Forward CG Issue

[CharlieZulu]

Hi Everyone. I'm hoping some of the more experienced builders can help me out. I recently bought a scratch built 4 place with an IO-390 up front. I've upgraded to 29 inch ABW's and had to install a couple of heavy auto exhaust resonators to replace cracked exhaust mufflers. It already felt quite nose heavy one up, but now it really is. Engine idle and it won't flare at less than 60 knots or so.

Anyway, obviously I need to get a set of scales and re do the W&B, but I've read that this is a common issue with the Bearhawks so was interested in how other people manage it. The forward CG is great for when I want to load up the plane, but I'd like to have the same characteristics 1 up without having to put 80lbs or so of ballast in the baggage compartment. Has anyone played with adding removable/adjustable weight to the tail or are there any other suggestions? Does anyone have any guidance in terms of what the 'ideal' CG is. I guess by ideal, I mean far enough back where you can stall it on with a decent amount of back stick left at engine idle.

Nick

[jaredyates]

You can find the ideal point for yourself by adding ballast in small increments, such as 25 pounds. Go a little at a time to be sure that you don't get too far aft. Tie it down well. I don't know how you'll be able to operate safely on heavy trips without having a good empty weight and cg to start from.

[Battson]

If you land slower with power on, that problem goes away. Alternatively, I just give a burst of power when I land if I can feel it isn't going to flare... You can easily make the problem go away with pilot technique.

Alternatively, put VGs under the tail wings, or put in elevator gap seals. Both those approaches also fix that problem very cheaply, without the need for ballast.

The forward CG certainly is GREAT when you need to load the plane up!! Much better than the alternative (aft CG) limiting your load.

[swpilot3]

Hey Nick.

I'm curious if your plane has the wood airfoil forms on the horizontal stab or if it's flat.

[bearhawk2015]

Put vg's under the tail, that's all I did and it fixed exactly what you're talking about

[jaredyates]

I didn't find that sealing the gap made much of a difference.

[CharlieZulu]

Thanks everyone for your feedback. I have put the STOL Speed VG's under the stab and have gap seals. That made a big difference to the problem when I first got the plane, but since I added the bushwheels, it seems to be worse than ever. I haven't really properly investigated yet as I've only flown it once empty since then. I'll do a new w&b and see where it comes out. I'm also wondering if my uncovered gear legs have changed the way the air flows over the tail?

And yes Battson, I'm sure a little better technique would help! If you're ever over in South Australia, I won't say no to a few tips! I've watched all your videos and read your posts so have used that method almost exclusively, but since the gear/wheel changes it feels a little too nose heavy for my liking. My home strip is 250m up a fairly steep incline with a steep approach to avoid buzzing the neighbours. It feels a lot more comfortable to me when the cg is back a bit.

[Battson]

My friend has a ferry tank, I wonder how easy the customs clearance is?? Haha

Do you have a profiled stabilizer? I would also be interested to know where your empty CG is located. I am amazed the problem is still there with both VGs and gap seals!

[CharlieZulu]

If you come via Tasmania and South Australia, I doubt anyone would even notice!

I'm pretty sure my stabilzer isn't profiled. It was built per the plans (around 2000 (#362 or so), not sure if they have changed since then). I'll have to check when I'm down there next but from memory it's flat.

[Battson]

Maybe that is the difference between our two aircraft's flare behaviour...
Bob has said that the profiled stabilizer has the same net effect as having a 25% bigger horizontal tail area. So if you can be bothered re-skinning just the stabilizer part, and using that together with your gap seals and VGs, then that might help solve the problem entirely.

[CharlieZulu]

My empty CG pre bush wheels and pre heavy exhaust resonators was 12.8 inches. Mind you I'm 220 lbs and the tanks were full so I would think that on the balance of that it should be well within limits. It will be interesting to verify the w&b as something doesn't seem to add up.

How did you profile your stablizer? Is that a modification in the current plans / quick build kits? I am getting someone to help me re cover the gear legs so may well do this at the same time.

[marcusofcotton]

I thought Mark (or perhaps Bob) had the profiled wooden strips available to glue onto the tail ribs. Checked the website and last newsletter but didn't see mention of same.

[Mark Goldberg]

I do have sets of wood strips that can be glued onto existing flat ribs to make them airfoil shaped. A worthy modification if it is not too much trouble. Mark

[patrickh99]

Do the ribs get primed first before the wood strips get epoxied on? Or epoxied onto the bare metal, then primed together?

[swpilot3]

I scuffed the primed/epoxied ribs, then used T-88 to epoxy the wood strips to the ribs. Then I used PolyFiber EV-400 and EV-410 Epoxy Varnish to seal the wood. Hopefully, someone smarter than me can confirm that's the way to do it, or give you better advice.

[Mark Goldberg]

What you did was very acceptable Bobby. I found the wood strips really stuck to the primered and top coated flat ribs after scuffing and then cleaning up afterward. It looked like the wood would break before the glue joint. Mark