Discussion on FLY5K

Discussion on FLY5K

I add several mails of the fly5k mailing group at Yahoo Groups. You can see here a small discussion I started around this subject. I started calling 2 stroke 2T. I learned the right words during this discussion.

Hallo everybody,

Last year I have lessons in basic mechanics and I saw for the first time the 2T diesel. I had to learn a bit more about it before I could give my lessons. Found out that those engines are smaller than others and give more power. Real power-engines! If you ask why they haven't been used in the aviation YET, I can give you the answer. 2T diesels need "compressors" (not sure if this name is right) to speed in the air to push the old fumes in the cylinder away. That "compressor" weights a bit too much. It adds so much weight that it is no longer good for light aviation. But ... do we need that compressor really?? We have a propeller that forces air backwards.

The following is just a idea. I hope that somebody can use it to make a lighter engine for the ultralight aviation. OK, here I go. On the ground we need to have some system to force the air in for the starting of the engine. But, once it is started, we have a turning prop. That prop can push air into a air intake. If one designs the air intake and cylinder in such a way that it is nearly in line, I guess the prop air will be a good help to force the old fumes out of the cylinder.

Could it be done? If yes, the light aviation can use such a small power engine.

PS. starting could be done with a bottle of compressed air.

Koen; I always enjoy reading your ideas... The recent one with the dual tail wheels on the wingtips .... reverse quickie setup was brilliant. The 2T diesel you mention obviously must be a two cycle ..... Did I miss some posts? A two cycle engine requires considerable pressure to flush out old mixture and drive in fresh air or air fuel mixture in the brief time the ports or valves are open. Two cycle engines of today mostly use the piston to accomplish this as it moves downward into a very restricted space in the crankcase forcing the air out of that space through a transfer port into the cylinder. This amounts to considerable pressure as the piston is most of the way down before the port opens. The Detroit and other blower fed two cycles also run considerable inlet pressure. You absolutely need a compressor of some sort for two cycle engines to work. It does not have to be excessively bulky or heavy though. A small vane compressor turning at high speed can move a lot of air. What is required is that the compressor be designed with weight as a consideration which is not usually the case.

A typical two cycle makes about 160% of the power of a 4 cycle of the same displacement... due to the inefficiency of crankcase pumping. A blower fed two cycle engine could easily double the output of a 4 cycle engine at the same RPM and displacement. The two cycle engine that intrigues me most at the moment is the Sterling diesel of the 30's which used a group of cylinders arranged in circle with the crankshaft running down the middle and a swashplate on either end which drove pistons... two in each cylinder toward the center of the cylinder. This allows porting at each end of the cylinder. Air in one end and exhaust out the other, it allows very high compression making it easy to create the compression ratios needed for diesels.... It eliminates the head... There is an injector at the middle of the cylinder where the pistons come together.... and no head or head gasket, it eliminates valves altogether, and the porting is away from the area where maximum temperatures occur.... and the icing on the cake so to speak is that each piston is exactly balanced by a twin moving in exactly the opposite direction at exactly the same time making this engine 100% dynamically balanced. It of course requires a compressor to feed the air... In this case they used compressor pistons... which is not an ideal solution... a vane or screw blower would be a far better answer. It is adaptable for efficient use as either a gas or diesel engine.... A gas engine would require timed fuel injection either into the intake air at the port, or
direct injection into the center where the diesel injector would be.... I prefer port injection for a couple of reasons.... mainly mixing, but also simple readily available components. I find this engine very compelling in it's simplicity as well as it's obvious advantages.... I work on engines as a large part of my business and have for many years.

The other advantage you didn't mention and it's a major advantage of blown two strokes is that you can then have a wet sump/oil pump for real lubrication. That removes 99% of the problems with two stroke engines. Using fuel injection then improves the fuel consumption to an acceptable level. Regarding the blower itself I feel a Roots type is the better solution since vane and screw types need lubrication.
David James

David, I've seen some recent work with w scroll type of compressor that looks good, no lube used in it either.
Bill Higdon

There is really little difference between roots and screw compressors.... they are just slightly different variations of the same thing. Commercial compressors use the screw generally as it is more efficient for producing high pressure air. The oil is not used for lubrication... the impellers do not touch each other.. they are geared at the ends. The oil is used for sealing the space between the impellers to achieve greater pressures.... and for cooling. I assume on vane compressors the oil is also used for cooling... many smaller vane compressors do not use oil. I do strongly agree about the lubrication system.... In fact the design I have in mind would use such large surfaces where the rod plate contacts the swash plate that there would be virtually no wear at all so long as there is oil supplied. The whole thing would float on a cushion of oil like a puck on an air hockey table. Rods would be short, and have a wrist pin on each end which would be supplied with oil from this area. The idea that appeals to me about the engine as far as gas engines go is the fact that with the intake port on one end and the exhaust port on the other, the air flow through the engine would be linear, and air with no fuel could be used to "chase" the spent gasses out of the exhaust port... followed immediately by a slug of air / fuel mixture...none of which would escape. It eliminates a lot of moving parts, and a lot of gaskets, and in general a lot of problems. What I am looking at more than anything else is direct drive... by doubling the CFM using two stroke technology you can eliminate the need for a redrive and the attendant problems. The ideal aircraft engine is and always will be direct drive... air cooled ( as much as I dislike air cooling ).
Simplicity = reliability

The ideal compressor would be a fan like the inlet stage of a turbocharger driven from the crank by a belt or gears, compact and light weight. I agree that the uniflow engine in this configuration would be compact, well balanced and efficient, but I have reservations regarding the swashplate crank, generally they are heavy and operate at lower rpm (in this engine size) than we are looking for here. Convince me otherwise and I may make a prototype.
Regards Mike T.

First of all.... I am talking about direct drive RPM.... let's say 2800. Now if we look at engine displacement.... 2" bore and 2" stroke... small and compact... 6 of these double ended cylinders gives us 72 cubic inches displacement approximately which will give us about 65 horsepower @ 2800 if we pump enough air in to about double the airflow of a 4 cycle engine of this displacement. We have a small compact engine turning a reasonable RPM for a prop....... What more can you ask for? Smooth and powerful. Now the matter of blowers..... Centrifugal or axial flow blowers do not create pressure well.. they volume. We need pressure to force our induction air into the ports rapidly when they open. Centrifugal blowers require lots of RPM to generate any significant pressure and are not ideal
for our application except as a pre-charging device... where a turbo could be beneficial. What we really need is a positive displacement blower of some sort. Now the issue of swash plate speeds.... I don't know where this idea came from??? Take a look at most of the automotive air conditioner compressors of today... they all use swashplates and multiple pistons arranged in a barrel configuration. I can tell you from experience that my ac compressor does not seem to vibrate excessively when I downshift and rev the engine up to between 4000 and 5000 RPM.... as I occasionally do to get max acceration .... it has never scattered from this.... and has approximately 280,000 miles of experience.... of course it has not operated most of those miles... perhaps 20 -25 %. Proper design using aluminum and a steel facing can make a very stiff swashplate assembly... an aluminum follower plate could be contained by a rim so that it always followed the swashplate exactly.... A return flange bolted to this could provide the return force, and a dog on a pin in a groove could prevent it from turning. Piston rods would be articulated... it is easier to do it that way as it allows a single large follower plate rather than requiring each piston rod to have it's own individual follower and some mechanism to prevent side load problems. Alternatively individual rigid rods running through bushings
and designed to fork around the swash plate with a follower on each side and a lower stabilizer bushing could turn each piston into a pump on the bottom side like a conventional two cycle engine... though you could not get 200% without turbocharging the inlet due to the displacement of the rod. I prefer the external blower... it is simpler. The problem with barrel engines in the past like the dynacam is point or line contact rather than parallel contact on the loaded surfaces. With the single plane swash plate you eliminate this problem. Here we make up for this by using two cycle to accomplish the same CFM as a palmer of the same displacement.... and we simplify the engine immensely. We are also looking at extremely well proven technology.... The swashplate system is widely used for AC compressors.... and all hydrostatic systems use hydraulic piston pumps of this basic design which are variable displacement. This is far simpler in principle.

That's interesting Bill, if it doesn't need lubrication then it comes down to weight/size.
Do you know of any links to a scroll type compressor?

Hi David,

First, I need to clarify: I'm not a 2-stroke fanatic, nor a 4-stroke fanatic. "Use the proper tool for the job" is as valid concerning aircraft engines as it is for building a Louis XIV armoire. I do confess to a bit of tunnel vision of late, as could be seen in my post (to which you replied).

My sole interest in aircraft concerns those which fall under FAR 103 and of those, I intensely dislike the "armchair under a barn door" variety, as the vast majority of them seem designed with enough drag to do a remake of Rocky Horror Picture Show. This necessitates the use of larger (relatively speaking) engines--Rotax 447, 503, or their equivalent. Their fuel consumption vs. the 5 gal. fuel restraint limits their flight time to something approaching that of the Me363. This leaves me relatively few aircraft to choose from.

The designs which interest me are those which have something approaching a useful radius, as I'd like to do a bit of distance flying (again, relatively speaking), in the area of 240 mi. round trip. The Aero-Corsair 25 hp engines, the equivalent Simonini and similar are first on my list, for several reasons.

The two planes that I find most suitable for my purpose are the Skypup and the CP150 Onyx. Both will fly at or very near the 55kts FAR103 limit, have acceptable rates of climb & TO/landing rolls for my needs, AND will achieve these with the smaller engines. The 'pup is happy with 20 hp, and the Onyx flies quite well on 12 hp. Both have rather severe restrictions on powerplant weight: Skypup-62 lbs, Onyx-45 lbs (incl prop).

The FAA's refusal to allow a weight variance for 4-strokes is typical government half-logic. The "logic" behind Part 103's weight limit is to minimize the risk to people on the ground. Allowing another, say, 50 lbs for a 4-stroke isn't going to appreciably increase the risk--having 550 lbs fall on you vs. 500 lbs isn't going to increase the amount of death inflicted--and might reduce it via somewhat greater reliability. However, they're adamant, the number of suitable 4-strokes meeting my needs is nil, hence my focus on 2-strokes.

Four-stroke power pulse: Anyone doubting the potential for prop-wrecking that is contained in a one or two cylinder 4-stroke need only ride an old-style Harley Sportster for a while. :)


Most of the work has been in Air conditioning and cooling, I saw a article in a Design magazine a while back that mention designing it for Suppercharging usage. Unfortuinantly I can't find it on the web.
Here are 2 links http://epubs.siam.org/sam-bin/dbq/article/36212

Gary, do you have anymore info on the aero corsair 25? Has anyone had any experience with the new Hirth 28 hp engines?

You mentioned the sky pup, I am a friend of Steve Wood (Sky Pup Designer) He originally tried to fly the Sky Pup with a 10 hp techumseh 4 stroke. He wasnt able to fly out of Ground effect with that motor.That made for a pretty dicy first flight, he made it over the fence at the end of the fields and then he flew around in ground effect until he found a place to land. But he definitely understood the need for inexpensive power plants.

My first experience flying a powered anything, was Seagull 7 Hang glider powered by a Soarmaster power pack. It should have been called a Sawmaster because I almost lost 3 toes! This thing used a Chrysler
West Bend 8.2 cu 2 stroke. That thing hadjust enough power to allow about 150 fpm rate of climb on a cold day. I needed more power.I designed a modification for those engines based on the German BMW
Heinkel He111 engine. That motor had 12 pistons, 2 cranks and 6 cylinders. I took two engines and made a coupling that joined the two cylinders together. They were syncronized by a timing belt that also
drove a reduction pulley. Because of the greater volumetric efficency two 10 hp engines delivered 22 hp. It worked well, but it was still unreliable

Ok I snipped out a lot... here's the rub: for an ULTRALIGHT, the limiting factor is EMPTY WEIGHT. If it tips the scales at over 254# you are not legal. If you keep it below that (and meet the other requirements) you are. A 28# engine is about 11% of your total empty weight, leaving more for the airframe. A 60# engine is closer to 25% of the empty weight, meaning the airframe has to be lighter to meet the standard.

Horses for courses- don't ask a quarter horse to run on the long tracks with the thoroughbreds, and vice-versa.

I also like 4-strokes, but realize that there aren't many that work on ultralights... and ultralight pilots generally are not concerned about fuel burn- we don't GENERALLY fly cross-country. (it's faster
to put it on a trailer and drive!)

I have read about scroll compressors for years .... I must confess that I am a bit confused about how they actually work. The description of the scroll compressor states that one spiral is fixed, while the other "orbits" around it. It is clear that they intermesh which means that the one that "orbits" cannot rotate.... so it must wobble. It is a fascinating principle. The precision machining and geometry required to attain the desired results .... all chambers sealed from each other forcing the gas to rotate into the center is impressive. Whatever is used to attain the desired wobble action must be very precise... needless to say the scrolls themselves must also be very precise. Not so many years ago this would have been virtually impossible to achieve with the available machining technology of the time. I would love to see one of these with the cover off.... a demo... you turn the crank... model. The same principle could be used for air compressors, for hydraulic pumps, for water pumps, and various other applications.

Good post Gary. While I understand your weight limit problem with US ultralight planes I also suffer from tunnel vision because I "think" Australian ultralight and that is a completely different thing. A Kitfox with a rotax 912 etc, a Pulsar etc etc fits into our ultralight category. I admit that our ultralights have to be registered and you have to be licensed to fly them though so the difference is not just in the weight/speed/ fuel capacity etc. I noted a couple of other posts pointing out that the US ultralight category puts the burden of pilot safety on the pilot so they seemed to think that it was their risk to use a two stroke but I find that a strange attitude since if it was my arse up there I would want to have it as safe
as possible, after all if I stay safe then the people on the ground are also safe.
Some people seem to think a well maintained two stroke is as reliable as a four stroke but the figures indicate that is not so. As an example a couple of my friends have had crank failures in new Rotax 582's, one @ about 40 hours and another @ about 100 hours. Poor maintenance? No. I also fly a two stroke but I hate the mongrel thing. It had a gearbox replaced at 100 hours, the new box failed at 112 hours. (B box) It failed because the crank seal was leaking and it sucked the oil out. Bad maintenance? Well yes and no, the "Expert" Rotax agent did all the work but failed to mention anything about the seal let alone change it. They only mentioned the possibility of it being the cause when I sued them (I won) But why should a seal fail in less than 100 hours? Answer it

I believe the centrifugal compressors would be suitable for this application as we do not require 100% purging at zero rpm, even at cranking speeds there is sufficient time for the minimal inlet air
pressure to displace some of the residual gasses in the cylinders, certainly enough to get the fuel to ignite and the engine to start, at higher rpm the dilution of the inlet charge by residual gasses would decrease. The major benefits are compact size and light weight.

>I can tell you from experience that my ac compressor
> does not seem to vibrate excessively when I downshift and rev the
>engine up
> to between 4000 and 5000 RPM....

Short stroke, small light weight pistons, very heavy swash plate assembly and spring returned to hold the follower to the swashplate, not ideal for an IC engine, certainly not the ones I have seen.

>A return flange bolted to this could provide the return force,
> and a dog on a pin in a groove could prevent it from turning. Piston rods
> would be articulated... it is easier to do it that way as it allows a
> single large follower plate rather than requiring each piston rod to have
> it's own individual follower and some mechanism to prevent side load problems.

This will work, but both ends of the conrods would need articulated or perhaps ball joint ends, still much heavier than a conventional crankshaft assembly - probably twice the weight. The crankshaft is one of the heaviest single items in a conventional engine. The engine with the lightest crank assembly for its displacement is a radial, unfortunately this cannot be adapted to a barrel engine.
Mike T.

The one problem that you might have with a swashplate commpressor for air is lubrication. The uses that they are used for now, they are bathed in oil, with essentially no lack of it. The oil, in some systems, is returned to the pump with the use of an oil separator while others are carried by the vapor and eventually return to the closed system of an a/c system.
Jerry Tanson


One of the problems is to get the 2-cycle diesel engine started. With a Detroit 2-cycle diesel, without the roots blower it would never start. I like your idea of the propeller and maybe with air scoops close enough to the propeller to pickup the air and duct it back to the cylinders it just might work----if you could get started in the first place. Anybody have any other or better ideas?

Hallo guys,

Sorry to reply so late. I totally forgot that I placed this subject.

OK, I saw a lot of very technical replies. I have to be honest. Most did overflow my brains. My English vocabulary in engine terms is not that good it seems. But I got a few things understood.

Things I did understand:
1) there are low weight compressors. Well, that is great. I noticed that the rpm of a diesel are very close to that of a "normal" 2T engine WITH reduction. So, if the compressor can be made in the same
weight range of a reduction, we still have no gain of weight. GOOOOD!

2) there is need for compressed air to start the engine. Hmmm, OK, does a compressor not create enough compressed air if the starter of the engine (thinking electrical starter here) runs a bit longer?
And ... if it does not have enough air pressure, does a car fuel station not have those tire filler bottles. Could we not place a simple nozzle where you can fix such a bottle onto and add some AAAAAIIIIIIR into the inlet when the starter runs. The bottle can stay on the airstrip. I am thinking about funfliers here. Those stay best near the same airstrip. And ... if you make a crosscountry flight, you will still be able to take off there. Unless, ...that country uses footpumps to pump up a tire. ;^)

3) A diesel 2T can be made very compact. Super! If compact means light ... SUUUUUUUUPER!

Things that I didn't see are a few advantages I think this system still has.

A) there is oil in the engine. OK, somebody already mentioned that this is better for the lubrication. That is right. Second, the fumes have less oil in it. That must be easier to have the engines into a possible heavier fume-regulation. Third, there is a posibility to add a temperature-measuring devise in that oil. It will give a correct temperature of the engine. Normal 2T engine have no temperature devise (Let say that I have not seem many). Those that did have one had it installed in the exhaust. That one is not rebliable, I have heard. There is a situation where it will lie a lot. Just a kind of situation where you need to see that you are in troubles. Something with a pressure-leak. Sorry, I forgot the

B) there is no spark needed. I have heard of many engine-failures due to badly maintained spark-candles. My HM14 with up-side-down mounted Hirth engine will ask a lot of spark-candle attention. That situation will be lost too in a 2T diesel. GOOOOOD!

C) No carburator needed. Carburators are a not that easy equipment. A lot can go wrong ... if I am right. A diesel fuel pump is that easy in concept that it needs a really hard kick to let it work not right.

The disadvantage I am seeing is the need for a camshaft and a supercharger. Both can be driven by the engine by a belt or gear. Ads a bit of weight. Not sure how much. Luckily ... those parts have mostly no problems in functioning if no belts are used. Having a belt CAN cause problems (I speak of experience (luckily it was in my car)).

My main idea is that the 2 stroke diesel has a lot of advantages in RELIABILITY towards the normal 2 stroke engine. And that reliability of the engine is one of the main reasons of accidents in ultralight
aviation. I once saw a list of the accidents in France of a certain year (forgot which year). A loooooot of the accidents were about having low altitude while having a engine failure. I repeat ... engine failure.

This mail is getting too long. Any comments already?

PS. can anybody guide me towards a good set of drawings with the
english names of the parts. Supercharger, turbos, diesels and so on.
I hope to be better in understanding the next mails that way.

I like your term " spark candle" We call them spark plugs. aside from that, you are doing well!

Dag Koen,

The diesel does need air and a 2-cycle is a good light weight choice. With the Detroit diesel in heavy
duty applications the roots blower was the perfect choice. It provided the much needed volumn for start
up and the necessary pressure for top performance. For really high output engines, a turbocharger was
installed in front of the supercharger (roots blower) to give it the added boast in pressure with volumn
that was needed. All this was sitting on the ground and while the less it weighed transfered into a heavier payload, the thing didn't have to fly.

Roots blowers are a very good supercharger and are popular, and have been for years, with the hot-rodders in this country, and have been used on the drag strips for decades. They are a proven piece of machinery. The engines that are available for aircraft that are diesel powered, I'm not familiar with but the Germans did quite some innovative research and developement before and during World War II. Check out the info on what they have done and see if you can glean anything that might help you. I know that they had the largest flying boat of the time and it was diesel powered.

I don't think that bottled air is the answer for what you are trying to accomplish because it's mostly pressure that's quickly spent. For start up, you need volumn and as the volumn increases with rpm as the
engine fires and revs up you reach a point where the pressure builds also. Have you thought of hand cranking the engine like the old timers used to. As I'm writing this, I'm reminded of the older truck
engines that had a compression release on the valve train that held the valves open allowing the engine to
crank to a higher rpm before engaging the valves and causing the engine to fire. The key here was rpm. That would allow for air to build up in what ever design you come up with for you air induction.
Thin on this and let me know.
Jerry Tanson


The key to the air induction of the 2-cycle engine is also what high performance 4-cycle engines use for
better scavenging and therefore more horsepower is called valve overlap. The pressure of the air exiting
the cylinder causes a siphoning effect that draws the fresh air into the cylinder. the fact that this
"fresh" air on a gas engine is an air/fuel mixture makes it possible for comprssion and ignition with a
spark plug. With a diesel, there is NO air fuel mixture and not enough volumn to be able to compress it to 500 degrees F. for ignition to take place when the fuel is injected into the cylinder. No, that was not a
misprint, I meant to say degrees. In a diesel engine, pressure and temperature walk hand in hand. The
pressure also has to 500 psi to achieve the 500 degrees to ignite the diesel. The Detroits I worked on had a comp ratio of 18/1. The Cummins and Caterpillars ranged from 18/1 to 22/1, depending on
their application. As 2-cycle engines, diesel and gas operate very different and each have special needs.
Jerry Tanson

I realize the subject here states two cycle and the topic is diesels but I was under the impression that most diesels in use were 4 stroke and were no different than gas except for higher compression and no ignition.

How many and what kinds of machines generally use two stroke diesels as opposed to four stroke? I own a 1971 John Deere 450 track loader and that is my only diesel experience.
Scott Perkins

Cummins used to make a very nice "small" 2-stroke 6 cylinder turbocharged diesel. A small volunteer FD that I was with for some years in the mid '70's to early '80's had a '75 American LaFrance Pioneer IV 1250 gpm engine with this engine and an automatic tranny. That Cummins had significantly more scoot, ran
cooler when pumping, and was more fuel efficient than the Detroit-powered versions in the 1000 to 1500 gpm range. My impression was that it was also more reliable/less expensive to maintain.

A telling comparison of diesel vs gas came during a 3-alarm shopping center fire when I was with Pantego VFD. We responded to the call at 2 a.m.-ish, cleared en route to station about 6:30 p.m., during which time our three engines--we also had a '69 Chevy C50 chassis'd 500 gpm A-wagon/grass rig w/350
industrial V-8 and a '40 Mack 750 gpm engine w/600 cid straight six--ran continuously for over 16 hrs, at various levels of work. The Cummins worked the hardest for obvious reasons.

It hit over 100 deg. that day, and we had trouble with the Chevy overheating (easy to solve w/any fire truck...if the water holds out...<g>), but the LaFrance & Mack were just fine. (routine practice with the old Macks was to raise both sides of the hood asap for better air flow through the radiator, and it had provision also for routing water from the pump thru the radiator/engine, an option that I had to use when the chief rotated me around to engineer's duty for a "break").

Fuel consumption: Cummins- 12 gals, Chevy 29 gals gasoline, Mack 46 gals gasoline. Our 1 ton Dodge 440 modular ambulance just fast-idled (and made one unrelated call) and burned 22 gals. Fast-idle = manually set the idle up w/throttle knob, to keep the alternators running fast enough to offset current
drain caused by the lights, rear a/c, etc. A 2nd 1940 Mack, sister to ours, belonging to another dept. (both were bought used from Ft. Worth FD in the '60's), used 35 gals, but their magneto still worked (dual ignition on those old beasts, distributor/coil on one side, magneto on the other).

In case you're wondering, yes, it was arson. Could've been worse, though: I was in firefighting school at the time and most of my class, which was composed mostly of people from FDs in the NW part of the county, spent all that day and most of that night fighting a major brush/grass fire. That's REAL work.

Remember fuel consumption depends on loading..... The so called "industrial" SBC of course does not belong in the same class as the Cummins, Mac, Detroit engines. (Gallons per minute * Pressure in PSI
/ 1710 )/pump efficiency = horsepower A simple side by side comparison without actually quantifying the work done is useless as a comparison.

You are right about the loading, that goes without saying. My statememnts about the different brands of
heavy duty diesels was to emphasize the changes that have taken place in the last thirty years. I
witnessed most of them. The engines are better today because of the latest technology. That means that
there is a better pool of knowledge to draw from in building something to fit your needs, if that's what
you want to do. So many different ways to go now than there was before. It used to be such a closed field
because of the thinking but that has really changed. It has really opened up.

So far the mails about this subject. Like you see ... a lot of advantages and still a few questions. I like to add now that there is a way to get these kind of engines started. Just use the system like mentioned by Jerry Tanson (hand cranking like oldtimers) but ... simply use a electric starter. I prefer not to stand in front of a rotating prop. ;^)

I hope you like the basic idea. If you are a expert and you want to add some remark, please do. I will place it here and give it also to the Fly5k Yahoo Group. Thanks in advance.