Here I am sitting reading ALL this info on engines most of which is pure cunjecture and terminology.............which engine "RIPS" which prop.........rpm figures with no mention of prop type or exhaust system......."unloading in the air"........."overpropping" "underpropping"............its ALL phewey!!

Solution.............all manufactures should be bold enough to put in every engine box they ship a graph of POWER VS RPM and TORQUE VS RPM TESTED ON A DYNO WITH OPEN EXHAUST.

No-one is telling me they dont have those graphs avaiable.
Lets see................Zenoah do it.......!!

How about it?

Kindest regards Ian B

Don't forget they would need to test this on every prop ever made which is in each engine's range. And of course, for this testing to truly be meaningful, they would of course need to test this with different gasolines (foreign and domestic) with all oils, too.

Or, a private interested party (such as yourself) could do the testing and then post the most valueable results here.

How about it?

Daren

Ian - an open exhaust reading would be nice -as would a proper torque and rpm curve- for lookee see.
Problem - what would you do with the info?
to most new flyers - the torque and power (rpm) mean nothing .
as for a dyno - --on aircraft engines -this is not really of much use - the why is that there is very little load at low rpm- a reading on a series of "loads" tell one a lot more about an aircraft engine.
the load , is typically a stubby prop looking thing that requires a known amount of torque to turn at a given rpm - these have been around for many years
Some engines run best with certain exhaust setups -
Some are designed specifically to run correctly on a tuned system -
A chart with each engine -giving optimum setups would be nice -
The use of std loads in not used here but at one time the load props were available from Germany .

I know that in Europe............(I used to live in Scotland) that our Zenoah engine all came with graphs for power and torque against rpm. I set up my engines by propping just slightly ABOVE the torque peak. If the torque peak was 6500rpm Id prop the engine to turn 6700rpm ON THE GROUND. The STATIC rpm IS the SAME condition as when pulling from a hover.........zero airspeed maximum rpm. If I needed more power and the NOISE constraints would allow............I would prop for more rpm.

The reason for doing this is that if you are BELOW the the torque peak (below in rpm) when you meet your maximum load situation (pulling from a hover) then the engine will have no more turning force available and readily lose rpm. If you are ABOVE the torque peak (in rpm) when you meet the max load condition then the engine has more turning force available to maintain rpm.

No guesswork, no fuss, no "RIPPING THIS OR THAT PROP" .....ugh

true - and I do the same -
TheZDZ160 . engine, has been plotted by someone in Germany and the results show on Amelung's site.
The figures show what was already known (and is really "enough info" for most), that the engine has a flat torque band from 6000-6500.
But what is not shown, is that a good pipe setup raises the torque and the rpm increase happens using the same LOAD- Even your Zenoah, responds well to a pipe. raising the torque.
My only point here is that an open exhaust reading may not tell enough of the story -especially on engines designed specifically to use tuned systems .

True a single torque & HP graph doesn't tell the whole story, but it is very informative about the engine's general operating characteristics. The point is, I would much, much prefer a graph to the all-to-common single "XX.XXHp" rating given by engine manufacturer - talk about being utterly useless.

For example, knowing the torque curve of my G23 really helped me in deciding on a prop that allows the engine to optimize the use of the power band. I wish I could have that for all my engines.

What I cant understand is why the manufactures dont include such info..............back home Zeoah engines are distrubuted by a gentleman called Toni Clark.........the engines are blue printed, the annoying inch or so of shaft cut off the back of the motor and then test run. With the engine comes the graphs as mentioned before and also graphs using regular bolt on box mufflers and PROPER full length tuned pipes at a couple of different lengths. Its a great source of info on the engine.
You get rpm numbers on several different props on the various muffler types also...........HARD FACTUAL INFO.
And guess what .........when you run the motor that is exactly what you get!!!!

I bet dollars to dirt........engine manufacturers have this kind of info as they test an engine for release (hopefully).

It doesnt cost anymore for a few extra lines of typing on the sheet of paper!!!

Here in the good ol USA- the object is to sell first - explain later -
The sad part and I know some of the mfgrs -is that they are concerned about supplying too much tech info -
The customer either gets confused (true ) or the info is contradictory to info supplied about thrust rpm etc -- this has gone on for many years - --glow engines rated a 4-5 -6 hp then some wild rpm figure to " prove_ it - all Bull shot
it is simply puffery -in legal parlance and it is common practice.
The product can be very good --or very bad - it remains up to the customer to sort it out - or take legal action --another good ol US institution (learned from the English)

That annoying inch or so on the back shaft is where the spring starter is mounted for those who can't or won't start the engine by hand....

Spring starters.............the most dangerous modelling device there is!!!

Or, the best invention since scrambled eggs.
Personally, I like mine on my G-38. Works perfectly.

Personally, I don't much care for scrambled eggs or spring starters. Personal tastes and pesonally safety, respectively. Every since I got my fingers whacked by an OS Max .28 spinning a wood prop at idle decades ago, I'd rather not touch that prop if I can help it. These days, I play with much bigger and angrier beasts. As much as I'm extremely cautious around that prop, all it takes is a moment of inattention to cost me my digits.

The only time I was ever hit by a gasser was on someone elses engine with one of those springs .
It was years back and I was looking at gas engines - this encounter did little to encourage me --
I already had formed an opinion onthe poor power to weight of those rehashed weed eaters
Obviously -tho - they have a group of people who like em --
Back then the only gas powered models around were barely able to flounder thru the air.
I stayed out of it till the newer, purpose built stuff started to appear.
3w/DA /ZDZ etc--
some guys really like the conversions tho ----
to each his own -

Dick, "purpose built" is a very relatively term. Zenoahs are "purposely built" for RC as much as many of the newer gasser brands are. The difference is mainly in their retaining the heavy mageto ignition. I'm sure you're aware of the fact that even some of the most prestigious (mostly American made) gassers that won tournaments and such also have rather humble industrial origins. As long as they are well designed and converted, these chainsaw heads do just as well as those European brands with supposed pure pedigree.

Then again, those thoroughbreds don't always perform up to their billing, either. I was very surprised to read the ZDZ50RV review by Clarence Lee in the August '03 RCM. The rather low 6.86:1 CR didn't jive with the pompous advertizement of high CR designed for high octane. Disappointing too was the 59.6 Oz weight - my Poulan 46cc with a very similar BCM muffler weighs right at 60 Oz. And that's before I make any attempt at lightening up the engine further, which is easily done given the generous cooling fins on it.

Most importantly, the power output wasn't near what I would expect from such a race horse. The ZDZ50RV only bested the lowly Poulan 46cc on CH Ignition by about 200RPMs.

As is often the case, "purpose built" is in reality mostly "purpose marketed". Unfortunately, unless someone like Clarence Lee spills the beans, most of us have nothing more than the manufacturer's words to go by.

So, how about those HP & Torque curves, huh?

Volfy,
Do you hand start your much larger and angrier beasts with your hand or do you have a MEGA electric starter. Either way you have to touch the prop at some point.
Like the man said, to each his own.
I lost the end of my thumb to my G-38 and it didn't stop me from enjoying the sport. Sometimes bad things happen to good people but that's no reason to stop doing something. Just don't do the same thing in the same way.

The test by Clarance Lee was actually more of a review of how the engine was done - -as a performance test? - it simply was not -he said as much - I am not criticizing him .
I hear some good comments about he Poulan - I know nothing about that engine -so I won't comment on it .
I have run the ZDZ50 on 22x10 MenzS and 22x8 MenzS
The ZDZ50 performance was I thought - good - low 7000 rpm's on the 22x8
and high 6000's on the 22x10 --
exhaust was not tuned on these tests but was a very quiet, small JMB can
I don't run the open stack type stuff
or the BCM
The ZDZ50 was NOT designed for that type muffler .
On tuned systems - which that engine was definately designed for -
the power increases quite a bit .
I don't have full power figures using the tuned systems - yet -- so I won't comment more than that.

One more thing - I don't know how Lee calculates the compression ratio on two stroke engines -so the noted 6.86 compression ratio seemed a bit odd to me .
(back when - that is about the compression I used on my Olds engine with a blower giving 12 lb boost )
On pipe tuned engines - really high compression is not good -
On the two strokes we have done for pipe tuning - we always lowered the compression -on glow, especially .
If the compression on glow was high, - the engine really heated /lost power
So far -on my gas engines, the spark ignition seems to control any problem -as long as the mix is set right .
the "high compression" on the ZDZ never really acted "high" and the compression RATIO (if calculated from BDC ) would be high but if figured from closed exhaust port - would be quite different - and different on each engine design they have .
Some of the group have as much as almost 25 degrees less exhaust open period.
I like the engines - as I am still a bit of an engine fancier - have been since I built my first 274 ci in flathead Ford
that has been a couple of years -----

Dick, you are absolutely correct about compression ratio.
There is only one way to calculate it on a 4-stroke.
On a 2-stroke, there are 2 ways. Full stroke or just that part of the stroke when the exhaust port is closed. The 2nd method alway results in a number in the range of 6-8.

Purpose-built aerobatic motors are designed for high power to weight ratio. Some hit the mark and others miss it.

Jim, I try to use a starter whenever possible. I have a Megatron, a Dynatron and a cheapo Tower HD starter. "Minimize" contact is the proper term, I suppose.

Dick, I am not criticizing the ZDZ any more than Clarence was. I am simply as surprised as he was that his findings were contrary to the manufacturer (or should I say importer's) claims. Clarence did state very matter-of-factly that the port timings and CR are consistent with an engine designed more for a tuned pipe application. However, the engine is NOT marketed (at least here in NA) as such. The engine is most commonly sold, and is most definitely advertised along, with a Pitts style muffler.

ZDZs are good engines, no doubt. However, high octane and low weight are the two primary selling points touted. I am only saying that the marketing of it would lead one to believe a wholy different picture than what Clarence revealed.

I never even considered a Pitts type muffler for mine - - but I know others may want that setup .
I think it is a good engine - I saw other engines on the same muffler and they also were down on power - but quiet.
Jim Bisson makes a nice product and he has no illusions about the way you control noise .
I see -tho -- many "flyers" who think that all mufflers are basically the same - -- not so .
The only "poor"comments I have seen on the engines' performance are from those using a restrictive setup -
I have checked two o fthese -flying H9 80 " Caps - all stock -on stock Bisson Pitts and Bambula 20x10 props .
these both turned 6900 here at 4500 ft elev.
The Caps both have fully unlimited power .
my 40 on a tuned can - 6800. Bambula 20x10-

The ZDZ-50 and 100 twin are way "different" than the rest of the engines in their line. They have very long exhaust duration and don't do very well (power-wise) on in-cowl mufflers. These engines are very similar to the ZDZ-40 and 80 twin as far as the lower end (same stroke), size and weight. The 40 and 80 twin run very well on in-cowl mufflers because of different porting. The 60 and 80 single also run well on in-cowl mufflers. I think ZDZ should offer a couple of porting options for the 50 and 100 twin - one optimized for in-cowl mufflers.

Unfortunately, Ian, due to the nature of 2-stroke engines. . altitude and mean air density really affect power output, so if a manufacturer gave you a torque/hP curve for HIS altitude. . it would be a bit different in say. . .. Colorado. Imagine the porting is optimized for a known 29.92" of pressure (Sea level), drop that to 27" of pressure at about 3000' and the curve will change. . not much, but enough to affect where the peak torque/hP numbers come out. True, a graph would help, but the higher you go, the more "approximate" it would be.

As for spring starters. . I've been bit by ONE gas engine. . a 74cc twin Zenoah, and the ignition was OFF. . spring starter got me and laid two fingers open. No stitches but I curse them every time I see them now. I want to KNOW what that prop is doing, not depend on some silly spring to flip it over for me. I hand start every engine I have, even my little .61 and .91 glo motors (though I use a glove on APC props to keep from getting cut by the back of the blade) I have absolutely zero concern about flipping a 150+cc gasser, or a little .049 glo, by hand. (Smeone is going to come on now and say how it's only a matter of time. . . . )

I keep wondering who is near or at full throttle in a torque roll. Seems that if you are not TR'ing at about 1/2 throttle, you need a bigger engine or lighter plane, if for no other reason than simple power overkill and safety. Marginal power in 3D and during hovers is a bad accident waiting to happen. I prop my engines to try to confine prop rip to the upper 10-15% of the throttle sticks movement on a level line, and leave it at that. That way, since I am at least 50% overpowered, I can easily fly Sequences at 50-60% power, and only get to full throttle if I make a mistake on a vertical upline and need to juice it to get me out of trouble or straighten the plane out. (or on the backside of a down avalanche. . . . ) I've always found that the static rpm turned by different props has little direct correlation to how well the plane flies with them. Take a really low drag prop, that may turn 400 rpm faster on the ground, and it may not pull the plane worth a hoot in the air. I have 4 different props, that all turn within 150 rpm of eachother (6300-6400). . .2 of them are marginal, 1 decent, 1 is very good at flying the plane (in sequences). Conversely the two "marginal" props pull out of a TR and accelerate the plane a lot better, while the decent and good "sequence" props are more sluggish and really lack the "Zip" needed for good 3D performance.

A "graph" would be nice .. but you still have to match props to the airframe and engine/exhaust combination, as well as your flying style and the type of flying you are doing. Seems no matter how much information a manufacturer can give you, it's still up to YOU to "tune" the combination, and looking at a torque curve is only part of the puzzle.

I'll stick to my "Mark1- calibrated and rebuilt (3 times) " ears. . . they do a pretty good job of letting me know what is going on.

Hi there Kris good talkin at ya!!

Here is the thing tho.........even if you do change altitude...........the power and torque MAY change BUT where those PEAKS occur does NOT. WHERE they occur are goverend by the internal fuction of the engine. There are variables but the variables are CONSTANT throughout the rpm RANGE...........

Yes Iagree SPRING starters are evil weight gaining finger eaters!!

What I was reffering to about hovering was where I prop my engines .....the max load situation..........zero airspeed and max rpm i.e. when pulling from a hover.....I was not implying that my planes hover at full throttle............take care buddy!!!
IanB

Also......what you are talking about in your last mail is the efficiency of the prop............what I am talking about is extracting the max aerobatic potential from the engine...........the best rpm for the engine to run at in its max load condition. (given noise considerations.....yada yada).

what device you need to put on the front of the engine to satisfy the above is the second consideration.........as long as what you put on the front is as EFFICIENT as you can get and meets the above your in good shape...........a prop does nothing but convert horse power into thrust........an efficient prop IS an efficient prop and an inefficient prop is...............
Of course as all of our airframes are soo much alike that "matching the prop to the airframe" is meaningless.............and personally........I STILL want MAX thrust via the most EFFICIENT prop at the OPTIMUM rpm for the engine in the MAX LOAD condition............see where Im at?

Kindest regards Ian

Ian,

I'm assuming you're saying a lot of this in jest, but since you've mentioned this, I would like to throw out a thought about airframes.

A 1/3 scale Sopwith Pup will need a different kind of propping than a 1/3 scale Extra 300. Different flight envelopes, different speed ranges.

Max effiency yes, but at what speed range and rpm? You still need to match the prop and engine to the airframe and mission.

To use a real-life example, NASA's Super Guppy uses the engines and nacelles from the Lockheed P-3, but the props from the C-130 (both airplanes use the same engine; the Allison T56/501D). Why? Different missions.

The P-3 is a speedy bird and needs props that are efficient at a higher speed. The Herk's props pull a bigger load, so they sacrifice speed for pulling power, but are still efficient. In both cases, the props are matched to the airframe and mission.

Interesting discussion.

Daren