straight foward dynaflite "bird of time"e-powered, winter 2012 build

[mred]

You can go 1/2" if you want to, but 1/4" to 3/8" will work fine. I used 1/4" on one of mine and 3/8" on another and they both worked fine. You just need enough so the covering has something to hold on to. If you look at the picture below, I only used 1/4" wide strips for this one and the covering stuck great. Just go over the inside edge and iron it down good and you should not have any problems.

Ed

[stuart]

once again,a pictures worth a thousand words...lol. the frame you spoke of was a top surface equal to the rib caps. i was thinking you meant balsa in between the ribs to fold the covering over and iron down. i like what you did but is it built up at all on the under side so it doesn't break with a accidental push?

one other question for all you e power converters of sail planes...did you go neutral with the motor angle or down/right thrust. at the moment mine is neutral.

I'm getting more motivated to completing this bird.

[Larry3215]

Stuart, if you take that spoiler servo you have pictured above and rotate it about 45 degrees counter clockwise, you will get a better spoiler leverage ratio.

If you do that and use a long enough arm, the arm will always be close to the outside edge of the spoiler during its entire range of motion.

This gives you the maximum resolution and the best leverage because of the angle when its fully open. The other big plus is that there is less direct force on the servo gears when the spoiler is fully open as its not pushing directly in line with the arm motion.

I will try to take some pictures of my Bubble Dancer to show you what I mean.

[Larry3215]

Here are some quick cell phone shots.

You can see as the servo arm travels, it stays in almost the same place relative to the top edge of the spoiler. Thus the leverage is always good.

Also, when its fully open you can see - I hope - how the spoiler is not pushing directly against the servo arm travel angle. That lowers the back pressure on the servo gears.

Hope that made some sense!

By the way, my spoiler blades will open a little more than 90 degrees using this technique. Also note the small magnet in the spoiler and a small screw in a balsa block to adjust the close position.

[Larry3215]

One other note - I didnt plan well enough ahead of time and made my servo bays too small. My spoilers are 2" or 2 1/4" wide and I couldnt fit a servo arm long enough to get all the way out to the edge of the spoiler.

[mred]

Originally Posted by stuart

once again,a pictures worth a thousand words...lol. the frame you spoke of was a top surface equal to the rib caps. i was thinking you meant balsa in between the ribs to fold the covering over and iron down. i like what you did but is it built up at all on the under side so it doesn't break with a accidental push?

one other question for all you e power converters of sail planes...did you go neutral with the motor angle or down/right thrust. at the moment mine is neutral.

I'm getting more motivated to completing this bird.

The strip I put on mine is not built up under it. I used med hard wood for the strip and it has worked out very well. I have never broken a strip from handling it, but I don't grab it by that part of the wing either. I guess you could break it if you mishandled it, but I have never had that problem. If you are really worried about it, you can put something under it to make it stronger.

As for putting your motor at "O", look at it this way. A glider has a high lift wing and is sensitive to air speed and will climb fast if the speed goes up. In fact, it will try and loop, so you are going to need some down thrust on a glider and a little right thrust never hurt either since P factor can affect your climb. Mine is set up so that I don't need constant down elevator during the climb.

One of the nice things about thrust angles is that the motor has a corner with extra clearance so you can run the wires through there. Looking at the nose the lower left corner has some extra room for the wires to go though and I put a former right in back of the motor with a corner cut off to hold the wires in place. Use 1/8" square strip of balsa in the front and back of that former so I can slide it out if I need to get to the motor. That's on both sides and it works great. I just use hard balsa for that and it stays in place very nicely and keeps the wires out of the motor.

Ed

[Larry3215]

On motor thrust lines - in my experience, pretty much all of these older designs have the CG on the plans way too far forward. That pretty much automatically forces you to add in a good bit of down thrust and/or program in some down elevator with throttle.

On my Mirage and Bubble Dancer Ive got the CG back almost at the neutral point and neither one of them now requires physical down thrust on the motor. I do still have 1 click of down with full throttle which gives me a nice straight climb on both.

Bottom line - its going to depend on where your CG ends up.

[stuart]

thanks for the advise on the thrust angles and the explaination on lift during acceleration under power.I'll have to research other threads for the BOT's optimum cg, but my guess is cg will be as designed and I'm going to sand the nose before mounting the motor to have a slight down /right. not wanting to chance wishing I'd done so before covering.

i also plan on extending the servo arms the length of the bay so it reaches to the top of the spoilers when opened.right now the servos are glued in and if i need to change them i'll dig them out.should be covering the bot soon.i have 3 rolls of monocoat red[and a partical roll] and bright yellow trim sheets for doing a design on the top wing.

the bummer right now is i have laryngitis and a nasty cough,i want to work on the bot fuse setting the motor and finishing sanding all the parts....deffinantly has to wait.....hopefully this weekend.

[Larry3215]

I understand your feelings on the cg issue. Just keep in mind that the science and practical contest experience behind soaring has come a long long way in the last 30+ years or so

There are NO modern sailplanes with the CG as far forward as any of these old woodies were recommending back then.

I should modify that to be any modern sailplanes that win contests

With the CG back:
1) the model will have a much wider speed range
2) lower minimum/landing speed (lower stall speed)
3) gentler stall
4) will indicate lift far better
5) will handle better in turns and when landing
6) it wont try to loop or balloon under power. Plus when you need to cover ground quickly, you can lower the nose and speed up without having the model want to balloon up.
7) it will have slightly less over all drag and thus stay up a little longer.

Whats not to like?

(hope you get well soon!)

[stuart]

DANG!!still have a voice like nails on a chalk board. did a little work on the wing and fuse and now see why you angled your servos in the spoiler bay larry. if i leave mine where they are, the cap strip for covering to adheare to doesn't allow for a extended arm except maybe a 1/4inch longer. i may just go forward and see how things work as is,but i would most likely damage the servos trying to spin them around.[stupidly used ca instead of hot glue gun. one of those things that may change latter.

i will be sanding the spoilers after the wing is covered so i get a tight fit when closed. then i'll cover the spoilers.

i mounted the motor and started shaping the nose,i made the motor easy to remove and will paint [or cover] the screws in the front you see,then poke thru the covering to get at the screws. inside the fuse i still have to dremal sand the pice with the blind nuts mor open up the middle so the motor gets more air.

just a few pictures and nothing is near done sanding....lots and lots of sanding to do.

[mred]

Originally Posted by stuart

thanks for the advise on the thrust angles and the explaination on lift during acceleration under power.I'll have to research other threads for the BOT's optimum cg, but my guess is cg will be as designed and I'm going to sand the nose before mounting the motor to have a slight down /right. not wanting to chance wishing I'd done so before covering.

i also plan on extending the servo arms the length of the bay so it reaches to the top of the spoilers when opened.right now the servos are glued in and if i need to change them i'll dig them out.should be covering the bot soon.i have 3 rolls of monocoat red[and a partical roll] and bright yellow trim sheets for doing a design on the top wing.

the bummer right now is i have laryngitis and a nasty cough,i want to work on the bot fuse setting the motor and finishing sanding all the parts....deffinantly has to wait.....hopefully this weekend.

I always go with the CG as marked on the plans to start with. While I agree that it is to far forward, it also makes for a nice stable first flight. After I get the glider trimmed out and flying right, I start moving the CG back. To check if the CG is in the proper position, enter a shallow dive. It only needs to be around 20 degs or so, you don't need to go into a screaming dive like some people say. Let it build up a little speed and then let go of the controls. It should pull out nice and slow. If it pulls out fast, the CG is to far forward. If it increases the dive angle, it is to far aft. What you are looking for is a nice slow level off in flight. If it continues the dive at the same angle, then you are at the neutral point and for me that is to far back.

I like a nice slow recovery and for me that is perfect. That will give you a glider that responds very nicely to commands and to the air movement around it. It will tell you what is going on and if you are in lift very nicely, yet it will not be super sensitive to control commands. If you go to far aft, it will respond to controls to fast and be unstable. I moved mine aft a little at a time and waited until I got used to each stage before I moved it some more. Going aft will make for a very responsive bird and a lot of people will not like it. It does take a little getting used to to fly one with an aft CG, but it is worth it to learn.

Above all, fly a glider with the CG that you like. Just because someone else uses a CG farther aft does not mean that it is right for you. Keep it where you like it and go slow moving it and don't go last your personal comfort zone. Each pilot is different and so is each glider. Not everyone likes the CG in the same place.

Ed

[stuart]

To check if the CG is in the proper position, enter a shallow dive, If it pulls out fast, the CG is to far forward. If it increases the dive angle, it is to far aft. What you are looking for is a nice slow level off in flight. If it continues the dive at the same angle, then you are at the neutral point and for me that is to far back.



Ed[/QUOTE]

thanks for the info ed,but i was just wondering if this is reversed.i think nose heavy increases dive...tail heavy cause lift,am i mistaken due to gliders being built for lift when building up speed. i will fly my models inverted to check cg and haven't flown a 3 channel plane since the herr cub many years ago.this is how the cub looks now after many rebuilds.

[stuart]

oh so much to sand!!! might just take it all outside no matter what the temp is. and yes,i really do need a larger work shop.

[mred]

thanks for the info ed,but i was just wondering if this is reversed.i think nose heavy increases dive...tail heavy cause lift,am i mistaken due to gliders being built for lift when building up speed. i will fly my models inverted to check cg and haven't flown a 3 channel plane since the herr cub many years ago.this is how the cub looks now after many rebuilds.[/QUOTE]

It may sound strange until you think about it. Nose heavy requires up elevator to keep the nose up during level flight, so as the speed increases the up elevator becomes more effective and it will bring the nose up faster. Everythign on a glider is set for one given speed and if that speed changes the effect of that will cause it to behave different then in level flight.

Tail heavy normally requires down elevator to keep the nose down because of the added tail weight or aft CG. Pick up speed again and the down elevator will have more effect, so the nose will go down farther increasing the dive angle.

With everything at a perfect balance the glider is stable and no changes will occur if speed changes unless you just get to slow and it stalls out, or you tell it to change.

Now I like mine with a little positive stability and that means a tad of weight in the nose so that it will pull out from a dive on it's own, but it will react slowly. I haven't timed my pullout, but it is somewhere around 5 to 10 seconds. Because it is so slow on the pull out, the nose will rise very little after it pulls out and the speed starts to drop again. I use very small control movements to control it during flight and seldom go past half, or 50% control movement. Works great for me, but like I said, not everyone will like the same thing. Try it and see if I am not correct.

Ed

[stuart]

ed,your original post omitted the corrective action of using the elevator that would cause a nose heavy build to pull up quick,this is why i asked the question...i fully get what your talking about,I've been flying for 5+years and figured you were talking about using the elevator to adjust the dive to level flight ....i look forward to playing with the cg soon...lol....

as far as the progress today,i sanded and shaped all parts up to using 180grit. i really am considering not being such a perfectionist with the bot as it's wing is twice the size of any other build I've done before and shaping around sheeting can be very exhausting what with making sure not to get sheeting to thin. i like going for perfection on 60"ws build and smaller......but.....

the way I'm thinking right now after a few hours of shape sanding is "will i see imperfection at 1000+ft.....thats where the BOT will really look best. doing lazy circles in a sweet thermal. covering will be over the week and final assembly i hope by next weekend. this is the longest I've taken to build anything cause weather permitting I'd rather be flying.

my next project is to enlarge the battery compartment in a great planes 300s extra kit i built long ago that holds 2 3cells4000mah 20c batteries in series to now take the new batteries for 7 or 8cell packs 4000mah 40c's. this is another reason to get the bot done now.


ed,thanks for following along and chipping in with great suggestions. I'm putting the advise Larry,your self and others to good use and hope others will learn from the bot EP build to help be successful with their own BOT.

[gramps2161]

Stuart been doing the lurking like I do when I don't have any words of wisdom to add to a build thread. Your BOT is looking great glad to hear you are enjoying the shaping and sanding.
That practice of carving and shaping with the sig kits is paying off big time with this graceful glider.

learning quite a bit actually from you thread with the folks giving the pointers and helping out with their experience.
Well back to the lurking mode and learning.

[mred]

stuart; I thought you understood that there are no control inputs after you set the dive and get a little speed built up. I said to let the controls go and I just take some things for granted as far as other people knowing what I am talking about. One of the bad things about writing things to other people.

On that battery you mentioned, you made a slight error. When you connect batteries in series you increase the voltage but not the current. When you connect then in parallel you increase the current and not the voltage. So your 20C batteries are still 20C when connected in series. To get a 40C battery you need to go parallel. What you are saying is that you increase voltage and current in series and you can't do that.

As for seeing perfection at 1,000 feet, you won't see that at 200 feet and if you take that thing up where it is really small in a thermal, you are talking about somewhere in the area of 3,000 feet. I went to 2,100 feet on a 2M glider and it is hard to see, but the bigger gliders can go higher and farther away then my 2M can. Now understand, that 2,100 feet was almost straight over head and I kept it pretty much over head when up there, but my Chrysalis has a pretty wide wing, unlike a lot of 2M gliders and is easier to see.

Take care with that glider and I hope you have many years of great times with it.

Ed

[stuart]

Ed,now i get what you described in the cg test,i admit i was confused but now get it. your saying if i fly a nose heavy plane and adjust my elevator to counter act it for level flight. then putting it into a shallow dive will cause the elevators position to create up as the bot gains speed in the dive with hands off the sticks....makes perfect senceand i'll be very interested to try it on the bot due to the elevator and horizontal being one pc in motion. it one concern i had with the amount of throw the design allowed for down elevator. this was noted in several threads and had solutions to increase the throws which i used. OKFLYER posted this picture of what he says is the nuetral position.
Attached Thumbnails





i think 2000ft might be pushing my eyesight even with the prescription sunglasses i use,just got my eyes checked and the Dr asked if i see floaters. doooooh,is that what those little things swirling around in the sky i see while resting at the beach looking into the deep blue. sure enough, but my mind blots them out unless i focus to see them.

oh well,getting old.

the next project i mentioned,those 20c batts are the old ones that fit both birds now.......the batteries i got new are 40c batts for the hog bipe and the extra. a little wider and the2 3 cells fit the hog fine to equal6cell 40c. it's the extra i need to enlarge the battery compartment for 7 cells. i p/u 3 &4cell batts 4000mah 40c to mix together. i may even go to eight cell for the extra. has yet to be determined.

should be down covering the bot but work can sure take the desire to cleanup the shop of all the sanding dust before i start covering.

[Larry3215]

Ive been debating bringing this up as its really off topic.... but the dive test isnt really a good way to check CG position. All it really tells you is how the model is trimmed.

I was recently reading an interesting thread about this subject and, IIRC, Joe Wurts (world champ in pretty much all categories of sailplane flying) made the following statement - you can easily have two identical models, both balanced at exactly the same spot and yet one model will pull out of a dive and the other one will tuck in a dive.

The only difference between them is the trimmed speed setting.

The dive test tells you your trim setting and thats all it tells you.

Gordy Stals (he writes the "Gordy's Travels" articles in RC Soaring Digest) came up with a much better way to test and adjust your CG on a sailplane.

I'll see if I can find his writeup and post a link.

[Larry3215]

Some of Gordy's articles on balancing sailplanes.

[stuart]

Larry,this is absolutely the kind of discussion i want on my build threads thanks for sharing.

i just read the first part of Gordy's method and can see theres so many folks who settle for less than balanced because their unwilling to experiment. what i like about his discussion is he refers his method to a moving elevator/horizontal as a one piece unit like the bots.

all my planes start with recommended cg till i can take them up high and invert them...if i only use a little down elevator[almost none]then I'm happy. i would think this principle would work also on a sail planes except i haven't flown the skimmer 600 inverted...,i don't like the idea of pulling a loop/gforces and snapping the wing.the skimmer has a modified wing with less dihedral and full length ailerons i added. so i could easily roll it but have settled for what i thought was a good glide ratio. plus the bots wing is n't likee any other plane i own so i'm guessing inverted isn't a good thing ...lol.

I'll read through the other points in the other 2 files, plus I'm going to research others findings on ep BOTS cg locations. it would be good if other pilots who fly sailplanes share their experience to finding the sweet spot on their gliders. interesting thought on the first file is Gordy say to chuck lead[remove weight]....some gliders need to be a certain weight to penetrate winds or thermals. the BOT i believe should be around 60 oz. i may need to add weight...again,soon to be determined.

this build is almost done and will always be easy to find by google/binging "bird of time" thats the beauty of including the models name in the build thread and not just title the build" building big bird"...lol....

[Larry3215]

If you need to add weight for different flight conditions, you add it on the CG rather than in the nose - thats ballast. That way the model still responds to lift the same way and handles the same way and does not need to be re-trimmed. The only change when you add ballast is that it will fly a bit faster.

I have changed Gordy's technique when I do it. Rather than a hand toss at ground level (and hope its not too nose heavy and drops the nose like a brick), I take it up a mistake or two and do the stall test at altitude. Its easy enough on a calm day to see how it reacts as you are feeding in UP trim until it stalls.

On polyhedral models I usually dont do the inverted test. I just run the CG back until the nose doesnt drop and then fly it to fine tune.

Im pretty confident that if you use Gordy's technique you will end up with a CG well back from the marked spot on the plans AND have a much better flying sailplane

As far as checking with other pilots on where they have the CG, they arent going to be flying your plane so why do you care? Put it where you like it

[stuart]

the motor and esc are set in place,and started covering the fuse and vertical fin/rudder.glued the ca hings in for the rudder and epoxied the vert fin in place. the fuse with all the curves proved to be a challenge and except for a few wrinkles along the back top side of the fuse ,I'm happy with how it looks. I'll post pictures after dinner and still have the the elevator half's and wings to cover.

[stuart]

hello to fellow builders here at wattflyer,and a good Sunday morning to all!

i will be covering the wings later this afternoon and have a question to all who have covered a polyhedral wing.

do you cover each top surface using 2 pieces of covering seamed at the deep dihedral or 1 pc straight across. the reason I'm asking is when i shrink the covering with the heat gun i don't want the covering to lift off the rib where the wings are glued. I'm used to covering wing with only a center dihedral built in,but the wing tip bend on the bot is pretty steep.

if i don't here from anyone before returning home i will have to search bot build threads and look for the 2 peace wing covering answer.

one thing a lot of builders do is make the bot 3 pieces for ease of traveling in cars. these builds are obvious as to the covering question.....

hope to have all covering done today ,then its install servos......then maiden,when weather and time permits.

[stuart]

finished the fuse and control surfaces,really need more experience covering rounded surfaces. the red monocoat shrunk nicely on the open flat surfaces,but the boom section is a little rough, i wonder how awful leaving the fuse square would have looked.......nahhh.better to sand and plane off all that excess wood to fly light.

i set the servos into their locations and still need to install mounting blocks to screw them in place. the battery fits perfect. the Rx will go with the rudder servo since theres plenty of room for it and its away from all the other electrics.

i search bot threads galore for the answer on weather to use 2 pc's of covering on the top side of the wing where the polyhedral tip rises up...i fear if i use one pc the area where the wing rises might cause the covering to lift also. i found no answers to my question. so i may play it safe and use 2 pc's .1st picture is the area in question for covering the wing.