Sorry, I guess I phrased that wrong, I was just asking if you treated the .53 as if it had the power of a .70 because you came so close. It was meant to be a compliment. A lot of people said the .53s were troublesome, Mine are not. Do you use a formula to make those yourself?

Dave,


I once found an engine review done by a prominent engine guy, in the UK.
It was on the web, but I cannot find it any longer.

It was at this URL, <http://www.nwmas.co.uk/engine_test_ys53.htm>, but this page is invisible now.

The engine was tached on APC props and 30% heli fuel.


Some numbers I remember are 12,700 RPM on a 12x7 and 13,000 RPM on a 12x6. Sport and even most competition .61 would not dream to show such numbers.

(It is for this I once wanted this engine)


Schpankme, JapanFlyer,


The general rule-of-thumb with three-blade props, when converting from two-blade props, is to reduce the diameter by one inch, or the pitch by two. Any combo is also good.

So if you ran a 13x6 2B, you can instead use a 12x6 3B, or a 13x4 3B, or a 12.5x5 3B.

Now that "hobbsy" has provided us some definite prop performance numbers, here's how the updated two blade and three blade prop charts look for the YS 53.

__________
Schpankme

Generally the props that we use are speed driven, i.e. a smaller diameter higher pitch (12x7 etc.) These create higher speed (airspeed) once they are turning at around 10-11,000 rpm. If you want better "pull" from the prop, use a larger diamater/smaller pitch prop. (12.25x3.75 or 12x4) You should go with the largest diameter that your enging can handle and lower the pitch (keeping ground clearance in mind). As an example, when a full size plane with a constant speed propeller takes off they use low pitch to develop thrust, or in Helicopter terms main rotors are very large diameter and very low pitch and produce a great amount of thrust. This is the most efficient combo. If you do aerobatics this will give you more power during climbs, 3d manuevers etc. On a given engine it should be propped to turn approximately 1000 rpm higher than peak horspower, this results in maximum power once the engine is under a load.

One should not concern themselves with Horse Power (HP) ratings it means absolutely nothing. Its torque that turns your prop, knowing the Torque Curve (RPM range) of your engine, will help you select the best prop for your application.

Do not be mislead by HP ratings.

Torque = Maximum prop (load) for peak RPM

HP = Minimum prop (load) for peek RPM

Note: maximum RPM limit set by manufacture.

_________
Schpankme

I usually go by the manufacturers peak horsepower/rpm rating, it seems to work best. (for me) I generally own only 2 stroke engines and the max q and hp are in the high end of the rpm range. For instance my OS 1.08FSR is 3.0 hp@ 16000 rpm, That is where the engine produces the most power, I try to find a balance between that high rpm and the amount of thrust I get out of the Eng/prop combo. Obviously I cant put a 12 in prop on the 1.08 just to get 16000 rpm, so my theory doesn't always work. I'm definitely not an engineer, so I go by what works on the plane. Largest diameter that the engine will turn, around a 4 pitch for aerobatics.

Spun,


The best thing you can do with the manufacturers claimed HP numbers, is to print them on toilet paper...
They are a worthless piece of information, as well as being lies, especially if the engine is used as it comes from the manufacturer.

Do a search on these pages for more threads that deal with this issue.

Just ignore them and only take into consideration the RPM an engine achieves with a given prop.
That is all you need to know about its power.

To spin an APC 12x8 prop at 16,000 RPM, you would need no less than 4.03 HP.


You are far more likely to have hair growing on your tongue, than an OS1.08FSR is to make this kind of horsepower...

This engine should be propped to spin 9,500-10,500 RPM, with a 15x6, or a prop of similar load.

I was using the 12 as an example, but I understand your point. I have a 16x8 on it now and it will pull my 62 inch span SU-26 straight up all day long. I think I am going to work up a way to measure actual pull the plane (prop/engine) develops in pounds. I had this engine turning a 14x8 master airscrew at 13,600 rpm on a stand with 15% powermaster fuel, and the sleeve was still in the carb. I am planning to use an 18x4 for 3D after I get the initial few test flights worked out. So the HP cant be far off.

14.0 14.0
8.0 Inches
13,600 RPM
5.00 HP
30.0 Lbs

Spun,


Take the tach you are using, go to the nearest cliff on your beautiful California shore-line and throw westward it as far as you can.
Don't even try to tell me it was with a standard muffler, because even nitroglycerin will not give you this...

Selecting of propeller for an engine at to example 3.5 ccm are not allways same propeller sizes each time, some has long stroke and need bigger propeller or some short stroke engine need smaller propeller. It is produced of torque of the engine it can run with bigger propeller, to fly faster need smaller propeller. Nothing of them in forum wrote about torque instead only hp/rpm??

Jens Eirik

Jens,


Have you noticed the 'long-stroke' engine has fallen out of popularity in the last 15 years, or so?

If you try 'crunching' the numbers; comparing between two engines with the same cubic displacement; one being over-square (short-stroke) and the other under-square, you will find that with the same BMEP (Break Mean Effective Pressure), both will make exactly the same calculated torque.

The single theoretical 'advantage' of a longer stroke, is that the smaller diameter piston has a smaller amount of friction.
But this item is a very, very small factor, in the calculation of the torque.

The reason for the slightly greater low RPM torque of a 'long-stroke' engine, is the smaller mixture and exhaust passages, that require longer to fill up the cylinder, resulting in a lower RPM torque peak.


Some current engines known as 'torquers' are, in fact, over-square, 'short-stroke' engines.
One is the MVVS .91, which has a bore of 27 mm and a stroke of only 26.

So "Long-Stroke" has become no more than a buzz word...

Yes, but you forgotten there are still to buy replica engines to example Mills engines and there are engine builders who are building long stroke engines.

Jens Eirik

This is true, Jens.


But I was referring to all the engine manufacturers making F3A engines, from 1980-1985 in the 10 cc bracket....
The OS Hanno Special SF, Webra and YS .61 Long Stroke, for example, are a long stroke engines.

I prefer to use the engine builder's terms of over-square and under-square, to respectively describe engines that have the bore larger than the stroke and smaller than the stroke.

The Fox Eagle .60 with a .905 bore and .937 stroke could be considered a long stroke engine as is the MVVS .61 and the MOKI .61 LS at 23x24 respectively. The Saito .82 is a real torquer and is way lopsided in favor of the bore, so as Dar says, the long stroke design having more torque is not a rule of thumb. Here is an interesting comparison Clarence Lee did between the MOKI .61 standard 24x22 and the the .61 Long Stroke 23x24.

Moki 61 Long Stroke Moki 61 Standard Stroke
11 x 7 12,800------- 11 x 7 12,900
11 x 8 12,100------- 11 x 8 11,450
11 x 10 10,300----- 11 x 10 9,900
12 x 6 11,600------- 12 x 6 11,300
12 x 8 10,300------- 12 x 8 9,950
13 x 6 11,100------- 13 x 6 10,500
13 x 8 8,200------- 13 x 8 7,750
14 x 6 9,000------- 14 x 6 8,400

The short stroke engine only had the advantage with the smallest prop. I have the LS and it's a shame they no longer make it. But the MVVS .61 has the same bore and stroke as the MOKI LS and it is a fine engine as well.

Well, I would but..........I know the tach works. So, I guess I will keep it. As for the muffler its an in cowl pitts style. Dont know what else to say.

Get a digital fish scale. Tie a large flat boot lace in a loop, and wrap it around
the tail of the plane......there is a large hook on the scale, and let her rip....
read out the "pull" in pounds and ozs.

I run my 1.08 on 15%, and a 14-6 prop. It turns about 13,500 as well.


Dave. (don't throw the tach either)

That sounds like a plan, I was leaning that direction. I will give it a try.

Spun,


Since you are new here, I tried to be easy on you.
But now that the forum bully has joined you, I will have to remove the gloves, so to speak.

It is either your tachometers are very inaccurate in a very optimistic way, or you are both lying through your fingers.

Engineering charts (and calibrated prop load calculating programs) don't lie and they are much more sensible to believe than these weird RPM claims.


Dub Jett will be thrilled to know that your measly, cheap OS 1.08 FSRs, with Pitts mufflers, make 72% more horsepower than his prime choice, 1.20 Sport Jett engine, with the JettStream tuned muffler.

Yeah, that would be the day...


Dave, you still can't read my name right, or did you forget?

Forget long/short stroke with our engines, they're all so close to being "square" that any minor advantage either way makes no difference. A very slight change in port timings will make more difference between styles of engines than anything else. All that a "short stroke" gives you is a marginally larger bore circumference (for a 2 stroke) to fit the ports in. In the case of hobbsy's Moki 61 comparison there's a 1mm difference in bore which means a little over 3mm (pi actually) extra circumference to be taken up by the 4 ports. Some of the extra area gained here is lost in that the height of the ports must be reduced because there's a shorter stroke (if you keep the timing the same). For a 4 stroke you can fit in slightly larger valves with a shorter stroke. There are model engines designed from the ground up with the ultimate goal being very high torque at low revs but their bore/stroke is 24/22.

Well, I will take a picture of the engine running with the tach in front, or I could have it independently certified if you like. I'm not a politician so I dont have any reason to lie about it. Tell you what go buy yourself one and try it out.

Spun....

....don't worry about that Guy, he doesn't know anything about that motor.
I don't know why he accused you of lying....not nice....

....that's just the way he is....a Jerk. []

He sells MVVs engines that's why he makes stupid statements like this:

"your measly, cheap OS 1.08 FSRs. "

Dave.

Right on, that explains a lot.

Keep in mind, the Jett 120 engine is a physically smaller engine. The BSE is a "60" block..... the SJ-120 is only very slightly larger (it started as a modified FanJett-95 crankcase - eventually became its own animal).

The OS 1.08 is a "90" block engine.........has a big crankcase, HUGE transfer ports, a pretty big carb, and is pretty efficient with fuel transfer in the crankshaft (big hole there too). "Breaths" very well. That extra internal volume goes a long way to providing fuel/energy/power.

I seem to recall my old OS 108 turning somewhere between 10-11K rpm with a 15x8 (may have been a 15x6... hard to remember) .. this in the 1985-86 time frame. It had gobs of power.

Basically, the BSE-120L performs the same........ 15x8 at about 11K rpm ---- just is a whole lot smaller/lighter engine. However, due to its size and construction, it can not 'breath' enough to make it much of a higher rpm engine.