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Old Aug 18, 2012, 05:33 PM
flying high
United Kingdom, England, Sevenoaks
Joined Nov 2011
77 Posts
Discussion
f-15 build Foam scratch build,

hi all, well sorry there's no pictures to kick this off as the camera is dead, but im building a 118% scale 33" wingspan f-15, ive build a mock up in about 60% form around 15" long just to practice, and it came out well, and free flys better then i thought, a very balanced plane, maybe a tad tail heavy but actually helps keep the nose up as its just a plane to check.

any way ive got every thing cut out and weights 250g or 8.5oz

i was going to get a het fan, but thought this is my first build and im more then likely going to nose dive it in to the ground at some point. so i went with these items

fan/esc combo
http://www.hobbyking.com/hobbyking/s...dProduct=11165

battery
http://www.hobbyking.com/hobbyking/s...dProduct=11912

servos
http://www.hobbyking.com/hobbyking/s...?idProduct=662

and got these connectors 3.9 grams each (using 4)
http://www.hobbyking.com/hobbyking/s...idProduct=9572

horns 2g per 4
http://www.ebay.co.uk/itm/1907058929...ht_1592wt_1037

i haven't accounted for thrust tube or nozzle yet, but cant see that being more then 10g.

breakdown
wire/rx/connectors 30g
fan/esc 139g
battery 239g
3 servos 27g (ailerons, elevators,rudder ) i may add another for flaps in the future
horns and rods 8g
plane/foam airframe 250g this includes the support strips

so am i right in saying auw is 693g or 24.44oz



so will that fan be powerful enough for this plane? considering how well the plane flys on its own im very looking forward to seeing how it flys! also be very tempted to give it a chuck out side once its built with no kit in it, such a big plane weighing 250g is crazy!!!

so would it be worth building a thrust vector or would i get enough control? or as its tail heavy any way not worth it
also would i be ok putting my laid out like this and my servos like this?
dont like them out on the wings.

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Last edited by wanna go faster; Aug 25, 2012 at 09:02 AM.
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Old Aug 18, 2012, 08:58 PM
flying high
United Kingdom, England, Sevenoaks
Joined Nov 2011
77 Posts
suppose ill work it out for my self?
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Old Aug 18, 2012, 10:06 PM
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BanditBushman's Avatar
United States, OH, Groveport
Joined Mar 2012
151 Posts
That fan should be enough, you might actually get away with installing retracts if you have enough channels. Look at some micro GWS retracts, i have em in my 32" WS F-15. Deff. not missing hand launch! Im sure someone more knowledgeable with vectoring will chime in soon.

-Nate
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Old Aug 18, 2012, 10:14 PM
flying high
United Kingdom, England, Sevenoaks
Joined Nov 2011
77 Posts
im not fussed about vectoring, and retracts would be pointless were i fly.
i hope the fan is, i just used a calculator with the motor,esc,battery and fan specs and stats 960g static, and full speed about 90mph thrust being 434g, efflux 124mph.

when the plans say sand the leading edge , is this the top edge? i guess i leave the lower edge sqaure or best to round that of a little but of course not as much as the top?

what do you use in your f-15? do you find it a easy plane to fly as it seems a balanced plane, but once over twice its weight auw im not sure how itll fly
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Last edited by wanna go faster; Aug 18, 2012 at 10:23 PM.
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Old Aug 19, 2012, 11:19 AM
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BanditBushman's Avatar
United States, OH, Groveport
Joined Mar 2012
151 Posts
The leading edge is the part of the wing where the wind will be hitting. I think of it like this its the part that slices through the air. Also my F-15 is a bobdaeronort design with a 32" WS. Its a pusher prop but im building a larger F-15 with my dad and it will have edfs. It depends on how you are going to control it. I use the v-tail function and its easy to fly once you have some practice in. Most importantly HAVE FUN with your new F-15. Im not sure how it will fly over its AUW maybe if you have a big enough fan then it wont be a dog to get around. Also now that i think of it, thrust vectoring in such a small model might be pointless. You already have enough functions for a parkflier. Mine has just the elevators. But with the v-tail it acts like it has ailerons and elevator

-Nate
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Last edited by BanditBushman; Aug 19, 2012 at 11:24 AM.
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Old Aug 19, 2012, 12:31 PM
flying high
United Kingdom, England, Sevenoaks
Joined Nov 2011
77 Posts
it isnt small by my standards, but i get what your saying, for a first "big" plane im going to just use 3 servos, one for each control surface

here's a pic ive built the forward fuselage and rear section





been out all week end so got to Finnish and then have the task of cutting and glueing the canopy and nose parts.
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Old Aug 19, 2012, 06:34 PM
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United States, OH, Groveport
Joined Mar 2012
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Nice progress! Mine is black so yours almost resembles mine.

-Nate
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Old Aug 19, 2012, 06:50 PM
ich bauen groß modell flugzeug
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United Kingdom, London
Joined Dec 2010
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Old Aug 20, 2012, 01:57 PM
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Lt599's Avatar
United States, WA, Shelton
Joined Feb 2012
678 Posts
Good work so far, the F15 is a neat aircraft When it comes to the EDF where do you plan to mount it? Also remember that you will need to have large enough intakes to feed the fan. You should determin the FSA of the fan and make sure that the intake openning of your ducting is at least 100% of that. I am currently building the Schumate F18 as a pusher but I intend on doing an aprox. 160% version with dual 70mm EDF's in the future. Have fun with your build. I will watch your progress. Lt599
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Old Aug 20, 2012, 02:46 PM
flying high
United Kingdom, England, Sevenoaks
Joined Nov 2011
77 Posts
ill measure the intake openings when i get home, i have no idea what the fsa of the fan is but its a freewing 70mm fan

ive found it a very easy plane to build, ran out of glue now, no were sells uhu por or even foam safe glue.

as for fan location ill figure that out once the battery/esc and servos are in place, then determine that using the cg point and use the fan to balance the plane, going to use a peice of round bar under the plane at the cg point then once it more or less balances on the bar then ill know ill have a balanced plane
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Old Aug 20, 2012, 04:36 PM
flying high
United Kingdom, England, Sevenoaks
Joined Nov 2011
77 Posts
ok so each side is 63mm x 43mm
or 126 x 86 together

so 63 x 43 x 2= 5418mm2
but 126 x 86 = 10836mm2

bit confused there! math was never my strong point

the inside motor tube is 310mm and the inside of the fan tube is 70mm.

so 3848.451 (35 x 35 x pi) minus 754.767 (15.5 x 15.5 x pi) = 3093.684 mm2

does that make the intake 350.3%?

is that correct? lol

also what is 85% of the fsa for the thrust tube ?


if any one is better at math!
ducted fan is 70mm hub area is 31mm
2 inlets both messuring 63mm x 43mm

also if the plane auw is 654 grams and the thrust is 1200grams what thrust ratio do i have?


thanks
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Last edited by wanna go faster; Aug 20, 2012 at 05:17 PM.
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Old Aug 20, 2012, 07:54 PM
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Lt599's Avatar
United States, WA, Shelton
Joined Feb 2012
678 Posts
I ran the numbers through my FSA calculator and you are good The FSA at 100% is 3093.68mm

Thrust tube diameter at 100% would be 62.76mm
Thrust tube diameter at 85% would be 62.76mm

Convert your intake openning to mm and see what you come up with for overall size. I will run some numbers also and see what we come up with for intake openning.

I will try to attach the FSA calculator again. I tried last time and it did not work.

Lt.599
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Old Aug 20, 2012, 08:00 PM
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Lt599's Avatar
United States, WA, Shelton
Joined Feb 2012
678 Posts
You can can try Beacons Fabri Tac to glue your foam. You can get it at any WalMart just test it first to make sure it does not eat your foam. You can use it on FFF just do not use to much, just a thin layer.
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Old Aug 20, 2012, 08:04 PM
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Lt599's Avatar
United States, WA, Shelton
Joined Feb 2012
678 Posts
Your intakes are fine. Total of 5418mm. Your thrust to weight is 1.83 almost 2 to 1! You should be more than fine.
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Old Aug 21, 2012, 06:13 AM
flying high
United Kingdom, England, Sevenoaks
Joined Nov 2011
77 Posts
sweet, im more then happy now, thanks for the download that makes it easier then remembering pi and doing double calculations.

im in the uk so no walmart unfortunately, i hear its a pukka store for almost every thing!

ill just wait a few days and get it from ebay.

also once i get back from work at around 8 ill get a picture of mine and my mates build, hes as far as me now. but hes cut his nose and canopys, which ill get on with later, i know i havent got any glue but itll get it started. also need to re-cut my wing as i cut the slot for the spar to deep. and the glue has softened the foam though to the other side. so i might use epoxy for that instead.
my dad has a hot glue gun but thinking thats major weight and thinking as the glue dry quickly itll become a messy diffucualt job

im actually using a carbon rod from a kite lol!
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