Sparrowhawk or RAF w/Sparrowhawk/AAI mod. hang angle??

Eric S

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Is there someone who remembers or could look up what the angle of the keel should be either in cruise flight (level?) or preferably in a hang test for a Sparrowhawk or a RAF w/Sparrowhawk/AAI mod.? I assume they were designed to be the same or nearly so?

I purchased a used RAF w/Sparrowhawk/AAI mod, but it only came with the Stock RAF build manual and no documentation regarding the Sparrowhawk modifications.

Thanks in advance for any guidance.

Eric
 

Kolibri

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Hey, Eric S., be sure to completely scour all the old threads about the Sparrowhawk.
It's got its own unique pieces and issues, and your question was probably covered in some old post.
You and dunc are recent buyers of them, so perhaps you two can share info?

I've never owned one, my RAF being pretty much a stock carbed EJ2.2.
I like the nearly center thrust line of the Sparrowhawk, and see it as a safer gyro than an RAF with H-stab.

Glad you're getting the Sport Copter rotor system for yours. It really adds to the performance and safety.

Regards, Kolibri
 

eddie

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The best way to balance it would be to level the keel,then take a digital level tape it to the inside of the door where you can see it,make sure its reading

the same as the keel then go fly what you want is the keel to fly level if its not then adjust the mast accordingly. I would think that the mods done

will make the RAF hang test invalid. Also kolibri's comment about the center line thrust is incorrect,its been proven that the thrust line does not make

the gyro unsafe,its the lack of an H-stab that's the problem,the centerline thrust probably would help with nose up nose down when applying throttle or decreasing throttle.

I fly a RAF with 230 HP and never got in trouble with the high HP,in fact its helped me stay out of trouble.
 

Eric S

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"be sure to completely scour all the old threads about the Sparrowhawk"

Funny you should say that. I read everything I could find before and after buying this gyro. My girlfriend once remarked "I think you're obsessed."

I've spent many hours on here and learned a lot, but have found no references to hang testing Sparrowhawks or RAFs with the Sparrowhawk mod.

Eric
 

dunc

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Eric S,

My used RAF/SH came with just the SH assembly manual, no RAF. I will show you mine, if .... PM me.

When I ordered my SC rotor system, I measured the difference between the lower and upper masts with a digital protractor - about 9.5 degrees- and they used that to build the SC mast. This assumes the previous mast setting was correct. I like Eddie's method very much, but it requires a flying gyro! If I need to adjust my new mast, will address it later.

I also plan to turbo my Subie with Eddie's guidance, but after some initial test flight with SC rotor. I am currently upgrading the aged/cheapo fuel pumps and filters in preparation to the final turbo effort. The "Open Deck" engine design requires more fuel pressure when boosted. The turbo will also add a few pounds, so final mast adjustment needs to wait until then.
 

Eric S

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dunc, I will PM you and we can trade emails and share manuals.

When I bought mine I knew I wanted to upgrade to Sport Copter equipment since I also have a single-place Vortex and know the quality, plus I had read about the problems with the old RAF blades and hub bars. I worked out a deal to train with the old RAF blades, but not purchase them with my machine. We used 2 different sets of RAF blades during training - 1 old set and 1 new. They needed drastically different amounts of trim and also flew at very different cruise airspeeds (65 mph on the old blades and 80 mph on the new blades). The difference must have had to do with the pitch of the blades, but unfortunately I didn't check while I was there and I didn't think to check the difference in blade speeds on the rotor tach. while flying.

BTW: I'm not a big fan of the RAF rotor tach. Mine doesn't usually register under 80-100 RPM and also bounces around unreliably when under 130-140 RPM, so that's something I'll need to work on.

Like you, Sport Copter wanted to know the angle between my lower mast (frame) and upper mast (cheek plates?). We tried hanging it from the rotor and then changed the mast angle back and forth during training to try and find the sweet spot where the gyro flew level at cruise and the stick had plenty of travel. All this while changing out rotor blades and trim springs.

I'll start over from scratch with another hang test once I get my Sport Copter equipment installed and ready to test fly.

Eric
 

Kolibri

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I like the nearly center thrust line of the Sparrowhawk (which has an H-stab), and see it as a safer gyro than an RAF with H-stab.
Also kolibri's comment about the center line thrust is incorrect,its been proven that the thrust line does not make
the gyro unsafe,its the lack of an H-stab that's the problem,the centerline thrust probably would help with nose up nose down when applying throttle or decreasing throttle.
I'll stick with my statement. The less the thrust line offset, the less an H-stab has to compensate for.
The stock RAF has a lot of offset (8-10"), and there's only so much even the Boyer H-stab can mitigate.
It does not absolutely eliminate risk of a PPO, especially at lower AS where the H-stab is less effective.

Actually, I recall you agreeing with this, at:


In a RAF you could probably get about halfway through a forward loop if you have little forward speed, and go to

full throttle and forward stick at the same time,I really don't think the stab would even begin to stop it

It would be an unrecoverable event.! With the HP I have application of throttle is done very carefully

at slow airspeeds.


Regards, Kolibri
 
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Doug Riley

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It is, in fact, very difficult to compensate completely for a HTL of 10", 12" or more using only an H-stab. By "compensate completely" I mean eliminate unstable responses to throttle changes at any airspeed. And by "unstable responses" I mean a reaction in which the aircraft speeds up, rather than climbing, when power is increased.

In a gyro with a 500-lb. thrust powerplant, a 10" HTL, and an effective H-stab lever arm of 5 feet, the H-stab must make 83 lb. of download at wide-open throttle. At slow airspeeds, this REQUIRES that the H-stab be deeply immersed in the propwash (because the aircraft's airspeed won't be enough to power the H-stab to make that kind of download). Anything less than complete compensation leaves potential "coffin corners" in the aircraft's flight envelope.

And that doesn't even address the issues of engine torque and cabin-pod aerodynamics, which also can crash you if not dealt with in the design.

IMHO, an aircraft intended for casual, recreational use should not have coffin corners that are accessible simply by changing the throttle setting. Obviously, others disagree.
 

C. Beaty

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Vittorio Magni, the well known Italian gyroplane stylist and originator of the Eurotub style, explained, while addressing a tour group from the UK that thrustline/CG relationship was irrelevant. “For example, forward propulsion of a helicopter is applied to the top of the mast and it doesn’t tumble over.”

Mr. Magni was reportedly a crackerjack helicopter mechanic before becoming a gyro stylist.
 

Eric S

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Installed and flight tested:

After installing the new mast, rotor head, and rotor blades, I did a hang test and it was the same as when the RAF equipment was installed. I have not installed the new trim system, so I'm currently still using the RAF trim springs/chains connected to the control rods.

I ran up and down the runway - balancing on the mains, then crow hops, then S-turns. After getting the blades up to speed and the nose came up, it took heavy forward stick pressure to balance on the mains, so I removed most of the nose up trim when flying crow hops.

Once I started flying the pattern, I had to add back in all of the nose up trim that I had taken out, and then added more and more but never did get it to trim for cruise speed. It would fly 60-65 (my desired cruise speed) while holding a little back stick pressure. In order to find the trimmed airspeed, I let go of the stick and allowed it to go faster, but had to stop it from accelerating when it hit 90 mph to stay away from VNE.

When on approach to land, if I reduced power to idle, it took very heavy back stick pressure to keep it at 60-65 mph. Jim suggested I don't fly it until I can get the new trim system installed. It will be around 2 weeks before I'll have a chance to get that done and do more test flying.

Eric
 

Doug Riley

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The stock RAF, with its extremely high thrustline, had hang specs that intentionally made it tail-heavy. This tail-heaviness allowed the gyro to fly more or less keel level, despite the powerful thrust moment trying to flip it forward. IIR, the spec was something like 4 deg. nose-down on the keel. A CLT gyro (that doesn't need tail-heaviness to counteract a PPO moment) will want somewhere in the 10-degree nose-down range on the keel.

Converting a stock RAF to CLT, LTL and/or a down-loaded H-stab will require a large change in hang spec -- probably heading back to that ten-degree-on-the-keel neighborhood. Adding a down-loaded H-stab, of course, does the same thing as hanging a hunk of lead on the end of the tail tube, except that the down-load isn't present during a hang test.

The original low-riding, no-HS Air Commands were quite HTL, but Air Command preserved the old Bensen hang specs, which assume CLT. As a result, the original AC flew very nose-low at high airspeeds and throttle settings. The sensation for the pilot was like a kid riding in a wheelbarrow, about to be dumped forward.
 

dunc

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Congratulations, Eric! Keep us posted. I don't plan to ever use the RAF trim system, and just received my SC rotor and trim systems, still in shipping boxes. Meanwhile being dragged down by my never-ending, non-gyro life demands, and in the middle of rewiring my RAF instrument panel to add missing circuit protection and use proper sized Tefzel insulated wires. Example: I think a battery isolation relay is a "must have" when the main battery cable is routed under the plastic fuel cell. Just being me.
 

eutrophicated1

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Larrys old carbed RAF on right & Boyer warrior on leftnotice thrust line difference. Larry Boyer seemed to have a handle on the old RAF's
 

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Eric S

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RAF Sparrowhawk hang test:

It hangs nearly level and flew within .4 degree of this attitude with a 190 lb. pilot at 60-65 mph.
RAF Sparrowhawk hang test pic.jpg
 
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Doug Riley

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Of course, the hang specs I mentioned are WITH the crew weight in place (the Bensen method) . In that case, the aircraft's horizontal datum line (typically the keel) should point downhill about 10-11 degrees; less if the aircraft is significantly HTL.
 
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