Edwin

My Feedback: (2)

There has been a lot of talk here recently about 20cc and 26cc gassers. Also in my club. I have talked to several club members that are showing an interest in smaller gas engines for 120 sized planes. I'm in the purchase que for one and serveral club members are real interested in how it does. Most everybody wants rear carb with a rear dump or rear facing muffler. This is due mostly to glow fuel prices. I've talked to a few engine dealers and it appears they are well aware of the shift that appears to be coming. They are also aware that rear carb engines are the most desirable now. Is anybody else seeing similar interest in their clubs?
Edwin

pe reivers

the rear carb small gasser has some drawbacks if compared to the front carb version (glow engine style)
rear carbs either need rotating disk induction, or a reed block. The former is more expensine, and the latter has gas puddling problems in the small engines, so the front carb is the overall best and well proven solution

Tired Old Man

My Feedback: (1)

The reed puddling thing depends a lot on how the makers design the reed blocks. Those with any sense will not make a straight walled reed block and they will minimize any excess cavity areas. The easiest of all the nduction types to work with a basic and simple piston prting with a cylinder mounted carb. Very difficult to go wrong and the power differences are relatively minor.

Unfortunately a side mount carb on a 20-26cc engine does not fit the cowls of planes designed around .90 and 1.20 glow engines. Aside from that, a plane that was perfectly powered with a 1.20 glow will be underpowered and heavy with a 26cc gasser.

TestPilot6

What is exactly gas puddling problems?

rmh

Well I know some guys think a tuned pipe is "cheating " - meaning they don't have / wonon't get one etc..
However :
A decent 26 -of which I found the Roto 25 and MVVS 26 to be the BEST- wil lturn a good 18x6 at 8500-9000static and easily 10000 in level flight - this gives a solid 17 lbs of thrust in most cases. And without any ear splitting noise. We used the Ed Skorepa carbon fibre pipe and did side by side comparisons with the engines setup for dead smooth midrange transition
You can get more rpm with other setups but they are not good aerobatic setups -which was our goal.
The carbon fibre system weigh 5 ouces and is more quiet than the MVVS pipe but performance is about the same
and far, far better than any non piped 26 all up engine pipe is the 2-2.5 lb range.
Gas puddling on the Roto was non existant -it is a rear drum rotary .all in all, the MVVS/Evolution -the best setup for smooth cowl setups. The reed valve engines in many instances accumulate droplets of fuel in some "corner" of the case and many do splutter in G changes .
The weedie types - are cheep - simple tho awkward to enclose and noisy but that suits what some want - so take yer pick! If you run wide open from take off till landing - a good choice.

tkg

My Feedback: (1)

Side carb, side muffler...no proplemo. Get a model with a radial engine cowl.
My Seagull Yak/G20 combo looks as clean as DH's Showtime, with a ?mark header and a tuned pipe. T O M coment about a 120 being underpowered with a 25cc gass is true in many cases. BUT a 90 sized plane with a 120 gasser is nice.

av8tor1977

My Feedback: (6)

I have three planes with converted Echo 24cc engines, and I couldn't be happier with them. One is a Great Planes Fokker DR1, another a 72" wingspan Katana, and the third a 72" span Giles 202. All of them fly great, and I don't see how they could weigh less, as the centers of gravity are right on with no ballast whatsoever. If they had lighter engines, they would need added weight in front to balance, and so the all up RTF weight would be the same. If anything, there is a weight advantage with the gassers, as they carry less fuel to fly the same amount of time as a Glow engine would.

As for power, my engines turn an APC 16 x 8 at around 92 to 9400 rpms; definitely not underpowered....

AV8TOR

Tired Old Man

My Feedback: (1)

There might still be 3 or 4 of those "BEST" Roto 25's sitting in the Chesapeak Bay where they ended up when they quit running. The planes were recovered but the engines were re-deposited in the bay after removal.....

Truckracer

My Feedback: (19)

Well there may be a new wave of 20 - 26 engines out there but I'm still looking for any gasser that will work well in something like a CUB and give performance like a large 4 stroke or OS 160 2 stroke. Now let clarify ..... I'm not looking for CUB like performance .... I'm looking for performance that borders on 3D! For that, there just isn't a gasser that will fit in the small cowl of a CUB or CUB like airplanes. And NO, I'm not going to hang a pipe on a CUB so don't even go there!

I like my Knife edge snapping to knife edge CUB takeoffs then climbing and turning on knife edge to multiple knife edge loops. Find me a gasser that will do that in an airplane this size and I'll buy one. Until then, I'm still stuck with messy glo engines on these airplanes and I find they stay home more in favor of gasser powered ones. No new wave for me yet.

rmh

We had absolutely no problems with how the Rotos ran- one di have a weepy casting tho
Not all model engines can be treated the same - we used 32-1 syn oil and they had perfect manners . and power equal with the MVVS 26 they did however weigh 1/2 lb more
The carb out the side setup just never appealed to me

But I have a leaf blower and a string trimmer with em ! perfect application.

Edwin

My Feedback: (2)

I'll let you know truckracer. I'm putting the 20cc in a busa 1/4 scale J3. I know it wont do what you're asking for but it'll give me an idea what it WILL do. I've seen rascal110's with a G26 that would hover. But that doesnt exactly fit in the cowl. The SV or RCGF might since they are rear carb. I know all the speculation, I've just got to find out for myself. I'm just a sport pilot and like scale flying. Should be good for me.
Edwin

Tired Old Man

My Feedback: (1)

Bill Hemple sells a 50% Cub. You can put a 150 in it and do all that you described.... World Models sells a 33% Cub that will handle a 106 and do the same. You just have to step up from the basement to achieve your goals.

Truckracer

My Feedback: (19)

I'm aware of the larger CUBS but thats not the issue of this thread. Point is that 20 thru 26 sized engines still don't replace their smaller, lighter, more powerful glo cousins. My performance goals are achievable with glo engines in the smaller 1/4 scale arena .... not yet using gas ... at least in certain aircraft designs. Yes, a pipe can make up the power difference but pipes just don't work well on all aircraft. I just don't see any great strides in the performance level of these smaller gassers.

Tired Old Man

My Feedback: (1)

Equal/equal, gassers have always been behind a glow engine. Until some significant things change it will remain that way.

For me, the quailfiers that make a gasser desirable are the reduced cost of fuel, easy access to more fuel when needed, eliminated glow plugs, minimum required number of tools at the flying field, post flight clean up, and ease of operation after the engine tune is set. Sure, one could fly 40- to 1.20 size glow powered aircraft but they would be small, twitchy, hard to fly in winds much over 10 mph, have wing loading a little on the high side for good aerobatic performance, and expensive to operate. I'm not one that feels a 20-26cc gas engine is the most effective way to do anything. Power to weight just isn't where it needs to be, adding tuned pipes exacerbates that situattion, and the planes they fly are too small and generally not designed around a gas engine, making for poor engine to airframe fit. For the money they are a waste of time, imo.

Perhaps the leading egde of a wave but the wave isn't strong enough to carve a good turn. You can go out in 1 to 3 foot slop or wait for a better swell and find the day much more enjoyable. The gassers should be saved for planes larger than 1/4 scale where the cost of flying using a glow engine might be measured in dollars per minute. Just another $0.02 opinion.

Bass1

HMMM, I wonder if those huge flounder I caught last summer were in proximity to that Roto Reef you guys planted!

rmh

As long as this is simply a posting of opinions -
How does a tuned setup exacerbate a bad situation -unless you simply don't understand the proper setup for a tuned exhaust.
Have you ever used them ?
Gas engines differ from glow engines in VERY minor respects. basically the materials used.
If one is discussing industial power equipment modified for model use then yes, gas engines are different
the power per pound is lower on th e conversions..
But they are inexpensive and fuel costs are low.
Make no mistake tho- a proper exhaust system can greatly improve the entire power band on any two stroke engine
Any.
The big caveat tho is that if you don't understand the application and use - the results will be reflected .
Their application does one thing: it increases the size of the charge in the combustion chamber
The pipe INCREASES flow thru the entire path -starting at the carb inlet. Incresased flow = bigger charge in the chamber.

Just an opinion
Based on running a lot of both types .
In competition

-

Kweasel

My Feedback: (29)

I agree, tuned pipes are must have items for 20-40cc gasoline burners. I can usually get enough power with 50+cc and a large non-tuned muffler though. Adding an expensive exhaust goes against the main reason for burning gasoline, (reduced cost).