joco1

Ive been flying my alpha 60 now for a couple monthes with a os 61 fx in it and i recently purchased a os fl-70( its my first 4 stroke) if i switch the motors and put the 70 in place of the 61 what difference can i expect between the two and would the 70 work in this plane?

Nathan King

You'll notice less power with the 70 four stroke. The CG will also move aft (unless you shift the battery around) since the four stroke is lighter.

joco1

really i was thinking it would be a little more powerful! what would be a good plane to put the 70 in?

ChuckW

The 70 4-stroke is generally appropriate for 40 size airplanes. It will fly larger planes of course but performance might not be that great. The 1.5 rule seems to apply in most cases. Take the size of 2-stroke you'd normally use in a plane and multiply by 1.5. That will give you a general rule of thumb for an appropriate 4-stroke. It won't turn as many RPM as the smaller 2-stroke but it will generate a lot more torque to turn larger and/or more aggressive props usually generating a lot of thrust. The 4-strokes are also generally cleaner with less oil on the airplane at the end of the day.

bigedmustafa

My Feedback: (2)

The FL-70 will fly the Alpha .60 just fine. You might like it better despite being down on peak power versus the .60 FX. The FL-70 will power the trainer with plenty of authority, will sip fuel at a lower rate than the .61 2-stroke, and will be more quiet in the air.

I'd highly encourage you to try the FL-70 before making a final decision.

ChuckW

Good point. A trainer is a lot different than something more aerobatic. You just don't need tons of power.

joco1

yea i think i will try it if for no other reason ive never even heard the sound of a 4 stroke !!

bigedmustafa

My Feedback: (2)

You'll be shaving 5.3 ounces (well over a quarter pound) of weight. You will most likely prefer the way the Alpha .60 flies with the lighter wing loading. Make sure you rebalance the plane before trying to fly it with the FL-70, though. A nose heavy plane flies poorly but a tail-heavy plane usually flies only once.

You'll also want to be careful about letting other folks fly your Alpha .60 w/ the FL-70 engine. Once folks get a taste for how well that combination should fly, they'll all want a turn and you won't get any stick time. The more I think about it, the better I think that combination will prove to be in the air.

Campgems

I think that you will find that while the motor weighs a little less, the mass of the motor will be furthur forward by about an inch, so it should balance out OK. If not, it will need less weight. On my four stroke, if I have to add weight, I use long screws on the front two motor mount lug holes and use 1/8" lead sheet (left over from some roof flashing) and make a U shaped piece with ears to go under the engine. Make them about 1/2 to 5/8 wide and each piece will add about 1 oz or more. Put a washer over the lead and then use a nut with thread lock on it. Just snug it down and the thread lock will keep things in order. That put the weight as far forward as you can get withoug adding weight to the crank shaft. I've used this on three planes now and have had very good luck with all three.

Don

PS, you will love the four stroke. Swing a 14x ?? prop. I like the low pitch ones as the acceleration is awsome and the breaking action on throttle down lets you keep up good airspeed on final and then put on the brakes when you cut throttle. If you get into trouble, just punch it and the four stroke will haul you out in a flash.

Jetdesign

My Feedback: (8)

For your next plane you can get the U-Can-Do 3D. It's perfect with a four stroke .70. Very gentle flying plane with 3D capability. Floats in for landings at almost zero speed.

MinnFlyer

My Feedback: (4)

Get a Graupner 12x7 prop for that thing and you'll love it!

You've never heard the sound of a 4-stroke??? Prepare to fall in love!

RCKen

My Feedback: (9)

Mike is absolutely right here. 4-strokes are very addicting!!!!!!

Ken

chashint

There is going to be a big power difference between the 60 2 stroke and the FL70.
The largest recommended prop for the FL70 is 13x6 and it is doubtful that it will turn over 9k with that.
The 60 2 stroke should be spinning a 12x6 at 13k or more.
There will be no power / torque advantage at all for the FL 70.

Campgems

Charlie, I am cranking a 13x4W APC on and O.S. 52 four stroke at 9600. I think you need to revisit your numbers.

Saying that "there is not power/torque advantage at all for rht FL 70" is only half right. HP, will be higher on the 60 2 stroke. Torque will be higher on the 70 four stroke.

You have to ask yourself "how am I going to use the power". If your answer is to make a lot of anoying noise and go really fast, by all means get a 2 stroke. If you have a plane the flys slow, IE a lot of the light 3D planes, the four stroke is a much better match. I've got that O.S. 52 on a Phoenix Fun Star which is a 40 sized 3D. I have to fly at 1/2 throttle or less. Even the manual warns against Full throttle.

I've also got a verison 1, quicke 500. It had an O.S. 40 on it when I got it. Wow what a hand full for a rookie. I pulled it off an put an Satit 45 on. What a disapointment. The match wasn't there. Ive now got an O.S 46 on it but have yet to fly it with that engine. I cracked a patch job on the LE that I didn't know was there, and haven't got it fixed yet.

A 2 stroke is the right answer for some planes, the four strokes for others.

Don

chashint

Maybe he will post to the thread again after he tries the FL70 to let us know how he likes it.
I am not trying to argue against four strokes I am a four stroke man all the way.
However if I replaced a 60 two stroke with a 70 four stroke the plane would feel extremely under powered to me. A 91 four stroke is much more comparable to the 60 two stroke.

Campgems

Charlie, I know what you mean about feeling different. I totaled out my 4*60 with a Mag 91 a few weeks back. I though I would try a 40 size 3D and one of the guys has a Pheonix Fun Star that he really likes so I got one. I dug out my remaining O.S .52 four stroke and put it on. It just sounded awful. No power at all. I did a couple quick adjustments on the carb and then finally pulled out the tach. The thing was running really well, it just didn't sound as healthy as the 91 did.

I think the 70 will be a little under powered from the 60 two stroke, but not by much unless he is looking for a rocket. It depends where on the power curve he want's to fly. Mid range, the 70 should hold it's own. Top end, the 60 will win hands down.

Don

Deathbunny_SG

My Feedback: (6)

My alpha 60 (with evo 61) didn't need more then half throttle once I put a real prop on it. While the 70 4 stroke is underpowered to the 61 2 stroke I think the 70 4 stroke should fly it very nicely. You might even get to use more then half the throttle stick, crazy concept I know

ChuckW

The FL-70 is a good motor but not a great match for the U-Can-Do. FL-70's use a carburetor with an air bleed idle circuit. This means fuel supply is constant at idle and the mixture screw controls an air bleed to adjust the A/F ratio This works OK upright or side mounted but it easily floods when upside down and difficult to get it idling right due to a constant rich condition. Maybe altering the tank level would help but that isn't always easy in an ARF. The discontinued 70 Surpass-2, the new alpha series .81 or a Saito .72 will not suffer from this since they use a more standard carb design.

As for joco1's Alpha, the more I think about it, the more I realize it will work fine. I have seen plenty of 40 size trainers with .52 4-strokes. They have plenty of power so the .70 should do fine in the 60 size plane. The smaller engine wouldn't be ideal in something more aerobatic or a warbird of course; good enough for the trainer though.

Bob Mitchell

What prop are you using? 11x7? 12x6?

I bought extra props when I got my 60, and I'm down to one spare at this point. I'm going to a 2 blade as soon as the last 3 blade expires.

Deathbunny_SG

My Feedback: (6)

I think it was a 12x6 apc but when I sold the alpha I gave the guy the spare props I had for it so dont quote me on it. The 3 blade prop that comes with it SUCKS. It is very good at making it fly slow but thats all its good at lol certianly not good at producing thrust. A normal 2 blade prop will realy wake that engine up you wont believe the difference.