Magnum XL RFS 91 Four Stroke (Full Version)

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brrzee -> Magnum XL RFS 91 Four Stroke (4/25/2008 10:06:05 AM)

Just wondering if anyone has had experience with this engine. I just purchased it from hobby people the other day. I am installing it in a SIG Skybolt biplane I am currently bringing back to life. Input or experiences would be appreciated

Thanks



w8ye -> RE: Magnum XL RFS 91 Four Stroke (4/25/2008 12:23:49 PM)

People are very well pleased with their Magnum 91 four strokes



MOTORMAN37 -> RE: Magnum XL RFS 91 Four Stroke (4/25/2008 1:30:52 PM)

They run allmost identically to the OS .91 surpass.[:D][:D]
http://www.rcuniverse.com/forum/m_2807824/tm.htm



Campgems -> RE: Magnum XL RFS 91 Four Stroke (4/25/2008 5:04:25 PM)

I've been flying one since Jan of last year in two different 4*60's, one of which is no longer with us. Close to seven gallons of fuel and it just getting time to check the valves. Nothing more than a click or two for major weather changes. Pull it out of the car, fuel it up and go fly. Just a great engine.

Just break them in per the instructions. Run them a tad rich. I run it about 500 rpm off peak. Three dead sticks in this time all in two days. I pulled the tank and replaced all tubing. Back in the air. No issues with the engine as long as you supply it with good fuel.

Don



brrzee -> RE: Magnum XL RFS 91 Four Stroke (4/25/2008 7:27:45 PM)

Thanks for the input, looking forward to getting it installed and running. As well, what sort of glow plugs are you running?



Campgems -> RE: Magnum XL RFS 91 Four Stroke (4/25/2008 7:35:30 PM)

O.S F plugs are the only thing to run in four strokes. At least that is what I'm told and what I've used. Actually that isn't so. I tried a fox and another brand in an O.S. 52 surpass and finally settled on the O.S. F plugs.

I also use Omega 15% Fuel. I tried the Cool Power and wasn't happy with it. Expecially after it ate the pickup line on my filling pump.

Don



brrzee -> RE: Magnum XL RFS 91 Four Stroke (4/25/2008 7:45:42 PM)

I heard that as well about people trying to only run an OS glow pug. Sorry for the all the questions, but what sort of engine mount is recommended as well?



Campgems -> RE: Magnum XL RFS 91 Four Stroke (4/25/2008 9:11:29 PM)

I highly recommend these

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXD630&P=SM

They take up a lot of shock of a prop strike and I fully believe that they have saved several of my engines as a result.

Just make sure when drilling for the engine, that you allow for the head of the socket head screw, lock washer, flat washer, and at least 1/8" to clear the carb. I screwed up my first by posistioning the engine to far back on the mount and when I screwed it to the firewall, I couldn't screw down the engine.

Don



r2champion -> RE: Magnum XL RFS 91 Four Stroke (4/25/2008 9:21:36 PM)

I have about 6 flights on my Magnum 90 4-stroke since the breakin using 1 tank and couldn't be happier. It was also my first 4-stroke and I think I made a wise choice at that. It couldn't be easier to start and just purrs right along with plenty of power, idles extremely well. I am very satisfied with it. I also use the OS F plug.



MOTORMAN37 -> RE: Magnum XL RFS 91 Four Stroke (4/25/2008 9:27:17 PM)

Any engine mount that is designed for a .91 fourstroke will work just fine. The Dubro mount is over kill and not needed for a .91.[)]



Ed Cregger -> RE: Magnum XL RFS 91 Four Stroke (4/25/2008 9:35:17 PM)

I have used the Dubro iso-mounts with 1.40 and 1.60 sized gasoline engines, such as the RCS 1.40, MVVS 1.60 and the Evolution 26GT. Come to think of it, I've also used the same 1.20 size Dubro mount with a Poulan 46, BME 44 & .50 and a Super Tigre G2300 (1.40).

I see that the price has come down a tad. For a while, they were selling for $30 plus.


Ed Cregger



asmund -> RE: Magnum XL RFS 91 Four Stroke (4/25/2008 9:53:01 PM)

I love mine to death, it is my most used engine and serves duty in my Katana profile and does tailtouches on a regular basis, GREAT engine!!!!!!



Ed Cregger -> RE: Magnum XL RFS 91 Four Stroke (4/25/2008 10:09:28 PM)

Back on topic.

I love my Magnum engines too. For me, it is a tie between the Magnum .52 and .91 four-strokes. Both are sweet running, dependable engines.

Just follow the break-in instructions and be sure to use fuel with at least some castor oil in the lube mix.


Ed Cregger



rlmcnii -> RE: Magnum XL RFS 91 Four Stroke (4/26/2008 12:51:02 AM)

Campgems,

I have been assisting an older fellow I know who is getting into RC. His entry plane is a Sig Kadet Sr. powered by a Magnum .46 two-stroke. It was my first, first-hand experience with any Magnum engine and it was a very pleasant introduction to these engines. We broke it in and got it tuned today. It runs very well.

Like any RC'er, this fellow is planning his next airplane and wants to go with something low-winged and a little more sporting. My suggestion to him was a 4* 60.

He also shows a bit of interest in a four-stroke engine and, because of his good experience with the .46, would be happy with another Magnum.

So, did you encounter any mounting or weight-and-balance problems with the .91 in your 4*? My thinking was that the .71 or.72 (whichever) may be a little low on power for this plane. I fly a Bruce Tharpe Venture 60 (fist cousin to the 4*) with a Saito .82. The .82 is fine but the plane could stand a bit more power. It flies very well but does not have unlimited vertical capability but then, neither do I!

This fellow probably will not want an over-powered plane, so if anyone has experience with a 4*60 with the smaller Magnum four-stroke, please don't hesitate to chime in. (Perhaps this thread will tolerate a wee touch of highjacking.)

Thanks in advance.



Campgems -> RE: Magnum XL RFS 91 Four Stroke (4/26/2008 4:42:16 AM)


quote:

ORIGINAL: rlmcnii

Campgems,

I have been assisting an older fellow I know who is getting into RC. His entry plane is a Sig Kadet Sr. powered by a Magnum .46 two-stroke. It was my first, first-hand experience with any Magnum engine and it was a very pleasant introduction to these engines. We broke it in and got it tuned today. It runs very well.

Like any RC'er, this fellow is planning his next airplane and wants to go with something low-winged and a little more sporting. My suggestion to him was a 4* 60.

He also shows a bit of interest in a four-stroke engine and, because of his good experience with the .46, would be happy with another Magnum.

So, did you encounter any mounting or weight-and-balance problems with the .91 in your 4*? My thinking was that the .71 or.72 (whichever) may be a little low on power for this plane. I fly a Bruce Tharpe Venture 60 (fist cousin to the 4*) with a Saito .82. The .82 is fine but the plane could stand a bit more power. It flies very well but does not have unlimited vertical capability but then, neither do I!

This fellow probably will not want an over-powered plane, so if anyone has experience with a 4*60 with the smaller Magnum four-stroke, please don't hesitate to chime in. (Perhaps this thread will tolerate a wee touch of highjacking.)

Thanks in advance.



The 4*60 will usually build tail heavy. With my first one, I used 5 1/2 oz of 5/8" sq steel bars behind the stock motor mount, the battery stuffed tight to the firewall and it was still a bit nose lite. Withe the second one, I used the Dubro mounts http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXD630&P=SM This moved the engine out just far enough that I got a slight nose heavy and after flying a while, moved the battery back about mid wing. This has worked very well.

One of the guys had one with a Saito 82 on the stock mounts and he need something like 10 or 12 oz to get it to balance out OK. I would think the lighter engines would end up requiring a pound or more at the nose. My feeling is if you have to add weight make it work so the Mag 91 on the Dubro mounts was the answer.

As for overpowering the plane, the 91 with a 14x4W apc prop pulls like a tractor. I seldom fly at more than about 3/4 throttle and the plane will putt around eaisly at 1/4. If you get into trouble though you have the reserves you need. I wouldn't go with anything less. You can always set the servo throw so you don't get full throttle. The plane will happly take off at just over half throttle and still have a good climb rate.

I really like the 4*60 / Magnum 91 combo. I will offer some advise on it though. Go with a Kit vs the ARF. There are acouple of areas that need re-enforcing and it would be a shame to have to tear off the coveing to get to the. They are quite easy when building, but a real pain after the plane is completed. I know because If found these weak points on my first Solo flight. I came in to low and hit the farm road that runs across end of the runway and broke the fuselage in half just behind the wing and ripped out the landing gear mount. It looked bad but I soloed and was certified a couple days later with it. Band aids and all.

Don



submikester -> RE: Magnum XL RFS 91 Four Stroke (4/26/2008 7:41:29 AM)

4*60 and a magnum 91 is a great combo I have a buddy who has that setup and he can fly for a half hour nearly on a tank of gas. It's crazy.

I have a 4*40 kit I hope to start on this year and I plan on putting a Magnum 61 RFS in it. Should be a perfect combination as well.

I'm just getting ready to start breaking in my third Magnum 91 RFS this weekend hopefully.



The Raven -> RE: Magnum XL RFS 91 Four Stroke (4/26/2008 10:53:49 AM)

I'm very happy with all my Magnum/ASP 4 stroke engines. To date the only issue I've had is one bearing replacement in an 80, which was my fault due to poor storage after running it in.

The 61 is a nice powerhouse
The 80 is pulling my P-40 around nice and scale like, although I probably should have used a 91 in that plane.
A spare used 80 is awaiting an Me-109
A spare new 61 is waiting.....for something, maybe a twin
A 91 is ready to go into a Dago Red Mustang and,
The 120 is fitted to the Zero I'm assembling now.

Many guys in the club use Magnum/ASP 4 strokes because of their reliability and low price. Powerwise they are probably 5-10% down on an equivalent OS but size for size they'll pull any plane around nicely.



rlmcnii -> RE: Magnum XL RFS 91 Four Stroke (4/26/2008 2:03:36 PM)

Campgems et.al.,

Thanks for the reply and the information about the 4* and the engines.

I did not realize that the 4*'s had a tendency to build tail-heavy. It certainly seems a lot better to use an engine or batteries for balance rather than lead. That answers my concerns about the .91 being too heavy for the airframe. Ventures apparently build a bit lighter in the tail. With the Saito .82, the three I have built will balance just by using battery positioning. (BTW, two of these are still in use. The first one was lost to the rigors of RC re-entry.)

I will let this fellow know about the shortcomings of the structure of the ARF. Planes this size don't take too long, and are not difficult, to build. Perhaps he will want to get into some building also. He'll be able to cover it in a color scheme that will facilitate discerning top from bottom!

Thanks for the information about the fuel efficiency also. I know that a well-tuned Saito will run on practically no fuel and it is good to hear that a well-tuned Magnum performs as well. Probably all 4-strokes, when well tuned, are very efficient. That is certainly true when they are run at less than wide-open throttle.

To be perfectly frank, I had a tendency to shy away from Magnums, probably because of their price. In many instances one gets what one pays for in this case, one may get a little more. Nothing quite as nice as a pleasant surprise.




panzerd18 -> RE: Magnum XL RFS 91 Four Stroke (4/26/2008 3:25:25 PM)

I have a brand new one waiting to go into a World Models Extra 300L 60-90. I am going to use the recommended 14x6 prop.



MOTORMAN37 -> RE: Magnum XL RFS 91 Four Stroke (4/26/2008 3:32:46 PM)

Rlmcnii,
You have really been missing out, if you have been staying away from Magnum 4 strokes. You cannot tell the difference, if you have the two side by side. They run identical, and in alot of cases posted here on RCU, they can even be stronger than the OS in the casse of the .91.[)][)]
When I bought 3/4 of a dozen of them two years ago, I bought them for $119.00 each shipped to my door. You had to buy each one seperate when they were on sale for $149.00 and use a $30.00 coupon off of a $149.99 order. So every box came with a $1.00 trinket in it too.[)]
I have sold all of my Saito's and OS's, and only run Magnum's and YS's.[)]



Campgems -> RE: Magnum XL RFS 91 Four Stroke (4/27/2008 12:08:10 AM)

Looks as if I get to do some off those "if I were to do it again" things on the 4*. I totaled mine this morning. I was flying a little earlier than normal and on final, I got a little disorented as you were looking under then sun when on final. I'm still not sure exactly what happened but I believe I was to slow. I mand my final turn to soon and then tried to correct and when I turned into the wind, I was slow enough that it stalled. I was still up about 75 ft and no response. Nose over and straight in. I haven't checked out the radio yet, but there is a small crack on the receiver case. The carb mount on the back plate broke, so I need a new backplate. I guess I'll do bearings also as it has a lot of hours on it and this is it's second really hard crash and blew apart the aluminum spinner back plate.

Those area's that needed re-enforcemnt held up well. Still, there wasn't much left. The wing center is crushed. I hit exactly perpendicular to the ground. It pushed the LE of the wing at the fuselage back about 1 1/2" inches and the TE around the screw late also is ripped up. I lost the LE on the two outer bays on the right wing. No rib damage that I could see. The fuselage was destroyed from the wings forward and there are cracks and blown out covering all the way to the tail wheel. It even pulled the vertical stab free from the fuselage and away from the horz stab, It ripped off the lower rudder hinge.

I'll post some photos of the engine later as I start to take it down for a cleanup and bearing replacement. I'll bet that when I get it back together, I don't even have to adjust the carb. We'll see.

Don




brrzee -> RE: Magnum XL RFS 91 Four Stroke (4/28/2008 2:13:05 AM)

The old motor mount in the Sig Skybolt was a sig. I am hearing though that you can use a Saito as well or Dubro like some of you have said. I think the .91 will be perfect for the skybolt. I am also thinking of installing a smoke system in it as well. The previous owner had a smoke system in it, with the Magnum .91 and said the plane was great! Did not fly to great when he ran it out of gas at a fun fly and pancaked it into the ground though...Oh well hopefully the rebuild will be a success.



TEBerg -> RE: Magnum XL RFS 91 Four Stroke (8/8/2008 11:13:29 PM)

I'm just completing the break-in on my Magnum 91FS..

Running an APC 14X6 and 10% Omega (synthetic/castor) fuel for break in.. I ran the recommended amount of time turning in the needle per the instructions. Then I moved the engine to inverted and finished the gallon of Omega and leaned her down to 1 turn open on the way.

I went 15% today.

At 1 turn open, the tach showed 8,700 on the 10%. I had some 10% left and tried to run 1/4 tank through the engine (on the test stand) and she would run the prime out but not pick up the fuel. Filled the tank to 3/4 full with 15% and she started right up and ran at 9,000 with just a little sag/worble on occasion. Finished the tank and let her cool..

Next tank I went to lean her out to find max RPM.. 3 clicks gave me 9,300 RPM, three more gave me 9,800; then one more over-leaned the engine. Backed off the needle, let her run cooler and tried again..

I ended up with the following: At 3 clicks lean from 1 full turn out gives me a nice 9,300 RPM running an APC 14X6 prop on 15% Red Max Synthetic Fuel..

I'll try this all again on the plane (Global Skyraider warbird) again and also check to see if I can get a slow/reliable idle. I'll also try the Master Airscrew 14X6 to check max and min RPM to see which the engine likes best.. Then I just have to double-check that below 1/4 tank in the plane I still get good fuel pick-up at idle or during transition..

Any feedback on the idle performance/transition of the MA K-Series compared to the APC on this engine???



XJet -> RE: Magnum XL RFS 91 Four Stroke (8/9/2008 12:23:05 AM)

Despite its greater blade area, the Mas K-type will usually put less load in the engine than the same-sized APC so you should get more RPMs

I prefer the MAS K-type on 4-stroke engines because it's tougher, a little heavier (smoother idle) and with a 14x6 you ought to be able to "rip" it in straight/level flight for that really cool sound and they're far more durable (especially when flying from tarmac).

Of course if noise is an issue at your flying field you may find that you'll be stuck with the APC because they're a lot quieter.



Campgems -> RE: Magnum XL RFS 91 Four Stroke (8/10/2008 8:00:39 PM)

With your engine as it now stands, make sure your are at least 400 RPM to the rich side of peak, but 500 to 600 would be better at this stage. The Mag four stroks take a long time to break in, and even though the manual may state 1/2 gallon of fuel, 1 1/2 to two is more like it. If you are running at, or near peak, you are going to overheat the engine and shorten it's life. When it unloads in the air, that 400 RPM on the rich is your buffer to prevent this.

I've got two of the engines, one yet to be run, but probably a case and a half through the other. It has survived two 4*60's and it never once gave me any problems. Running a little on the rich side keeps them performing like that.

Don



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