inverted engines
 

i'm getting ready to build a cub kit and am wanting to keep it somewhat scale with maybe a couple extras, BUT... i want to keep the engine concealled as much as possible, and in doing so will have to mount it upside down with just the pitts pipes sticking out the side instead of the entire upper half of the engine. i had problems on another aero machine with getting the engine started and maintaining it running to try and fly; is there any tips or whatever i could use to rid these problems? maybe a glow system on-board and how much do these cost and are they really necessary and all those other questions i can't think of right away?[:o]

RE: inverted engines
 

rcplanes12, the most important feature to setup, is the fuel tank. If possible the centreline of the fuel tank needs to be in line with the throttle spraybar in the carby, or as close as possible to it. On board glow system wont be necessary. So when mounting the engine, do some checks before screwing the engine mount in place, you may have to mount it as high as possible, to line up with the fuel tank. Bill - the_madgenius down-under in Australia.

RE: inverted engines
 

You never mentioned the engine you will be using or what type of CUB. If a four stroke, I have been told they are much better at running inverted, Two strokes are much less so. The two strokes glow plug will be sitting in a sump, when inverted. Four strokes are generally off to the side and higher up on the cylinder head, when inverted.

It's your call on whether to invert, or not. Fully cowling an engine has it's disadvantages, also! Are you going to compete with the cub or not. Even if competing, judges don't discount for having a cylinder head sticking out of the cowl. Side mounting points the exhaust down, helping with clean-up.

Personally, I will avoid inverting at all costs! However, that is me and it appears designers seem to think inverting is the way to go! I don't think much of designers, which will design an airplane that will use an inverted two stroke.

RE: inverted engines
 

Bill, I've always been told and most installation drawings I have seen show the centerline of the tank lower then the centerline (spray bar) of the carb. In fact all my Magnum and O.S. owners manual give a figure approximately 1/4th to 3/8ths of an inch lower. However, this measurement is dependant upon the size of the engine, so read your owners manuals! Also, it is more important that the engine thrustline align with the thrustline of the design! Don't just go and change this arbitrarily! You need to raise/lower the fuel tank to match the engine at the airframe's designed thrustline, not the other way around.

Mark DeSchane, Mode One, AMA 59157

RE: inverted engines
 

I have several planes with inverted engines. Starting and running them is no more or less challenging than any other orientation. The key to starting any engine is to get a good prime. The key to running an engine is proper tuning. Learn how to start and tune an engine and you should be able to operate it any way you want. When the engine is inverted and cowled access is a bit more difficult. While it's true that in theory the glow plug could be sitting in the sump that someone else pointed out, and flooding is often quoted as an issue, in practice, it's actually quite difficult to flood an inverted two stroke. The reason for this is simple. Any excess fuel that comes out of the spray bar and into the carb is going to drip on the ground, not into the engine.

Having said all this, why are you installing a screaming 2 stroke with a pitts muffler in a Cub? There's an unwritten law that only 4 stroke engines should go in Cubs! ;) If you go with a 4 stroke, the muffler will be significantly smaller and easier to deal with.

RE: inverted engines
 

A couple of ideas..........

First off, if you're interested in keeping the scale outline as pristine as possible, you need to consider the Slimline "sport" Pitts mufflers. Their pipes come out 90degrees different than the regular Pitts mufflers. The difference might allow you to mount the engine completely cowled and still have the pipes also go down. And if that works but the pipes don't reach out far enough, get those flexible exhaust extensions and use them (or just use the straight part of them).

And about how an inverted engine runs..... What you encounter is that they're SOMETIMES harder to start. They're going to run fine. And how they start is biased by two things. One is that the usual carb placement (upside down) means the engine is actually going to be harder to flood through the carb when filling the tank. And the other is that it might have a tendency to flood once you start flipping the prop, or finger choking, or trying to prime it. All of those things are well within our ability to control.

So the bottom line on starting an inverted engine is that we have to simply pay attention to each one and see what set of details each engine needs.

I flew competition CL precision aerobatics for years and years. You have to signal when you're ready to begin your official flight attempts AND THEN start your engine. And you're on the clock while starting that engine. And your flight time is finite. The judges quit scoring you when your total time runs out PLUS you also lose the "full flight" bonus! And nobody had electric starters. We all hand cranked the suckers. And darn near every model had a tightly cowled, upside down engine. And I don't remember in all those years but only a couple of guys who couldn't get a one or two flip start. Those guys simply paid attention to how they filled the tank. And how they primed the sucker. And what condition the glow plug was in. And the guys who couldn't get their engines to start almost always had trouble no matter what engine they had at the time. They either didn't or couldn't pay attention to the fueling and priming details.

I use a hand crank fuel pump. I count the number of revolutions it takes for each model to fill the tank. I watch the "overflow" fuel line like a hawk when fueling. When fuel shows, I stop cranking and do 1/4 turn back. I watch the carb to see if it's syphoning. I plug the fill line right away. When I'm starting a brand new model or brand new engine for the first time, I make careful note of whether or not it is dry when the starter is applied. If it is, I play around next time I crank it to see if priming is needed or not and what method works.

It sounds like a lot of things, but they're things that take no time at all and make for better times later on.

If you really can't get the hang of a balky starting engine, I got another piece of advice. Stand up, look around at your flying buddies and yell, "HEY ANY OF YOU GUYS EVER FLY CL STUNT????" <GRIN> And another "pearl of wisedom"..... don't ask help from anyone who has inverted engines and bandaids on his fingers.

RE: inverted engines
 

BTW...... There is never any excuse for us to flood our crankcases through the carb. Even if you have an electric fuel pump that puts out 50 gallons per second and would spray wash a cement truck from 20 yards, we got no excuse.

Our engines have crankshaft induction. Well, most of them do. And those crankshafts are connected to the props. And we can turn those props anywhere we want them.

So take a couple of seconds and see where the prop is when the crankshaft is closed. When you fuel that baby next time, put that prop where the crank is closed and not a drop of fuel is going to be forced into the case.

And if the engine is oriented such that the fuel collects over that closed hole, figure it out. Maybe you can dump it by tilting the model etc etc etc.

But some engines are 4strokes and the intake goes directly to the head. No worries mate. Figure out where to position the prop so the intake valve is closed etc etc

RE: inverted engines
 

We're getting some fine information on how to start and operate inverted engines. This is all great and if you want to do so, have at'r! I'm sticking with mounting side or upright as this simply makes life easier. For beginners, which is where this topic resides and where I make the assumption Rcplanes12 skills are, what possible gain is there in complicating matters by suggesting inverted-fully cowled engines, other then esthetic value?

For us guys who've been in this hobby for a while and want to, inverted and fully cowled is just fine.

RE: inverted engines
 

Learning how to do more advanced things, both building and flying, is what takes a beginner away from being a "beginner" and into intermediate. You got to do it sometime, and some are ready before others. If he wants to stick his engine in upside down, I'm all for helping him do it. I have four inverted setups, all work flawlessly.

RE: inverted engines
 

I hardly think inverting your engines is what makes one advance in this hobby and leads you away from being a beginner!

RE: inverted engines
 

It is one of many things that does just that.

RE: inverted engines
 

I'll tell you exactly how it helps a beginner evolve... it involves learning a new skill set. ANYONE can run a glow engine in the upright or sideways position, unless they are totally inept, or cant read instructions. Inverted mounting makes you think about your tank position, fueling and priming practices, etc. Beginners dont have worry about all this, that's why they are "beginners". But you cease to be a beginner when you branch out, learn new skills and techniques, and apply them to more complex aircraft. Anytime a beginning level flyer learns a new skill, no matter how small it may seem to some, it takes them a little further down the road from a beginner to a more advanced level. Not everyone wants to putt around on uncowled sport planes for the rest of their lives, just because they are "easier" to deal with. I was a beginner at this time last year. Now, I'm just about to finish a Pitts Model 12 Monster, and it will have an inverted 4 stroke (Saito 150 or 180). I am fully confident that I will have no problems getting the engine to run just fine, because I've researched it, and know what needs to be done. If you dont like inverted engines, dont use one, but dont try to discourage someone from trying something new just because YOU have not had sucess with it.;)

RE: inverted engines
 

Does this mean when I fly my Cub with a K&B .61 Twister w/ pitts muffler I should be all mopey and not having fun? :D

RE: inverted engines
 

Nope, because you chose the twister instead of the screamer. :D BTW, which pitts are you using and does it fit right? I tried one model that fit the exhaust port ok, but part of it was too long so the stacks weren't centered on the prop line.

RE: inverted engines
 

Chuck, if memory serves, it is a Bisson. The exhaust pipes are slightly off-set from the center line. I fit a new cowl after the engine swap. The Twister replaced an old baffle piston K&B .61 that I couldn't get to hold a low end needle adjustment. After the swap, I found all the old engine needed was a new 15 cent "O" ring. I'd post a pic of the Cub, but it is so beat up I'd get booed off this thread. I have an idle .70 FS I could put in the Cub, but the K&B runs so sweet, I hate to mess with it.

RE: inverted engines
 

I should expand on my earlier post. I didn't mention that my first inverted setup was my second airplane, and when I built it, I'd only been flying 6 months. So maybe it doesn't take one from beginner to intermediate by itself, but added to all the other things that are the more challenging way to do something, I may have got there a little quicker. I'm all for easy, don't get me wrong; easy is good, but it ain't always the best.

Tim, don't worry about how your Cub looks; have you noticed that most every full-size Cub you've ever seen show their age, too?

RE: inverted engines
 

I've been involved in this hobby off and on since 1968. I have 21 years as a member of AMA. I would think my experiance speaks for something! I'm not going to sit here and list all my accomplishments in this hobby, only people with inflated egos do this. I'm satisfied with what I've done and that I have helped many people along the way. My opinions are only my opinions. In this topic I have attempted to help RCplanes12. However, you know what, I have no idea what his experience is! I have said over and over, if he (or all of you) want to invert, have at'r!

Fair winds and following seas!

Mark DeSchane, AMA 59157

RE: inverted engines
 

If I don't mount my engine inverted, will flying the plane inverted achieve the non-beginner rating??[sm=spinnyeyes.gif]


Mark

RE: inverted engines
 

ONLY if you can do it backwards blindfolded!:D

RE: inverted engines
 

Hhmmm! I've got a pusher-prop, & some cheap sunglasses, that oughtta do it![8D]


Mark

RE: inverted engines
 

Thanks. The one I tried was a Slimline. I thought I checked with Bisson and they said they didn't have one that would fit the K&B, I'll have to check again.

RE: inverted engines
 

Chuck, sorry but I suffer from CRS. I just checked the Tower website and it was a Slimline I used on the K&B. Back to the original theme of this thread, I agree with Mode One that unless a beginner is ready for some aggravation in his or her life, it is better to avoid things like inverted engines, on board glow systems, cowls with the resultant fuel valves, fixed wings where you are tempted to never peek under that hatch and things like that.

RE: inverted engines
 

man, i don't know what the heck to do. i think i've moved on a little more away from the "beginner" experience level in just some of the engineering attempts and complete re-engineering tasks, but for some reason, the take off and inverted engine business is jacking me all up. i don't know if i can even try to mention competing with the cub. BTW, it's a GP .40 kit. 76" span and probably about 5.5 scale, seeins how the 5 scale is a little bigger and the 6 scale is a little smaller. plus i'm going to put split flaps on it and try for opening/closing door and was even tossing the idea of the green house cockpit of the L-4 grasshopper. more of a frankenstein than anything i would attempt to call it. i don't have much help or support from the wifey as far as buying and building whatever kits i want and she can't understand the thought of having a full squadron or fleet of aircraft to choose which one i want to fly on any given day. if i want a new one past my limit of 2 :(, i have to get rid of one, because i can't fly them all at once. now that would deffinately have to take me on to intermediate or possibly advanced flying skills. but all in all, i'm using a .40 fx from O.S. and a bisson pitts. i would love to switch over to a 4-stroke, but again, the money and wife thing. should have bought a plane instead of the wedding ring. damn budgeting!!! i was just thinking of putting the engine in inverted so i could install both sides of the "dummy" engines and hide my embarrassing 2-stroke engine that should be a 4. :D i do believe in scale very much, but with the engineering feat that i must overcome to achieve what i want anyway, i may as well make it from my own imagination of how i think mine would be built if i had a full scale one to compare it to. so, no, i don't think i will be attempting the scale comp's with this one. maybe some day down the road i'll trade the wife for an aero machine worthy of my skills and competition.[8D][8D] i wasn't aware of the fuel tank centerline and carb centerline business before. the plane was my messerschmitt, which is designed for the inverted engine, but i may have had the tank the wrong way. i ran the motor for probably 3 tanks on a test stand to break it in, so i thought it was running great. just for some reason when the plane is right side up or the engine is inverted, it's a pain in the butt. it's an O.S. .32. the .40 may be a completely different beast and may be a lot better than the .32. well, thank everyone for the input thus far and i will try to decide what i'm going to do with the wife :D, and pick out the next project. i do have a thread going in the kit building forum that is going to include all of my construction photos and nightmare re-designing for all of my ideas if anyone would be interested and i figure out how to put photos in the posts. it's titled "split flaps on a cub" or something like that. going to be very interesting to see the out come and actually fly it. scare the !!!! out of me to fly it actually. i sank a lot of time in building my trainer and after all the stories i heard about learning to fly starting on a tail dragger, i kind of got a little sick and naseated when zero hour came. anyhoo, this is getting way too long and i'm probably putting people to sleep or something. adios.....[8D]

RE: inverted engines
 

Tail draggers are no problem! Love'm, don't hardly build anything but, anymore. Do you remember the old adage about "Only believe half of what you see and nothing you hear (read). Keep this in mind with what is told to you here and you'll do fine!

Pay better attention to what your local fliers say, as they will be the ones who DO help you! Sometimes obtaining information here is a lot like drinking from a fire hydrant!

Go ahead and mount your engine inverted. If it works out, great! If it don't you can always side mount or mount it upright, with a few hours work!

RE: inverted engines
 

The location/height of your fuel tank is the main issue. If you invert your engine and install the tank in the stock position , you will have problems. If you lower the tank to "at or slightly below the carb line" then you should be fine.