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F3jeb
103 Posts |
 Posted - 12/28/2003 : 2:29:39 PM
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What is the best way to find the proper angle of incidence on ether a standard Mantis or/and with the Terry fuse?
The first Mantis I got the angle of incidence for both tail and wing came out fine, by luck I guess, subsequent Mantis wing and Terry fuse setup I was not that lucky.
If you have a proven process I would greatly appreciate it.
Thank you
Jose
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Tom Pack
8 Posts |
Posted - 12/28/2003 : 2:52:25 PM
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| What I did with my PM is to mount the wing to the fuse forward section and the tail to the boom.......while they where apart...... then I slid the boom into the fuse and set it upside down on the work table. I shimmed the boom up so it was level, ie: "0" degrees and then shimmed the wing until it was at "+1.5" degrees. You need to have a incidence meter...this is the one I have http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXET66&P=7 but this one is newer and costs less and looks to be more accurate http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXPW71&P=7 I then screwed blocks to the table to locate everything and then took it apart and glued it together.....checking the incidence the whole time.....once it was dry I then took the tails and wing off and reinforced the joint between the fuse and boom........ |
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F3jeb
103 Posts |
Posted - 12/31/2003 : 3:45:56 PM
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I need help with finding the correct angle of incidence for both wing and specially V-tails.
Jose |
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Tom Pack
8 Posts |
Posted - 12/31/2003 : 7:57:07 PM
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OK! If you have the MH32 wing then 1.5 degree positive on the wing in relationship to the tails. I mount my tails to be in line with the boom...the cord line lines up with the boom.......so when the boom is set at 0 degrees you can set the wing to + 1.5 degrees. I found it easier for me to do as I replied earlier and mounted the tails to the boom and the wing to the fuse and then joined the fuse to the boom......that way I could jig it up so I could get the incidence correct without having to come back and shim the wing later on.....first and formost you need a incidence meter to accurately measure the angles.  |
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Phil Barnes
100 Posts |
Posted - 12/31/2003 : 9:12:18 PM
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One convenient thing about the Mantis (Either the classic "stick" fuse or the Luchenbach fuse) is that you can easily change the incidence angle of the wing at any time.
I have not yet built a Mantis with the Aegea wing or with the Luchenbach fuse but I would expect that if you just put the tails on at zero degrees incidence to the boom and mount the wing to the pylon with the bottom of the wing sitting flat on the top of the pylon then the incidence angles will be pretty close to what you want. The only other variable would be the exact alignment of the tail boom when you glue it into the forward pod/pylon assembly. I would just sight from the nose of the fuse down along the fuse and tail boom to check that. Check to see that the tail boom is in alignment with the forward fuse by just eyeballing it. The boom should just continue the natural line of the fuse rather than creating a discontinuity or kink just aft of the pylon.
Perhaps those who have built the Aegea/Luchenbach Mantis can confirm this. Remember, I haven't actually built one yet. I will build one in the next couple months and that is exactly how I plan to do it. I have never used an incidence meter yet on any plane although I may check this one now that Tom Pack has given me a number to use.
The classic "stick" Mantis should have the correct incidence if you just build it according to the included directions. The tail goes on at zero incidence to the boom. The wing sits flat on the pylon. There is no ambiguity about the angle of the pylon relative to the boom on that one. The pylon was made with the forward end 1/16" taller than the aft end which should set the wing's angle of attack correctly.
If when flight testing any Mantis you decide that the angle of attack is wrong then it is very easy to adjust. You simply need to insert a shim between the top of the pylon and the wing. If you have a ply plate on the bottom of your wing that sits on the pylon then you can either take a sanding block to it to give it a bit of an angle or you can add a piece of balsa to the plate and sand the angle on that. If your wing sits directly on top of the pylon (as I have seen with a number of the Aegea wings) then you could just add a shim to the top of the pylon.
That covers the mechanics and construction aspect of angle of attack or incidence adjustment but you may also be wondering how to tell when the angle is correct. This is, once again, incredibly simple once you understand what is happening. The following is true for any sailplane, not just the Mantis. I have seen many posts in other groups that show a great deal of confusion about this and I hope this clarifies and simplifies things a bit.
The first thing to understand is that the only thing that matters is the angle of attack of the wing relative to the tail. We talk about setting the tail at an angle relative to the boom and the wing relative to the fuse etc. but that is all just a way of indirectly getting a certain relationship between the tail and the wing. If you are flying a slope racing plane or maybe even an F3B plane then you might be interested in having the fuselage meet the air at just the right angle for minimum drag at high speed but for the purpose of a thermal duration plane I think we can neglect that for now and just worry about setting the tail relative to the wing.
The above may simplify things considerably if you didn't know it already. Here comes some more simplification; The only reason that you need to align the wing to tail is so that the plane will spend most of it's time flying around with the elevator or the ruddervators at zero deflection or at a minimal deflection angle. This condition will be less draggy than a condition where the surfaces are rarely at zero deflection or are more deflected than necesary. If you have a plane with an all flying stab then there is no such thing as proper incidence other than just setting the elevator trim at the transmitter to avoid having to hold an elevator input all the time.
With the above simplifications in mind we can move on to the procedure of determining correct angle of incidence. I just build a new plane as described in the first couple paragraphs. I just eyeball the angles and aim for something close based on whatever guidlines are available. In the case of a Mantis you can go with my descriptions or with Tom Pack's method or any other method you like to get somewhere in the ballpark. Then just take the plane out and give it a gentle hand launch straight ahead. Do enough hand launching until you think that you have your elevator trim set so that the plane will fly at a normal thermaling speed with hands off the transmitter stick. Now look at the elevtor/ruddervators and see if they are neutral or deflected. If they are neutral then you are done. That is the correct angle of incidence. If the elevtor/ruddervators are deflected up then you need to shim the leading edge of the wing up, cahnge the transmitter trims to neutralize the elevatot/ruddervators and try again. Keep readjusting the incidence and test gliding until the plane flies hands off at a normal thermaling speed with the elevator/ruddervators neutral. You may want to do some additional fine tuning after you launch the plane and have a chance to do some more flying at altitude but the concept is the same. You just want the incidence set so that the elevator/ruddervators are neutral with the plane flying at thermal speed. It's as simple as that.
With a Mantis, the simplest way to adjust the incidence angle is to put a shim between the wing and pylon. With other planes, other methods may be simpler. The important thing to remember is that there is only one incidence angle to worry about. The angle between the tail and the wing. On my old Merlins I used to cut most of the way through the tail boom, crimp the cut line closed and reglue the cut line(and reinforce the repair). That was the easiest way with a Merlin since it had two piece plug in wings with built up wing roots on the fuse. On other planes it might be easier to shim the stab or V tail mount (actually, that could be a good method for a Mantis if you have built a one piece removable V tail). On a plane with an all flying stab you need only to retrim the stab at the transmitter or with a pushrod adjustment.
I'm not entirely clear exactly what Jose was asking for. He probably knows most of what I just wrote but hopefuly I hit on the bit of info he was looking for. It certainly was a good question at any rate.
Phil |
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Tom Pack
8 Posts |
Posted - 01/01/2004 : 12:52:24 AM
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Phil,
You are correct with the standard Mantis......you can't screw it up! The way I arrived at the 1.5 degees is from measuring my son's "Mantis Classic" and using that measurment on the new one.....+1.5 degrees......That and I talked with a bunch of different people that all agreed that the 1.5 was a good starting point....Having a meter takes all the guess work out of the equation.....with the two part fuse ie: Luchenbach, there is the possibility to screw it up.....  ..... but if you use a meter there is no way you can miss........I always use the upside down method with v-tails.....that allows for all four point of the flying surfaces to sit in the same plane....the two tips of the tail and the two tips of the wing......so even if your fuse is a little bit off the wing and tail are square to each other and at the correct angle.... |
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F3jeb
103 Posts |
Posted - 01/04/2004 : 11:27:26 AM
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Thank you for the response, your answers covered what I wanted to know.
With my traditional mantis, MH342 and Phil fuse, I notice after a while of use, landings and wing adjustments, the sandpaper in bottom of the wing would eat up the wooden platform on the fuse. This created an un-even platform for the wing to sit on, although relatively easy to fix with small shimmies I notice/struggled maintaining that optimum angle of incidence. Tom your incidence meter comes in handy if I take a measurement once is all dilled in and record it so when is shifts I can find it easily back in the shop.
When I built the Terry fuse, with the help of Fritz, we paid very little attention to the V-tail’s angle of incidence in relation to the boom... I like Phil’s method of setting up the incidence during construction and then tweaking the wing until it is just right, the process is organic in nature so it is perfect for field work.
During one of my conversations with Terry last year, for the V-tail construction he suggested to draw a horizontal line on both sides of the angled pine block then align the leading and trailing edges of the ruddervators with the line, then glue in place.
With this information I should be able to setup correctly and re-adjust it if I loose it.
Thank you
Jose |
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How do I find the proper angle of incidence?
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