I'm pretty new to airplanes. I've already have about 20 flights under my belt with my old Verus trainer which I let get to far out and lost it. I had a HB .40 PDP on it and it flew great and had quite a bit of power. I'm now getting a SkyRaider mach 1 as everyone in my area has said it's the trainer to get with it's semi symmetrical wing and the constant winds we get here in Kansas. I've seen a lot of people running 4 strokes and I just love the sound of them and their low speed torque so I decided to pick up a ASP FS52AR motor. From what little I can gather it looks to be a fairly good fit to a .40 sized trainer be it maybe a tad under powdered which I'm thinking might be a good thing. I don't need speed just something less messy and more fuel efficient.

I'm asking for any advise you guys can give me. Prop size I'm unsure about. I was running a 10x6 with the HB and was thinking a 11x7 APC would probably be the ticket. I think it's recommended to break-in with a 11x5 and I plan to run 3-5 tanks through it on the bench for break in. I'm pretty sure the FS61AR sleeve and piston drop right in and something I'm thinking I might do in the future if it's too under powered. Any advise is welcome and I'm just making sure I'm not crazy or something. I'm thinking if I like it enough I'll pick up the FS91AR for my super stick which is my next plane that I plan to set up too in the future. I got into it a little to soon and had a very hard landing that broke the wing. I'm working on repairing it currently and put a stronger motor on it. It was running a Super Tiger 40 that just didn't seem to have enough power for it. Several of the fliers at my park have switched their entire fleet to four strokes and they all said it's amazing and they will never go back to a 2 stroke.

Maglin:

I am quite surprised you have not yet received replies to your original post. It has some interesting points.

First of all, I looked at the Skyraider MK1 and it looks like a nice aircraft. If you have 20 flights on your previous trainer, can take off and land successfully (well, all except your last flight that is), you should do ok with that plane.

I am a tad bit hesitant to go ahead and acknowledge the Four Stroke engine for a new student. Four stroke engines can be a bit more difficult to set up than two strokes, but I think once you get the hang of it, it will be ok. But, the focus here is to get you flying and "qualified" to continue on your own. If it's power you are worried about, well, you can get a good two stroke, such as an OS AX engine, in the .46 to .55 cu. in. range. The AX series of engines are powerful engines and will give you good overall power for just about anything in the size range of the Skyraider MK1 or even larger. One of the mods here put an OS .55 AX in a plane that I thought would be much better off with a 70 size engine, but it flew just fine with the .55 AX so that would be my recommendation.

That is not without saying that the four stoke won't do, as it will do just fine. The low end torque, especially when prop'ed correctly, will give you lots of take off power although it may not give you the RPM for high end speed as a two stroke would, but, it will do just fine for a trainer, especially if you have several friends at your field that are experienced with four stroke engines. Just be careful when buying them that you don't just opt for price versus brand and quality. Just remember that cheap is usually that, cheap, although I must admit that I am not familiar with that particular engine. I hope someone here will post as to their experineces with the ASP four stroke engines and can fill in the gaps.

I am somewhat partial to two strokes (as you can probably imagine from the content of this reply) because I've flown just about everything I have with two strokes with on exception, and that was quite a few years ago.

As far as prop size is concerned, go with what is recommended for that engine and stick with that for a few flights to get the feel of what it has to offer. When I started out, I did what I assume you are probably doing, and trying to find the right fit for your engine-plane combination, and I bought a boat-load of props. Added to that was, well, hard landings caused me to break a few props, so I bought several spares of what I was using, and, at the price, heck they were only a couple of dollars each, I bought them 5 at a time. And, I bought several sized and played around with props of different width and pitch. Just remember that lower pitch will give you more RPM, more power, but less speed. Going higher in pitch could load the engine down to the point where it does not operate in it's optimal RPM range, whatever that may be.

You are probably aware of this, but think of the prop pitch as gears in a standard shift car (automatic too, but it's more obvious in a standard shift). Lower gears will pull harder but you are limited in speed.. 20 mph may be top speed in first gear at the red-line RPM). Higher pitch will give you more speed, but it takes longer to get there. an 11-6 prop, the 6 is the pitch means, that in ideal conditions, one rotation of the prop will move 6 inches of air through the prop, or will move the plane 6 inches. If you work that out, at 10,000 RPM, you would move 60,000 inches per minute (6 X 10,000) which works out to just over 83 feet per second or just under 60 statute miles per hour at max RPM, and as I said, ideal conditions, which is not realistic, but good enough for explanation. Changing that to an 11-4 prop changes those numbers to an end product of 55.5 feet per second. I'm sure you get the idea, or probably already knew this, so I won't digress.

If you want to experiment with prop selection, why not do it while having some fun.. buy a few of different sizes and go ahead and see how it works out for you.

Anyway, best of luck.

CGr.

I have owned two of the Mach I Skyraider. The first was for instruction and was powered with an OS 40LA. It was a terrific combination, and I found I put far more time on it flying as a sport plane than for instruction. The plane is an excellent design, a great flyer. I did not recommend it as a "first" plane because the assembly instructions are so minimal for a new flyer, and while built as a good flying plane, it is not as robust as some other trainers and might not survive some of the harsh realities of training. Trainers lead a hard life! My buddy, an experienced flyer liked it so much he bought it from me. After I sold it, I bought another. The instructions did comment on not overpowering the plane, it was designed for a .40 engine, and I found it to be good advice. Overpowering it isn't going to break anything, but the design doesn't need it, and the additional weight detracts from the flight characteristics. My buddy was fond of hovering it on the .40LA. Go figure!

Both mine were set up as tail draggers. Enjoy.

G'day

I too have had two Skyraider Mk 2 aircraft. The first had an LA 46 and it was a great combination. Sadly I rarely got to fly it. The president of the club to which I belonged at the time loved to borrow it to teach newcomers. He liked it so much that it was rarely available for me to fly. When I did fly it, I really liked it.

Eventually, many years later, I bought a second one. I put a Saito 62 in it and it was even better than the first. The Saito flew it really steadily and with a 12 x 5 prop, it was a little slower but perfect to fly. Your idea of a Magnum 52 four stroke will work well. I am a real four stroke lover and I found the Skyraider with the four stroke fine. The down side is that four strokes do tend to be easier to damage in crashes.

Later I put a Super Tigre 51 in my second Skyraider. It was brilliant but sadly I then sold it to a young lad who forgot to pull the antenna up and the model crashed. I helped him to repair it but on the first flight after the crash the receiver failed after about 5 minutes and it again crashed. It seems that the Rx was damaged in the first crash. It looked OK, it worked OK (for five minutes) but then it and the plane died. I did manage to repair the Super Tigre which needed a new needle valve assembly for the carby.

There used to be a Skyraider Mach 2 low wing too. I tried one of these but as it was quite a bit smaller than the Mach 1, it just found it a bit small. That did not stop just about everyone in the club buying one and flying them with AX 46s and fluttering the ailerons and elevators. One member had one with an OS 48 Surpass four stroke. I liked the way it flew.

Enjoy your Skyraider. I did.

Mike in Oz

Thank you for the replies. I'm actually almost finished putting it together. Just picked it up today. My buddy that is teaching me is also helping me to build all my planes. I'm going to run a HB 40 PDP for it's first few flights. I still have to break-in the four stroke and I know the HB and how wonder it flew my last plane. I also have a Super Tiger 40 but even with a new needle the carb is just a bear to tune and it has horrible transients and is responsible for one plane to get a little banged up having to come down dead stick.

As far as the Mach 1 goes I'm amazed at how much was put together and how well it's put together. So was my friend. He still flies his Alpha 40 and is thinking of getting a Mach 1 or 2 just because they seem pretty cool. So I'll get used to the new airframe with the 2 stroke and then try the 4 stroke and will be able to compare.

Your Magnum .52FS will be perfect. I have owned and flown that combination and can vouch for it.

I have taught numerous people how the fly RC and, while the Mach I is not a self leveler like a Sig Kadet, it is an excellent flier.

A few years back, a buddy picked up 2 of the original Sky Raider Mach I's (before they went to the basket weave covering) for a good price and gave me one. I built it as a float plane and used the Mag .52FS. Excellent combination. I finally grew tired of it and gave it to another seaplane flier (less the engine, of course) who had crashed his seaplane.

I had 2 of the Magnum .52 FS engines and both were excellent. I used the pair of them on a few twins since they were so reliable for me. Hobby People and Global hobbies has excellent warranty service on the engines. I managed to bash a Grumman Widgeon twin in the water. Some time later, on another twin, the bearings started to get noisy. I shipped then to Global Services who rebuilt both engines and shipped them back to me at no cost. That's hard to beat.

Thank you for the replys. I have the four stroke installed with a new 12oz. round sullivan fuel tank to allow me some more room to run the throttle over the tank. That and I didn't like the tank that came with the model. It kept getting air bubbles in the fuel line. Didn't want to mess with it really at least not at this time. I couldn't use the engine mount that came with the Mach 1 as it wasn't long enough to give me the space I needed for the carb behind the engine. I used my SF engine mount I took off my Super Stick and it worked like a charm with a little drilling of new mount holes and moving the nuts over on the firewall. I have 4 tanks through the motor 3 of which I did on a test stand. Thing seems to have a good amount of power with the 11x7 MAS prop I have on it. I ordered a 11x6 and 11x7 APC prop for it as the LHS didn't have any in stock. I plan to go out in the morning for it's first flight on the four stroke and I don't forsee any issues. I would have to say the hardest thing about changing over to a four stroke was the carb placement and it's control linkage placement being in the center of the fuselage. I'll report back on how it ran and my impressions of it over the 2 stroke.

Compared to the HB engine it's actually smaller in physical size. It might even come in about the same weight. I couldn't tell a difference by hand. As I've read the idle isn't perfect yet but it's not broke in fully yet. From what I've read over the course of a gallon of fuel the idle will stabilize and clean up. I did have to adjust the valves as they where a tad on the loose side. I set them up at .003" cold and checked them again after I ran it WOT for a few minutes. The motor was at 280* and they still had about .001" clearance so I think it's pretty much perfect atm. I didn't bother with checking the cam as it runs good and I didn't want to tear it all apart. I'm surprised at the internal finish of the ports on the head. I was figuring I was going to have to do some porting and finishing of this cheap engine, but the finish is excellent.

G'day Maglin

With that 12 Oz tank, you will be able to fly for about a week. I think I had an 8 Oz in mine and it was more than enough with a four stroke as they do use less fuel.

My latest trainer (I just like flying them) is a Sig Kadet LT25 in which I have put an Enya 36 Four stroke. I have a 6 Oz tank in it. I flew it yesterday for two 10 minute flights and there was still quite a lot of fuel left each time. If you want to try building from a kit, the LT 25 and LT 40 are great easy to build kits which you can build very quickly and which fly really well. Your 52 would be great in the larger one.

Cheers

Mike in Oz

So I have to thank a new friend who happens to be an experienced pilot who managed to control a very out of wack elevator. Upon take off it was vertical and then straight down and then vertical and so on and so forth. He managed to land it off the runway in the grass and we adjusted all the flight surfaces and he was able to trim it out. I had to add a bit of down thrust to the motor as it would just start to clime on power. I have to say the four stroke is a huge win. I started with a 11x7 MAS prop and it was fast. The motor was spinning 11K RPM on the ground and not to sure how much in flight unloaded but it was screaming. My only other 11" prop was a 11x8 APC. I put that on and now was right at 9300 RPMs on the ground and it was a lot more manageable in flight with no over revving. It seemed to actually slow the plane down some probably because it is to much pitch for the motor but it was the ticket until my 11x7 and 11x6 APC props arrive.

The cheap little four stroke idles at 2600 rpms currently and every tank it got better. I've got maybe 8 tanks through it now. I think I flew it for about 20 minutes and still have just under a half tank of fuel in it. It does really well on fuel. My other buddy was so impressed with it he is going to get one. Anyways I'm very happy with it. I thought it was going to be to small and it's just right as was mentioned earlier. It also is very fast even compared to a .40 2 stroke with a 10x6 on it. If anyone reading this is considering going four stroke don't worry about the ASP FS52AR. It's perfect. On a great side note. I had almost no oil on the side of my airplane after 4 tanks through the engine. That has to be a huge bonus in my book.

If you were getting 11k on the ground that will damage your engine. 4 strokes will get into a condition called valve float where the valves stay open past the peak of the camshaft and then slam closed. That's really rough on your springs first, so the rpm where valve float will happen goes down into the normal operating speed of the engine. Eventually your valve will break and usually will destroy your piston and score up your cylinder.

Thank you for the information. That is why I put the 11x8 prop on it. I actually was thinking about making some new valves out of some stainless steel to help with valve float and to put some over sized valves in it to see how it would handle. I'm going to play around with a spare head that I'll order to compare. It does seem to run pretty fat at mid throttle which is where I want to run it most of the time for now. I'm thinking of seeing what I can do to get with the mid of the curve. Might just have to make a new carb and experiment.

How are stainless valves going to help with valve float? The only 2 ways to change that are heavier valve springs or lighter valvetrain components as far as I know. The former takes away some of your torque while the latter requires working with Titanium. Or maybe you know something that I don't?

If you are getting 9600 RPM with a 11x8 prop I think I would stick with that one. 9600 RPM is pretty much the sweet spot for that engine. You should avoid over 10000 RPM with 4 strokes