jim walker

I'm thinking of buying an Accel Katana GS 70 ARF. They say that inexpensive engines will fly it great on the website. Is this true? I'm looking at engines like the GMS .76, Tower .75, and the SK .80/.90. Will these engines allow me to do the entire 3D envelope with enough authority at my altitude (4000' ASL)? I really can't afford much more than these at this size. If these engines won't get it I'm going to get the .40 size and slap on a .46 AX though I'd prefer the larger 70 size.

Thanks for any and all input

Jim

Dewey2

My Feedback: (24)

The SK 90 might. If i was you I'd put a Super Tiger 90 on it, their a good running cheap engine. You also could build a moose can pipe, for even more power and throttle response.

jlobster88

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I would go with the Magnmum .91rfs 4-stroke instead of the Super Tiger .90. I know that it is more money but in the long run i think that the 4-stroke is the way to go. I have the Accel Katana .70 with the Magnmum .91rfs, This plane is a great flying plane, and has plenty of power.

jim walker

I'd love to put a .91fx or four stroke on this guy, there's just no way I could afford the whole package if I went that route. After doing some number research and reading some reviews I decided to go ahead and get the Accel GS 70 ARF and the SK .90. If there's any interest I'd be glad to post my impressions of this combo. If it does well out here in the desert at 4000' ASL it should be a real winner at lower elevations.

Jim

John Wells

My Feedback: (10)

Hi Jim, I live in K.C. at about 1100 feet. I'm using a ST 90 with m.c. mjuffler and macs header. Another local guy has the KAT 70 with ST 90 and factory muffler. Either will work well. If you decide to go with the m. c. muffler, get the macs long header, not the extra long or the short one. The ST 90 likes a short header with the can, so, chances are, you'll be cutting off a lot of that header. The reason for shortening it is throttle linearity. With a longer header, the 90 loads up a bit on low end. I kept chopping an inch off, and trying it again and again until I got it close. I have the extra long header, and I'm into the bend now. I really need to buy the long version (which macs didn't have when I wanted one) so I can cut some more length off.

The ST 90 is plenty of power for the KAT 70. I use an APC 15X4. When I ran the stock muffer, I ran an APC 14X4. If you are going to 3D a lot, try to get a good, linear throttle. I've seen these planes fly great with Saito 91's, and Thundertiger pro 61's. You picked a great plane, and it will no doubt, go down as one of the all-time favorites with a lot of the ProBros.

JW

jim walker

John,

Thanks for the encouragement! I assume you meant the same engine I'm talking about (Kangke SK .90 engine) when you referred to the "ST .90" engine. I plan on trying the stock muffler first, but if I feel like it's not enough power I will keep your suggestions in mind... thanks.

I chose the Accel Katana GS 70 after watching the video of it electrified at 6 pounds. It was seriously overpowered and floated like tissue paper. It looked like a breeze to hover and knife edged well. This will be my first large 3D plane, up till now I've only been flying electric foamy 3D planes. My skills have come a long way and I felt it was time to move things up a notch. Also I was tired of having to wait for almost dead calm days to practice hovering and torque rolling.

Thanks again,

Jim

Dave McDonald

My Feedback: (19)

The ST 90 that John was referring to is the Super Tigre 90. I've flown John's Kat 70 and it's a great match up.

My Kat 70 has a Thunder Tiger Pro 61 with a BCP*. Plenty of power, great throttling, and 100% reliable. Perfect for low level 3D flying!






(*Beer Can Pipe)

jim walker

Thanks for setting me straight Dave. I have a couple of questions then. First, what servos do you recommend for this plane. Second, can you explain these engine ratings they post. ST says their .90 has 2.5 BHP @ 14,800. SK says their .90 has 2.6 BHP @ 16,000 but then right next to that it says "practical RPM 10,400". What does it mean??? Is there any way to convert the numbers for a direct comparison?

Thanks, Jim

mnrcaerobat

My Feedback: (197)

Hey Mcddd. Let's see a picture of that beer can pipe. How does it hold up?

Dave McDonald

My Feedback: (19)

My Kat 70 started out with Futaba 9252 digital servos, but were later replaced with Futaba 9202 coreless servos. I liked the speed and accuracy of the 9252 digitals.....but didn't like the high current drain per flight of the digitals.

A buddy of mine is flying his Kat 70 with Futaba 3004 servos with moderate 3D throws and they seem to work well except during aggressive 3D flight.

I can't remember what servos John was using. Maybe he will post his setup.


BHP=(Torque)*(RPM)
If the amount of Torque changes, the BHP will change.
If the RPM changes, the BHP will change.

The only way to truly compare different engines is to plot out a curve of how much Torque each engine produces at a variety of RPMs. Unfortunately, the BHP figures published by the engine manufacturers are the MAXIMUM amount of BHP represented by a single point on this curve.....which is pretty much useless information unless the comparison is made with identical RPMs.

It's also important to note that knowing the maximum BHP of an engine doesn't tell you anything about how that particular engine will perform when operating at all other RPMs.


It means that the factory is trying to impress you with BHP information that has no real practical value......especially when it comes to 3D flight since the engine is rarely at full throttle.

For example, the ST 90 is rated at 2.5 BHP@14,800 RPM. But since we have no idea what the BHP of the SK 90 is at 14,800 RPM, there is no way to directly compare the BHP between these two engines with the information given by the engine manufacturers.

The SK factory apparently calculated that the SK 90 produces it's maximum BHP rating at 16,000 RPM. So what size prop would let a 90 size engine spin at 16,000 RPM? Maybe an 11x6? So they tell you that the "practical RPM" is 10,400 RPM.....which means the prop size should be selected to allow the engine to peak out at 10,400 RPM or less. It might help to know what the BHP is at 10,400 RPM, but the SK factory didn't publish that info.....and neither did the ST factory, so we still don't have enough information to compare the two engines.


No, not with the maximum BHP figures that the manufacturers usually publish.

Bottom line:
Don't put much faith into using the factory BHP ratings to compare different engines......and especially different brands of engines.


Works great!

Here's a link to a web site with some video of my Kat 70 with the BCP on the TT Pro 61. It's the last video at the bottom of the page. While you're there, be sure to watch the video of the Saito 91 powered Kat 70 flown by Gary Seeloff. (hey, who needs two ailerons?)
http://www.mmrca.org/ss2005/

markktm

My Feedback: (1)

I also have a Katana 70. almost ready to fly. What are good low range throughs.

mnrcaerobat

My Feedback: (197)

I like your beer can pipe, and would like to make one. It looks like a bottle, but a aluminum one. Are they still available?

depfife

My Feedback: (14)

I think they are still available is select markets. If you offer to pay for a full one, I am sure someone will volunteer to drink the beer and mail you the empty.

wahoo

My Feedback: (59)

I have a OS 61RF with a header and tuned pipe. The tuned pipe weighs 2.6 oz and all together 4.4 with header and silicon connector. I have never run the engine or cut the header to the correct length yet but was just curious as to the advantage of using a beer can over a premade tuned pipe. What does the beer can weigh ?

Thanks,
John

mnrcaerobat

My Feedback: (197)

That sounds ok to me. Someone let me know if you are interested.

Dave McDonald

My Feedback: (19)

An empty aluminum beer bottle weighs less than 2 ounces. By the time you install a piece of tubing to connect to the header, and an exhaust tube, the weight would be about 2.5 ounces. Therefore there is no real weight savings over a real tuned pipe.

The biggest advantage of using a MCP (or BCP) over the tuned pipe is the way the engine throttles. The throttling on a tuned pipe isn't very linear as the engine tends to "get on" and "fall off" the pipe during throttle changes. Since precise control of the engine RPM is very important during 3D flight, these sudden RPM changes due to the tuned pipe effect are very annoying to deal with. On the other hand, the MCP (BCP) can provide a similar power boost to a tuned pipe.....but without the RPM surges during throttle changes. The throttling stays fairly linear all the way from idle up to full power, and everywhere inbetween. This is why I vastly prefer the MCP (BCP) over a real tuned pipe for 3D flight.

mnrcaerobat

My Feedback: (197)

What did you install in the bottle for tubing? I assume you cut the header and installed that in the can. Can it be soldered in there?

wahoo

My Feedback: (59)

Thanks for answering my question but now i have one more.

What seamless container would you guys suggest for and OS FSR 90 ?

Thanks again,
John

Dave McDonald

My Feedback: (19)

Cutting off the end of the header works fine for the adaptor. I happened to have some aluminum tubing from the local hardware store that's the same size as the header, so I used it instead. The intake and exhaust tubes on the bottle in the photo were installled with some aluminum brazing rod called Alumiweld, but slow curing JB Weld works great too.

For the 90 FSR get a mousse/hairspray can that measures 2" diameter by about 10" long. This is the size can that I was using on my ST 90, and it's the same size that John Wells is using on his ST 90. An aluminum beer bottle is also about the right size for a 90.

Just keep in mind that the old OS 90 FSR is based on the same size case as the 108 FSR and is a lot heavier than the newer OS 90 FX, which is based on the 61 FX case. IMHO, the old OS 90 FSR would be way too heavy for a Kat 70.

wahoo

My Feedback: (59)

The 90FX weighs 19.5 oz mine weighs 23.5 I'm putting the FSR on the V2 which has an increased wingspan so i see no trouble whatsoever in using it.

And for whats its worth i wouldn't trade this FSR for 3 FX's


Thanks,
John

krayzc-RCU

My Feedback: (31)

had a chance to take mine out sunday i working on triming the girl out since its the 2nd time out to the field it was a windy day, i really think i am going to enjoy this kits if the wing doesn't snap. mine goes into a spin with full elevator on 3d rates is there somethign i need to mix in to stop this?

jim walker

Wow Dave, great video! Thanks for all the info as well. I guess I'm just going to have to try this engine and see what it will do since there's no way to figure it out from advertised data. The advertised weight for this engine with muffler is 26 oz. Does that seem too heavy for this airframe? Do you think a beer can pipe would benefit the SK .90? If you think it would, is the mousse can what you'd recommend for this engine as well? Are BCP's lighter than the stock muffler? Where do you get a header and that tubing that can withstand exhaust gases? Is your BCP mounted to the fuselage somehow? I don't see anything in the picture. Sorry for all the questions, I come from an electric background and am an accomplished pilot, but a glow newbie.

Thanks, Jim

TailTouch

My Feedback: (54)

Hi Guys.
I am selling mine either as completely RTF with Saito-91 or airframe only.

Check out the classifieds.

Thanks.

jim walker

I found the Macs header and silicone connector in a kit on Tower's site. Now I just need to find an aluminum beer bottle. Dave, what did you use to make the exhause tube toward the end of the bottle? What did you use for the fuel tank pressure take off? Do the positions of these tubes make any difference?

I received the SK .90 yesterday and it weighs 19.5 oz without muffler. This is comparable to the 90FX, but the stock muffler weighs a ton at close to 8 ounces. I'm motivated to make a BCP just to save the 4-5 ounces of dead weight! Better throttle response I agree is an absolute necessity for 3D as well and that's the other reason I want to make one. I'd appreciate any and all information you can give since this is new stuff for me.

mnrcaerobat

My Feedback: (197)

I looked around here and could not find the beer bottles at any local stores.