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Phil Barnes
100 Posts |
 Posted - 04/22/2004 : 2:57:37 PM
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I have gotten many requests to buy cross tails (or straight tails, T tails, whatever you like to call the non V tail, Bubble Dancer style tails)like the type that I built for my new Aegea Mantis. I normally like to get some substantial test flying results before I start selling something new but so many people have asked for this that I can't hold off the hordes any longer.
I did not build these new tails with production in mind so I must offer many disclaimers before accepting any orders;
1) I don't know if the sub fin will survive awkward landings. It could break off from a side slip style landing or maybe even a hard pancake style landing with a ballasted model. I built it with a sub fin just to make it look like a Bubble Dancer. I have only flown this model on two days and have only had one slightly awkward side slipping landing. I cannot guarantee or even guess what sort of abuse the sub fin can take.
2) To do the pushrod system that I used requires the cutting of long slots under the pylon for the pushrod guide tubes to exit. The cutting of these slots almost completely cuts the pylon off the fuselage. You must reinforce this area after the guide tubes are installed to return the proper strength to the fuselage. You can see some pictures of how I did it in my "fuselage finishing" post. I would never have suggested a system like this for a production model as it requires a certain level of craftsmanship and effort to do this and the results of doing it wrong are pretty bad.
You can see pictures and descriptions of these tails in the "Phil's new Mantis" and "fuselage finishing" posts. If you are still interested in obtaining this type of tail, here is the offer;
I will include the vertical and horizontal tails, prehinged. Also included will be the airfoiled pylon piece and a piece of carbon plate material for making the stab platform and control horns. Introductory cost will be $100.
To make the tail assembly exactly as I did will require the following;
1) creation of threaded hardpoints in the stab pylon for two stabilizer attachment bolts. I can post some instructions on how to do this.
2) cutting of the two control horns and stab mounting plate from the included carbon sheet. I do this with a band saw and a sander.
3) creating two epoxy hard points in the center of the horizontal stab for the mounting bolts.
4) You will have to purchase and install teflon guide tubes and .070 carbon rods for the tail linkages.
I can either post more detailed instructions here and/or include some instructions with the tails.
If interested, just send me an E mail.
Phil Barnes
philipdbarnes@verizon.net |
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drela@mit.edu
12 Posts |
Posted - 04/22/2004 : 10:13:39 PM
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I put the sub-fins on the AL, BD, and SG mainly to reduce torsional loads on the boom. But any boom which can withstand the big torsional loads of a Vtail, will easily take the loads of a conventional vertical tail completely above the boom. The bottom line is that there is little reason for a sub-fin if the boom is torsionally very stiff, like on Terry's fuselage.
I think that the sub-fin is also illegal for F3J, in case that matters to anybody.
Mark Drela |
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berniew
36 Posts |
Posted - 04/26/2004 : 4:16:04 PM
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What Dr. Drela said, can the X tail be made with no rudder sub-fin?? I know this might be a big change but the sub-fin seems like too much trouble.
I also think I would exit the rudder pushrod from inside the boom and the elevator pushrod from the side of the boom. This seems like it would be easier as there is only one hole in a less stressed area to patch. I would cut a slot for the front of the elevator for the Teflon tube to exit, put the tube in place and put a piece of carbon sleeve over the slot. This would be wet out, covered with heat shrink tube and shrunk with a heat gun, forcing out the excess epoxy and creating a smooth finished surface.
Bernie
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Phil Barnes
100 Posts |
Posted - 04/30/2004 : 10:09:27 AM
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I have sold all of the first batch of Aegea Mantis cross tails. I'll make another batch but this time I think I'll make some without subfins. I'll increse the size of the vertical fin (above the boom)to have the same area as the original fin/subfin assembly. I wonder how much interest there is in this. Drop me an E mail if you are interested in either type of cross tail. When I get enough interest I'll go ahead and make another batch.
Phil |
Edited by - Phil Barnes on 07/07/2004 6:41:29 PM |
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Phil Barnes
100 Posts |
Posted - 04/30/2004 : 10:24:02 AM
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Bernie's Idea of running the rudder pushrod inside the boom could be good. Just use the balsa support as described in other posts for the V tail pushrods. The elevator tube could exit the fuselage on top of the boom at the aft point of the pylon. This would have the disadvantage of partially obstructing the ballast compartment and the tow hook but would have the advantage of not structurally weakening the pylon. Just thinking out loud right now. This could be an option if you are squeemish about cutting slots in the side of pylon and needing to reinforce those slots as I did.
Bernie is suggesting also running the elevator pushrod inside the boom and then exiting it through a slot ahead of the stabilizer to connect to the elevator horn. This could work also. You would need to support the pushrod tube inside the boom with balsa supports like on the V tail installation or some other support method. You should also reinforce the boom wherever you make a slot for the pushrod exit. The biggest hazard with the Luchenbach fuselage boom is splitting of the boom since the boom has such a thin wall. A wrap of glass around the boom covering the exit area is all it would take to avoid the splitting problem. As long as your pushrod exit slots are narrow (just big enough to exit the pushrod sleeve) then you don't need to worry about weakening the boom in terms of bending strength or stiffness and so no carbon reinforcement would be needed at the pushrod exits. By the way, you should also put a wrap of glass around the boom just ahead of the fin/subfin assembly to prevent the boom from splitting ahead of the fin.
I had to come back and edit my own post after going back and rereading Bernie's post. The more I think about his ideas the more I like it. The two pushrod guide tubes would still be on the sides of the boom as I did but they would stay inside the boom. They would be attached to a balsa support just like with the V tail models but the support would lay horizontally inside the boom instead of vertically. The guide tubes would exit through slots ahead of the surfaces they are to connect to. The slots would be reinforced with a wrap of glass or carbon sleeve (buy carbon sleeve from CST). Bernie's carbon sleeve idea would very well and look cool too.
For those not familiar with carbon sleeve, this is something woven from carbon tow. It is woven into the shape of a tube or sleeve with the fibers all running on a bias to the long axis. The sleeves are sold in a variety of diameters. The diameter is variable. You slide the sleeve over the object (tail boom in this case) that you want covered with the sleeve. You then pull the sleeve tight (by pulling on the ends) and it constricts or contracts down to the size of the thing it is wrapped around. The stuff is normally used to give tube shaped things torsional stiffness or to prevent buckling of top and bottom spar caps on a built up spar, or in the case of the Mantis boom, to prevent the boom from splitting.
Phil |
Edited by - Phil Barnes on 04/30/2004 10:41:07 AM |
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Phil Barnes
100 Posts |
Posted - 04/30/2004 : 11:36:50 AM
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Instructions for assembly of the Aegea Mantis cross tails
The following will be some notes/instructions for the assembly of the Aegea Mantis cross tails exactly as I did on my Aegea Mantis. You can see pictures of my model with good views of the tail assembly in the "Phil's New Mantis" thread.
Included with the cross tails were;
Prehinged horizontal stab
Prehinged fin/subfin assembly
Stabilizer pylon
Carbon sheet to make stabilizer platform and control horns
Pattern sheet to lay out the platform and horns
Small bag of cotton flox for the making of threaded hardpoints in the pylon for the stabilizer bolts
Overview:
The Stabilizer pylon and platform are glued to the boom and reinforced with a wrap of fiberglass that goes all around the boom and up the sides of the pylon and under the stab platform. there are two threaded hardpoints in the pylon to accept two 6-32 stabilizer bolts. The fin/subfin assembly is glued into a slot in the tailboom. That joint is reinforced with fiberglass and the boom is reinforced with a wrap of fiberglass just ahead of the fin to prevent the boom from splitting. The stabilizer has two hardpoints for the mounting bolts.
Creating the threaded hardpoints in the pylon:
Drill two holes all the way through the pylon about 3/16" or 1/4" diameter. Mix a batch of epoxy (I use West systems 105/206) and cotton flox into a thick stringy paste. Fill the two holes in the pylon with this mixture. Be sure the holes are completely filled with no air pockets. I just force it all through from one end using an old razor blade as a sort of putty knife until the mixture oozes out the other end of the hole.
Coat the threads of two steel bolts with carnuba (car wax from any auto supply place)wax. Rub the wax deep into all crevises of the threads. Run the bolts through a nut to remove excess wax. You want the bolt completely waxed but you don't big buildups that would prevent you from molding the threads (the bolt is being used as a thread mold). Take some of the epoxy/flox mixture and rub it into the threads of the bolt and then insert the bolt into the two holes in the pylon. The still wet epoxy/flox mixture will ooze out the other end of the hole as you insert the bolts, just wipe away the excess. The purpose here is just to mold the bolt threads in the epoxy/flox mixture and to avoid air gaps as much as possible. The flox gives the threaded hole some strength so the threads don't break off. Set this aside to cure.
You may elect to use long bolts (maybe twice as long as the pylon's height) to mold the threads. That way you can see enough bolt length outside the pylon to align the bolts vertically while the epoxy cures. I would just eyeball them to see that they are close to vertical. After the epoxy cures you should be able to remove the bolts with a semi large screwdriver. I use two 6-32 steel bolts about 5/8" long to mount the actual stab. The weight is trivial so I wouldn't think of using nylon bolts.
Creating the stabilizer hardpoints:
You need to create two hardpoints in the horizontal stabilizer so that the bolts can be tightened without crushing the stabilizer. Put a piece of masking tape on the bottom of the stab in the center. Use a circle template to draw two 3/8" diameter circles centered where the stab bolts are. My bolt holes are centered about 7/8" and 2" back from the stabilizer LE. Use a sharp Xacto blade to cut away the skin where you drew the two circles. Use the knife and a small screwdriver to dig out the foam all the way to the top skin of the stab. Fill the two holes with a mixture of epoxy and cotton flox. Use an old single edge razor blade as a scraper to remove excess epoxy/flox mixture and to level it to the stab bottom. Once all excess epoxy is removed. you can peel off the masking tape. After this epoxy cures you can drill the two hardpoints for the stabilizer bolts. If you don't drill them exactly right the first time, you can enlarge them slightly until the bolts will go through and align with the threaded holes in the pylon.
I don't actually remember at this point how I got my two holes drilled correctly to match the pylon. Here is one idea that just ocurred to me; Stick a piece of masking tape on top of the pylon. Use an Exacto blade to cut two small holes in the tape that are aligned to the bolt holes. Transfer this tape to the stabilizer and use that as a drill guide. That will get the hole spacing correct and if you just keep all of your holes on the centerline of the stab and pylon then the stab should also end up perpendicular to the boom.
Slotting the boom for the vertical fin:
Put some masking tape on the end of the boom so that you can write on it with a pencil. Mark the center line of the boom on top and on bottom of the boom. I used the actual foam cutting templates for the fin to draw airfoil shapes using the center lines as a guide for the correct position. If you have airfoil software then you can just print out an HT12 airfoil for this purpose. If not you can just cut the slots by trial and error. I cut the slots with a dremel cutoff wheel. If you don't have accurately drawn lines then just cut the slots narrow at first and trial fit the fin. Enlarge the slots until the fin goes in. If the boom is already assembled to the fuse then you will need to get the fin to be vertical relative to the fuse. I just tack glued a spruce stick across the top of the pylon and eyeballed the fin perpendicular to that. I would widen out one side of the slot in the boom until the fin was perpendicular to the stick. It helps to cut the slots undesize at first and widen them as needed to make the fin perpendicular. You can also make simple slots about 1/8" wide at first and insert a piece of 1/8" balsa in the slots. Widen these slots out as needed to make the fin perpendicular and to fit the airfoil shape of the fin. The slots do not need to be perfect. The fin will be tack glued in with CA and then epoxy fillets will cover any imperfections in the slot. The joint is reinforced with glass patches over the boom and about 3/4" up onto the fin (you can see this in the pictures). A glass wrap is also needed ahead of the fin to prevent boom splitting (this could happen with awkward side slip landings that put a large side force on the subfin).
More Later |
Edited by - Phil Barnes on 07/07/2004 6:40:26 PM |
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Phil Barnes
100 Posts |
Posted - 07/07/2004 : 6:38:56 PM
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I have made another batch of cross tails. I made most of them without subfins this time. The picture below shows what you get when you order a set of cross tails except that you get either the vertical fin/subfin or the vertical fin without subfin, not both.
Image Insert:
18.04 KB
I have not built a model with the new fin design so I can't post any pictures of the finished installation. The idea was to sand the root end of the fin (it has a balsa root rib) to match the curvature of the boom. This could be done with a sanding tool made by wrapping sandpaper around a dowel or tube of some sort. Then just epoxy or CA the fin in place and reinforce with some glass.
Some sort of tail cone would be nice for cosmetic reasons and to help protect the rudder. You could just glue a piece of soft balsa into the end of the tail boom and then sand it to a nice shape. I would then put some light glass over the balsa tail cone.
I recomend gluing the fin on the boom with the hinge line flush to the end of the tail boom. Do not move the fin forward to put the fin trailing edge even with the end of the boom since that would put the tail group too close to the wing (tail moment too short). |
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Tom Pack
8 Posts |
Posted - 07/08/2004 : 12:16:28 PM
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>>This could be done with a sanding tool made by wrapping sandpaper >>around a dowel or tube of some sort.
Use the actual boom itself with sandpaper taped to it.......works like a charm! |
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bertmagin
9 Posts |
Posted - 01/15/2006 : 4:46:12 PM
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I am building (assembling?) an Aegea Mantis with Luckenbach fuse. I decided to try to p[ut the rudder and elevator pushrods inside (similar to Bernie's suggestion). I am using CST .070 push rods. how long would the fuse slot need to be? My slot at present is ~0.6" and this is not enough (i.e, there is binding of the pushrod). I'm concerned about enlarging the slot and weakenig the fuse. Would wrapping the whole thing with glass (pushrod sleve et al) take care of my concerns?
Might have this thing done for the next CASA contest.
Bert
Bert |
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Phil Barnes
100 Posts |
Posted - 01/17/2006 : 1:18:39 PM
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| You need to make the slot long enough so that the pushrods don't bind. That means the pushrod needs to be almost perfectly straight and the slot needs to be long enough to allow that. If you are doing Bernie's method then you have just the one slot in the boom for the elevator pushrod to exit. The slot would end up maybe 2" long (just a guess) and you could reinforce this with glass over the slot and pushrod tube. |
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bertmagin
9 Posts |
Posted - 01/17/2006 : 8:08:31 PM
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quote:
Originally posted by Phil Barnes
If you are doing Bernie's method then you have just the one slot in the boom for the elevator pushrod to exit.
I'm confused ... easy to do. Bernie indicates in his post above that both rudder and elevator are run internal. Seems to me to imply two slots. They could be in differnet areas (elevator in front of stab and rudder aft of stab).
Bert |
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Phil Barnes
100 Posts |
Posted - 01/17/2006 : 10:33:35 PM
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The Luchenbach boom is real large in diameter so if the rudder horn is short enough then the pushrod would just end at the aft end of the boom and stay just inside the side of the boom. I don't have a Luchenbach fuse or boom anymore to look at but I think that is what he was talking about. You might end up slotting the aft end of the boom a bit for the rudder pushrod or if you think the rudder horn needs to be longer then you would end up with a second slot further forward on the boom for the rudder pushrod exit.
The bottom line is to do whatever it takes to exit the pushrods wherever they need to exit to align to the rudder and elevator horns without binding the pushrods and don't worry about making slots in the boom. The slots only need a bit of glass to tie things back together again.
The reason why a bit of glass is all that is needed comes down to that old "stiffness versus strength" idea again. You hear that now and then if you follow some of the groups. The tail boom is another thing that is "sized for stiffness". The carbon boom never gets any where near to breaking because the amount of carbon used to make the boom is enough to prevent excess flex and that amount of carbon is a lot more than what is needed for breaking strength. When you cut a slot in the boom you only need to add enough of a repair to return the strength and to prevent the boom from splitting where the slot was made. You don't need to make the repair with the same type and amount of material that the boom is made from because you are sizing the repair for strength which takes a lot less material than a stiffness requirement.
You should make a good effort to keep the pushrod runs straight enough to avoid binding but as a last resort to eliminate binding you can switch to a smaller diameter inner rod. Leave the larger rod inside the sheath while gluing the sheath in place. Then remove the larger rod and use one size smaller for the actual pushrod.
Bert, since you live close and shipping would not be involved, let me know if you need some smaller inner rods. I could find some .060" and .067" stuff in my shop. But like I said, see if you can get the .070 in without binding first. |
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Tom Pack
8 Posts |
Posted - 01/18/2006 : 01:20:16 AM
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| Just courious......why not just put the pushrods on the outside of the boom? No sloting....no repairing.....and I doubt that the increase in drag will effect the plane at all. I have a Avagetis that I'm getting ready to build...Ava fuse, Agea wing, and Oleg cross tails and I'm going to run the pushrods on the outside of the boom.....where I know that they will be secured 100% of their length. |
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Phil Barnes
100 Posts |
Posted - 01/18/2006 : 11:49:08 AM
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quote:
Originally posted by Tom Pack
Just courious......why not just put the pushrods on the outside of the boom?
That's what I did with my Aegea Mantis:
http://forums.flyesl.com/topic.asp?TOPIC_ID=43
Its just a matter of preference. Some guys want the pushrods inside. |
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bertmagin
9 Posts |
Posted - 01/18/2006 : 2:16:47 PM
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Phil - Thanks for the help... I think I'll be OK with the .070 rods now.
Tom - Directions I can follow... choices on the other hand... well I'm just not an experienced enough builder to be trusted  . I could patch the small slot I have and go external... that might be what I end up doing. However, isn't there still a hole/slot near the wing pylon/fuse that needs patching/re-enforcement?
Bert |
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Phil Barnes
100 Posts |
Posted - 01/18/2006 : 5:36:25 PM
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quote:
Originally posted by Bert
I could patch the small slot I have and go external... that might be what I end up doing. However, isn't there still a hole/slot near the wing pylon/fuse that needs patching/re-enforcement?
Yes. It would be a pair of slots under the pylon which pretty much cut the lower fuselage off of the pylon. That's how I did mine a couple years ago. Check out the pictures here;
http://forums.flyesl.com/topic.asp?TOPIC_ID=44
http://forums.flyesl.com/topic.asp?TOPIC_ID=43
I put a couple layers of kevlar over the slot since I imagined the entire winch line load attempting to pull the lower fuselage away from the pylon. I wanted to be sure that I had a real strong connection to tie the fuselage back together. |
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Cross tails available for the Aegea Mantis
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