Boats and foils comparison

MaxHugen

Super Anarchist
I can't argue with the force vectors shown in the diagram, but...

The first time I went skydiving, it was in a small plane - IIRC a Cessna. The RHS door is taken off for easy egress, and as I was the first to jump, I was right at the open door. When the plane banked right, I expected centrifugal force to keep me in the plane, but I nearly fell out, there seemed to be no force there at all!

Go figure?  :blink:

 

jaysper

Super Anarchist
10,172
1,295
Wellington
I can't argue with the force vectors shown in the diagram, but...

The first time I went skydiving, it was in a small plane - IIRC a Cessna. The RHS door is taken off for easy egress, and as I was the first to jump, I was right at the open door. When the plane banked right, I expected centrifugal force to keep me in the plane, but I nearly fell out, there seemed to be no force there at all!

Go figure?  :blink:
Strange.

I went for a ride in one of our Air Force's helicopters a few years ago and was facing outwards towards one of it's (open) doors.

Whilst I did have a seat belt on, I never felt it kick in as the chopper went into a spiral.

 

The Advocate

Super Anarchist
I can't argue with the force vectors shown in the diagram, but...

The first time I went skydiving, it was in a small plane - IIRC a Cessna. The RHS door is taken off for easy egress, and as I was the first to jump, I was right at the open door. When the plane banked right, I expected centrifugal force to keep me in the plane, but I nearly fell out, there seemed to be no force there at all!

Go figure?  :blink:
It may have banked right, but did it turn right :ph34r:

I have a similar experience, different outcome. I was in a rescue helicopter sitting in the jump seat. As we approached the target the crew chief opened the door closest to me and shortly there after the pilot threw the chopper into an extremely steep banking turn that had me looking out the open door directly at the water. At that moment the only thing I could think of was the pissy little polyprop sash belt I was secured to the seat with and how I wasn't falling out. Then I realised I could hardly lift my arms...

 

DryAxE

New member
16
15
Slovenia
So much talk was already about the foils, what im curious about is why Italians who are in really good stable control of their boat fly the hull so high, especially at high speeds. I think they do it intentionaly. Is the pressure at the hull height really that beneficial to VMG or is it worsening it by pushing boat away from course.

Can italians with their hull shape and leaving some gap create venturi effect under hull at high speeds to suck their hull down and increase righting moment?

Its strange because Italians have never bothered with batwing sail to lower point of power delivery, seems like they have enough righting moment to carry more sail area higher up. Those two boats are really different beasts.

 

The Advocate

Super Anarchist
So much talk was already about the foils, what im curious about is why Italians who are in really good stable control of their boat fly the hull so high, especially at high speeds. I think they do it intentionaly. Is the pressure at the hull height really that beneficial to VMG or is it worsening it by pushing boat away from course.

Can italians with their hull shape and leaving some gap create venturi effect under hull at high speeds to suck their hull down and increase righting moment?

Its strange because Italians have never bothered with batwing sail to lower point of power delivery, seems like they have enough righting moment to carry more sail area higher up. Those two boats are really different beasts.
It would make some sense that the faster you go the higher you fly to maintain the same pressure between the hull and the water.

I might be talking shit though.

 

mauriciogfj

Member
228
122
Brazil
I can't argue with the force vectors shown in the diagram, but...

The first time I went skydiving, it was in a small plane - IIRC a Cessna. The RHS door is taken off for easy egress, and as I was the first to jump, I was right at the open door. When the plane banked right, I expected centrifugal force to keep me in the plane, but I nearly fell out, there seemed to be no force there at all!

Go figure?  :blink:
Radius does it!

First time skydiving? I'll bet you were focused on gravity.

 

MaxHugen

Super Anarchist
It would make some sense that the faster you go the higher you fly to maintain the same pressure between the hull and the water.

I might be talking shit though.
It's likely to be a factor of the sea state... if there are "waves" (hahaha) they will want to fly a bit higher to avoid them.

Could also be that at high speed the flight controller has way less reaction time, so plays it a bit safer and stays higher.

But I could be talking sh*t too. :p

 

The Advocate

Super Anarchist
It's likely to be a factor of the sea state... if there are "waves" (hahaha) they will want to fly a bit higher to avoid them.

Could also be that at high speed the flight controller has way less reaction time, so plays it a bit safer and stays higher.

But I could be talking sh*t too. :p
I think yours is more believable shit lol

 

MaxHugen

Super Anarchist
I reckon the outboard wing is fully ventilated when the tip is out. It's easily visible from the overhead shots. Could be why etnz has pitting all around the hinges on the outboard wing. Funny how the pitting on the inboard wing is most visible on the leading edge...can't find the shot right now but was notable.
Ventilation wouldn't be the cause of pitting, that happens due to cavitation. I too would be interested to see that pic if you can find it.

Cavitation does often begin right at the leading edge, as that where there's a massive drop in pressure.

 

MaxHugen

Super Anarchist
I would think so..showed as white in the shot. I'll keep looking for it,I think it was a zoom of a weta shot about a week ago. The hinge area makes sense as low pressure in the cavity, the leading edge wasn't mentioned and doesn't make sense to me.
Cavitation will occur where the local pressure is lower than the water vapour pressure. As well as the leading edge, the upper hinge point is definitely another candidate to promote cavitation:

image.png

 

Stingray~

Super Anarchist
12,249
3,341
PNW
Wouldn't that have more to do with the vertical component of gravity acting on the resultant rotational force of RM vs sail loading?
Oh, absolutely!
 

Glad you brought that up Victor! I had completely mistaken the component of gravity’s vector.. 

 




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