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Tail Heavy Plane

fliteadmin

Administrator
Staff member
Admin
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#1

In the past we've talked about the importance of balancing your airplane. You've heard us say that anything can fly as long as you have enough thrust, lift and BALANCE!

RC planes work like a fulcrum, a little weight in the tail equals a lot of weight in terms of CG (Center of Gravity). So the further back the weight is from the CG the more leverage it will create and the more unbalanced your RC plane will be. Flying even a slightly tail heavy plane will be much more difficult to fly compared to a nose heavy plane, and in today's Flite Tip we show the importance of balance, CG, and the effects of a tail heavy plane.

We put a bunch of weight in the tail of the plane to show the extreme effects of a tail heavy plane. Here's a few things to look for to know that your RC plane is tail heavy and needs to be balanced:

  • The take-off will pitch up violently
  • Pitch sensitive response
  • Sensitive to any input
  • The plane will want to porpoise around when trying to roll

In the video we also go over some basic maneuvers to help control your tail heavy plane and land it safely. One maneuver that can work with a tail heavy plane is to back off the throttle and put the plane into the wind. Remember that your pitch is going to be very sensitive, but as long as you're careful with your elevator you should be able to bring it in safely.

I hope this test helped show you the effects of an Aft CG plane and some tips to control and land it safely. Usually a properly balanced plane will give you the best performance in all aspects of flight.

Be sure to check out more great tips on our main site website!


Links mentioned in this episode:


How To Balance Your Plane

The Ventus

Retractable Landing Gear - Trojan T-28
 

Attachments

bmsweb

Site Moderator
#5
I've flown a tail heavy . . sorry extremely heavy P51D Mustang once! . . . the flight lasted 0.8 seconds :mad:

Nice flying and good to see Dave Join the team!. I've been a subscriber to Dave's Channel longer the FliteTest's :eek:
 

keek

Junior Member
#6
I've learnt how terrible a plane flies tail heavy the hard way :p flew a scratchbuilt 2m glider recently which was about 5cm off the suggested cg but was too excited and took off anyway, ended up hovering the entire flight :eek: the glider was in a high alpha position 90% of the 5 min flight and was incredibly hard to control. it then looped on me at a low altitude and had just enough time to pull up and land almost flat on its belly, broke the tail off but nothing a little hot glue cant fix! :D
 
#8
I've learnt how terrible a plane flies tail heavy the hard way :p flew a scratchbuilt 2m glider recently which was about 5cm off the suggested cg but was too excited and took off anyway, ended up hovering the entire flight :eek: the glider was in a high alpha position 90% of the 5 min flight and was incredibly hard to control. it then looped on me at a low altitude and had just enough time to pull up and land almost flat on its belly, broke the tail off but nothing a little hot glue cant fix! :D
Do you have a video?? That sounds funny :)

JB with these glasses made me think of byron from hk for a second
 
#9
To safely find the CG of your plane hang your plane level from a hook in the ceiling like you would do a model in your bedroom when you were a kid. Hang a plumb bob from the same hook. The Plumb bob will point to the CG of your plane EVERY TIME. No matter what size, construction method, material the plane is made of, this works every time. Physics don't care. Here is a picture of a Delta flying wing while I was measuring it.

39946_1360060847327_1405715559_30852229_4092354_n.jpg

I used to use the old pencil in a board trick, I've used the back legs of an overturned chair and who hasn't used their fingertips. Problem with your fingertips is you can actually 'lean' into a wing and tip it straight. I've seen airplanes whose CG's weren't where they were supposed to be because of that. I also have patched more then one pencil hole in a just finished airplanes wing. I am clumsy. Lets just leave it at that. In the late 70's a club member showed my club how to use the above CG sling and I've used one ever since. I always try to pimp the CG sling out ever since. Besides your plane you only need three things.

1. A suspension point. I use a screw in the exposed rafter of my garage but any point that can hold the weight of your airplane will do. I've used tree branches, just remember that any wind will have your airplane rockingback and forth.

2. Next, you need to make a couple loops of lighweight cord or twine big enough to go around the wings and nose of the plane and reach p to the hook in the ceiling. I actually just have one big loop that I suspend from the middle.

3. Finally, you need to make a plumb bob. I've used everything from a nut tied to a piece of kite string to an actual contractors plumb bob.

place the loops around the rear of the wing and the firewall or front of the engine. I used to just put it around the wing but in some cases, usually with flying wings that require a more forward CG you can't keep the nose level and the plane will just rotate nose down in the sling. Hang the plane from the suspension point and adjust it so that it is sitting level. With high wing planes hang them in normal flight attitude. With low wing planes, hang them inverted. With ANY airplane it doesn't really matter we are just positioning the plane to make measurements easier. Now, suspend the plumb bob just above the airplane from the same hook.

Theory. What we are actually doing is suspending two plumb bobs from the same point. Plumb bobs work by creating a line from the suspension point towards the center of mass of the Earth. Plumb bobs are always vertical, they built the Pyramids with plumb bobs. When you hang your airplane from the hook you make a plumb bob out of it. The center of mass of your airplane will hang directly under the suspension point. The actual plumb bob will be pointing to the center of the Earth as well and the point where it intersects your airplane will be the CG of the plane. The reason we hang it with the wings and nose level is because the CG is a three dimensional measurement. It's best to just measure two dimensions at a time and mostly we are worried about fore and aft CG then lateral (wingtip to wingtip) cg. So we neutralize the vertical (top to bottom) axis.
 
#12
To safely find the CG of your plane hang your plane level from a hook in the ceiling like you would do a model in your bedroom when you were a kid. Hang a plumb bob from the same hook. The Plumb bob will point to the CG of your plane EVERY TIME. No matter what size, construction method, material the plane is made of, this works every time. Physics don't care.
No offence but where did you learn this from? As its just completly wrong. Only thing this idea would be good for is to find the middle of a plane not the centre of gravity.
What you need to do is, work out where the centre of gravity should be, using one of the many online calculators. Hang it from that point and add/remove weight to make the plane sit flat.
 
#13
My bixler is tailheavy but I find it easier to land because that you will automaticly flare wich is really usefull in short landing zones. But turning in the wind isjust horrible!!
 
#14
No offence but where did you learn this from?
AMA Newsletter Editors newsletter? But that's not fair, I sent it in back in 89 or 90 and I learned it at a club meeting pre 80's of the Capital City RC club in Topeka, Kansas but don't remember who brought it in at the time. And evidently I've not said something correctly because you don't understand AND it works every time. Doesn't have an option not to.

BUT, pictures is worth a thousand words, though I'm afraid these camera phone ones won't do, we'll give it a try though.

My just completed raptor is now hanging from a hook thats hanging from a light fixture. It is suspended by a loop of string and has been adjusted so that it lies relatively flat. You could put a bubble on it, allowing for the weight, and see that it's horizontal to the Earth but close enough for a clear reading is good enough. A plumb bob is then suspended from that same point. I put the plumb bob string between the two passes of the suspension loop. It is centered. As the center of mass of both these "Plumb Bobs" hang in a ray that starts at the suspension point and continues to the center of mass of the planet, they BOTH occupy the same ray, ergo the plumb bob points to the center of mass of the airplane. Weight then should be moved around on the airplane so that the desired CG position for the plane is under the plumb bob.

Far away shot for complete suspension viewing:


ok, it's a little off horizontal
Close up of plumb bob pointing towards desired CG with battery pack location found.



And although it's just in front in this picture, I hadn't waited for the whole assembly to stabilize, so it swings back and forth a bit.

After going through multiple demonstrations, hanging and showing the current CG's of multiple planes whose CG is both known and un-known, I invariably get one guy or two that will say "Well that works for foam and those SPAD planes you fly, but it won't work with balsa" Or some junk like that. I'm here to tell you, if you could find a place and cable to suspend a full size 747 by and then hang a plumb bob from that same point, the plumb bob will point to the CG of the 747.

Further clarity. This is not the Intended or Designed CG of the plane. The point where the aircraft operates as intended. The point or range that is given on a plan. This is the actual CG of the aircraft which you need to put in the intended CG range. Perhaps I wasn't making myself clear on that because your statement that this will only find the center of the airplane, which I assume you mean a top planer view and that I need to work out where the cg is, hang the plane from that point and then add weight till it hangs level. Well your method is pretty much the same thing I'm doing, but I'm not putting a mount on that point. I'm suspending it from the sides. The Current Center of mass of the plane will be directly under my point of suspension.

I could probably find some other way to say it but I'm betting the pictures actually will bring the point home. The method I've shown works, guaranteed, it can't not work. If you say different it's because I haven't explained it correctly.
 
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earthsciteach

Moderator
Moderator
#15
I think I've wrapped my brain around this. Think of it as one of those Pirate Ship rides at an amusement park (Big pendulum ride that swings back and forth).
pirate-shop-ride.jpg

If everyone sat on one side of that ride, say the stern, the bow would swing further out. Hang a plumb bob from the axle and it will point straight to the center of mass of the ship.

Using the published or desired cg for the airplane, you can move components around until the plane balances so the plumb bob points at that cg. Pretty cool method!
 
#19
Been pimping it about 20 years, ever since my plane slid a bit on the pencils with big erasers balancing stand and punched a hole all the way through the brand new silkspan and doped covering. You know, final balance as I was out the door to go 1st flight it? Plane was green and white I was all red turning purple. But the biggest reason I use past the fact that you can put some english on your fingertips is instead of paying 20-30 bucks for a CG machine or the effort to make your own, this is just tyeing a loop of cord and putting a weight, I use a lot of 1/4x20 nuts, and finding some suspension point that will hold the weight, which are everywhere and free.
I'm cheap.
 
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