BBriBro

My Feedback: (2)

I finally got it in the air today ! The engine is a joy to listen to, It just barely ticks over at idle. I have seen 1200 RPM, but it'll idle all day at 1400. It has a very low pitched pleasing exhaust note, and even with the straight pipe, it's not very loud in the air. The engine doesn't have a whole lot of power, I am used to unlimited 3D type planes, and this is the 1st "conversion" I have actually flown, so I don't have anything to compare it to. The airplane is a Bridi Big Bee, 96" span, 1630 sq in. weighs 14.4 lbs. Turning a master airscrew classic 18x6 at 7000 RPM, on the WYK-61 (9mm) carb. I am hoping for a bit more with the 10.5 mm WYK-16 carb, (when it gets here) I think the all up weight is decent considering the weight of the engine, I guess all the lightening holes paid off. The airplane flies well, just not what I'm used to. It's been a long long time since I have flown an airplane that you can fly full throttle in level flight for extended periods of time. I enlarged all the control surfaces, (just habit I guess) the rudder looked a bit short, I think making it taller helped the looks. the ailerons were so long, and so skinny, they just didn't look right. the elevators got about 1/2" more chord, ....just because. The wheels are 5" Kavan air filled treaded, and boy are they light, it's deceiving when you pick them up, they weigh less than 3" hangar 9 wheels.

Couple of things. I am using the stock spark plug, which isn't a resistor plug, I did a long range check (80+ paces) and it was solid, I also am running PPM, (not PCM) but the radio is fine, maybe magnetos aren't as bad as battery ignition for interference ??

the only "issue" I noticed, was that the engine didn't want to run inverted. I know it's not an issue on the weedeater, which makes me think it has to do with airflow. If I do a split ess, it's fine, cause you pull as soon as it get inverted, but with the slightest amount of "push" it instantly loads up, and stumbles real bad, regardless of throttle position, so I have to roll right side up, or pull out, and then it's fine again. Strange, it does it every time, but ride side up, runs like a top. I have heard of trouble with cowled engines, and odd airflow to the carb, (where it senses atmospheric pressure) but with mine all exposed, I wouldn't think that would have any effect.

DougT

My Feedback: (1)

That is one NICE looking plane/motor! [8D] Even though it won't 3D, I find it relaxing just putting around the sky with an easy to fly, super-reliable engine. Love the color scheme.

Hopefully your new carb will help. If you ever remove the pump cover/gasket, let me know if there's a small spring making contact with pump diaphram. I'm sure with an electronic ignition/LiPo battery you could save yourself 1/2 # and have excellent top end and idle.

Keep up the great work.

Doug

fwman1

My Feedback: (22)

I LIKE it. You are a very good builder! I bet it sounds great. You should post a sound clip. Congrats!

av8tor1977

My Feedback: (6)

Wow, nice work and thanks for the update. Nice pics, though large and it takes a while to download for us poor dial up guys.

The plane looks great, and the workmanship and installation are excellent. The performance you got bodes well for my idea of a large old early 1900's style plane with a four stroker. Do you have plans of running/using the 31cc engine? I sure would like to hear about that, as that is what I would use.

Sorry but I can't comment about your inverted problems. I don't have any four stroke conversion experience, and I've never encountered this with the two strokes. I mount my tanks well back on the c.g. with these guys, and never have a problem, though I do notice a small difference in mixture between full and empty tanks that people say doesn't happen with the pumper carbs.

One little comment though. I think you might want to put a tube on that breather hole in the valve cover. It will probably emit some oil mist, and perhaps a little blowby that is natural to any engine. It would be nice to vent this somewhere that won't result in it getting on the plane, and that would also keep dirt from entering the valve cover area. Just a thought...

Oh, I would definitely change to a resistor plug!!

Thanks again, and please let me know about that 31cc you have.
AV8TOR

BBriBro

My Feedback: (2)

Thanks for the props guys ! It's been a fun project for sure. I don't mind a relaxing flyer for once, But I am curious why it won't run upside down, and ideas ?

Yes, there is a "cone" shaped spring in there, smaller diameter on one end than the other. What is the significance of this? (why do you ask)


sorry, I think you mentioned that before, But I don't know how to "link" to them. If I upload through RCU, when you "click for full size" they are not really full size anymore, RCU shrinks them This is the lowest res setting on my camera, the files are only around 50-60k each.

I don't think so, I'm not sure what I'm going to do with it. The 25 looked so much smaller and more compact, and I just liked the overhead cam The 31 is over a pound heavier, It would be worthwhile with electronic ignition, but thats a lot more money for "experimenting"

My tank is on the CG too, shouldn't be a problem with a walbro. It's very strange, you can "pump" the elevator while inverted, and it sounds like I'm throttling back when it gets Neg Gs. almost like I'm working the throttle stick, and not the elevator, It's so quick to respond, it has to be some sort of airflow problem. Even if it were sucking air, it wouldn't be instant, with 12" of fuel line from the tank to the carb.

I considered doing something with the crankcase vent. I know on cars (and this thing too) they connect it to the airbox so that it reburns it's crankcase vapor (blowby) for emissions reasons. It doesn't seem to emit anything, (that's part of the reason I mounted the engine upright) there is a wire mesh "filter" in the valve cover, might trap some of the stuff that normally would blow out. I also thought about dirt going in, but with no air filters (on most model engines) I figure if the stuff entering the combustion chamber through the intake doesn't hurt it, neither will anything in the valve cover.

I intended to get a resistor plug, but forgot until I was on my way to the field, I figured I'd range check it and see, and I have had far less "range" with other airplanes that are set up more "proper" so I'm not sure If I should just fly it as is, since it works fine. I was in the mindset to just kill the engine if it started glitching, but I had no trouble. I flew about 4 or 5 flights, over 20 min each with no trouble (this thing will fly a long long time on 20 oz)

BajaBob-delete

WOW thats very nice.

Hobbsy

My Feedback: (102)

Very nice Brian. Did you make that pipe? Also where did you get the engine?

BBriBro

My Feedback: (2)

yeah, I got the 5/8" tubing from wackerengines (I couldn't find that size anywhere in aluminum) and the flange is 1/8" aluminum bar from home depot. The engine came from [link=http://smallenginewarehouse.com/ProductList.asp?Category=Engine&Supplier=Honda]http://smallenginewarehouse.com/ProductList.asp?Category=Engine&Supplier=Honda[/link]

Hobbsy

My Feedback: (102)

OK, now I'm hooked, I gather that you made the prop driver and the mounting plate too. And Thanks. The reason I'm asking all this, I have an ACE BigBingo kit still in the box, that would be the perfect engine for it.

DougT

My Feedback: (1)

BBB,

That spring is the key difference in carbs for 4-strokes vs. 2-strokes. On a 2-stroke, the alternating + and - case pressures move the carb diaphram back and forth and pump the fuel. On these 4-stroke carbs there is no alternating + and - pulses, just -. On a 4-stroke, the - intake pulse sucks the diaphram down and then the spring returns it, creates the oscilating motion, and pumps the fuel. That is why just swapping on a standard 2-stroke Walbro doesn't work well.[] That is also why I would like to tap the crankcase and run a +/- pressure line to a new intake spacer so it can have +/- pressure pulses. That way you could have an infinite number of 2-stroke carbs to choose from.

Let us know how it flies.[8D]

About the pics. I don't believe the large size has anything to do with the pixel resolution. I think it is the size you shoot them with on your camera. There should be a setting you can change. For example 640 X 480 is a smaller picture size than 1240 X 960.

Also, how tall is the engine from crank centerline to the top of the valve cover? I've got a project that I would like to try this motor on but my Ryobi seems too tall at 6.5".

Doug

BajaBob-delete

I tried a seperate pulse line for different carbs,it pumps like no tomorrow.It would work if the internal metering of the carbs I tried was closer to what I needed,a WA 167 too rich,with needles closed all the way down and a WT 644 too lean.

I went back to the stock type of setup with a rotary.Rotary carbs perform better than butterfly types anyway.
Even at engine speeds of over 12k the WYK series pump well enough using manifold.
If your lugging engine hard enough to cause a condition that you very low vacuum,then possibly reducing load may be the solution or a smaller carb.If your revving to 7000 I would say this is not the problem.

I've also mounted rotary carbs upside down and they worked well for the most part,they should work in any angle.But,I did have some trouble and came to the conclusion that either the primer bulb may have caused some problems or the air flow was upsetting mixture.

BBriBro

My Feedback: (2)

No, I bought the prop hub and mount from [link=http://www.carrprecision.com/Pages/prod02.htm]http://www.carrprecision.com/Pages/prod02.htm[/link], I don't have a lathe although I've been considering it lately with all the "work" I've been doing


I remember discussing this before, but It didn't "click" , now I understand the difference between the 2 and 4 stroke carbs, maybe I missed the part about the "spring" before, anyway, if you remember from another thread of mine I tapped the intake manifold and ran many different 2 stroke carbs and they all pumped fuel fine. I tapped the intake only because the pulse holes didn't line up, and I was quite surprised how easy it was to set it slobbering rich, so fuel flow wasn't an issue, the carbs were just too big, and these rotary barrel throttles just seem to work better than the butterflies, (on this engine anyway) much less airflow I guess, the butterfly carbs dribbled a lot of fuel, I'm guessing the venturi just wasn't sized right for the amount of air this engine pumps, whereas the barrel throttles don't even have venturi, it's just a constant diameter, which might work better with low airflow.

I actually have a cheap camera, it doesn't give specifics, it has "small, medium and large" for the physical picture size, and "low, medium, and high" for the resolution. I am taking all the pics in the smallest size, and the lowest resolution, which equates to the smallest file size. (roughly 800x600, it won't go any less) there isn't much else I can do except link to them, since I have them hosted remotely anyway. how can I create a thumbnail that links to my server, without uploading them to RCU ?, (where they get reduced in size)

Crank centerline to top of valve cover is 5 3/8"

BBriBro

My Feedback: (2)

Interesting, I noticed the primer had fuel in it, even though it has never been used, it has been blocked off since I took the carb out of the box, so there is some seepage somewhere. I am hoping the WYK-16 will fix the problem, since it has no primer. too bad it has to come from Japan. (I've talked to Walbro quite a bit in the past few weeks searching for just the right carb)

BajaBob-delete

Took me a month to get a WYK-113 from dealer,the carb wasn't in the Walbro "pipeline" so I had to wait.
If the non primer solves problem then it was obviously the primer bulb,the umbrella valve in bulb,(orange thing) could possibly leak fuel past it,making it run rich.Even if thats not leaking, the fuel in the passages could "run" to main jet making it run rich for a while.
I also had some strange things happen at WOT,I set throttle EPA to just shy of WOT and most of the problems went away,that problem turned out to be a lean condition.
I takes a while to sort out carburetion on these things.Its a pain in the neck,but well worth it.

BBriBro

My Feedback: (2)

The WYK-16 isn't an "active" carb in the US, But the walbro tech told me he could get it from Japan. I'm guessing that the ones with mixture screws will become increasingly harder to come by, since even weedeaters have to meet emissions standards now.

So, if you had an engine mounted inverted, with the primer bulb now on top, would the engine just flood out, until the primer bulb was empty ? I didn't realize the fuel could just "flow" out of the bulb so easily.

BajaBob-delete

I don't think its supposed to flood,some engines come with butterfly type of carbs with the bulb mounted "up" they run fine,but they also meter fuel into the venturi differently.They have a series of holes that come into effect at different throttle openings ,where the rotary all the fuel flows though tube in center of venturi.
But I've never seen a rotary with the bulb mounted on top on a standard yard tool.Its a guess on my part that in the upside down position that its possible thats it causing it to run rich.Its been my experience on the bench with the rotarys that they run rich inverted,it could just be the particular carb I have that does it.I had to adjust it to to run good in this position.

Maybe mount it up on bench and see if you can't work out the reason for it changing,a double check of the metering lever height and needle and seat wouldn't hurt.

There are good diagrams of operation and fuel passages here:
[link]http://www.shark-racing.com/Ingles/Tecnica/Tecnicaing.htm[/link]

Willdo

This thread sprang up in a hurry!
It's a geat looking machine, first real publicity the little Honda has had.
I guess the lube system works good too, congratulations, that's a great effort, maybe the Hondas will have more credibility now!

DougT

My Feedback: (1)

I've also noticed that primer bulb equiped carbs don't like to be inverted. My WLY on the Ryobi lost about 200 rpm if I remember correctly being turn over. I gained it back by flipping the carb/manifold back over. The engine also lost about 1000 rpm being inverted and wouldn't run as nicely as right side up.

BBriBro

My Feedback: (2)

I just read some specs on the Honda [link=http://www.honda-engines.com/gx25.htm]HERE[/link], they claim the peak torque is at 5000 RPM, is that the RPM I should be propping it for? this is a question for all engines in general, should we be propping for the peak torque RPM or the peak HP RPM ? Maybe I'll try a substantially larger prop, like a 20x6 (if there is such a thing) , I'd like to get more static thrust, speed isn't important to me.

Edit, BTW am I on the right track, thinking the APC props (which normally work better than most) are not the "best" for these relatively slow turning engines? And that the MA classics tend to produce more thrust at these "lower" RPMS ? How about Dynathrust? It outta idle even better with all that weight, Anyone have any suggestions for props turning less than 7000?

BajaBob-delete

Planes are probably the same as boats, pitch it till you get the best vehicle speed or performance.
With boats you get to a certain point with pitch that drags rpm down so that speed is lower than a prop that lets it make more revolutions. Too little pitch and is over revs,you have to find that balance.

DougT

My Feedback: (1)

Honda vs. Ryobi comparo

Honda crank center to top of valve cover = 5 3/8"
Ryobi crank center to top of valve cover = 7"

These pics are as close to the same scale as I can manage.

Smokin Cap

My Feedback: (49)

I just put in a Honda GSX 31cc in an old Bud Nosen DR-1 Triplane. No problems running upside down. Gonna test fly it next Saturday.......plane is heavy at 21lbs!!! 72" Top wing and balences where im guessing the CG is. Swinging a Master Airscrew 20X8 at 5200 rpm. Im like the starter of this thread. Im used to my 31% Extra with a 3W-75 at 19lbs. Im not sure if this thing will pull it into the air but we will see next week. Here are some pics of it in the Cowl.

BBriBro

My Feedback: (2)

I think with boats, you want speed, since acceleration isn't of too much importance. With an airplane, you need a combination of both, in fact for my usual style of flying, I run large, low pitch props, I don't want the airplane to go 100 mph, but I want lots of thrust at zero airspeed (for 3d flying) This airplane obviously isn't meant for 3d, but I still would rather have static thrust over speed, for shorter takeoff rolls, quicker response in a go-around etc. speed just isn't where it's at for me.

DougT, nice comparison pics , I'm glad I went with the Honda

qm1usn, nice !! I bet on the DR-1 you need the weight on that short nose, perfect !

BajaBob-delete

True.
Most of my efforts have been in upper rpm range power,It would be interesting to see how much midrange or 5000-8000 rpm the power could be improved.

Smokin Cap

My Feedback: (49)

Just did the wing loading calculations for the DR-1. I have 1860 sq inches of wing and the plane weighs 21 lbs. That gives me 26 oz per sq foot. This is a Bud Nosen Kit. I know this because "Bud Nosen Model Products" is stamped on alot of parts. I cant find any reference to Bud Nosen kitting a DR-1 at any time in the past[sm=confused.gif]. I used a Thrust calculator to find out how much im gonna have. I figured im putting out 11.2 lbs of thrust on my MA 20X8 classic. That is alitte over 50% thrust to weight ratio. Should fly fine.

Well.... turns out im only putting out about 6 lbs of thrust (fish scale). That explain's the horrible performance on its only flight so far.[]