Safety/Horizontal Stabilizer

[robertstodaro]

Here are a couple of stabs I made for my machines, they'er made from scrap Boeing honeycomb floor plate with wood dowel leading and trailing edges Speed-taped on. Yes, I said taped!

Both machines flew rock solid in bumpy conditions after the installation.

They were just plane scary in bumpy air before.

Both stabs have struts underneath.

The Tee tail is 4 sq/ft in the propwash, the keel mounted stab is 6 ft in freeair and was probably too big.

They both cost less than 10 bucks to build.

 

[rfi]

Art Evans said the extended horizontal stabilizer made the ship fly like a Cessna 210---that solid in pitch. The extended keel and large stabilizer on Pat McNear's RAF 2000 makes it fly like a Cessna too.

We have been missing the boat for years in using a short coupled horizontal stabilizer. Paul Patterson's modification of his RAF 2000 will extend the horizontal stabilizer back about two feet and put it about 8 inches up in the prop wash. It should be an extremely stable ship with the seven inch drop keel modification.

 

[Aussie_Paul]

IMHO, moment arm is better than size when it come to dampening.

That is probably why the tractor felt so "solid".

Aussie Paul.

 

[Doug Riley]

No opinion needed, Paul, you're correct as a matter of scientific fact. Here's why:

1. The HS has more leverage on a longer arm. The stabilizing moment for given amount of load on the HS increases in proportion to the length of the lever.

2. The HS makes more lift to oppose oscillations. If a gyro is oscillating in pitch at one cycle per X seconds, a HS that is way out on a long tail boom is seeing a faster relative wind created by each oscillation. It's farther away from the pitch axis, so the up- or down- breeze that it "feels" as the tail falls or rises is stronger. More relative breeze, more HS lift. Lift is a function of the SQUARE of airspeed.

If you use an arm half as long and double the HS area, you can compensate completely for #1. Doubling the HS size won't make up for all of the loss of #2 (the airspeed effect), since that's a "square" function. The short-coupled, double-size HS will have only half the damping ability as the longer-coupled, smaller HS.

 

[Ga6riel]

Cody
Quality paint should give you the UV protection you need in your area
of course the colours or the lack of count too
white being the most desirable, for it is better not to let composites cook
red is second to black I think in re radiated heat

 

[John Stahl]

I believe that the farther the HS is from the center of mass the more leverage the HS has. The more leverage an HS has the more stable the aircraft is.
Since the tail boom is a lever where is the fulcrum?
Is the fulcrum stationary?
Or dose the fulcrum move to equalize the forces applied to the lever?

 

[Mike Schallmann]

The fulcrum is the CG

 

[Doug Riley]

The fulcrum is the gyro's center of mass (=same as CG). All forces applied to the frame (unless they pass right through the CM) create moments (=torques) centered on the CM.

Example: A HS creates 20 lb. of down-load. The HS's aerodynamic center is 5 feet back from the CM. The HS therefore is applying 100 ft.-lb. of tail-down torque to the frame.

 

[John Stahl]

Then how far back is to far back for a 2x2 6061 T6 tube?

 

[Dean_Dolph]

I asked this question in another thread but in a different way. I was asking what the bending and torsional strength limits of the 2 X 2 tail boom were.

However, in calculating the max load, I'm now wondering if some consideration shouldn't be given the various keel attachment points and related holes. I'm thinking this complicates the calcs somewhat.

 

[Doug Riley]

Here's back-of-the envelope version for bending. If the tube is a cantilever beam, then its bending strength is easiest to express as a moment.

The moment is about 1600 ft.-lb. For a load at the end of a cantilever beam, divide the moment by the length of the moment arm. For a Gyrobee tail tube (fully cantilevered), the arm is about 4 ft., so the yield load is about 400 lb.

But, but, but... The max load is about 2/3 as high if the bend is in a diagonal direction. The fatigue load limit for 6061-T6 depends on the number of cycles, but can get down into the 12,000-14,000 PSI range. Obviously, this reduces your limit load to 133 lb. Holes can easily cost you 40-50% of the tube's strength, on top of the fatigue problem.

On the plus side, Bensen-Brock tail tubes are shorter than the 'Bee's, and are not fully cantilevered. If you put a HS out of struts in back of the rudder like Art Evans, however, you've effectively re-introduced a cantilever of 4 ft. or so.

The original 2x2 Gyrobee tail tube, which was about a 5 ft. cantilever, would take a "set" after awhile from tail-down landings. Ralph reduced its length for this reason.

I don't have a handy formula for the onset of buckling of tube walls that happens in a twisting failure. Some of the engineering types may have one.