different strokes for different folks!
before we end this evening, lets look at a little of the set up options.
The plane is going to be somewhere just less than 2.5 lbs.
I am am going to set it up to accommodate the Dons Wicked 3000 KV 450 outrunner.
I will also set this up to accept the XF fan from Hobby Lobby. I am contemplating a Little Screamer's edf motor or the Dons Wicked edf motor.. This fan is increadibly light and has a full shroud to enhance the flow on an external mount like the starfire will have.
I will use an extended 10mm stick mount to accomodate the set up once the outrunner set up is proven.
I am going to use the 9g hextronics servos as of now but that may change if the newer sub micro metal gear high torque servos arrive before the install part gets here, other wize it will be just the simple stuff for expedediance.
motor mount set up
As the "plans" for this kit are wide open to the interpretation of the builder for configuration, slope or power or thermal, we are planning to set this one up powered with an outrunner.
Because there is no set point for a thrust line, we need a little TLAR engineering.
I can not even begin to tell you how many times I have found myself faced with this dilemma in the past trying to convert something to E so here is my little trick to get it close.
Take the CG point on the wing and draw a vertical line at the root.
Take the center of the LE and the center of the TE and draw a line as close as you can connecting all three lines.
As this is designed to run fast and the motor is relatively close to the thrust line, we are going to start out setting up with the motor parallel with the thrust line (that is the line you just drew.)
I would normally go with light weight stuff, even the motor mount but as I do not have the luxury of knowing if my estimated thrust line is correct, I am going to opt for the motor mount that provides me the most adjustment until I know for sure if my TLAR was right.
The closer to the thrust line you get the less likely you are to have pitch up or down when accelerating or decelerating.
I am going to use a 5" 10mm sq beam mount and placing most of it in the foam. I would normally dig into the foam but I think the Center of Gravity should work with this particular motor as it is relatively light in relation to ther similar output motors.
Draw a dot through the center of the leading edge
Draw a dot through the center of the trailing edge
Draw a dot through the Center of Gravity
Connect the dots
Make all changes in thrust line from the center of gravity.
My motor mount beam will be 5" long and will extend slightly past the center of gravity.
I am going to set the Motor thrust puch the nose down slightly when the power is on. I am going to tilt the front of the motor mount bearer up 2 degrees from the 0 line I drew.
If you are using a high power motor for speed. I would use at least 1 degree of down thrust..
once you have established the thrust line, mark it on both halves of the wing at the root.
Take your motor mount mount and figure how deep it must go to allow for it to me flush with the bottom of the wing.
Mark the line.
Move to the bottom of the wing and subtract the thickness of the keel from the total width of the motor mount. divide by two and mark the width of the beam on the foam.
Now you are ready to cut the slot for the motor mount.
Start with a metal straight edge and a new razor blade. start slow and even gently pressing to the proper depth. Move the the side and cut in parallel to your building surface on the line you marked.
Do this for both wing halves making sure it all lines up
learn from my mistake
Well....when they tell you that gorilla glue foams a little, they are telling you based on a low average relative humidity in the room you are working. I made the mistake of rushing to get the spars set and left them overnight while the humidity was wayyyyyyy up there . . .typical south eastern summer humiity and man did I get a lesson!
The issue is that I set up a critical part of the plane in the beds then went to bed leaving the foaming traits of the glue by the way side . . .
When I came down in the morning, both the 48 and the star fire were lifting out of their beds from the glue expanding dramatically.
I have never really seen this but then again, I have never tried to set up spars while it was as humid as it was!
What I got was a warped mess with the spar lifting out of the core 1/4" at some points.
This makes for a messy dillema!
Now - I used regular gorilla glue on the starfire and the white - fast drying / low foaming formula on the 48 mcw . . .there was no differnece in the foaming of either once the humidiy is added into the equation!
The only difference is that one foam explosion was yellow and the other was white!
What a mess!
The fix was that I had to dig BOTH the spars and the glue out and redo the whole area . . all because I left this unattended for the entire drying process.
What I learned from this
1) never glue the large critical areas whithout checking up on the process at the 15 /25 and 45 minute points once you set the spars.
2) Make sure you weigh the whole thing down . . .the entire span (like I showed in the 36" build) so that there can be no uneven pressure on the spar. This keeps the glue in the joint even when it expands.
3) do not use more glue than you absolutely need as more = more mess and spread out when it expands . . if it gets outside the spar channel.
4) try not to use the gorilla glue when the humidity is very high (if it's raining - wait) unless you want the foaming action...
Digging these spars out was done with a dremel tool and a router bit and the spars were unusable once I finally got them out!
servos and long wings
the "default" length of every servo lead out there does not come close to the distance you need to go with this bird.
there are two solutions:
Buy a servo extension -
(needs to be soldered onto the servo to extend the lead)
buy a servo extender and plug it in
(needs to simply be plugged in but has an ugly connector that has to be accommodated in the routing of the wire trneches in the foam)
I am a type A and like the security of having my leads nice and clean with no big ugly connector. I have also been doing this with my servos for years so it is not a big deal to me . . . . . . .
If you choose to solder the extension, simply stagger cut the leads so that the 3 wires are cut with 3/8" length differences to allow for the heat shrink wire tube once you join the wires together.
The wire lays real flat and nice if you do it right and is a cleaner and safer install as the extensions can get corroded and remember - there is no way to get to them once they are in the wing!
Take a rule and draw two parallel lines 1/8" apart from the servo wire exit on the servo to the radio box are on the top of the wing that you drew earlier.
I know it is "early" but . . might as well get one thing down while you are in the area!
Take a piece of music wire . . .I use 1/16"
take a z bender and bend one end of the wire and see if it fits in your servo arms.
If it doesnt, take a drill and - gently - drill the second hole down from the top of the servo arm out to accommodate the wire.
Do not use the top one as it WILL break too easily. It weakens the servo arm.
You will not need as much throw as the servo is capable of giving so moving it in slightly will assist you in controlling the model later too. It also allows you to keep the servo shallower in the wing and the wire closer to the wing which reduces drag!
Last edited by pval3; Sep 10, 2008 at 01:25 PM.
cutting the spars
this requires at least an hour to set up and work . . . .
please give yourself the time to set up and do right as you only really get one shot at cutting into the foam.
I am a clean freak since my garage and hobby building area are co located!
The worst part of working with any foam airplane is cutting out the slots for the radio gear. The Dremel tool is fantastic at cutting the foam but it leaves a foam bead deluge throughout the room. It makes a mess!
Because of my unwillingness of getting foam dust all over my automobiles, I had to get creative.
The easiest way to make this work without leaving hours of clean up is to fist cover your entire work area with a .99c plastic tarp from your local discount store. Cover as much area as you can going up and around your work area. Take a vice and mount it to the leg of your work area and run a shop vac or regular vacuum cleaner tube through. Allow the tube to protrude over the center of your work area and make it hang over your work area. This will suck all of the dust out of your work area and foam off your project while you are running your Dremel tool.
Place the core beds on the table on top of the plastic tarp and your wing into the core beds.
The Shop vac has more than enough suction to pull up the debris from cutting if it is 4” – 6” above your work area. If the tube is secure it will not drift and tr to suck up the tarp!Here is the spar line marked. The wing halves have still not been marked as the most important part of the whole set up is yet to come.
Carefully and SLOWLY begin moving the cutting bit into the foam in the center of the area you are going to be clearing. I would recommend starting in the battery bay as this will give you a good feel for the resistance of both the white foam and EPP. Remember that anywhere there is a glue joint, the bit will stick slightly – take your time!
Go only 1/8 “ deep at a time and follow the lines slowly and test fit the gear into the wing. It should all fit snugly.
Here is the Dremel 1/8 routing bit that I picked up from my local hobby shop. This is the best thing to cut the foam and EPP without tearing it up.
Lay the wing in the core beds upside down and place a metal yard stick over the top to provide for a straight line and support for your hand while you are cutting.
You only need to go down into the foam the depth of the spar – this is just below the head of this bit. Take your time and use a nice even movement through the foam and EPP. The EPP cuts a little slower than foam if you move fast.
cutting the radio battery and wire trenches
While you are at it, you might as well do the rest of the cutting as the dust only needs to be cleaned once!
Just a point of info . .
this is the fourth cutting job i have done in my garage in the past 5 months. Out of all the foam cutting I have done in the past, the method I have pointed out has the least amount of clean up of any technique I have tried yet as the vacuum catches the dust before it gets out and about!
On this and the 48" build, I did the cutting with my wife's car in the garage while I was working.
I did not have any dust on her car in the am after using this method. Her car is dark metallic and shows everything . .other than the regular garage dust, there was no "fall out" from the cutting...this would also work in your house to minimize your cleanup from building.
Take the wing and flip it over, take a sanding tip from yor dremel kit and gently turn it on a slight angle in relation to the surface of the wing.
Using gentle strokes in the center, cut a trench leaving about 1/4" from the sides and the corners as well as the bottom of the wing battery box.
Switch to the same router bit. Cut the corners out little by little and test fitting to make sure you are not going too deep or wide.
Lay a straight edge on the foam to guide your hand for the servo wire trenches .. take these down 3/8" and 1/8" wide.
Take it slow, there is no reason to rush this process as the better everything fits, the stronger the airframe is.
try fitting it all together
now that you have cut the trenches for all the radio gear, try to fit it all in it's place.
I have found that the wires pose a significant challenge to making things fit, so plug it all in and try it out to see if it will fit in the alloted space.
You may want to think about your antenna placement if you are using a spektrum receiver to ensure that it will not be close to the carbon spars or make sure you have a plan for the ESC wires to come out to the motor as well as pass from the battery box to the esc compartment.
Think it all through . . . . and while you have everything plugged in, reset the zero point on your servos and trims to ensure that they are set properly and have full throw in both directions, no binding on the arms in the trenches . . . .now is the time to figure this out not after you bury all this under foam, spackle and covering!
I hate the mess of dremeling foam and do not mide the faom fumes of a hot wire cutter so i got creative for cutting spars..
This is not my idea but just my implimintation of some one else great idea.
I went to radio shake and got a 2 d sized battery holder and a few batteries
I cam home and took a 2 inch by 2 inch piece of light ply i had about 1/8 inch thick (not critical) I then took a bit of cutting wire found on E-bay (Stainless leader may work) and i made 2 small holes on the edge of the wood
I then took the heating wire and mad a half loop aroung my carbon spare to size it up and used the ply as my depth gadge the wire stick out past the edge of the wood as deep as i want the cut
then i use clip leads on the battery holder and the heater wire and use a strait edge and run the ply along it and the wire is heated and melts a nice grove I have also make a key hole shaped wire as well.
As to the Poly Glue and water I always spray my glue to get it real wet but i use a plasit or siliconized wax paper barrier and a 3/4 inch flat bar over the top od the spar slot and about 30 lbs of lead to hold it down
That way the glue foams away and impegnates its self into the foam better
I also lay some siliconized wax paper (wiltons parchment paper) un the wing beds under the wing in case the glue pushed through the other sid (happens with epp more than eps)
Any ways thought i magh toss a few ideas out
thanks for the cool tool idea paul
Hey paul .
thanks so much to that tool idea. . . can you upload some pics of your iteration so that we can see the finished product . .
Any thing that makes this easier is cool with me . . .tools rule!!!! - bet you could never tell that from seeing my hobby desk - - could you
Your plate method would be a heck of a lot easier to manage as the dremel takes a carefull hand to cut the right depth...
I am getting quite skilled with it after all these wings but . . . . . . . . I hate setting up all that drop cloth!
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