raston

Hi there.

I am trying to decide between the Roto 25 cc engine ( http://www.rcshowcase.com/html/engines/roto25.html )
and the MVVS 26 cc engine ( http://morrishobbies.com/product_inf...867d26814f8724 ).

Its going into a Giant Scale Planes 71" Spitfire (weight approx 11 lbs)

Both engine should physically fit nicely, so I need some feed back from those with experience (preferably with both engines). Which one is the best? Is the MVVS really capable of putting out almost a whole extra horsepower (according to spec comparisons Roto25 = 2.8 HP and MVVS 26 = 3.8 HP) on 1 extra cc?

Thanks in advance for your help.

pe reivers

The roto yet has to walk the path that MVVS did, though both have similar cantilever crank construction. So have the big Tigres, and by now many others.
The 26cc cc mvvs is not just one cc more, but has added technology like a graphite plated piston, inheritance from formula one engines, and as far as I know, is the only engine for RC use that has this feature. This is a tremendous help in achieving the power curve they were after and get away with it.

The MVVS engineers realy understand gas flow in a two stroke engine. That is why the 26cc churns out the power of a 35cc in a 26cc package. These results made them discard the 25cc glow engine they had previously. This engine was a winner as well, which goes to show..

rmh

I would have to see a heads up comparison - with same prop loads and similar exhaust setups - before I made any claim of who has what -
Horsepower is a calculated figure - based on torque -which can be directly read -
BUT--- changing exhaust setups raises torque - so unless both have similar setups -It is really a guessing game
Also - one is a drum valve setup one is a front rotory valve (crank rotary valve) - they cowl in differently -
When someone gives a tuned pipe rpm number - it also may be a pipe setup for absolute max power on a given prop.
The catch is that for nice smooth sport flying -A particular pipe setup may be steppy or just plane critical to needle setups
There ain't NO free lunch -
When we do a piped setup for aerobatics -we demand that it be an easily throttlable - no flat spots and very very quiet .
again another set of parameters that another piped engine user may not want or need .
Both good engines - so based on your needs -- don't get blindsided by a tuning that may not apply to your model.
are you more interested in a compact muffler that is super quiet - or is noise not an issue -

Charley

My Feedback: (2)

I would think that the Roto would fit in the Spit's cowl, inverted, better than the MVVS. This is because the front of the MVVS's carb is only about 1/4 to 3/8 of an inch behind the prop drive washer. Considering that the bottom of the Spit's cowl is a long curve, I'd expect that quite a bit of the carb would show behind the prop. I had to relieve the right side of the cowl on a H9 Cap quite a bit to clear the carb when I installed an MVVS 26 in it side-mounted and the Cap has a blunt cowl front.

I'd advise you to look for some pics of the MVVS installed in a Cap or Extra, etc.

CR

jaka

Hi!
Read that you had thoughts of getting a 25-26cc engine for your 71" Spitfire.
I would strongly advise you to rethink here because a 25-26cc engine is way to big for a plane this size and would put too much weight and load on the airplane. You mentioned 11 pounds (5kg) ready to fly, a 15cc-17cc (.91-1.08)twostroke would be much better, or a 20cc (1.20 fourstroke).
I have a MVVS 25cc engine with steel silencer in my SIG CAP 231 EX (5kg) and it makes this airplane fly real well with 3D and hovering capabilities..but I would not like this power in a spitfire that was a bit smaller in span.
My Great Planes GEE BEE R-2 on the other hand also weights 5kg but it is powered by a 15cc MVVS engine and flies this airplane real well too, doing big 100-150 m diamer loops, but it doesn't perform like my CAP performs...more scale like the way a Spitfire would fly.

Regards!
Jan K
Sweden

the Wasp

My Feedback: (1)

maybe he should look at the RCS 22cc gasser motor, it should be lighter than the MVVS and Roto.

Jim

cadconversions

My Feedback: (21)

I'm trying to decide between these two motors as well for a CGP Pitts M12. Any help there would be appreciated as well. Both look fantastic but I'm leaning towards the MVVS 1.6 a little for the front mounted carb. Round cowls so it doesn't matter to much. I need 6" from the firewall to the prop washer so either should mount fine.

Thanks Guys.

Kevin

cadconversions

My Feedback: (21)

Guys, thought I would update this post... I've purchased the Roto 35vi for a future project (actually intended it for the one above but at 64.6 oz RTF minus ign. bat I decided it was to heavy) and have purchased the MVVS 1.6 for the Pitts M12. Everything I read about the MVVS motor is great and it's light weight for a gasser.

The roto motors (expecially the 35vi) are works of art and function. I'm in awe everytime I look at the motor.

Kevin

BlueMax3

My Feedback: (1)

Hello,

The MVVS 1.6 and Roto25 were my final two choices for a KMP Hurricane (72" wingspan), that has an even narrower cowl than the GSP Spitfire, which I also have. First, I don't think the weight will be an issue. Even with a 120, weight will have to be added to the front. On the Hurricane, installations with 120s have been requiring 1-1.5 lbs of lead. On my GSP Spitfire, I have a Saito 100 and have a lot of lead up front. I don't remember how much, but it is at least 1.5 lbs. So, I don't think that either the MVVS 1.6 or the Roto25 are going to be too heavy. As for fitting in the cowl, I think they will both fit with some cutting, but there may be an issue with the muffler. I don't recall that a wrap around style muffler was available for the MVVS 1.6 and the side mount inverted muffler won't fit inside the cowl. The Israeli distributor for MVVS was offering for sale a pitts muffler for the MVVS 1.6, but it was way too big. I purchased a wrap around supersonic muffler for my Roto25 and it fits pretty well, even in the Hurricane. I might have to make a small cut in the side to accomodate the part of the muffler that attaches to the engine. I just cut the hole in the cowl for the engine head last night and will be working on this weekend, so I'll see if I can get some pictures. There is more room in the Spit cowl, so this would be less of an issue.

Travis

fiery

My Feedback: (2)

Travis

I understand the supersonic wrap-around muffler sold by RCS for the ZDZ 40 bolts right up to the MVVS 1.60, although you will need a 1/8" (3mm) soft aluminium spacer to clear the lower cooling fins.

The spacer came with the MVVS "black box" muffler. if you dont have one, you can easily make one up to suit. I did, and my spacer seals without any RTV - it has "molded" itself to the exhaust manifold face and the muffler stack face. I thought it would leak, but it never has over many months of use.

fiery

BlueMax3

My Feedback: (1)

Fiery,

I did not know that the supersonic wrap around for the ZDZ 40 will fit on the MVVS 1.60 engine with a spacer. That's a good option to have. Hopefully the dimensions are available so that Raston can see how it will fit in the cowl. All indications are that both engines are well made and reliable, so I don't think anyone could go wrong with either choice. I will post on my experience with the Roto25 once I get it running, which will hopefully be in a month or so.

Travis

fiery

My Feedback: (2)

Hi Travis

I have just found out that Bisson have introduced a "wrap-around" muffler for the MVVS 1.60.

However, there is no picture or specs for it on Bisson's web site yet. Hopefully they will be
posted soon.

How dos the KMP hurricane go? Have you flown it? Are the retracts suppied stout enough for flying off a reasonable grass strip?
I've had my eye on one of them for a while as a "next" plane for my MVVS 1.60 IFS but was a bit worried the landing gear may not have been up to it. PM me if you like, so as not to go "OT" on this thread.

fiery