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Toobuilder
11-09-2013, 09:01 AM
After months of threatening to buy a Rocket on this forum, I finally made good yesterday. I've been after this particular airplane for a while, but kept getting steered away by other airplanes with better paint or fancy interiors. In the end though, it was hard to ignore the fact that the airplane has only 58 hours on it and the engine and prop are factory new. Yesterday's trip home was the first time the airplane had flown in nearly 2 years, but it worked perfectly. This weekend is going to be spent tearing it apart to ensure it holds no surprises. You will be seeing plenty of this airplane on this forum in the future- I have many mods planned.

looks like the Hiperbipe goes to Minnesota next weekend, so I figured it was a good chance to take a group picture.

http://i1294.photobucket.com/albums/b613/toobuilder1/image_zpsd056d94d.jpg

diamond
11-09-2013, 09:03 AM
Congrats and more photos please.

Mike S
11-09-2013, 09:04 AM
I like it...........or maybe I should say "them" :D

dealfair
11-09-2013, 01:46 PM
Oh Yeah Baby!!! Congrats Big Time Michael! I'd love to have that Rocket. Or the Hiperbipe too. Geez, both are beautiful. Difficult to NOT love airplanes.:D

vlittle
11-09-2013, 02:19 PM
Congratulations, Mike.
The HR-II is a wild beast, but easy to fly! Enjoy it, and keep us informed on the modifications.

Let us know what benchmarks you will be using for as-built (8500 density altitude wide-open-throttle cruise is a good one).

Just for comparison, my HR-II, with 20 hours on it is giving me 214 ktas (up from 212 thanks to some speed mods). I've run ground speed calibration runs, and there is no detectable error from the indicated TAS and zero-wind GS.

I have a few knots to gain yet, but it's fun trying something and making progress.

131RB
11-09-2013, 06:51 PM
Congratulations Michael ,
A terrific choice IMHO. I am on course to have 100hrs on mine it's first year and that's with it down for 2 months for paint. I couldn't be happier with the performance and I imagine you will enjoy yours just as much.

Ryan

Toobuilder
11-09-2013, 06:54 PM
Thanks everyone.

The airplane is still coming apart so no opportunity fly it again yet. I did find a pretty nasty issue with the roll servo going over center and locking things up with full left aileron deflection. That didn't show up on my preflight, so I'm glad I kept things conservative on the flight home and didn't try any victory rolls. If tomorrow does not hold any surprises, I should be able to put it back together and fly in the evening.

pierre smith
11-10-2013, 05:10 AM
Thanks everyone.

The airplane is still coming apart so no opportunity fly it again yet. I did find a pretty nasty issue with the roll servo going over center and locking things up with full left aileron deflection. g.

Serious stuff and could have had a horrible outcome.

Wise move indeed.

Best,

Toobuilder
11-10-2013, 07:15 AM
Yep, I shudder to think about it now. It was fine when moving the controls slow - as with the end of runway "free and correct" check, but a rapid movement against the stop created enough inertia in the servo to put it over center. And short of breaking the servo off its mounts, there would be no getting it free again. The only saving grace was the fact that gravity would help pull the arm free... But only if you apply pressure into the roll! a completely counterintuitive act that would likely be impossible to process as the airplane is rolling out of control.

Eddie P
11-19-2013, 09:11 PM
Wow, that's scary. If this was a standard setup, where did it go wrong (installation wrong, etc)? What is your plan to re design the servo interaction so this can not happen again?

Congrats on your new Rocket other than the servo! Well done on the conservative approach with the new plane.

Toobuilder
11-20-2013, 07:05 AM
The fix was as simple as lengthening the servo pushrod a few turns on each rod end. This ensured the control stick hit the stop well before the servo arm was dragged past 90 degrees. A secondary stop on the servo arm would be the ultimate safety feature, but as it stands now, the servo stops at approximately 60 degrees, so no amount of flex or slop in the system will allow it to snap over center. This autopilot will be removed and sold soon anyway.

Toobuilder
11-20-2013, 08:21 AM
Congrats and more photos please.

Sure: ;)

http://i40.tinypic.com/28krh4z.jpg

http://i41.tinypic.com/2igykaw.jpg

http://i43.tinypic.com/313n2tc.jpg

stinson pilot
11-20-2013, 10:18 AM
Michael, that is a great looking Rocket!

Too bad you can't keep the HB for those day's only two wings will cure!

Congrats...I've been an RV fan since the RV-3.

Eddie P
11-20-2013, 10:43 AM
The fix was as simple as lengthening the servo pushrod a few turns on each rod end. This ensured the control stick hit the stop well before the servo arm was dragged past 90 degrees. A secondary stop on the servo arm would be the ultimate safety feature, but as it stands now, the servo stops at approximately 60 degrees, so no amount of flex or slop in the system will allow it to snap over center. This autopilot will be removed and sold soon anyway.

Thanks for the write up, I can easily visualize what you are saying now. It is surprising what a small overlooked item in design suitability / installation can do for the "unexpected" technical ramification on related systems.

PS - awesome hangar!!

flyboy1963
11-20-2013, 10:50 AM
geeze Mike, too bad the weather is so yucky there eh?...and you have to put up with those pesky hangar mates. She's a beauty to be sure....I think I'd wear out the paint just waxing it!

hey, pop quiz guys..what kind of wings are hanging on the back of the hangar door! :confused: is this yet another project????

Toobuilder
11-20-2013, 11:16 AM
Thanks for the write up, I can easily visualize what you are saying now. It is surprising what a small overlooked item in design suitability / installation can do for the "unexpected" technical ramification on related systems.

PS - awesome hangar!!

Every autopilot manual I've seen cautions the installer against going over center. From this experience, I'm going to make sure I'm WELL outside that possibility for future installs. In this case, the system was rigged to work ok in normal circumstances, but was right on the ragged edge. A little flex, slop and inertia got the system into the critical zone.

Sometimes the "obvious" problems are pretty subtle at first.

Thanks for the word about the hangar... It's functional, but I have a LONG way to go to get it up to the standards I want.

Toobuilder
11-20-2013, 11:23 AM
..hey, pop quiz guys..what kind of wings are hanging on the back of the hangar door! :confused: is this yet another project????


One of many, unfortunately. Not seen (because I'm standing above them on my mezzanine) are another airplane, 5 classic cars and other "time vampire" stuff.

flyboy1963
11-20-2013, 12:22 PM
...I may not be schmart, but observant!

you have the reference to a PA-20 in your signature! ( duh!)

one of may favourite ol' Pipers, but I, too am victim of the time vampires!
( well put!) so nothing hanging in my garage....yet!

F1Boss
11-20-2013, 01:22 PM
Nice machine indeed. Be careful when descending from a higher cruise altitude - pull the RPM down to help control speed.

Also, you should be aware that about 30% of the HR2 fleet has been over on its nose. Might think about a case of oil in the baggage when solo, or be VERY careful with the brakes, and taxi so slow (with S turns) that everyone complains.

I moved the main axle centerline fwd 2" on the F1 when it was in development to reduce the nose-over tendency. That worked out pretty good.

Carry on!
Mark

Toobuilder
11-20-2013, 02:07 PM
Thanks Mark. I'm very considerate of the gear geometry/light tail so I hope that awareness will be enough to keep me out of trouble. The more you get on the brakes, the more the gear moves back and the lighter the tail gets.... It's a long way from the "bushplane rugged" RV-8 gear, but has not presented any issues yet. I treat the main legs like they're made of bamboo, so all my landings so far have been squeakers. I will have to work to maintain that vigilance.

floridawing
11-20-2013, 02:30 PM
Very nice rocket, congratulations! PM sent.

Bevan
11-20-2013, 04:15 PM
The fix was as simple as lengthening the servo pushrod a few turns on each rod end. This ensured the control stick hit the stop well before the servo arm was dragged past 90 degrees. A secondary stop on the servo arm would be the ultimate safety feature, but as it stands now, the servo stops at approximately 60 degrees, so no amount of flex or slop in the system will allow it to snap over center. This autopilot will be removed and sold soon anyway.

Michael, could you draw what you are describing here? I would think that the neutral position for all the arms are 90 degrees (relative to each other) and they move each direction from there maybe 45 degrees (60 degrees max) or so for a total of 90 degrees of sweep. Is this what you mean?

Bevan

Toobuilder
11-20-2013, 05:05 PM
Michael, could you draw what you are describing here? I would think that the neutral position for all the arms are 90 degrees (relative to each other) and they move each direction from there maybe 45 degrees (60 degrees max) or so for a total of 90 degrees of sweep. Is this what you mean?

Bevan

I’ll try come up with a graphic, but in the interest of time try to describe the setup better:

In my airplane, the roll servo is mounted to the left side of the main torque tube at the very front. The servo itself is found under the left side, front floorboard, in front of the wing spar and front stick, with the output arm mounted approximately the 5:00 o’clock position (neutral). The arm on the torque tube is also attached below the pivot point at the 6:00 o’clock position. The length of the attaching pushrod is approximately 14-16 inches.

As originally rigged, (viewed from the aft, looking forward) full left aileron would drag the pushrod to the right, towards the center of the aircraft. Of course, the output arm on the servo would follow and move from the 5 o’clock position towards 3:00 o’clock. As an unlikely set of circumstances, the main torque tube hit the primary stop at the same exact time that the servo arm hit 3:00 o’clock and lined up the servo pivot, rod end and pushrod all in a straight line (center). This masked the issue because when moved normally, gravity and basic geometry would not let the arm move further than a direct line, but rapid movement would generate enough inertia to allow the servo to go just past 3:00 o’clock, hit its stop, and lock over center.

Lengthening the pushrod moved the output arm on the servo back towards 6:00 o’clock in neutral which ensured the aileron torque tube hit the primary stop long before the servo could go over center. Now, the servo only hits about 4:00 o’clock at max travel, and no amount of inertia, slop or flexing will let the arm get anywhere near the 3:00 o'clock, over center condition.

Clearly, the geometry on this system is less than optimal and the servo travel to aileron movement is not going to be perfectly linear, but at least it is safe and I have full control deflection available.

Bevan
11-20-2013, 07:43 PM
Thanks Michael. I understand that completely. The 3 o-clock position was the problem. Now that it has been adjusted to the 4 o-clock position at max travel, I wonder what is the max travel in the other direction? Hopefully not beyond 8 o-clock.

I was concerned that I didn't understand your situation and risked having the same problem myself (which I now know that I don't) so thanks for the explanation. This stuff is critical for safety.

Bevan

Toobuilder
11-20-2013, 08:32 PM
Thanks Michael. I understand that completely. The 3 o-clock position was the problem. Now that it has been adjusted to the 4 o-clock position at max travel, I wonder what is the max travel in the other direction? Hopefully not beyond 8 o-clock....

Glad I got my explanation across better this time!

As for the other end of the travel, it's not even close. The system was biased off center, if that makes sense. It's closer to balance now, but not perfect.

One point to consider here is the fact that my "o'clock" references are approximations and really used for illustration. In a perfect world, the pivot point of both the servo and torque tube would be the same height and the attach points for both would be in plane, making a simple 90 degree parallelogram. In this case however, the torque tube pivot is quite a bit higher than the servo and the attach point for the pushrod is not directly under, but off to the side of the stick. This makes it more difficult to maintain the desired 90 degree (relative) angle between the pushrod and respective arms. In this case you strive for a mechanical average - not providing linear travel but at least providing equal throw either side of neutral. The original installer built in so much off center bias that it went over center one way, but wasn't even close on the other.

The bottom line is to make sure that no matter what configuration system you have or how the arms are "clocked" the points described by the servo arm pivot point and rod end attach point don't point straight down the pushrod and aim directly at the opposite attach point in either limit of travel.

Bevan
11-20-2013, 09:07 PM
Absolutely. Amazing that it was flown in the config that it was without incident.

Bevan

Toobuilder
11-21-2013, 07:08 AM
Indeed. And many times at that - to the tune of 58 hours!

I think that this illustrates the point that while a good pre flight inspection, run up and conservative ferry flight is a reasonable precaution on a "well proven" aircraft, the individual nature of E-AB aircraft still requires a detailed look at all systems ASAP. Even with the basic structure to plan, a builder may unknowingly create a safety issue with "freestyle" add on systems like this AP installation.

vlittle
11-21-2013, 08:45 AM
Indeed. And many times at that - to the tune of 58 hours!

I think that this illustrates the point that while a good pre flight inspection, run up and conservative ferry flight is a reasonable precaution on a "well proven" aircraft, the individual nature of E-AB aircraft still requires a detailed look at all systems ASAP. Even with the basic structure to plan, a builder may unknowingly create a safety issue with "freestyle" add on systems like this AP installation.

Autopilot servo installation for the Rocket is an engineering task. The geometry and throws must be determined properly.

For example:

http://www.vx-aviation.com/sprocket/photos/controls/pitch_roll/roll_servo_attach.jpg

This illustrates the 90 degree concept of the pivot axis with the push-pull tube. Once this is achieved, then servo throw can be adjusted by selecting the appropriate holes in the servo arm and control horn. Being close to 90 degrees allows symmetrical operation which should help with autopilot tuning.

The push-pull tube will also intersect the servo arm at 90 degrees.

Toobuilder
11-21-2013, 09:01 AM
Excellent illustration Vern. You can clearly see how unintuitive the actual geometry can be. My pushrod is not anywhere close to the "90 degree" point you have illustrated, but to be fair the angle described by the main pivot and attach point is not a severe on my airplane. That said, I'd say mine was "eyeballed" to less than optimal effect.