diceco

I just put a very slight curve in it to match the curve of the seat. Just used my fingers. Now when I look at it side ways I see no light anywhere between the reed and the seat.

Just did a test comparing a 9mm venturi carb to an 8mm. It gained 85 rpm and 0.8 lb thrust. The 9 is the biggest carb I have. I assume you are happy with the idle on your 12.7mm carb???? What sort of RPM's do you get at idle?

diceco

Racinrc14

My Feedback: (7)

Sounds a bunch like EGR and it lowers the quality of the intake charge.
TKG


That's why I suggested a one-way or check valve to keep the positive exhaust pulse out and only allow the negative impulses through.

combatpilot

I can get it to idle pretty darn low but it is pretty rough and has lots of vibrations. I am hoping that the electronic ignition will help this as it will retatrd the timming quite a bit.

I didnt bend my reed vave physically but when i readjusted the reed stop it held it flat to the backplate as it should be. I am wondering if bending the valve like you have may have made it stiffer. maybee not or not to where you would notice lol.

I would really like to see how you measure static thrust. I am thinking maybee fabbing a test stand for this.

I may also have found a solutiion to those darn slits but i need a cylinder to experiment on. ajonr i think is sending me one and i should have it by the end of the week.

I did some shopping and i got my carb for under 15 bucks delivered from e-bay.

aj0nr

Combatpilot-
I sent of a box this morning.I put a regular head in it.Did you want one with a slit in it too?

combatpilot

Yea I did but thats ok i can get it latter and experiment on it. I am wanting to get this engine testing done as i really want to get it on the plane and I can play with that latter.

diceco

My stand is nothing more than a drawer with heavy duty slides. The drawer pulls on a digital "fish scale" that I got at Wall Mart. It was only 20 some bucks if I remember correctly. The scale goes up to 50 lbs and appears to be pretty accurate based on some dead weight measurements. I screw the platform down to some saw horses.

Here's a 25cc Husqvarna brush saw conversion I just finished running on the stand.

diceco

combatpilot

DRAWER SLIDES? damn could it be that easy. Ya i tend to overcomplicate things. I was imagining a linear bearings and roller bearings lol.

I knew I shouldnt have scrapped out that filing cabnet last week. It had some real nice heavy ones. darn it guess im gona have to do some scrounging lol. I need to make a new test stand anyhow as mine has suffered from vibration damage.

andrew66

i am hoping that for safety's sake there is a stop/limiter of some sort (other than fish scale) I have heard of people using an old skateboard with a track make with 1x1 boards. but the drawer idea applies to the KISS rule.

Racinrc14

My Feedback: (7)

That's a great idea, and I love the megaphone exhaust stinger!

Racinrc14

My Feedback: (7)

Combat, when the electronic ignition come in, what's the plan for setting the timing?

combatpilot

A cable would make a simple saftey stop. Its darn cold here today to and I really dont feel like going to the shop when its this darn cold. It sounds like a good day to go scrounge a drawer. I cant wait to get the parts from ajonr. I know im gona spend hours staring at them in comparison lol.

Flathead

My Feedback: (11)

Hey Combat, I am back but still to cold to do anymore in the shop. FYI, I use mostly Electronic ignition, and do some advancing when it is running, but gotta be careful. Would love to have you stop by on your way to Colorado some time, I am about 2 miles off of I 70. My wife says "IF YOU DON'T CLEAN UP YOUR SHOP, I AM GONNA DO IT FOR YOU". I might be safe, she never did learn how to start the Model T, and that's the first thing inside the door. Hope it warms up, I really do need to clean the garage. my e-mail is [email protected]. Kep up the testing, and I will send my info as it happens. Flathead 4

combatpilot

To cool I am definatly gona have to stop by.

Darn thing still aint here. darn boat must be slow lol. anyhow I haddent had a chance to figure on timing. I was hopeing it came with some instructions. I have been told you set the hall sensor right in the middle of the magnet. I will have to wait to see it i guess.

I made a trip to the habitat for humanity store. Look at the killer drawr slides i scored for a dollar.



I will try and get a new test stand together in the next few days. Thats how it is one project begets ten more lol[&:]

I got my tig welder out today and practiced. I think Im gona try and make my own muffler.

diceco

Yeah, there's a stop on the slide. In addition I have a wire link made from coat hanger that restrains the "drawer" when I'm just running the motor up for tuning etc. and I replace that wire with the fish scale when I want to take thrust data.

That exhaust stinger is an old "Clark" Irish tin whistle. It already had the holes in it so I just cut a hole in the stock muffler and stuffed the end of the whistle in and brazed it up. It works great and it's pretty quiet.

I thought I was done with the reed mods but I just couldn't resist taking it one more step further. I measured the force to open the reed to the stop (set to 1/8 inch) for three different configurations.

120 grams for stock reed and clamp
52 grams for contoured reed and clamp bent so that only the mount end of the reed contacts the clamp
30 grams for a reed with a bean hole cut in it to reduce the "spring" area.

I chose to cut a bean shaped hole in the reed as apposed to a waist, the argument being that with the wider links it would provide better stability than with the waist configuration with only a central link. I hope it holds together. A broken reed floating around in the crankcase even for a few revolutions might not be too good!

Of course all this reed work is arm chair engineering at it's best. One could make a whole project out of the reed design for the Ryobi. When the engine is running the reed is probably vibrating at the frequency of the motor speed and who knows what the inertial response of the reed is and whether reducing the spring force or the mass of the reed will help it or make it worse. The response of the reed depends on both the spring force and the inertia of the reed of course. I'll run it up tomorrow and see if there is any change.

Sorry once again for the out of focus photo. My camera doesn't do close focus well.

diceco

BTW: There is no indication that the reed has ever hit the stop on any of the engines I've seen.

combatpilot

Damn thats a great idea on the bean shape cut. I am really interested to see how your test comes out as mine had no change from reed to reed to reed. Interesting to see how much force is required to open the reeds. I had no way to test this. Man it will be great to see some comparision on the reed tests.

combatpilot

Hey dieco I was just rereading some of the posts and i was noticing that your not listing you rpm that you recorded with the test just the rpm differences. I was just wondering what kind of rpms your running. also could you list all your mods so far and what your top rpm for these mods together are. Thanks so much.

andrew66

Well i did get to run my engine today. Only for a few mins. It was damn cold out, and i couldnt get to the mixture screws the way the engine was set up. I did get a bit of video, but its just too hard to video tape stuff without a helper. I should have parked the truck so i could have set the camera up facing the engine. Oh well. But at least today i got to see if the engine would even run with the mod. Once i get my mount set up, and engine tuned, i will run this thing for at least an hour to see if the ring will hold up. If it was going to fail, i think it would have right away, but i want to be sure.
I will post the video, once i get it converted so youtube will play it.
http://www.youtube.com/watch?v=rHt9GfY8UmM

Racinrc14

My Feedback: (7)

Andrew, you ground out the material between the ports, correct? And the ring didn't fail right away? Sounds good so far. It'll be interesting to see if removing those areas makes any difference. Did you compensate for the gain in crankcase volume?

andrew66

as far as case volume goes, i have done no mods. basically i have a new jug bolted on an old short shaft case, with a one ring piston. I really need to get a frank bowman ring for this, cause the gap is huge, and compression is down. Since it hasnt run very long, the ring may need to seat again before i will get any real compression. I wish that i had a recent pic of what i did to the ports, but the pics were on a computer that has crashed.

Edited cause I found out how to get the pic from the other thread...

diceco

I did the test run of the "bean cut" reed today. It caused a LOSS of roughly 300 rpm and 1.3 lbs thrust! I went back to the solid reed, repeated the run and got the same performance data I had gotten before with that configuration.

So to summerize the reed test experiment: modifying the reed clamp gained about 60 rpm and 0.2 lbs thrust. Combining the reed clamp mod and the cut away reed lost 300 rpm and 1.3 lbs thrust. The conclusion is: modify the reed clamp and contour the reed to fit as close as possible to the seat, but do nothing else and you'll gain a little power.

Right now I'm at about 7220 rpm and 13.5 lbs thrust. That's with an APC 18x8W prop.

The engine configuration and mods are:

Newer style case with integral fan shroud, two runner per side transfer ports.
Two ring piston.
Long shaft crank with small counter weight.
Heavily chamfered and port matched-to-crankcase transfer ports. See photo in previous post.
Stock muffler with single 1/2" EMT exhaust pipe.
Reed valve stock except for slight bend in contour to match seat.
Reed valve retainer bent so that contact is only at base of reed.
9mm venturi Walbro carb.
C&H ignition set at 30 deg. BTDC

My next move is to get a bigger carb!

The speed and thrust of the motor is very dependant on the prop one uses, of course. When I set this motor up originally, almost a year ago, I had tried three different props, APC 18x8W; APC 18x6W; Master Airscrew 18x8 Classic. The APC props outperformed the MA prop. For the exact same motor conditions I got about 0.8 lbs more thrust with the 18x8W APC than with the MA 18x8 Classic prop, even though the MA prop was turning about 100 rpm faster. When comparing the two APC props they both delivered about the same thrust but the 18x6W turned 500 more rpm than did the 18x8W. I've heard that you don't want to turn a Ryobi much more than 7000 rpm static so I've stuck with the 18x8W APC. The APC prop is just more efficient than the MA prop, at least in the sizes I tested. My only complaint with the APC props is their weight, but all the nylon composit props are heavy. If I were really flush I'd get carbon fiber! I'll try wood first.

diceco

diceco

Wow.... that is some scary big looking transfer ports! I hope they work!

diceco

andrew66

i really wish i had a tach so i could tell. I will have to get one soon. maybe someone could also try this mod? i will run this thing a little longer in this config. to test the longlivety of this.

combatpilot

Dieco I just dont understand why that bean cut reed valve lost power. In my tests it just didnt matter what reed it had it came out the same. the only thing i can figure is witht he bean cut shape it just dosent seal as well as the full reed as the reed stop cant keep it contured and sealed to the base. I dont know this for sure as i cant see your parts. Try the waiste cut shape and see what your get there. could be interesting. I cant belive that newer style head and cylinder runs that good. I would like to see the combustion chamber of that cylinder. I think your gone asee a big power increase with that new bigger carb. at least 300 rpm in my opinion.

I worked on changing my port timming to 150 degrees today. I will run that test when I get a chance. From there I will work on case stuffing. sure wish that darn comp ignition would get here.

diceco

On the bench the reed looks to be sealing the seat perfectly. Unless the reed is distorting and bending out of shape during operation I'm not sure it's a sealing problem. Although it would be of interest to try the waist cut it would be of academic interest only as you've shown that there is no improvement. Besides I've only got one more stock reed to experiment on and I'd rather not bugger it up!

I think it's more likely an inertia problem. The reed has got to change direction 7000 times a minute. That's over a hundred times a second! I bet with so little spring force on the reed it's lagging behind in getting back down to the seat as the crankcase pressure builds up on the piston's down stroke. In fact it may be still on the way up as the crankcase pressure turns around from negative to positive!

Measuring the force to open the reed on your set up with the waist cut in the reed might be interesting. If you have a digital postal scale or a spring postal scale or kitchen scale you can get a good idea what the force is. I took a tooth pick, stuck it into the intake port at the edge closest to the opening end of the reed and balanced the whole backplate assembly over the platform of the scale (the end of the toothpick rests on the scale platform) and pushed down until the reed was just barely off the reed stop set at 1/8th inch. If the scale measures in ounces there are about 28 grams in an ounce so you can compare what I got.

As for the newer style cylinder with four transfer runners, I believe there are huge gains to be made by smoothing out the entrance to the transfer ports. The flow coefficient, and thus the effective flow area, of those ports just has to be abysmal with those blunt facing surfaces facing the flow. I not only bullet-nosed the web separating the two runners but also matched the outer edges of the ports to the crankcase so nowhere are there forward facing steps in the flow path. I bet you are right about the difference in cylinder volume (compared to the older cylinder, ie compression) but I'm not sure how to improve that situation with my setup. The only other cylinder I've got is the one with decompression slots.

diceco

andrew66

I got to run my engine again today. Unfortunately there is no video cause my camera died on me. I got the mixture set pretty close, but the high end should probably be just a touch leaner (again thats where a tach would be nice). Idle and transition are really good. I still get a bit of a hesitation when i snap the throttle shut (probably faster than the servo can move) but other than that, it runs great. Ive got a good start sequence down, and it usually starts after a few flips, and occasionally on the first flip. I have about 1 1/2 liters through this engine, and a total time of about 1.5 hours. I like to keep a log of the time on the engine, but it was hard to do that when i was setting the mixture, cause it did die on me a few times. The ring seems to be good, and compression is starting to come back. I really wish i could get an rpm reading. I think right now im on the high side of the limit with the 18-6, and i would like to get a 18-8 to be safe. I kinda want to tear down the engine and inspect, but its running good right now, and i would hate to jinx it.