First gas engine question
 

I just purchased my first gas engine, a VVRC 20 cc which I'm putting on a Four Star 120 build. The engine has good reviews, but the manual that came with the engine is very limited in information for a Newbee. The manual mentions to use a hard mount. I don't exactly know the reason for this, but I do want to run the engine on a test stand first for breaking in and my own education. Is it ok to run the engine hard mounted on a test stand, or should it have some shock absorbing mounting?

Lamar

Just install it in the plane, run several tanks thru and then fly. I have one and it's a great little engine. Keep it slightly rich and all is well, I use a Zoar 17x6 or APC 16X9 on mine both work well! Treat it well and it will be there for you! Love mine!

Soft mounting or vibration absorbing mounts will ruin an engine. Always secure the engine rigidly to an airframe. This will increase the overall mass and thus the vibration. Soft mounting will focus all the energy of the moving piston into the engine. It’s a sure way to wreck one. Gasoline engines do not need to be broken in on a test stand like the nitro ones. Long periods of static running on a test stand is another sure way of destroying an engine. Rigidly mount the engine in your plane with the needle valves set at the manufacturers recommended settings and fly. I believe the VVRC engines come with a Walbro carburetor. If they do not recommend any needle valve settings you can use 1 ½ turns out for the low speed needle valve and 1 out for the high speed. Dan.

As long as the engine has adequate cooling and the proper oil/fuel mixture I doubt there is any difference between static running and running it in the air frame. When I worked with the university aero design students we did extensive engine testing in a small wind tunnel with the engine statically mounted and never noticed any difference in performance or integrity of any of the engines tested. The engines were tested with fine pitch props run near their max recommended rpm and with over pitched props that really loaded up the motors. You just have to watch the temp, make sure you have a good oil/fuel ratio and what ever you do try not to run it lean.

Like I said I doubt the motor knows it’s statically mounted or sitting in an airframe. Go ahead run it in the stand. One thing to consider is if you get it running perfect in the stand and it runs less than perfect once you install it in the airplane you might suspect there is a problem with your installation. In a test stand its easy to work on the engine without worrying about possible hanger rash to the airplane.

I know guys with hand built motors as well as the odd radial or two that have been running on a test stand for years without problem. These guys just get a kick out of running the things and never intend to put them in a model.

Dennis

By the way, since you are new to ignition engines, you should be aware that you can not comingle any components of the RC system with the ignition system. I know things are cramped in a 20cc planes but it is something that should be avoided as much as possible. This is particularly important around the receiver and its antennas, so be careful with your installation. Below is a quote from the Futaba website. We have to assume that if anyone knows what they are talking about they do. Dan

“Guidelines for setting up gasoline engine models.
All ignition equipment, including an electronic kill switch, must be mounted at least 12", and preferably 14", away from all radio equipment, including throttle servos, etc. Ignition kill switch should always be on opposite side of fuselage from radio kill switch. All pushrods going to anything related to the engine must be non-conductive (just nonmetal clevises is not sufficient).”

I have a lot of respect for most Dan's opinions, but that quote from Futaba has not been updated since most of the hobby went with 2.4ghz radios, therefore I don't place a lot of weight in it at all. It is advice generally completely ignored by many or even most flying today. It's now old school thinking. It's nice to know, and advice still followed religiously by some, but not generally necessary or even observed by the majority of flyers today. I do however, advise a lot of caution regarding range and ground checks. Make those final checks thorough ones. Just as an example, I have a 10cc gas engine running in a .45 size Extra. The receiver, battery, ignition module, throttle servo and opti switch (all the exact same components I would be running if it were a 30cc plane) are all mounted and functioning as designed in an area the size of my fist. Don't misunderstand what I'm saying. Because I've done that doesn't make it right. The point is it works. Oh, and it's all running on one A123 battery.

Regarding break in and test stands, I'm from the mount it and fly it school as well - but that may be because I'm pretty familiar with the engines. If I were getting ready to run/get to know my first? I see no harm in the test stand while familiarizing/getting to know your engine. I like the idea presented earlier, and also believe there's some merit in getting some confidence in it like that to help with installation issues as well.

Seeking perfection in your needle settings though, is pretty much a waste of time. It's fair to assume they're going to change when the engine is airborne. Many (MANY!) wonder how in the world that engine just quit on the maiden when it was running perfectly on the ground. I'm here to tell you it was out of adjustment. Get used to that idea, and be ready for it when/if that happens! Keeping the plane within gliding distance of the runway on those first few flights is part of a good plan...

To answer your question directly, it is OKAY to run the engine hard mounted on a test stand. It does NOT NEED to have a shock absorbing mount.

Often there is more than one way to accomplish something and either mounting the engine in the model and fly it or do a test stand run is a matter of personal preference. Since you are new to gas engines I would suggest to run the engine on a test stand. That way you can learn a bit about the starting process and initial adjustment of the high and low needles without the danger of risking the model if something goes wrong.

The engine doesn't know if it's on a test stand or in a model. If the engine is mounted in the plane and flown, it will run a little higher rpm (once airborne) because it will unload a bit. It will also get more cooling air since it is flying through the air in addition to whatever air the prop throws back onto the engine. On the down side, and assuming the engine is in a cowled plane, you may encounter overheating if you haven't allowed for adequate ventilation to get the hot air out of the engine compartment. An overheat condition will almost always result in a engine that stops running. Now you risk the plane if you can't glide to a safe place to land.

Therefore, I suggest you test stand run the engine for a number of reasons. You can always take an electric fan and direct the air flow at the engine which will give you additional cooling beyond what is given by the prop. That would be similar to the same effect that occurs if actually airborne. It gives you the opportunity to become familiar with running the engine without risking the plane. Learn how to tune the engine (setting the needles) without risking your plane. The engine should run with the needles set at the initial factory setting but is almost never the optimum setting for a engine and you need to learn how to do that. Also as the engine breaks in, additional adjustment to the needles will probably be needed. So, for the first gallon or two of gas, expect to have to make a few adjustments along the way. You certainly don't need to run an engine through a gallon of gas on a test stand but long enough to see that it runs pretty reliable.

By the way, you don't actually have to have a test stand. You can go ahead and mount it in the plane and do your test runs there without actually flying the plane. I don't do that because I have a test stand and I don't like to put needless vibrations to the airframe. These gas engines do shake a bit more than glow engines. If you do use your airplane as a test stand be sure to attach the wings as they help absorb the vibrations of the engine.

So, either way works. Again, its a matter of personal preference.

Indiomike

I started flying my VVRC 20 about two minutes into the first tank. No need to ground run them any longer than it takes to put the initial tune on them. Don't run it rich, just be sure to have 32:1 gas/oil mix. 40:1 is OK after a gallon or two, but I run 32:1 in all of my gas engines and have never fouled a plug. I fly with the owner of VVRC, so I get good advice.:D

ABSOLUTE NONSENSE!!! A soft rubber isolation mount actually helps the engine and the airframe. All of my gas engines are soft mounted and I will not use one without a soft mount. Where do people get this crap? Obviously never actually used one.

Some engine manuals do describe a procedure to follow on first running and break-in. My first gas engine manual stated that I should run 2 tankfuls on the ground and then fly. My second engine didn't come with a manual since I purchase used, but I followed the same procedure with no problems. I ran the engine on the ground while mounted on a plane, but without the cowl installed. The 4-Star 120 should be ok since it doesn't have a cowl anyway. The first tank I ran at slower engine speeds and gradually increasing to approx 4000 rpms. The second tank I gradually increased engine speed to max while checking that the engine is not overheating or leaning out and backing off the throttle to let cool down before stepping up to the next higher engine speed. You don't have that ability if you fly the plane immediately.

Soft mount, hard mount the debate goes on uselessly of course. The engine doesn’t care but everyone seems to think it does. Horse pucky. Take a look at engines today some are soft mounted many are hard mounted. Hard mounted dirt bikes produce a ton more internal forces than any airframe could. Your lawnmower shakes, vibrates and bounces over uneven ground without a problem. Soft mount every car, truck etc is soft mounted. Soft mounting simply reduced engine oscillations and noise to the frame/passengers in a vehicle mostly for comfort.

Some RC exhaust manufacturers will not warrantee their exhaust systems with a soft mount.

My earliest bike was a 1956 Arial Red Hunter it and most bikes I have owned since have all had the engine hard mounted. Norton came along with their feather bed frame (soft mount) it reduced some of the engine oscillations to the rider they claimed better comfort. It had nothing to do with engine durability or longevity. I have never heard any manufacturer claim as much.

If you really think about it does it matter where the oscillation occurs? It could be between the engine and airframe but some will be transferred to the airframe anyway.

If you hard mount it the oscillation will occur between the landing gear and ground when not flying and between the airframe and the air that surrounds it when in the air. In the latter cases the airframe will absorb and dissipate much of that vibration. In our application is comfort a consideration? Absolutely not so the only consideration is the effect on the other components of the airframe. Balance the prop and spinner and I doubt you would see any problems unless the motor itself was badly out of balance or had a bent crank from a previous ground strike or crash.

Get real look around and see how many are hard mounted vs. soft mounted.

In my opinion balancing your prop/spinner is more important than whether your engine is hard or soft mounted.

Dennis Pratt

Yes, the prop and spinner HAS to be balanced, there should be no argument there. That is one absolute requirement that cannot be argued.

Thanks everone for the replies back. Lots of good advice. As I mentioned in my first post, the VVRC 20 manual is very limited. I downloaded a copy of a DLE 20 manual from Tower, and this manual is a lot more informative for a Newbee. Scince the engines seem to be almost the same, can I utilize the information they provide on my VVRC 20 engine?

Lamar

One thing soft mounting does for sure is reduce power. A rigidly mounted engine just has more, period. I learned this in all of my years pylon racing. You can bet, you will never see a racing plane with a soft mount. Soft mounting on aerobat's is done mainly to reduce noise, which are the types of planes MTK sets up and flies. Which is understandable, but it depends on your application.

As I don't have a 20cc size, I would set as in the DLE manual, it is at best a starting point. all of my engines starting at 26cc up to 62's all seam to set at the following Low needle 1 1/2 open, high needle 11/3 for starters, and remember the low needle controls the mid range.

That said good luck and keep your fingers out of the prop as gas engines wack a lot harder then a glow of the same size.

Cheers Bob T
AMA13377

And please remember that the so called "factory carb settings" are only a starting point, and a setting that hopefully guarantees the engine will start for you. You MUST then tune it properly yourself. The exact needle settings you end up with will depend on your fuel, oil, fuel/oil mix, prop, temperature, barometric pressure, humidity, stage of engine break in, and the phase of the moon. :) People often tend to think that engines can just be run with the factory settings, but in fact, those are only gross settings that must be optimized by you when you run your engine.

When we tune glow engines, when we get close, the optimum setting is dialed in a "click" or two at a time. A gas engine with it's needle valves setup for a screwdriver are often over adjusted to the point of passing the optimum setting. The needles are sensitive, and when your tuning is close to optimum, a 1/8 turn of a needle is a lot. Often times just a screwdriver blades width of a change is all that is needed.

AV8TOR

Well said

Thank you. It's rather a "pet peeve" of mine that so many people don't understand that an engine must be tuned; that the factory settings are only a starting point.

AV8TOR

Let the engine get up to operating temperature before making adjustments.

Use the oil/fuel mix you will be running in that engine. A different mix/oil product may have a different viscosity which will affect how much fuel will pass through a given orifice.

Make only very small adjustments no more than the thickness of the screw driver blade. Wait until the carb and motor catch up with the adjustment you just made. Unlike the nitro engines it’s not necessarily instant. I have seen guy fail to wait for the carb/engine to stabilize keep making adjustments and go right past the optimum setting. Take your time it’s not a race.

Be reasonable when you open the throttle you can snap it open by hand much quicker than a servo can. These carbs usually do not have a fuel pump and opening them to quickly tends to zero the vacuum. With piston ported engines this can cause fuel to spit back out the carb and the engine to quit abruptly as if too lean. Reed valve or rotary valve is less susceptible to this. There is no need to open the throttle faster than the servo will open it.

I like to ease the motor to full throttle and set the high speed. The transition thru mid range is now set with the low speed needle. Remember after a few adjustments on the low speed recheck and adjust the high speed as needed.

Dennis

Have never used a test stand for breaking in an engine. Actually, I have only mounted the engines in the models, started them, tuned them, ran a tank of fuel thru them, then off to the flying field. All my engines have been broke in, in flight. To date, never had a engine problem, with my engines.

Years ago we used to run larger one design 82" spanned racers with engines up to 2.2 cu.in glow, Mokis MDS' etc.. I built mine lightly (12# compared to 16+ of every one else's) and mounted the Moki 180 on the only soft mounted set-up at those meets. The lightness of the crate and adequate power of the 180 produced some very fast results, usually the fastest at those meets. Of course the quietness was terrific, some 10 dB lower than most

I have never run F1, Formula 500 or other F3D types tho so I don't know about the smaller crates.

Thank you ahicks for respecting my opinion. It’s not my opinion. It’s Futaba’s. I too read the DLE manual for their 20cc engine and would you believe it, they have the same opinion. Keep the RC and ignition system separated and don’t use metallic pushrods. It sounds like the OP should get in touch with the manufacturer of his RC and see what they say. Dan.

http://manuals.hobbico.com/dle/dleg0020-manual-v1_1.pdf

I'm like Lamar, just getting into gas but I have a fair glow background so this thread is informative to say the least, so thanks to all for the comments. I have an Evolution 10cc and a DLE 30 and both owners manuals recommend breaking them in the airplane in flight conditions, the thought being, and Evolution goes into detail on this, is to climb to put a load on the engine and dive to aid in cooling. Evolution goes onto say that it will likely not break-in if run on a test stand or just flown around in level flight, DLE manual is rather Spartan and just says aircraft in flight conditions, to that effect. That philosophy agrees with what I was taught so many years ago for motorcycles and employed that method dozens of times with them, never kept the engine at the same speed for the first 1,000 miles, load the engine to expand the rings and unload to release ring pressure and allow lubricant flow up the cylinder and to cool the engine, always had good service from those engines. Of course that procedure doesn't apply to glow and I don't recall a recommendation for a glow other than a test stand break in. I might be a little off on Lamar's question because I'm as much in the dark about the hard vs soft mount controversy as he is, just thought it might be helpful a little.

Well, I wish someone would have told me this when I first started with gassers. DO not use a stopper tank. This topic always creates an argument, but unless you like your plane full of raw gas, heed the warning.

Many will claim they have never had a failure, but if you have ethanol in your gas, no stopper will be compatible. Just be safe and use a fortitude , Bennett or Fiji water bottle style, screw on cap.

The general consensus on break in is to do it in the air. Glow engines gain cooling from the fuel, while gas engines do not as much. So they really require flying to stay cool. But then again, I have never bench run engines much. I prefer to do it all in the plane.

I have had a DLE 20 in my old Pica FW 190, and it has performed great. I run a 16-8.

I'm currently mounting a DLE 20 in a Hanger 9 Ultra-Stick Lite so I'll file that stopper and prop selection in the old data banks, thank you.