March 1999
Just wanted to leak my brains on you for as long as I can and try to let you know how things are going and some of the things that are on my mind. I have a news letter partially completed, but completing that is much more difficult and time consuming than throwing some random thoughts at you this way. Some of this may be repeated in the letter later.
I am planning to leave for Spruce Creek (Daytona Beach area) within a week to take the plane to have it painted prior to S&F. It will be there for about 3 weeks prior to S&F for the paint job. We have designed the scheme and it is really going to be classy. Blues, turquoises, etc.
The plane is flying better every day as I continue to tweak things. I put 3 hours on it today. I was taking off on the water when I heard a sharp report like the plane had been shot or something! A small vibration set in that I didn't like so I went back to the airport to check it out. Found a nasty nick in one blade of the prop and on further inspection discovered that a 3/8" AN flat washer had apparently come out of the engine compartment thru the bottom augmentation slot and the prop had projected it thru the right side of the scupper! The washer was "stuck" half way out of the side of the scupper and the entry hole in the top of the scupper was quite evident. On inspection, I found nothing loose or missing on the engine or in the engine compartment so the washer must have been one that found a real good place to hide until that flight? I always inspect for that sort of thing very thoroughly before I button things up, but this comes under the heading of "Never say Never". As you are building your plane, just prepare yourself for the fact that there are going to be things that you discover you screwed up on once you start flying. I don't believe that you would ever find a home builder that has completed and flown a plane that would disagree with that prediction. The more complex the aircraft, the more surprises. If you KNOW you are going to make SOME mistakes, then you will try harder not to make any. Then you will make some anyway. That's not to say that the mistakes will necessarily be catastrophic. Most of the time they will be easily corrected and just be aggravations. Leaving a washer in the engine compartment was not a catastrophic oversight. But because I really am super careful, it was a washer and not a 1/2" wrench!! If you complete your plane and you have any tools missing, don't fly.
The flying has really begun to be enjoyable. I have over 20 hours on the plane now and this is the third one for me. I can tell you that if you are not tensed up for the first few flights of a new plane, then you have no test pilot experience. Don't get me wrong, it is one of the biggest thrills I can imagine. But I have a great respect for the unexpected and until all the "washers" have shaken out and you get a good feel for the plane and you've got the pitch of your prop set just right and you've begun to be comfortable with "the numbers" (landings, etc.), it is hard to really relax and enjoy the experience. I am beginning to reach that point and it really feels good.
There is a speed at which the Glass Goose gets "on step" in the air. On my current plane moderately loaded, that is at about 100 kts.. During the early flights, I had too much pitch in the prop and wasn't developing the HP to go faster. On top of that, the over pitched prop was causing a minor vibration that I was not entirely comfortable with, but I blamed it on the vortex generators not being tweaked properly and because of my previous experiences, I just knew that as I continued to fly the plane that I would become more aware and sensitive and that things would just naturally work out if I just kept my antennae up. After all, it has been several years since I've flown these things and I am having to give myself my own refresher course. Anyway, since I wasn't developing the proper RPM from the engine, I started flattening out the prop. One degree at a time. With each degree things improved. The prop pitch and the RPM's and the speed are now coming into focus. It has become clear (as my memory should have told me) that the plane likes speeds over 100 kts. At 100 kts., the plane gets "up on step". It levels out and gains speed easily with a small increase in throttle. Also, a lot of small vibrations dissipate and things just "smooth out". I am still not satisfied with the pitch of the prop and tomorrow I am going to take out another degree. I will do this until I am getting 2500 rpm minimum on takeoff. Believe it or not, I flew the first 10 or so hours without seeing more than 2200 rpm. I really think I was in a condition that I have told others to avoid. I was apprehensive of speed. Yes, with all my hours, I was still concerned about letting the plane go faster. Having experienced flutter, I guess I just naturally worked up to higher speeds slowly. And that's not all bad as any professional test pilot will tell you. But, I think I was slower to progress than I should have been. I can now say that no more than an hour or two should be invested under 100 kts, if that. The flutter problem is a thing of the past and the plane is just much easier and more comfortable to fly at the higher speeds. By the time any of you fly, I will have determined a good dependable prop pitch to start out with, and you may see speeds of over 100 kts on your first flight.
You may think that determining the pitch on the prop on a plane is a simple matter of chocking the plane and running the engine up? If the revs won't go high enough, then you kill the engine and flatten out the prop until you get the proper revs, right? Sorry, not on a Goose. The pusher configuration causes the prop to start cavitating at much over 1500 rpm if the plane is not moving. This can seriously damage the prop. So, it becomes a matter for some experimentation.
On the initial taxi tests, it's not hard to accomplish a lot of the same thing you would if you could do a static test. You give the plane 1500 or so to get it moving and then as the plane increases speed, you quickly advance the throttle. If you don't feel really powerful acceleration, and don't see at least 22 or 2300 rpm then you chop the throttle and go flatten out the prop some. You also have to beware of the condition in which you would have the prop TOO flat initially. This condition can give you an indication of plenty of take off power, but can result in low potential airspeed and struggling flight onceairborne. It can be alarming for an inexperienced test pilot to see his tach going to 3000 rpm and his airspeed barely above takeoff speed once airborne. A runaway engine and a struggling aircraft are no fun. Like I said, I am rapidly reaching the point of having an initial prop pitchthat anyone with 160 - 170 HP will find very comfortable as an initial setting.
These reflections are not intended to be self flagellation, but are passed along in hopes that you all may profit from them. It is my sincere intention that the experiences I pass along and the problems we have solved will make your initial flights trouble free. I wish it were possible for me to portray to you the vast difference between the nightmare I waded through with my original Seahawk, and the relatively problem free test period for N96GG during the last month or so. I had a frustrating problem with the idle on the engine which necessitated removing and reinstalling the engine and turned out to be so simple as a loose compression nut on a primer line. I had to work out the prop pitch, and I had a washer come out and nick the prop. Other than that, no real complications.
There are still some things that I want to change or improve, but that will be going on forever. One thing I have discovered with this plane is that more care and concern is going to have to be taken concerning the wiring and the routing of the wiring to the instrument panel. I am finding that "induction" is a real problem. That is the condition in which a wire running parallel to another "induces" a current through the influence of it's "field". All wires carrying a current have a field surrounding them and parallel wires literally pick up power from the active wire. As an example of a problem I am experiencing, when I key the mike on my COM radio, the engine instruments fly all over the place. Also, my fuel level system isn't even close to accurate. My fuel flow indicator system works fine so I have a backup, but after S&F I will probably do some serious rewiring and shielding. There is also the possibility that twisting some of the wires will eliminate some of the problems. If any of you have any other suggestions, I will certainly appreciate them.
We have the problem that there are only 2 possible routes to the instrument panel. One along each side of the canopy. If you devote one side to the antennae coax, then everything else has to go along the other side. We also have some fairly high current carrying wires in that group. So how do you keep the very low current wiring such as EGT and CHT wiring from being influenced by the larger wires? I'm not in favor of relays to solve this problem. They are just a source of something to go wrong. There has got to be a better solution. I'm sure this is going to require some experimentation and I wish I could do it like NASA would with a multi-million dollar lab and teams of engineers that would work for a year and come up with a solution that would cost about $30,000 per copy. But we will probably do it the hard way and in a few months have a good solution that probably only requires a few bucks or a few cents or maybe even nothing but time or a change in approach to solve? Don't get me wrong, I have a lot of respect for those guys with the big bucks. I just can't afford to do it that way, so I, or we, will do it anyway.
Along with working out the
small things during these initial flights, I have journeyed to another
lake within my test area and over to numerous other airports to visit friends
and show them the plane. If the weather will allow, I am going to fly the
plane down to my lake house tomorrow to complete the hours required before
the plane is signed off and released from it's restrictions. I've been
on the water numerous times and the plane is the same "jackrabbit" off
the water that I remember (really BETTER than I remember).
It's a BLAST!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Blue Skies & Tail Winds
Tom
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