Falcon 880 Setup tips?

[rdeis]

Hey, all. I'm about ready to go fly a new-to-me Falcon 880. The tips on this one are flat, not raised with dihedral like some others I've seen, and it has a sheeted foam V-Tail.

I don't have the plans or instruction book, can you give suggestions for starting control throws and CG to get me in the ballpark?

[threcixty]

Hey Rob... I am not sure about the V tail, but try something like 3/4" up and 1/2" down at the T.E. of the elevons, Same thing on the ailerons, and guessing that it is a 3021 Falcon, use around 1/8" down on the entire trailing edge of the wing for camber. I tried using from 1/16" to 1/8" reflex, but the 3021 did not respond too well to that. 30 degrees down flap with 15 degrees down aileron works great for launch, and 90 degrees down flap with 15-30 degrees DOWN aileron works great for landing. The standard "crow" landing setup with the ailerons up was more difficult to control then using down aileron. You are on your own for the rudder setup on the V. Funny, I still have most of the 880 your dad sold me with the arrowshaft hinges.. Still a great airplane! I still have my Thermal Eagle nib from the 94 nats... One day!
Good luck!
Jim Schoon

[threcixty]

Forgot about CG... I cannot remember the root chord, but 40-42% back from the leading edge worked well on my planes.. Very slight positive static stabillity using the dive test.
Jim

[jtlsf5]

Hey Rob... I am not sure about the V tail, but try something like 3/4" up and 1/2" down at the T.E. of the elevons,

WRONG!! First, the movable surfaces of a V-tail are ruddervators (elevons belong on a flying wing). Second, differential on a V-tail is just the opposite of what you use on a wing. To wit, you want more down than up. Two to one down to up is a good place to start, or whatever your radio system will allow.

Also keep in mind that yaw with a V-tail works just the opposite of ailerons. To induce right rudder, the right ruddervator goes down and the left goes up. Left rudder is just the opposite.

threcixty's camber set is OK but CG should be about 4.5" aft of the LE on the 10" chord. Launch is too extreme, I suggest about 3/8" down across the entire TE; don't stagger the flaps and ailerons, its inefficient. Ailerons should have about 75-80% differential; try 3/4" up and 3/16" down.

The settings for the V-tail are a crapshoot, it depends on how the V was added. If the fuse was cut off ahead of the fin and a V added on top of the oval fuse portion (shorter tail moment), then less throw is needed. If the fuse is the stock length (fin sides cut off, V added) then a bit more. I would try about 1/4" up and down at the TE of each ruddervator for elevator, and 1/4" down plus 1/8" up for rudder function.

JT (18 year old Falcon 800 owner, 12 year old Super V 100 owner)

[threcixty]

Like I said... I don't know about the V tail :rolleyes: Jim T is right though, I got that mixed up. Funny, I'm only 28 and have flown Falcons as long as you have! Sure was tough fitting standard S148's in the flap bays because mowing lawns does not afford mini servos! Those were the days.
Jim (the younger one)

[rdeis]

Hiya, Jim! I wondered where that airplane had gone... This one came out of Jack Dech's basement along with a bunch of other stuff in various stages of disrepair that's waiting to get fixed up and sold. :)

Also keep in mind that yaw with a V-tail works just the opposite of ailerons.

Roger that- I have a V-tail-ified Spirit 2m also. The tail's a bit small, I think, but it's flying pretty well.

The settings for the V-tail are a crapshoot, it depends on how the V was added. If the fuse was cut off ahead of the fin and a V added on top of the oval fuse portion (shorter tail moment), then less throw is needed. If the fuse is the stock length (fin sides cut off, V added) then a bit more.

That sounds backward to me? I should think a longer tail moment means less throw... (It looks like the fin was cut off.)

Thanks for the suggestions. I got the last wiring bits soldered up this evening, hoping to take it out a week from tomorrow.

[rdeis]

Sure was tough fitting standard S148's in the flap bays because mowing lawns does not afford mini servos!

Heh.. I was a bit better off than you since I was throwing papers, but then I was paying for dates, so maybe it was a wash.. If you have told me then the amount of money I'm going to drop on a new airplane this summer I'd never have beleived it possible!

[jtlsf5]

That sounds backward to me? I should think a longer tail moment means less throw... (It looks like the fin was cut off.)

I think you are mixing up tail volume with control throw. Smaller tail feather on a longer tail boom is equivalent to bigger tail feathers on a shorter tailboom. This is an aerodynamic balance effect.

Regardless, the shorter the tail moment, the less control surface throw you need to induce the same change in flight path. This is control sensitivity.

JT

[rdeis]

Hah- so I am. I was thinking of the throw as a force generator rather than an AoA setting. I should know better!

[Daryl Perkins]

With the V-tail, any reference to the Falcon 880 original CG is no longer applicable. While the stability numbers may have remained in tact with the mod, I wouldn't count on it. Stab size, V angle, tail moment can and will effect your TVC.

Go here - http://h1.ripway.com/cloudyifr/files.htm and do the math.

You will not want to run more down than up throw in pitch, but in rudder function only. 2 to 1 is probably a bit extreme. Maybe start at 1.5 down to 1 up, and wiggle the rudder stick in flight. Adjust until you get neutral pitch response as rudder is applied.

I have MANY hours on the Falcon 880. GREAT model, and WAY ahead of its time. However, Mark almost killed the popularity of the 3021 by recommending a CG on the plans that was more than 1 1/2 inches forward of the neutral point of the airframe, and if flown CG'd according to the plans was a total pig.

Have fun with it, and please let us know what you think.

dp

[Ed Franz]

A V-tail on a Falcon? What is the world coming to!

I was just looking at my building manual for the Falcon 880, found it while looking for something else. I loved mine, one of the best thermalling planes I have ever flown. After you got the CG right anyway. :-)

Ed

[rdeis]

A V-tail on a Falcon? What is the world coming to!

I didn't do it, honest! It came to me that way! :)

I'll take some pictures when I get it all cleaned up and flying nice.

[Ercoupe Ed]

Interesting thread. I have a chance to buy a really nice used Falcon 880 with all the servos for a hundred bucks, just add a battery and receiver and fly!
This one has the dihedral tips
JT, you probably flew against this ship, it was Bob Steele's sailplane.

[Ed Franz]

Interesting thread. I have a chance to buy a really nice used Falcon 880 with all the servos for a hundred bucks, just add a battery and receiver and fly!
This one has the dihedral tips
JT, you probably flew against this ship, it was Bob Steele's sailplane.

Don't even stop to think about it, buy it!!!! Or, sell it to me. :-)

Ed

[rdeis]

Don't even stop to think about it, buy it!!!!

Since I've got over $100 in servos alone in mine, I'd have to agree!

I was looking back in the RCSD archives and read that the tip design was based on new technology at the time called "eppler tips." It was originally meant to be drag reduction, but added some nice handling qualities as bonus. Was the dihedral part of that idea?

[threcixty]

Yes.. polyhedral at the tip, plus effective dihedral from the sweep of the l.e. fwiw, I had both straight tip and bent tip Falcons, and they flew the same, but the bent tip falcon was less likely to grab a tip when flying in that enormous tumbleweed that PPSS used to call a "flying field". Remember the weed cutting contest before the first howling coyote contest???
Jim

[rdeis]

The weed cutting I don't remember-- but I do remember some very confused (and inebriated) locals coming to see the source of the green UFOs!

I still have the stickers.

. "If you see a strange light...
. ... I`m flying at night!"

[rdeis]

Yes.. polyhedral at the tip, plus effective dihedral from the sweep of the l.e.

Ah, so an early version of ideas that led to the scheuman(sp?) planform and crescents, then? Very cool. Dad really liked the one crescent planform airplane he had.

[threcixty]

Last time I was out, your dad was flying freeflight hlg's at the soccer field.. Freakin incredible! That guy was like Dr. Drela, but 20 years before his time! How is he doin anyways?? If I come out anytime soon, I have a Falcon 600 that you are welcome to have. I never flew it, it just sits around and looks cool in the shop. Take care man!
Jim

[rdeis]

Almost there.. I had to add 3.25oz of lead to the nose for an AUW of 68 1\8. I could rearrange the radio gear to do a bit better, I think, but that`s going to have to wait for another time.

[threcixty]

It's fly fine.. My 100" Falcon flew with a pound of lead at 85oz, and it still felt light. Hell, my Banshee was 50oz, and I always flew it with lead too.
Wonder how the obechi is holding up after all those years! Should work fine.. I launch the crap out of Barry's Mako when I come out there and it does fine.
Jim

[rdeis]

Wonder how the obechi is holding up after all those years!

Don't even mention such thoughts.. I watched a Maestro fold up because the 12 year old sheetwood let go. (Or maybe it was just the 12 year old Ambroid...)

Neat old airplane, that one, with an amazing mechanical flap/aileron/elevator mixer that's still around the shop somewhere.

[rdeis]

2 Easy hand tosses and 4-5 flights off the high start this morning. CG's about right, the rest is going to take some time to learn. I keep wanting to slow it down too much in the thermal turns.

Here are my models:

[Gldrpilot]

Rob,

It was great to see you out at the field yesterday. You Falcon looked great! What a nice ship! I have one in the box...I may get around to building it sometime.

I'm not sure about a v-tail on a Falcon but yours sure flew pretty well.

Enjoy,


Chris Keller
PPSS past pres. and member
Colorado Springs, CO

[rdeis]

Thanks Chris. Hopefully I'll be a regular presence this year- at least after Soccer season dies down. The Falcon's going to take a lot of stick time before I'm competitive again, but I'm looking forward to it.

It certainly seemed well behaved- should make it fun to fly.

[rdeis]

How is [your dad] doin anyways?? If I come out anytime soon, I have a Falcon 600 that you are welcome to have.

Dad's doing great- and is interested in your little Falcon if you get out this way.

[threcixty]

I lied about the 600! I still have a fuse, but no wing :( Seems that the g/f decided it was too large to move to ABQ and made it into a "two piece wing" for the trash guy. She was even nice enough to improperly dispose of 4 new hs85's that were in it as well. Either way, if you have a wing, I have a fuse. You are welcome to that. I need to come up there in about a month to get my car e-tested and registered, and hope to have my f3b plane done by then. It is tough to build molded planes when my job keeps sending me to Reno for the week.. Gives me about 12 hour weekends to play around! Maybe someone up there needs a pilot!
Jim

[rdeis]

I know how to test if I need it, but I'm not sure how to make it actually *happen* with my 8103 without increasing the down elevator throw as well.

Any ideas?

[rdeis]

Figured it out! Combining the mechanical linkage and the end point adjustment, I set up the ruddervators with more down than up and suggested. Then I used the multi-point free mix to limit the down throw on the elevator function only.

Elevator slaved to elevator, on the positive input side the mix has zero slope and zero output. On the negative input side, the mix has a -30 or so slope for a positive output that cancels out part of the down elevator.

When rudder commands are given, the mix has no effect and I get the extra down travel for differential. When up elevator commands are given, there's no extra effect, I get he full EPA travel. When down elevator commands are given, the mix kicks in and reduces the down travel to roughly match the up.

Very cool!

[rdeis]

Now that I've flown it a bit, I have new questions-

Did any of you find your Falcons to be a bit tippy?

I haven't made the adjustment to flying fast yet so I stall out of thermal turns a lot more frequently than I should, and when I do my Falcon invariably roills over and makes the most elegent spin entry I've seen in a long time.

Asythetics aside, I'd rather not spin the airplane...

Is this tendancy common to Falcons, or it is just mine? Maybe adjusting the tips could mitigate it?

[jtlsf5]

Falcons, no; V-tails, yes. Check two things. One, that you have enough rudder mixed to the ailerons. Two, make sure you have plenty of differential in the ailerons. The overly short tail moment on your Falcon makes the tail twitchy, regardless of whether you have sufficient tail volume. Volume affects stability in normal flight, moment affects dynamic stability, ie turning.
JT

[rdeis]

OK, so keep a close eye on fuse attitude in the turns, and use more rudder and/or differential to keep the fuse aligned?

[rdeis]

The overly short tail moment on your Falcon

Moment is the same as the original, though I can't vouch for the area and angle.

[jaizon]

Hmmm.... now you guys have me thinking. When I put the Falcon 880 in storage (1991 or so) I had not known about the c.g. issue. I only flew it twice but as I remember, I did not like it at the time, i.e., it seemed touchy.

Any suggestions for throws in general for the 100" version (normal tail) and most importantly where that c.g. should actually be?

Thanks.

Preston

[Daryl Perkins]

The Falcon 880 was a very benign model. Super easy to fly. If you're getting it to spin, you must be letting it get WAY too slow, or... and this would be my guess, your V is too small or ineffective.

d

[rdeis]

Sorry if I misspoke- By "tippy" I don't mean to imply "twitchy."

It *is* easy to fly in general. Smooth and well in control, and not at all on the edge of any sort of trouble until I start circling it, and I'm certain that I am indeed letting it get waaaay to slow in the thermal turn and stalling it-- it's just that the stall behavior from that position is rather exciting!

(I will run the tail measurements through the stability spreadsheet just to see... I'm curious about that now.)

[rdeis]

I stripped a flap servo and re-checked all of the throws and etc after fixing it, and the tendancy to stall into a spin seemed to go away. Tried a few different things to reproduce the behavior and couldn't do it. (Magic, my least favorite solution. :confused: )

On the plus side, the first round of the contest yesterday morning was my best flight ever with this airframe- maxed the time easily and landed for 90. Woot!

Naturally, all of this newfound confidence meant that I had to futz with it to try and get a little more roll control with the brakes on and shoot for the 100 landing next time, right? :rolleyes:

I added some up throw to both ailerons, and on the next couple of fights I could no longer thermal to save my life- fell in and out of spins multiple times-- it would start out in a nice turn, then slow a bit (then slow too much!), and then pivot on the inside wingtip and fall over. Ack!! Quick thumbs with top rudder and down elevator would catch it, but it was like wrestling a greased pig. It still launched like a dream, and was well behaved searching for lift and signalled OK, it just wouldn't let me turn it.

Didn't hit me until I got home-- increasing only the up throw increases the differential, does it not? And too much differential might kick it into a spin in a turn as if the rudder was hard-over?