Flyfalcons

Do you have a measurement of the pitch and diameter of the prop? A friend's ZDZ80 will swing a 26x10 two bladed prop with a top speed of around 65 or so. Thrust is good, it will take a 25 pound plane and accelerate it vertically.

gvincent

I have not actually measured the pitch, but if I remember correctly, it's susposed to be a 24-12. We had to limit the diameter because of ground clearance (thus a smaller, tripple bladed prop), and the pitch is designed for cruise at around 106 mph. I'm already forgetting the numbers, but I think the plane is around 22 lbs (ballpark).

Any opion on the prop setup?

Desertrat

My Feedback: (2)

That Zinger setup looks like a real PITA. Have you looked here for props?
http://www.desertaircraft.com/props.html

Mejzlik and Bolly make some really nice 3 bladed props, both of which I would guess are more efficient than the Zinger setup, but this is just opinion....

Very curious to see if all the drawing board calculations work out in real life. Good luck with your project, and keep us posted!

gvincent

I just posted this in the ZDZ forum for Mike Dooley. If any of you guys have any advice, I'm all ears.
---
We just ran our new ZDZ 80 and are having some problems with it.

First, the engine stutters at lower RPM. We also had a problem getting a spark--sometimes it would spark, sometime it wouldn't, and this was without changing our setup at all. This was not due to the 1-minute ignition safety cutoff.

Second, we're getting a max RPM of 5000, which is corresponding to a max power of only 4 HP. This is less than half the expected power and is not enough for the planned aircraft maneuvers.

This is with a 3-bladed Zinger 22-12 prop, the Bisson inverted Pitts muffler, and with 87 octane gas and Valvoline multipurpose 2 cycle engine oil (TC-W3 certified). This oil was used instead of the Penzoil. This data came from a static test during the engine break-in period. The engine was run at around 3000 RPM for a gallon (around three hours, total). All the recommended instructions were followed as carefully as possible.

engine test

On the plus side, we're getting twice the fuel efficiency that we had planned for (at least at 3000 RPM), so that's good.

We are very concerned with these two problems. What could be causing the ignition problem? And as for the power loss, we need to solve this problem rather quickly. Is it the prop? Is it just the break-in performance? Is it due to the test being static and not in flight?

Thank you for your assistance,
Graylan Vincent
University of Washington Aeronautics & Astronautics

Diablo-RCU

My Feedback: (1)

I'd ditch that prop. Get a Mejzlik 2-blade 24x12. Should turn about 6500 rpm if everything is adjusted properly on the engine. Is the timing of the ignition adjusted properly? If in doubt, move the sensor holder all the way clockwise (most advanced timing) and try to run the engine again - recheck the rpm. also, cut 1/2 inch from the outlet tubes on the Bisson muffler - less restriction and about 300-500 more rpm. Make sure you are using a fully charged 4-cell ignition battery of at least 1200 mAH capacity - otherwise the ignition will be weak and the engine will not run with full power. I use a 2700 mAH NiMH pack on mine.

rmh

The oil you selected may have fouled the plug--
get an identical plug for a replacement test-
I have setup many of the ZDZ80's and if done per the book- everyone works well.
a 5 cell batt will ruin the ignition-
the Zinger prop setup is not the best setup available -but will run.

gvincent

We'll check the plug the tomorrow--we've got two others, both from RCS. I'm curious, how will a 5 cell battery ruin the inition? For the break-in test, we used a DC power source. I'll find out what it was set at, but we had two experienced flyers there checking the setup (one of them flys a ZDZ 80), so I doubt that was the problem. They seemed to think it was the prop, but this seems to be too dramatic of an RPM loss to be caused solely by the prop. That's just my opinion.

Bill S

My Feedback: (-1)

Part of your problem may be due to using 87 octane gas. I think ZDZ specifies the use of 93 octane gas in all of their engines because of the higher than typical compression ratios used. I know this is true for my ZDZ 40cc and ZDZ 50cc engines.

Also, I'd be wary of using a DC power supply for the ignition instead of a good, fully charged battery, as recommended above. Unless your power supply has extremely good regulation and very low internal impedance, it may be loading down and causing the symptoms you described.

Bill S.

stalspin-delete

Just got into the tail end of this discussion. And truthfully sounds like some trolling being done.
one ft. cord 4 ft.long, 22lbs, box wing, its still a bipe. 4lbs of fuel. come on guys look at some of the IMAC planes that literally blow holes in the sky with more weight and the same power.
just to add something from my experience, a 69-75 cc engine burns about 2oz of fuel per min. WOT. Based on 4.5lbs of fuel is aprox 3/4 of a gallon (96oz)= about 48 mins of flying time. Surprised your "prof" hasn't gotten involved. senior year????????

gvincent

Ok, I talked with our group members who did the test. The oil worked fine, and didn't clog the plug (they had called around to find the best oil since no one had the recommended oil in stock). The gas was 87 octane, which is what was recommended for the break-in period as per the RCShowcase instructions that came with the engine (dated 11/2002). We'll switch to 93 octane after we get to the 6th gallon (we're still breaking it in), or probably even sooner. There was no battery between the power supply and ignition, but it was one of our good lab power sources, so it should behave bettery than a battery (we had a constant voltage). The spark gap distance was also checked, so that's not the problem.

I plan on chopping off the round tips of the muffler exhaust as soon as I know for certain that they will still clear our cowling.

I'm looking into buying a 3-bladed Mejzlik 22-12 to replace the Zinger. Anyone know what size spinner we'd need for this? I'd like to get as small (and cheap) of a spinner as possible.

Other than replacing the prop and chopping the exhause pipes, we'll just continue to break it in, switch to a higher octane, and advance the timing if all else fails.

Has anyone else had such low RPM's during break-in?

Graylan

Diablo-RCU

My Feedback: (1)

You are misreading the instructions. Nowhere does it say to run a ZDZ motor on 87 octane gas. An RCS motor will run on 87 octane, not a ZDZ! RCS sells ZDZ motors as well as their own brand (RCS). I would also spend $10 on a 4-cell nicad battery for the ignition - just to be sure you are getting enough voltage and current to the ignition. To save money, don't bother with a spinner - it's only for aesthetics. A 22x12 3 blade Mejzlik will be too small of a load. Use a 24x12 2-blade Mejzlik.

strato911

- Mathematically a 3 bladed 22 X 12 is more load than a 2 bladed 24 X 12. I've never tried it since I am just starting to get into gasoline powered aircraft, but your statement sounds flawed. What is the basis of your statement?

gvincent

I'll go over the prop sizing calculations again on monday, but a 3-bladed 22-12 is greater of a load than a 2-bladed 24-12. We originally calculated needing a 2-bladed 24-13, and wanted a smaller diameter, thus the 3-bladed 22-12. The problem is that this calc may have been done at 8200 RPM, which we now know to be unrealistic. I'll redo the calc for about 6600, and see what that gets us.

As for the gas, we received a document entitled "Gasoline Powered Engine Basics" with our ZDZ 80 engine. The very first point of the very first page reads,

"1. Regular pump grade gasoline of at least 87 octane should be used."

The document is authored "RC Showcase, Inc. November 2002." It mentions both ZDZ and RCS engines, but the rest of the packet is specifically for the ZDZ engine. We are trying to follow the instructions to the T so as not to void the warranty, but I can see where the confusion came in. I just read Mike Dooley's posts in the ZDZ support forum, so we'll use a 93 octane from now on.

As for not needing the spinner, is it really a good idea to turn the engine over by hand without a starter?

I'm sure we've got some batteries around, so we'll try using those from now on.

Can you explain what Dick Hanson meant by,
"a 5 cell batt will ruin the ignition"?

While we're on the subject of batteries, think it's possible to get an hour out of the ignition batteries? Our systems guys are looking into this, but I could use some seasoned opinions to throw at them.

Thanks,
Graylan

Diablo-RCU

My Feedback: (1)

Calculating prop load?
I know of no equation that can calculate prop load accurately since you don't know anything about the area or airfoil of each blade.

My seat of the pants WAG tells me a 22x12 3-blade prop is too small for a ZDZ-80. Most people who run a 3-blade prop for aerobatics are using a 24x10 or a 24x12. That's why I recommended a 24x12 2-blade prop - so the engine will turn around 6500 rpm on the ground, and so you will get the high speed you want. If you need even higher speed, drop down the diameter to 22 inch, but use even higher pitch (14-16"). But, I don't know if there are good commercial props available higher than 12" pitch.

On 100cc motors people run a 25x12 3-blade prop.

Bill S

My Feedback: (-1)

Regarding your question -
Can you explain what Dick Hanson meant by,
"a 5 cell batt will ruin the ignition"?

The specified voltage range of the Falcon ignition is 4.8 to 6.0 volts. A fully charged 5 cell Nicad pack will produce on the order of 7 volts, or more, which will exceed the maximum specified voltage and possibly burn out the ignition module.

Also, the importance of a low impedance power source should not be disregarded. That's why RCS recommends using a 4 cell NiCad battery and not to use a NMH battery, although some are using NMH batteries successfully. NMH batteries have a higher internal impedance than NiCads and their voltage will momentarily decrease more with each of the short duration, high current, ignition pulses than will the voltage of NiCads.

The length and size of your battery leads is also a factor here. Long and/or small gage wire leads will increase the impedance and give you a greater voltage drop at the ignition module, resulting in a weak ignition spark and poor engine performance.

Bill S.

tshcat

My Feedback: (1)

It seems you can use a little help from R/C guy from Purdue (like in big 10 Rules)

There is a lots of good stuff on the flowing web site.

http://www.rcfaq.com/

When you get there, click on props. Then go to the bottom of the Page and down load the thrust caulator Program. I have used it and the results are very good.

They all so have a good data base on differnt engines (Prop/RPM).
You can see what results other's have had with there engines.

Good luck --== Ted ==--

rmh

Wow- I can see how confusion is created.

My comment on the 5 cell - - holds - stay with 4 cells AND plenty of amperage - ditch the friggen power supply.
The Falkon is simply not designed to accept voltages over 6 v -even with teeny tiny amperage supplies.
Someone at your school must know something about current requirements for spark ignitions.
This ignition is NOT like some US made ones - it requires a supply having a fair bit of amps
get a Sanyo 1200 ma 4 cell nicad-they are relatively cheap .
the oil ? I can't believe that Pennsoil aircooled two stroke is that hard to get - -even our local Maverick stores have it - as do some K Marts.
Prop load?
Diablo is right on target - the little 22" three blade is not much load --and the prop load charts are not worth a pinch of puppy poop.
None of em.
I hav 24x12 and 26x10 Mens Ultra three blade props -- and load is close to 26x10 Bambula and 26x12 MenzS-
Gasoline- 87 will run fine - at our 4500 ft elev - I have zero problems with it -and 91 oct shows no measurable or detectable differences.
Theory - higher octane GASOLINE, will burn slower - preventing detonation.
As long as detonation is not present - power will be fine --in fact - to obtain most power - use the fastest burning gasoline which does not detonate.
So-- 87 should be fine.
I have run performance augmented automobiles (hot rods)-- since 1954 and the stories about which gasoline does what never cease -
simply buy an octane (and watch where you buy the stuff) which delivers full power with no detonation.
The class project sounds like it will be fun and hopefully a real education for all.
When I went to college - the only elective course was plowshare design.

gvincent

Ok, we had the chance to test the engine again last week with some good news and some bad news.

First off, I have to explain that we aren't testing the engine on campus, partially because of noise but mainly because a former student took the test stand and is using it at the company he founded, about half an hour away, which is where we're testing.

The bad news is that we broke the prop. Well, actually, one of the company employees (a former student from our department) broke the prop. He was trying to tach it and got way too close with the handheld tach and shaved the trailing edge off two of the three blades. He's lucky he didn't loose any fingers.

The good news is that one of the other employees flys the same engine and showed up half an hour later with his Menz 26-8, so we threw that on there and the RPM's picked up to 6,300. This was a huge increase from our Zinger's 5,000 RPM. This means I have to buy a new prop to replace that dam* Zinger. Darn.

So, looks like it was the prop all along. I had also cut the exhaust tubes on the muffler by about 1/4" (Bisson Pitts inverted), but I seriously doubt that this has much to do with the increase. The engine ran really well, had great pickup, and idled down to 1900 if I remember correctly.

Details:
48 deg F, 100% humidity (partially raining), 93 octane with 40:1 Valvolene. Total of about 3 gallons through it. We also tried 60:1 Amsoil with 87 octane, just for schitz and giggles. Ran smooth the whole time. Still working on the thrust data--should have that tomorrow.

We were using a power source because our batteries haven't arrived yet. Dick, I think you're right about the power source--when we revved the engine, I saw it drop from 5.0 V down to 4.7 V. At the time I didn't think anything of it (too tired to realize what I was seeing). I'm hoping that this is limiting the ignition and that we will get even more RPM's out of the thing with batteries. Too optimistic?

Anyways, now I have to re-choose a prop. Does 6,300 RPM sound a little slow to anyone else for a 26-8? Here's a question--we need both speed and power (who doesn't) to be able to get up to ~106 MPH (our designed maneuvering speed). Is there a minimum pitch that I should look at to get up to this speed? I know that speed is going to depend on pitch and RPM, which is dependent on prop size, and so forth, but for say a 24" Menz or Menz Ultra, does anyone have any recommendations? I could do calculations all night, but I'll trust experienced advice over theoretical numbers any day.

I'll try to get some photos online of the engine test setup this week, and maybe some shots of the plane. The fuselage is nearing completion but we're still working on the wings. The whole thing is yellow kevlar so it really is quite an ugly airplane. We've nicknamed it the CornDawg (University of Washington = Huskies).

Flyfalcons

You'll certainly want more than a 26x8 if you are looking for speed. A ZDZ80 is happy turning a 26x10. I have a couple 24x12 props (Bolly and Mejzlik, very high quality) that I may be interested in selling because they don't fit my application of slower aerobatics with a Zenoah GT-80. Maybe we could meet sometime.

Flyfalcons

Oh, just to make clear that my props are two bladed.

Tobias Schlegl

Hi!
FYI, the german ZDZ distributor has tested different props on all ZDZ engines. You can find the results on:
http://www.amelung-modellbau.de/de/pg_19.html

As i was told the ZDZ engines need quite a long break in time to reach full power and like large mufflers with long headers. Falkon gives a range of 3.8 V to 6.7 V for the ignition power supply.

Tobi

Antique

My Feedback: (4)

Like TKG said way back in the discussion, you will need at least a 16 pitch prop turning over 7000 rpm to go 106 mph..Just ain't gonna happen with the current setup....Speed takes POWER, something the ZDZ doesn't have at the RIGHT rpm..We're using Zenoah GT80 engines in sleek 25 lb Formula One race planes, turning 9000 rpm in the air and clocking 150 + mph...Engines are stock, burning gas, with specially made props...Same engine on glow with a 16-12 test prop turns 11.000 rpm..The Glow powered formula One planes are flying 170+ mph, engines unloading to 11,000 + in the air......No one has tried a ZDZ 80 yet, maybe this year....
Zenoah engines are made to develop their power at 9000 rpm..Says so right in the Instructions...
The specially made APC race prop turns 7200 rpm on the stock engine on the ground..,

rmh

R-- the ZDZ engines are rated to 8000
and powerwise - on setups with pipes - they wail pretty well- I was getting over 7000 yesterday on a stock 80 single --using a huge 10-80 KS pipe on a rather short header - the prop --a 26x10 Mejzlic.

If I was going for revs -I would look at the 100 cc twin -- this has almost 170 degrees of exhaust timing -
I tried one -with various exhaust setups--and on the 10-80 pipes it ran extremely well --but I believe it could easily be a high rpm setup.
The 80 is around 150 exhaust -- but has huge 6 channel intake porting - should be very good as a racer - setup right.
I don't race airplanes - so I will never know ---I typically load em down to mid 6000 range - noise etc..

Antique

My Feedback: (4)

Yup, made for aerobatics...And we can't use tuned pipes or cans, just an 8 inch straight pipe....Pretty amazing speeds for such a small engine....We're going only 234 mph with our 289 cc racers...

rmh

I am more familiar with making 283 cu in run - but that sounds fast .