In an earlier post we mentioned having learned the hard way to take propeller manufacturers’ performance claims with a healthy dose of skepticism. Now that we have had an early taste of the Veem interceptor propellers, we can tell you they work as advertised on FPB 97-1.
The Veem props have a dovetail slot machined into the trailing edge of the blades, and interceptor strips are slipped into the slot to increase pitch. We can confirm that they effectively increase pitch by 10%, and thicker strips have been ordered to give the FPB 97 a bigger bite.
Time to change these interceptor strips at anchor is under 30 minutes.
Veem’s website page with info on their interceptor props is here.
Posted by Steve Dashew (December 5, 2014)
December 5th, 2014 at 11:34 pm
Interceptor is a name given — it seems in this business — to any device that alters the pressure profile on the trailing edge of a hydro body, in effect pumping up the circulation. In the aero biz we called it improving the Kutta condition – ie blunt trailing edges [and even trailing edge wedges] on the MD-11 or certain bizjets [aka Dassault] In this case it provides the effect of a steeper [for lack of a better word][as opposed to flatter] pitch to a prop. I am surprised no one has done this before Veem. NAIAD has something they call interceptors that alter the pressure profile below the transom as opposed to other efforts at trim tabs in the past. It does the same thing, albeit with less length to the local flow field – as with the Veem props here.
Please correct me if I am wrong Steve.
December 5th, 2014 at 11:44 pm
Correct. Essentially the interceptor builds up a volume of water or air ahead of it and alters the flow regime. While fairly commonin shipping, and some wings, Veem are the first prop builder to use this technique of whick we are aware.
December 6th, 2014 at 5:14 pm
Am we safe to assume no performance numbers for the FPB-97 will be published until after the “larger bite” interceptor strips are installed, tested and confirmed optimal?
December 7th, 2014 at 12:51 am
Hi Matt:
There are several items holding us back. One of these is a larger set of interceptor strips, which should be here end of next week. We also need to get the engines uprated, which should also happen soon. Then we need calm conditions, so we can average runs in two directions to zero out current. Finally, all of this has to be integrated with the process of builders trials, finishing the last details, and wringing the bugs out. Then there are the two weeks at the end of the year that most Kiwis take off. It might be early January before we have the data to release. But we will slip a few details out in the interim so as not to leave everyone hanging.
December 8th, 2014 at 4:17 am
Hi Steve
so how about some nice interior and detail photos to keep us entertained while waiting for the performance data?
December 8th, 2014 at 9:39 am
Hi Bessel:
We are limited by a non-disclosure agreemwnet with what we can show. But there will be some details in January.
December 6th, 2014 at 8:24 pm
Steve,
Is there any chance they could run themselves out of their groove and then perhaps unbalance the propeller? Probably too light weight not to matter?
December 7th, 2014 at 12:41 am
As this is our first experience we have to assume this is not an issue. In any event, it is simple to change or replace them.
December 7th, 2014 at 12:05 pm
Does the interceptor increase the chance of cavitation?
December 7th, 2014 at 5:32 pm
Veem claim cavitation is not impacted by the interceptor strips. However, when you increase pitch and hold disc area and diameter constant blade loading does increase, which in itself will lead to an earlier onset of cavitation.