Seaplane Design - A Forgotten Art (lecture by Prof. Dr.-Ing. Elmar Wilczek)

[overscan (PaulMM)]

https://www.fzt.haw-hamburg.de/pers/Scholz/dglr/hh/text_2021_05_20_SeaplaneDesign.pdf

 

[red admiral]

Thanks

It does seem like a lot has been lost in this area. Some interesting data points on there - you can also put the late 40s Shorts/SARO/Supermarine concepts on there as well and they all largely seem to trend the same way.

I wonder how much impact the scale of the hull/fuselage makes to the considerations. For ships its a big driver e.g. Froude number

 

[riggerrob]

Finally an explanation of the effects of ventilating the step!
I just wish that that lecture slides contained a bit more detail and a few more conclusions.
I will need to re-read those slides a second time to fully understand them.

 

[riggerrob]

If the prof.'s notes are accurate - making planning tails so much better - why is anyone still building seaplanes with short hulls?

Is it something to do with short hulls (e.g. Petrel) being lighter?
Do short hulls perform better at the very low airspeeds of Petrel?
Is porpoising less of an issue on slow hulls?
Is Petrel powerful enough to blast its way through that sharp "hump" in water-drag?

 

[Nik]

Is there any take-off / un-stick benefit from 'blowing' the step(s) ??
Or does the necessary hardware out-weigh the gains for small-ish aircraft ??

 

[Mark Nankivil]

If the prof.'s notes are accurate - making planning tails so much better - why is anyone still building seaplanes with short hulls?

Is it something to do with short hulls (e.g. Petrel) being lighter?
Do short hulls perform better at the very low airspeeds of Petrel?
Is porpoising less of an issue on slow hulls?
Is Petrel powerful enough to blast its way through that sharp "hump" in water-drag?

I would say it is simply part of the design trade off - if you step the aft fuselage you change the volume and likely increase the weight of the aft fuselage , especially if part of the designer's goal is to keep the horizontal stabilizer high up like the Petrel. The Rotax 912 is a reasonably powerful motor for its size/weight too.

Enjoy the Day! Mark

 

[AeroFranz]

Is there any take-off / un-stick benefit from 'blowing' the step(s) ??
Or does the necessary hardware out-weigh the gains for small-ish aircraft ??

Getting rid of the step certainly reduces cruise drag. It's probably more of an issue of fast seaplanes, at low cruising speeds it may not be worth the trouble. There are probably other considerations, but in general deep steps help the seaplane run 'clean' on the water.
I read that the later models of Short Sunderland had a more faired step and did not takeoff as nicely as the older ones that had a conventional step.