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Old Dec 05, 2012, 12:16 AM
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Maybe it wasn't all pilot error !!!!

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Originally Posted by Dan_D View Post

WOW... what a difference between FB SUE and NEKKID SUE. It took 80% throttle to get FB SUE moving... and then things happened FAST. My big problem was oscillation from a positive feedback loop.

[snip] But here is a typical flight:

[snip] ooops, she's banking too far, less rudder... rocking back the other way, TOO FAR... more rudder... OOOPS, BANKING THE FIRST WAY AND ROLLING INTO A DIVE ... RUDDER THE OTHER WAY AND UP ELEVATOR... oh wait... she's rolled upside down now...

That was the report of several days ago. I had assumed it was all my fault. But then Al posted the link to the video of the Old Fogey, and in that somebody said something about "too much dihedral causing Dutch Roll"... and he described what I had been seeing on Fat Bottom SUE. So I went and did a little reading on Dutch Roll.

A long quote out of Wikipedia:
Dutch roll is a type of aircraft motion, consisting of an out-of-phase combination of "tail-wagging" and rocking from side to side. This yaw-roll coupling is one of the basic flight dynamic modes (others include phugoid, short period, and spiral divergence). This motion is normally well damped in most light aircraft, though some aircraft with well-damped Dutch roll modes can experience a degradation in damping, as airspeed decreases and altitude increases. Dutch roll stability can be artificially increased by the installation of a yaw damper. Wings placed well above the center of mass, sweepback (swept wings) and dihedral wings tend to increase the roll restoring force, and therefore increase the Dutch roll tendencies
(all color and emphasis mine).

One thing I didn't tell you before... in the SE thread Al says "If built light and with plenty of dihedral it can fly slowly and is completely self-righting - just let go of the sticks and it straightens itself right out . It also protects all your electronics ( especially your motor ) and your prop" . So I thought - You want dihedral? I can give you dihedral !!! SO, I put a LOT of dihedral on this one. He said 7" to 8" ... I figured I needed all the help I could get so I put in about 9". Hmmmm

So, now what do we have... a plane with the wings high over the center of mass ... a very large dihedral, and swept wings. I pretty much built the definition of a plane that wants to Dutch Roll.

Returning to Wikipedia we read
This is one of the basic flight dynamics modes of an aircraft (others include short period, fugoid, and spiral divergence), and a classic example of a positive feedback system.
I had noticed it was behaving as a positive feedback system. I had assumed it was all me, yanking and cranking on the sticks. However, I didn't have that problem with NEKKID SUE. I saw some tendency for me to over-correct, but it wasn't a positive feedback cycle.

So Al... I think I may have discovered another edge of the envelope on SUE.

Don't add too much dihedral.

However, in the final analysis it was still all me... Not as pilot, but as airplane builder. I didn't follow the instructions and I put in too much dihedral. Well, I'm learning. Good thing these planes cost $2 each (unless you drive to the next state for your foamboard, but thats a different story).

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Old Dec 05, 2012, 02:35 AM
Hot glue held together by foam
United States, WA, Vancouver
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Watching that video is the first time I've heard of Dutch roll - and I'm DUTCH ! But that's one of the things I like most about watching RC videos and reading on RC Groups - always more to learn !

So what do you think of that " Old Fogey " plane , Dan ? Not as easy to make as a SUE , but it looks like a GREAT flyer ! Might be a good choice for a night flyer .

Al
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Old Dec 05, 2012, 03:03 AM
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Originally Posted by balsa or carbon View Post
So what do you think of that " Old Fogey " plane , Dan ? Not as easy to make as a SUE , but it looks like a GREAT flyer ! Might be a good choice for a night flyer .

Al
Well, apart from an XB-70 and an X-15, I'm not that dedicated to flying things that look like "real airplanes". Just my personal bent. I guess that's one reason I jumped at the idea of the SUE... I didn't mind that it looks like a paper airplane, until the Missus said something. So for a night flyer I'm happy with a motorized kite... already looking for bamboo at the gardening supply places, and considering what fabric to use for covering.

Wait until you see the NEXT SUE. I have SUE TOO waiting until it stops raining, and so in the meantime I've almost finished building a test plane for the avionics for MEGA ME SUE. It's a regular sized SUE, but it has flaps, elevators, and TWO rudders All possible because of the TH9X... although the original firmware isn't very good and I'm not sure it's going to be able to handle everything I want. I'm going to send off for the upgrade kit in the next day or two, and hopefully it will be here when I get back from my trip. Then I will be able to upgrade the radio and make all sorts of tests...

For example - will it be better to use a large rudder with much less movement, or a small rudder with more? By tying the flaps and elevators together as BIG elevons I can see if I want bigger control elevons or smaller ones with more defection... and I'm looking forward to the first time I flip a switch and the flaps go DOWN, the elevators go UP, and the rudders go LEFT and RIGHT... and the throttle goes to ZERO. I wanna see her STOP dead in the air. The only remaining thing after that is have the chute deploy... so when I find myself upside down and heading earthwards I can hit the PANIC button

And watch the airframe rip apart, the servos strip, and the battery fall off. *LAUGH*

Of course... the value of the results will be significantly reduced by the fact that I am still a rank newbie and can't tell inherent instability from pilot screw up. But hey... I'm learning !!!! By this time next year I might even be landing in some attitude other than nose straight down.

Ad Astra
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Old Dec 05, 2012, 03:40 AM
Hot glue held together by foam
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Joined Aug 2010
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So you're thinking RC kite for a night flyer ? There's a forum for that !
http://www.rcgroups.com/rc-kites-723/
I actually tried that about a year ago , the thing flew pretty nice !

RC thrust vector kite (1 min 55 sec)


FAT BUTT SUE , NEKKID SUE , NEXT SUE , SUE TOO , MEGA ME SUE ..... I'm having a hard time keeping up with all your girlfriends ! How DO you do it ?!?

Enjoy ,

Al
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Old Dec 05, 2012, 06:20 PM
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SUE TOO maidens...

After a long day of work, I noticed that it wasn't raining outside. It was cold, but calm, biting cold, but dry. Sorta. FLYING WEATHER

So, I grab up SUE TOO and head out for her maiden flight. Lets ignore the fact that it's getting dark.

Flight 1:

I get out to the Ad Astra Aerodrome, check field conditions (no sheep, no horses, no people), notice the sun is low on the horizon, check flight controls... Hmm, one of the elevons is low. Okay, I try to adjust the bamboo skewer linkage and *SNAP* ... The hot melt glue holding the control horn to the elevon comes off. Back to the Aviation repair facility. I use the time to heat up the hot melt glue gun to make a cup of coffee (Sumatran) and we're outside again.

Flight 2:

Make all the checks, run the throttle up to 60% and give her a toss. Oh wow, tail heavy. REALLY TAIL HEAVY. Okay, trim, use elevators... hmm... The plane is going away, time to turn. It isn't turning with ailerons. Note to self... when using elevator one loses some of the aileron function on elevons. When using a LOT of elevator, one has NO aileron left. WAIT... I have rudder still !! Try adding rudder... it's turning. Reduce thrust... hey, it's sorta under control. With less throttle I can reduce elevator... I can sorta turn, in one direction. I make a pass around the field, and actually bring it in for a landing... Not a shoooshhhe soft landing... more like a controlled crash ! BUT, nothing is broken !!!

Okay, readjust battery position, adjust the linkages to add a little elevator to the neutral position, and ...

Flight 3:

Did you know that depth perception goes way down using a medium-tone purple foam board plane in the twilight ? I launched her... we made a few circles. I went up, I went down. There were a few moments when I almost had the plane under control. Then, I flew it into a tree thinking that there was a lot more distance between the plane and the edge of the field. BUT, the fates were with me. She slid back outta the tree and landed totally ungracefully, but undamaged, in a heap.

Flight 4:

Surely the fact that it's DARK doesn't mean anything. Well, not really dark. I can see the difference between a black cat and ... oh wait, that's a dog. Okay, one final flight. Check controls, run up the throttle, and give her a heave. She's off. She's ... out there somewhere I hear her. She's still up in the sky. But DANGED if I can see her. Okay... hit the throttle cut switch and hear the HHMMmmm.... *THUD*

I find her. She's OKAY. I take SUE TOO into the house and show her proudly to the Missus. "WOW, it's not all crunched up!"

Then I comment... "I ran out of light before I ran out of plane ! "

"That's remarkable! But when you start at noon and can say that, then it will be really impressive.

*sigh* She's right yanno...

SO... What did I learn today?
  • You can't depend on elevons to make up for lack of trim
  • rudder still works, even with elevon
  • I need a better adjustment method for my control linkages
  • it's a Very Bad Idea Indeed to fly under conditions of limited visibility when you are not instrument certified... and don't have any instruments anyway
  • It IS possible for an Olde Phart to get better at this...

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Old Dec 05, 2012, 07:44 PM
Hot glue held together by foam
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Joined Aug 2010
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So was that Sumatran coffee the rare pole cat poop coffee ? Google it if you don't believe me ! Fun fact , I was BORN in Sumatra ( Medan ) soon after Indonesia gained it's independence from the Netherlands , a long , long time ago .

Anyway , enjoyed your flight report as always ! Sounds like a good late afternoon's flying if nothing is broken and you learned a few things . Just curious , what are the dimensions of the elevons on SUE TOO ? Any photos of your new SUE's ?

Al
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Old Dec 05, 2012, 08:56 PM
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Quote:
Originally Posted by balsa or carbon View Post
So was that Sumatran coffee the rare pole cat poop coffee ? [snip]

[snip]Just curious , what are the dimensions of the elevons on SUE TOO ? Any photos of your new SUE's ?
Al
Just Peet's... that civet cat coffee is something like $300/pound !!!

SUE TOO is just regular SUE (with some nose reinforcement with bamboo skewers). The difference is that I used CH1 and CH2 for the elevator servos, and then used the pre-defined elevon mix in the TH9X.

NEXT SUE will probably not maiden until after I come back from the trip. She's the different one - each wing TE has two 5" control panels, each with it's own servo. The rudders are each 2.5" long, each with it's own servo. That means 6 servos for those control surfaces. Throttle will require channel, so it's good that I have an 8 channel receiver. I ordered the programming board for the TH9X this morning, so I'll be using EP9X as the firmware to gain the ability to make a series of different mixes...

I might make a MINI MEGA ME SUE before going to MEGA ME SUE.... i.e., use standard foam board to make a smaller 3 panel one like the one you showed... and use that as the development bench for the multi functioned controls. I am imagining putting the flaps on the flat panel, the elevator/elevons on the uptilted triangular dihedrals, and putting a rudder on each keel/fuselage. Think of something that very vaguely resembles a P-38 Lightning without the central nacelle.

Photos will follow, but it's too dark to take them tonight.

Ad Astra !!!
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Old Dec 05, 2012, 09:34 PM
Hot glue held together by foam
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The reason I asked about the dimensions of the elevons on SUE TOO is that for the elevators to be effective as ailerons , they need to be made longer . 2" x 6" is not long enough to work as ailerons , and also they should extend out to the wing tips . Here is an elevon SUE Nighstone made , notice that the elevons are full span .


http://www.rcgroups.com/forums/showt...6#post22864326

Al
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Old Dec 05, 2012, 10:25 PM
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Dan what are you using for pushrods with zbends on both ends or are you using linkage stoppers? I like bending music wire with a z on one end so it comes out with a twist instead of a straight z bend one of the flight test videos demonstrates that real well. I like the barrel of the link stopper on the horns some guys put them on the servo end but then just adjust the trim with a set screw clinching the straight end of the wire. Removable and adjustable easy peasy
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Old Dec 05, 2012, 10:43 PM
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What I've found out so far with elevons is you really don't need too much travel if you are flying fast enough for them to work but if you fly too slow they won't work anyway cause theres not enough air going over them. Maybe you should try adjusting your linkage to reduce your rates some. I put one of my planes spinning like a drill bit trying to make a right turn and lawn darted that into the ground in a glorious thundering crash that needed a garbage bag to pick it all up lol.

I think for flying slow a rudder and dihedral is probably the best way to go. I'm curious about that old fogey plane on how he makes an undercambered wing with the polyhedral on it. I never tried to make one before. Seems to me like it would be easier to cut some pieces of foam like ribs to hold the under camber shape and just use a regular dihedral but it looks kind of different.
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Old Dec 05, 2012, 11:35 PM
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Quote:
Originally Posted by balsa or carbon View Post
The reason I asked about the dimensions of the elevons on SUE TOO is that for the elevators to be effective as ailerons , they need to be made longer . 2" x 6" is not long enough to work as ailerons , and also they should extend out to the wing tips . Here is an elevon SUE Nighstone made , notice that the elevons are full span

Al
I had wondered about that... which is why I made NEXT SUE with a total of 2" x 10", albeit split into two parts. Okay, when my herd of servos arrive, I see where I am headed ... wider control surfaces. I've also been reading more on dihedral, spiral divergance, dutch roll, and coupled roll/yaw... and I think I've been using TOO much dihedral. Next one... FLATTER.

Ad Astra.
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Old Dec 05, 2012, 11:51 PM
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Short cuts mean ... crashes !!!!

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Originally Posted by Low and Slow View Post
Dan what are you using for pushrods with zbends on both ends or are you using linkage stoppers? I like bending music wire with a z on one end so it comes out with a twist instead of a straight z bend one of the flight test videos demonstrates that real well. I like the barrel of the link stopper on the horns some guys put them on the servo end but then just adjust the trim with a set screw clinching the straight end of the wire. Removable and adjustable easy peasy
*sigh* Looks like I cut corners again, and am paying for it... again..

Right now I am using bamboo skewers cut to 1/2 inch less than the distance. I then cut two lengths of stiff paper clip wire and put a Z bend on one end, and a L on the other end. I use heat shrink to capture those to the skewer, and then use a drop of CA on one end to lock that end tight. The other end can slide, but not easily. The L bend is put through the control arm of the servo, and then a drop of hot melt is dabbed onto the end of the L to act as a "lock washer". It doesn't rub against the control arm.

The method of adjustment is crude... I grab the arm of the servo, and the skewer, and pull or push. It doesn't slide easily, but it does adjust. I have my suspicions that it has been self adjusting in flight, but I haven't proven it. Adjustment isn't precise.

Yup... looks like I need to order some link stoppers. I wish there was a local hobby shop so that any nifty neat things like that didn't mean a week wait and shipping costs. Still, two or three packages of those little linkage thingies should fit in a first class envelope, and that will be less than the cost of gas to even a local hobby shop. Do you have any style or brand you recommend ?

Ad Astra

Dan
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Old Dec 06, 2012, 12:20 AM
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xoqdaos

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Originally Posted by Low and Slow View Post
What I've found out so far with elevons is you really don't need too much travel if you are flying fast enough for them to work but if you fly too slow they won't work anyway cause theres not enough air going over them. Maybe you should try adjusting your linkage to reduce your rates some. I put one of my planes spinning like a drill bit trying to make a right turn and lawn darted that into the ground in a glorious thundering crash that needed a garbage bag to pick it all up lol.

I think for flying slow a rudder and dihedral is probably the best way to go. I'm curious about that old fogey plane on how he makes an undercambered wing with the polyhedral on it. I never tried to make one before. Seems to me like it would be easier to cut some pieces of foam like ribs to hold the under camber shape and just use a regular dihedral but it looks kind of different.
I loved that description... "spinning like a drill bit 10000 times". I can see it. I can FEEL it.

I know what you mean about that wing. I can see how to do it with a few strategic slices and some glue.. but it would be neat if he can do it in one swell foop, without resorting to a vacuum press (which shouldn't be too hard to make).

However... the Old Fogey doesn't hold a lot of appeal to me. It looks vaguely like a Piper Cub or a Cessna. Those planes are based on a set of design compromises which don't limit us. We don't have to look anything like that. Let me try to explain. This is my thinking... corrections are welcome.

A small passenger plane has to carry 2 or 4 people, some cargo, etc. People come in quantized sizes, +/- a bit. The design of the fuselage is shaped by historical trends... for many many years fabric coated trusses were the only strong method ... then monocoque construction came along, but it retained the form of the old planes. So... small planes tend to be designed with a fuselage that looks vaguely like the fuselage of a Sopwith Triplane... a motor compartment, the people compartment, and a capacious tube back to the tail feathers. The people compartment is enclosed nowadays, but apart from that you can pretty much hold up a Cessna next to a Sopwith, knock off two wings, and they are the same plane.

We don't have those same set of criteria. So, our planes don't have to look like anything from the past. Consider the Nutball, the SUE, various flying wings, etc. We can put the tail feathers in front (canard), the prop in the middle or in the back, etc. We don't need to carry cargo, so instead of a fuselage with volume, we could use a 10 mm carbon fiber tube and stick the tail feathers way out in back... or front... or ... with computer controls, gyros, accelerometers, etc., we could possible stick the tail feathers in front, int he middle, and at the back... and with enough lifting stabilizers, maybe we throw away the wings... a big old fuzzy arrow I don't know. Imagine a huge childs Jacks... one of those jacks with 6 rods coming out from the center (the skeleton of an octahedron). Now put control and lifting surfaces on the end of 5 of them, and the motor on the sixth. Because of the long lever arms any control surface would have a lot of force, and you could use computers to turn them all simultaneously taking into account Ackermann differences, etc. No place for a pilot, but it might fly like a little maniac (unless I'm flying it... at which point it is DOOMED... )

Anyway... I got carried away. My point is this.. I'm not a modeler. Nothing wrong with being a modeler... some of my best friends are modelers. But that's not my cuppa tea. For me, the thrill is in making stuff that is new and different. That's what I did in my "career", and that's what is appealing to me in these scratch builds. So, in my eyes, the SUE is a form over function craft and that's one reason I took to her ... whereas the Old Fogey has a lot of unneccesary history, and it's just not grabbing me.

I look down... and notice I am standing on a thing labeled xoqdaos . Then I turn it over in my mind and realize I've been ranting again. Sorry.

Ad Astra...
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Old Dec 06, 2012, 12:28 AM
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United States, WA, Moses Lake
Joined Feb 2012
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I don't know about brand I am using the gws ones from hobbyking thing is they do ok but the screw is kind of smallish wish I had bigger ones I bought from a lhs and they might have been dubros I like them better cause I lose screws and they take a 4-40 screw that I can get locally they are just a bit bigger size but easier to work with.

I use .047 music wire. That might be a bit heavy but the only other wire I could get was .032 and I thought that was too wimpy. Well only cause I need longer ones cause I have to move the servos as far forward as I can get to balance my wing. If your links are shorter I'm sure the 032 would be ok.

Just make sure the link stopper barrels are going to be big enough to fit whatever size music wire you use and all trims are even and precise. This is your steering wheel man don't go cheap here or nothing will ever fly you gotta give yourself a fair chance lol. If your linkages goof on you its not a plane anymore its a scud missile. Don't ask me how I know
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Old Dec 06, 2012, 01:00 AM
Hot glue held together by foam
United States, WA, Vancouver
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Quote:
Originally Posted by Dan_D View Post
*sigh* Looks like I cut corners again, and am paying for it... again..

Right now I am using bamboo skewers cut to 1/2 inch less than the distance. I then cut two lengths of stiff paper clip wire and put a Z bend on one end, and a L on the other end. I use heat shrink to capture those to the skewer, and then use a drop of CA on one end to lock that end tight. The other end can slide, but not easily. The L bend is put through the control arm of the servo, and then a drop of hot melt is dabbed onto the end of the L to act as a "lock washer". It doesn't rub against the control arm.

The method of adjustment is crude... I grab the arm of the servo, and the skewer, and pull or push. It doesn't slide easily, but it does adjust. I have my suspicions that it has been self adjusting in flight, but I haven't proven it. Adjustment isn't precise.

Yup... looks like I need to order some link stoppers. I wish there was a local hobby shop so that any nifty neat things like that didn't mean a week wait and shipping costs. Still, two or three packages of those little linkage thingies should fit in a first class envelope, and that will be less than the cost of gas to even a local hobby shop. Do you have any style or brand you recommend ?

Ad Astra

Dan

Dan ,

I use that pushrod adjustment method on all my scratch-built slow flyers . But on the end that I want to leave adjustable , I use silicone fuel tube instead of shrink tube . The silicone fuel tube grips the pushrod and the wire tight enough that it doesn't slip during flight , but it's still adjustable by hand . and the longer the piece of fuel tube ( and wire ) is , the more surface area there is to grip .

Also , it's easy enough to check for slippage during flight , by making a mark where the rod goes into the tube and seeing if that mark has moved after a flight .
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