downthrust on biplane pusher models

[g_kandylakis]

Well, it has already been mentioning, but while uploading the Supermarine Walrus Profile publication on the Plan Gallery, I had a look again and thought I 'd post a page here as well...

Quite a lot of "rearwards downthrust" in most examples we have seen, almost never the other way around.

George

The complete issue:
https://hpa.aeromodelling.gr/plans/details.php?image_id=932

[OZPAF]

I'm not sure if this has been done to provide an additional nose down pitching moment or the reverse!

As the high mounted motor would apply a nose down pitching moment to offset a possible nose up effect from the drag(this doesn't look likely), then perhaps it has been angled to direct the air flow onto the tail.

There is a comment in the design coverage, stating that the engine nacelle was angled to starboard to give better airflow onto the tail for balance(ie trim balance). Thus the thrust line angle in elevation may be to offset the high thrust line?

Details, details.

Thanks Gary for an interesting report.

John

[dputt7]

What a great resource this has become so quickly.  I am sure that the up elevator is the key. Get it to glide with some up elevator set the motor to 0 deg.s and find some LOOOONG grass. Can't wait to start the rebuild and do some testing, just have to finish my current project.
                       Thanks to all that contributed
                                               Dave

[OZPAF]

There is a comment in the design coverage, stating that the engine nacelle was angled to starboard to give better airflow onto the tail for balance(ie trim balance).

I was a little confusing here - the nacelle was angled to starboard in plan - possibly to offset torque. However as they were considering prop airflow effects on the fin - I feel that they would also have considered it for trim in pitch. This would have been very effective due to the tail being so close to the prop - in plan and elevation.

That sounds good - however I suspect that if I'm correct - the elevator trim setting will be different under power and on the glide.

John