Which is the stronger engine?

Windwalker,

These two engines are not on the same turf.
The MVVS (with a silencer) costs almost twice as much.

Below 12,200 RPM, there are not many engines that can spin large props as fast as the MVVS. The recommended prop sizes for it include the 14x7 (and the 15x5, about equal in load). It is timed and tuned for large props and low RPM, in the interest of lower noise levels; especially with the full length tune pipe, or the tuned silencer.

In the OS web site, there is a review for the .61FX and Clarence Lee did a review in RCM on the MVVS .61, of which the MVVS .77 (which he also tested) is a stroked and bored version.
The MVVS had a 2,000 RPM advantage over the equal displacement OS, on the 14x6 prop size.

So you can see the clear bias toward lower RPM levels.
The bias is greater in the larger displacements. The MVVS .77 and .61 provide equal power from about 11,500 RPM.
At lower RPM, the .77 excels.

With regards to the Tower .75; the .61 proved to be the strongest low-cost .61 around, in the shootout by Dave Gierke, in MAN 05/2003.
If the .77 is anything like it, it will be likely to out-rev the MVVS on smaller prop sizes; 12x6/11x8 and less, which are not at all in the usable size range, for the MVVS.

Thanks Dar-

What I'm looking for is a 60-90 size engine that really revs to put in a Patriot or similar type speed/sport... also want it to be light, since it's going in a 40 size plane. And please don't say a Jett-yes they are great engines but I can't spend that kind of $$$ unfortunately so it will have to be something else. If anybody has an idea on an engine that revs like crazy, is lightweight and doesn't break the bank I'd love to hear it!

WW

WW,

If you are looking for a very high horsepower engine, with an RPM advantage, it is going to cost you.

A Jett .90 is a clear candidate, able to spin a 12x6 (or an equivalent 11x8.5) at 14,700 RPM.

If you want to reduce your costs, you may be able to find a Rossi/Picco/OPS/YS .60-.65, from the beginning of the 80s, when F3A was limited to 10cc and RPM was in the 14-16K range. Some are offered in NIB condition, will definitely undercut the $335 asking price of the Jett and will be equipped with a full length pipe.

If you go for this possibility, you can get a 12K peaked engine, like the OS Hanno Special.

A 12x12 prop at 12K RPM is more HP and calculated pitch speed, than a Jett .90. It costs less too.

How fast do you want to go? This Patriot thing goes 120-125 mph, with a Rossi .53.

Hi Dar,

You give great information as always!

Correct me if I am wrong, but I am thinking the Tower 75 has a weight advantage because it uses the same size case as a 61, whereas the MVVS uses a 91 size case and weighs about the same as a newer MVVS 90 size engine that could replace it.

Ernie

Hi!
MVVS .91 has the same case as the MVVS .61!
.91 weights 552g and .61 549g

Regards!
Jan K
Sweden

http://hem.passagen.se/airracing

That mistake is a logical result, considering the long stroke nature of the .61 in MVVS's quest for low rpm performance.

OT?
I think this is the crowded population realm that Europeans are in for some years now, and American citizens still have to enter.
It takes some getting used to the idea of low rpm performance, because in the beginning, screaming noise is mistakenly considered synonimous to power. I did, and so did many others, until we compared old .60 Webras in good condition (16000 rpm, 11x7) with the low rpm setups as used on ST, OS (12000, 12x8) and the mighty MVVS @ 10000, (14x7)
The Webra hardly got off the grass, where the larger props had no problem at all. The Flight envellope was about the same.

I've been running the TH .75 for about the last 8 months on a CGM Tiger 60. It will turn 11,000 on the ground with an APC 13x6 on 10% Byron's fuel. For $99 it has a lot of bang for the buck.

Gary

Yes I thought about the old OPS, Picco, Rossi idea tho' the YS seemed a little heavy-sure would be nice if some mfg.'s made 50-60 quickee or pylon motors I'd love to have a 60 size SE quickee-type engine or three but all they make are 40's. Also would rather have something that parts were readily available if needed - which is why the MVVS-Tower engines were mentioned...Thinking about looking at some of Webras new motors since they have a rep for being light and high revving, but would still like other ideas if anyone has any?

I fly the Patriot with a Jett-50 and it hooks along pretty well

The biggest concern I would have with your proposed set-up is how nose-heavy you will be... That is a looong nose so a little more weight on the nose needs ALOT of weight in the tail-[X(]

Dar is SUPER knowledgeable about all the weight/rpm/prop. stuff- Seems like my Rossi-65 with full-pipe would haul ***** on a Patriot but no idea compared to the Jett-50... Takes some thinking and planning with the firewall/engine compartment-

Remember an OS-91VRDF will turn a 10x10 pretty well if you are serious about speed!

Razor, do we need any modifications ( crankshaft, prop, etc ) to use a ducted fan engine for normal prop use ?

James G.

Thank you.

WW,

If you mount an engine that would make approximately 3 HP at about 16,500 RPM and more at higher revs, like a dedicated ducted fan engine, you would be spinning a 10x10 at this 16,500 RPM.

The Rossi .65 is a dedicated 12K peak engine. The manufacturer claims a very doubtful 3.8 HP at 12K for this engine.
Going to 16K with this engine, will get you no where.
I somehow find it difficult to imagine this engine, spinning a 14x9 at this RPM, when an MVVS .77, with the tuned silencer can manage 12,200 only on a 12x8, or a 13x6.

The Rossi .65 is a similarly tuned engine with 17% less displacement, that cannot possibly achieve over twice the volumetric efficiency, of its peer. 12,200 RPM on a 12x8 prop is VERY respectable performance. The highest number in the MAN .60s shootout, on this prop size (the Fox Eagle), could only manage 10,950, which is nearly 28% less HP absorbed.

The beginning 80s F3A engines, tuned to 14-16K are invariably full length pipe equipped, which moves the CG back, when compared with a short muffler engine.