By design the GOAT is meant to be taken apart quickly and efficiently. It is meant to be reduced to two wings, the horizontal stabilator, the basket and the tail section. The reason for this is that as a glider it can't get far with out being taken to a launch point in the first place.
By design our "SUPER GOAT" tail section can't be easily separated from the main basket. The tubes are riveted and the control cables can't be taken apart, Because of this up to this point we have been limited to towing our GOAT (The Pelican) on our local runway for a a few minutes of flight.
To resolve this issue, we decided to build a trailer that would allow to take it to farther places where to launch. To build this trailer we had to take a few things in consideration.
1. It hast to be sturdy!
Main roads here in Peru are asphalted like anywhere else.. get to far from a main path and you will find harder roads from flat gravel to totally unimproved trails that only a 4X4 can go through. Taking this in consideration, our trailer needs to hold the glider tight but softly to protect it from the bumps and shakes of the road.
2. It has to be light.
The terrain here in Peru is quite abrupt. There are very tall mountains (up to 18'000 feet!) within 20 miles.. I've driven up the mountains many times, you can be sure that if your vehicle is not in good shape it will overheat.. add to this the weight of a trailer and do the math.
3. It has to be easy to use.
Nothing worse than adding time and complexity to the Pelican assembly process. We want the trailer to receive the glider with a minimum of work, while guaranteeing that it will protect the plane.
After last weeks tows, we noticed that the tow hook being at the nose of the glider, quickly overpowered the elevator action, bringing down the nose, and stopping the climb. The result of this, was a mild climb angle until the glider got close to 70 meters (With a 200 meter rope) where the climb rate tapered off to nothing.
To improve on this, we decided to take the idea from larger gliders and change the tow hook anchor point closer to the C.G. of the plane. Since I learned (way too long ago..) to fly gliders on the venerable Schweizer_SGS_2-33, my thought was to place the tow hook, somewhere close to the mid point between the nose and the wheel (The wheel being at the C.G.)
To place the hook, Juan drilled tow holes on behind the skid and then used a larger diameter tube slit in half to use as reinforcements at both sides of the the bottom tube.
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With this new setting we still use the paraglider release line, but now connected closer to the C.G. and with the added security of an auto release feature. (If the glider ever moves ahead of the rope, the line releases automatically)
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With all the changes now in place, we moved the glider to the runway an connected to 200 meters of rope. The wind was about 10 KPH , so we told the car driver to tow 10 KPH slower (40 KPH) and to be extra "steady" on the run as I expected the glider to be a bit more "nimble" since the rope would not have as much leverage to keep it straight as when towed from the nose.
First tow went perfect. The wind was aligned with the runway and the glider got in the air pretty much as when towed from the nose. The change came when I gained altitude and increase the pitch to climb faster. It was clear that the elevator had a lot more authority over he plane. Once I was 30 meters over the ground I increased the pitch even more and the plane went straight up !
I know that when towing is hard to notice the G's you are really putting on the plane, so I was watching closely the speed indicator to make sure not to exceed VNE (~ 45MPH)
Within seconds I was at 100 meters and the car downstairs still had runway to keep towing. From my limited experience on auto tow I keep reminding myself that controlling the speed is counter intuitive. if you pull the stick, the glider speeds up , to lower the speed (and climb rate) you have to push the nose down.
All in all the tow seemed to me pretty straight forward. most of the ride, I kept the stick close to the middle, pushing forward every so often when the speed tried to creep up.
I released at 120 meters, which I consider is as much as I am going to get from a 200 meter rope. (about 60% of the length of the rope)
Next flight we increased the rope, but did not gained as much altitude. I believe the wind above went down when I got above the heights of the mountains surrounding the runway. (Our runway sits on a venturi created by the mountains on each side)
I did a third tow, and again with no much difference in height .. max for the day 120 meters.
Now, a word of caution..
After my test flight with the new hook connection, (I felt everything was fine) my friends who the previous weeks have been flying the glider just fine, now had quite a bit of trouble keeping it flying straight. One deviated from side to side of the runway until he finally got control of it... The other one released almost immediately because he felt he lacked control.
We are still trying to figure out if it was that to me it "felt" fine, because of my previous glider experience (About 20 years) or if the wind changed in some way. In any case, we are moving the hook back to the nose until everyone gets more experience with the glider.
I took the log of my Flytec vario / gps / recorder and loaded it into an OpenOffice spreadsheet, where I parsed the data to get some neat numbers for the latest flight of the Pelican.
First, the original video of the flight :
Here is the climb altitude in meters, plotted vs time in seconds:
It shows a steep climb to 80 meters, and then a bit slower descent .. the reason it goes below zero, is not because we crashed and went underground, but because our runway has quite a bit of slope. it is about 20 meters lower at the end.
This one, is the climb/descent rate on m/s Vs time in seconds:
It seems to agree with a steep climb at about 4.6m/s, then a dip (need to look for that on the video) and then a slow descent at about 2m/s .
I think that the bottom dip at second 49, is because a bad GPS distance computation during the turn.. (Someone knows how to take care of that?)
This is aircraft speed, (computed from the GPS log, so it skews way off during the sharp parts of the turn)
The speed is calculated from the GPS lat/long deltas plus vertical speed component, so I am sure there is quite a bit of error there. Still, the graph shows most of the flight between 35 and 70 kph.. about what the nominal stall to VNE is listed for a goat.
And finally, the GPS Lat/Long data plotted as points on an x/y axis.
I am guessing it is a pretty ugly graph, (Looks flattened to me) because I have not yet compensated on my formulas for the fact that lat and lon degrees don't map 1:1 on an x/y graph.. ( It is more like 10:8 depending on the latitude. )
Anyway, it still illustrates the plane taking off from left to right, making a turn and back to the runway for landing.
You can clearly see the data points (1 per second) spreading out as the glider speeds up and then closing together after the landing on the top right.
Gap seals! What a difference something so simple can make.
After a brief email conversation with Mike Sandling (Designer of the goat) where he commented he was surprised to see the ineffectiveness of our alierons, (something that we also noticed but thought was part of the design..) we decide to figure out what was happening.
Mike suggested it may be the control lines.. So, we checked the tension of the control cables, and those where fine.
* BTW our GOAT is a slightly modified version of Mike's original, it was built for us as a kit by Mike Balogh of New York (Excellent workmanship, and really nice guy to work with)
The Super goat uses all steel cable controls and a more "ultralight" type of build on several other items. Mike Balogh calls it a "Super Goat".
On the super goat, the aileron control works using a two foot axle which has on one end the control stick and on the other a small arm where the control cables connect.
[picture of the arm goes here]
Then, we checked the travel of the aileron and the control stick.. and that was OK, but we noticed that the to get full travel on the aileron, you had to move the control stick full travel too.. something that is quite difficult because 3/4 travel, the stick is already hitting my legs!
I still have to check for my options here.. one would be to extend the control arm at the other end of the axle that the stick is attached to. We are still debating on that one.
The third idea was an actual mistake on our part.. On the rush to fly the little plane, we delayed the install of gap seals on the control surfaces.. Oh, what a difference that made!
Car tow at 50kmh, 600m runway, 200m rope, Max Altitude 120m
This video is *after* we installed the seals, and although I still have the problem with the control stick hitting my legs, it is clear that I am not using nearly as much rudder as I did in my previous flight.
On this flight, I am able to make a much better turns, losing less altitude and feeling in better control of the plane. I am pretty sure that if we resolve the control arm issue, the plane will be even sweeter to fly.
Last think I want to mention is, how easy it is to fly ! I mean, if there is a plane to teach someone how to fly (Very inexpensively by the way).. This is it!
Along with my flight, we got several other ultralight pilots to go for a ride (Just short take off and landings) and the consensus was clear; this is a very gentle plane. It flies almost in "slow motion" making it ideal to teach newbies how to fly.
My idea is to get a zero time pilot to do a few lessons on our slowest tandem ultralight and then switch them to the goat to further their learning.
We continue doing short flights on the Pelicano, and it performs great!
Today we car towed to 230ft agl for a full pattern with a normal downwind and a bit of an extended base to loose some altitude. Finally a small zig zag on final to get it down even more.
It flies really nice! Handling is very gentle, mostly rudder input as the ailerons don't do much.
The wind was about 3mph, the car towed at about 30mph. We used 200 meters polipropilene line tied directly to the car. We have not set up a for a car side release yet, so the drivers assistant was prepared to cut the tow line if necessary.
Initially it took a bit to get it flying, (Probably because of the no wind situation) but once in the air it went straight up. I kept the climb rate slow until I got enough altitude to recover from a rope brake, after that I pulled back and it started climbing really fast (About ~ 900fpm)
It could have kept on climbing, but we ran out of runway, so I had to release..
According to my vario logger, best rate of climb was 4.4 m/s to about 72 meters agl.
Next time, we will try with a bit of wind, and I am sure we should get 100 feet more.. (At least)
Taking very rough numbers.. I estimate the average L/D to be around 11/1
release at 70 meters/ time to touchdown 57 seconds. = -1.22 m/s. Asuming 30mph (13.3 m/s) / -1.22 m/s => L/D = 10.92 Of course, this is flying a pattern, so best L/D might be way better..
There is no bigger reward to someones dedicated hard work on a project, than seeing it take flight in the sky in a flawless flight.
Yesterday after 9 months since we started this adventure, we finally assembled the "Pelican" super goat ultralight, and took it down the runway for it's maiden flight. It was just wonderful.
Here in Peru, March is in the middle of summer season and the weather is just spectacular. Conditions where CAVOK with a sunny 26 Celcius (79F) and a light breeze from the ocean. The flying club at is best, with Gerardo at the Parrilla (BBQ Grill) cooking all sorts of good stuff for a great gathering.
The news of the first flight of the pelican had already reached most of the club regulars, so they showed up with friends and families. By noon the crowd grew to twenty something flight aficionados.
To the side Gamal and Juan where ready for the final assembly of the wings and cabling. The assembly process went slow, as we had to deal with many assorted details and obstacles typical of the last details of any project.
Assembling the wings was piece of cake, by now we done it so many times, we knew all the tricks.. We recruited a few volunteers to hold the wings, two at the root with the bolts ready and two on the tips helping to align the wing as it got connected.
The order of assembly is simple.. wings to the plane, struts to the wing and finally struts to the plane. this order and a little oil on the connecting points made our life a lot easier.
Regulating the cables for ruder and elevator, took time and patience as Gamal who is a perfectionist (Which in this kind of ventures is very good!) carefully adjusted the connectors to keep the controls perfectly centered.
Next where the ailerons, rod connectors and fixed flap adjustment. Meanwhile I worked checking the aircraft for proper weight balance. (We added a few kilos at the nose, to make it go down like the manual calls for)
A hundred other details showed up, which through out the afternoon were taken care of, (including a well deserved lunch break for Parrilla!)
By 4 pm the aircraft assembly was almost ready, our great friend Daniel ( an expert paraglider pilot with lots of experience winch towing) mounted a payout winch on to the back of his truck, preparing for our first tow.
A pay-out winch is a towing contraption that uses a regulated brake on the rope spool to "let go" of tow line whenever the tow pressure exceeds the set value. The idea is to keep the tow pressure on the glider equal at all time, regardless of wind gusts or vehicle speed.
By 5 pm everything was set. The glider was ready on the runway with the truck 50 meters ahead.
We connected the towline to our release system (Fashioned from a paraglider towing system) and ran multiple static release tests before the real flight.
With his safety helmet on, the pilot (Yours truly) sat in place, safety belts, wing runner briefed, communications headset tested.. everything checked alright.
1st flight.
Daniel set up the towing brake to about the same tow pressure as he uses for paragliders and Gerardo at the wheel took of for steady 35 MPH over the dirt road that makes our runway. Wind was almost straight at 5 MPH, the glider started moving slowly, (to slowly) and the nose digged-in against the road. I pulled the stick back as much as I could, but at this low speed the elevator had not much control to be of any help. My wing runner was still holding the wing so we just kept going (the plane never actually stopped.. just bumped a bit) , this time getting a bit more speed.. A few seconds later I felt control on the flight controls, pulled the stick a bit, and the aircraft softly raised in the air.
Once in the air, I felt I had good control of the glider. I easily controlled altitude with the elevator to keep me below 3 meters in the air, the ruder was also quite effective while the ailerons less so.
At this point I am going along chasing the tow truck which raised a hell of a dirt road dust "smoke curtain" behind it !
Seeing the cloud ahead of me, half way down the runway I pulled the tow release and quickly got wrapped by the dust cloud, effectively making my first landing IFR ! visibility was at most 20 meters, but the glider flies so slow, I had all the time in the world to land with calm. I must have glided 50 meters from the release point and rolled 30 more on the ground.
The plane flew beautiful! The flight controls where perfectly centered, once you are flying they are responsive and gentle. Landing was easy, and everything seemed to run on slow motion, as the speeds are so slow. It remind me a lot of landing a paraglider on a gentle wind.
Flight #2
We set-up the exact same way, this time adjusting the tow winch brake for higher pressure setting.. it seems that the initial low speed of the previous tow, was due to the spool releasing rope to easily, effectively keeping me to slow to fly.
Go, Go Go!. I am in the air again, this time with much better control, off the ground, 1 meter.. now 2, then 3, 4 ... I leveled the aircraft at about 5 or 6 meters (~20 feet) of the ground. The tow vehicle now kept on the down wind side so the dust did not bother me. I flew for about 300 meters before releasing and gliding about 100 meters before touching down. Roll distance took 100 meters more.. I did not used the nose skid to stop the roll.
Flight #3
Now confident that the flight characteristics of the plane are very gentle, and that the plane construction held on nice, we ventured for a bit more height. Once again we increase just a bit break pressure on the tow line. The wind also increased maybe to 10MPH right along the runway and the sun was getting low to the west.. getting close to sunset. The day was just beautiful for a true glider flight.
Plane ready. Tighten line. Go,Go Go!
This time The plane was airborne within a few meters and kept climbing steady. 10 meters, 15 meters, petty soon I have used half of the runway and I am 30 meters high. I realize at this pace I won't be able to land straight ahead, as the glide ratio will probably put me over the fence ahead, so I keep the stick tight and keep on climbing as much as I can for an eventual 180 on to the taxi way.
Now the tow vehicle has reached the end of the runway and my line goes relaxed! I release the line and start a gentle right turn, (Maybe too gentle!) that did not allowed me to go back on the taxiway but set me up for a soft landing on a field to the north of our airfield. Once again the landing felt just like a paraglider landing, almost like in slow motion.
Even it was just my third flight, I felt, I had a lot of control to set the glider exactly where I wanted. With a minimum of a tail wind, the ground roll was about 50 meters before I dug the nose and came to a fast stop. feet down, wing gently on the ground.. Awesome.
After that, a nice celebration took place at the clubhouse with over 20 people toasting for our new plane !
It has bee quite a while since my last post, as work has kept me (far) away from the Pelican project, but now I am back in Lima for a month or so, so we are moving full speed ahead on the project.
While away, had to find something else to do :)
While I was away, Gamal and Juan pretty much finished the fabric covering of the whole plane. The covering took a while (because of other planes getting on the way) but it was pretty much uneventful, except for an issue with the aileron tips.
The issue was with the tip of the aileron. Specifically, the when the aileron was covered with fabric, the tip area bent under the stress of the tightening fabric. It could be that to the fabric was heated to tight... but my guess is that there should have been one more rib on the aileron between the last one it had and the end of the aileron.
The reason I think this, is because the aileron has ribs evenly separated, except the end rib, which for some reason is placed at twice the separation than the rest. I am guessing that this left the tip vulnerable to bending by the fabric pressure. Our solution was to add another rib and an end plate before the re-fabric work. So far it seems to be holding well, except for a little rubbing with a small spot on the plywood that covers the end of the wing. (our solution for this, was to file away the plywood "tip" )
As I mentioned before, we used Stewart Systems Ekobond as our adhesive and it has worked quite well, with the added benefit that it is easy to work on and a no "nasty fumes" chemical.
After the fabric work, a hand of Dope paint was applied and soon after a second hand with aluminum so to protect the fabric from UV.
At this point, the only thing missing is the cosmetic paint cover, to make the aircraft look good.
I am expecting that tomorrow , we might be able to give it a first tow to see how it behaves.
