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Boom Size and Cowling for 91/101 JAE


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#1 NeilSharman

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Posted 15 June 2017 - 09:20 PM

I received my 91/101 Truex Short kit from Joe but havent yet ordered the boom tubes.

I measure the holes in the tub and sponson frames are around 10.5mm? What size booms are you guys using? 

Was thinking I should just open the holes and use the 1/2" solid booms? or would 3/8" be sufficient?

Also, where do I get a cowl for this kit?

 

Thanks in advance.





#2 Amp Eater

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Posted 15 June 2017 - 10:12 PM

 You can do a search this was mentioned:

 

Per post 30#

http://www.intlwater...ic=38726&page=2

 

The boom tubes are 3/8" solid carbon fiber rod. You can try thick wall tubing but you may want to step up to 1/2" od. 





#3 brad nichols

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Posted 16 June 2017 - 12:20 AM

Depends on power?? I built one for an OPS 90 and used the 5/8" aluminum booms and for a 67 90 I run 1/2" aluminum booms. I made the cowls for these boats e-glass or carbon. The OPS 90 boat had a 5" tub so air ducts were added along the cowl for air.

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Edited by brad nichols, 16 June 2017 - 12:22 AM.


#4 mercguy

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Posted 16 June 2017 - 08:52 AM

Neil

I am using 3/8 solid carbon rods for mine. Doc Turner has a nice cowling on his 90 JAE. Mark Bullard made the cowling for him. I believe Mark has a vacuum setup for making the cowling, his number is 256-303-6423.

Bill Hoch



#5 NeilSharman

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Posted 18 June 2017 - 03:56 PM

Thanks for the info guys, this will be enough to get me going. I plan on running a cmb 101.



#6 Carl Van Houten

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Posted 13 July 2017 - 06:58 AM

Boom tubes, everybody uses them but...they are not very aerodynamic. Think about what is happening behind them when you increase the diameter.

 

-Carl

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#7 Jim Allen

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Posted 13 July 2017 - 10:58 AM

Boom tubes, everybody uses them but...they are not very aerodynamic. Think about what is happening behind them when you increase the diameter.

 

-Carl

Whats happening behind them is the same no matter what the attitude of the boat is. Air foiled shaped things, even those with some amount of down force, will become neutral at some point or maybe lifting if the attitude changes enough. What about the effects of the boats varing speed on stationary airfoil shaped things?

 

JA



#8 Carl Van Houten

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Posted 13 July 2017 - 12:11 PM

 

Boom tubes, everybody uses them but...they are not very aerodynamic. Think about what is happening behind them when you increase the diameter.

 

-Carl

Whats happening behind them is the same no matter what the attitude of the boat is. Air foiled shaped things, even those with some amount of down force, will become neutral at some point or maybe lifting if the attitude changes enough. What about the effects of the boats varing speed on stationary airfoil shaped things?

 

JA

 

It is the accepted evil of the rigger design for most. I have seen some trying the airfoil carbon tubes. I'm not sure how much they would actually help with speed or handling but they would have to be better than the aerodynamic nightmare seen in the photos. Your right, their surface area would add unwanted lift at some point of AOA to the model but by the time the nose gets up to that point, the area of the tub would become the real problem. I am sure this subject has been beaten to death at some point.


Edited by Carl Van Houten, 13 July 2017 - 01:21 PM.


#9 Grimracer

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Posted 13 July 2017 - 01:54 PM

at subsonic speeds it just does not play a large a role. parabolas and rounds are just fine at our speeds.

Can they be improved.. yes.. but the payback is just not that large.

Grim

#10 brad nichols

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Posted 13 July 2017 - 02:33 PM

The days of the Pahrana are gone. I think they bent because it only had the one plate??

 

Brad



#11 Carl Van Houten

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Posted 13 July 2017 - 03:45 PM

at subsonic speeds it just does not play a large a role. parabolas and rounds are just fine at our speeds.

Can they be improved.. yes.. but the payback is just not that large.

Grim

I don't want to blow Neil's thread up so let's not get crazy here but I do want you to take a piece of boom tubing the same diameter and total length (both tube lengths combined) that you run on your hydro, hold it in the center and hang it out the window at 80 mph (let somebody else drive) :D and see how small of a role it plays. It is a lot more drag than you think. Is it worth improving? I did that and I thought DANG! This is a CRAZY amount of drag. Another thing to remember is that all of the INDY cars have gotten away from round tubes in their suspensions and spend stupid amounts of money designing aerodynamic tubes because it has been proven that it is worth the effort and money to do it.

 

Just for the record my hydro has round boom tubes on it too.  :D Sorry Neil.

 

-Carl


Edited by Carl Van Houten, 13 July 2017 - 03:47 PM.


#12 NeilSharman

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Posted 13 July 2017 - 11:04 PM

Carl its a good discussion, so blow it up what evs  :D



#13 Amp Eater

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Posted 14 July 2017 - 02:32 AM

K & S Engineering has this to cover up carbon tubes. 

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Edited by Amp Eater, 14 July 2017 - 02:33 AM.


#14 shoboat

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Posted 14 July 2017 - 04:58 AM

Carl,

If you want to look at the real drag problem
on most of our hydros look at the engine cowling?
Lots of drag there on most boats. We tried the teardrop
shaped boom tube cover from K&S and did not find it worth
it at all. Now when we played with cowl designs in a mock up
Wind tunnel you could not believe the drag. For top speeds
on a record boat this maybe important, but only if you are close
to the record speed already. For most this is not even worth spending
much time on. The set up and Propeller are the right areas to play in as
you well know.

Enjoy Testing This Weekend,

Mark Sholund

#15 Carl Van Houten

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Posted 14 July 2017 - 06:12 AM

Carl,

If you want to look at the real drag problem
on most of our hydros look at the engine cowling?
Lots of drag there on most boats. We tried the teardrop
shaped boom tube cover from K&S and did not find it worth
it at all. Now when we played with cowl designs in a mock up
Wind tunnel you could not believe the drag. For top speeds
on a record boat this maybe important, but only if you are close
to the record speed already. For most this is not even worth spending
much time on. The set up and Propeller are the right areas to play in as
you well know.

Enjoy Testing This Weekend,

Mark Sholund

The round boom tubes are a just nasty drag element that everyone has to accept.

 

There are a few cowling contours being used that are obviously not very air flow friendly for sure. When you see things like this It makes you wonder if they are intentionally imparting loads onto the tub to tame some undesirable quirks out of their model?




Edited by Carl Van Houten, 14 July 2017 - 06:26 AM.