between 3/4 and full while airborn there is no difference in my G-26. Any clues what could make this happen and how to fix it?

I is as lean as it can go then backed off from 7000 RPM ground with a MA 18x6 wooden

i am not as worried about ground RPM, but i swear if i try to lean it, no luck i dies.

I am more worried about proformance in the air. .. the dead zone in the throttle must go!

any help would be great guys!

That is actually pretty normal. Most 2-stroke gas engines are at full power before the throttle plate is fully open

There are several ways to get the stick to be a full rpm at full stick.

1) Use a throttle curve if you TX supports its. Some do and some don't. If not then use a programmable mix that supports a multi-point curve, then do a throttle to throttle mix and do a curve there. Find out what max RPM you are getting while at full stick, now while in the mix, slowly raise/lower the curve (depends on the TX brand/type) until you hear the engine start to drop rpm then bring it back up to full rpm, Now move your stick until you get 1/2 the rpm you had at full stick and move the curve to make the stick be at half way, then move the stick to idle and set the curve to get the idle you want. Now if you have peaks and valleys between those points, then using the multipoint curve clean them up so it is a nice line from low to high. Now your stick with show an rpm increase all the way up.

2) You can also get very close mechanically, as an example, If your carb arm is one inch from the point when the control arm (clevis or ball link) connects to where the rod is in the carb for the throttle plate (pivot point), then you want a servo arm connection that is roughly 3/4ths of an inch from the servo arm screw (pivot point) to the control rod connection (clevis or ball link).

I personally use the throttle curve method. As the engine breaks in it's easy to reset the curve to get the rpm increase you will see and if you go to a bigger prop you will need to retne and set the curve. It's as easy as changing the TX versus possibly having to chage the servo arm connection. Plus if you do some hovering you can flatten the curve around that point to make the throttle less sensitive.

The torque peak on a G26 is at 9000 rpm, the HP peak is at 12,000.....A prop that will only turn 7000 on the ground is too much load, use less pitch or smaller diameter...
The stock G26 muffler is an rpm killer...You will see around 800 more rpm with a less rectrictive muffler...

Just to confim everything that bubbagates said, its normal for the last 1/4 of the throttle to have no effect, as bubba says the easiest way to overcome this is with a throttle curve on the Tx.

Mike

The G-26 should do better than that. It's possibly not broken in yet. However, the bottom line is - too much prop. At 3/4 throttle, it's turning all it can turn. My G-23 turned an 18 x 6 at 6800.

I disagree with those who say there isn't much difference in 3/4 throttle and full on these gassers. I've run a G-62, G-38, and G-23 and had good, full, even throttle response all through the butterfly range.

Dr.1

Both pf the g26's I have from Ralph turn an 18x6 Mezjlik at 8000, one I bought directly from him and another was a brand new from Horizon that was sent directly to Ralph and then sold by the person from my club who never ran it. I'm sorry I did not see the rpm figure before so I do agree that you are not broken in yet or the prop is a wider blade than the Mezljlik. I'm not familiar with the MAS props in that size.

I have yet to see an engine that did not need some kind of curve to realize a nice change in rpm from idle to full throttle and that's with a good throttle servo setup to get about 125% resolution on both the low and high sides

The noted power curve thingy is quite normal in butterfly valve carbs. The carb shaft is 5mm, the valve plate is 1mm, and for a certain amoint of rotation does not influence the gas passage because the shaft is still there as main flow barrier. Once the valve gets out of the shaft's "shadow", the valve angle will have effect.
A solution to the linearity problem is to tune full throttle at i.e. 75%, where the rpm loss is about 50 rpm. With this valve setting, response to stick inputs is mech improved.

i figured it was a butterfly issue. After all these carbs are NOT MENT TO HAVE AIR RUSHING OVER THEM. If you add a little turbulance then i multiplies the problem. Plus the 'displacement' (if you will) that the screw gives while at full throttle could closely measure a 3/4 open butterfly if you see what i am saying.

I know that those RPM's sound low. . . they probibly are and i am going to try a few different props to see what happens. But there are a few aeronotical thoughts in that as well when dealing with a prop on the ground in the B.S. measurement of 'static thust' vs. a prop 'unloading' in the air. I am not discrediting those of us that get all hung up on ground RPM, but the fact is that has almost nothing to do with how it flies a plane. (i said almost)

Ralph is correct about the muffler i am sure, and i would like a new one as well a few props to try.

I might use a little throttle curve just for my own thumb to brain link-up. But i think i might 'rig' it with some throttle switching. i.e. thro1 high idle (start mode) ... thro 2 low idle with thro curve adjustments ... thro 3 low idle with NO thro curve. That way i can continue to switch and monitor thru' the summer to make sure when it seats a little more.

another note...

I might not be the best mechanic with these engines, but i am no dolt in the schoolastics of aerodynamics and aerospace science. i can assure you guys that while 'static thrust' and max ground RPM do hold a place in this hobby/sprot it will not always tell you how your bird will fly with its power-system in the air. That is not 30 years of experiance, thats about 1200 years of hard physics

i honestly expect a few Forum a#$ whoopings for that statement. Who knows maybe i can Gallaleo (spelling?) myself in the forum world!!!!

anyway, thanks for the expert advice guys. . .thats why i am here.

Well Unc, I'm rather pleased to encounter one of the few that understands that high static ground rpm does not always correllate to high "unloaded" airborne thrust. I've been trying to get that across to people for the last couple of years with little effect. Often the higher static rpm equates to less short distance thrust, but adds more speed instead. The opposite of what 3D flyers are really looking for.

As for the throttle linearity, something that I've found helps even things out without performing a throttle-throttle multi point mix is to set the linkage for the throttle servo as close to the servo output shaft as the arm will permit, and set the linkage for the carb lever as far out as it will permit. Not perfect, but a little better.

Mr. Silver,
HAHAHAH, well you and me will take on the world, bud. I guess you used the correct lexicon and put it in more of a modeler's terminology, but YEAH, you are absolutly correct my friend. Its soooo funny, man... All of these 35%+ ers that sit at there trailers and say, "oh, that RPM is way too low. . . your not getting what you paid for... thats too rich... let me try... why dont you buy a carbon prop... whats you static thrust, min is xxlbs ... " ect.

I hate that stuff man. It's the same guys that never fly and correct your whole rutine while polishing there pretty planes and talking about there POWER EXPANDERS and REGULATORS and how i am not 'SAFE' if i do not have a servo connected to my kill switch (even tho my radio is programmed to shut the engine down by full thro close). I just smile and keep flying. You want to know the catch, man? I fly a SIG Rascal 110 (the big un) with a G26, and not only do i out fly most of those guys (heck all of 'em), but i can almost IMAC the whole thing. . . WITH A RASCAL!!!!!! They cant accomplish one solid aerbatic move without a programed switch or some complaint about there bird or radio. While the whole time they think they are the experts because they tool out to the field once a week or so. Give me a break man!!!! I'll get my advice from the PROVEN experts, Ralph, Don (dons hobby shop - nationally renoun)ect... But, I just like to fly man. If my birds good, my engine is good, and my radio is great then I'm tickeled pink.

I will jump off of my soap box.

So, can i pick your brain about some real IMAC planes, and your recomendations?

-Evan

p.s. ever seen those guys have to land in a Kansas cross wind? It's ugly enough to say, "landing. . .let me know when you are finnaly clear!!!!"

No flame suit needed Evan[8D] With an Abell muffler and Mejz 18x6 my RCIGN1 converted G26 turned 9000+ on the ground from day one (properly tuned). Of all the props I tried that one seem to be the best suited for my particular Edge I had it in. I tried a lot of props.

Although the high RPMS could be a plus. . . if your prop and engine combo doesnt unload right in air. . . then its wrong. Even if it says 11000 RPM or 7000 RPM if it doesnt unload right. . . YOUR WRONG! I will try new props and mufflers, but not in the intent of the highest RPMS that man has ever seen with a G-26. Just for performance in the air.

p.s. As sure as i sit here, and i give you my word... I now have over 25 flights on my new g-26 that idles at 1700-1800 reliable RPM. Inverted, spins, snap(ish) rolls, hammerheads, ect ect ect. all with heavy on and off throttle work, BUT HAVE NEVER, and am willing to bet, WILL ever, have one single dead stick landing. Just food for thought in the quests for the superior RPM challange.

(stock magneto ignition)

-that is in NO WAY a discredit or sideway sander to RCIgnitions (Mr. Cunningham) I have seen and heard what he can do to engines. . . truly amazing, truly a gift. If i had some extra bucks laying around. . . Ralph you would have them all in a week!!!!!!!

No problem, they run the same either way...The instruction manual says to use a prop thet will turn 7000 t 8500 while flying...Many customers using many props have found the Mejzlik 18-6 to give the best performance...The stock muffler cut 800 rpm from a less restrictive one...
I don't know what it turns in the air with that prop, but the peak torque happens at 9000 rpm, the HP is at 12,000...Why run a prop that won't let the engine run it it's best torque range ?

true.

I am presenting my openion on a few artilces i have read written by Don of Don's hobby shop about RPM and difference between ground and air rpm. It is very insightful and i can not remember what magazine it was in, but it was very informataive. I talked to him ad nausum about it last week and he explained it even further. But it was sited by actual rpms and facts! He had a few ways to measure air rpms accurately vs. thrust ect ect.....

basically when you have wind already flowing over the prop (air rpm) it will allow the spool up to hapen quicker and your peak rpms are always higher in the air PROVIDED THAT YOUR ENGINE IS NOT TOO LEAN TO HELP FUFILL THE GAS NEEDED AT THE HIGHER RPM. So basically my 7000 rpm zenoah should be spinning around 8200 to 8500. I have bought one of the on board rpm meters and will install it to see whay happens.

I am going to try some mufflers (slimline, ect..) to see what happens first. then i will try one of those mejzliks!!!!!

Mr. Cunningham, please do not think i am trying to discredit your work or your findings. . . like i said i would love to send you some engines!!!!! I am more addressing those that worry sooooo much about RPMs and then complain when they do not have a reliable engine to bring the bird home.

i guess it should also be said that i am NOT flying 3D with this engine. . . that is why tuning ext is different. that being said, it is all about 'what you like'.

Evan

It will turn a Mejzlik 18-6 @ 8500 on the ground using a Slimline Pitts here at 7000 feet...
Other props turn less..I have used PK, Menz S, Xoar, APC, Zinger....I haven't flown a plane with any of these...My customers like the Mejzlik best....The Mejzlik is the most expensive...

Ralph,

If you want to know, I'll get hold of a PT model 18x6 and toss it on one of your G26's and let you know. I'm not sure but I do own a few 22 and 23 inch PT model one and they look very close to the Mezjlik's almost to the point of calling it a clone.

The engine I'm referring to runs the Mezjlik 18x6 currently and has been a real powerhouse on a Super Stearman. It's been so long since I actually tach'd it I do not remember what I am getting but it was right where you sais it should be when I first got the engine

No problem, I tried some other props that were close, the Mejlik was always better..Too bad they cost so much...
7000 sounds low, he needs to try it without the muffler....