Comparison of ST G20-15 and MVVS 2.5 cc diesels for stunt u...

The ST G20-15 and the MVVS 2.5 cc schnurle diesels are both high performance competition engines seperated in time by @ 40 years. According to engine review in the July 1961 Aeromodeller, the G20-15 peaks at @ .32 HP at @ 15,000 RPM. According to the Aug 1997 Aeromodeller review, the MVVS peaks at @ .56 HP at @ 20,000 RPM. MVVS figures vs (G20-15 figures) are: 9 x 4--13,100 RPM (12,000), 8 x 4--16,200 (14,000-14,800).

G20-15 turned a 10 x 3.5 at 10,300 RPM and 11 x 4 at 8,400. The 11 x 4 gave about .23 HP. No figures on large props for the MVVS. Various props were used so the figures are not absolutely comparable. My G20-15 diesel figures are in agreement.

It's been suggested that the MVVS is a possible replacement for the G20-15 diesel because of availability and price.

Hi Jim,
I believe I met you at VSC this year. Rusty Brown and I ate breakfeast with you several mornings at the Rodeway Inn.

I own three MVVS .15 diesels and they are real honeys. Mine seem to like the APC 9 x 5 prop best. Although I haven't checked the RPM, they easily fly my full size Flite Streak in the mile high air we have here in Denver. Probably what I like best about them is how user freindly they are (once broken in). I use Red Max ball bearing blend diesel fuel and rarely touch any settings on the engine. Just choke and flip. They tend to burp and hiccup for 20 - 30 seconds until warmed up and then fly great. Easy to start, inexpensive to buy, not fussy and plenty of quiet smooth power. I wish all my glow engines were that easy!

Chris Brainard

Hi Chris,

Good to hear from someone with experience with the MVVS. I've never seen one run. It sounds like a useful engine, which I would not have thought from reading the review.

I've just bought an MVVS 2.5 and am looking forward to 'getting to grips' with it.

I had a G20/15D in the mid-late 70's which I never ran and flogged on to someone for a £5 - but it was very tatty - the Super Tigre logo etc had all been filed off (for some reason) and a very poor attempt had been made at replacing the tommy bar comp screw with an Allen screw.

The guy got a new head for it and later said it went very well.

Tony

PS Any comments on the CS Rivers Silver Streak replica? They don't look too hot!

As for the Rivers Silver Streak (I had one), the originals were known to be very nice engines but broke the cranks a lot at the steps for the roller bearings. As I understand it, the CS is a true replica, and the same trait will be no doubt replicated, augmented by not nearly as good of metallurgy. I wouldn't buy one to run. The MVVS should be a nice piece. The outwardly similar MVVS 2.5 RL came out in about the same timeframe as the ST G.15, about '64/'65. I had several G.15's, which I liked very much. The piston/liner were virtually indestinguisable and interchangeable with the MVVS (sorta had one), and of course neither had boost ports. The ST G.20 was only made for about 5 years before the G.15. I never owned a G.20, but my flying buddy Bruce Tunberg did, a glow. It was much less powerful than the G.15 and heavier. Is the current MVVS 2.5 boost ported? Steve

Hi Jim, I am a fan of the MVVS motors but there are a few quirks to them. They are not made on cnc equipment so there is a difference in every engine. Also there is a problem with the fuel nipple being soldered on. Mine has broken off at least 3 times. However I've never had a really bad one and the differences in rpm are not acute. Incidentally an MVVS with a 6/6.5 has turned 20k for me that is impressive for any 15D. This was done to prove to an argumentive g;ow owner that a diesel can turn to the same rpm as a glow. Seems everyone thinks that a diesel in just a low rpm lump. As you know it isn't so.The comparison was against a Cox Conquest which is no slouch in the motor dept.

I had a MVVS 15 in a Fierce Arrow 400 with a 9x5 prop and it worked fine until it blew the rod, It only had 10,000 laps in a Team racer I don’t know why it blew. I then put in the ST G 20 and it flew the same with the 9x5 prop. I put a Russian 15 RV Team race diesel in a Stuka stunt plane and it worked great. The only trouble it flew for 30 min. On 2 oz of fuel
Willis

Jim,
When I suggested the MVVS as a replacement I could not do a comparison with my G20 .15. My MVVS was originally an RC engine, and I fashioned a venturi from an electrical spacer that is held in place with an Enya needle valve. Fuel enters the venturi at a single port to the rear where it matches up with the needle valve hole. It ran well but I do not know how it compares to a "real" CL version. I will probably switch to a "store bought" venturi/needle valve assembly eventually.
It's good to hear that others have had success with it.
There was a discussion awhile back on one of the boards about the MVVS diesel being ABC like the glow, but it is not. It is standard iron/steel.
Rivers: I have an original Silver Streak (.15). I only had it in one plane, a Flite Streak Jr. It was WAY heavy for that plane and would only fly level - but fast . I had been wondering if the replica had the tapered roller bearings. That was answered.
George

Jim..neither ST nor MVVS are great stunt engines..they are great
(or were great..) racing, combat and sport engines and they
can be used in stunt models..I've used both engines in race
and 80MPH combat ships and done quite well with them..also
flown numerous sport stuff too...the best .15 diesel I have
ever used for stunt remains the PAW .15TBR..the PAW .19TBR
is better yet...incidently..the MVVS 2.5cc diesel will pull
a 360-400sq" combat ship 82-83mph..015"x60'lines..8x6 prop
this is without streamer...my ST-G15RV diesel with Cox .09
venturi(t/r setup) would fly 79-80mph sans streamer..easy
starting too...If you don't want to buy another engine..
then I suggest you use the MVVS 2.5d...It can pull a 9x6"
very well..once well broken in(2-3 hours)..is yours the
rotating barrel variety?? mine is and seems to run and handle
better than the older fixed ones...email me off this board
for more diesel info..thanks ..Tony

I am using my G20-15D's in smaller Old Time Stunt airplanes. Example, DEMECO Sportwing and A-B All American, and Gullow A-B Trixter Profile. For this I think they work very well. Part of the fun of OTS is showing up with a unique airplane and/or engine. Diesels are still pretty unique in US stunt circles.

Three points of view: (1) Many original OTS airplanes were flown much faster than the norm today. (2) Small light airplanes need a faster lap time than big heavy airplanes to give the line tension I like. (3) Small engines need to be run in such a way as to get all the useful HP they can produce.

I think one could fool with larger low pitch props and get a pretty good conventional stunt flight out of a G20-15. Something like a 9 x 3 or a 10 x 2 might work well.

Jim, waay back(just after the last ice age)..I flew with
Bob Adair at USAF meets(early 60's) and he used to fly a
Goldberg Shoestring powered with a G20 15d..with 9x6" props
He used it in open stunt and sandbagged a lot of very
surprised competitors...it flew beautifully...
those models you mentioned are on my personal list to
build and fly someday..I've built and flown a Super Clown
and a Tomahawk..both CLC kits..the Super Clown is powered
with a Marz .15d and the Tomahawk uses an Oliver TigreIII
..CS repro(great engine..)..the Super Clown is the better
flyer..I set the flaps to give 10 degree deflection...
............Tony

George wrote "I had been wondering if the replica had the tapered roller bearings. That was answered." Roller bearings, but in this case, not tapered. The rollers run on a hardened sleeve in the crankcase and direct on the shaft, in wide grooves. Which of course create stress risers, leading to crank failure. Steve

For what its worth....I have flown PAW .15's in Jr. Lightning Streaks, and find that I had to go from .015" 52's to .015 60's to tame it down. The PAW.15 TBR running on a 9-6 Master Airscrew prop was turning over 11,000 here in the hot weather of Mobile, Alabama. The estimated speed on the .015" 52' lines was over 65mph, turning 4.2 sec. laps. (isn't that about 65mph?)I had plenty of line tension, and could do any maneuver from any point in the circle, even in a good breeze that kept the R/C planes on the ground. I just HAD to do that, to rub their noses in it just a little! I'm presently building an Estes Ringmaster for a PAW .19TBR, and will most assuredly have plenty of power, with a small fuel supply. Don't ever underestimate those PAW engines....they are really strong, run fast, are thrifty on fuel, and are extremely user-friendly, after they are broken in. And do they ever last! They are also quite inexpensive, and are very powerful for their displacement. I am also finishing up a UK-made Freebird 5 for a PAW .40, which is a HORSE of an engine. It will be running a 12-6 or 13-5 prop, turning in the 9,500 to 10,000rpm range. And you can get one from Eric Clutton for about $125, already run-up and he tells you what props are good for any particular PAW engine. Give them a try....you won't be disappointed. Chuck Potts in Mobile, AL

Looks like we've gone tangetal here with the PAW stuff.. I'll
validate what Cuck has observed about the PAWs...I get similar
rpm fig's as he does..I have an All American Senior pwr'd by
a PAW .19TBR(left-hand crank)..all up wgt. without fuel is
approx 24 oz....you can almost substitue the Fox .35 stunt
with the Paw .19tbr. I'll have to check my notes..but I think
I was getting over 10k with a 10x6...I'm sure the Fox can
ultimately pull a bigger prop per given rpm than the PAW..
such as an 11"-12" dia....Like Bare I am using diesels for
power almost exclusively for the past five or six years..
Getting back to the MVVS 2.5d...I was getting 11k+ with a
9"x6" APC...my choice of the PAW over the MVVS is ease of
handling and predictability..the MVVS has more power at higher
rpm..for stunt I like the idea that the PAW is approx .75oz
lighter than the MVVS...(I think!) Tony

Speaking of PAWs!
On the latest Stunt News cover, George Aldrich is holding a profile Peacemaker. Someone (on another board) mentioned that it is powered by an Oliver Tiger .21. I never owned an Oliver .21, but the engine appears to me to be a PAW. Anyone know for sure?
I know George mentioned several times that he enjoyed flying a full size Flite Streak with a PAW .19 pointed out about 15 degrees.
For those who do not get Stunt News, it was a nice and fitting picture of GMA holding a diesel powered Profile Peacemaker, a plane he designed and published in Aeromodeler magazine. George had a big smile. Looked like he was having a lot of fun that day.
George