|Mar 06, 2011, 07:37 AM|
Simple Build KFm9 pod and boom gliders with excellent performance
If you want a simple build and an excellent performance you might like to try this one or back at page 4, I have a new build that is making some super smaller gliders..
page 1 is a 1.7M span using 3mm foam sheets...powered with a blue wonder..a real floater that will thermal well
page 2 is a 48" span which uses 2mm foam sheets...pure glider ..a basic slope trainer or flat field job
called the 'No Brainer' because the maths needed for the steps are simple and no virtualy no calculator was needed.. even the body is a simple thing to make and flying the thing requires little or no thought... no brains needed for a superb flight
The 1.7M wing is a new KF section/profile designated the KFm9... with an 8" chord it can use 4 layers of 3mm foam to get a thin wing (target 7% of the chord for wing thickness on all the gliders)..with the steps as shown in pic1 below.. all the numbers are easy and the cuts straight, so an easy fast build..
1.7M span.... 200mm(8") chord ...length 39" tail to spinner front....Blue wonder 1300kv motor.. 7.5x4.5 folding prop... 3 cell 500mA-800-1300mA lipo fit..
AUW with an 800 is 16.5oz
COG on all the KFm9 wings....a safe place to start is at 35%....make possible to adjust later to 38% or more if thats how you like it... at 40% its getting a bit sensitive for me but will still fly ok
Lets start with the wing
Laminating is done using UHU por adhesive..this is a contact adhesive that is spread thinly onto the two areas to be fixed, left to dry , then they are pushed together.. you get one chance at this so be acurate when you line the layers up.. do the laminating on a flat surface.. I use a glass coffee table top as my flat surface..
For each layer, before adding glue, mark the area where contact /glue is needed, then spread the glue, old plastic cards do a good job getting the glue on very thinly. take great care in positioning, accidental contact will stick layers just when and where you dont want to..
note as seen in pic 3 there is a position in layer2 where the spar goes..this little bit of foam should be removed , leaving the layer in two half strips.. so mark which is the front strip and which is the back strip... like pic4
I wont go into more detail , what is important is that the step locations are as marked on the lines drawing, the spar is in place and is sandwiched/covered by the outer layers, and the wing has been made flat..
Actual spar positions can be varied, the usual/common wing spar location is arround the 33% of chord but its not essential.. on this wing it could have been taken further forward ok but not so ok if moved rearward.. The spar I thought does need at least one layer above and below..
However when the wing was all done it felt a bit too bouncy/floppy so additional small dia CF rods were let into the wing, see the next post
|Mar 06, 2011, 07:37 AM|
The wing with just a single central spar felt too bouncy, so two CF rods of 1.5 mm were slotted into the center panel outer skins about 1/2" in front of the spar location in the thickest area on the wing...each layer is first slotted with a blade, then the slot opened up with a pen point and the rod glued in with UHU por to fit flush to the surface of the foam..
Note the rods must be vertically opposite one another... also before tape covering the wing let the glue fully dry..
Leading edge.....carve and sand to a nice sharp profile..this takes a while...see the rough idea in the first pic in post 1..
Note...a good leading edge will make a lot of difference
EDIT....This wing is going very well.. its plenty strong enough and has a great glide..if you follow the build carefully you will be very pleased with the end results
|Mar 06, 2011, 07:38 AM|
The no brainer wing is all done ..you can use it on any fuz..but here is what I built for it...
note the pics show my original build... on this build I fixed the rear bar for the bands by binding and CA'ing the joint..so its about 1" behind my box fuz...
It works, but it is important to follow the guide drawings and build the fuz box a bit longer to include the rear crossbar in the main fuz block..and note here as you laminate the block layers use some epoxy smeared arround the cross bars to strengthen the area
The original had to be modded to extend the main block as the trailing edge was not supported and the wing was getting creased
I also used an old bit of fishing rod for the boom.. ok again, but a bit flexible, so better to use a 5-6mm CF tube instead..this will fit better into the main fuz block of 3mm layers
To start laminate the 4x3mm layers of depron to the boom..make sure the boom starts 2" away from the front of the block, and cut and laminate arround that..
Cut out 4 layers to the required width and length. mark a center line on one length..
The boom is cool melt glued to this layer making sure all is nicely positioned along the line.
Now trim fit the next two layers either side of the boom and the last layer over the top as a cap..
Fit two cross bars into one of the outer layers .epoxy them in and smear some epoxy on the depron..this will be the botom layer on the fuz block
As a reinforcement add a 1" wide strip of thin ply on the bottom layer, it goes from the front of the boom to the rear of the fuz block
Note the difference between the revised drawing and my original build is the Fuz block now is longer to keep the rear cross bar in the main block... My original crossbar was behind the block and the rear of the wing ended up getting creased by the bands pulling it down and having no support..i have now extended the block to give my wing support at the trailing edge
|Mar 06, 2011, 07:38 AM|
It seems an odd time, but now we make and fix the V tail.. fitting the servos and pushrods
By making all the rear at this stage you can see where your bits have to be fitted to get a COG of 35%
The instructions for the build are in pic1
Using two layers to make the tail lets me fit in a fabric hinge.. this is a totally slop free system and makes for a strong V tail ..cover the tail with the usual colored tape..does a great job..
The pics here show an uncovered tail glued to the boom ...Its easier to cover the tail then glue it to the boom, then add some tape over the boom and glue joint as a cover..
Fitting the sevos was a bit of a puzzle.. to get straight pushrod runs I ended up with the arrangement shown.. this makes it impossible to remove servo arms, so it is vital that you have your arms at vertical with the servos centered.. then glue em in with cool melt...As can be seen the servos fit nicely in the block with the horns not quite touching the boom..5gm servos are more than enough here..
The pushrods used were 1.5mm CF and were guided every 3-4" using a small length of plastic tubling taped to the boom..I used a quick link system at both ends bound and CA'd to the pushrods
Ive made a few more pod and booms since this one and if you position the servos forward in the pod you can have them standing vertical, which is much easier, the pushrods then are sloped down to exit the fuz at much the same level. you just need an extra guide tube at the rear of the fuz
pushrods are 1 or 1.5mm cf and are threaded through guide tubes taped to the boom.. the tubes are 3-4" apart and stop the rod flexing and loosing force at the horns
|Mar 06, 2011, 07:39 AM|
servo location ...position the center of the servo 65mm in front of the rear cross rod...
fuz sides again use 2 layer of 3mm....cut four parts of 40 x 400...laminate to make two sides... taper the rear 150mm of each down to 25mm, this is for some shape at the rear...glue the sides to the main block so the outside edges all line up.... at the rear pull the tapered section in as seen in pic1 to leave a 25mm gap for the push rods to exit..
Motor block....I made a block of 7 layers of 3mm ...to fit between the sides of the fuz....I drilled this and epoxied a shortened tube mount for the blue wonder
The sizes on the drawings show show the fuz lengths to line up near to the folding props spinner..the nose block should be recessed between the sides to allow the motor to also fit between the sides... I used about 5 degrees of down thrust and 3 degrees of right thrust when epoxying in a tube mount... I would suggest upping this amount to 8-10 degrees of down, because it pulls the nose high with full power and constant down input is needed to keep the climb from stalling..
I still havnt changed my thrust angles.. my motormount is a tube type and was fitted into the nose block by drilling and gluing so is not easdily altered...what I do is usually climb at only half power or less...with low power it will climb slowly but almost hands off...all nice and easy..
Nose shaping....once the motor and spinner is in position add/glue depron bits to the fuz around the motor till you can sand and shape the front to better match where the spinner has ended up...make sure you leave enough clearance for the airflow round the motor....
Note ...after cooking one motor on a hot day the knife has come out and the 'nice shaping' has been totally removed leaving the motor full exposed for better cooling
|Mar 06, 2011, 07:39 AM|
Finishing the fuz.....
With the servos installed the top of the fuz should have one more 3mm layer added as a wing seat going along the top between the cross bars...
Fitting the gear.... fit a long strip of velcro onto the ply plate inside the top of the fuz, from the motor block back to the sevos...
The esc goes at the front ..the rec goes at the back...leaving a long free area for your battery..
If youve used a blue wonder and 5gm servos the 35% COG should be easily obtained by moving the battery about in this area..
Now last chance to make sure to check the workings of your servos..I had to remove some depron to let the arms get to their full travel..I also added some silicon tubing on the quick links to make them secure..
When you are all set you can glue on the rear lower decking..2x3mm layers..this covers the servos and the rec..
At the front a short fixed deck of 2x3mm layers with a fabric hinge to hold the lower hatch 2x3mm layers to whatever length closes the fuz..a small block of scrap depron on the inside atthe rear of the hatch will act as a locator for accurate closure
Give the fuz a smooth shape by rounding the corners except for the wing seat
Cover the whole fuz with colored stick tape
|Mar 06, 2011, 07:40 AM|
V tail...requies a mixing setup on your radio or a Vtail mixer to be fitted between the receiver and the servos
looking at the tail from the rear...up elevator gets both surfaces up and down gets them down
rudder left gets both surfaces going left, right gets them going right..If you are unsure just look at each tail half in turn, from the rear, with them orienated vertical, like a more nomal fin and rudder..left is left and right is right
remember these are not tailerons.
Trimming and flying
Test glides first..you are to adjust the respective trims and the cog position to get a nice flat stable straight glide..
Start with the TX trims... with a firm level push.. trim it out for a nice glide.. now throw it harder.. did the nose go high/flare up, if it did your model is nose heavy and the up trim you have used is making it flare up... move the COG back a bit by using the battery position.. retrim and go again..
The idea for stability is to have a very slightly nose heavy setup.. near to the flatest glide will be a good stable flat glide..you want a hands off glide that will land itself...
When you are happy add power.. not full power 1/3-1/2 will be fine..we are looking for a hands off stable slow and steady climb.. Reduce power if the nose pulls up too much and dab the stick forward to flatten it out..if needed cut the power and it should glide itself down..
What you dont want is for the nose to flare right up, then the model will stall and likely crash..you must keep the model as level as possible..
What we are doing here is adjusting the downthrust on the motor.. idealy as power is added the downthrust will cancel out the uptrim set for the glide..
Most modelers prefer there own trim.. for gliders I like adding power to give me a steady climb, full power to give a steep climb and half to give me a hands off slow climb...
To adjust/increase the downthrust you have to loosen the motor and put packing under the top of the motor..
If you cant adjust the thrust lines, you have to think about adjusting trims as you alter the power
When I made the prototype I didnt have enough down thrust. so each time I powered up to climb I have to keep dabing or holding in some down. to stop the nose getting too high..Thats fine when you are a competent flyer..luckily I found that on low power it will climb ok hands off with no stalling
That is why I have increased the down thrust to 8-10 degrees, I only have about 5 degrees and this results in a very high nose up at full power
video of maiden
please note I only got the start of the session ..the best flights were missed..
|Mar 06, 2011, 07:40 AM|
Final pics and sketchup files
|Mar 06, 2011, 10:41 AM|
If Ive forgotten anything please pm me....dave
edit after many flights.... this is a real pleasure to fly...easy and stable..it can be slowed to zero speed and parachuted down, with all nice and stable..it will pick up any lift thats there, and will thermal fine...overall its very very nice...
with my limited storage space this is definately a long term keeper
|Mar 06, 2011, 11:40 AM|
Joined Apr 2005
You just have to recapture the best flights for us. Looks like a real good floater, yet has good control authority. Bet it will be a good light wind sloper also. I may just have to order some 3mm stock. More vid please.
|Mar 06, 2011, 01:48 PM|
will do as soon as the weather improves...perhaps tuesday off the slope if the forecasts hold
Ive found a problem on my build that is already corrected for on the extended fuz drawings....The bands are damaging the rear of the wing causing creases where the wing has no support at that rear crossbar...so now Ive got to extend the fuz top block back to support my wing..easily done and already catered for on the new drawings
|Mar 08, 2011, 07:48 AM|
Here is another video showing how nice and easy this will fly
A windy day flight..some nice and easy flying...1.7M span ..blue wonder 1300kv 3 cells 7.5x4.5 folder.. the model will fly and climb slowly almost hands off at only 1/3 power..half and full power makes the model go up faster and a lot steeper, so needs some controlling..
This is an easy flier..I used 3" dihedral ,under each tip,and its great for me, more stability could be added for beginners by increasing the dihedral to 5"
|Mar 08, 2011, 07:51 AM|
Ive been trying to get the brake working on my glider with no luck, the brake setting was selected but the prop kept spinning... untill I read that you should set the throttle max and min on an esc..???? what ??? never done that, just use the esc.. .
But I tried it ...throttle top ..beep beep.. throttle bottom.. beep..... and now the brake works..
well I never realised that....
|Mar 15, 2011, 06:54 PM|
Another session with a working brake and the glide is further improved...as an example..I made a downwind turn for a landing approach, and then came by 20 ft above my head so I had to go round again... and its hard to judge it correctly, its always going by, rather than landing at my feet..I am too used to power models with a steeper angle of glide
Only one fault remains on my prototype build and thats the boom... it is an old fishing rod top section and flexes so much that the tail gets fluttery at times, especialy when you try to aerobat it....even sitting on the ground the wind can get it wobbling about...It looks like it should be a problem, but in fact its fine..
But do use a 5 or 6mm CF tube as shown on the plans..
The fishing rod will do for me, a rebuild is not worth the while.. its a keeper as it is...it simply looks odd now and again and does not affect the flight at all..
|Mar 28, 2011, 06:10 AM|
Ive had even better flights now, Ive recently extended my glide times in some very light lift that was coming off the roofs of the houses at the end of my field.. the sun was working well and the warm rising air was just enough to keep the glider from loosing height...
This wing is a super gliding wing and more than strong enough.
My next wing is going to be a 2M build with dihedral at the center and two separate wing panels
EDIT...actually ive since built 2 smaller span versions..one for my flying buddy and a pure glider(DLG) for me..so a bigger one might never get made..ive also got disracted with pitcheron models using the same KFm9 build..
|Thread||Thread Starter||Forum||Replies||Last Post|
|Wanted Art Hobby Glider 1.7m-2m||bradley_r1||Aircraft - Sailplanes (FS/W)||0||Apr 19, 2009 04:19 AM|
|Wanted Art Hobby 1.5M, 1.7M or 2M Glider||rvillegachapa||Aircraft - Sailplanes (FS/W)||2||May 31, 2008 02:09 PM|
|Discussion Easystar or slo-v.....NO BRAINER RIGHT?!||xFxLxYxExR||Electric Plane Talk||10||Jun 09, 2006 09:10 AM|
|Sold NIB 1.7m Libelle E glider||dr.E||Aircraft - Sailplanes (FS/W)||16||Sep 21, 2005 10:44 PM|
|The Best Overall Parkflyer Value: A No-Brainer||wannabe||Parkflyers||48||Aug 31, 2004 10:36 AM|