C of G

[Yenn]

To get away from the conveyor belt, try this.

 

My taildragger was on the ground this morning and I had to push down on the tailwheel to prevent it falling onto it's prop. This really happened and it was not caused by wind, and the C of G is in the correct position. Why?

 

 

[Guest Redair]

was it upside-down?

 

Redair.

 

 

[slartibartfast]

Manoeuvring on a slope? With a flat tyre? And it hit a rock?

 

 

[Guest RogerRammedJet]

Cause someone was doing a high power runup with the wheels chocked!

 

Rog

 

 

[Guest TOSGcentral]

Methinks that Ian is having a bit of a game?

 

However, it does offer the opportunity to look at a favoutite hobby horse of mine - which is 'feeling' the C of G by lifting the tail of a static aircraft.

 

So often in the past have I heard people say - "that aircraft is unsafe! The C of G is so far aft! Just lift the tail and see how heavy the tail is!

 

The critical issue is that when in flight the aircraft is balanced around its centre of pressure on the wing! This is a point that is able to move forward and aft due to the angle of attack of the wing when the aircraft is at, or above flying speed.

 

The amount the C of P is able to move forward and aft is determined by the aircraft design and the aircraft's actual weighed C of G position in the flying attitude.

 

This has nothing to do with how heavy the tail feels when you lift it - or in Ian's example - can nose over by itself! That (normally) is a product of where the C of G position is when the aircraft is static.

 

A heavy tail simply means that the mainwheels are a long way forward - eg on a Thruster taildragger or, alternatively, on an aft engine mounted tricycle 95.10 that sits on its tail when you get out beause your personal weight is required in the cockpit to keep the aircraft on its nosewheel when it is on the ground.

 

Academic point? Not really. For example the Vampire's design was critically impaired by mounting the main wheels too far aft so that it sits at a level (and more marketable attitude) when at rest.

 

That is a bit of a problem test flying one because the damn things can stay on the ground (demonstrated) to in excess of 70 knots and you have to 'snatch' the stick to get them into a positive angle of attack where they will fly! Once in the air they behave normally if within the correct C of G range.

 

Aye

 

Tony

 

 

[Guest Decca]

Ian is it possible that you’re maneuvering the Starlet by holding the tail wheel up a little high, with no pilot in the cockpit, & the main wheels have gone far enough under the wings (cg) to create a tipping moment?

 

I know you say the cg is correct & of course without the normal pilot’s weight behind the maingear then the cg would be changed. Just a thought.

 

Regards, Decca.

 

 

[Yenn]

Dead right Decca. I chocked the mains and lifted the tail, holding it from going too far with a ope to the mower. Then I could easily wash the underside. Of course with a pilot in it would have to tip a long way further to get the Cof G forward of the mains.

 

Of course Tony you are also right I was having a bit of a game, tipping a tail dragger forward with the pilot in place would show you roughly where the Cof G is.

 

 

[Guest Decca]

Yaaayyy! Must admit post *1 had me for a while but had to have a punt on the cg shifting forward without the pilot. Thanks Ian - any more curly questions that don't involve conveyors?

 

Regards, Decca.