Twin-Air 45 build thread
12-15-2003 | 10:27 PM
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From: Evans,
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Twin-Air 45 build thread
I posted a thread about a month ago asking for some recommendations for a Twin-Air 45. Based on the responses there are several of us watching this forum that are planning to build one this winter. My kit finally arrived and I started the build this weekend!
I wasn't sure what to expect when the kit arrived. I have never seen this plane, and I haven't seen any real detail on the build on the web. I figure others may be curious on how the Twin-Air goes together so I figured I'd post some pics as I go along. If you have built this plane before please provide any advice you may have!
I was looking for an easy-to-build, easy to fly twin engine plane that I could hang my two spare OS 46FX motors on. I based my selection wholly on the recommendations that I saw on many of the threads that have been posted here.
OK, so step 1- opening the box. The quality of the wood is top-notch, everything is laser-cut, and the plans are rolled. All good signs. The kit comes with a very small instruction book with few pictures. It more or less gives the order of the build, but much of the "how-to" detail is left to the builder. Not a problem for me (I hope) since I've built quite a few kits and this one looks pretty simple. But I could see this being a problem for some first-time builders.
The tailfeathers are built from lazer-cut 1/4" pieces that fit together like a puzzle. 1/4" sticks are run around the fin and the rudder to stiffen it up. The parts fit perfectly and it only takes a few minutes to complete it all. (I haven't added images since the big RCU merger, here goes my first try)
I wasn't sure what to expect when the kit arrived. I have never seen this plane, and I haven't seen any real detail on the build on the web. I figure others may be curious on how the Twin-Air goes together so I figured I'd post some pics as I go along. If you have built this plane before please provide any advice you may have!
I was looking for an easy-to-build, easy to fly twin engine plane that I could hang my two spare OS 46FX motors on. I based my selection wholly on the recommendations that I saw on many of the threads that have been posted here.
OK, so step 1- opening the box. The quality of the wood is top-notch, everything is laser-cut, and the plans are rolled. All good signs. The kit comes with a very small instruction book with few pictures. It more or less gives the order of the build, but much of the "how-to" detail is left to the builder. Not a problem for me (I hope) since I've built quite a few kits and this one looks pretty simple. But I could see this being a problem for some first-time builders.
The tailfeathers are built from lazer-cut 1/4" pieces that fit together like a puzzle. 1/4" sticks are run around the fin and the rudder to stiffen it up. The parts fit perfectly and it only takes a few minutes to complete it all. (I haven't added images since the big RCU merger, here goes my first try)
12-15-2003 | 10:48 PM
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From: Evans,
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RE: Twin-Air 45 build thread
OK, now that I know I can post pics, next are the wings. The first step is to edge-glue balsa sheets together and then cut them to size. This plane uses a lot of sheeting and it looks like the engine nacelles are glued directly to the sheeting on the wing. I used the masking tape and white glue method to join them all, then sanded them flat.
The sheeting for the bottom of the wing is joined together on the plans, then the lower spar is glued to the sheeting, and the ribs are glued in place over the top. I was surprised to see that the spars are balsa instead of hardwood. But I guess with all the sheeting hardwood is probably not needed.
A hardwood landing gear support is glued down between two hardwood ribs with a balsa rib located in-between. BTW the instructions tell you to do this AFTER gluing the ribs down (not sure how) but I did it as one assembly. Additional hardwood reinforcment is added to the hardwood ribs, and a hardwood retaining block is added to keep the landing gear from rotating.
The instructions have a picture with an optional hardwood support glued onto the balsa rib, but then the text says that this piece is not included. I am not sure how I will reinforce this assembly yet.
The trailing edge strip is glued on next, and then sheer webs are added at the front edge of the trailing edge sheeting. As you can see in the pics this is as far as I have gotten so far.
The sheeting for the bottom of the wing is joined together on the plans, then the lower spar is glued to the sheeting, and the ribs are glued in place over the top. I was surprised to see that the spars are balsa instead of hardwood. But I guess with all the sheeting hardwood is probably not needed.
A hardwood landing gear support is glued down between two hardwood ribs with a balsa rib located in-between. BTW the instructions tell you to do this AFTER gluing the ribs down (not sure how) but I did it as one assembly. Additional hardwood reinforcment is added to the hardwood ribs, and a hardwood retaining block is added to keep the landing gear from rotating.
The instructions have a picture with an optional hardwood support glued onto the balsa rib, but then the text says that this piece is not included. I am not sure how I will reinforce this assembly yet.
The trailing edge strip is glued on next, and then sheer webs are added at the front edge of the trailing edge sheeting. As you can see in the pics this is as far as I have gotten so far.
12-16-2003 | 07:37 AM
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From: Evans,
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RE: Twin-Air 45 build thread
Yeah, that twin rudder setup looks good on this plane, doesn't it. Let's see, a built-up sheeted stabilizer to increase strength/stiffness, some sort of linkage to join the rudder surfaces... I'll consider it.
Questions- the original rudder is swept back, I assume to add coupling for some reason. So would building the rudders vertical help or hurt flight characteristics? How about size of the control surfaces. I generally can't get enough rudder, so would making them similar in size to the original be too much? I assume that locating them more in-line with the prop wash would only help performance...
Questions- the original rudder is swept back, I assume to add coupling for some reason. So would building the rudders vertical help or hurt flight characteristics? How about size of the control surfaces. I generally can't get enough rudder, so would making them similar in size to the original be too much? I assume that locating them more in-line with the prop wash would only help performance...
12-16-2003 | 08:41 PM
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From: Mary Esther, Florida, FL
RE: Twin-Air 45 build thread
Walt:
The LG blocks span three ribs, as you know but others may not. The ply reinforcements are on the ribs at each end of the block, and truly, adding a reinforcement to the intermediate rib adds nothing but weight. Don't bother with it.
The rudder is big enough as drawn, but some more wont hurt. It has been said more than once that there is no such thing as too much rudder on a twin.
You could leave the bottom of the rudder hinge line as drawn and run it vertical instead of having the angle to the rear. Changing the trailing edge to vertial instead of swept would still give you a little increase in rudder area, but a greater change in the fixed/movable ratio giving effectively a greater enlargement than actual.
You could also extend the trailing edge of the rudder, but you'd have to cut an angle in it for elevator clearance.
Finally, you could leave it as drawn. The airplane is a great flier just the way it's designed.
The picture Twinman posted is not a Twin-Air 45. Nor is it a bash of the Twin-Air 45. It is, instead, a Twin-Air 25. And the twin rudder option is shown on the plan. But if you want to go twin rudder on the TA 45, have at it. But as I said, it's a fine plane built stock.
Bill.
The LG blocks span three ribs, as you know but others may not. The ply reinforcements are on the ribs at each end of the block, and truly, adding a reinforcement to the intermediate rib adds nothing but weight. Don't bother with it.
The rudder is big enough as drawn, but some more wont hurt. It has been said more than once that there is no such thing as too much rudder on a twin.
You could leave the bottom of the rudder hinge line as drawn and run it vertical instead of having the angle to the rear. Changing the trailing edge to vertial instead of swept would still give you a little increase in rudder area, but a greater change in the fixed/movable ratio giving effectively a greater enlargement than actual.
You could also extend the trailing edge of the rudder, but you'd have to cut an angle in it for elevator clearance.
Finally, you could leave it as drawn. The airplane is a great flier just the way it's designed.
The picture Twinman posted is not a Twin-Air 45. Nor is it a bash of the Twin-Air 45. It is, instead, a Twin-Air 25. And the twin rudder option is shown on the plan. But if you want to go twin rudder on the TA 45, have at it. But as I said, it's a fine plane built stock.
Bill.
12-17-2003 | 07:41 AM
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From: Evans,
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RE: Twin-Air 45 build thread
As much as I would like to I don't see me "hanging it by the prop" or doing complex IMAC maneuvers with the Twin-Air. So the optimum rudder configuration for me is more a cosmetic thing than anything else. I am surprised to hear that the dual-rudder option is shown on the 25 plans but not on the 45. If there is any way someone could give me a look at the 25 plans for it I would be very interested. And after thinking about it, gettting the control linkage clean would be my biggest concern. It will be several weeks before I need to make a comitment so there is plenty of time to consider my options.
How about dihedral? The plans call for a total of 4" which seems like a bunch. I don't want the plane to fly like a trainer! I am hoping it will have more of a 4* feel.
I am still working on the wing but progress will be slow this week- long work days! But I have the next two off for the holidays so I should move along pretty quickly once we reach the weekend.
Walt
How about dihedral? The plans call for a total of 4" which seems like a bunch. I don't want the plane to fly like a trainer! I am hoping it will have more of a 4* feel.
I am still working on the wing but progress will be slow this week- long work days! But I have the next two off for the holidays so I should move along pretty quickly once we reach the weekend.
Walt
12-17-2003 | 04:47 PM
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From: Mary Esther, Florida, FL
RE: Twin-Air 45 build thread
Walt:
Apologies, sir. The twin rudder optin was not on the Twin-Air 25 plan, it was instead on the preliminary Twin-Air 15 plan. I am attaching three shots of that section of the plan. You will note it says the rudder linkage is "Left to the builder."
On the dihedral. With a "Hershey Bar" wing, you can look at the front view of the airplane, mark the center of each wing panel, and draw a line between these two points. This line roughly shows the center of lift. If the true center of gravity is below this line, the airplane has positive roll stability, If it is above this line, the airplane has negative roll stability. This is why a really good aerobatic high wing plane will have anhedral; the wings bend down rather that up. Other things will affect this also, so this method is just a rough approximation, it will get you in the ball park
For an absolutely neutral stability, all centers will be at this CG point. The thrust line, the roll center, the aerodynamic leverage of the rudder an elevastor all will be on a line through the CG. And they also will conform to the datum line of the airplane. That's why rudders are usually wider at the bottom, the Cap series is an extreme example of the rudder being biased toward neutrality. And the center of drag should also pass through the CG.
Please remember, Walt, while the Twin-Air is a really fine airplane, it is not intended to be competitive in pattern competition. It wil, however, fly the pattern, but other planes do it better.
If you want a twin that will do a really god job in pattern build the Duellist 2/40 Mk II. Please note this is not the one kitted by Pica, although the Duellist Mk I kit from Pica can be built as an almost Mk II without any great effort.
Bill.
Apologies, sir. The twin rudder optin was not on the Twin-Air 25 plan, it was instead on the preliminary Twin-Air 15 plan. I am attaching three shots of that section of the plan. You will note it says the rudder linkage is "Left to the builder."
On the dihedral. With a "Hershey Bar" wing, you can look at the front view of the airplane, mark the center of each wing panel, and draw a line between these two points. This line roughly shows the center of lift. If the true center of gravity is below this line, the airplane has positive roll stability, If it is above this line, the airplane has negative roll stability. This is why a really good aerobatic high wing plane will have anhedral; the wings bend down rather that up. Other things will affect this also, so this method is just a rough approximation, it will get you in the ball park
For an absolutely neutral stability, all centers will be at this CG point. The thrust line, the roll center, the aerodynamic leverage of the rudder an elevastor all will be on a line through the CG. And they also will conform to the datum line of the airplane. That's why rudders are usually wider at the bottom, the Cap series is an extreme example of the rudder being biased toward neutrality. And the center of drag should also pass through the CG.
Please remember, Walt, while the Twin-Air is a really fine airplane, it is not intended to be competitive in pattern competition. It wil, however, fly the pattern, but other planes do it better.
If you want a twin that will do a really god job in pattern build the Duellist 2/40 Mk II. Please note this is not the one kitted by Pica, although the Duellist Mk I kit from Pica can be built as an almost Mk II without any great effort.
Bill.
12-17-2003 | 10:19 PM
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RE: Twin-Air 45 build thread
ORIGINAL: Build-n-flyer-RCU
"As much as I would like to I don't see me "hanging it by the prop" or doing complex IMAC maneuvers with the Twin-Air. So the optimum rudder configuration for me is more a cosmetic thing than anything else."
"As much as I would like to I don't see me "hanging it by the prop" or doing complex IMAC maneuvers with the Twin-Air. So the optimum rudder configuration for me is more a cosmetic thing than anything else."
Maybe one idea to control both rudders is use three ball joint connections on a bell crank in the center of the elevator to each rudder.
Use two more ball joint type connectors at the rudders. What I am talking about is to minimize linkage play due to extra joints. A "tee type bell crank" with pull pull to the servo would be better than a push pull rod.
Why would you listen to me. I con'd a poor builder at my field to put five engines on a Kadett!!!
http://www.rcuniverse.com/forum/m_10...tm.htm#1060914
Twinman
<<Corrected your quote, TM.>>
12-18-2003 | 05:48 AM
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From: Evans,
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RE: Twin-Air 45 build thread
Twinman, you are killing me! I started this project thinking it would be a "no-brainer" build and now I find myself sitting in the office daydreaming of various control linkage options for twin rudders! And the engineering diploma on my wall is only making it worse- lets see, can I calculate the amount of deflection that a control rod oriented cross-wise from the airflow would have at say, 60 MPH and how much would that alter the relative rudder position...
Seriously, if I can come up with a control linkage option that makes me happy I may give it a shot. Minimizing the slop introduced by all the connectors that would be required is a factor. I also don't want to have highly visible control rods and bellcranks. And the rudders would need to have equal deflection as they are moved back and forth. I'll fire up Autocad this weekend and start drawing up some concepts.
Bill, are you saying that the 4" dihedral called for in the plans is the correct amount for this plane to have neutral handling? If I want to practice aerobatics I'll fly my Extra or Nobler, and if I want to go nuts I'll put up the Pizazz. But that doesn't mean that I want this plane to fly like a trainer!
Like I said, progress this week is slow due to work hours (and sooner or later I will need to find some time for Christmas shopping), but I will be back at the building board this weekend and will post updated pics.
Walt
Seriously, if I can come up with a control linkage option that makes me happy I may give it a shot. Minimizing the slop introduced by all the connectors that would be required is a factor. I also don't want to have highly visible control rods and bellcranks. And the rudders would need to have equal deflection as they are moved back and forth. I'll fire up Autocad this weekend and start drawing up some concepts.
Bill, are you saying that the 4" dihedral called for in the plans is the correct amount for this plane to have neutral handling? If I want to practice aerobatics I'll fly my Extra or Nobler, and if I want to go nuts I'll put up the Pizazz. But that doesn't mean that I want this plane to fly like a trainer!
Like I said, progress this week is slow due to work hours (and sooner or later I will need to find some time for Christmas shopping), but I will be back at the building board this weekend and will post updated pics.
Walt
12-18-2003 | 02:24 PM
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From: Mary Esther, Florida, FL
RE: Twin-Air 45 build thread
Walt:
The dihedral, as designed, flies very well. If you cut it by one half the plane will still fly well, and you would find it easier to flip the plane on its back. But it is designed to fly inverted as a somewhat afterthought, note the airfoil of the wing and the positive incidence.
Yes, you can re-engineer the plane to neutral stability, but I would advise your not doing so. Stock it will fly like a very advanced trainer, I think you will have enough "Knee-knocker" factor without doing any mods. Wait for your next twin to enter pattern competition.
Do you have G2? Get some stick time with the Twin Star simulation, alter the specs to agree with the Twin-Air. It will still lok like the Twin Star, but it will fly like the Twin-Air. And you can change the dihedral in the simulation to see how you like it.
Regards twin rudders. Two considerations. In normal flight you want a bit of "Ackerman," having the ruddder on the inside of the turn deflecting more than the outside. But at the same time, rudder deflection to counter offset thrust, as with one engine out, even deflection is more efficient as the airflow hitting both ruddders is nominally parallel. But still, the one on the side of the running engine will have more airflow and greater effect, so the differential throw really wont hurt. Your choice.
If you don't have G2, try it on a friend's computer. Great practice, when you hit the "K" to kill one engine the software will randomly pick which engine to kill. You can even do the single engined flights, take-off to landing without risking your real model. Highly recommended.
Bill.
The dihedral, as designed, flies very well. If you cut it by one half the plane will still fly well, and you would find it easier to flip the plane on its back. But it is designed to fly inverted as a somewhat afterthought, note the airfoil of the wing and the positive incidence.
Yes, you can re-engineer the plane to neutral stability, but I would advise your not doing so. Stock it will fly like a very advanced trainer, I think you will have enough "Knee-knocker" factor without doing any mods. Wait for your next twin to enter pattern competition.
Do you have G2? Get some stick time with the Twin Star simulation, alter the specs to agree with the Twin-Air. It will still lok like the Twin Star, but it will fly like the Twin-Air. And you can change the dihedral in the simulation to see how you like it.
Regards twin rudders. Two considerations. In normal flight you want a bit of "Ackerman," having the ruddder on the inside of the turn deflecting more than the outside. But at the same time, rudder deflection to counter offset thrust, as with one engine out, even deflection is more efficient as the airflow hitting both ruddders is nominally parallel. But still, the one on the side of the running engine will have more airflow and greater effect, so the differential throw really wont hurt. Your choice.
If you don't have G2, try it on a friend's computer. Great practice, when you hit the "K" to kill one engine the software will randomly pick which engine to kill. You can even do the single engined flights, take-off to landing without risking your real model. Highly recommended.
Bill.
12-18-2003 | 04:50 PM
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From: Evans,
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RE: Twin-Air 45 build thread
I am very familiar with ackerman from my old stock car racing days. But I don't see how ackerman would be necessary on the rudders of a model airplane. My instinct would be to set up the linkage to keep them as parallel as possible (and be very happy if it comes out close!)
I have G-2 but never have tried flying a twin on it. I'll have to take a look this evening to see if I have the Twin-star loaded up and play around with it a bit as you suggest.
I have G-2 but never have tried flying a twin on it. I'll have to take a look this evening to see if I have the Twin-star loaded up and play around with it a bit as you suggest.
12-18-2003 | 05:16 PM
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From: Mary Esther, Florida, FL
RE: Twin-Air 45 build thread
Walt:
The differential rudder travel reflects the inside rudder, just like the inside wheel, traveling in a smaller circle than the outer. But even more is similar to differential aileron travel - the inside rudder, with more deflection, has greater air drag and increases the effect on the yaw of the airplane. Many flying wing designs with twin rudders do not deflect the rudder at all toward the center of the plane, all deflection is to the outside. Right. The right rudder only is deflected for a right yaw, and vice versa.
Bill.
The differential rudder travel reflects the inside rudder, just like the inside wheel, traveling in a smaller circle than the outer. But even more is similar to differential aileron travel - the inside rudder, with more deflection, has greater air drag and increases the effect on the yaw of the airplane. Many flying wing designs with twin rudders do not deflect the rudder at all toward the center of the plane, all deflection is to the outside. Right. The right rudder only is deflected for a right yaw, and vice versa.
Bill.
12-19-2003 | 09:25 PM
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RE: Twin-Air 45 build thread
Build-n-flyer-RCU, William Robertson.
To all others........I got them going!!! This is going to be neat!!!
A real show stopper at the field. Why be normal.
An engineer??? I got him!!!!!!
Tee Hee!!
Twinman
To all others........I got them going!!! This is going to be neat!!!
A real show stopper at the field. Why be normal.
An engineer??? I got him!!!!!!
Tee Hee!!
Twinman
12-20-2003 | 01:22 PM
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From: Evans,
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RE: Twin-Air 45 build thread
John, please jump right in!
I'm ready to sheet the upper half of the wing now. Then I'll get started on the other one. The build will go fast now that I am off for the holidays. I'll post some pics showing progress later on.
I'm still considering the twin rudder option, but haven't done any "design" work yet. John, if you have any advice on this I'm all ears! I am interested in improving performance and certainly don't want to do anything that will hurt it!
I played around with the Twin-star on G-2 earlier this week. If the Twin-air flies like the G-2 model I will be very happy with it. Very easy to fly and land even with an engine out, and aerobatic performance is good. But my experience is that performance of the computer model is not necessarily the same as the real deal...
BTW I posted some pics in my gallery so you guys can take a look at what I've built and flown over the past year.
Walt
I'm ready to sheet the upper half of the wing now. Then I'll get started on the other one. The build will go fast now that I am off for the holidays. I'll post some pics showing progress later on.
I'm still considering the twin rudder option, but haven't done any "design" work yet. John, if you have any advice on this I'm all ears! I am interested in improving performance and certainly don't want to do anything that will hurt it!
I played around with the Twin-star on G-2 earlier this week. If the Twin-air flies like the G-2 model I will be very happy with it. Very easy to fly and land even with an engine out, and aerobatic performance is good. But my experience is that performance of the computer model is not necessarily the same as the real deal...
BTW I posted some pics in my gallery so you guys can take a look at what I've built and flown over the past year.
Walt
12-20-2003 | 02:14 PM
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RE: Twin-Air 45 build thread
Ok, where to start (without getting a caution from any of the moderators 
?
First, let me say, I'm always interested in your comments and suggestions on how to improve my kits.
Now, Bill is right-on most of the time, he's off just a little on the incidence on the wing. The wing has 0-degrees incidence (trust me on the math here). In fact the engines, stab, and wing are all 0-degrees incidence.
The plane does fly well inverted with a little down-elevator.
Ok now for the Twin-Tail discussion: The picture of the plane shown is indeed a Twin-Air .25 and not the .45 and the plans segment Bill showed is from the Twin-Air .15. Of the four Twin-Airs, only the .15 prototype had drawings for the twin-tail.
I'm attaching two pictures of the linkage used on the twin-tail Twin-Air .25.
To describe the linkage: there is a phenolic arm glued into each rudder in-line with the fin. On one end is a 'Z' bend and the other has a clevis for adjustments. Comming from the servo in the fuse is a control rod to a 90-degree bellcrank. The bellcrank is connected to a short control rod with an 'L' bend and a wheel collar. The 'L' bend goes into the bellcrank and the other end is soldered to the control rod that goes from rudder to rudder.
If there is enough interest in a twin-tail option for the Twin-Air and we can agree on a solid design (with linkages) I'd be more than happy to include it in the kit.
John
----------------------------------
There's Something in the Air
?First, let me say, I'm always interested in your comments and suggestions on how to improve my kits.
Now, Bill is right-on most of the time, he's off just a little on the incidence on the wing. The wing has 0-degrees incidence (trust me on the math here). In fact the engines, stab, and wing are all 0-degrees incidence.
The plane does fly well inverted with a little down-elevator.
Ok now for the Twin-Tail discussion: The picture of the plane shown is indeed a Twin-Air .25 and not the .45 and the plans segment Bill showed is from the Twin-Air .15. Of the four Twin-Airs, only the .15 prototype had drawings for the twin-tail.
I'm attaching two pictures of the linkage used on the twin-tail Twin-Air .25.
To describe the linkage: there is a phenolic arm glued into each rudder in-line with the fin. On one end is a 'Z' bend and the other has a clevis for adjustments. Comming from the servo in the fuse is a control rod to a 90-degree bellcrank. The bellcrank is connected to a short control rod with an 'L' bend and a wheel collar. The 'L' bend goes into the bellcrank and the other end is soldered to the control rod that goes from rudder to rudder.
If there is enough interest in a twin-tail option for the Twin-Air and we can agree on a solid design (with linkages) I'd be more than happy to include it in the kit.
John
----------------------------------
There's Something in the Air
12-20-2003 | 04:54 PM
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From: Merrimack, NH
RE: Twin-Air 45 build thread
Bill,
It's good to be back.
Here's a first shot at a Twin-Tail for the Twin-Air .45. We still need a linkage.
John
---------------------------------
There's Something in the Air!
It's good to be back.
Here's a first shot at a Twin-Tail for the Twin-Air .45. We still need a linkage.
John
---------------------------------
There's Something in the Air!
12-20-2003 | 05:24 PM
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From: Evans,
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RE: Twin-Air 45 build thread
Thanks John!
I don't know if there is interest by others, but if you are willing to work with me a little on this I will definitely give it a shot! (I am sure there are other Twin-Air builders watching this thread closely, right? ...right? Where are you guys?)
BTW I caught the Bill's incidence "error" but was afraid to mention it. I had my hands full with the ackerman and dihedral debates!
I was able to sort out your linkage setup from the photos and description and it looks quite simple. And I see you have the control hookup on the rudders in-line with the hinge lines to keep the control surfaces parallel as they are cycled. Some questions-
I assume that you have flown the plane in the pic. Does the control rod positioned just in front of the elevator hinge line disrupt airflow enough to make a noticable difference in the elevator response while in flight?
The plan pics for the 15 that Bill posted appear to put the back edges of the rudders in-line with the elevator hinge. Obviously, this is not the case for the 25 that was built since the rudder hinge line is even with the elevator hinge line (at the rear end of the fuse). Were the rudders simply pushed back?
The pics seem to show that the rudder surfaces extend below the elevator line, and the elevator ends are cut back to allow rudder travel. Is this correct? If so, then the rudders must be positioned at the very outer edge of the stab (not positioned at the line where the stab tips are glued to the forward part of the stab assembly as shown in the 15 plans)
And finally, what impact does the twin-tail have on flight characteristics on the 25 "prototype"?
Assuming that I decide to go for it- I can send you ACAD sketches before I start building anything if you are interested in taking a look...
Walt
I don't know if there is interest by others, but if you are willing to work with me a little on this I will definitely give it a shot! (I am sure there are other Twin-Air builders watching this thread closely, right? ...right? Where are you guys?)
BTW I caught the Bill's incidence "error" but was afraid to mention it. I had my hands full with the ackerman and dihedral debates!
I was able to sort out your linkage setup from the photos and description and it looks quite simple. And I see you have the control hookup on the rudders in-line with the hinge lines to keep the control surfaces parallel as they are cycled. Some questions-
I assume that you have flown the plane in the pic. Does the control rod positioned just in front of the elevator hinge line disrupt airflow enough to make a noticable difference in the elevator response while in flight?
The plan pics for the 15 that Bill posted appear to put the back edges of the rudders in-line with the elevator hinge. Obviously, this is not the case for the 25 that was built since the rudder hinge line is even with the elevator hinge line (at the rear end of the fuse). Were the rudders simply pushed back?
The pics seem to show that the rudder surfaces extend below the elevator line, and the elevator ends are cut back to allow rudder travel. Is this correct? If so, then the rudders must be positioned at the very outer edge of the stab (not positioned at the line where the stab tips are glued to the forward part of the stab assembly as shown in the 15 plans)
And finally, what impact does the twin-tail have on flight characteristics on the 25 "prototype"?
Assuming that I decide to go for it- I can send you ACAD sketches before I start building anything if you are interested in taking a look...
Walt
12-20-2003 | 05:28 PM
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From: Evans,
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RE: Twin-Air 45 build thread
I started my last post before seeing the previous two! (OK so I took some time out to look at the plans before submitting it). I guess I've got to get quicker!!! -Walt
12-20-2003 | 05:29 PM
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From: Sacramento, CA
RE: Twin-Air 45 build thread
John,
Count me in also. I have a Twin-Air 45 to build. It's nice looking kit, and I bought it due to all the good things that have been said about it here on RCU.
Count me in also. I have a Twin-Air 45 to build. It's nice looking kit, and I bought it due to all the good things that have been said about it here on RCU.
12-20-2003 | 05:47 PM
#24
RE: Twin-Air 45 build thread
NortheastAero
John,
Ref Twin air 45.
Will put my money where my mouth is. Offer it twin rudder and I will call you Monday........shhh! Wife might see!!
Twinman
John,
Ref Twin air 45.
Will put my money where my mouth is. Offer it twin rudder and I will call you Monday........shhh! Wife might see!!
Twinman
12-20-2003 | 05:52 PM
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From: Merrimack, NH
RE: Twin-Air 45 build thread
Walt,
Let's see if I can get to all of your questions. On the Twin-Air .25 prototype shown, the rudder line and elevator line are in-line. This necessitated trimming the ends of the elevator to account for the rudder's travel inboard. I never noticed any adverse problems by having the control rod for the rudders right next to the hinge line for the elevator. Though I suspect it accounted for a little whistling now and again.
As for the design posted here, I have moved the rudder inboard from the ends of the h. stab. This strengthens the joints between the fin and the stab. By doing this I also needed to change the rudder so that I did not lose so much elevator area. So the rudder hinge line moved forward and the rudder moved up above the stab. To keep the looks up, I also maintained the shape of the fin/rudder with a sub-fin under the stab -- which has its own benefits.
As for the rudder differential. That's a tough one. The math is right in that differential will help in turns by reducing drag on one rudder while increasing throw on the other. The practical problem is achieving differential in a model this size is going to cost you in weight and in complexity. Maybe its for the .60 size, but I'd go with parallel movement rudders on the .45.
John
----------------------------------
There's something in the Air!
Let's see if I can get to all of your questions. On the Twin-Air .25 prototype shown, the rudder line and elevator line are in-line. This necessitated trimming the ends of the elevator to account for the rudder's travel inboard. I never noticed any adverse problems by having the control rod for the rudders right next to the hinge line for the elevator. Though I suspect it accounted for a little whistling now and again.
As for the design posted here, I have moved the rudder inboard from the ends of the h. stab. This strengthens the joints between the fin and the stab. By doing this I also needed to change the rudder so that I did not lose so much elevator area. So the rudder hinge line moved forward and the rudder moved up above the stab. To keep the looks up, I also maintained the shape of the fin/rudder with a sub-fin under the stab -- which has its own benefits.
As for the rudder differential. That's a tough one. The math is right in that differential will help in turns by reducing drag on one rudder while increasing throw on the other. The practical problem is achieving differential in a model this size is going to cost you in weight and in complexity. Maybe its for the .60 size, but I'd go with parallel movement rudders on the .45.
John
----------------------------------
There's something in the Air!
