• Become a Subscribing Member today!

    The Biplane Forum is a large global active community of biplane builders, owners and pilots. From Pitts to Skybolts, to older barnstormers, all types are welcome.

    The Biplane Forum is a private community. Subscriptions are only $49.99/year or $6.99/month to gain access to this great community and unmatched source of information not found anywhere else on the web.

    Why become a Subscribing Member?

    • In addition to our active community, our content boasts exhaustive technical information which is often sought after for projects and maintenance. This information has accumulated over the 12+ years the forum has been in existence.
    • We are also a great resource for non biplane users, since many GA aircraft are built the same way (fabric and tube construction).
    • Annual membership also comes with two BiplaneForum.com decals.

    Become a Subscribing Member and access the Biplane Forum in full!

    Subscribe Now

Rigging and propeller/engine questions

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

asport22

Well-Known Member
Supporting Member
*
Joined
Apr 17, 2012
Messages
555
Reaction score
268
This isn't a biplane question, but you guys seem to appreciate a good mystery - or a good opportunity to explain nicely how what seems like a mystery is really a complete lack of understanding of how things work. :)

1. The Jodel seems to take a lot of right rudder - enough that at cruise, the right rudder pedal is about 1/2 way to the floor. The wings are level, as near as I can tell, with the ailerons centered (and a lot of right rudder). However, does that really mean that the only reason for the ball wanting to be out to the right is needing more right rudder? How can I troubleshoot between a roll trim problem and a rudder trim problem?

2. I am stumped by an engine/prop problem. Again, I can't figure out how to tell which is at fault. I have a C-85 and a ground-adjustable prop. The first few flights, it seemed like climb was a bit slow, and the engine wouldn't turn more than about 2300 RPM, so I reduced the pitch setting a couple times, to the point that I think it is quite a bit flatter than it should need to be, based on cruise speed being a good 20 MPH slower than I expect. Now it climbs pretty well, and will turn up 2500 RPM in level flight. The odd thing is that I have to pull the throttle WAY back - like 2/3 back - before the RPM comes down to 2300. And when climbing, I can pull the throttle back half way without seeing a noticeable reduction in climb rate. It seems like if I can climb at half throttle, I should be easily able to overspeed the engine in level flight. I can't think of any situation short of a constant speed prop that should result in essentially constant RPM over half the range of the throttle. (And yes, I have checked, and the butterfly movement corresponds to the throttle movement.) The prop manufacturer thinks maybe the prop diameter is one inch too much, but while too much prop diameter will restrict max RPM, it doesn't seem like it would result in this "constant speed" effect.

I had started thinking maybe it was a carb problem - it has the Stromberg carb, and I have read that the venturis for 65 hp and 85 hp are interchangeable, so I was thinking maybe the small venturi was installed and was restricting airflow downstream of the butterfly. But when the airplane was wrecked, it had a 70/47 McCaluley on it - I don't think it would have turned that if it had the wrong venturi. So I'm really back to thinking it is the prop, but I just can't rationalize how a prop can exhibit this sort of non-linear behavior. Any ideas?

Thanks!

Warren
 

Latest posts

Back
Top