Flight trim problem on a Brodak Fire cat

[Jim z]

 Built a Brodak Fire Cat per the instructions.  Fox .35 for power. Test flew and noticed an odd trim problem, I’ve never seen before.  From outside of the circle the wings appear level, but the control lines seem to be angled downward towards the handle…looking up at plane from the handle the lines seemed to be angled up toward the plane, where the lines enter the plane the wings are level.  Kind of hard to visualize just reading about it.  Very odd looking from the handle.
Could this be a problem with the wing mounted so low on the fuselage?  Any help would be appreciated.

[Rick Campbell]

Bob has it right. So go on eBay and find a set of old-school metal hub super heavy Veco or Perfect brand wheels. They're out there and not silly "antique" money either.  Use the smallest/lightest muffler you can find.

[Ken Culbertson]

The Fox 35 is probably overkill for powering this plane so weight is probably not an issue BUT:  Most planes from this era relied on heavy wheels to balance the VCG.  Problem was that very few cared about that much back then and most flying of this type of plane was over grass hand launched with no wheels.  If you can take the extra weight great, go for the wheels., but if they are going to make you nose heavy and or overweight I would just live with it.   What you are seeing is also in a way a symptom of not enough tip weight.

Ken

[Dave_Trible]

The original Firecat kit came with solid hard rubber wheels-weighed plenty.   That probably took care of most of it.   I have one I built just a few years ago from one of the re-make kits that came out.   I just slapped it together as we always did and found the ship wants to hunt badly (without flaps) as the speed increases.   I think the kit fuselage cutouts for wing and stab were not accurate and so are out of line with each other.   Sometime maybe I'll check it with the incidence meter and see if I can cut the empennage loose and align it better.   This was my first large control line airplane in 1965.   I'll always have a soft spot for it-just like it to fly better.   I destroyed the original and the Fox .35 on it with a vertical dive into the old Swope Park KC concrete flying circle.  Under the soccer complex they built over it that chip in the concrete lies buried for time eternal.

Dave

[Colin McRae]

I recently completed a Brodak Yak-9. Being a semi-scale warbird it also has a low wing. Even lower than the Firecat.

I actually did its maiden flight yesterday and noticed the same vertical CG phenomenon. I was already aware of this, and I could have built the kit with dihedral but elected not to maintain its OTS eligibility.

I did use heavier aluminum landing gear which probably helps a bit but kept the wheels light. I'm hesitant to use heavier wheels which will just add overall weight. Plus, with heavier wheels north of the horiz CG I might have to also add tail weight. All going in the wrong direction for overall model weight and wing loading. Everything is a compromise.

With that said the model flew quite well. Well enough for the simpler OTS pattern, but will not be a good model for the full pattern. But I'm ok with that as my model is intended for sport flying and maybe OTS someday as my flight skills increase. I also built my Yak with operable flaps and again the model flies reasonably well even with the vertical CG issue. So, I'll just live with it.

[Jim z]

 Thank you everyone,   Good info.

[Jim z]

This is not meant to cause any angst among our group, but... If you were to go electric you could lower the battery placement and probably achieve the proper vertical CG for this plane.

Bob Hunt

.            I haven’t tried electric yet ,  might be worth trying,    Thanks Bob.

[Dan Berry]

Bear in mind that when this and many other planes were designed there was no such thing as lightweight wheels.
My Hurricane from a Brodak kit had this problem. Vintage wheels solved the problem.

[Motorman]

Ask Banjock how to trim it. He always wins Old Time with his.