Hello,
I have a few questions on how adjusting the CG will change the characteristics of my plane.I have a Hobbico Avistar with a TT Pro .46.It is probably a tad nose heavy,and I have flown solo about 10 or 12 times.Been practicing landings,and doing alot of sloppy aerobatics.Here are my questions.....

1.Will moving the cg back make it easier to slow down for landings,or harder?

2.Attempting to do large loops,or climb very far,the plane wants to roll or yaw out of vertical.Will moving the cg back make it easier to maintain a vertical climb?

3.The plane is hard to get it to stall,and I cannot get it to enter a true spin.If you are familiar with this model,do you think moving the cg will fix this,or will it take something else to get it to do spins?


thanks,
JT

An AFT CG will allow you to land at a slower speed.

Geistware, you sure are a stickler for the details...

JT,

I have had a couple Avistars and I flew one of them today.

First off, if you have a Pro .46 on it YOU WILL NEED some weight in the tail. About 4 ounces...

Basically as far as aerobatics and standard flying goes, there is absolutely no advantage to having a nose heavy airplane.

Even when the Avistar is balanced on the main spar, it becomes nose heavy with fuel. So it almost makes sense to have it a little tail heavy...

A tail heavy airplane is generally more responsivee, especially in the elevator department.

It will be especially touchy at slow speeds while flying long with it's nose up, instead of down or straight and level.

It will help eliminate some of the down elevator needed for inverted flight. Spins will also improve...

Start on the main spar and slowly move it back 1/4 of an inch at a time until you've got it just where you want it. If you have to, cut a hatch in the back of the fuselage for the battery. Do everything you can to avoid adding weight.

You've got a great engine/airplane combination. What prop are you using?

I am not a aerodynimics engineer but from what I understand you have to play with the location of the center of lift and the center of gravity of the plane. Moving the center of gravity behind the center of lift is dangerious but will allow you to decrease your landing speed.

BottleRocketWar, Thanks for the compliment!

using an 11*5 prop,do you recommend I try any others?
seems to have plenty of power

I've been trying a lot of aerobatics with it.I can fly inverted all over.I can do consecutive rolls,and tight loops inside and outside.But when I try large loops,I have trouble keeping it from sliding out of it on the vertical part.Probably because i'm not coordinated on the rudder.And I have done spirals,but can't get a true spin.

I am currently running it with 2 batteries and 2 switches(something I picked up online).One battery Is mounted in the rear of the fuse,behind the wing.The front battery is almost right on the cg so taking it out won't change much but I may take it out to make up for adding weight to the tail when I start playing with cg.It balances where the instructions say,with just a slight nose down attitude.I'm thinking about putting some sort of tail skid on the back to add weight and protect the tail.I have tried cutting a small hole in the fuse and sticking weights thru with epoxy,but they already broke loose.So I thought maybe a tail skid,and I can figure out a way to attach weights to the skid where I'll have better control of getting them stuck on good.

For a rubber-band mounted wing, an 11x5 on the TT 46 Pro should give plenty of speed. I wouldn't change it. That's what I run on my Aresti to keep the speed reasonable as well as gaining some extra thrust on uplines. Using an APC will add to the nose-heavy condition but will provide noticeably more thrust. To help move the GC back, try a wooden prop: Zinger Pro, Bolly, or MA are better than TF or Zingers. Does MA make an 11x5 wood prop? Don't think so...

Great plane, BTW: I flew mine yesterday with my buddy training on the buddy box.

WHY??? what is the advantage of that??? its a trainer not a large scale airplane. if your that concerned with flight times.. buy a few battery packs.. you have to come down for gas soooooooo whats 3 seconds to change a battery pack???? please enlighten me.. for that has me confused. also if you want more speed try an 11x7 or 8 prop.. youll lose alittle vertical but increase speed.

The 2 battery packs were originally for balance,why use dead weight when an extra battery will do the trick?But the idea is not just extra flight time,it is for extra safety.Let me find the link........

http://www.rcbatteryclinic.com/parallel.html

It sounded like a good idea at the time.But like I said,If I have to add more weight to the tail to get an aft cg,I will probably remove the extra battery to make up the difference in added weight.

hmmm interesting.. but to each their own. i prefer to keep it simple. i just put in 1800 mha packs and fly till my thumbs get sore!! as for the aft cg.. just be careful how far back you go. too much and the plane is unflyable. nose heavy is good tail heavy is bad. if you want to do aerobatics i recommend you get a plane designed for that purpose. hate to see that you planted a balsa tree. aft cg will make the model really pitch sensitive. i personally dont find that appealing. but good luck to you with your aerobats.

Thanks,I will take it a little at a time.That is why i asked in the first place....wasn't sure what to expect.But I do think it is a tad nose heavy,and I think this is making it hard to slow down for landings.Won't know til I try I guess......

On your large loops that always go off track in the vertical and just past as your softening the elevator pull. I think of course a little left thumb help is needed but if you add a few more degrees right thrust it will help considerably in the manuver.

John

Also check the lateral balance and the rudder position. Both being a little off will make your plane fall out of loops.

All this is getting just a little too complicated!

You need to take the battery on the CG out. It's dead weight. Doesn't make any sense that instead of moving the original battery back, you added a seperate battery. Get rid of the battery on the CG and the extra switch. Keep it simple! Just use the standard battery and set it up per the instructions.

The weight does not need to be INSIDE the tail. If you want to experiment by adding weight to the tail, just get some stick on weights and add a couple drops of CA and stick them on the tail as far back as you can get.

Go buy yourself an 11x4 and see what you think. Try an 11.5x4 for more thrust than both props. It will give you a very noticable increase in THRUST.

You don't want speed on that airplane, regardless of the aerobatic manuever. There will be enough speed with a prop with a pitch of 4. Going above that will give you no gain and just less braking for slowing down and downlines. Keep the pitch around 4.

I think it's your turn to go out and try some of these things now...

Planes are not "probably nose heavy" or "probably tail heavy".

They either are tail heavy (according to the suggested CG) or are nose heavy - or right on.

If you "think" it's nose heavy it only takes 5 minutes to find out.

I balanced my avistar dead on the recommended CG and haven't had a problem yet in any aerobatics I've tried or slow flight. In a stiff wind right down the runway I once brought the plane down vertically from 15 feet to right on the runway.

On a roll I can make 1 complete loop without the nose sagging at all if I do it quickly with no evelator input needed. If I go for more than 1 roll in a row I need a tad of elevator or a touch of attitude up before I start to come out level.

Thanks for the advice....and just so you'll understand,I did not realize the battery in front was not making a difference to the cg until later on.There was no room to move it back due to the placement of the servos.I went through a whole lot of trouble installing the second battery behind all the radio gear in the rear of the fuse.It is a royal pain to get to.The servo linkages have to be removed,and a whole lot of cursing has to be done.It seemed to balance perfectly after that,so I left the first battery in.It was only recently that I realized it does not change the cg whether left in or taken out.I flew today for the first time without it.The extra 4 oz does not make much difference either way.Having the spare battery gives some added security in case one fails,or one switch goes out.But I will experiment without it as well.I did not get to experiment with changing the cg this flight,but will next time.This plane is alot of fun,and makes me look good hehe.

moving CG back will be great, now watch out though. if your engine quits dont stall it because it has an increased risk of going into a flat spin and with out engine power, your plane is dead. sorry to be so negative but ive seen this happen too many times(punch me if sombody already talked about flat spins in this thread)

That is how I crashed my Avistar. I was practicing flat spins and I ran out of gas and the plane would not come out of the spin!