Rotor Head Angles for Tractor Configuration

[RockyMeLad]

I'm sure I'm just over-looking something simple, but my numbers just don't make sense.

In a standard "pusher" (like my DesertBee), the rotor head has typically 18-20 deg of pitch range. With a nominal 10 deg tilt during straight and level flight, having the center of the pitch range at-or-near this is considered "ideal", as it allows adequate pitch control range. Since the DesertBee is designed for the keel to be parallel with the flight path when straight and level, the rotor disk is level with the ground (or at least within a degree, close enough) at full forward stick during taxi operations. In addition to taxiing, a standard procedure to recover from the onset of blade flap is to "level" and unload the disk.


In a conventional gear tractor configuration, the ten degree rotor tilt is the same during flight. The head is the same (18-20 deg pitch range). BUT. . .
the frame does not set level with the ground during taxi or take-off. All of the pictures of flying examples show a tail-down angle of 7-15 deg. The nominal range of pitch control lets the disk be "level" with the frame at full forward stick, but that makes the disk a minimum of 7-15 degrees tilted during taxi and take-off.

Intuitively this fits Rudy's, "That aint right!"
So what am I missing?

[Alan_Cheatham]

Conventional gear tractor gyros should be designed to allow extra forward tilt of their rotor heads to compensate for the fuselage angle while sitting on their landing gear. Michael Guard's (chuter) tractor is designed this way, so is my tractor which sits at a ten degree angle on it's gear.

[chuter]

I use a RFD rotorhead which has extra range of movement in the pitch axis; I think it's about 28 degrees total.

[RockyMeLad]

Originally Posted by chuter

I think it's about 28 degrees total.

OK. That appears to be the "missing" information.

Which of course begs the next question. . .
Do you have to lean forward to get enough throw in the stick to level the rotor?
With my fat tummy and short arms, I only have about 12" of pitch motion in the stick without leaning forward.

[Vance]

Originally Posted by RockyMeLad

OK. That appears to be the "missing" information.

Which of course begs the next question. . .
Do you have to lean forward to get enough throw in the stick to level the rotor?
With my fat tummy and short arms, I only have about 12" of pitch motion in the stick without leaning forward.

Hello Rocky,

That can be managed with leverage if you don’t mind a little higher stick forces.

Less movement at the stick needs more force to accomplish the work.

In other words, if the stick travel works for you now you can move the head further with a little more force by changing the leverage.

Thank you, Vance

[chuter]

Do you have to lean forward to get enough throw in the stick to level the rotor?

Rocky,

I have to lean a little farther forward to get mine in the forward lock position, but it's not bad, and I never have get anywhere near that far forward while flying.

[RockyMeLad]

Vance,

Yes, I understand the trade-off there. I like the lighter feel and longer throw. I guess another way of saying it is "less sensitive". It is a preference not an absolute, but a strong preference.


Chuter,

OK, I just don't want to have to lean too far, even for taxiing. Reminds me of the WW-II cartoon by Bill Mauldin where Willie and Joe are laying in the mud with bullets flying over them. Joe says, "I can't get no lower Willie, Me buttons is in the way." Well in my case, "I can't lean forward more, me harness is in the way", and I can't get the stick back any more... me tummy is in the way.

Fortunately I'm still redrawing my sketches. Maybe less angle of the body to the ground, a slightly longer throw of the stick, and a moderate increase of the stick to rotor ratio will give me a reasonable compromise. Luckily the forces involved are responsive to Newtonian physics calculations, so I'll know what I'm going to have.

And yes, I know that loosing the belly enhancement would improve a lot of things. It's just going so slow. I figure that if I design it for a fat boy, it will work. Then when I loose weight, it will be great.

[Alan_Cheatham]

Now try getting that increased stick throw in an enclosed cockpit, sometimes the compromises in aircraft design drive me nuts. Luckily, I'm genetically blessed and don't have to worry about "belly enhancements".

[Brent_Brown]

Make it a tri-gear and none of this is an issue.

[Alan_Cheatham]

Originally Posted by Brent_Brown

Make it a tri-gear and none of this is an issue.

Unfortunately, because of the nature of the beast, tri-gear tractors have some serious limitations and are not the best configuration. Because the rotor likes to operate at a high angle of incidence (referenced to the ground) during take off and landing, the tricycle gear gyro starts having issues with rotor to tail clearance problems during these phases of flight. In other words, each degree a taildragger gyro sits on the ground is another degree the rotor can operate at while maintaining the same rotor to tail clearance distance. Watch Ron Heron's take-off and landings in his Littlewing and how quickly he is able to bring the rotor to rpm and take off, and how slowly he can land, mainly because the tail dragger configuration allows him to operate the rotor at high angles of attack.

[Brent_Brown]

that is BS

[Alan_Cheatham]

So is having to "balance on the mains".

[gyromike]

A tricycle gear tractor should be no more difficult to takeoff in than a tricycle gear pusher like a Bensen.

Jim Eich and Arliss Riggs didn't seem to have any trouble with theirs.

And "balancing on the mains" isn't required.
I routinely takeoff on the tailwheel on my Bensen. Land on it too.

[Alan_Cheatham]

Originally Posted by gyromike

And "balancing on the mains" isn't required.
I routinely takeoff on the tailwheel on my Bensen. Land on it too.

Well, that's kinda my point. If your going to takeoff and land on the tailwheel, why not just start with a taildragger to begin with.

[RockyMeLad]

Originally Posted by Brent_Brown

Make it a tri-gear and none of this is an issue.

True, Brent. The "angle of the fuse" is no longer an issue, but. . .

One of my design goals is "off piste" flying. Nordic or cross country skiing is much more fun with less work (in my estimation) than the boring up and down at groomed ski resorts, and "off airport" operations is far more realistic out here where airports are few and far between. So the added weight of a "front wheel" capable of safe non-airport operation is significant. Also the FWers all agree that it's practical to use a two wheel semi-road with a tail-dragger, but not most tri-cycle gear. The argument "sounds" logical for gyros, too.

Like Mike I have taken off with the rear wheel "not quite off" terra firma. It works, but I suspect only with "light" weight on the rear wheel. Too fine a line towards flying behind the power curve and never getting off the ground.
Landings on the other hand are mostly tail-wheel first, then settle on the mains and tail until stopped or almost so (depending on wind).