Cg

[zies8]

If one were to make modifications to a homebuilt aircraft like so many have my question becomes this. How is the CG envelope determined on a "new plane". Is it necessary to become a test pilot and experiment with the planes forwad envelope and rear envelope until you push the envelope so far that problems arise?

The answer to this question would be very important if one were making modifications like nose extensions, altenative engines etc. etc.

[Waiter]

You will need to study up on aircraft Center of gravity, weight and balance, and how this is calculated. This is basic Pilot stuff. If you have an Operating handbook for the LongEZ, its very well documented in there. If you don't have a copy, send me an e-mail. You must have a complete understanding of this concept n order to understand the importance of the numbers and their relationship to each other.

 

If you don't change the mounting position (FS#) or size of the canard, AND, you don't change the mounting position (FS#) of the CenterSpar and wings, then the published CG numbers should remain the same. The CG envelope is the Center of Gravity that the canard and wing (and their relationship to each other) are designed to operate at. When your finished, you want the aircrafts actual W&B to fall within the LongEZs CG envelope.

 

Generally, most of the modifications you see have little or no effect on published CG. A W&B within the CG envelope can be accomplished with careful planning and building, even if you make many of these modification. For instance, Most LongEZs will tend to be aft CG and will require some ballast (MAYBE). If you know this from the start, you can easily build so that your plane won't be aft CG and won't need any ballast. I have a 45 lb MT prop on a 6 inch extension. I still don't need ballast to stay in the envelope.

 

 

IM DOING THE INSTRUMENT PANEL FS FROM MEMORY, IT IS WRONG, WHEN I GET THE CORRECT NUMBER I WILL EDIT THIS POST

 

FS or Fuselage station is the location in inches from a certain point on the plane. In the case of the LongEZ The reference (datum) is the instrument panel. The Instrument panel located at FS40. This is the reference datum. All measurements for the canard, wing, landing gear, canopy, firewall, etc etc etc are measured reference to this number. On an idea LongEZ, the nose would be FS-0, But keep in mind, the nose changes from plane to plane, so Rutan decided to call the Instrument panel the Datum. (Most Certified aircraft make the very first bulkhead the reference datum, i.e. the pressure bulkhead behind the radome (big jets), or the firewall (Spam cans). If you go in front of the instrument panel, the number subtracts from the datum, IN FACT, if you measured my airplane, the nose of the plane is located at FS-Negative-14, i.e its located 54 inches in front of the instrument panel.

 

IMPORTANT: If for some reason you move the instrument panel, make sure you correct for this when you do you weight and balance measurements.

 

The Bottom line, IMHO:

 

Unless your an Aeronautical engineer and know how to calculate this kind of stuff, The Canard and Wing must be located exactly as per plans. This is one set of parameters that must not be messed with.

 

When your finished, you will perform a flow blown Weight and Balance. The aircraft will be accurately weighed and measured. You'll then determine / adjust your W&B so it falls within the "First Flight" box of the CG envelope.

 

Waiter

[Waiter]

The instrument panel is at Fuselage Station 40. This is correct. All FS measurements use this as the reference. (LongEZ)

 

Waiter

[zies8]

Thank you for sharing your knowledge.

 

 

Mike