Crescendo Build

[Tyger]

Once they realize there is no tariff due (per your declaration), and that they do not need to collect any more money from you, they will probably send it on forthwith.

 

[Brian Jackson]

Once they realize there is no tariff due (per your declaration), and that they do not need to collect any more money from you, they will probably send it on forthwith.

No such luck. Received email and text that I owe $240 for import duty. I could attempt to contest it but I'm told the package will be returned in 5 days if unpaid. Do I chance it or just pay up and get the thing here? At this point I'm probably just going to pay it to avoid delay. Got a plane to build.

 

[Sv.grainne]

No such luck. Received email and text that I owe $240 for import duty. I could attempt to contest it but I'm told the package will be returned in 5 days if unpaid. Do I chance it or just pay up and get the thing here? At this point I'm probably just going to pay it to avoid delay. Got a plane to build.

You could contest it but with the clock running....

 

[Brian Jackson]

Paid in full. That pushes the total rotorhead cost to nearly 3K, but at least it's coming without further delay. My hope is that Customs didn't rummage through the box after I spent time communicating with GyroTech Poland to handle and pack it in a way it will arrive absolutely scratch free. Plus I didn't want to chance them discovering the drugs and guns.

 

[Doug Riley]

I hear echoes of Warren Zevon here...

 

[Brian Jackson]

I hear echoes of Warren Zevon here...

Well you are a lawyer, Doug. Well played

 

[Brian Jackson]

It arrived.









This is one extremely impressive piece of hardware. Machining and finish are perfect. Hard to believe I'm actually holding a rotorhead of my own. Proud father?

 

[Sv.grainne]

Thing of beauty!

 

[Sv.grainne]

Do you have the time and patience to go back now and try to find out why you were charged duty on exempt materiel?

 

[Resasi]

Sturdy looking bit of kit, what does it weigh Brian?

 

[Brian Jackson]

Do you have the time and patience to go back now and try to find out why you were charged duty on exempt materiel?

If purchasing overseas again I will be better studied going in, making it clear these are exempt items. As for this purchase it's just a life lesson in things to check.

 

[Brian Jackson]

Sturdy looking bit of kit, what does it weigh Brian?

The doctor weighed it when it was delivered but I'll have to check. We were just happy it had all its fingers and toes. Surprisingly however it already has 108 fully developed teeth.

 

[Jazzenjohn]

That's nice! Is it a single or double bearing model? It looks like it could be a 2 place head.

 

[Brian Jackson]

That's nice! Is it a single or double bearing model? It looks like it could be a 2 place head.

Hi John.

It has one double-row bearing listed as '3206 A-2RS1TN9/MT333'. The teeter block is four-bearing + bushing which is replacing the existing bushed-only type teeter block that came with the blades and hub bar. This head is used on two-place ships and beefier than what I've seen used on most 'Bee designs. I have worked with the factory to make sure the blades and the head are suited for the mission and AUW.

If the mission from the start had been 'fast and powerful' I may have chosen different blades. I kinda went the opposite direction, wanting the ship to be a platform for learning rotor management. (Yes, physics nerd). Gyro-Tech Poland made a set of now-discontinued high-lift carbon blades I was able to purchase. Their Vne = 70 MPH, so she's not going to be a speed demon. The ship will be intentionally heavier than UL to keep blade loading in the range needed.

Next up: finish machining the vertical strut mast attachments. Have progress photos to share when they are complete and installed. Starting to feel pretty good about this project. Just didn't realize it'd be years in the making.

 

[Doug Riley]

It IS pretty, Brian.

As a self-confessed physics nerd, I'm sure you're aware of the geometry of offset gimbal heads. The rotor disk blows back during forward flight at an angle of 2-3-4 degrees aft of perpendicular to the spindle axis. The rotor thrust line, being itself square to the plane of the rotor disk, then leans forward of the spindle. We therefore locate the head's fore-aft pivot ahead of the spindle.

Nominally, that pitch pivot ought to be placed at the intersection of the rotor's thrustline and the torque bar. It turns out, though, that if you place the pitch pivot even farther forward than that, and balance the resulting nose-down bias with a trim spring on the back end of the torque bar, you create a helpful, variable soft link between the rotor and the airframe.

Why this review of old hat? A very tall rotor head may require more pitch-pivot offset than the standard 1" to preserve the excess-offset-plus-spring setup. If this head is offset more than 1", that's probably good.

Wonder why the blades are limited to a very modest 70 mph airspeed? Gyro rotors generally get happier at higher airspeeds up to 100 mph o more, as long as the teeter hinge can accommodate the increased teetering action.

 

[Brian Jackson]

It IS pretty, Brian.

As a self-confessed physics nerd, I'm sure you're aware of the geometry of offset gimbal heads. The rotor disk blows back during forward flight at an angle of 2-3-4 degrees aft of perpendicular to the spindle axis. The rotor thrust line, being itself square to the plane of the rotor disk, then leans forward of the spindle. We therefore locate the head's fore-aft pivot ahead of the spindle.

Nominally, that pitch pivot ought to be placed at the intersection of the rotor's thrustline and the torque bar. It turns out, though, that if you place the pitch pivot even farther forward than that, and balance the resulting nose-down bias with a trim spring on the back end of the torque bar, you create a helpful, variable soft link between the rotor and the airframe.

Why this review of old hat? A very tall rotor head may require more pitch-pivot offset than the standard 1" to preserve the excess-offset-plus-spring setup. If this head is offset more than 1", that's probably good.

Wonder why the blades are limited to a very modest 70 mph airspeed? Gyro rotors generally get happier at higher airspeeds up to 100 mph o more, as long as the teeter hinge can accommodate the increased teetering action.

Hi Doug.

One man's review of 'old hat' is another's revelation. Though I'm somewhat familiar with this concept, its execution is new to me. Thank you for this clear explanation. I will measure the offset distance tonight. Regarding being a physics nerd I'm an eagerly interested student rather than a know-it-all.

On the blades, going back through my email comms with the factory, here is their description:

The modified blades are no longer produced in our factory because they had a maximum speed limit of ca. 110 -120 kmph. Above this speed, the lift force is was big that the gyro still wanted to climb.

The blades are a good choice for small constructions that do not fly very fast. However, since nowadays the customers want to fly fast, we decided not to produce the modified blades any more. The original blades work as well on small constructions and there is no speed limit on them.

 

[Doug Riley]

In-n-teresting.

Of course, the lift force that a given rotor produces depends on two things: disk angle of attack and the aircraft's airspeed. If your rotor produces "too much lift" at a given airspeed, you move the stick forward until it makes just enough lift for level cruise (assuming that's what you want). If you "run out" of forward stick travel at only 70 with an offset gimbal head, something unusual is going on. The blade airfoil section might have extra reflex that twists more pitch into the advancing blade as it goes faster (keeping in mind it that, as the gyro speeds up, the advancing blade experiences higher and higher airspeeds, while the retreating blade experiences lower and lower airspeeds). This "extra blowback" effect is certainly better than the opposite, which would tend to induce airspeed runaway.

When you examine your rotor head, you might simulate a rotor thrustline coming down from the center of the teeter bolt, angled forward at its lower end by, say, 3 degrees compared to the vertical axis of the head. See if this line passes ahead of, or behind, the pitch pivot. Ideally, it'll land aft of the pivot. If it lands forward of the pivot, then that, too, could produce the behavior that the manufacturer reports.

I'm attaching a scan of an old article by Chuck Beaty that illustrates the operation of the Bensen-style gimbal head with trim spring and excess offset. Hope the Forum program doesn't choke on the file size.

 

[Brian Jackson]

Saved the files and will pore over them this weekend. I am also surveying/3D modeling the head and doing an accurate profile plot of the blade section. Will have some real-world numbers to share and analyze soon. The head needed to be precisely modeled anyway to work out the geometry of the overhead stick and its linkage.

I seem to be saying 'thank you Doug' a lot lately. There's still much to learn about such deceptively simple looking contraptions, and the expert advice is sure appreciated. I'm also very thankful Todd let the Forum stay up. Can't imagine someone trying to do this on their own.

 

[Resasi]

The contributions of the knowledgeable Forum members has always been a hugely important aspect.

 

[wolfy]

Hi John.

It has one double-row bearing listed as '3206 A-2RS1TN9/MT333'. The teeter block is four-bearing + bushing which is replacing the existing bushed-only type teeter block that came with the blades and hub bar. This head is used on two-place ships and beefier than what I've seen used on most 'Bee designs. I have worked with the factory to make sure the blades and the head are suited for the mission and AUW.

If the mission from the start had been 'fast and powerful' I may have chosen different blades. I kinda went the opposite direction, wanting the ship to be a platform for learning rotor management. (Yes, physics nerd). Gyro-Tech Poland made a set of now-discontinued high-lift carbon blades I was able to purchase. Their Vne = 70 MPH, so she's not going to be a speed demon. The ship will be intentionally heavier than UL to keep blade loading in the range needed.

Next up: finish machining the vertical strut mast attachments. Have progress photos to share when they are complete and installed. Starting to feel pretty good about this project. Just didn't realize it'd be years in the making.

I may have missed it Brian if already posted, but what blade loading are you aiming for?

wolfy