I just bought my first plane. It is a Hobbico superstar with an os 40la. The plane had never been flown or started. I have never flown an airplane. I took it to my local club to get some training. The instructer tried to take it for the first flight but couldn't get it off the ground. We tried bigger tires and a 10 6 and a10 5 prop. He said the motor is fine for the plane but the grass runway was slowing it up too much. He suggested I try again when the grass starts thinning or go with a bigger motor. I don't want to have to worry about checking the runway each time before I fly. He said it's kept at about 1.5" I'm running 15% nitro. Is getting a bigger motor the best choice, or do I have other options,ie fuel,prop? Thanks-Andy</p>

I have run several trainers with the LA .40 and it really is under powered for even a 40 size trainer, I'm flying on hard pack too. I get away with using them but it isn't my first choice. You can try a prop like an 11X4 APC, maybe some bigger foam tires. Fuel isn't going to help you at all. Bigger engine is maybe the best choice.
If I had my way OS would stop making the .40 and just have the .46. The difference between the two engines is night and day. You wouldn't think so but that little bit of size difference makes a big change. There are also a lot better choices in the cheaper engines then the LA series.
If your going to be flying from A GRASS FIELD YOU MAY WANT TO LISTEN TO THE REGULAR PILOTS THAT FLY FROM THAT FIELD. tHEY KNOW THERE HOME TURFF.

Iunderstand the 40LA is very underpowered. Iwould say a 40 size trainer will be much happier with a high power 40 like a Thunder Tiger Pro or even a Thunder Tiger GP42. But if you have the money a good 46 would be a great idea.

Thunder Tiger Pro-46 with an 11 x 5 prop.

Andy,

It is difficult but no impossible to make a tri-gear trainer to take-off from less than perfectly trimmed grass with an OS LA 40.

If you need to keep your LA 40, you could do as I did:

I was doing it for a while, but just after I replaced the stock wheels by lite (foam) type 3" diameter for the main and 2-1/2" diameter for the front wheel.

I also had to change to a 11x5 APC propeller, and hand to extend the gear down so the prop's tips clear the grass.

The location of the main wheels respect to the CG (assuming the CG is properly located per manufacturer's instruction) should be close enough as to facilitate the rotation of the plane when you input elevator up during the last phase of take-off.
It is also very important to beef-up the gear, so it does not bend towards the tail during take-off.
With the fuel tank empty, the plane should turn nose up with a light push on the tail, and then return to normal position by itself after release.

In normal take-off position, the wing must have a small but positive incidence angle respect to the ground.
If not, sliding the front gear up or down, can achieve that attitude for the wing and fuselage.

As stated above, any experienced pilot of your club know how to check those little but important details.

Read this article:

http://masportaviator.com/2006/08/09...d-up-part-two/

I have 2 Superstars, and 10" is the max you can run unless you extend the front gear and ran a little bigger tire. If you can get the front up a little bit, I would try a APC 11x4 or 11x5.

The LA 40 is the best running, easiest to tune .25 sized engine I ever owned.

I fly this airplane off desert hardpan and gravel with a well used LA-40 and a 11x4 prop, with no problems.

The trick is reducing the friction between the airplane and the ground for takeoff and in my case I stick some wheels between the two Now what you need to do is reduce that friction between the airplane and the ground, just use big old wheels the biggest you can fit.

Big wheels, APC 11x4 and you will be fine.

The simplest fix is to install a .46LA and save the .40LA for another smaller plane down the road. The .46LA is built on the same crankcase as the .40LA so it will bolt right in and, yes it is much more powerfull. It weighs about the same (.1 oz lighter) so C/G won't change but you should check it anyway. Your observation of an "under powered" problum is valid when flying this aircraft/engine combo off grass that in any longer then a putting green! The other suggested engines will also fix the power problum but may not be as direct a bolt in replacement as the .46LA will be. Changing props or wheels still using the .40LA won't fix it, "been there done that !"

Go ahead and install larger diameter tires WITH the engine upgrade, this will help get the prop up a little higher and not cutting as much grass on your takeoff run as grass cutting slows down the engine RPM as well as the aircraft itself. Remember for each 1 inch of tire diameter increase you only gain 1/2 inch more prop clearence and if you go from a 10" prop to an 11' prop you just lost the grass clearence gain from the bigger tires. Your back in the grass cutting business! Do engine and tires but stay with the 10' prop as these planes have short landing gear (well you could build new longer mains and nose gear too and then use an 11' prop). It dosen't end does it ?!?!

Andy your obvious next step is bigger wheels and an 11x4 prop before you go off buying another engine just yet, good grief.

John

On my LA 40s , Fp 40s and all the others I use the APC 11 X 4 prop for the thrust. We are on grass. One thing not mentioned is to have the airplane sitting so that the wing is at a positive angle. We have had newbies, and not-so-newbies, with BB 45s and 46s on their trainers who can't get off the ground when the wing is at a negative angle.

I do not have that particular trainer, but do have 2 Right Flyer 40s, and an Eagle 63. All take off just fine with my bushing, airbleed carb .40 engines.

Ken Erickson

John says "good grief" start with big wheels and a 11x4 prop and from a cost standpoint he is right. However, as I pointed out the landing gear is short on a Superstar 40 and the 11' prop puts you deeper into the grass cutting business but go ahead and try it, not much money involved in a prop and tires. Save the engine upgrade for step #2. I'll bet you still need the enging upgrade, but of course I'am not always right! I know from having flown this combo that once in the air the .40LA will fly the airplane just fine, it's just a problum getting airborn with tall grass. Give us some feedback after swaping tires and prop.

Most modelers don't realize just how much improvement can be achieved with a simple propeller change. You want to prop this engine to reach at least 12,000 rpm on the ground so that it is closer to it's peak power. Going to a lower pitch larger diameter will make it pull harder on the ground so it will accelerate better to flying speed.

I agree with John, Ken, Grey Beard, and others. Try the 11-4.

Bigger diameter tires too.

If none of that works, hand launching always does.

You could also try a 10 x 5 prop. Why go to 11"? I'd normally run a .40LA with a 10 x 6 prop.

Actually the OS LA 40 was discontinued almost 2 years ago and only the OS LA 46, 25, and 65 is being offered now. Tower still has parts available for the LA 40.

Maybe that's why I keep getting them in trades?? I don't buy or use the smaller engines these days except on trainers. The .40 is a good running engine but I had a lot better luck with the ,46.

Hi!
The OS LA 40 can swing many different props sizes. But a 10x6 is too small for the average high winged trainer (150-160cm in span).

A much better prop size is a 11x5, 11x6 or 12x4 APC or RAM prop. Do not use the white tipped MA props though!! Those are the worst props on the market performance/sound wise.
A 11x4 could be used but is not that suitable for a high winged trainer powered by an OS LA .40 engine at sea level. I use props that size on our clubs two trainer airplanes powered .28 two strokes.

Iran a 10X6 Scimitar on my (old beat up heavy) PT-40 with an Irvine 40 and it flew awesome. Lots of power , so Iwould think the LA40 would be fine with one just a little less speed and power.
Ibelieve the 10X6 is the go to prop for .40 size engines.

You might get someone to help you to change the landing gear configuration. If you could eliminate the nose wheel and move the main gear so that the wheels' axles are at the leading edge of the wing (plane level) and mount a tailwheel to the rudder these modifications would reduce the ground and airborne drag and lighten the airplane a little. This small weight change will improve the performance, too! It's a little 'testier' learning to take off and land but once learned- never forgotten. The next thing to consider if the prop/ wheel changes don't help and you don't want to modify anything is a larger engine. I'm partial to the 4- strokers. You will most likely want another airplane and an engine on hand dictates your choice in airframes in many cases.

A friend and I have Twinstars, he uses the 46LAs with 10-7 props and I power mine with 40LAs 9-7 props. His plane is only 1-2 mph faster than mine. Its a good thing that the LAs use little fuel, we have to land after only 10 laps.

The problem with using much more propeller than a 10 x 6 is RPM. The .40LA should be propped to turn in the high 11,000's. Many propellers used today are suggested by the manufacturers for noise reduction, but don't always allow the engine to develop good power.

Depending upon the trainer, you'll need a different prop. However, get the engine turning up in its best RPM range and THEN choose the prop that allows the engine to turn up AND fly your model well. If it's an 11 x 5, a 10 x 6, a 10 x 5 or a 9 x 7 or 8...who cares? It's how the plane flies when the engine's running correctly.

You should be able to take a .40 sized plane off with a .30 engine, so the LA should be enough.  However tall grass is another thing.   Does your club not mow the grass short?  They should be.  If the grass is short, then is the engine performing?  You should be fine with 11,000 RPM on a 10-6.  An 11-4 prop would be better from grass.

Also the plane and technique.

Make sure the wings are level with the ground front to back when resting on its gear, or just very slightly down.  Too much down force and it may have too much drag to take off, and when it does it will leap off and could stall.  If the leading edge is higher than the trailing edge it could take off prematurely and stall.  The stall could be at a very low altitude like fractions of an inch, may give a hopping effect. 

For the take off technique on grass or dirt fields.  Be sure not to use down elevator during the take off run, this will cause aerodynamic drag on the wing, and cause the wheels to dig in, both will slow the plane down.  Also do not use up elevator as this also caused aerodynamic drag.  Just keep the stick in neutral.   In fact keep it in neutral till it lifts off the ground, or appears to be at max speed ready to take off.  Now pull the stick back ever so slightly.  When off the ground ease up on the backpressure on the joystick.  Let the model level off and gain airspeed.  After it gains airspeed increase backpressure till it is in a normal climb.

Testing testing testing, start at a baseline and go both directions until you find one that makes it do what you want .

Something doesn't seem right here. My 7-1/2 pound LT-40 takes off in about 150 feet with an LA-40 and that's in tall grass, using an APC 10x6

7.5 lbs LT-40? where did the extra 2 pounds come from? Payload?