## Re: [pop-pop-steamboats] Re: Interesting pop pop boat engine experiments.

Expand Messages
• ... As with anything else in the homebuilt realm, it varies considerably (and is a bit hard to measure, since the exhaust is also hot), but the best of them
Message 1 of 10 , Jul 8, 2011
Daryl Foster wrote:
>
>
> What is the velocity of a pulse jet engine exhaust?

As with anything else in the homebuilt realm, it varies considerably
(and is a bit hard to measure, since the exhaust is also hot), but the
best of them will put out several times the volume of a leaf blower at a
similar velocity without augmentation.

> Could you clarify your last paragraph:-" I'd bet
> you get between 20% and 80% increase in thrust, measured by the beam or
> draft of the boat (same waterline length) that can be pushed up to hull
> speed" Reaching hull speed with a putt putt seems unlikely without a
> very major break through if that is what you are suggesting.

I was mostly suggesting hull size vs. speed as a means of measuring the
thrust increase due to the augmenter. An alternate would be to measure
the size of a drag paddle (just a flat plate in the water at the boat's
transom) that reduces the augmented boat's speed to that of the same
boat without augmentation. You'd run the boat with the drag paddle
installed, but raised out of the water (so the weight is as nearly the
same as possible), then mount the augmenter(s) and run the boat again,
increasing the depth of the drag paddle each run until the speed is the
same as in the control run. Knowing the area of the drag paddle and a
little hydrodynamic math (flat plate drag is one of the simplest
calculations) will let you calculate how much extra thrust you're
getting (if any).

--
If, through hard work and perseverance, you finally get what you want,
it's probably a sign you weren't dreaming big enough.

Donald Qualls, aka The Silent Observer http://silent1.home.netcom.com

Opinions expressed are my own -- take them for what they're worth
and don't expect them to be perfect.
• Thanks Donald. I measure force now at bollard pull with the setup shown in a photo in my photo album. In this photo the engine is mounted on a testing raft
Message 2 of 10 , Jul 9, 2011
Thanks Donald. I measure force now at bollard pull with the setup shown in a photo in my photo album. In this photo the engine is mounted on a testing "raft" that adjusts to most size engines. If using a boat it is attached to the gram scale and if the boat is light or resonates a lot baffles are attached to reduce the shuttle. The boat could easily be weighted to equal the weight when then augmenters are installed. Due to the pulsing of the engine an average has to be decided on. To improve accuracy I video the scale when the engine is running. When played back at high speed the strobe effect usually pegs the pointer in a very narrow range. Do you think that your suggested testing method would be more accurate?

--- In pop-pop-steamboats@yahoogroups.com, Donald Qualls <silent1@...> wrote:
>
> Daryl Foster wrote:
> >
> >
> > What is the velocity of a pulse jet engine exhaust?
>
> As with anything else in the homebuilt realm, it varies considerably
> (and is a bit hard to measure, since the exhaust is also hot), but the
> best of them will put out several times the volume of a leaf blower at a
> similar velocity without augmentation.
>
> > Could you clarify your last paragraph:-" I'd bet
> > you get between 20% and 80% increase in thrust, measured by the beam or
> > draft of the boat (same waterline length) that can be pushed up to hull
> > speed" Reaching hull speed with a putt putt seems unlikely without a
> > very major break through if that is what you are suggesting.
>
> I was mostly suggesting hull size vs. speed as a means of measuring the
> thrust increase due to the augmenter. An alternate would be to measure
> the size of a drag paddle (just a flat plate in the water at the boat's
> transom) that reduces the augmented boat's speed to that of the same
> boat without augmentation. You'd run the boat with the drag paddle
> installed, but raised out of the water (so the weight is as nearly the
> same as possible), then mount the augmenter(s) and run the boat again,
> increasing the depth of the drag paddle each run until the speed is the
> same as in the control run. Knowing the area of the drag paddle and a
> little hydrodynamic math (flat plate drag is one of the simplest
> calculations) will let you calculate how much extra thrust you're
> getting (if any).
>
> --
> If, through hard work and perseverance, you finally get what you want,
> it's probably a sign you weren't dreaming big enough.
>
> Donald Qualls, aka The Silent Observer http://silent1.home.netcom.com
>
> Opinions expressed are my own -- take them for what they're worth
> and don't expect them to be perfect.
>
• For related stuff go to: http://www.cogulus.com/archimedes/essays/essay1.html
Message 3 of 10 , Jul 9, 2011
For related stuff go to:
http://www.cogulus.com/archimedes/essays/essay1.html
--- In pop-pop-steamboats@yahoogroups.com, "Daryl" <darylcanada73@...> wrote:
>
> Thanks Donald. I measure force now at bollard pull with the setup shown in a photo in my photo album. In this photo the engine is mounted on a testing "raft" that adjusts to most size engines. If using a boat it is attached to the gram scale and if the boat is light or resonates a lot baffles are attached to reduce the shuttle. The boat could easily be weighted to equal the weight when then augmenters are installed. Due to the pulsing of the engine an average has to be decided on. To improve accuracy I video the scale when the engine is running. When played back at high speed the strobe effect usually pegs the pointer in a very narrow range. Do you think that your suggested testing method would be more accurate?
>
> --- In pop-pop-steamboats@yahoogroups.com, Donald Qualls <silent1@> wrote:
> >
> > Daryl Foster wrote:
> > >
> > >
> > > What is the velocity of a pulse jet engine exhaust?
> >
> > As with anything else in the homebuilt realm, it varies considerably
> > (and is a bit hard to measure, since the exhaust is also hot), but the
> > best of them will put out several times the volume of a leaf blower at a
> > similar velocity without augmentation.
> >
> > > Could you clarify your last paragraph:-" I'd bet
> > > you get between 20% and 80% increase in thrust, measured by the beam or
> > > draft of the boat (same waterline length) that can be pushed up to hull
> > > speed" Reaching hull speed with a putt putt seems unlikely without a
> > > very major break through if that is what you are suggesting.
> >
> > I was mostly suggesting hull size vs. speed as a means of measuring the
> > thrust increase due to the augmenter. An alternate would be to measure
> > the size of a drag paddle (just a flat plate in the water at the boat's
> > transom) that reduces the augmented boat's speed to that of the same
> > boat without augmentation. You'd run the boat with the drag paddle
> > installed, but raised out of the water (so the weight is as nearly the
> > same as possible), then mount the augmenter(s) and run the boat again,
> > increasing the depth of the drag paddle each run until the speed is the
> > same as in the control run. Knowing the area of the drag paddle and a
> > little hydrodynamic math (flat plate drag is one of the simplest
> > calculations) will let you calculate how much extra thrust you're
> > getting (if any).
> >
> > --
> > If, through hard work and perseverance, you finally get what you want,
> > it's probably a sign you weren't dreaming big enough.
> >
> > Donald Qualls, aka The Silent Observer http://silent1.home.netcom.com
> >
> > Opinions expressed are my own -- take them for what they're worth
> > and don't expect them to be perfect.
> >
>
• ... I very strongly doubt it -- but it would be a lot easier to set up for those who don t have a scale that reads in fractional grams. -- If, through hard
Message 4 of 10 , Jul 9, 2011
Daryl wrote:
> Do you think that
> your suggested testing method would be more accurate?
>

I very strongly doubt it -- but it would be a lot easier to set up for
those who don't have a scale that reads in fractional grams.

--
If, through hard work and perseverance, you finally get what you want,
it's probably a sign you weren't dreaming big enough.

Donald Qualls, aka The Silent Observer http://silent1.home.netcom.com

Opinions expressed are my own -- take them for what they're worth
and don't expect them to be perfect.
Your message has been successfully submitted and would be delivered to recipients shortly.