C-ARF 3.3M Yak CG

[pfact]

I am just finishing a 3.3M C-ARF Yak and need help choosing a CG point to start with. Currently, the plane weighs 42 lbs with a ZDZ 210 up front. I have the wings in the aft position I need to add nearly 2lbs to get it to balance at 310mm back from the leading edge of the wing just outside of the fillet.

Can you tell me:

1) Are your wings in the forward or aft position, the plane will be used for 3D

2) Where do you have your CG set?

3) Did you balance your elevators and/or rudder?

Thanks,

Phil

[obeid]

WHEN YOU FLAYIT YOU WILL KNOW THE SG POINT

[Flyinhigh]

I have my wings in the aft position, for now, but would like to try moving them to the forward position next chance I get to fly. I never measured the location of the cg in mine, but it is just behind the spar - maybe an inch behind, and it is pretty neutral. I will say this - all the feadback I have received about this plane says that the cg range is huge - like 3 inches huge. You can fly with confidence as it is the easiest tracking plane I have ever flown, with take-offs and landings easier than a trainer on a flight sim. It flies with such little airspeed it is truly amazing. I never weighed mine, either, but guessed it to be around 45 lbs with a 3W CS 170 and KS 1090 tuned pipes. What kind of scale did you use to weigh yours, and do you believe it to be accurate? 42 lbs is very light for this plane - good job if it's actually 42 lbs - that 210 will pulll like a freight train. I did put almost 2 oz in the counter balances of the elevators - about 1 3/4 oz of steel rod and epoxy, but not in the rudder. I just tried to neutralize the weight of the elevators.

[jasonw415]

Flyin high is right. It has a huge cg range. I fly mine with the wings in the foward position. I'm running a da150 with greeves pipes and every damn component except the seiko is in the cowl. 42 lbs. does seem very....very light. This plane flies sooo damn straight it doesn't need much tweaking. With the wing in the forward position it has to be the most stable high alpha plane out there. Blowovers are cake from 40 ft. Everybody is always talking about "rock solid harriers"... this plane actually lives up to it. It flies well tail heavy. It flies well nose heavy. The area it lacks is high energy flight. A very crisp and more importantly, very predictable plane. Have fun!

[snap a saurus]

My wings are in the forward position, a great 3D airplane, normal setup except for Seiko replacing the 4 rudder servos in the same location and a smoke system behind the fuel tank, DA150 with stock mufflers, weight is at 43.5 lbs, this is my second one, have been flying the 3.3m Yak since it came out.

[pfact]

Thanks for the input guys.

42 pounds is surprisingly light - we put the plane on our EZ balancer which sat on top of a wooden platform on an accurate bathroom scale. The first reading came in at 39 pounds which seemed improbable so we double checked the zero and the weight of the balancer & wood and came up with 42lbs. It was built light by using cans instead of pipes, fewer servos (2x8711s in each wing, 3 for rudder, 1 in each stab all running on 7 volts). Since weighing we added 90g of lead to balance the elevators and a smoke tank. We have a fish scale due to arrive this week and will re-weigh it and let you know what we get.

Based on your posts, some phone calls from other 3.3M pilots, and a few PMs it looks like 2/3 of planes are flown with the wings in the forward position. Since no one knows what their CG is, it must be irrelevant.

Another question: are the travel distances in the manual for the aileron and elevator enough? If not what did you do?

Did anyone play with the wing or stab incidence?

Phil

[snap a saurus]

I did not do any mods to increase throws on the aileron, I just went with all I could get, I must admit it's a lazy roller, on elevators I have 45 Deg, on rudder, I have close to the max and it's enough to do knife edge loops with ease, the Yak excels at knife edge flying.

[pepatrick]

	Quote: Originally Posted by snap a saurus
	I did not do any mods to increase throws on the aileron, I just went with all I could get, I must admit it's a lazy roller, on elevators I have 45 Deg, on rudder, I have close to the max and it's enough to do knife edge loops with ease, the Yak excels at knife edge flying.

Snap...I saw you knife edge the Yak at Joe Nall. It was the slowest high alpha knife edge I have ever seen.

As far the 42 lb 3.3 Yak...Im sorry...but I gotta call BS on that...Unless you weighed it without the landing gear..especially since the ZDZ 210 is about 1.5 pounds more than a DA-150.

[JagerBomb]

I have had 4 of these birds. With a Da-150 and 1090's they weigh 47lbs with no fuel and no smoke system. They fly great with the wings in the back position and the CG at 310mm. I have also flown it extensively with the wing in the forward position which will move the CG back approx 50mm. It also flew very well there, though a little tailheavy but still in the range. It required more knife edge mix in the forward position. I build light and don't add anything in the way of "beefing up". My weight was on a certified scale with fifteen servos. It sounds like you're only running ten which is good for about 3/4 pound in weight savings; not enough to overcome the weight of the larger motor. The plane is a lazy roller which is why I centerhinged mine for 50 degrees of aileron throw. The elevator and rudder throws are more than sufficient with the size of the surfaces. Post some pictures of your setup, I'm curious why you would need 2 pounds with that heavier engine.

Mark Trent

[pfact]

Mark & Snap,

Here are some photos of what I have done. As you can see I have the batteries (LiMn) in the tail, they are as far back as I can reach and there is nothing in the plane forward of the landing gear. The ignition battery is on top of the motor dome in the cowl but, its a light weight LiIon. I even positioned the SWB tray more aft than usual. It is anchored to a 3/16" piece of plywood that is laminated to the underside of the roof of the pipe tunnel (it's very stiff).

I moved the wings to the forward position tonight - it now balances 300mm back from the LE. From what I am hearing from you guys this should be an OK starting point. I also rechecked the weight with our new fish scale - its reading 44 lbs 3oz.

Deflection of our ailerons has kept me busy. The control horns were not well installed - they are twisted and differ by 5mm in reference to the hinge line. To get some more throw I lowered the attachment of the control rod by 8mm. I now get 47 deg down & 40 deg up deflection with the servos at their absolute limit of travel - if the control horn had been closer to the hinge line I could have gotten more. Hopefully it will more than a "lazy roller". I am counting on the 8711s delivering 500oz+ of initial torque. 50 deg would be great, but I'm not sure how to center hinge the ailerons (not sure I want to either).

Phil

[Flyinhigh]

Nice

[JagerBomb]

	Quote: Originally Posted by pfact
	Mark & Snap, Here are some photos of what I have done. As you can see I have the batteries (LiMn) in the tail, they are as far back as I can reach and there is nothing in the plane forward of the landing gear. The ignition battery is on top of the motor dome in the cowl but, its a light weight LiIon. I even positioned the SWB tray more aft than usual. It is anchored to a 3/16" piece of plywood that is laminated to the underside of the roof of the pipe tunnel (it's very stiff). I moved the wings to the forward position tonight - it now balances 300mm back from the LE. From what I am hearing from you guys this should be an OK starting point. I also rechecked the weight with our new fish scale - its reading 44 lbs 3oz. Deflection of our ailerons has kept me busy. The control horns were not well installed - they are twisted and differ by 5mm in reference to the hinge line. To get some more throw I lowered the attachment of the control rod by 8mm. I now get 47 deg down & 40 deg up deflection with the servos at their absolute limit of travel - if the control horn had been closer to the hinge line I could have gotten more. Hopefully it will more than a "lazy roller". I am counting on the 8711s delivering 500oz+ of initial torque. 50 deg would be great, but I'm not sure how to center hinge the ailerons (not sure I want to either). Phil

Phil,
Nothing in your post adds up. You've added all kinds of weight with your equipment choices. Powerbox, SWB tray, and a 1lb fuel tank and smoke. When you said 2 pounds I thought you meant it was needed upfront but now I'm guessing it's needed for the rear? These planes almost never come out noseheavy.
I did notice your plane is a newer version without the carbon netting. I 'm putting mine together now as we speak. I could only hope that the newer version CG's different. I would love to mount the rudder servos in the tail.
Also that is very abnormal to get over 35 degrees down on the ailerons because they bottom out on the wing even with moving the pivot bolt down. I would love to see this plane in person, will you be attending the nall?

Mark

[JagerBomb]

http://www.flyinggiants.com/forums/f...-ailerons.html

[pfact]

Actually our plane has a manufacture date from 2005, it must have been sitting in the warehouse for a long time (I guess the Schulman scheme isn't very popular). I approached the build based on reports from others expecting it to be tail heavy. I initially had the batteries up against the motor dome and the servo tray more forward. Now, I only the smoke tank and Powerbox are front of the wing spars.

Given the relatively light weight and odd balance my guess is C-ARF went light on the resin on this one. I think they are all different - across the web people report a wide range of final weights. I don't think C-ARF uses pre-preg glass so I'm guessing they might have been short on resin the day they made mine.

I spent a lot of time on aileron throw. What stopped the downward movement of the ailerons was the control horn hitting the aft edge of the L wing, once I notched the skin and cleaned up the back edge of the wing I picked up a few more degrees of down aileron. The end result is that lower lip of the aileron tucks into the wing much better so that the left control horns sit flat on the bottom of the wing. The right sided horn is 5mm further back so it is unable to touch the wing surface. We had the same issue on the our Bobcat, C-ARF 2.6M Yak and 3.0M 260. Upward movement at this point is limited by the servos and 2" SWB servo arm. If I changed to the C-ARF servo arms I could get some more up but not down.

Joe Nall is doubtful for us.

Phil

[pepatrick]

Mark...I agree..it does not add up. One..42 lbs even with lite resin..I think that most people that report what their plane weighs is usually full of it anyway. There are just certain limits that you go cant beyond without structurally messing up the plane. 47 degrees on alierons...I want to see pics of the the throw meter. I dont care how much the arms are cut....and I am pretty sure that only the recently built 3.3s were made without the carbon web. Whas up??..I dont pretend to know everything..but I know the CA Yaks pretty well.

Phil, Im not trying to stir up trouble...but the numbers just dont make any sense for this plane. In any case..your build looks very clean and regardless of the weight..it will fly great.