Volfy

My Feedback: (23)

Above a certain displacement, the greater volumetric efficiency potential of a twin will overcome the addtional parasitic drag compared to a single. Likewise, above a yet higher dsiplacement range, a twin will loose favor to a 4cyl for the very same reason. Good design can stretch that break even point, but there is no defeating the inevitable.

Still, none of this matter to the single most important aspect of any engine - price, which accounts for a great deal of ZDZ80's popularity. I hope MVVS prices this 58cc comparable to the 50-55cc crowd.

f2racer

Just a quick note. I spoke to Robert at Morris and supposedly the 58s will be in either next week or the following week. He also said that those "crazy" Czechs are working on something completely new (at least in this hobby) as well... A liquid cooled version of the 58cc, supposedly for applications where cooling is an issue!

Antique

My Feedback: (4)

Nothing new about water cooling..Zenoah makes water cooled engines for model boats..Bruce Hnson's 50cc water cooled racing twin is 12.87 HP and turns 18,200 rpm..
The G26 marine engine turns 12,000 rpm stock...

Flypaper 2

Wish they would come back with the torque, hp graphs that they used to put in the old mags. They didn't lie. For instance, high performance engines,ducted fan,etc, the hp rise was very slow till it got to a high rpm, then an abrupt rise to high hp.at, say 18000 rpm. When you backed up to 10,000 rpm, not a lot of hp, or torque. The only way it would be usefull would be with reduction gearing, then throttled back, would be pretty useless. With the graph you could see the actual HP and torque at, say, 7500 rpm.

pe reivers

Mmmm..

Maybe that is why Mr Svajda was so curious about the construction of the watercooled converted 1.60 engines that I had made for a twin hull boat. We had an opprtunity to exhange a few words and ideas when at the show in Dortmund.

I will receive <one> 58 test engine and <two> new type red heads in a few weeks time. Morris gets the rest :-(

ketil

I Wonder And i Wonder?

When you have an engine,you start it let it go fore a bit,and reads the rpm on full throttle.
1 is this the rpm the factory reads?

2 when the plane is airborne and make top speed,the rpm is a lot higher than when its on ground, is it possible that you have a higher hp in air than on ground?

3 in a dive ,can you over run the engine on rpm?

4 how do you know what rpm you have in a top speed plane ?

some one thought about this?

Ketil

DKjens

My Feedback: (50)

1. Who knows what the factory reads, should be a cold and a hot reading.

2. I doubt the unwinding of the engine in flight has great significance in this/these particular applications, being aerobatics and 3D. In racing and with pipes, it most definetely has significance, and yes, a 2-stroke "on the pipe" has more HP than not "on the pipe".

3. Again, I really doubt you can over run a 2-stroke engine. With 4-strokes it's a different matter, again especially if on a race application where the plane will fly at a significant speed. That is why you should not underprop a 4-stroke glow engine.

4. I suppose you get one of the new 3W ignitions and record the rpm range throughout the flight ha ha.

DKjens

rmh

That is one interesting HP reading --for a 50 -
Ihave a new ZDZ50 NG which really sparkles -but I doubt it is even remotely close to 9 hp -
One point about porting ---
even tho a twin has more porting area - the business of EFFECTIVE flow rears it's head -
this is kinda confusing stuff -unless you look at how fluids flow thru large and smaller "tubes".
Hot rodders and NASCAR guys figured out how to make flow benches many years ago -that told em what was really going on.
I played about with watching how water changes flow rates when the shape of inlets/outlets were radiused differently. Learned a bit from that ---
These little air pumps (our engines) can be made to deliver unbelievable flow if all is set up to do it .
four stroke engines in cars now use variable length intakes /valve openings etc -and the flow is stabilized over broad rpm ranges.
simply tipping the ports to different outlet angles changes the whole picture.
The thing that must drive the engine designers nuts, is the habit -in the USA anyway --of putting an abysmal piece of plumbing on the exhaust outlet - which wrecks any real performance flow setup.
Some setups will tolerate this -others will not .
my new NG engines tolerate it pretty well but after a fair bit of doodling with the good /bad and the ugly exhausts - I noted some interesting (to me ) performance changes .
The use of a more restrictive muffler - still affects rpm on bigger props -more than it does on smaller props .
Adding a correctly tuned setup - makes the entire rpm band smooth out and run harder - a lot - and throttle response at low rpm is even faster --
this is a bit of a surprise - the exhaust timing is quite low - but the intake porting is very directional and is of a different relationship to exhaust timing than previous designs.
So - maybe - the MVVS really has a trick setup which really cooks - we will see.
Looks like we all win -we get more power for same size setups .

f2racer

Pe, looks like Morris has the scoop on the liquid cooled 58s... Check this link out:

http://morrishobbies.com/mvvs/58cc_gasser_liquid.html

pe reivers

Mmmm..\
That looks a lot better than the liquid cooled 1.60 conversions I did last year. In fact, it looks great!
The clean-cowled Spitfire now is within grasp, using functional heat exchangers. Another up-side: The "speed" I build with, enables them ample time to market the engine.
I just wish, MVVS would spend more time producing engines, so I get my full orders, instead of small parts of it.

pe reivers

Small update on real life numbers on the MVVS 58

I acquired a few engines, so now I can publish results.
Since MVVS still does not provide a dedicated tuned pipe, I tried two setups:

The first (not recommended) test was with a very restrictive pitts muffler as produced for the 2.15 engine. Using this muffler and a 22x10 Menz-S prop, the engine turned a happy 6300 rpm. Throttle response excellent, idle quite low, below 1500 rpm. This was used for running in, and no prolonged full throttle runs were asked for.

The second was using a friend's Krumscheid tuned pipe for the ZDZ50 engines, and a long header. According to the Krumscheid manual the chosen total length would tune the engine between 6500 and 6800. This is the rpm that MVVS quotes as max power output.
With this setup and the same 22x10 Menz-S prop, the engine now turned 7450 rpm cold, 7400 warm. Thrust was 31lbs. This is 600 rpm over the top for this engine. This could also be judged by the "snoring" sound of the membrane intake, indicating reeds closing under less favourable conditions due to mass momentum. (BTW, the Carbon reeds are very thin and flexible.)
Absorbed power for this prop and rpm is an esimated 7.5 hp, and in line with the thrust measured.
This pipe was not produced for the 58cc, but rather for the smaller 50cc ZDZ. It may be possible, that Krumscheid will produce a pipe for the MVVS soon, and that MVVS will produce the headers.
Since the 22x10 prop is too small, I have ordered a 24x12 prop to try next, in order to get rpm down to about 6500. (8.26 hp and 50 lbs thrust acc to my spreadsheet)

Conclusion:
The engine likes to breathe, and will then produce loads of power. If restricted, power will decline sharply, though the engine seems to accept it willingly.

(typo 41 lbs thrust corrected to 31 lbs)

rmh

Thanks for the report!
I have the new ZDZ50NG-which is a comparable engine .
Ijust put the 50 thru in cowl muffler tests -to see how well it responded to very restricted breathing.
I have, 22x10 and a 22x8 MenzS props which Ikeep as referrence.
on the Supersonic muffler - I got 6400 on the 22x10 and 6900+ on the 22x8.
adding proper tuned systems to these ZDZNG engines really allows them to run ---howevr -in the US , most modelers do not use them as it typically requires some airframe fitting.
The 50 NG also performs better on larger tuned systems
I
have a wide assortment of pipes and tuned cans etc., but when I do rpm readings on these - I get much dis belief from some modelers --
The rotary valve breathes very well -as you know -at high rpm .
I have not run the KS full length tuned pipe on this one -but I expect it will show a sizeable increase--
I presume you used the KS 1070 pipe .

David_Moen

Looking at my two-stroke dirt bike, it seems that other industries have adapted to the fact that a tuned pipe does not have to be straight. We should be able to come up with some sort of turned pipe that folded back on itself to provide the length required and still fit in front of the firewall. Anyone out there have some talent with a TIG welder who wants to build the next "must-have" giant scale RC product should get busy!

Antique

My Feedback: (4)

Sorry guys, I don't get the BIG deal..... An old loose G62 will turn a 22-10 Zinger 7000 rpm all day long, with no pipe at all....40 lbs thrust ? My spring scale on a G62 at that rpm with that prop shows 28 lbs.....How come a 22-10 Menz has 40 lbs thrust ? A good customer told me his G62 shows 34 lbs thrust with a 24-8 prop, don't know the rpm..
FWIW..The ThrustHP chart shows about 37 lbs thrust, and we all know it's wildly optimistic...
Color me confused [8D]
And the "top" for a G62 is 13,500 when it's in the chainsaw...
We run G62s in our racers at somewhere around 9000, no pipe, just an 8 inch straight pipe...
I guess the extra 4ccs puts it in a different class....
Just got a report from a customer..G62, 22-8 prop, Mac's pipe not really tuned yet, 8000 rpm...

DKjens

My Feedback: (50)

Well, here are my engines for the next 3 planes. The MVVS2.15Gas on the 35cc Macs pipe turns the Mejzlick21x8 at 7000 and is going on an OMP 80" Edge540P that I will be building over tthe holidays. The DA50R has only has 14 oz of fuel through it, and will go on my 3rd DiablotinXL that I am getting in January/February. The can is a KS60. The MVVS58i is going on my Wild Hare 28%Edge540T, that I should receive this week. I hope I can fit that can in it, it's a JMB80/70/400 so it should let the engine breathe quite freely and be quiet.
DKjens

rmh

Nice assortment -
The DA setup looks about right for length -for good aerobatic setup - you will like this engine--
The JMB can be on extremely short headers - as short as 5".
Who anodized the Mac's setup?
I have a pair of Mac's -I think they were for 1.2 cu in -with muffler sections -- these work pretty well on 35 cc engines . I test ed them on ZDZ40 and tho they worked -they were too small for best boost.

pe reivers

There is no big deal.

what matters, is good reports, stating kind of engine, prop type, engine type, and results achieved with that combo.
I do not care much for unloaded rpm in a chainsaw, or 7000 rpm all day. I never test an engine that way.
Thrust was measured. Since I do not have a dyno, power is calculated. Not by thrust-HP, but nonetheless mainly based on Abbot-Boucher formulae.

In your undocumented suggestions, there is no mention of prop type which were used to achieve the RPM, nor do you mention data on the exhaust type. For simplicity, let's skip atmospheric condition and altitude. That way you present data, myth is born, and the reporter takes no responsibility.

When measuring thrust using fish scales, the front surface and drag factor of the plane or test stand behind the prop must be considered, because it's drag does influence the fish scale reading. Tests with a parachute behind a plane showed that the plane could not taxi, even at full power! A fish scale would have presented an extremely low reading in that particular test.

Antique

My Feedback: (4)

OK, documentation..There are no myths, I take full responsibility, all tests are facts...

Engines, Zenoah G62, Zenoah G26, MVVS 1.6 older style.
Propellors, Zinger 22-10, Mejzlik 18-6.
MUfflers, none.
Fuel, 87 octane Texaco gasoline, Amsoil 50-1 racing oil.
Altitude 6800 feet.
Air temperature, 70 degrees, humidity 20%
G62, 7000 rpm with 22-10
G26, 9000 rpm with 18-6
MVVS, 7800 rpm with 18-6, small carb, 8200 rpm with a WA167 11.1 mm carb..
Thrust from a scale on the tail wheel of an airplane, 17.5 on the G26 and 28 on the G62..The MVVS was not on an airplane...The MVVS was here because the stock ignition was faulty. I made a sensor bracket for it and put one of mine on it, timed at 28 degrees BTDC...

rmh

Pe- In checking actual thrust -not calculated thrust - I find that the calculated info is missing something - because I get nowhere near the numbers offered.
That does not bother me - beacuse I have yet to see any calculated data on prop thrust which has any degree of accuracy.
I live at 4500 ft altitude and the actual thrust vs calcs -even with altitude compensation - is always optomistic -
I also ran tests last week on MenzS 22x8 prop vs Bambula new example 22x8 - which has a narrower blade. a raked tip and thinner cross section, than earlier examples of Bambula.
My thought was that this sample would run faster - just from a visual study.
Repeated tests , however - showed it to be over 500 rpm slower than the MenzS 22x8 !
The manufacturer responded that they do NOT use this type comparison - rather -they use dynamic (flying comparisons) for tests.
This is a valid comment-to me . And useful.
In doing the same tests in the past - we found that the blade which showed lower static test results - often provided as much thrust (in motion) and at much lower noise as the model gained speed .
I do however, , use the static tests to compare engine setups- pipes /carbs/timing etc..
A very striking comparison recently was in using the Mejzlic 26x10 - vs a 3W 27x10
on a 100 cc ZDZ.
the larger prop ran over 6000 and pulled hard on the ground
the smaller prop ran over 6700 and I would have guessed that it was inferior in vertical pulls at low speed.
Not so --
On the heavy model (almost 30 lbs) - the smaller prop easily performed best - in any maneuvers.
I have given up on a lot of my early ideas on prop design.
Appearances are quite deceiving.
Until I fly the prop -on a particular application - I simply can't guess or calculate ( a scientific guess ) actual response.
The racing setups on the g62 are far removed from a good aerobatic prop setup -- at least that has been my hands on experiences.
The best ones I have seen and run - will not pull the aerobatic props as hard as similar purpose built engine -- but they will rev freely!
My last experience with G62 was a 4 lb example --with electronic ignition on a open stack exhaust -
it was not happy on 24" props -which my ZDZ60 easily turned - just a different breed of cat --

Antique

My Feedback: (4)

Yup....same with the G26..Not happy with an 8 pitch prop....

David_Moen

This should answer a few questions.

This is one of the airplanes used by MVVS in testing the 58. It's wingspan is 2.56 Metres (104 inches), and it weighs 11.5 kilograms (26.1 pounds). Prop used is a 26 x 10N Mejzlik. A JMB cannister is used, no idea which one. The engine produces enough thrust to hover this thing with "40% excess traction".

DKjens

My Feedback: (50)

So David, do you think that engine, also on a large JMB can but with a slightly longer header, is going to haul my 16 lbs 84" Edge around alright?[8D]
DKjens

pe reivers

Thanks for the update Ralph.
I had no idea you live that high in altitude. I understand you have tested Jim's 1.60, which is a late MkII, just before MVVS started with the graphite coated piston production. These engines do not perform well without the tuned pipe, and are not happy with a carb in excess of 8mm, unless very well run in. They tend to bind, and loose power. (The latest 1.60 sports a huge 13mm carb)
It was this type II engine that I have tested in the beginning, and with a bit of perseverance, good power can be extracted from it. Remember we discussed the possibility of changing the ignition?
I measure thrust with scales, and then add calculated fuselage front surface drag to get the total prop thrust. I use prop pitch speed as the speed of the moving air column in the centre of the prop wash vortex. The air moves faster than that, but you got to draw a line somewhere.

To Dick as well,

Static thrust measurements as such are of no real value for flight performance, as you well know. They serve however well for comparison purposes between engines, and to calculate horse power according to the hydrodynamic (air) brake principle. That way, we are able to compare data from all over the world, except from you guys, who live up there in high altitudes? Despite power loss, will the prop spin faster with less thrust?
Inquiry mind wants to know.

David_Moen

Err....methinks you are going to have to post your flight reports in the helicopter forums

I will be very interested to see how you mount your cannister.

rmh

Pe -- that question about how engines with propellor loads act at higher altitudes is a knotty one
Here is the sword to cut that knot--
Logic-- if we keep ascending the engine will loose power and the load will also diminish ( prop spinning in air.
The internal resistances of the engine will NOT change.
If load decreased faster than air supply to the engine - the revs would increase as the combo got into more rarified air.
at some point the prop would spin like crazy - just before the engine ran out of air.
Does that make sense?
Of course not.
So - expect lower power at higher altitudes--and more rpm req'd to get same thrust--on same prop
That curve is not known to me .
On my electric motors - we simply add more prop pitch to get same performance at sea level -or at least try - as the model is flying in thinner air.
The electrons work the same --
best guess on the IC engines, is that the % charts for normally aspirated full scale craft - will supply proper info.
we see % decreases ranging on a line = to airdensity loss - to that % + increased friction (more rpm reqd losses)
Some day I hope find a clear chart on this ---
One of the US yokels insists I get my high rpm readings due to the higher altitude. here .