Hi Folks,

I have the GP J3 ARF and I plan on installing an OS FS-70II Surpass 4-Stroke. The instructions call for the engine to be mounted on its side which forces much cutting of the cowl. I think that this detracts from the overall great looks of this bird and I was thinking about mounting the engine inverted which will result in less cutting of the cowl and generally better appearance.

This is my first 4-stroke and I am wondering if there are any problems associated with running the engine inverted. I know about hydro lock - is there any other concern that would make side mounting a better choice? I would prefer a better running steup over a more cosmetically pleasing one, however, if I can have both I would like to mount the engine inverted. Thanks in advance for your assistance/opinions.

Steve

The biggest issue is getting the tank low enough so fuel doesn't siphon through the engine continuously. That can be a real pain.

Some people have done inverted with absolutely no trouble, others say it's horrible, but the trouble can usually be resolved with a remote glow igniter tied to the throttle.
Dennis-

Hi Dennis,

Thanks for the info. Do you (or anyone else) know if mounting the engine on its side as opposed to inverted would be significantly better or only marginal - given the same fuel tank location?

Steve

I like to stick to the MFG's plans as much as possible, besides, a REAL cub has heads sticking out of the cowl. I have also had some 4-strokes run great inverted, and some run poorly for no apparent reason.

But the Main reason I don't like to invert an engine (Especially a 4-stroke) is that if you nose over, you grind down the Rocker arm covers (Or worse)

Stick it out the side, you'll never see it at 500 feet.

Good point - I never thought about the nose over situation (That is why I came to the Universe with the question). I will mount it sideways and avoid the headaches. Thanks for the tip.

Steve

Steve, I have one of those very cub's with the engine mounted inverted. Mine will be 5 years old this may and presently has 214 flights on it. I to like the clean look, and have had a number of people ask me why I don't have the jug's hanging out the sides. They all scoff when I say then it would look like every other cub, but I just like it that way. Anyway, I do not have siphon problems. You will probably want a remote glow adapter though.

The following are a number of observations a friend and I have made on the plane.

I have over 200 flights on the model and Bill's has verified these findings with his Cub. In all fairness to the kit I must say that I am not a slow and steady kind a guy, I like to be going mach 2 with my hair on fire low enough to see the top of the wing as it passes by me. I tell you this because that means that when I go to the field this plane gets the worst treatment, and always gets the call if the weather is to bad for my other, more dear to my heart models. As a result I can vouch for the strength and stability of the model, it has been landed with a negative ground speed on a couple of occasions. It has also given 92 of the neighbors their first taste of flying models, without skipping a beat. We all know what putting a rookie behind the sticks can do to a model, but this one got nothing but first flights.
From experience I've learned that those fake engines that we hang off the cowl never stay on, some where between flight 50 and flight 300 they always fall off. So I left them off, its all a matter of interpretation anyhow and I like the clean look. Under the cowl I mounted an old reliable ASP .80 4 cycle for power and it is a little big but I may fly off water some day so that would be just about right. I mounted the engine inverted to keep the cowl sides clean, I don't know if an actual cub existed like that but I like the look. Bill on the other hand decided to mount the dummy engine head on his cub with the head of his Saito .80 sticking out of the cowl on the other side.
The first change we both made to the plane is install the second landing gear wire. When we get to the field we fly! Sometimes the wind will challenge us with a crosswind landings which require an approach with the up wind wing low, having to set it down on a single wheel and hold it there until all the flying speed is gone. Having to do this, that one wheel needs to be rigid and its alignment must not change if it hits the runway a little harder than preferred. That second wire insures that to be the case because it does not allow the main wire to bend back.
The second wire (1/8in. dia. Cold rolled steel) was bent to fit behind the hinges for the landing gear pants and then attached to the first main wire just in front of the wheel axle, wrapped with copper wire then soldered. Extra landing gear straps were used to hold the second wire in place right over the covering, the cabin floor is light ply with hard wood in the corners which is acceptable for bearing the loads this wire will see. And the screws where taped into the mounting block for the landing gear pants hinges and struts.
The kit comes with rubber bands to hold the axle end of the landing gear pants to the landing gear wire. Having an inverted engine I had quite a bit of exhaust hitting the landing gear pants and would go through rubber bands quickly. Bill came up with the idea to use nylon tie wraps there and the problem of having to replace those rubber bands regularly was solved.
When I had 22 flights on the model the EZ hinge that held the strut to the fuselage broke. I repaired it with another EZ hinge and the one on the other side later broke at 42 flights. At which point I decided to go with out them until I figured out how to fix this correctly. I had glassed the wing center section while in the initial build. I used 2 inch wide 6 oz. Glass and recovered the center section with a role of 21st Century fabric I bought with the kit. Bill's EZ hinge on the strut broke at 22 flights also, and 48 flights.
While Bill was building his GP Cub he pointed out to me that the instructions state that the model should not be flown without the struts. I had missed that while building mine so I reattached the struts and soon after another of the EZ hinges broke and they came off until a better method of attachment could be found. Then I read of using coke bottle pieces to replace the EZ hinges so I pulled all of the EZ hinges and replaced them with plastic cut from a Dr. Pepper bottle (it was a bit flatter than coke) and put a bolt through it. The first flight with the newly refurbished struts I forced the screws into the same holes I had drilled for it, I'm a war bird jockey so stop laughing. Well you guessed it, the model was all out of trim. I realized that I had warped the wing when I forced the struts into the same holes right after it veered left on liftoff. But god watches out for fools and mode 1 pilots and I got it back down, took the struts off and everything was straight again. To this point I had contended that the struts where just for looks because the mounts in the wing were attached to balsa ribs. So after re-drilling the fuse strut mounting holes everything was back to normal and the struts seam to be holding up nicely now. They have about 125 flights without a failure.
We have to work for a living so it is a common occurrence for us to leave our planes in the car while working and it did not take long for us to see pulled seams. At first I would pull them back and re-tack them but soon that was no longer possible. After the last re-tack things were beginning to look pretty shabby so something had to be done. I did not want to recover the plane because of the cost and the time it would take, so we had that extra 21 century film, and I picked up a pair of pinking shears at a garage sale years ago ( you can probably find a pair at the local fabric store). You guest it, we covered the edges of our models with pinking tape and it looks pretty good if I do say so myself. Mine has spent four summers in the van and none of the pinked seams have shown any signs of pulling or delaminating. Now I think it will last.
When adding pinking it is important to decide how far you are going to go. A full size has two sizes of pinking a smaller width, we used 1/2", for strengthening internal surfaces like Ribs, and longerons. A larger width that is used to double those areas where the fabric is seamed, We used 3/4". In places where it would not be obvious I increased the width to 1", like the wing leading edge, or the bottom of the fuse. The pinking shears I had were only about 6" long which left us with a cutting surface of about 4" because the ends were prone to not cutting the fabric and deforming it. I also Had problems cutting in straight lines and keeping a consistent width, though we did finally solve those problems with lines drawn on the separation paper on the back of the covering. I used a lot of the pinking that was cut before the lining process and had no real problems applying the pinking tape in straight lines. But Bills was much nicer with the line cut pinking. How much pinking you care to use is up to you, but remember that the smaller pinking is applied first then the larger is applied over that to tie all the ends down.
The plane flies like a Cub should with a stall speed of around 20 mph, a maximum level speed under power of 60-65 mph (ours are over powered and with correct power it would probably be closer to 55-60), and a dive speed with full power of about 70-80 mph. It will do all the maneuvers you expect and it's a great deal of fun to try to imitate the full scale with the engine cutting out during inverted portions of maneuvers and diving for speed prior to the start of a maneuver. I just need to get my War Bird mind to account for that diving while setting up a maneuver. Normal level flight can be sustained with three or four clicks of throttle on the straight portions of the pattern and 5 clicks in the turns. Takeoffs are also interesting, I pin the tail for the beginning of the roll out then relax the elevator to about a ΒΌ up once the plane starts moving. It hopes off rather quickly (three point takeoff). Using the rise to the mains then liftoff method can also be used but one has to be careful with the amount of rudder added. Landings can be floated in, or dove to the runway at a low throttle setting. I was particularly happy with the ability to dive to the runway without picking up to much speed to land. Even after a long throttled back dive to the end of the runway it does not build up energy, which means that a slip is not required. Mine has flown in the calm of the afternoon when shadows were to long for my War Birds, or to give people that come to the field to watch a chance to try the hobby, or in 30+ mph wind when the rest of the sport fliers would not fly their planes. All in all it is a very good flying and versatile model that has taken all the punishment I've dished out to it with no worse a maintenance record than any kit I personally built for the purpose this model has filled for me.
We quite often have impromptu three point spot landing contests at the field and this model can holed its own. It requires alittle throttle as I begin the flair to keep it flying long enough to get the tail down. But I've competed against upto 1/3 scale Cubs and we all had fun. And thats what really counts! I've never seen any bad habits weather in the design or from wear and I have given this model every opportunity too. The next modification I plan to try is the addition of floats, but that will have to wait for now.

Good Luck

Joe Felice

Hi Joe,

Thanks for all of the info. I too have been making some mods. I already have done the pinking tape seam covering, the center wing joint glassing and I have decided to install the Hangar 9 1/5 scale Cub gear. Their gear is more scale like in appearance and is alot more durable than the GP wire gear. It installed with minimal mods to the fuselage such as adding a hardwood block inside and inserting threaded brass inserts. I plan on flying scale like and I have not decided whether to mod the wing struts yet. Since this is my first 4-stroke, I am going to mount the engine on its side per the instructions just to avoid any possible bad first 4-stoke experiences. I can always mount it inverted with an onboard glow later as a learning experience.

Regards,

Steve

Steve, What I do to break in an engine is install an onboard glow and run 20% nitro. The 20% nitro gives me the broadest idle range possible (the higher the nitro the broader the idle range), while the on board glow is insurance. I try to not touch the engine for the first fifty flights, because at fifty it will be well broken in and I only need to mess with it once. Of coarse as I am running those fifty flights the engine will get richer and richer and need one or two tweaks along the way. But the important thing is I don't have to stay on top of it, and can weight until I'm positive it is rich then make an adjustment.

At fifty flights I put the final tune on the engine. Once happy with that I remove the onboard glow (usually requires increasing the idle trim). Once happy with that I count the clicks, or turns on each needle valve and record it (in the planes log and written right on the engine box).

When installing the onboard glow battery I usually use those plastic tie raps to mount it to the engine mount. That puts all the weight up front for those first flights, so when it is removed it moves the CG aft.

The strut hard points in the wing are hard wood glued to the balsa ribs and they break out very easily. Well I should rephrase that, they do not come out from normal wear. But when the EZ hinge for the struts break near the fuse the strut can drop well below the wheel. That leads to a wing low landing and if the strut hits the ground while you are still moving it will most likely pull out one or both of those wing hard points.

I like to do my own version of the flying farmer routine with it, so I've loosened up just about all of the glue joints at one time or another so if something does not look or feel right give me a holler.

Good luck

Joe Felice

Hi Joe,

Are you refering to Roger Lehnert? I will sure miss seeing him at the Sussex Air Show - hope it is resurrected some day. I will let you know how my Cub turns out. Thanks again for all of your advice.

Regards,

Steve