MTK

Ran the 19x13 hybrid last night. Well, well, I finally have a load that appears to be too much for this engine. The prop will be modified to make it more of a narrow blade and we'll see how the narrow version will behave...

Full throttle RPM dropped to 6800 on the 19x13 but it isn't only rpm. The engine got hot and rpm dropped down to 6500 within 30 seconds at full revs. I didn't try to retune it or anything, just went with the needle settings I had.

I also tried an 18.5 x 9.5 extra wide blade APC. This prop was turned with as much authority as the 19x11 or 20x10...back to 7600 at full revs, 6800 at mid throttle and a low of 1600 at idle. The interesting thing about this prop was a rather linear throttle response; every click of throttle resulted in an rpm change. I will fly this prop and see what it does in the air. It is a heavy prop tho, weighing in at 165 grams, more than 2X hybrid prop weights.

Well my model needed a little more nose weight anyway..... R&D will continue to fully characterize this engine

rmh

I hope the OS works better than the other gassers we tried .
The basic problem in single cyl engines is an unbalance which is typically stuck at somewhere around 3000rpm

The ignition curve can be tailered to lessen this thump
We tried various motormounts which can help but it all adds up in more weight
If you want to use lighweight Carbon fiber fuselages - the problem can get worse as the lighter the fuselage the more resonance you encounter .
Wood done right soaks up various resonant stuf much better but you also have to fiddle with locations of formers and such to cancel low rpm nodes.
Hope you get a good workable combo- I used Ed Skorepa pipe and we finally threw in the towel as the electric could be built much lighter and power was more constant.

MTK

Thanks. The OS is about the best I've tested so far regarding pattern power requirements but I have not tested all of them. The better set-up is the DLE55cc as I've discussed before but it is heavier and requires much more careful building. The power curve is the best yet for pattern compared to Anything I've seen in pattern

I am very curious about the new DLE35RA rear exhaust coming out in a couple months.

I am well aware of electric developments. My buds are at that leading edge of the best electrics. But that is not where my interest is right now.

A friend brought Petrel over for a quick review and mod session....Oldie and goodie, Dick?

airborne2.4

DLE35RA!? Is that just a rumor?

MTK

Actually the OS33GT works fine in 11 pound pattern planes. OS has done alot to get us torque where we need it. I do not lead the throttle at all with this engine as compared, say, to the SAP180. The SAP180 was not really close to the YS170..the OS is at least on par with it, now, after about 6 gallons

I saw a considerable "thump" at around 3K with the SAP180. I don't see that with the OS...much smoother output throughout the curve. And the rubber isolation mount works well on glass and carbon fuses. No need for heavy wood reinforcements/absorbers. One of these days I should take a movie so you guys can see what I see and hear. Also figured out how to build a nose ring around the hall sensor that works well. The soft mount and nose ring added around 5 ounces to the airframe....

MTK

I tried the APC 20x10.5 PN this weekend, before the contest. The engine turned this prop well. I didn't get lots of run time tho because clearance at that grass field was a potential problem. As I get more run time with this and the 19.5 x 11.5 PN, I'll post here.....

MTK

The 20x10.5 APC has been working very well on the OS. This is the same prop guys are using on the YS175....

It needed slightly richer LS needle to improve the idle in flight. Transition is very good and all flying is basically done at half throttle, controlling speed. In low to moderate wind, I use about 10 ozs gas for two Masters flights back to back, around 15 minutes flying time. Also, got to fly the engine in 85F temps yesterday. No problem with cooling....it is continuing to impress.

The only thing better would be to have the same engine in a rear exhaust configuration

riot3d

Matt,

The 20.5x10 PN works even better on the 175.

Adrian

papaone

Hello Matt

I aggree with Adrian.
Last wednesday I tried APC propeller APC 20.5 x 10 on my Harmonie Evo and 175 CDI. It's better.
The runs are slower. On my plane there is less torque effect.
Claude

MTK

Claude and Adrian,

As well as the OS turns the 20x10.5 I believe it will have no problem with the 20.5x10. It produces a lot of power especially in mid range where the YS has been king thus far

My issue is clearance with the current landing gear. The model needs one inch more clearance to work better on the grass fields we fly off of in New Jersey. The 20" props hit grass and carve a visible path. Annoying!!

My current gear mold has the room so I'll probably make another set of gear sometime after Pocono contest. Just don't want any more side projects (I am at the finishing stages of my new design), but this one is unavoidable

MTK

The 20x10.5 is working great....... So well in fact, decided to change to an 8 ounce tank today. It gives me around 14 minutes run time, nearly enough for two masters schedules back to back. Plus, 14 minutes is much more neighborly to my flying buds

sps3172

Matt,

Are you still chasing a rich spot in the midrange with this carb?

Just out of curiosity, how far open is the butterfly held at idle (expressed in number of turns on the idle speed screw from fully closed)? Also, is there any sort of 'half round' cut from the throttle butterfly (near where the plate meets the inner wall of carb venturi)?

Depending on answers to the above, I may have a suggestion to lean out the 'fuel curve' of the carb in the midrange.

- Steve

MTK

Steve,

Well, it is ever so slightly rich at just above idle, maybe around 3-3.5K rpm. It clears up fairly quickly so I'm not sure if it is just getting warmed up and still clearing its throat, so to speak. True mid range, around 5.5-6.5 K is very close. Judging from the plug color
it is just about right. That's where I fly practically everything. Throttle curve I run is a backwards and sideways "S" almost linear from point 0 to point 2, fairly flat curve from point 2 to point 5 and nearly linear again to point 7 which is max

There is never any need to go to full revs even in strong wind (20+). I check full revs every now and then, but only with the nose straight up to check to see how well the engine is cooling under full load. In 85 degree environment the plane can still be snapped with full authority after a vert climb of 600-700 feet, without sag. That's plenty, but we haven't had 95 degree temps yet so we'll see..... Baffling is a must and mine comes within 1/4" of the fins

The idle speed screw was pitched long ago so to answer the second question, I really don't know. I close the thottle butterfly within 1/32" and usually that works pretty well. I tend to run the idle mixture based on the load I'm running. For example, the 20x10.5 needed about 1/16 turn (about the blade width of the screwdriver) richer on the LS screw such that it would settle down better in flight (downlines). The 18x10 3 blader and 19x11 2 blader require a leaner idle speed.

One thing I've noticed that I haven't been able to identify cause for is the fact that inverted downlines (45s usually) the engine seems to want to rev a bit more than when upright. On the 45 down snap that works to my advantage but on the square on corner, it's a disadvantage. I suspect plumbing but not certain. The carb is not set-up for equalization and that may also be a contributor.

Does all this make sense? Did you get my earlier response?

sps3172

Matt,

[DISCLAIMER] Info below may be old hat for you.....I do NOT mean to suggest that I know better, by offering suggestions. I just thought I'd throw this out here as I didn't see it mentioned elsewhere in the thread, and more info is usually not a bad thing ]

Not sure about an earlier response..... I did send a PM earlier, but I presumed you'd get to answering that when you had some time....no reply here yet.

On to the carb....

"Most" Walbro carbs have some sort of small cutaway in the butterfly that forces air to enter the carb right over the low speed/progression jets when the engine is at idle. In an ideal world, at idle, ALL of the air would be entering the carb via that cutaway (i.e. butterfly is closed fully), instead of allowing some air to bleed by the slightly open butterfly. When the butterfly is held slightly open to achieve desired idle speed, the vaccum over the aforementioned jets is reduced and one has to open the low speed needle to compensate. As the throttle is opened, the velocity and vacuum increase in the carb and jets now flow too much fuel for partial throttle.

Provided you can kill the engine with the ignition, I would suggest that you start enlarging the butterfly cutaway. You need to creep up on this.....but as the cutaway is enlarged, you will have to close the butterfly to maintain the same idle rpm. You'll also have to re-lean the L needle as you just improved the vacuum over those jets. In the end, with the engine recieving ALL of it's idle air through that cutaway, you will have the leaneast midrange possible with your particular carb jet sizes. Does this make any sense?

Also, you mentioned adding fuel to get the engine RPMs to settle during a downline.....

Here's my .02 on that. Rather than add fuel to an engine that 'hangs' before settling to idle RPM, one should lean the L mixture such that the RPM never settles (stays 'hung', if you will)....then mechanically reduce the throttle to lower RPM to desired idle speed. Tuning this way means, of course, that you'll have to make up for that missing fuel on the top end by opening the H needle. Again....did this make any sense? Also, I'm not positive this is what's happening in the air, in a dowline.....but it might be another tool/trick to keep in your tuning qiver none the less.

- Steve

MTK

Steve,

Send me your direct email address. I replied to your PM but obviously it never exited RCU servers, a very common problem in my experience

sps3172

Hi Matt,

I sent contact info via PM, but in the event that it doesn't make it.....

[my RCU USER ID] @ yahoo . com

burtona

My Feedback: (50)

btt

computermonkey

My Feedback: (90)

Hello MTK

I have read several of your post on pattern flying and gas engines.

A year ago I picked up a Moki 180 gas engine. A couple of months ago I was able to picked up a AeroSlave Symphony and ever since I have been thinking about trying to put them together.

Can you PM me about your experience with the Moki and pattern plane when you get time? I am also looking for a wrap around header for this engine.

Thank you.

MTK

Hi CM,

I have no experience with the MOKI 180 gasoline engine. Your best bet would be Pe Reievers. Look him up in RCU. Looking at the engine specs it should work well. I hear it is similarly ported to the glow version.

I had the Moki 180 glow about 15 years ago. It was built like a brick outhouse and was fairly powerful as I recall. Eventually I put it into a racing application with a full Macs pipe and it worked well there turning a 16x16 or 16x14 apc.

I had it soft mounted and it was far quieter than any of the other 1.8 - 2.2 cuin engines being run in the racing event, but with no loss in power.

computermonkey

My Feedback: (90)

Thanks Matt,

I'll continue looking for a wrap around header and see if I can get the two together in the future.

MTK

It's been a couple months since posting here since there wasn't anything interesting to post. Well, just yesterday I decided to take the OS out of the plane for inspection and general maintenance. It has about 10 gallons of gas through it, some 50 hours of actual run time so it was due.

Spark plug...... slight build up of brownish stuff, lead probably; avgas is low lead, not no lead. Easily cleaned

Top of piston........ similar slight build up; scraped off with a piece of plastic

Rest of piston......... almost pristine; very clean

Head........ super clean; no build up at all which surpised me a bit; I've been running fairly large loads on the engine and thought I might be running it rich to haul the load. Not so!

Liner........ pristine

Con-rod and bearings......... pristine......Actually the whole lower end is super clean looking brand new. I was quite pleased. Probably should have taken photos but simply forgot

I've run other gas engines that haven't fared as well after 50 hours of operation. The OS engine continues to impress!!!

highfly3D

Can you tell us how will this engine perform in the Masters sequence. How well can this engine fly those difficult maneuvers.

papaone

Hello Matt

You have a lot of experiences in gas engine.
Have you any advices for a quieter and cheap canister or exhaust pipe for Rear exhauts engines as PTE36R or DLE35R ?
Claude

MTK

Hi Claude,

The best combination is to soft mount the engine and use a tuned pipe. The sound is similar to a well tuned OS140RX or slightly better. Not as quiet as an electric but in the air, it's in similar territory

The pipes I have used and recommend are the ESComposites 30G or 40G and the the Mintor 38cc pipe. They are very lightweight and put out much better torque on larger props. I have never used a muffler or canister so I can't give any suggestions there. But I think that you will get something from a soft mount. The soft mount that's best is the Hyde style rubber isolator. I make my own custom mounts and nose rings that are based on Merle's design

Edit there is just enough space on the crankcase around the front bearing to design and install a nose ring. My nose rings for gassies have a recess for the Hall sensor such that the sensor doesn't touch anywhere. Clearance is small on the order of 1/2 mm on top and 4mm on either side. The front of the nose ring is flared out suchthat the prop drive washer doesn't touch. I usually chamfer the aluminum drive washer's tail end to eliminate any possibility of touching. It takes careful planning and carving to get a ring to work right, but the final result is much better flying set-up

vatechguy3

My Feedback: (11)

i understand the purpose of the soft mount, but what does the addition of a nose ring do for you?

tony