Is it tailheavy?

[buildflycrash]

I still need to push ( a tiny bit ) when inverted.

QQ 85" Yak - DA50

the ballance is behind recomended ( but I still need to push)
Wing rock pretty bad in harrier (even when I'm almost to a hover)
dosn't land very well (or I don't land very well)

This is my first Gasser but I have been flying for several years.

[Reza]

Where is exactly your CG? 7 3/8" or 7 1/4"? It's normall to push a tiny bit for inverted unless you get your CG at around 7" from trailing edge. Now once you make it that tail heavy, you will have a hard time landing it. Plane wants to balloon out. Please give me more info and I will help you out the best I can. What kind of problem in landing.

Thank you,
Reza

[KrisW]

Sounds a bit tail heavy. Most planes require a noticeable amount of "push" when inverted.

Here's how to tell if you are tail heavy or nose heavy:

Trim the plane for level flight at 3/4 throttle, do it in both directions to make sure it's righteous. Then come in and pull to a 45 degree line. Note the line, whether the nose wants to drop or climb (it wil probably want to fly straight ont he 45), then roll inverted and see what the plane does.

It's as simple as that. If the nose drops a little, it's close to neutral. If it does not drop at all, you are slightly tail heavy, if it climbs inverted you are TAIL HEAVY. If you have to push pretty hard to hold the nose up inverted on the 45, you need more tail weight.

It's that simple. Many "neutral" planes will change flight characteristics and appear slightly tail heavy and tend to balloon at lower airspeeds, especially if you are heavyhanded on the right stick. This is where flying a "neutral-slightly tail heavy" plane teaches you to NOT throw the stick around, but to finesse the plane at all times. Finesse is a good thing.. I'd rather fly a neutral-slightly tail heavy plane than a nose heavy pig any day (but, that' just my style)

[notorious_benny]

Heres a trick I have learnt while flying IMAC. And this is the way I set up all of my models now. It not my method I pinched it from 3dubya, the trainer huck dude!

Set your cg to a conservative position by the manufacturers reccomendation. Also set thrust lines as suggested, we will play with them later though.

Now before taking off set your elevators to 'zero' trim ie the elevator is in line with the stab.

Now fly you model, you will most likely need to hold a little bit of up in to maintian level flight, this is normal. You need to fly a line where the cg has little bearing on the way the model behaves as well as the thrust lines.

So.... fly vertical downlines with the motor at slow idle. What we are looking for is to see if the model pitches either towards the canopy or the gear when no elevator input is given. This will tell you if your airframe is truly 'neutral' (incidence wise not cg)

My Yak 55sp passes this test with the elevators zero trimmed. If your model passes this test then it is time to check thrust lines (if it dosnt, for the time being you can give elevator trim until the model drops vertically down though really the incidence of the stabs/wing will need a tweak ouch!)..... So turn it around and fly vertical uplines to see what effect the motor has on the line. Ie up down/side thrust. Adjust until your model flies a true straight upline without the need for elevator input.


By performing the above we have our model as close to 'zero' trim as possible ie the wing, stab and motor are not 'fighting' each other. Now you can perform the 45 degree inverted line test that was outlined above by Kris W to fine tune your cg. I personally like the model to gently drop its nose in the 45 line so I adjust the cg for this trait. (Slightlt nose heavy)

The reason I outlined all the above is that if your thrust/incidences are all outta whack in the first place they will all effect the behaviour of the model when you roll inverted, especially inverted 45 lines. In all honestly I think that fine tuning the cg should be one of the last things you do.

Dont trim your model to maintain altitude straight and level, we arent flying circuits here are we. Keep it trimmed so that it will drop vertically perfectly straight. By doing this the model will behave very similarly inverted as if does upright. ie you will need about the same amount of down elevator while inverted as you do up elevator while upright, after all once your in advanced IMAC you spend just as much time inverted as upright. So why have to fight the model everytime its inverted.

As an aside a lot of models need more down elevator while inverted because they are trimmed to fly hands off while straight and level (ie normally a little bit of up elevator trimmed in)

Hope this helps. It has certainly helped me with my competition flying

[RustyTumbles]

I might give that a go with the extra benny. Normally I do the CG first then thrust lines, mixing etc. As per peter goldsmiths trimming guide.

[notorious_benny]

Goldmsmiths approach is a little 'old fashioned' (more traditional approach to trimming. It still works but makes the plane feel different).
He obviously likes his planes to trim while flying straight and level.

[KrisW]

Funny thing is. . if I trim my plane according to Benny's way of doing it. . it becomes a nose heavy PIG long before I ever get to try a 45 degree line.

If you are adding up elevator trim to a plane, then it is tremendously nose heavy, IMO

Most planes require positive incidence, or down elevator trim, on the tail, to fly level, because something has to make the tail lift, and the only way to do it is by giving some lift to the stabilizer Even a Sr. Telemaster uses this. Rolling inverted, with "down trim", will make the tail droop, but the wings incidence will increase, keeping the aircraft flying straight and level. You can actually see this change in AOA by watching closely and comparing the planes angle when inverted or upright.

This is borne out with . . . what happens when you roll inverted??? A truly "neutral" plane will just keep flying level, no matter if it is upright or inverted, once it is trimmed for level flight. What happens on vertical downlines is an entirely different story, however, because there is no gravity pulling the nose or tail down, and then you get purely aerodynamic forces acting on the airframe, and it will pitch or tuck in accordance with how you have the plane trimmed (assuming 0-0-0 incidence). It will also (even with 0-0-0 and no trim) tuck or pull due to drag on the airframe, especially so with a low-wing design, since the majority of the drag is below the thrust line.

My planes usually require about 2% down mix with the throttle at Idle in order to do a perfectly straight vertical downline. Considering that my time at idle, when flying, is very scant, setting a mix for this works out pretty well.

This is why the "45 degree test" is probably the most accurate test of the planes overall CG and trim. It will show tail heaviness that would otherwise be mistaken for a "Neutral" plane on a horizontal line, and will ignore most trim or incidences that would make an aircraft pull or tuck on a vertical downline.

Peter Goldsmiths techniques may be "old fashioned". . but they have been shown to be extremely helpful and accurate when setting up a plane for best overall flying performance. The object is to get the plane to fly straight, with a minimum of control inputs. .no matter what kind of plane it is. And with an aerobatic aircraft, following Peter's recommendations will get you the truest flying plane in any attitude or orientation, and at 90% of throttle settings.

[SleepyC]

	Quote:
	Peter Goldsmiths techniques

BOOk NAME??
Available? where?

[Danny Gray]

Hey all I just flew three tanks of glow thru a profile the same as Sleepy Cs. Cg set as per destructions I had to push very little inverted. Low and full thottle was on. C cant wait to fly with you again!!!!!!!!

[KrisW]

	Quote: Originally Posted by SleepyC
	BOOk NAME?? Available? where?

Actually, I believe it is posted on the IMAC site. . . very informative.

[notorious_benny]

I deleted this post. I cant be bothered debating an idea with "He who is never wrong"

[feral63]

well that would have to be a first for you benny.

	Quote: Originally Posted by notorious_benny
	I deleted this post. I cant be bothered debating an idea with "He who is never wrong"