It is easy to add a lot of drag with a windshield on an ultralight or motorcycle. The windshield has to be real close to your body, when there's not an enclosed cockpit. The farther from the pilot, the wider it has to be, adding drag. And the tiny CorsAir engine on my plane doesn't have enough poop to add more drag to my plane. I also had to be concerned about disturbing the cooling air to the engine, and smooth flow of air to the prop. The quasi-sherical top part of my windshield really helps minimize drag and smooth the flow. It makes you feel like you're under the canopy of a sporty kit plane, like an RV.
It is surprisingly roomy behind/under my windshield. I can turn and tilt my head any way without touching the windshield with my head or headset. I can easily scratch my nose, adjust my glasses, or even don and doff my headset. The windshield pivots up out of the way for entry and exit. The front of it clips to the belt of my safety harness.
I made the top part of the windshield out of part of a motorcycle fairing ($50) from J. C. Whitney. I needed its dark tint to keep the sun out of my eyes and face. It works and flys excellent. I like it better than wearing a helmet.
I rebuilt the windshield, making it much better, with less drag, reflections, and wind in my eyes. It swings up, well out of the way, to enter or exit the cockpit. It just uses friction in the pivots to hold it up or down. It has stops that limit its travel, stopping right where it needs to be.
If anyone is interested how it's coming with the carbon wing I'm building... The carbon cloth I ordered, to fabricate the wing spar, has been back ordered for the last 2 months. I just found out there is a world wide shortage, and not to expect it until at least December. I've already completed everything else I can for the new wing. So construction is on hold, indefinitely. Fortunately, my present wing still works fine. I'm still flying about 4 days a week. I have almost 800 landings on my Mantis so far.
whats your mantis ? is that what ya call your creation ? or is that another flying contraption ya have ?
...sorry to hear about the cloth shortage Man thats realy bad ... I wonder what company bought it all up ??? hehehehe
glad I don't need any ! sheez !
Haing in there and fly safely...
and no fair getting heat stroke out there in the Texas SUN ! been hot here too !
The word on the carbon shortage, from Aircraft Spruce: Boeing got a big military contract that is using carbon cloth, as fast as the manufacturer can make it... and they have priority over everyone else. I'm not sure if there's a shortage of carbon fiber manufacturing, or weaving capacity. My impression is both. I decided I could make the spar out of Kevlar and S-glass istead of carbon. But Aircraft Spruce says that Kevlar is back ordered indefinitely (from the same weaver) too. So I decided to stick with carbon. They gave me a due date of Dec. 1st for the carbon cloth... But that could easily get pushed back again.
Fortunately, I had enough carbon cloth on hand to complete all the ribs and leading edges. I also have the uni-directional carbon for the spar caps and carbon rods for reinforcing the trailing edges.
Some years ago, I bought some carbon cloth from a discount distributor. It was like burlap, compared to the high quality cloth from Aircraft Spruce. So there's probably only one manufacturer that makes the real, aerospace quality cloth. Hopefully they're ramping up production to meet demand.
Bowing eh ? well my brother in law will be workin his tokis off then ! hehehe he worka at Bowing .
wonder if its the new Raptor jet fighter .or something else ? maybe the Aurrora ? hhehehehe that we're not supposed to know about ...
I just finished repairing my rotor blade.... I fiberglassed it as usual... that'll teach me to drop it ! ....
as Sonny sayz "BUTTERFINGERS !" HAHAHAHAHA
.... i realy should get a "chatter board " so i can do better work.... looks like someone took a hammer to a car hood on the flat surface !.... ... don't have any of the glazeing puddy ... so fooie on it ...close enough for who its for ! HAHAHHAHAHAH
... who cares what it looks like as long as it flys !... !
My CorsAir engine failed. Fortunately, I was in the pattern when I noticed it wasn't putting out full power. I disassembled it, and found the upper con-rod needle bearing had failed.
As I continued disassembling the engine, I found a fairly long list of other things that were worn... mostly from the failed bearing. The wrist pin and con-rod were both worn where that bearing runs. The con-rod's wear was microscopic, but I wouldn't feel comfortable using it in an aircraft engine... especially since this failure might point to that bearing as a weak point. The crankshaft is pressed together with the con-rod. So to replace the con-rod, you have to replace the whole crankshaft. The piston's skirt was deeply scored. The cylinder was scored slightly. So I need a new engine.
The dealer said he would give me a discount, since I don't need a carb, starter, exhaust system, nor reduction drive... And this engine isn't expensive to begine with.
The cause of the bearing failure is uncertain. But I'd suspect the damage began a long time ago, when I ran the engine with the stock, Walbro, pumper carb. That carb metered very inaccurately, and kept going leaner as I'd fly. There were a few times when it went so lean, the engine barely ran. At those times, the piston was badly overheated, and lubrication of the bearing was likely compromised.
So I should be back flying in a couple weeks. It will be nice to have a new engine. With my perfect carburetion now, it should last much longer.
I considered trying a different engine, but there's nothing better available that would work on my plane. Once I finish the new wing, other engines would be possible. I could even run a derated Rotax 447. I keep hoping a new 2 cylinder engine will become available in the 25 to 30 Hp range. I would convert a Kawasaki 250 Ninja motorcycle engine if I had a machine shop.
Sorry to hear the engine gave up the ghost !
Well You are working that little engine very hard ya know ! your useing every pony it gives ya ! a bit bigger engine so you could throttle back might help some !
glad you didn't go down when the engine died on ya ... that could'a been messy !
... glad your OK !
if it were me , I think i'ed opt for a bit bigger engine so I didn't have to work it so hard ... it would mean re doing almost everything ya have back there but in the long run it would be better I think .
after all , you've already proved the IMPOSSABLE and made it fly on such a tiny engine in the first place ! which is no small accomplishment in itself !
now make it easier on you !
how about 2 little engines side by side so if one fails you can get home on the other ? ... its a thought !
rebuild that one and buy another !
you could set them both at above an idle to cruse with ! hehehehe !
Haing in there !
it'll be tough on ya not flying for a few weeks but I think you can handle it without going bonkers on us Right ?
Have you tried buying carbon fiber from other sources? I was window shopping for supplies the last few days and found many sources of carbon fiber and graphite. There also seems to be plenty of kevlar. I am not sure if it is the style you are looking for though.
As for your engine, how lean did it get with the old carburetor? Was it leaned enough to where the temperature and power went back down, IE lean of peak? Or was it just leaned enough to severely overheat itself?
Does anyone know of any other sources? I knew of one place that sold prepegs and non prepreg materials, I will look for it's link.
Edit: I found tons of placing just by searching google. Many places mention the shortage. Hopefully you can find what you are looking for though.
Thanks for all your research. A few years ago, I bought 100 yards of carbon cloth from (as I recall) carb.com, looking for the best deal on 5.7 oz plain weave cloth. It was like burlap, poorly woven with gaps between every tow, and full of broken and stray fibers. I bought my next roll from Aircraft Spruce. There was no comparison. It was woven perfectly, with no gaps or imperfections. It was probably made of better, stonger fibers too. I learned my lesson, to only buy true aerospace quality fabric from a company that appreciates the difference. The difference in price between the good and bad stuff was small... maybe 15%.
That makes me gunshy about buying Kevlar from anyone else too. I'd only want the real aerospace quality stuff, which is the only kind Aircraft Spruce will sell.
Aircraft Spruce is seeking another supplier. But there is none with that quality. Apparantly there's only one weaver that makes the good stuff. Hopefully they're ramping up production. A lot of companies have carbon cloth on their web sites, and in their catalogs. But almost everybody is out of stock. And how could I be sure it is the good stuff. I trust Aircraft Spruce... If there's any of the good stuff out there, they would get it. They have back orders for thousands of yards of it.
About my engine... The short answer is yes. It went well past peak EGT and peak power several times before I addapted the float/slide carb from my old Hirth F-33. A couple times, it lost so much power, it couldn't maintain altitude. Once, I had to land on a rural highway to adjust it.
The CorsAir dealer says he has almost 500 trouble free hours on his engine. I have done some research to gain some insight into why that bearing failed. At this point I'm about 50/50 between overheating and overloading, although both could have contributed.
This engine has no spark advance system. So at idle, the timing is way too far advanced. My plane doesn't have brakes. So I was idling my engine quite slow. So there is tremendous force on that bearing as the engine fights itself. Combustion is complete well before TDC, and the prop and flywheel inertia are having to force it through.
It makes me think the re'drive belt problems, I had with my old, Hirth F-33, were caused by this. I learned my lesson. I'll be idling my new engine faster, to where it runs smoothly. I'll just have to kill the engine if I need to stop short.
I just fabricated a releasable weight on the tail of my plane to empirically test to see how far I can move my CG back to gain efficiency.
My new engine was just shipped today (Tuesday). So I should have it by Monday.
From my experience, the real quality difference of carbon cloth has more to do with the handling of the material than the actual weave or yarn. Most fabrics are made from relatively standard yarns and for the most part, the properties of one are not all that different from another. They all have similar strengths and moduli, although there are a few variants that do have higher strength values as well as more stiffness, at an increased cost of course.
Carbon fabrics in thick weaves can be difficlut to wet out (in a wet layup) so it is best to work in the thinner, 3k tow weaves, which are generally about .006" thick (or thereabouts). Those fabrics may look to be poorly or loosely woven but in reality they are not - that's just how the process creates the fabric. The loose weave allows a better penetration of the resin and the fabric behaves better on compound surfaces, even with the Style 282 plain weave type.
In all cases though, the graphite must be worked carefuly since overwork with the squeege can create a literal rats nest of a mess. The average unique fiber length in a graphite yarn is less than six inches - overworking the material loosens the yarn's binders, allowing the short fibers to detach and fuzz up. Poor handling of the cloth can do this also so if you got a fuzzy, uneven roll of material, it was most likely damaged by the weaver or by someone handling the material incorrectly prior to rolling it up. Not good, especially for structural applications.
Aircraft Spruce does tend to carry the right stuff but you'll most likely get a much better deal somewhere else. I followed the above links only to discover that many variations of the fabric were out of stock or very expensive. If a distributor asks too much more than $20 per yard on a 50" wide roll of Style 282 T-300 material (on orders of a full roll), then it's a good idea to look elsewhere.
For other sources, try looking at the marine suppliers also - they carry many of the same materials we use for aircraft (actually the marine industry is where most of our material came from in the first place). One local supplier I sometimes use is Fiberlay (www.fiberlay.com) or Tacoma Fiberglass (don't have the web site in front of me).
Thanks for the excellent discussion on the properties of carbon cloth. I knew most of that, but I'm sure many will bennefit. I have layed up over 200 yards of 5.7 oz, 282 style, carbon cloth. I assure you, the difference between the "cheap" stuff, and the good stuff was/is huge. Like the difference between burlap and satin. The stuff you describe with the 5" long fibers, and how it handled and looked, was the cheap stuff.
Judging by how the good stuff looked, handled, and wet out, and your description, I'd say the good stuff had its tows made of continuous fibers. You can handle, brush, or squeegee it as much as you want, without getting a single loose fiber. The tows are layed into the weave, wide and flat, so there's no little holes in every tiny square between the tows. So you can't see light looking through the cloth.
The weaving process is completely different too. With the cheap stuff, if you pull a tow off a cut edge, the tow is stays wavy, like it was in the weave. With the good stuff, it's completely straight. The good stuff wets out easier too. It also is thinner per ply in a completed layup, even though the cloths have the same weight. So you end up with a much leaner resin to fiber ratio.
I have no problem wetting out 5.7 oz carbon with Jeffco Medium or Poly Epoxy. Yes, the 5.7 oz cloth is pretty thick... probably as thick as 10 oz glass. The hardest thing about it, is that it doesn't look much different when it's too dry, or properly wet out. But an experienced eye can tell the difference. You can also develop a slightly different layup technique:
For large layups, you don't use a brush. If it's flat you use a squeege. Any other shape, you just do everything with your gloved hands. Make sure everything is at least 80 degrees F. Use plenty of resin for the first ply, but work fast... spreading the resin, wetting out the cloth, and stretching everything away from the center with just your hands. Then quickly roll out your second ply. As you get it to lay flat and stretch it with your hands, it soaks up all the excess resin from the first ply, yeilding the perfect fiber to resin ratio for the first ply. Then add resin to the second ply. Continue with the plys, working fast. So it's only the final ply that you have to be careful not to use excess resin. By then you've got it down, and it's not hard to get a perfect ratio. This technique works excellent for glass too.
Just a quick note here, according to Hexell and a number of my other sources, all graphite yarns (regardless of the specifics of the material) are made up of a series of fibers that vary in length. There is no such thing as yarns with continuous fibers, although some are longer than others (and yes, aerospace materials tend to have the longest, highest quality yarns). Each yarn is then made up of thousands of these fibers in the same way that any thread is made up of short fibers from a cotton plant or sheep's wool.
The releasable weights on the tail worked out great. First, I tested with 4.5#. The plane was stable and stalled normally. Then I added another 4#. Same results. So I decided to move my cockpit back 7" to move the CG back 3.5".
Moving the cockpit is a lot of work. So testing with the tail weights saved me from having to move the cockpit many small increments.
My Mantis climbs, glides, and cruises much better. Stall speed even got a little better.
I'm still breaking in my new CorsAir engine. It hasn't freed up yet, after 7 hours.
The carbon cloth to make my new wing spar, that was back ordered until December, is now back ordered indefinitely.
My new engine finally freed up after about 10 hours. But it didn't quite put out as much horsepower as my first one.
So I just eliminated my intake silencer, and gained a couple horsepower, and lost a couple pounds. I'm using a simple ram-air scoop with built in air filter. See the attached photo. It is much louder in the cockpit... but not bad inside my headset. My 3 stage intake silencer was so effective, you couldn't hear anything from the intake. Prop noise was by far the loudest sound. Now the intake roar is a loud, sharp buzz, that's twice as loud as anything else.
That extra 2 horsepower helps a lot in the hot afternoons. The engine winds up above 7,100 RPM at full throttle. 7,550 RPM is red line. So my Mantis weighs 226#, including the parachute now.