swap prop or replace engine?
 

I'm running a hand-me-down OS .40 FP (about 15 years old but with low hours) on my Tower 40 trainer swinging a 10 x 6 Master glass prop on 15% Cool fuel. The old .40 runs like a champ and starts every time but just doesn't seem to pull that well at full throttle. Take offs are a bit slow and touch and go climbs leave me wanting more out of the engine. Should I try a different prop or replace the engine? I've got my eye on a Magnum .46 as an alternate.

RE: swap prop or replace engine?
 

A ball bearing .46 will definitely provide more oomph but will weigh more and may require a rebalance for correct C of G. I'd try another prop first.

Get an APC 11 x4 and an APC 11x5 (and maybe an MA 11x5 and 11x6) prop and try those. They should provide more thrust than the 10 x6.

One of the guys at our field has an OS FP .40 in a trainer. He tried many different prop combos and ended up with the best overall performance running a Bolly 10.5 x 7 prop on his. It was far superior in thrust and speed to the MA 10 x 6 he started off with.

RE: swap prop or replace engine?
 

[whoops - duplicate post]

RE: swap prop or replace engine?
 

ASP 11X5 works well. I run that prop on an OS 40LA, a friend runs the same prop on his 40FP. Both these engines are on the WM Sky Raider Mach I trainer, great flying plane.

The Magnum 46XLS is a terriffic engine, certainly a lot more than is needed for a trainer, but keep it in mind for that "next" plane.

RE: swap prop or replace engine?
 

Drop down to a 10x5 prop and retune. You will be amazed at the difference.


Ed Cregger

RE: swap prop or replace engine?
 

....if you are going to stick with the MAS prop, go with a 10-7, or a 10-8 for better performance. ;)

RE: swap prop or replace engine?
 

I have to disagree with you this time, Amigo.

The little .40 FP (and its clones) need to get up on the ports, hence my recommendation of a lower pitched prop.

I have discovered that this little engine really likes to rev up and comes alive with less of a load. The props you recommend are the equivalent of running an 11x6 on this anemic little engine.

More pitch will require more engine, which the .40 FP ain't, but it can do a surprisingly good job if a 9x6 or 10x5 is used. BTDT. <G>


Ed Cregger

RE: swap prop or replace engine?
 

....Ed, have you tried the toothpick 10-6 MAS props on a .40 ? I have....in fact I have tried
the 10-7, and the 10-8. They all work. I started out with 10-6's on my Twin Star with a pair
of little Magnum .40's.....the engines were screaming like mad, so I went with some more
pitch to try and slow them down a tad. The seven pitch didn't change much....the eights did
slow the engines down....but the speed of the plane increased almost to the point of being
too fast for it's own good.

I suspect you are just guessing about the MAS props performance on a 40 engine. I had the
Tower 40 trainer as well, with a S.T. 40 on it, so I am familiar with the plane as well. The OS
40 will pull the 10-7 or 10-8 no problem on 15% nitro. The small MAS props are easy to turn,
and high RPM's can be acheived. My little OS .40 fx turns a 9-7 MAS at 16,200 RPM.

Look at the toothpick prop on the Viper racer. If you don't use these props on a regular basis
ED, like I do....I wouldn't say it won't do it, without first trying it.

Trust me on this, the Tower 40 trainer with the OS 40FP engine will show a nice increase in
performance by switching to the props I have recommended. I would'nt have recommended them
without the knowledge necessary....in fact, I'll bet the engine will turn a respectable 12,000 revs
with the 10-8, and show a respectable increase in performance as well. ;)

Wanna bet ?

FBD. :D

RE: swap prop or replace engine?
 

Iraqvet, while these guys are bickering, I'd just like to add that I have repropped several trainers owned by students of mine with FP 40s and LA .40/.46s to achieve exactly what you want to achieve: to recap, take off performance and touch and go climbout.

The FP .40 and the LA series of engines seem to be happiest propped on the ground to turn at about 11,000 -12,000 rpm. Obviously, if take off thrust is important, we should get the largest diameter prop onto the trainer that the FP .40 can spin at those rpm levels. All prop loadings and rpm levels being equal, an 11 inch prop will almost always produce more thrust than a 10 incher. You will definitely see the difference when flying them back to back.

The APC 11x4 will probably do at least 12K; the APC 11x5, probably about 11,500 or so (very rough rpm estimations here). The MA 11x6 is a much lighter loading prop than the APC 11x6, and it should spin at maybe 10.5 - 11K on the FP (BB .46 engines pull over 13k with this prop), so it's at the high end of a recommended prop load. An APC 11x6 is probably too much of a load for the .40 and .46 bushing engines.

So in summary, get a few MA or APC props from 11x4 thru 11x6 and try them out.

RE: swap prop or replace engine?
 

Thanks for the input, guys. I'll try a few different props recommended and see if there is some improvement in flight performance. I'd rather spend a few dollars on props that buy a replacement engine at this point....hopefully I'll graduate off the trainer by summers' end and save the 40 for a future plane.

RE: swap prop or replace engine?
 

.....I got a little surprise today, I did some Master Airscrew testing on a run of the mill
Magnum .40 in the Twin Star of mine. I hadn't run the engines for about a year and a half
and the fuel is opened 2004 vintage, but what the hay....;)

10-6....13,500
10-7....12,700
10-8....11,850

(get this)

10-9....11,100

Yes, Boys and Girls....you can use a 10-8 MAS prop on a .40 size engine. ;)

FBD. :D

RE: swap prop or replace engine?
 

Are we missing the real problem here which I see as a lack of lubrication for the bushing engine. I have seen real power increases in the bushing engines when changing to a fuel having more oil with a good percentage of castor for the bushing rather than all synthetic oils.
FBD I am glad you can turn those RPMs with youir bushing engines on Cool Power fuel.

RE: swap prop or replace engine?
 

Mr Motor....

....you will never catch me using Cruel Power in any of my engines. [X(]

FBD. :D

RE: swap prop or replace engine?
 

That is why I felt the power problem wasn't as much prop as the type of fuel used. I didn't think you could get that power from a bushed engine using that fuel.

RE: swap prop or replace engine?
 

IraqVet,


Why in the world would you want to punish this engine with CruelPower???

This engine has an ABN P+L set, which according to [link=http://www.osengines.com/faq/product-faq.html#q2]OS' Q&A[/link], will run much better, on fuel that contains a lot of castor oil (CP contains none at all).


Also, this engine has a bronze bushing bearing, that also requires castor oil to live long...

The CP fuel may keep your plane a bit cleaner (but you do have to clean it anyway), but it will half the engine's life, if not more than that.


Morgan themselves recommend their own '[link=http://www.morganfuel.com/omega_main.htm]Omega[/link]' fuels for ABC/ABN engine; not their CoolPower.

RE: swap prop or replace engine?
 

....another way to enhance the performance of a .40-.46 engine is to use
prop #404 or #405....but don't tell anyone....

....it's a secret. ;) ....(wide blades)

http://www.zingerpropeller.com/Tractor.htm

FBD. :D

RE: swap prop or replace engine?
 

I bought the fuel because it was the only fuel left at my LHS that day.... the engine is 16 years old, I think it has already seen and passed it's half life....how much more can I expect out of a $50 engine?

RE: swap prop or replace engine?
 

IraqVet,


I guess you can expect ~50-60 hour life-span from the P+L, if you use fuel with a lot of castor oil.

Since you wrote in the first post that it had low hours, I guess taking better care of it would be quite beneficial.


50 hours is about 500 flights, which is a few years for the average modeler.

On 5% nitro fuel, you can expect ~11,600 RPM on an MA 10x6 prop.


This is definitely not a powerhouse, but it is respectable.

RE: swap prop or replace engine?
 

That engine is designed to use castor based lubrication, the more the better. ;)

RE: swap prop or replace engine?
 

gotcha. I'll stop by another LHS and pick up some castor fuel and a few different props. I wished my instructors had caught the fuel issue earlier...

RE: swap prop or replace engine?
 

IraqVet,


Sig Champion fuels are 50/50 castor/synthetic lube at 20% total oil.

PowerMaster GMA are 50/50 castor/synthetic lube at 22% total oil.


These fuels are great for this engine.

There are others.


On a trainer, the 11x5 size would be more suitable; better breaking performance, although it will spin a bit more slowly than a 10x6 prop.

RE: swap prop or replace engine?
 

Hi!
During my 32 years in this hobby, competing and teaching new flyers there seems to be a slight missunderstanding regarding props for those plain bearing .40-.46 OS engines used in high winged trainer aircraft.
Many newcommers think that 10x6 is the right prop for it ...but it isn't! A much better prop size is a 11x5 or a 11x6 APC ...or RAM. I did not say that performance is vastly superior with those props, it isn't but the gain is more calm flight characteristics compared to the "hysterical"10x6 prop.
15% nitro is also a waste of money as the OS FP engine runs equally good on just 5%.

RE: swap prop or replace engine?
 

I'm going to have to cast my vote for the larger props (11-5, 11-6, et al) on the .40FP as well. A good while back when the FPs were were still fairly new...most of us had a nickname for the FPs. A nickname that can't be repeated here.

Quite by accident we learned that the "<expletive> pathetic" FP engines turned in a much more convincing performance when a LARGER than what was then accepted prop size was used.

Lastly, it's sad to see a good basic engine as the FP vandalized through the use of a fuel containing a feeble, thin synthetic oil with all the lubricating qualities of worn out anti-freeze. Please run some real oil in this engine....while you still can.

RE: swap prop or replace engine?
 

As I commented in another thread tonight, it depends upon the airframe you are flying, its OAW and your expectations.

When flying in the dead of Summer when the density altitude was at its worst, we used to drop back to a 10x5 with excellent results. An 11x5 or 6 would not have provided us with enough ground clearance for the trainers of the day. Some of the larger trainers, such as the Kadet Senior, etc., would have had plenty of ground clearance with even a 12" prop, so they might have done just fine with the 11" props. I am all for anything that works satisfactorily.

What did surprise me with the OS.40FP and its clones was how well they responded to the 10x5 props when used for competition fun flying. Again, we are talking about an unusual airframe when compared to just about anything else flying in R/C, so it goes back to the application. Obviously, the OS .40FP will handle 11" props, but it really comes alive and on the ports on something smaller than a 10x6. That is all I was trying to point out - not that the 10x5 was THE prop to use. Only that it was a surprisingly good alternative for lightly loaded airframes where instant throttle response is at a premium.


Ed Cregger

RE: swap prop or replace engine?
 

....I put a 9-7 MAS scimitar prop on a Tower trainer with a S.T. 40 and it flew great. :D

In fact, it hauled arse.

FBD. :D