I was fortunate to have access to four different engines all at the same time for testing and comparison. To say the least it was a task of some duration, but one that gave me special insight and understanding of not only gas engines both propeller selection.
My approach for all the engines was to first break them in using a 24:1 mix of gas and oil: rich with oil (Polaris Premium Synthetic Blend), but plenty of lubricant for the break-in. I ran 87 octane (blended with ethanol) as that is what is available in this area. Each engine had one gallon of fuel run through it with the designated break-in prop. For the first three quarters of the gallon the engines were run no more than 10 minutes and then allowed to fully cool. During each 10-minute cycle the throttle was manipulated to make sure a variable RPM was achieved. Cylinder head temps were taken with an infrared temp sensor during the runs to make sure nothing was overheating. All starts were by hand.
Towards the end of the each gallon I would advance the throttle from stop to stop periodically. With the exception of the SPE-43cc engine I never touched the needle valves, but it was just too rich in the 100 degree air and 60% humidity to run well so I leaned that engine back very slightly to improve the run. All the engines were run with a 6 volt NiMH battery with a capacity of 1200 or greater mAh: the 3mm 50cc TOC was run with a 4.8 volt battery.
My tank was about 18 ounces and three runs consumed the full tank for all the engines typically. The throttle was varied within each ten minute run multiple times. Starting was easy, and once I established a routine for choking, the process became very predictable. I found it necessary to choke all the engines before each start. I also found they started better if I cracked open the throttle just a bit to allow some air. After starting, I moved immediately to idle to allow for warm up.
I set the props to load compression at about 12:00 and to break-over at about 10:00 to 11:00. It is easier and safer if your flip is away from the engine and down. Periodically I would re-torque the prop to the hub. Early runs typically were full of vibration that settled out after a gallon or so and after I backed off the oil and adjusted the carburetor.
All the props for this project were provided by Master Airscrew . Started in 1977 by Fred Jamieson, the Master Airscrew brand is well known among flyers worldwide. The fine people from Master Airscrew provided me some information I want to share with you regarding their line of propellers.
In their shop they produce all their injection molded props starting first from CAD designs. Props between 6" and 20" are produced and then tested for strength continuously throughout the production process and checked for balance, warping and appearance. The nine professionals working at Master Airscrew ensure, through their combined total of almost 100 years of service, that each and every prop leaving the shop is perfect, and I can confirm that claim. Their wooden props are imported from Italy.
Over the last thirty years they have been innovators by paying close attention to the needs of modelers. They offer a high quality prop at a good price and great customer service. Be on the lookout for their new line of Formula One Series propellers: they are sure to be a wonderful addition to an already excellent lineup.
All props required their center hole to be drilled out and at least two smaller prop bolts to be drilled. I used a drill press and set up a jig so I could make sure I centered the hub bolt. The prop washer helped me align the two secondary bolts. The props were then checked for balance.
Balancing of the composite props typically was not a problem; My method was to sand off or scrape off the heavier end until I felt comfortable that no more should be removed. If needed, I sprayed clear acrylic paint to the light tip in layers to add weight. The Master Airscrew line of props was exceptional throughout the testing process.
All props bolts had torque applied using PB Swissís torque drivers, ensuring uniform compression of the prop hub. Wooden props require re-tightening after each run until the prop settles into the hub. Torque settings were approximately 3.0 ft lbs / 36 in lbs.
I constructed a test stand using lite-ply and fiber-glassed the front, sides and all corners. This is important to make sure the stand does not rattle, vibrate or come apart. The fiberglass also keeps the fuel from softening the lite-ply. Surprisingly, you get very little fuel on the firewall with gassers. I mounted the stand to a large picnic table so that there was no chance of any movement.
The test stand was hinged so it could tilt forward. The stand was tall so a cable was connected to the stand and the picnic table with a fish scale in the middle. A second cable was attached to the stand to make sure nothing could move forward beyond the movement of the scale which proved very effective.
I want to be clear that I am not making any comparisons of the engines through their break-in. The rich mixture and higher oil content just do not make the comparisons worth much. The break-in process is a necessity though.
I began the break-in of the four engines with the SPE-26 and followed with the MLD-28. Both engines share the same firewall bolt pattern and the SPE 26, SPE 43 and MLD-28 share the same three-bolt prop hub pattern.
I used the original equipment and then replaced it when the prop testing was done. I found no problems with any of the plugs.
The MLD-28 and SPE-43 engines were early prototypes. At press time the MLD-28 is being sold with a different CDI ignition and velocity stack as the MLD-28S. The SPE-46 was upgraded from the SPE-40. The SPE-43 is being shipped with a different timing setup and some slight internal modifications from the engine I tested.
The SPE-43 looks like a blend between the SPE-26 and the MLD-28 with a flat cylinder head and an angled spark plug. There are some subtle features like a larger Walbro carburetor, longer hub bolt, and two-click choke. Running the SPE-43, results in a great sounding engine with a slight thump-thump sound of a bigger engine.
|Configuration:||2C single Cylinder Head Cooled|
|Number of Bearings:|
|Ignition:||CDI Electronic Ignition with Auto Timing Advance|
|Spark Plug:||Champion RCJ6Y|
|Power Supply:||4.8v - 18.0 volt|
|Weight with Muffler:||3.2 lbs|
|Muffler Type and Weight:||Single Exhaust|
|Maximum Output:||3.4 BHP|
|RPM Range:||1,300 - 9,000|
|Oil:||2-Cycle High Performance Synthetic|
|Prop Selection:||18 x 8 through 21 x 8|
|SPE 26 Engine Cermark Link:||Cermark SPE 26|
|Cermark Homepage:||Cermark Homepage|
SPE-43 Engine Includes:
The SPE-43 looks like a blend between the SPE-26 and the MLD-28 with a flat cylinder head and an angled spark plug. There are some subtle features like a larger Walbro carburetor, longer hub bolt, and two-click choke. Once running the SPE-43 results in a great sounding engine with the slight thump-thump sound of a bigger engine.
The SPE-43 took a little while to start. I hand cranked everything, and it finally brought it to life, but this is an unusual engine that does not have the rings seated. The two-click detent on the choke helped once I got the engine to fire.
From the first start I could hear other differences than just the exhaust. At idle you can hear the crankcase, which is typical of larger engines. Through the first few tanks I thought the engine was running rich, but I left it that way. I later leaned the engine slightly too smooth things out and make the engine run much better. As I got to know the SPE-43 I found myself constantly tweaking the needles possibly because of air leaking into the carburetor. The more I ran the SPE-43 the more I could see fuel and oil working its way outside the carburetor. I ran one gallon of fuel through the engine before the prop tests.
I probably had the most difficult time prop testing with the SPE-43. The bolts were 5mm too short with the velocity stack, and I was always on the needle valves, which no other engine required. Between prop changes I would start the engine to find that it was way out of adjustment, a very difficult issue. Ultimately, Cermark provided a new CDI module and this stopped what I thought was a carburetor problem. The insulation within the spark plug cap was leaking spark to the ground.
I had to be careful when starting these engines to never assume the next flip or the last flip would not start the engine. I had to listen for that hint of ignition and be ready, and that was especially true of a backfire. Be positive with the flip, don't hesitate or back off, and follow through with a good flip. I always wore a big leather glove and had no problems
Iím not sure why, but a prop came loose on the SPE-43; It broke the two 4mm bolts and spun forward. It took some time to clear the broken pieces out of the hub, but that was the only time in all the engines I had anything happen during a start or run.
The exhaust stack fell off, the weld broke, and the ignition sender rubbed the prop hub but I donít think this had any negative effect since the contact was not rubbing but rather the plastic housing.
I had low head temps in the 130 degree range and 100 degree crankcase temps in my runs.
As a side note: I noticed as the prop sizes went up I had to be very careful that my tachometer readings were accurate. Many times while running outdoors I got reflective readings off the larger props, and the tachometer bounced around. I used a bright light source on the other side of the prop to make sure I was getting accurate readings.
Wooden props require you to re-torque them after every few runs. You can haphazardly do this by feel, but the correct method is to use a torque gauge. I used PB Swissís Torque handle to make sure I got the exact torque on all six bolts. This is especially important since there is no center 10mm bolt to tighten. I applied torque to each bolt in a sequence to 3.02 ft lbs/36.29 in lbs. I tightened the bolts in sequence because head bolts on motors have tightening patterns to spread the load across the head.
|Prop||Low RPM||High RPM||Thrust|
|18 x 8||1680||9200||10lb 12oz|
|18 x 10||1680||8040||14lb 12oz|
|20 x 8||1680||7170||15lb 13oz|
|20 x 8 Wooden||1890||5850||14lblb 1oz|
|20 x 10||1500||6780||15lb 8oz|
With the exception of the miss at high end that was generally sorted out with a new CDI module the SPE-43 was a great engine. The CDI also calmed the need for tweaking the needles, and in the end I got good runs on this engine. As I mentioned before the new version of the SPE-43 engine has been modified. The one tested was a prototype. You will see it again in upcoming reviews.
This SPE-43 is a real hauler capable of moving some big stuff. I was impressed with the power and thrust across the props, noting a pull at over 15 pounds. Once the carburetor was right it transitioned well as is realistic for a larger plane with the speed at which it transitioned. For the money, this is a good engine that will last a long time.
Properly treated, these Cermark engines are well worth the money and will last a very long time. Product support from Cermark for my testing has been excellent; whatever I needed I was provided and they responded quickly to my needs with a phone call.Last edited by Angela H; Nov 18, 2008 at 10:18 PM..
Would you be kind enough to share your thrust measurement techniques? Example, What was the height of your engine above the surface? The distance to the scale use and any math you might have used to calculate the published thrust value? I am interested because I would like to make a test rig for testing my gas engines. I use only wood props and there is not much engine data available for wooden propellers.
Press Release: MLD & SPE Engines - June 12, 2009
Currently all 3 gas engines, SPE-26 (v-4), SPE-43 (v-4) and MLD-28 (v-5) are completing their updates and modifications. The process has taken much more time than we have anticipated. The final round of testing and approvals should finish after the week of July 4th, 2009. Because of required quality assurance process, we can only ship out the back-ordered engines after all inspections and tests are done. The corresponding manuals will become available after July 17th.
The areas of improvements are the electronic ignition systems (CDI), the vibration, the low-to-mid range throttle response curve, the carburetor, and other non-disclosed areas. As result of the updates and upgrades, you will have a better SPE or MLD North American engine. For those of you who may be concern with the North American SPE and MLD engines that you already own. Please do not be alarmed. The engines simply undergo improvements. We have simply executed the update process poorly, hence the gap in their availabilities.
Please contact us, if you have any question.
Press Release: SPE-43 Engines - July 28, 2009
North American SPE-43 are being shipped to dealers and customers as we speak. They have gone through all of the required quality assurance process. The areas of improvements are the electronic ignition systems (CDI), the vibration, the low-to-mid range throttle response curve, and other non-disclosed areas. Please contact us, if you have any question.
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