EVERYONE's Engine is the "best to buy"....Kris has numbers, I have numbers, you have numbers.

We all have opinions, and we all have experiences. Some aren't the SAME as others. Imagine that.....

The motor opinions always seem to float around someone ELSE'S numbers....funny...and the motors that folks report as puny (or noisy) are someone ELSE'S motors. Hmmm.

There are folks who are staunch supporters of Kioritz motors. Heck, there's probably some folks out there that prefer the Ryobi conversions....

Get facts - which in THIS game means "opinions" or "experiences", and weigh - weigh very carefully what you read.

BUT BUY WHAT YOU LIKE !!!!

And will you guys STOP telling me that my ZDZ and Taurus engines aren't any damn good????????????????????

Hey Bob:
Of course you bought the right engines!

And Kris:
It just dawned on me, there's an easy way to test your theory about the rotary valve motor running out of breath at high rpm. Just do comparative tests with smaller props on the ground. If one engine is ported for high rpm power, it will show up with smaller props. However, someone could argue that the rotary valve motor was designed for a torquier power band to run larger props at low rpm where prop efficiency is higher.

That would work, except for one small problem .. smaller props require less horsepower to turn up, so the motor would happily spin away.

an easy way to explain it is this. . 2-stroke powerbands are peaky, the power goes up as the rpm increases, to a certain point. . and then that's it, the power stops. Ask any 2-stroke motorcycle racer about it. Everyone thinks these motors have "torque" but they don;t. .they have a small amount of torque until they start getting into their powerband, then it increases very rapidly to a peak, then drops off even faster. Piston or disk timing makes it even peakier, while reed valves (which "adapt" to airflow needs) tend to smooth it out a bit. so, that quick dropoff after peak Hp experienced with disk or piston ported motors is softened and made more gradual by a reed valve. remember, Hp is a function of torque versus rpm. . and the torque is dropping off as the rpm increases so when the engine runs out of breathing ability it REALY drops off fast and the Hp jsut dies above that point. .call it a built-in rev-limiter.

BTW. . My 3w and DA150's both turn the menz 32-10 well in excess of 6100 rpm static, and as high as 6400 rpm on the ground. .things get really noisey really fast on takeoff, usually ripping the prop at full throttle as the wheels leave the ground (10 feet). . . . .don't see any ZDZ 160's doing that.

Kris said:
That would work, except for one small problem .. smaller props require less horsepower to turn up, so the motor would happily spin away.


Yes but all props, (big or small) require a lot more power to spin faster. The prop load (horsepower) is an exponential function of rpm. That's also why the low rpm powerband or holes in that powerband don't mean a whole lot for our application. It requires very little power to turn the prop at low rpm and accelerate it through a flat spot in the powerband.

A small prop on the ground is a good simulation of a large prop in the air when it unloads...that was my point.

Hi All.
My $0.02 on this issue.

In regards to limitation of creating more power due to lesser resistance of the air on the prop while in flight.

Your theory about restricted breathing of engines equipped with rotary valve seems to be logical.

BUT, IMO we all should check the rpm of respective engines on the ground and compare them, since most of fliers this days are about brute torque when 3D ing. and not racing the planes around to get them disintegrated by flutter, that makes this argument irrelevant, because we can not achieve any more rpm in hover position than on the ground, by saying, the prop is being ripped somebody mean that they do not use throttle management correctly or prop is to small or wrong load. Most of riping props at our field happens on down lines and not when airplane is pointed up.

I head used ZDZ40RV with DIABOLITON muffler and this engine outperform all others of the same size by far.

And yes, you get 300-400 rpm with tunned canister and you can use it when you need it, on up line, on the other hand your engine does not run out when you forget to bring the throttle down on the down line. In the way that helps the pilot .

Unless you are racing pilot, you do not need more rpm (power) with increased speed, that is my logic.

There is about 6 ZDZ at our field in use and all of them are superior in power to anything else of the same size. that would proof's the point that rotary valve is superior for our application.

I have never seen another 40, 60, or 80 developing same or better power than ZDZ.

Just to let you know, I am not bias, I fly Brison, 3W, ZDZ, BME, WEBRA, about 15 in all.

Thanks for reading, Jack.

Okay. . a very good case in point here. . i hae one of the RCS180 rotary valve engines on my 118" "Tele*******" trainer/nightflyer. It turns a 18-8 master Airscrew "Scimitar" prop at about 7900 rpm .. not exactly a big powerhouse. The thing is, it spins the same rpm at half throttle as it does at full throttle. . not one rpm more. I tried a 17-8 APC. . same story. . 8200 rom at half throttle, and at full throttle. . no difference. In the air, the sound on a full-throttle level pass, at about 50 mph is basically the same tone/note (frequency) as when it's in the pits, to me meanign that the engine, even unloaded at full throttle, is not turning ANY more rpm. . you gotta sk yourselves why??

The WHY of it is that the disc valve can;t flow air any faster than it already is, no matter what load is on it, or how fast the planeis going. An APC is a touch less draggy than a Scimitar, and its 1" smaller diameter with the same pitch, yet it only gained 200-300 rpm. Facotr in having the same rpm anywhere above the half throttle point, and its OBVIOUS that the choke point is not the carburetor, but in the porting and disk valve timing.

For comparison sakes, a Vera 31 cc Ryobi conversion, with reed valve induction, will turn the same prop at the same rpm, BUT, there is a difference in rpm between half and full throttle. . . . I measured the carburetor bores, the RCS bore is larger by 1.5 mm, meaning that the Vera's carb was more of a restriction, so it had a more "linear' power curve in relation to the throttle setting. Obviously the RCS180 is RPM limited. Since it has MUCH healthier ports than the Vera (YUCK ports), the only possible restriction would then be the intake valve. . think about it. . the valve is timed to flow air to a certain point. . anything above that is never gonna happen. . .just like the ZDZ rear induction motors.

just imagine how strong the ZDZ80 could be if it had a REED!!!!!

Oh Kris:
As I already pointed out, maybe you missed it.

There are 2 versions of the ZDZ-40 side exhaust motor.
One has a rotary valve, the other has a reed valve.
The reed valve motor is offered at a lower price $340, vs $410 for the rotary valve motor. That's because reed valves cost less to make!

Ask Dick Hanson which motor is stronger, I belive he has both. Trust me, you aren't going to like the answer.

If you don't like his answer, send an e-mail to Mike Dooley at RCS and ask him. Oops, you won't like his answer either.

Think about all those glow motors with either rear rotary valve or front rotary valve (crankshaft). Are they starved for high rpm power because of the rotary valve? I don't think so. If a Nelson or Jett pylon motor could be faster with reeds, don't you think they'd have 'em?

Dick Hanson tried a longer duration rotary valve in a ZDZ-80 - an easy modification to cut the disc. He got it from Randy Villines. No improvement.

its not whether I like the answer or not. . but WHY the answer is the answer.

people quote all sorts of numbers for stuff without examining the "why'; of how it occured. . is the "reed" setup even more restrictive??? Perhaps with a smaller total inlet area?

If what you infer is true. . then the ZDZ160 would be turning a SUBSTANTIAL amount more RPM than a DA or 3W 150. . fact is, with comparable exhaust setups the ZDZ is weaker in every case. The 3W and Da rip props all day long in level flight, and the ZDZ160, with the same exact prop .won't! We'll use the menz-s 32-10 for example. Everyone says the ZDZ is quiet and won't rip props. . . . it has 10 more cc's and the vaunted 'disc valve" and it can't out-turn a smaller motor with a reed valve?? Cmon, where's the logic here???

As for talking to Mike Dooley? I have, several times. . and the answers to "tech" questions were more a re-direction of the question than a factual "here's what's happening and why" answer. I had to basically pin him down on the 160 and it's development problems when first introduced before he'd admit to it. if the representative is not totally forthcoming. . how can you believe (with no doubts) the next thing he will tell you? Only two "engine people" I have talked to will lay it all out on the table. . Keith Baker and Dave Johnson. . with everyone else I get a sales pitch and promises. The promises have never rung quite true, unfortunately. And THAT is what sets the products of BME and DA apart. . let's get all the FACTS on these "reed valve" ZDZ's. . . .then make an honest comparison. I think it would be easy to see whats going on, or not working, and why.

Kris:
If you want more design details, It's alwasy best to talk to the engine designers. Dave Johnson, KB...and for the ZDZ, talk to the engineers in the Czech Republic. The US distributors for 3W and ZDZ didn't design them, so I wouldn't expect them to have all the info that you might want at their fingertips.

When I worked for a Yamaha dealer, the factory didn't tell us any more than they thought we needed to know. In fact, they hardly told us anything. I remember trying to get the design specification for hardness or yield strength on a bent axle, in an attempt to determine the cause of failure. Never did get an answer from on high. You would think that someone would like to know that they screwed up the heat treatment.

My point exactly ..

We are getting 3rd hand information from the importers, who aren't even engine designers/builders. Then it is in their best interest to sell us the product. . AND a bit of a "reputation" comes along and you suddenly run into "performance one-upmanship' and all the facts get blurred. .

I guess you could say I'm a bit of a skeptic . .. but being a "techy" I can afford to be.

Hi Diablo,
I am flying a hanger 9 33% cap232 with a zdz 120 and it rips the prop all day long and I don't understand why Kris insist that they will not do this.It try's to rip on the ground at full throttle.I'm not going to get into a pissing contest here over this subject I'm just letting you know they (zdz) will infact rip the prop.I have two other zdz's in my shop and they also do the same.People are alway's very impressed with the power plant in the cap.

gee. . WHICH prop???

Zinger 22x8 of course

gotta remember, it WAS 4:20 in the morning when Thomas wrote that!

Yah. . My TOC100 tips a 28-10 Mejzlik (not menz or bolly) at 3/4 throttle on Supersonic mufflers in the air.. all day long. You would figure a 120 should be doing it with a 30" prop. . the 3W 120 does it without pipes!!! And it will also swing a 30-10 or 30-12.. .I know guys who do it. . . .on supersonic mufflers.

Like I see, every body make a discussion of the power of the engines but all measurements are in ground and with out load.

The reality of this is that 200 0r 300 rpm at top end in ground is not much' if you don't know the range of torque of your engines.


All this engines don't have the same torque at the same rpm by this way any engine that you have,you have to test the difference prop to get your better balance in power/torque and weight of your plane.

The prop is the transmission of your engine and you have to choose the prop in reference of the range of torque of your engine to get the most advantage in the flight.

Also we have to had in the brain that +CC=+torque

All this engines are excellence and can't go wrong with any of your choice, all depend of you type of flying and what you want.

There are no bad engines just bad mechanic!!!!!

By other way that my experiences, tell me the rotary valve have much better torque/ transition of mid to hight and reed valve have much better torque transition from low to mid. Its your choose.

So much of the time these arguments go on without much factual information. It is nice to see to people(Kris and Diablo) have a good discussion about the differences with these two engines. I have learned a wealth of knowledge from both of you. I own both zdz and 3w engines. The are both wonderful powerplants. Mike Dooley at rcshowcase is wonderful along with Andrea his secretary. Gerhardt at Aircraft International is fantastic. I have purchased engines from both of these reputable dealers. They have both provided me with ample information about their engines. I just recently bought a 33%Staudacher which I am putting a 3w 100b2 on. I will try the new zdz 100 on something. I am back ordered on it. It's funny now how you buy the engine before the plane. There is something really wrong with that statement.

Anyway, I am just a supporter of a nice intelligent discussion between knowledgeable RC'ers.

Barts

Now. . go call DA (520-722-0607) and BME (254-836-0735) and see what THEY have to say . . . I'm sure you will be even more pleasantly surprised.

I left those two engines manufacturers out. I apologize Kris. I will sing the praises of them to. I have a 35% Carden "Baby Edge" with a DA 100 in it. It is absolutely ballistic. I love it. I also have an Airwild 27% Edge 540t with an early bme 44 in it. It is wonderful to. When you have been in this hobby as long as I have, trying out all of these manufacturers is a must. I am finishing up one of 3w's 40% 330l's. I am going to put the new zdz 160 in it. I will keep everyone informed.

Later
Barts

ARGH!!!!!!!!!!!!!!!!!!!!!! Ok, whatever you do, don't hit the escape key!!!!! Now I have to start over!

Ok, I couldn't let this one pass. I have both a ZDZ80 and a DA100. The DA is, as of yet, untested. The ZDZ80 is pretty close to new, but has been flown a few times.
Kris when was the last time you tried to call DA? The last half dozen times I called I had to put my phone on auto redial and wait half an hour to talk to someone! This DOES NOT affect their product or service IMHO. They are still great.
As far as how these engines rate, keep a couple things in mind. First, the ZDZ was designed in Europe with European flyers in mind. They ALL run cannisters and big props to keep the noise levels down, so the ZDZ was designed this way. No, it's not an all out top RPM engine. It is, however, a great torque producing engine that will swing props similarly to 100 twins. And what is it with "ripping the prop"? So what! If you rip the prop, you are overspeeding it. Get a bigger one!
Now, that being said, it's not all rosy with my ZDZ 80 either. Due to flying site noise restrictions, I had to use a can in my 35% Lanier Giles that the 80 is mounted on. It was a pita installation and to top it all off, I lost 500 RPM over the J&A pitts muffler. I got around 6000 with the pitts.
In all, everyone has to make their own choice. It's a matter of heresay until you get YOUR engine in YOUR airframe at YOUR location. I wouldn't hesitate to buy another ZDZ from RCShowcase. They have been the most excellent company to deal with since I've been in this hobby (10 years....just a pup still). As far as DA, I have no doubts that this will be an excellent engine also. I chose it for my latest project because it was available to me (used) at a great price. If I hadn't found it, I would have used a ZDZ 100.

Ok, managed not to delete it this time........good luck with your decision(s).

-Aaron

P.S. --Now donning my flame retardant suit <G>

As a matter of fact. . (this is funny) I dialed the number to DA this afternoon. . it rang. . was picked up on the 3rd ring. .Kevin handed it right to Dave Johnson who was standing beside him. . ..and I touched base with him on a few thigns that are ging on (Like . . the DA50 is SHIPPING!!!!!), props that DA is getting in and the wonderful niavete of the average GS modeler when it comes to engine selection. . . I didn't even buy anything. . but he knows I will and that he is my first choice for parts, props and advice.

What did he say about the DA-50?????

Dan

Dave said that they had done a bunch of re-work and refitting of parts on the DA-50 to get the power optimized (like DUH. . good idea). One figure he said for their testing was a freshly built DA-50 turning a 24-8 menz-s at 6400 rpm. . . .On muffler, not pipe. he said he'd be sending them out as quick as they got built, starting with back-ordered customers and working them off first. . must be a HECK of a back-order list.

Props, props and MORE props. . mejzlik has a 25-12 3-blade they are testing at the moment, and other sizes coming out. . AM is in short supply, as always, and DA is working their butts off to keep up. .

and other things, but hey, my memory isn't THAT good

O.k., you have had enough time to make your decision, what are you planning to buy??

BME!!!!!

No, not you Kris, JIMMY THE EAGLE since he started this thread.