The prop is matched to the hp. Having more hp and the same prop just wastes the hp/displacement as the smaller engine can spin the smaller prop to redline.

[Edit by JamesB on Wednesday, November 11, 2009 @ 11:01 PM]

A friend installed a Limbach L2000 on his RF5B and he change to the larger propeller. I am building a couple of Limbach L1700 with 94mm cylinders (1914cc). I hope to to reuse the std Hoffman propeller by adjusting the blade stops. There are few RF5B with 1776 and 1835cc engines running fine with the std Hoffman.

Collin

what benefit will you get if you build a L1700 with 94mm cylinders and up the capacity to 1914 cc in terms of Hp, torque
and is that conversion just as simple as bolting new cylinders in place of the 1700cc ones?

Kadir

The 94mm cylinders is a cheap way to get more cc's. The engine case and heads have to be machined.

Collin

"Steve, I would prefer to go for the larger engine, 1915cc. What is the performance of that engine? Considering the Limbach at 1700cc was 68hp, is your 1915cc more powerful having more cc at same stroke?

Kadir, I think they use different math than we do. We rate the 1915 at about 65 hp and a 1700 at about 55 hp

Steve Bennett
Great Plains Aircraft"

What is the math?? is Limbach 1700 not 68Hp?

Kadir

I intend to have my Hoffman HO-V62R/L150 overhauled by the manufacturer next month.

I am a little scared about upgrading my engine to 1915cc as that might be too much for the prop.
do you think I could run my standard prop with a 1835cc engine upgrade without too much trouble
or would you say I could get more Horsepower with the 1915cc conversion for the same cost and
stop worrying about what it may cost me in terms of over stressing the prop + too many RPMs and
any associated performance loss, noise?

Kadir

This is the same prop that is on my Grob 109 and it has 2100cc Limbach that develops about 85HP with a 3400 redline.

Note that you can also fine tune the pitch of the V62/150 to keep your rpms in the proper range, by an adjuster on the Hub.

See the instructions below, it takes only a few minutes to adjust the pitch settings with the prop mounted on the engine.

It take a little practice to adjust pitch in flight but the trick is to be at the right rpm when you shift the prop pitch.

To switch from climb(fine) to cruise(coarse) pitch your rpm must be above 2200 rpm.
To switch from cruise(coarse) to climb(fine) pitch your rpm must be under 1500 rpm.

I marked my tach with these two settings.

If you follow these simple guidlines you will have no problems.

--------------------
Ray
RF4D #4057 N-1771 Rectimo 1400cc
http://picasaweb.google.com/jb92563/FournierRF4D
http://www.touringmotorgliders.org

May the 4's be with you/ Jörgen

Sooner or later this old wooden princess is going to make an aeronautical engineer out of me.

So your advice is to go with the higher capacity for more horses and adjust the prop.

In an earlier post Collin adviced me to adjust the blade stops, but I did not know what he was on
about untill I read your post.

I hope Collin is getting some progress with his engine rebuild, I will be following him.

Thanks again

Kadir

If the engine weight is about the same as the normal RF5 engine then I would get the
biggest one that is still in the correct weight and size range.

You can probably go as high as the 2185cc engine for the Hoffman prop as long as the engine is not significantly heavier
and still fits in the cowling.

Also with the prop adjuster ring you may end up turning the ring a couple turns to get the pitch/rpm right.

Just be sure to mark your starting point so you can always go back.

A good static RPM to aim for with the Hoffman prop in the climb setting is 2750 - 2950 rpm as per my Grob 109 manual.

You will then get around 2200 rpm static in the cruise position.

[Edit by jb92563 on Thursday, February 25, 2010 @ 02:11 PM]

--------------------
Ray
RF4D #4057 N-1771 Rectimo 1400cc
http://picasaweb.google.com/jb92563/FournierRF4D
http://www.touringmotorgliders.org