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RCS 1.40 Model Airplane Engine Review
 By Cliff Griffin November 9, 2000-- Updated 1-25-01

RCS 1.40 model airplane engine review by Cliff Griffin. For more information, check out the RCS 1.40 on their web site at http://rcshowcase.com/RCS%20Engines.htm
In a nutshell, this engine is definitely THUMBS UP!!! 
Displacement 21.5cc/1.31ci (measured)
RCS direct price $389
Muffler price $75
RCS predrilled Dubro mount $32
Weight, bare engine w/Carb 28.7oz
Muffler weight 5oz
Ignition weight 4oz
RCS/Dubro mount 5.9oz
GP 1.20 mount, cut to fit 3.4oz
RCS provided Spinner Nut 1.6oz
*It's a capable, light gasser that will compete with average 1.20's in power and weight. (Mid to upper 8's with an APC 16x8.)
*Only needs an 8oz tank for 10-15+ min flights.
*Ignition will run on small AAA, 250mAh packs. I LOVE this!!!
*Complete accessory set included.

*No major flaws to overcome.

*To get good power, an oversized carb is used, which degrades throttle response and needle consistency, although it is still useable.
*Mounting tabs are smaller than standard.

*Throttle and Choke levers are awkward. (See text) 

RCS 140 mount dimensions.jpg (74716 bytes)This is a rotary valve engine, with the valve drum driven by the back end of the crankshaft. It has roller bearings on the bottom of the rod, which allows you to run standard 2-stroke gas oil mixtures. The top end of the rod is just bushed though. The machine work on the inside of the engine is very good--better than my ST2300, but not as clean as my TT1.20. On the outside, the machine work needs some improvement--the mounting tabs are on the small side. 

I broke my RCS 1.40 in on the test stand, using the predrilled Dubro mount. (Unfortunately, the pre-drilled mounts are no longer available.) It was a clean installation, but I chose to use a GP1.20 mount to mount the engine onto my plane. The GP 1.20 mount is considerably lighter--2.5oz lighter--and also slightly shorter than the Dubro. Even though I was replacing a heavy converted 25cc Homelite weed-wacker engine, I wanted to keep the weight back as far as possible. (Coincidentally, I saved almost a pound with the new engine, and also picked up over 500rpm with the same prop. The Joss Stick suddenly became fun again! Switching over to the TT 1.20 muffler made another noticeable difference. Imagine what it would do with a mousse can pipe!)

Flight and Performance
I've been flying my RCS 1.4 in a 9lb, 11oz Stick, testing it out. (As weighed on a "calibrated" scale at my local packing & mailing store.) The engine has good power for that size of an airplane, and the vertical is only limited by my fingertips and my eyesight. I currently have the smaller carb on it, but I'm probably going to try out the larger one here soon. (Most of these engines ship only with the larger carb.) The smaller carb has been giving me mid 8's with an APC 16x8, which matches my YS1.20 on 10-15% nitro fuel. This is pretty typical for 1.20's--the better ones offer over 9k with that prop, and others are down around or under 8k with it. From comparing the numbers I've seen from other RCS owners, my power output is down a couple hundred RPM, but every one else has been using the larger carb.

For the Performance update with the larger carb, jump to the bottom! 
Engine RPM with APC 16x8 prop
RCS 1.4, one gallon through it, small carb 8,500 @ 66F, (8700 @84F)
RCS 1.4, 1+ gal, large carb, and TT 1.20 muffler 9,100 @ 70F
YS1.20NC with 10% nitro, well broken in 8,500
TT1.20 Pro, 5% nitro, one gallon through it 9,000
Click here to see additional prop/rpm figures  

The throttle response is pretty typical of a smaller gasser--there's a small jump around 4k or so where it smoothes out. It is not even in the same league as my YS in this department. In addition, the needles on the carb are much fussier than any of the other gassers that I've worked with. The RCS requires tweaking with 20 degree swings in temperature. One foggy morning I adjusted it, and by afternoon when the fog burned off it needed readjustment. On the other hand, a recent last flight was 9 minutes, and I had almost 1/2 of my 8oz tank left in it afterwards. Another ten minute flight, with considerably more WOT time, consumed about 2/3 - 3/4 of the 8oz tank.  (I have the timer on my Futaba 8UAFS to turn on if my throttle is 3clicks above idle, and it does not count below that. That means that the 10 minute flight is actually 10 minutes of time above idle, and I DO idle mine on the down-lines, etc.) I currently have about 1.25 gallons through my RCS, and at 5-6oz per flight, you see how long it can take to break the thing in.

So far, I slightly favor the RCS ignition over my C&H units. I have two C&H's, and neither of them would keep an engine running on a standard AA battery pack--they both required more capacity. That is the only bad thing that I can say about my C&H's. This RCS ignition has been flying trouble free with little 250 and 275mAh packs. I get about 30 minutes of flight time out of them, and when they dead-sticked the plane, I cycled them on my A4, which showed that the full capacity of the battery had been utilized--I actually had to charge the batteries for a couple seconds before the A4 would recognize them as 4 cell packs. This is favorable, and also quite contrary to my experience with the C&H ignitions and under-sized battery packs. Recently I switched to 720mAh NiMH packs, and will report back on their performance. Note that RCS doesn't really recommend using the tiny battery packs. I don't know why, but they sure work well for weight critical applications!

Finally, the current ignition is rev-limited at 12,335 RPM. RCS will bump that up to 15k at no charge though. I was earlier told that it was 9k, but that is not the way they are currently shipping them.

I am pleased to see a competitive gas engine in this size range. It will fly most planes that a typical 1.20 glow engine will. The best 1.20 glow engines will definitely have more power (unless you go with a better muffler), and probably have a more linear throttle response. On the other hand, takeoff weight will be similar for either the RCS or glow engines, but gas is very cheap and considerably cleaner. My personal flying abilities will not be hindered at all by the throttle curve, and I love the simplicity of gas engines. (All you need is your transmitter, plane, and a jug of fuel, and you are ready to fly! No more glow starters, electric starters, field boxes, and only minimal cleanup after each flight day.)

There was a very complete set of accessories included with the engine. There was a spark plug wrench, a very nice looking (but heavy) spinner nut, and rubber grommets for mounting the ignition like servos are mounted. Also included is a spinner adaptor, if you want to run a typical spinner with a nut on the prop. It was refreshing to see all of these accessories standard, so you don't have to round them up.

Basically, I highly recommend this engine. The instructions are anemic--they are limited to one small sheet of paper. If this is your first gasser, then read the instructions on the BME web site! However, the benefits to gasoline operation are well worth the small quirks that this engine has. ( See the BME manual here: http://bmeengine.com/bmemanual.html )

If the new carb works as well (And I'm certainly looking forward to it, since the smaller one doesn't have a choke) then I am probably going to swap out the YS on my (Kopp-Landau built) 1/4 scale Laser, which is currently right at 9lbs. I expect the takeoff weight to be very similar with the gasser in it. We will see... rcfaq

Update 1-25-01 I installed the new, larger carb. Unfortunately, it didn't help the performance at all. I tached the engine with the smaller carb, then swapped them out immediately after. The larger carb is noticeably MORE difficult to tune than the small one, and added -0- rpm to my APC 16x8. I'm wondering if the stock exhaust is too restrictive. I was really disappointed, to say the least. I know that there is some baffling inside the muffler, and I'll have to see if I can remove some of it to help it flow better. NOTE: I have since removed some of the baffling inside my muffler. (I drilled through the muffler, and cut the baffling out, then soldered a piece of alum. back on.) Unfortunately, this did not improve the top end RPM. rcfaq


Archive notes: Note that the engine in this review had an issue or two that is no longer applicable to current engines. If you are purchasing a used engine, you may want to ask about the age of the engine if it hasn't been run and had these issues resolved. They are minor, but do take some minor tweaking to get the engine in running shape. First, the engine came with a pre-drilled engine mount. This is great...except that the engine wouldn't bolt up with some slight metal removal. Secondly, the carb was at an angle such that a hole had to be drilled into the mount to allow the fuel tubing to be routed through it. This was highly inconvenient when you needed to change the tubing. Fortunately, the carb has been rotated so this is no longer an issue. Third, while my muffler looks similar to the web site, it wasn't identical--one mounting bolt required an allen wrench to be shortened to tighten it up. The current mufflers match the photo, and don't require this special wrench. Finally, I had some radio interference problems which were caused by the spark plug cap rubbing on the spark plug. A hose clamp solved this problem. RCS is now shipping engines with a different spark plug cap which does not have this issue.  

Like I said, these issues are all minor and will not detract from the running of the engine, and have been resolved in current new engines. If you are one of those guys that needs to be able to throw four mounting bolts at the engine and have it run without even checking so much as a bolt, then these things may annoy you. If that is you, then you need to ask questions when you purchase a used engine. Otherwise, you might spend an extra half hour or so getting the engine ready, and then you'll have an excellent power plant for a plane that requires a 1.20 sized glow engine.


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