Prop blows out at speed

[Simon.O.]

Now I have my Lipos in the 2S rigger I have a few setup and handling issues.
On a 432 metal prop it hoots along well
With a 434 carbon it screams along..............but as it gets to I guess top speed the prop has a tendancy to blow out and it looks like it is about to trip over.
A 534 plastic octura will do the same.
I feel that it may be the 34mm prop climbs/ramps out as water speed increases.
The speed is great it just looks wrong kicking the tail up every 10 metres.

I have been told that a 632 is a good prop for a 2S rigger with a 8S motor.
Is it likely that a 632 will stop this problem.

[detox]

You may have too much angle on the strut which maybe pushing the stern out of water. Try setting the strut level with hull.

[Hydro111]

sounds like the tail is poping. try bringing the strut up

[Simon.O.]

On this rigger there is no angle on the strut. It is set at 0 deg and allows 5deg AoA on the sponsons
If I move the strut up more then the AoA on the sponsons will increase. This may produce more drag but it is worth a try.
Given that the CoB / Cog of this rigger is back near 20%of the afterplane there is no chance that the prop is too lightly loaded !
I will give it an honest run with the strut higher and see what happens.

[andym]

Simon use the x632, detounged and with just a little edge cup to reduce lift and I think your problem will disapear, good luck.

[Simon.O.]

Simon use the x632, detounged and with just a little edge cup to reduce lift and I think your problem will disapear, good luck.

Andy, you make it sound so easy.
Reducing the tongue, I can have a go at.
Cupping the tips scares the sh1t out of me.
o.k where are the files and pliers, I'll give this a go.

Firstly I think I'll get a raw 632 and clean it then see what it does.
I have pages of reading in my trusty folder that tells me a bit about props and cupping etc. AndyM wrote some of it and some is from Brian.B.

I'll let you know how this one goes next week.
I am on duty for 4 days from Friday and there is a day bush walk that we (family) need to do before then.

The smoke controller for the 4S rigger has arrived. !!!!
GAME ON !!!

[tylerm]

Hopefully your coupler will be here sometime this week as well, ill get it out to you asap so we can hear how the rigger goes!

[Fluid]

What has happened is you have exceeded the blade stength of the plastic props. They are flattening pitch and flexing excessively when you are running with the prop hub on the water surface. The plastic Octura props are notorious for this. I am not sure what a "434 carbon prop" is.



.

[Simon.O.]

Over the weekend I thined the blades on the metal 432 a little and got a good edge on the blades. I did a 632 as well.
To the pond this morning for a few runs. The 432 held well so on went the 632, I still had blow outs as speed with the 632.
A bit of ballsat went in the rear and this tamed it down a little, then something very strange happened, it jumped in the air, landed flat and wnet beautifully flat and straight..................no rudder.

It was close enough to tennis ball and get it back to shore.
I now have to make a new rudder but suspect that the standoff flexes at speed and allows the rudder to rake back causing lift. Am I close here.

Either way I now need to fab up a new rudder and will make a stronger standoff that will be adjustable so I can set the rake and caster.

These damm lipos are killing my boats. Excellent, more power= more speed thus more damage. Build stronger and go faster, that is not so hard.

On blade bending. I killed a plastic prop on my big test mono with a 7XL on 4S.
The plastic 42mm had the blades bent forward, that was fun. More to come on my mono quest.

[tharmer]

Mayby Octuras flex as well if they are modded too thin. That's why some folks harden them.
-t

[Meniscus]

Simon, what size shaft are you running? I believe I have an Octura metal x632 in 1/4" that I was going to give to a newbie here locally. You could try it, but it's not detounged yet.

Let me know how the rest of the testing goes. You suspicion that the rudder was angled would certainly explain the additional lift. Anyway, let me know if you'd like to try it.

[Flying Scotsman]

[QUOTE=Simon.O.;86697]A bit of ballsat went in the rear and this tamed it down a little, then something very strange happened, it jumped in the air, landed flat and wnet beautifully flat and straight..................no rudder.

It was close enough to tennis ball and get it back to shore.
I now have to make a new rudder but suspect that the standoff flexes at speed and allows the rudder to rake back causing lift. Am I close here.


Simon, my knowledge of riggers is zero, but the flexing makes sense and resulting in increased rake and then failure of the structural strength.

Douggie

[Simon.O.]

tharmer My props are not thined that much, so they wont flex. It is the plastic props that flex and die.

Ben I run a 1/8"shaft, the 632 I have is fine, thank for the offer anyway.

Douggie I did a bit of bench testing on the old rudder stand-off and can see that iit would flex allowing the rudder to rake back and produce lift. I now have a much stronger bracket there, and a new rudder. The other one broke as a result of hitting floating debris.

It will be a few days before I can get on the water again due to work.

[Meniscus]

No problem. Always willing to help

[Simon.O.]

Update.
I have made a new rudder stand-off that is a lot stronger than the last pretty looking brass one. I had to make a new rudder too, well I made up 4 at the time.
it is a lot shorter this time.
I set the caster so the leading edge of the rudder tucks forward a little.
On the pond and a quick steering test at 3/4 power and it still turns like a slotcar.
At wot it is not the best idea to give it to much rudder, no crash just a bit edgy.

Prop blow-out. Not at all, either with the 432 or 632.
There is a lot that can be done with rudders as I already have read but now I have first hand experience. Thanks, Jeff and Jay.

Two little gems I feel like sharing.
1. Rudders do not have to be deep or wide. This one is 1"(25mm) wide and 1-1/4" (30mm) below the strut.
2. Rigger Cob CoG Cg can be a LOT further back than 10-14% of the afterplane and still go like a rocket.