Nuebee Builder Questions

[barnstorm2]

Ok you old salts! Time to help out a first-time builder.

Symptom: 2-place side by side. Running full fuel and 2 200lb occupants flys in a slightly nose-down attitude requiring back stick pressure. Trim spring is already stretched way tight.

Of note: My HStap on my tall is NOT exactly parallel with my keel. It is sitting a few degrees up in the front!

Question One: Would it be OK to instead of making the HStab parallel instead to make it a few degrees down in the front?

Question Two: Would moving my teeter bolt position on my Dragon Wings have any effect on this or other issues switching from one person to 2 person flight?

Question Three: Does chewing gum left on the rotors loose it’s flavor overnight?

[Chuck Irby]

Tim, I will address the most important of your questions first. It depends on the gum, the weather and most importantly, how used the gum is! My opinion is that the HS should be parallel with the keel and you shouldn't have to change the teeter bolt location. Have you done a hang test?

[Doug Riley]

Yes, the chord of the HS should be parallel to the desired stance of the craft in flight if the craft is a CLT machine. If the thrust line is above the CG at all, the leading edge of the HS should be from 1-4 degrees lower than the trailing edge -- again, measured relative to the DESIRED stance of the craft in flight.

This is a simplified version. We'd need to know a lot more about your craft to refine it. In general, however, the HS should be set between a strictly level position and a leading-edge-down position of 1-4 degrees. Leading-edge UP is undesirable.

If, after all this, and assuming that you don't have a thrustline that's significantly above the CG, you will need to alter the hang position of your rotor head by changing the cheek plates. If you DO have a significantly high thrustline, fix that first... don't rely on the Band-Aids of HS adjustment or hang position tinkering.

As you get the machine's in-flight stance more level, you'll need to slack off the trim springs.

Changing the teeter bolt height won't have any effect on the in-flight stance. This adjustment is used to minimize two-per-rev vibrations.

[rehler]

To correct the nose low flying you need to change your cheek plates. Don't expect the HS to correct this.

I know this is a lot of work, but the hang test should be used to locate the rotor head (cheek plates) so it is close to correct (near 11 degrees nose down keel) with one and two occupants.

However ... I suggest you make the cheek plates so it flys level (11 degree hang test) with you alone if this is what is to be done most of the time with only an occational rider (then it will fly nose down with the second person on board). Or, if the gyro is to be used for training and flown with two occupants often, then set it for you and the expected "average" weight of students (then fly nose higher alone or lower with a heavier student).

[Doug Riley]

Ken's post assumes that the gyro does not have a significantly high thrustline. If it does, it will fly nose-down even though the cheek plates are adjusted correctly. The nose-down stance in such cases will get worse as you fly faster than normal cruise and can become quite dramatic (and dangerous).

A HS with negative incidence, located in the propwash, can compensate for small thrustline mislignments. "Small" means in this case on the order of 1"-3". A HS cannot compensate for a 6," 8" or larger misalignment on a pusher gyro. Changing the cheek plates does nothing whatsoever to compensate for thrustline mislignment of any magnitude.

[rehler]

Doug,

I think there is some confusion here. For example:

1. A gyro with properly located cheek plates (hang test) will fly level regardless of the thrust line to CG offset, with or without a HS. Only a "change in speed" (throttle) will create more or less thrust, which will then push the nose down or pull it up - as the thrust (throttle) is changed.

2. The speed of flying does not affect the "push over" effect of a high thrust line.

3. Flying speed only affects aerodynamics, such as drag or HS pitch. An unusual amount of low drag will pull the nose down more the faster you fly. An unusual amount of high drag will push the nose up more the faster you fly. A HS pitched nose up will push the nose down more the faster you fly.

[barnstorm2]

Thanks guys!!

My gyro does not have a high thrust line offset.

The stab is currently a few degrees up in front, and I hope that is the source of my problem.

The gyro was hang-tested for a single person, not 2-people with extended range tanks. I will re-hang if the HStab does not correct the problem.

Outside of new cheek plates, are there other remedies? Moving the battery from under the seats to under the engine perhaps?

Thanks again!

[barnstorm2]

Side View for reference

[Doug Riley]

Well, Ken, a gyro with any GIVEN hang angle will fly more and more nose-down as the thrustline is moved higher and higher above the VCG. This is a by-product of the need for the rotor thrustline to move farther forward of the CG. You can also achieve the tail-heaviness that is required for level flight with a high thrustline by moving the rotor head forward or moving ballast back.

Speed per se does not affect the amount of PPO moment. However, an increase in LEVEL speed above cruise requires more throttle, which certainly does add to the PPO moment (because it produces more thrust).

[Udi]

I agree with Ken that new rotor cheek plates may be required. Tim has mentioned that the problem occures with two people aboard, so apparently it's ok with one person.

Tim, in a two place machine you want the second person to sit close to the location of the machine CG with only the pilot. Suspend a plumb bob from the teeter bolt when you hang test the machine with one person on board. A perfect two place machine will have this line passing in line with the passenger center of gravity.

The best solution is to move the teeter bolt (i.e. cheekplates) forward and then rebalance the gyro so it hangs at 11 degrees with only one person, and not much more with two people.

Udi-

[rehler]

Doug,

I still think there is some confusion, at least on my part.

You said: "a gyro with any GIVEN hang angle will fly more and more nose-down as the thrustline is moved higher and higher above the VCG". This does not address the issue, as the VCG does not move up or down while flying a gyro (unless the pilot stands up or does something to change the VCG location).

But you said: "an increase in LEVEL speed above cruise requires more throttle, which certainly does add to the PPO moment (because it produces more thrust)". This is true, but the added thrust is offset by the added drag of the rotor, so the gyro's attitude remains the same doesn't it? It seems that the nose would not go down unless there is a lot of low drag or the HS is pitched noes up.

I don't believe the thrust offset would cause the gyro's nose to go down in steady speed flight.

[Doug Riley]

Ken: I must have timed out. Here's what I tried to post, more or less:

I'm speaking of unaccelerated level flight. Assume a gyro in such flight, at cruise speed. Assume also that it has a high thrustline and that the resulting PPO moment is not fully countered by a down-loaded HS or other aerodynamic device. Such a gyro must fly with the rotor thrustline ahead of the CG in order to hold the nose up against the PPO tendency.

Now assume that the gyro speeds up in level flight by adding power. At higher airspeeds, the rotor flies at a shallower angle of attack. IOW, as the gyro speeds up, the rotor becomes more nearly level. (The pilot experiences this as a need to move the stick forward when power is added to avoid climbing.) As a result of this levelling, the rotor's thrustline swings aft, closer to the CG. If the craft were to maintain its former stance in the air, the nose-up moment caused by the rotor would decrease -- at precisely the time when it needs to INCREASE (because power has been added).

Result? The nose drops, moving the CG down-and-aft relative to the rotor thrust line. This preserves the nose-up moment of the rotor, at a cost of flying quite nose-down at high speeds. The effect is very real, and can be rather scary. You feel like a kid riding in a wheelbarrow who's about to be dumped out forward.

Note that rotor drag doesn't increase as airspeed increases. It actually goes down! Check the graphs in the FAA Rotorcraft Flying Manual or the old Bensen manual. TOTAL drag goes up because of the effect of fuselage drag, but THAT drag isn't applied way up at the teeter bolt, so it doesn't necessarily cause a nose-up reaction.

[Brent_Brown]

I would get the HS parallel with my keel or 1 to 2 degrees low and hang it so that it is 9 degrees at the keel solo and 12 gross. I am going to put over 100 pounds of gas in the front of my tractor and plan to do the same. That is 12 degrees max at gross and 9 empty, so with full fuel I can climb out and empty I can still push the nose down to land.

[barnstorm2]

Anyone have a set of alum plates I can use as check plate models they want to sell?

[barnstorm2]

Also,

How significent a difference would you guess moving the battery behind the seats would make?