Tail heaviness

Guys,

I am building a Shark .45 and it is coming out where the CG looks like it will be at 30-32% of the MAC. I know more modern stunt aircraft can fly with this aft of a CG but the tail volumn of the Shark runs about 20-21 percent of Wing Area. Will it fly reasonably with this far aft of a CG or am I going to have to do some alterations like less weight in the tail section and/or more weight in the nose section to get it to balance no more than 26-27% of MAC?

Hi Jim,

Yeah, it's likely to be a bit twitchy with the CG that far back. It will help a bit if the overall weight is heavy as well. Surprisingly this is one of the only potential saving graces of tail heavy airplanes is that most of them got that way by being a little "gross" to begin with.

For reasons I don't really understand heavier wing loading ships seem to live with aft CGs bettter than lighter loaded ones. The will not only tolerate it and remain stable but there is an added benefit in that control surface deflections needn't be as great for a given turn and thus maneuvering drag is reduced.

On the down side for the Shark design is the smaller than normal less than full span flaps. Generally speaking this makes a ship more responsive and can lead one to prefer a more forward CG. It's no accident that most of the top designs today are full span flapped and also utilize aft CGs.

It would be very interesting to get hands on with the Beringer airplanes that did so well at the WCs this year. They are the antithesis of lots of modern US thinking and clearly fly exceptionally well. My suspicion is that we'd find them trimmed a little more noseheavy with repect to the MAC but that's only a guess.

On the Shark I think I'd try my very best to get the CG up to at least 25%MAC for the first flights even if it takes large chunks of temporary ballast to achieve it. It can always be removed if flight tests indicate it isn't necessary.

Good luck.

Ted et al --

As an aside to that question, what is too nose heavy? The plans for the Brodak Flite Streak show the CG at 11%, which seems right nose heavy to me. Makes sense that stunt ships (stretch a little and call the Streak a stunt trainer) should be a little more stable than our old combat planes, but my memory says 25% was a tad nose heavy, 30% was about right, and any more than 35% would make the Little Old Ladies in the crowd cry, "Can't anyone go out there and help that poor man?"

Now, George Aldrich has inhaled his share of balsa dust over the years, I'm sure, but should the Streak CG really be that far forward?

> (...)but my memory says 25% was a tad nose heavy,
>30% was about right, and any more than 35% would
>make the Little Old Ladies in the crowd cry, "Can't
>anyone go out there and help that poor man?"
>
You've got about a 10% misplacement. For combat we'd have placed 15% as nose heavy and 25% as too squirrelly. 20% was just about right (here in the U.S. - it's my understanding that over in Europe they often will put it at 25% and then can only fly with narrow handle spacing).

The Streak design does tend to feel more sensitive by nature than other more or less similar designs. I'd have to build a new one to see where I ended up liking the CG to be these days.

Ted,

I did some more work on it. I now project that it will balance at the 27% MAC. If I narrow my handle adjustment - it has a 4 inch bellcrank, I think that I will be able to keep it fairly agreeable in flight characteristics. It also has the positive incedence in the stab as well. I should have it ready for a maiden flight hopefully by Saturday AM, if the weather cooperates here in N. Alabama.

Helium.

I think Hunt makes all of his stuff with it.

See Ya

Peabody

On a more serious note, consider gutting the tail surfaces and using mono-coat/minimal finish.

I believe that it's better to chop something off than add (much) nose weight!

As Bill Winter once wrote, "Simplicicate and add lightness."