Returning to the Gyro World!!

[jamessj]

After a 30 year pause, I am returning to the Gyro World. I bought a air command UL gyro kit in 1987, powered by a rotec engine. I built it over the course of about 3 weeks between college semesters, got some instruction, and then proceeded to fly it through 2 engine rebuilds. When it was time for its third engine rebuild I was in the service and didn't have time, so I parked in the barn. Due to life intervening, that is where it still sets. Now I finally have the time, space and $$ to finally get back to gyros. This time, I am going to get fully licensed and build an enclosed Gyro. Not sure of the type yet, was thinking of a Little Wing but from the time I started to think about returning till now, it appears no one makes the frames. I would like to get a kit to save some time in the build. I have a well equipped workshop and could do a plans built but that is a bit more than I want right now. For the past week, I have been going through the threads here, a lot of good information and thanks to all that take the time to post.

 

[rickeylogan]

so, are you selling your air command?

 

[shootthrees]

Where in Texas are you?

 

[jamessj]

I am just north of Dallas.

My 447 is from before they started the redundant mast on them, there is a service bulletin on the Air Command website in this regards, I am going to put a redundant mast, go through everything and do a total rebuild and repower with a 582. I am the original owner and have all the documentation from purchase till now, including the build log so I shouldn't have an issue getting it registered.

I am going to do another build, I want to do something with an enclosed cabin but have not decided on which one yet.

 

[Aerofoam]

This is me thinking out loud.., but this seems like a reasonable thread for the content.
I have a 447 (Upgraded to 503) that had the doubled mast installed, but not the CLT, or extended square tail boom.
I haven't taken a tape measure and angle gauge to it yet, but from eyeballing the side profile, it looks like
there would be a few fairly easy mods to improve the CLT and engine configuration without going full high profile.

The first very easy change would be raising the seat 3" to 4" which wouldn't take much and would significantly change the thrust line relative to center line mass.
The second modification is more involved, but since you are switching to a 582 and redundant mast at the same time, you would be dealing with
some of these things anyway.
If the engine was turned right side up, it would put significant mass above the thrust line and get rid of the upside down issues at the same time.
I didn't even check to see if the pre-rotator can be flipped......
The engine would have to move backwards at least 4" to clear the mast rake, but from purely unscientific eyeballing, it looks like the cheek plates could be reversed to move the hub back to approximately the right location. Realistically you would maybe use the originals to experiment with CG and hang testing, then just make new ones with the appropriate dimensions., of course the seat could be moved forward a little if needed
and the tail boom would need to be extended, probably to the original longer boom spec.
All of this would separate the mass balance longitudinally, which is normally not a good thing, but this is a small enough separation
that it may just serve to dampen pitch response a little.
Anyway, I have been pondering this geometry and am interested in opinions from anyone who has flown 447s and modified them.

 

[Doug Riley]

The redundant mast is nice, but the more important engine mount change on the original A.C. is getting rid of the holes in the mast at the seat back. These holes create a "tear-on-dotted-line" breakage point.

Make replacement engine-carrier attachment plates wide enough to put the bolts just OUTside the mast. These bolts will clamp the mount to the mast down low on the plates. You can install one 1/4" bolt thorough the plates and mast, or run short lengths of angle aluminum down to the landing-gear blocks. This will eliminate any possibility of the mount sliding up or down the mast.

Flipping the engine to plugs-up is good, but it's a change that begets half a dozen other changes. You have to move the engine back if you do it. That means making a new-longer 2x2 carrier tube. Moving the engine back ruins the (already very slim) rotor-prop clearance. It also puts the prop practically in line with the rudder. Will you move the rudder back by building a new tail tube? You'll need to lengthen the rudder cables, too. You must obtain a longer flex shaft for your Wunderlich prerotator.

When you raise the rotor height (as you will need to), you'll have to rework your control pushrods.

On the plus side, an upright engine likely will last longer (because of better oiling to the crank bearings) and be easier to start. Mine used to flood all the time with the plugs down. Many choice words said on those occasions while nursing palm blisters from pulling the starter.

Useful to know: my open-frame Air Command 447 had a measured HTL (height of prop thrust line above CG) of about 6." When you move a weight on an airframe, the aircraft's CG moves in the same direction, but by a fraction of the distance you moved the weight. The fraction is the same as the ratio between the weight of the object you moved and the gyro's gross weight. Example: If you move an 80-lb. engine up 6", and the gyro's gross is 550, then the CG moves in the same direction by 6 x 80/550, or 0.87 inches.

Kind of disappointing. Moving the pilot, who's heavier than the engine, is more effective, but structurally complex.

 

[Aerofoam]

Thanks for the input, this kind of discussion can avert a lot of wasted time and mistakes!

"Flipping the engine to plugs-up is good, but it's a change that begets half a dozen other changes. You have to move the engine back if you do it. "

Yes, I addressed that and moving the rotor aft to keep proper CG will restore some of the lost prop clearance. (maybe still use the same flex shaft too.)
What I didn't include, but was thinking, was that when the longer tail boom gets added, it should be dropped enough to keep
prop/rotor clearance sufficient. This drop should be minimal, maybe just stacking the boom under the current keel tube. this slight drop should keep the landing gear
changes to a minimum. maybe just longer upper tubes (hopefully with shocks).
I think it might be worth it, the material is still fairly cheap and the construction is fast and dirty by aircraft standards.

"When you raise the rotor height (as you will need to), you'll have to rework your control pushrods."

I think the rotor height change would be minimal, if any at all, but the other can of worms
I might open is a folding mast design, only I was thinking it could
fold sideways 100 degrees into the waiting cradle frame that could clip on the frame, or the trailer.
This would make solo rigging much easier as the hub
would fold over to about 4.5' AGL and be fully supported. This is about chest high and very easy to deal with.
The push tubes would have to be modified, or re-built anyway to allow quick release.

"On the plus side, an upright engine likely will last longer (because of better oiling to the crank bearings) and be easier to start. Mine used to flood all the time with the plugs down. Many choice words said on those occasions while nursing palm blisters from pulling the starter."

I am just going through mine and dealing with things the PO didn't keep up on, it does start rough and after removing the plugs, I discovered they always have some oil residue in them from being on bottom...I have experienced the choice words too....

" Moving the pilot, who's heavier than the engine, is more effective, but structurally complex."

I think I can get 3" to 4" by just making spacers between the frame tubes and seat and making a new upper mount for the mast.
You are right, this is the most effective way to make an improvement to CLT ratio, the engine position mods are a lot more work,
but if a lot of those airframe sections are being replaced for other reasons anyway, the mods are not a lot of additional work and could be worth it.

 

[jamessj]

Air command offers an upgrade kit to convert the older models to the Elite center-line thrust configuration, I am going to use that, the mast upgrade and send my rotor head back to them for inspection and rebuild then add new rotor blades. Things have really progressed compared to when I first started, I have been reading everything I can on it.

 

[Aerofoam]

How much is that kit?

 

[jamessj]

.Depending on how old your machine is, it could vary some, its going to cost me about $2k because I need the horizontal stabilizer and the extended boom, it will raise the seat 14 inches as well.

 

[Aerofoam]

Wow, that is a lot of seat height.
I already have the stabilizer and redundant mast, but still have the short tail boom.
I have a rough plan for a semi drop keel and converting the landing gear to a suspension type.
Only about a 4" height gain...