Yak13

My Feedback: (17)

Hello Pattern guys

I just maidened my new Arrow, wearing a Picco 80 RE.

I suppose I have the CG wrong but please let me know if I am missing something. The plane flies "unstable" in the roll axis. It tends to increase roll to whatever side it starts banking. It is also extremely responsive to aileron input. I set up low rates at 65% w/ -50% exponential, and it is STILL too responsive.

I have checked everything and the plane (bought used) is perfectly straight and very light.

Supposing it was tail heavy, I added 3 oz of lead to the nose. It improved some, but seems to require more!!!

Totally puzzled. I supposed such a nice build should not require nose weight if using the Picco 80.

Help!!!

Ed

Yak13

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Here with my MK Atlas

flywilly

My Feedback: (121)

Hi Ed,
First, really nice looking airplanes!
As for the Arrow's aileron sensitivity - the CG has little, if any impact on aileron sensitivity much more so on elevator response (which is not the problem). You did not indicate how much actual throw you have, but I would guess that you have too much throw, especially given that you have an '80' for power (plenty of airspeed). How is the aileron response at low speed? I would try reducing the throw by %25 -%50 of the current maximum. You can probably remove the nose weight, too. The Arrow does not have an exceptionally long tail moment and with an '80' sized engine, plus retracts it is pretty hard to get it tail heavy.
Good Luck

Yak13

My Feedback: (17)

Thanks Flywilly.
I will reduce the throws mechanically, but as I stated, the main problem is that it just continues to roll to either side as soon as it starts banking. That is, if I set at 30º it will continue to roll ON ITS OWN until it is close 90º. Thats to either side. I also setup aileron low rate to 60% AND -50% Expo The responsiveness was reduced but the situation mentioned above was not.

flywilly

My Feedback: (121)

Hi Ed,
Just to be clear (for me), you initiate a bank then neutralize the ailerons and the Arrow continues to roll. Is there any slop in the aileron linkage? Are the ailerons sealed (no gap between the aileron and the wing)? I actually had this problem with my first Arrow; the cause was a bad RX which let the ailerons drift - this was more than 30 years ago. Does the Arrow show any rolling tendencies when in level flight (upright or inverted)?

Lnewqban

I would verify how the roll develops when starting from inverted and also knife edge on both sides.
If the roll improves, then it is possible that the CG may be too high for some reason (due to vertical location of engine, battery or fuel tank maybe).
For stable flight, the vertical location of the CG should be at or just below vertical location of the center of lift.
If not, the CG will be trying to over-roll the plane, so it can adopt the lowest point respect to the center of lift.

Yak13

My Feedback: (17)

Thanks guys. I'll be out of town this week but will verify and test all the ideas as soon as I'm back.
Ed

bjr_93tz

To be honest, I would have guesed that rolling into the bank would suggest a nose heavy condition with the plane wanting to drop it's nose into the bank to steepen it rather than drag it's tail a bit and hold the nose up if the CG was more rearward.

If built according to the plan, the CG should be about an inch forward of the main gear with an empty tank, as they tended to put the main wheels only about an inch at most behind the CG so they could "rotate" scale like for takeoff.

Another guess might be the .80's running a larger prop than originally designed? I Know I can gain thrust going up in prop diameter with my Curare but anything over 11.5" and it just feels like the prop pulls and pushes the nose around a bit, where with the smaller dameters (~11") it's less noticable but the prop is less bitey.

flywilly

My Feedback: (121)

Two interesting possibilities. I would probably discount the first suggestion regarding the vertical CG placement, though plausible, the design of the Arrow precludes having equipment far enough from the center of lift to have an impact (the fuse top mounted pipe puts all the equipment at or slightly above the C/L with no real option for relocation). The nose heavy condition is logical, but Yak13 added 3 oz of nose weight and observed a slight improvement in the aileron sensitivity. If the Arrow was nose heavy enough to cause unwanted roll issues I would expect it would require significant up elevator trim to maintain level flight and have very 'mushy' elevator response.
Of course it is very hard to make a diagnosis from 3,000 miles away (or more)! I think we need more information, here.
After looking more closely at the photo of your Arrow, I wonder if that is an original Arrow or a Quality Line (Hobby Barn) Arrow 800. The wings appear to have more span than the original Arrow. The original Arrow had a span of 63" and a length of 55". What are the dimensions of your Arrow? Also, what is the construction (wood or glass and foam)?

Yak13

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Thanks flywilly.

The construction is all wood with FG top. I am out of town but will thoroughly check everything as soon as I return.

Ed

flywilly

My Feedback: (121)

Hi Ed,
I checked my MAN Arrow plans and the CG is almost exactly 1" in front of the main gear per bjr above. I would check the servo resolution and centering. Do you have a servo test function on your transmitter (I know Futaba has it, or at least the higher end radios)? It will cycle your servos slowly from end point to end point and you can check for anomalies like dead spots, twitches, etc. If the servo centers accurately on the workbench then try checking it with the engine running. Check all the connection points of the aileron linkages for slop. If it is set up for one aileron servo driving the ailerons through torque rods, check the clevis pins and the torque rod holes.
Keep us posted and good luck!

Yak13

My Feedback: (17)

I finally was able to complete the improvements and fly the Arrow. Still have to tune the pipe, but with FAI fuel it is doing over 150 mph on every pass. Unlimited vertical (at least up to where I could still see it). I used the Futaba 16SG w/ telemetry. Really nice radio by the way.

150!!!

doxilia

My Feedback: (3)

Whoa! 150!!

Gualtieri Picco power for ya!

David

Timthetoolman1

My Feedback: (6)

Is it still rolling by itself?
I suggest bringing down the exponential to 25%.
If you pull up to a 45 degree climb and roll inverted while still at a 45 and let go of the sticks, the nose should start to drop slightly. If it drops too fast it is nose heavy. If it begins to climb then it's tail heavy.
As far as the rolling, it does seem like your servos are doing something weird. Those servos aren't slowed down are they? I know my radio has the option of slowing down servos.
How did you set up the ailerons? Are they matched to each other by mixing or slaving? You might check out the ailerons on the bench while your throttle is at high (it doesn't have to be running).

If by improvements you are saying you fixed it then good job. What was happening?

They are both beautiful planes.

Tim

Yak13

My Feedback: (17)

I flew it with no nose weight. Balanced where the plan states. It is still rolling slightly and the ailerons are extremely responsive, but flyable. I have it set up on independent channels, flaperons enabled to slow it down a bit.

I'll reduce throw on the linkages and fly it again.

I can't wait!!!

Yak13

My Feedback: (17)

By the way, the Picco carb is extremely critical. 7 turns on the low end and 3 on the high end finally got it running. My first Picco carb!!!

doxilia

My Feedback: (3)

Ed,

no doubt the ailerons are responsive ... You're flying 150 mph! Think pylon control deflection on low rates. You probably only need 1/8" or 3/16" tops each way at WOT. You might want a landing mode for different throws.

Just a thought.

David

Yak13

My Feedback: (17)

I will start right at 3/16".

Thanks David

doxilia

My Feedback: (3)

Ed,

another thought. I'd make sure your servos and linkages are rock solid. At that speed you might be getting some flutter issues if they aren't. Also, one of your servos might be drifting under load causing the model to roll. Either the right aileron is dropping or the left is rising. I suspect the latter.

While at it, check your elevator too. I'd also put your rudder on P-P if it's not. The rolling tendency might be coming from rudder.

Say, what crank rpm and prop are you turning on the P80?

David

Yak13

My Feedback: (17)

Good points.

The rudder is PP but I can reduce throw mechanically to eliminate slop. Aileron servos are new hi torque digitals and linkages are now fixed and rock solid (which was the main reason for the problem).

Another problem was the engine had down thrust. Now it's zero. Funny, that eliminated the down elevator trim!!!

This is definitely a different plane that the Atlas. Very different flying characteristics

doxilia

My Feedback: (3)

Good stuff Ed.

Do you have any figures on the Picco 80? Prop?

150 is pretty hard to hit with these designs although they can exceed that. I know of a Phoenix 8 which is e-powered (clean airframe) and hits 170 on an electric 10x10 prop. Just curious about the power being produced by your setup which I suspect is in excess of 3 bhp or 3200 W.

Also, how much does she weigh and how much fuel do you carry?

Cheers, David

Yak13

My Feedback: (17)

David,

I will get more precise information when I fly it next. For now I can tell you:

Picco .80 FIRE w/Picco tuned pipe
APC 11.5x12.5 Narrow prop trimmed down to 10.75"x12.5
FAI Fuel with 20% oil (Omega FAI with Klotz Castor added)
Static RPM= 12,700
I got 13,300 RPM on the bench on a slightly shorter pipe. The Picco never unloaded during this flight
Speed checked with Futaba 14SG & Telemetry using Futaba GPS

speed-panzer

My Feedback: (1)

Whoohoo, nice plane / engine combo.
A very straightforward calculation (better an estimation) by prop pitch 12,5" and let´s say 13.000rpm results in 154mph.... but without any prop efficiency factor taken into acount.
Are those APC props so true ?

Anyhow, I´d love to see and hear it passing by. Enjoy!

doxilia

My Feedback: (3)

Yup, pretty impressive numbers.

Ed, thanks for the info. By my calculations, on 20% FAI, the engine is producing:

2.44 [email protected]
2.62 [email protected]
2.81 [email protected]

the first power figure corresponds to the power output of the NovaRossi Speed/13 on 10% nitro which is a 61. However, we can see that the power output goes up significantly at small 300 rpm increments. That's due to the crank output going with the third power of rpm.

It would be interesting to see how it does on more classic geometries such as a Rev-Up 11x7.25/7.50/7.75. The engine will probably exceed 15.5K and maybe more especially on some nitro.

Once (or if), the engine is broken in, it might pick up a little on straight Omega (17% oil).

David

Yak13

My Feedback: (17)

David, could you explain your calculations? Remember this is a Narrow prop.