Help! Hangar 9 20cc P47 Balance issue

[Fireflite88]

Hello, is anyone on here flying a Hangar 9 20cc P47 running a larger than 20cc gas engine?

I bought this ARF and threw a 26cc RCGF motor with a wrap-around pitts muffler.

From day one it flew as if it was too tail heavy. The airframe, with an empty fuel cell, was balanced at the recommended 4.25" being a touch nose heavy.

Nose weight was added from day one as well to achieve balance on the bench.

I exhausted all trim on my elevator. It flew like crap almost uncontrollable. Before the second flight, I rechecked everything on the airplane. I mechanically added a little nose down and brought my trim back to center. I added a little more nose weight.

The second flight same issue but not as bad, still exhausting my trim by 75%. Although this time I nose over on the rollout.

I again, inspected everything on the plane and this time I went in and adjusted the sub trim. On all subsequent flights I am able to fly controlled but never hands-free for more than a few seconds.

This isn't sitting well with me. I want my control surfaces as neutral as possible.

Now I have a feeling that with the added nose weight is in fact attributing to my nose overs. I can achieve a good glide slope slightly nose down with about 60 degrees of flap. I can grease the landings, but the dang rollout. With every landing, once I touch down, I am walking a fine fine line of trying to hold just enough up elevator, throwing my flaps back up, and trying to keep it level so that I don't get airborne again.

Thinking about it, if I didn't have so much nose down on these control surfaces that may make it a little easier to roll out and not have to pay all my attention to finessing the elevator.

So again none of this is sitting well with me and I was wondering if perhaps I need less nose weight (getting well back to being neutral) and needing more right and down thrust angle?

I've decided to post a thread because almost all H9 P47 20cc threads I found are running electric setups. Any advice from any experienced pilots would be greatly appreciated!!

 

[The Hangar]

I don't know of anyone on here with one of the Hangar 9 P-47's... You might have better luck posting on RCG. Anyways, I'll tag a couple people who fly larger birds that might be able to help you out. @SquirrelTail @speedbirdted @JennyC6 @Joker 53150 @willsonman @L Edge @F106DeltaDart

 

[PsyBorg]

Sounds to me like either the elevator is not in line properly or maybe the main wing AoA is off creating the illusion of a tail heavy situation. specially after hearing you think it is tail heavy yet nosing over on taxi / takeoff.

 

[JennyC6]

The manual should have right/down thrust specs; definitely worth a check alongside the incidences. P-47s are not known for being particularly twitchy or sensitive with regard to CG and it should fly fine with a 26cc engine on it; the recommended 4-cycle for it will weigh more than the RCFG 26cc you have fitted.

 

[Fireflite88]

I don't know of anyone on here with one of the Hangar 9 P-47's... You might have better luck posting on RCG. Anyways, I'll tag a couple people who fly larger birds that might be able to help you out. @SquirrelTail @speedbirdted @JennyC6 @Joker 53150 @willsonman @L Edge @F106DeltaDart

Thank you for your response. I figured it would be a longer shot but I posted the same entry across all major forums. Until then I will keep plugging in my Hypothesis'.

Sounds to me like either the elevator is not in line properly or maybe the main wing AoA is off creating the illusion of a tail heavy situation. specially after hearing you think it is tail heavy yet nosing over on taxi / takeoff.

I thought that as well but upon checking the incidence of both surfaces they show to be right. Again thank you for your responses!

 

[PsyBorg]

The only other thing I can think of is since you stepped up in motor size the added power with the original down thrust may be the culprit not pulling the nose down enough making you think its tail heavy

 

[Bricks]

One way to check thrust angle is get the aircraft trimmed fairly close pull vertical at full power, watch what the planes does if it pulles to the canopy then need more down trust, pulls away from canopy then more up trust. Pulls left or right correct with washers between engine mount and firewall.

 

[willsonman]

So, every person I've talked to that has flown this airplane has had nothing but a fantastic experience with it. Whether electric or gas the CG will be the same. That said, In the nose of my airplane, I have the electric motor, ESC, ABS 3D printed dummy radial, sound system with resonator box, hardware and modifications for funtional cowl flaps, hardware and modifications for functional oil cooler vents and waste gate valves, and my flight pack is a 7000mAh 6S pack and a 2200mAh 3S pack for the sound system. That is a LOT of extra hardware up front to balance this model. While my airplane is far from stock, @wilmracer built his bone stock with all HH hardware. Mine is 1.2 pounds (15.2 pounds) over the stock weight (14 pounds) and has ZERO bad habits or issues. The following link is a playlist for my P-47 project.

Carl uses a 8000mAh 6S pack with no additional ballast for CG... it's a BIG pack. Carl's review of the bone stock version is here:

Now, to address your specific situation. For those who do not own the airplane, there is no way for the wings to be at an improper AoA as the wings plug into the fuselage. The H-stab is similar in this way in that the hole for the stab to be inserted is cut perfectly to accept the H-stab. Really the only thing to go wrong here is what has been mentioned already. Namely, Elevator centering, CG, and thrust angle.

A couple of notes on each...
I use the method of centering the elevator by clamping a paint stirrer stick to the the top and bottom of the H-stab/elevator assembly. I clamp at the leading and trailing edge and then set the servo connection in the fuselage. This one is tricky since you use two elevator servos. Make sure they are the SAME. You can verify this by measuring up from a build table to the edge of the elevator and make sure the stab is level. Ensure the measurements are the same.

CG is always done inverted. Make sure that you have the proper gear to check this. It may be worth setting up a vanessa rig to get the most accurate result. Carl has a GREAT video on this subject as well.

Thrust line is what it is. Additional torque will be minimally impacted by angle and has more to do with back-torque into the air frame. What WILL influence this transfer is the mass of your prop. Carl and I are both flying with 16" props. While my initial flights were done on a MAS Classic prop for the sound, I found that the Xoar WWII style prop is far better in terms of rotational mass and stability. This prop is less than HALF the weight of the MAS prop and I am convinced it does a far better job in maneuvers because there is less centripetal force that I am fighting with aerodynamics. Carl flies his on an APC-E prop... again, far lighter than a MAS prop. It may be worth getting a wood prop in your situation as the recommended 18" prop would likely exaggerate this issue but this is assuming on my part that you are not using a wood prop to begin with.

I suspect that you already know ALL of this as this is not a beginner's airplane at all. It does fly nice but it requires careful setup like any larger warbird.

 

[wilmracer]

@willsonman did a really comprehensive breakdown so I don't have a ton to add. You mentioned the initial CG was 4.25" and was a touch nose heavy. Is the CG still there or has it shifted further forward with your testing? And are you certain the fuel tank is centered on the GC and isn't shifting the balance during the flight? I'll second what willsonman said... these are great flying birds and I'm sure there if you can figure out the issue you'll love the way she flies.