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09-12-2008, 04:19 PM
I'm just putting together an approx 36" (900mm) Fokker Dr1....no instructions....anyone help me with the C of G on this type, and the relative wing incidences?..I'm told to only have up on the ailerons...no down, and a leading edge down incidence on the top wing?

Any thoughts/ideas would be most welcome


Thanks

Ray

Old Fart
09-12-2008, 04:53 PM
Ray,

Might want to look at Steve (Jetset44's) CG on his depron Dr.1, give you a rough idea. I can tell you mine needed to be more nose heavy that that - Dr.1's (and most radial engined biplanes) tend to be very unforgiving of being tail heavy

http://www.rcgroups.com/forums/showthread.php?t=425387

Bill G
09-12-2008, 05:05 PM
I'm just putting together an approx 36" (900mm) Fokker Dr1....no instructions....anyone help me with the C of G on this type, and the relative wing incidences?..I'm told to only have up on the ailerons...no down, and a leading edge down incidence on the top wing?

Any thoughts/ideas would be most welcome


Thanks

Ray
I just flew my Guillows DR1 yesterday, for the 3rd time in a year or so.
Much better, after an adjustment to the top wing. The top wing had more positive incidence than the other two wings. The plane would fly in a constant climb/stall/dive/recover/climb... mode, in fairly quick succession. Made it difficult to fly, to say the least, considering that the top wing tends to tip the plane due to it's high location on the aircraft.

The first mod which helped was to shim up the front of the elevator. In stock position, excessive down elevator was needed for level flight. This plane does not need much positive wing-elevator incidence, if any. Downthrust may help excessive climb, depending on incidences and other things. Right thrust seems to be essential. With insufficient right thrust, I have found the plane to need merely a tap of left rudder to enter a very hard left turn.

As for cg, the best way to arrive at a flyable cg is to build for it. Mine is very near the le of the bottom wing. Obviously the tail needs to be built light. I mounted all equipment including the battery, forward of the bottom wing. The servos are in the fuse keels directly behind the firewall.

I had stolen the overpowered 12mm Feigao from the plane, replaced it with a brushed IPS, and had barely enough power to fly yesterday. The plane's flying so much better that it's getting a bl Feigao installed again today. Pic from last fall:

degreen60
09-12-2008, 06:27 PM
I checked the plans I have for a 1/12 scale Dr1 and it shows the COG at 50% on the top wing. Wings have 0 incidence.

09-12-2008, 06:49 PM
Really appreciate all the help....I'm ok with a ball park C of G normally on my WW11 aeroplanes, but this triplane is so close coupled, I don't think there is much room for error...especially if the C of G is too far back,,,

again thx all....will post some pictures as soon as I can..

be safe and be happy

09-14-2008, 05:07 PM
Here is the aeroplane, so far...I am going to use ailerons/ elevator and rudder, hopefully using a closed loop system when possible......

Any thoughts would be very much appreciated..

degreen60
09-14-2008, 05:47 PM
Here is the aeroplane, so far...I am going to use ailerons/ elevator and rudder, hopefully using a closed loop system when possible......

Any thoughts would be very much appreciated..

I used pull-pull on all my WW1 airplanes but one. It makes the tail lighter than using push rods. I use upholstery thread. I install the plastic tube from cotton swabs in the fuselage where the thread enters and exits. I run the thread from control horn on control surface into fuselage into fuselage, through holes on each side of servo arm, out of fuselage to other end of control horn on control surface. Pull just tight, don't put a strain on anything. Center control by slipping the string in the servo arm. Wedge the string in the holes in the servo arm with pegs. Test fly and adj center as you want by removing pegs and slipping string. When you get controls where you want glue the pegs with white glue(white glue and be removed with water if you need to readj the surface). On elevator I put a control arm on each side, then make a loop from upper ends through fuselage and loop on lower end through fuselage. I put a small glass bead on the loop inside the fuselage. Then install a loop through the servo arm and tied at the glass beads. Once I get the elevator lined up I glue the glass beads solid to the threads. Using this method you can use a split elevator.

Bill G
09-16-2008, 04:02 AM
Really appreciate all the help....I'm ok with a ball park C of G normally on my WW11 aeroplanes, but this triplane is so close coupled, I don't think there is much room for error...especially if the C of G is too far back,,,

again thx all....will post some pictures as soon as I can..

be safe and be happyThat's pretty much where I'm at on this plane too. I have my cg at the LE of the bottom wing, and it still wants to roll from side to side. Flyable, but not exactly a fun time.:eek:
I re-installed a geared 12mm Feigao, which gives the plane ample power again, as I just flew it 2 days ago. I heard from one other guy who had the same problem with a Guillows, while several others had good flyers.

One problem with this plane is getting good info on it. There's just not that much out there, if you're building one. Sure you can get info on ARFs, but for us builders, we just have to work through it and experiment. I added 1/4oz of nose lead and will give it another try soon. Too windy today, as we just had 60+mph Ike winds last night and lost power. Not exactly small DR1 flying weather.

Looks like you have your DR1 well under way. Should be flying soon I hope.

7car7
09-17-2008, 09:59 PM
Here is the aeroplane, so far...I am going to use ailerons/ elevator and rudder, hopefully using a closed loop system when possible......

Any thoughts would be very much appreciated..

Like Degreen, I also use upholstery thread for the pull pull. I joined it with spyderwire. The upholstery thread is nice, because it's flexible, and the spyderwire is not. Using both gives a little, and makes it easy to get a good tension on it.

I used just one servo for my ailerons on my latest plane, with pull pull. And I acheived differential. It's very easy to do, and again, by using spyderwire AND upholstery thread, gives a bit of flexibility, yet authoritative action for where it matters most - the up position.

Let me know if you've got more questions.

Bill G
09-18-2008, 01:40 AM
Just another note on CG. I added another 7gms noseweight to the little 20" Guillows, which moved the CG maybe 1mm forward, now just a hair ahead of the bottom wing LE.
Night and day difference. Flew today in more wind that I should have, and while it's still not perfect, it's much easier to fly, not rocking back and forth wildly. Maybe another 7gms will get it spot on.
The other thing I noticed is that it seemed to have much more power, although now a bit heavier. Flew pretty well at 1/2 throttle, instead of needing near full. Gotta get the CG forward on this plane, and apparantly it will not fly well if only a small amount rearward of where it wants to be.

flypaper 2
10-04-2008, 03:53 AM
Built a few tripes over the yrs. To get the CG, draw a line or drop a string down from the leading edge of the top wing to the bottom wing. Now measure from that line to the trailing edge of the bottom wing. CG would be 1/3 of the length of that line. For instance, if it measures 9 ins. from the string to the trailing edge of the bottom wing, the CG will be 3 ins from the string, or the leading edge of the top wing. In other words, treat the front of the top wing to the back of the bottom wing as one wide wing and measure back 1/3rd from the leading edge. You can build the front of the fuse very strong on these as the short nose makes it hard to get the CG far enough forward. Might as well use the weight for strength rather than add lead.

Gord.