nexxa

It almost done. My Great Planes P51. It's a .40 size. I build it strong and right.
I want to install my OS.91 FX 2 stroke on it for speed.

For extreme speed on this kind of engine, what is your prop suggestion. The plane weight 8.2 pounds (with the engine, gear, retract, pump....)

SitNFly

My Feedback: (54)

I use a 13x8 on mine. I imagine for speedburning you'd try a 12x9, or 11x10 if they are available.

nexxa

Thanks. Do you know your engime RPM with a 13X8 on?

SitNFly

My Feedback: (54)

Sorry, haven't tached it in a while. Somewhere in the mid 10's, though.

speedster 1919

My Feedback: (3)

Best 90 size prop is the 12x8 MAS K prop. Better ground clearance too.

Cyclic Hardover

My Feedback: (3)

APC makes an 11/11. I have a couple. I have built a few of these for myself and buddies. Run the 61 fx and does real good. My current one is the WM .40 P-51 with a Saito 100.

Kostas1

Sorry,
but don't you think that it will be overpowered?
This engine (I have my new OS 91FX ready for installation on my Corsair 60size),
will bring the wing loading too high.
With all the negatives from that.
That's my oppinion ofcourse.
If i was supposed to decide for an engine in a 40size plane (that i want to squeeze alllll speed from it ),
personally,
i would go with an OS 50SX ( APC 10x6 ) or an OS 61FX ( APC 10x6 again ).
And you can use your engine on a nigger project.
Enjoy,
Kostas.
Greece

MJD

My Feedback: (1)

Ditto on that suggestion. You can always mail order them form APC if they are not at your LHS.

I HOPE you meant "bigger" [X(] ! The "b" and "n" are right next to each other.. easy mistake.

Overpowering is the whole idea! Why would you use a 10-6 prop for speed? That's a general purpose prop. If you want fo go faster on a .45-.50 size sport engine, then 9-7, 9-8 would be places to start, or 8-8/8-9 on a small clean aircraft (which a P-51 is not). RPM + pitch = speed.

MJD

Kostas1

Yes,i meant bigger,duhhh.
Yes,if you want speed you must go down on dia and play with pitch,but i think there is no reason to try this with a 91FX!!!!
Way tooooooo BIG i think.
I mentioned in my previous post for wing loading,what do you say?

SitNFly

My Feedback: (54)

Kostas, go take a look at the Jett Engineering site in the Hall of Fame area. There is a picture of a 40 size GP Patriot with a Jett 90 mounted in the nose. More power is gooooood!

Kostas1

Ah,not always.
I have a different oppinion and i told you that overpowering a 40 size model with a 91FX will not be good.

Cyclic Hardover

My Feedback: (3)

It'll be just fine. I ran a WM 40 size with a G90 for 2 years and it was a nice plane. Wing loading? Maybe a little but the wing loading is high
on these things anyways. Shoot my Saito 100 flys great in my other WM 40.

The green one here was about 7 years ago. Its the WM 40 with a G90. Lasted two years and succumed to battery failure and flew off into the South 40. The other is my current WM 40 Miss America with a Saito 100. They really do fly well

You want to see what "overpowered" flys reliable? Click on "My Models". I have had most of those planes for a few years and fly just fine

Kostas1

That's my oppinion,
that's your oppinion,anyway.
I mentioned what i am thinking.
Personally i wouldn't waste my 91FX for a 40 size model P-40.
If i wanted speed -S-P-E-E-D- i would buy a pylon racer or a deltawing.
Enjoy.
Kostas

Cyclic Hardover

My Feedback: (3)

After owning and returning two 91fx's, I would not own or reccommend that engine when a G90 is equal and much less in cost.

Kostas1

Ahhh,
very sad,
really sad to hear.

Cyclic Hardover

My Feedback: (3)

I don't want to make myself sound "anti OS" here . I have owned or have most engines they make and happy with them all except that 91. I have no confidence in it at all. So with that, my general sport engine is several G90's with no complaints

buzzingb

My Feedback: (2)

I think the 91 will turn the 40 size into a great sport flyer. I currently run a 61FX on a somethin extra and love it. The 91 is about the same weight as the 61 but with a little more power. The somthin extra can easily handle the 61 and could handle a 91 if I had one to install. If you don't need the power with the 91 use the throttle.

Kostas1

I'm not gonna give you more facts that you will have problems using the OS 91FX in a 40 size model.
YOU WILL HAVE PROBLEMS
And if you'll try it i don't want to see it.
Anyway.
It is sth like trying to fit a Ferrari's engine into a VW Polo.
Just like that.

Cyclic Hardover

My Feedback: (3)

Well, Iguess he's right, the problems you encounter will be the same as any other engine you install in the plane.

ravill

My Feedback: (11)

I don't know about all the OS 91 bashing....

I own 6 of them and two have been inverted in WM 51's....Yeah I had problems....not enough fuel in the fuel tanks!

Take everything with a grain of salt. OS makes good reliable engines. I think everyone knows that they are certainly NOT the fastest engines out there!

Cyclic Hardover

My Feedback: (3)

Thats funny on the fuel tank. I have like a 16-18 oz tank stuffed in mine. I don't like to run out of fuel.

I never knocked the performance of the 91fx, just reliability. Like i said, I have darn near the whole OS line up and that engine is the only booger I ever had .

Hey, maybe if we install the ST carb???

MJD

My Feedback: (1)

You haven't given any fact, only opinions. Others here have described their success, and showed us photos of sussessful conversions. Those are more like facts. This forum is all about people who have done exactly what you say not to do, and they've done it successfully. Have you done it before and had problems? Then tell us facts about it. There are a bunch of people stuffing .90's into .40 size aircraft and having a ball flying it. You've made your point, you don't think it's a good idea. We get it!

Wing loading is what it is. If the aircraft comes out at an acceptable wing loading and the CG is where it should be, it doesn't matter if it has a .40, a .61, a .75. a .90, or a small block V8 in the nose (well maybe not the last one). Landing a properly balanced .40 size sport ship with a .90 in the nose is probably less difficult than landing a pylon racer.

Yes small deltas and pylon racers are inherently fast, but some people enjoy overpowering other aircraft designs - that's their choice.

MJD

Kostas1

Cyclic Hardover

My Feedback: (3)

Well, you have to hand it to Kostas, it's not the brightest move on paper but it works just fine. If you have never seen it done, it may sound rather stupid.

That .90 2 stroke or the Saito 100 or YS 110 is probably the limits here. With proper structural improvements, they hold up really well. TRY IT, YOU'LL LIKE IT

Kostas1

Yes,in this case yes,improvements are important are i think they are NECESSARY.

Also if you must add 10oz's on the tail to balance the model,this is just RIDICULOUS.