inches,
then that governs how effective that aileron is. A high-roll
rate aircraft might have ailerons that are cut into the trailing edge 12 inches or so. That aileron would have a stronger effect on the wing when it left the neutral.

The Mig-15 has relatively short ailerons, and a suitably
matching slow roll rate. The F-86's could out roll MiG-15's
easily.


Christopher Tarana

[flyinggriffin]

The bad point of a symetrical airfoil, is that it produces less lift for the same area as a flat or semi symetrical. The rather low aspect ratio probably doesn't help its glide very much or its stability.

[jarno]

I don't know about the planes we are taking about here, but if I were a plane designer I would try to achieve quick roll rate by concentrating all possible mass near the roll axis. At least no fuel tanks in wings.

-- Jarno

[AlaskaAV]

Another good question Steve. Really helps new pilots and simmers become more aware of what makes their aircraft fly the way it does.
Still waiting to hear about the deadstick landing on Kodiak Island.

Ernie

[ChristopherT]

LAST EDITED ON Feb-24-03 AT 02:41PM (EST)[p]>The bad point of a symetrical airfoil, is that it produces
>less lift for the same area as a flat or semi symetrical. The rather low aspect ratio probably doesn't help its glide very much or its stability.

Thanks, FG! I suppose a lack of stability might be considered an asset in an aerobatic plane. As long as it was managable!

Christopher Tarana

[bilbo]

LAST EDITED ON Feb-24-03 AT 07:15PM (EST)[p]LAST EDITED ON Feb-24-03 AT 07:12 PM (EST)

good point if you are designing a plane for maneuvorability,
we are talking about the Christian Eagle and Pitts Special and they are both Biplanes. As such they don't need quite as much wing span as a monoplane. -notice I didn't say wing area. The wider wing span of a monoplane or otherwise larger aircraft can increase the moment of inertia factor as the plane rolls & the wing can cause wind resistance against the roll. One of the primary reasons why it isn't a good idea to try to barrel roll a 747.
Bilbo
P.S. One other word to add for the inverted issue discussion: "Dihedral"

[ladamson]

>The bad point of a symetrical
>airfoil, is that it produces
>less lift for the same
>area as a flat or
>semi symetrical. The rather low
>aspect ratio probably doesn't help
>its glide very much or
>its stability.

The Pitt's doesn't "glide"................. I know :)

Pull power & it decends rapidly, but the drag prevents it from building up too much downhill speed. One other item not mentioned, but at least I was told this; is that each of the Pitt's (S2B at least) wings are mounted at a slightly different incidence angle, so they won't stall at the same time. Can't say it's fact, as I've never seen it in writing, but the Pitt's pilot was quite knowlegeable on the subject.

Ladamson

[salmendra]

Now let me make a beginner´s question taking advantage of Steve´s point here.

On basic terms I always learned that lift is created by air going faster on the upper side of the wing (because it is curved and thereofre longer) than the air on the lower side which more often than not is straight. That creates a low pressure zone in the upper side opposed to a high pressure zone on lower side which "sucks" the airplane up.

Now something is missing here or a simetrical wing would not be able to fly. Same goes for the use of flaps which increase the lower side curvature. What am I missing.

Thanks and regards

Sergio Almendra
Curitiba - Brazil

[lnuss]

Thus is exposed the fallacy of the Bernouelli explanation of lift. While that is a factor on the high lift airfoils such as a Clark Y, and to a lesser extent on many others, there are also a number of other factors involved. Stick your hand out the window of a car at high speed, and you can use the angle of your hand to move your arm up and down. That is nothing, really, but deflection of air. And a paper airplane flies, but there is no rounded airfoil there.

Another factor is that there is a strong downwash off of any wing, thus bringing Newton's 3rd law into it.

In other words, it is not as simple as the "standard" explanation would imply.

[HR]
Larry N.

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[Shawnc]

Does the Eagle has the same angle of incidence as the Pitts?

"God has spoken to me and has given me 15... 10 commandments"

[Khirsah13]

That's done to help with snap-rolling and other aerobatic maneuvers. On the pitts the top wing has an angle of incidence about 2 degrees greater than the bottom wing if I remember correctly. This causes the top wing to stall first, allowing for a very quick snap roll, without stalling the entire airplane. Tis what I've been told by our resident Pitts pilot and my boss (who used to own one, too).

-Khir
Private ASEL
"When logic and proportion
have fallen sloppy dead,
and the White Knight is talking backwards,
and the Red Queen's 'Off with her head!'
Remember what the dormouse said:
'Feed your head. Feed your head.'"
-Jefferson Airplane, White Rabbit

[salmendra]

Larry
Thaks, I knew there should be something wrong with the explanation above. Never thought about the paper plane though.

Best

Sergio Almendra
Curitiba - Brazil

[bilbo]

Just to get technical here. Jane's cites that the
Pitts has 1 deg. 30' angle of incidence on the top wing and 0 deg. on the bottom. A bit less than several GA monoplanes that i looke d up that generally have a 2 deg angle of incidence. Probably because any more angle of incidence on the Pitts and it woud need much more nose to sky while flying inverted. This angle of incidence difference between the top wing and bottom would have been typical for bipes to reduce the severity of the stall. The Stags were known for this but as we know the stags had the lower wing forward of the top.

The dihedral on the Pitts is 0 deg on the top wing and 3 deg on the bottom. Probably (jsut guessing) because it would be a real pain to fly for long distances trying to keep her on the straight and level.

One other stability factor not mentioned yet is the 6 deg. 45' sweep back on the top wing measured at the quarter chord.
Bilbo

[lnuss]

LAST EDITED ON Feb-24-03 AT 11:51PM (EST)[p]Well, I see some factors identified on roll rate, but there are some other things, too. One is that it is easier to get a high roll rate with shorter wings. But there is one specific thing I was thinking about that is on some Pitts aircraft, but not all. I'm not sure that the Eagle uses them though-- anyone know what I'm talking about?

Maybe this picture of an S-1T will help:

http://www.frankenthaler.de/acro/pittsteam/Bilder/s1tphoto.jpg

Compare it with this picture:

http://www.yellowairplane.com/Pitts/Carlos_Macomb.jpg

[HR]
Larry N.

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[ladamson]

>LAST EDITED ON Feb-24-03
>AT 11:49 PM (EST)
>
>Well, I see some factors identified
>on roll rate, but there
>are some other things, too.
>One is that it is
>easier to get a high
>roll rate with shorter wings.
>But there is one specific
>thing I was thinking about
>that is on some Pitts
>aircraft, but not all. I'm
>not sure that the Eagle
>uses them though-- anyone know
>what I'm talking about?
>
the "spades"..................unless I've forgotten what they call them..

Ladamson

[lnuss]

You've got it in one, Larry...

[HR]
Larry N.

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[flyinggriffin]

I don't know if the Eagle is originally supposed to have the spades, but I know there is a local show pair called "Iron Eagles" that use the spades. The engine is also about the biggest you can stuff into the front of the airplane. They are both highly modified and one of the birds tried to kill its previous owner.

I thought the difference between the Pitts and the Eagle, besides the paint scheme was that the Eagle was offered just as a kit, while the Pitts could be purchased from Christian as either kit, or fully assembled. The engine options were totally different too. You used to see a lot of Christian Eagles in trade a plane when someone would build them, fly them a few times and find out that it is not something you want to take even on a short cross country.

In regards to biplane wings. I think the term for the relation of the angle of incidence is decalage. You want to avoid having both wings stall at the same time. I would imagine that the low speed handling would be lousy if they did. The buildup of drag right before the actual stall would be so abrupt you would would have a very nasty abrupt event. The distance between the two wings is also critical and the stagger. Building and rigging a 60 inch model biplane is a hair pulling task. Building a full size one must really test your blood pressure.

[AV8nvrtd]

Wow, what a response. Great answers and they were mostly right on the money. The Eagle is almost exactly the same as a Pitts. There are a few structural differences and of course, many different engine and propeller options compared to the certified Pitts. I would compare it to the S2B version of the Pitts for handling and performance. Yes, this plane had spades. They are an option for all kits sold. I think that you had to have these installed after purchasing a completed aircraft. I'm not sure if there ever was an STC for this option.

The flight was nice but a little rough dodging around some weather in southern AZ. I think (after a nice demo flight if I do say so myself) that this is a sold aircraft.

By the way! Bilbo!!!! Is that Tom out there? If so, haven't heard from you in awhile. How ya doin'?
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[bilbo]

doing fine Steve!:) It's good to see that you're still around also. I hope that your flight was ok and that you didn't spend too much time inverted. (You might run head first into one of those Saguros.)
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Been rather busy here with taking care of a few things. Sometimes life gets in the way of simulators as you know. I had started making a Tri-Motor for FS2002 (1/2 way done) but I think that I'm going to trash it for obvious reasons (FSCOF) and am thinking about doing a Monocoupe these days. I like that era on aircraft.
Bilbo

BTW. While trying to find some info on the Christian Eagle, I ran into a site where they had posted a few photos of John Denver flying his Christian. Nice looking plane!
Also for simmers, there has always been an inherent defect in the sim in that the flight models are basically based on a Cessna type aircraft. many flight model engineers try to input the exact numers for the flight models and in the case of multi-winged craft it's not possible. I particularly had this issue with modeling a Fokker DR-1 Triplane a while back.
So, modeling a biplane flight model presents a problem for these reasons:
A)You can't really model two distinct wings. You are only allowed one angle of incidence or one dihedral input.
B)If you input the correct wing area, it comes out as too much in the flight model. I'm not an aeronautical engineer but I believe that the reason is that some of the wing area on a biplane tends to cancel itself out because of the proximity of the other wing or because of the difference in the angle of incidences between the two wings. Any ideas?

[Shawnc]

Spades primarly help with the control forces, but the S-2B and the S-2C have the same roll rate (same wing length, B has spades).

The biggest diffrence is the Pitt's them selves a S-1 Ultimate is a mighty diffrent beast than the S-1C.

"God has spoken to me and has given me 15... 10 commandments"

[lnuss]

I expect you're right, Tom. Certainly there is some sort of interference between the two wings, and you can't model a partial stall with only one wing but, like you, I don't know that much about it. Also, we need to get prop drag modeled, since it has such an effect on aircraft behavior.

One of the problems with table-based flight models is that you are limited to the tables and parameters they decide to provide, and it's made more difficult with the lack of docs, since most of what we do know is reverse engineering and guesswork. Since COF will have the Wright Flyer, either they'll have a very special one-off flight model for it, or else they'll have a biplane model in their inventory and, given that they are supposedly using this flight model to be as accurate as possible it almost has to accomodate biplanes (or is that wishful thinking?). The fact that there is also a Jenny and a Vimy lends credence to them having to do SOMETHING to account for biplanes, if they want them to behave reasonably.

And since I've seen several notes here and there that they are even trying to get the Cub to handle right (even on the ground), maybe we'll come a bit closer to what we all want (or am I dreaming again?). We can also hope that they'll give us better documentation (meaning something) on what's left of the .air file (I presume they'll put more parameters in the .cfg).

BTW, I saw that site on Denver, also. Besides the Christen Eagle, they also had pix of him and his Waco.

BTW, Tom, I'd love to see updated versions (for ACOF) of your Staggerwing and Spartan- love those birds, though a Monocoupe would also be nice. Or you could do a 1929 Parks, the bird that Bach wrote about in Nothing By Chance.

[HR]
Larry N.

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[bilbo]

Ah yes prop drag. My one experience was on the Twin Bonanza you can really feel the difference when the pilot pulls back on the prop controls. It's a bit like driving a 4 speed std. tranny car in 3rd gear and letting off the gas. Almost like lowering a speed brake or flaps.
And of course the issue with the air files and MS not documenting the facts. Even if they were documented it can get very serious on the learning curve with some of the graphical edits that I've seen in the AirEd files.
I guess with COF, for many aspects we are going to have to sit it out and wait for the program (In eager anticipation ..........of what I will need to upgrade next ;)
I can't wait to try a few of those earlier models. Looks like they're probably leaving out the Sopwith and maybe the Corsair F4U -but that one was never really documented in the ads for FS2002 anyway. They were maybe testing out importing CFS2 planes and maybe forgot to delete it. hehe.
I have the Stag imported into GMAX but have not had time to work on her. It would need a total work over. Like creating a complete new skin. I would like this because I can do the wing ribbing pretty nice in GMAX. & I would like to experiment with doing a metal flake paint job. I saw one being restored with a sharp blue metalflake. With the reflections, it's probably dooable. The Spartan as well with all tht aluminium shining BUT I've heard that there is unofficial work on a commercial version by a group that I'm not really involved with. If I only had more time and money....
Bilbo

[lnuss]

More time and money -- yeah. I know what you mean. Well, whatever you get a chance to do. I just thought I'd put in my vote }>

[HR]
Larry N.

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