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Twin-Air Mods

Old 10-25-2005, 08:04 PM
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OldRookie
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Default Twin-Air Mods

I like the basic layout of the Twin-Air, but I have a real hard time with the ugly wing tips, and would like to make it look like a 1 or 2 place plane.
Would modifying the wing tips change the flying characteristics of the plane?
Would the kit as it is , lend itself to making a higher turtle deck and put on a Extra type of canopy?
Good sale price on this kit, would have to act by next week if I decide to do this.

Greg
Old 10-25-2005, 08:24 PM
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William Robison
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Default RE: Twin-Air Mods

Greg:

You like the Twin-Air but not the tips? Bash-em. Don't like the canopy? Bash-it.

That's the great thing about a kit. If you don't like some part of it you can change it as much or as little as you like. So long as the basic layout is left alone and the plane doesn't get too heavy you can do almost any mod you like. And it still flies as well as the stock plane.

In other words, have at it.

Bill.
Old 10-25-2005, 10:12 PM
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Default RE: Twin-Air Mods

The Twin-Air is about as good a platform for 'bashing as you could find. As long as you don't change the airfoil or the engine location I am sure it will fly pretty much the same. And the fuse is all just heavy balsa sheeting over formers so the sky is the limit as to what could be done with it.

Walt
Old 10-26-2005, 02:46 AM
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Default RE: Twin-Air Mods

Greg, you may be interested in this thread.

http://www.rcuniverse.com/forum/m_21...tm.htm#2105751

Cheers, Greg
Old 10-26-2005, 07:15 AM
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Default RE: Twin-Air Mods

How about this for a kit bashed Twin-Air.

First when it was built, we bashed it into a mock 1930's airliner with the reverse slant windshield, more rounded wing tips, re-shaped fin & rudder and little tip fins.

The next mod after flying for several months was to make it into a tri-motor. Still flies great.

We are planning a third mod of converting it into a sort of Savoia-Marchetti, Italian tri-motor with radial cowls and a further re-shaping of the wing tips, tail and cockpit/turtledeck.
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Old 10-26-2005, 07:36 AM
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Default RE: Twin-Air Mods

I should really say some more about the Twin-Air. You might call it the 4* of the twin world. It is an excellent basic design with many good design features and no bad ones that have to be compensated for.

It has a fairly large wing area so the wing loading is light enough to handle mods without the plane getting too heavy.

The wing is constant chord so you won't be getting tip stalls. It is very easy to handle at any speed. If there is one knock to the wing, in my opinion, it is the small ailerons. I come from the 3D area so I would prefer wider ailerons for increased roll rate, but most people won't even notice this.

The fuselage and nacelles are skinny and streamlined so the plane is clean, low drag and relatively fast with any power.

The fuselage is relatively long making the plane nice and groovy in pitch (looping) maneuvers.

The horizontal tail area is fairly large so CG placement isn't all that critical.

The vertical tail and rudder are large. The rudder is plenty large to handle any yaw from an engine out. Even without out thrust, you should not have any trouble handling the Twin-Air with an engine out. At half throttle, you can fly around on one engine and turn or land in either direction.

The main gear is widely spaced so you won't have any steering or tip-over problems like on a narrow gear plane.

In the construction area, it is an excellent kit. Everything fits. The balsa is good, and it's made out of real balsa, not cheap, easy-to-crack lite ply. The ribs are flat on one side so you can built the wing flat on the table. You won't notice any difference when inverted, by the way. The tail is sheet, not sticks, so it won't fail in a hard snap roll and you can re-shape easily. The nose gear block mounts to a 1/4 ply firewall type bulkhead so when we wanted to add a 3rd engine, all we did was remove the nose block and bolt the engine mount in place. All the doublers and strength were already built in.
Old 10-26-2005, 10:24 AM
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Default RE: Twin-Air Mods

Hey Ed,

While you are at the next round of mods to your plane why don't you try some new, bigger ailerons for us as well? I may actually give this a shot on my Twin-Air some time over the winter.

Walt
Old 10-26-2005, 12:17 PM
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Default RE: Twin-Air Mods

Greg:

Bashing is not limited to kits, of course, but starting with a kit is, I think, easier. You kniow what's inside when you start, the changes are easier to plan.

ARF bashing can be rewarding too. Here's my C-3/10 in before and after pictures.

Bill.

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Old 10-26-2005, 02:38 PM
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Default RE: Twin-Air Mods

You want big ailerons-I can do big ailerons. I was thinking 2" aileron stock with 1/4 tri-stock on the LE for a 2 1/4" total. That's what I used on a TwinStar and now it really rolls like a plane should.
Old 10-26-2005, 08:19 PM
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Default RE: Twin-Air Mods

Ed, I have seen your definition of "rolls like a plane should". Its a good thing that your airplanes don't have living pilots!

But I agree that more roll performance wouldn't hurt. If you try 2-1/4" and are happy with it then maybe I'll try 1-3/4"

Walt
Old 10-27-2005, 12:06 AM
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Default RE: Twin-Air Mods

NT FLYER...Thanks for the heads up on that thread. The plane is close to what I had in mind.

Thanks all for your input. Looks as if I have some ordering to do.

Greg
Old 10-27-2005, 07:50 AM
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Default RE: Twin-Air Mods

Walt,

Since I flew F-4s in the Vietnam war I can assure that speed and roll rate are life to a fighter pilot. The T-38 trainer will roll so fast at full deflection you can't count the rolls. As I recall, it rolled at 2 rolls per second, 720 deg/sec. When they built the Navy F-18, one of the major problems was the lack of roll rate. The contractor had to go back and make several costly mods to meet the roll rate requirement. The F-111 wasn't much of a dog fighter, but it could roll. I flew the FB-111, the SAC bomber version. Looked the same, but had different stuff inside. I was flying with a new navigator in the wing who had come from B-52's. We were cruising along to our refueling point and he mentioned he had never been in a roll. I popped the stick over and did a roll before he could think to say anything. I think it would do over 1 roll per second.

The amount of g's means a lot, but you can't pull g's until you establish the bank. If one plane gets to the bank quicker, then he is pulling around the turn before the slower rolling plane-loser.

If you will check the web, and I don't have the site, there is an article by one of the original Flying Tigers about the Zero vs. the P-40. We have all been told how the P-40 was obsolete and how great the Zero was. He says the opposite, that he never worried about a Zero or an Oscar. They both had very heavy controls near and over 300 kts. He stated that all you did was gain speed, and the P-40 was faster, and roll and turn. After a couple of reverses, you were after him. Unless you are really dumb, you never go into a steep turn and stay there in a fight. You move around a lot. A steady turn is a target.

What he said about the Zero reminded me a lot of what we were taught about fighting MiGs. The MiG-21 also had a slow roll rate at low altitude, below 15,000. You did the same thing as the P-40, roll back and forth, pulling for a small turn and soon your angle off increased. At high altitude, that's another thing, the MiG was better.

Roll rate is life, otherwise the military wouldn't go to such great lengths to insure their planes roll like mad.
Old 10-30-2005, 01:13 PM
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Default RE: Twin-Air Mods

Ed,

Nice comments.

As to the aileron width, I do get a lot of people asking if the ailerons can be made wider. Most of these questions come during construction. Once someone gets the airplane in the air, they are satisfied with the ailerons. There is plenty of roll rate there. I also fly 3D and had some monster ailerons on other planes -- I fly a 42% airplane with 5%-7% aileron throw for precision aerobatics and the rest is for 3D.

The Twin-Air (Sport-Air, Tri-Air etc) are sport planes and not 3D planes. However, I have drawn up a modified wing for these kits with a 1-1/2" aileron instead of the 1-1/4" aileron currently used. The two ways to go on this are:
1) just lengthen the aileron (and the wing chord in the process) or
2) increase the aileron by decreasing the rib in font of the TE. I'm looking at both.

Old 10-30-2005, 03:41 PM
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Default RE: Twin-Air Mods

Well, I got my kit ordered.
I have a lot of decisions to make before beginning my build.
Engines...Os 46FX, Os 50SX, MVVS 50.
Retracts...Yes or No
Horizontal stab...1 or 2 rudder
Turtle deck...what shape(may help knife edge)
Ailerons....Wider?
Color & trim scheme...?
I've been reading all the old threads. There are a lot of good ideas.

We'll see,
Greg
Old 10-30-2005, 06:30 PM
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Default RE: Twin-Air Mods

John,

I put 2" aileron stock with 1/4 tri on the LE for a 2 1/4 chord on a TwinStar. I also put in 2 HS 5245 mini-digitals. Now that increased the roll rate. I just like a fast roll rate and like you said, most people don't want or need it. The Twin-Air 45 rolls fine, it's just that you can count them.

Regardless, The Twin-Air is the 4* of the twin world, easy to fly and can be kit bashed into anything.
Old 10-30-2005, 07:02 PM
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Default RE: Twin-Air Mods

Ed,

One of the things that I learned at the Atlanta multi fly-in is that I have a lot to learn before I can keep up with you and Robby! The roll rate on the Twin-Air is plenty quick as-is, and even if I had more aileron I'm not sure how much I would use it. I just like performance and it seems like the next thing to do

I've been flying my Twin-Air a bunch the last few weeks, using it as a warm-up before flying the P-61. I have the engines really dialed in now (46FX's with Ultrathrust pipes) and the plane is really fast. I was worried a bit at first about the airframe handling the load but I haven't had any problems.

The secret to knife-edge with the Twin-Air is power/speed. My plane wouldn't quite hold it with standard mufflers, but with the tuned exhaust its no problem.

John, its reat to see you on the board again- its been a while!

Walt
Old 10-31-2005, 06:32 AM
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Default RE: Twin-Air Mods

The Twin-Air does have a skinny fuselage so there's not much side area for knife edge lift. Speed is the key when you don't have the area. Your plane does move, I'll say that. I have a couple of Ultra Thrusts, but not a matched pair for .46's. I might need to get a set.

Flaps is looking for 3-views of a Bernelli CBY-3, a twin engine, lifting body plane from around 1947. Vincent Bernelli from Texas, built planes with an airfoil shaped fuselage. Walt, if you were at the meet on Sunday, you saw the one that didn't fly. This was the model before the CBY-3. The CBY-3 had a wider fuselage.

In the Bernelli designs, the fuselage was a big airfoil and its lift supported its own weight. I don't know why the idea never caught on.
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Old 10-31-2005, 09:26 PM
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Default RE: Twin-Air Mods

Ed,

I was there Saturday but not Sunday, so I missed the Bernelli plane. But the pic looks cool. I really like unusual looking "scale" and that plane looks like it would be a fun one to build and fly. BTW I just looked through the Nov issue of Model Aviation and see that the event is covered in the district V report. There's a pic with me flying (got my better side ) but no pics of my Twin-Air!

We are going to do it again next year, right?

Walt
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Old 11-01-2005, 02:23 AM
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Default RE: Twin-Air Mods

Wally,, Wally,, Wally,,
Yes,, a good shot of your 'better side'..

Reason your Twin Air isn't in photo is we all
were waiting for you to bring it down close enuff
to take some shots at it,, errrr, I mean,, OF IT..
yeah,,thats it,, 'of it' .... [:-]

With all the practice you have bene getting in
we damn well expect you to show us old folks
a few tricks... Got it!!!

As to the subject athand..
I'm all for Johns #1 choice..
"just lengthen the aileron (and the wing chord in the process) "
This will also lessen wing loading which is always good
on a multi... Take it from someone who knows..
Heavy singles fly crappy... Heavy multis fly even worse.. [:'(]


Robby
Old 11-01-2005, 06:16 PM
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Default RE: Twin-Air Mods

Count me in for one next year.

Robby, how about it? You were the CD.
Old 11-01-2005, 08:40 PM
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Default RE: Twin-Air Mods

I got my Twin-Air yesterday.
That was pretty fast John! Nice job on the kit.
I have decided on the OS 46FX's for power.
Still have more decisions to make before starting, and also have to finish up my Extra 300S.
Got something to keep me busy this winter.

Greg
Old 11-01-2005, 09:01 PM
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Default RE: Twin-Air Mods

Yes Ed <all> ,,, the Multi Meet is a definate thing for 2006...

Only this time better and more advance advertising...


Oh,, and did ya notice, Walt, they did put a pic of *MY*
planes in the mag.. naa naa naa... {{duckin'}}} pg176

xxxxxx xxxxxx
Old 05-01-2006, 08:32 PM
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Default RE: Twin-Air Mods

If I modified the twin tail vertical stabilizers to look more like a sport plane, would it change the characteristics of the Twin Air?
I was thinking more along the lines of a stabilizer on a pattern plane.
I put a turtle deck on mine with a canopy. It kind of looks like the turtle deck of the Ultra Sport.
What would wing tip plates do for the Twin Air if anything at all? I have seen posts by Ed Moorman that pointed out that wing tip plates extended below the wing tip could eliminate coupling problems. How about it ED? (Knife edge)
What do the wing tip plates do for the new Funtana design? They extend both above and below the wing tip.
I just can't live with the stock wing tips.

Greg
Old 05-01-2006, 09:15 PM
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Default RE: Twin-Air Mods

I have not noticed much pitch or roll coupling with my Twin-Air.

As for the tail, a good rule-of-thumb for horizontal tail design is 20%-25% of the wing area. For the vertical tail, 10%-12% of the wing area. Longer fuselages can use less and shorter ones need more. You could easily put a vertical like the Dual Ace on the Twin-Air. Basically, if you keep the area about the same-don't decrease it-you can do just about anything with the shape. At least, that has been my experience.

Tip plates will increase the roll rate, lower the landing speed and stall speed and make spins and snaps harder to do (you'll need more elevator). Downward only plates will decrease the effective dihedral. Upward plates will increase the effective dihedral. What I generally do on a high wing plane with a flat wing (they roll with rudder) is to make plates from lite ly and screw them on. I fly, try knife edge and trim the bottom off until the roll stops. For a .25-.61 size sport plane, a good distance is about 3/4" down only. If your dihedral is correct, full plates on the order of 3/4" all around will be about right. Once I get what I like, I dress them up with some balsa laminated on and sanded, then covered to match the plane.
Old 05-02-2006, 12:15 AM
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Default RE: Twin-Air Mods

Thanks again Ed.

How about the shape of the rudder?
Some are parallel LE & TE
Some Taper small top big bottom
Some hinge lines are perpendicular, some angled.
How about the vertical stabilizer that extends to the outer extent of the rudder?
Would any of these change flight characteristics of the Twin Air?
Sorry for all the questions.

Greg

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