Scat2 can't clime!
Primus
degrees pitch, it can't clime even 15 degrees hill, any suggestions?
What if I lower the pitch angel?
Is changing the skirt will Help?
Thanks in advance.
--
HoverRover
H...@xanta.com
hover...@my-deja.com
awfully steep pitched , it should be more like 30 degrees I believe.
The 277 scats are drastically under powered anyway and a 15
degree is probably about as steep as you can expect with a run at it.
You should be able to climb the average boat ramp with a little bit of
a run .
Do you find that you have a lot of lift but little thrust ? If so
there's a real good chance the pitch is indeed set too steep.
Doug
In article <RnnP5.32$Am6.7...@news1.pvt.primus.ca>,
Sent via Deja.com http://www.deja.com/
Before you buy.
SEVTEC
>From: "Primus" H...@xanata.com
>Date: 11/11/2000 9:36 PM Pacific Standard Time
>Message-id: <RnnP5.32$Am6.7...@news1.pvt.primus.ca>
>
>Just bought Scat2 with rebuilt 277 rotax and 6 blades multiwing at 45
>degrees pitch, it can't clime even 15 degrees hill, any suggestions?
>
>What if I lower the pitch angel?
>Is changing the skirt will Help?
>
>Thanks in advance.
>--
>HoverRover
>H...@xanta.com
>
Lets test the Scat to see if it will climb 15 degrees, with numbers.
First, a 15 degree slope is a lot steeper than one might realize, and the best
way to measure it is with a carpenter's level and a tape measure. Just hold
the level level and measure down with the tape measure. The slope is the
arctan tape measure dimension / level length.
Power of the 277 is 26hp max, so we will figure 23, as it isn't a perfect test
cell world. Next cut power by .67, to 15.4 as about 1/'3 of the disc is
blocked off for cushion charging.
Next, from momentum considerations we have to calculate the effective diameter
of the thruster. At static thrust the effective diameter of a cylindrical duct
with an axial extent of at least 50% of the fan diameter so fan diameter is
effectively 32 *sqrt2 or 45inches. Now we have to deduct for the fact that 1/3
of the fan area is blocked off for cushion flow, and this reduces the effective
diameter for static thrust to 37 inches.
Static Thrust = 7.27*(power*effective diameter)^2/3 or 95.5# (remembering to
correct for units.)
Before we get off the deep end I did static thrust tests. A 277 Scat was
tested (Sevtec does test other craft) and got 90#, so I can have confidence of
the calculations. ( I also got a totally unreasonable, inconsiderate for non
participating bystanders 94dB(A) at 50 feet over gravel noise level for this
craft.)
Next, the weight we wish to push up the hill must be determined. Guessing,
340# for the craft, 175# for the operator, and 20# for gas, that is 535#
Ideally the thrust required to push the craft up the hill it would Weight * sin
15 degrees, which is 138#. So we know that there is no way this craft is going
to static up 15 degrees unless the driver is very light.
Put a bigger engine in the Scat, say a 440cc with the same specific output as
the 277, we get 95*(440/277)^2/3 = 129#. Even if the craft does not change
weight, we still cannot static the 15 deg hill.
I am sure some of you have seen the video of the 16hp Sevtec Vanguard climb my
backyard ramp with only 16hp for both lift and thrust. (The video does not do
justice to the steepness of this hill, as it is even hard to mow, due to
steepness.) The lower hill is only 23 degrees, and the upper hill is only 16
degrees. The secret is inertia, turning 25mph of kinetic energy into 16 1/2
feet of potential energy. The biggest problem is that the hull has to make the
transition from level flight to the abrupt steepness of the initial hill.
Barry Palmer, for <A
HREF="http://members.aol.com/sevtec/sev/skmr.html">Sevtec</A>
hover...@my-deja.com
Changing the skirt won't help unless you have a good deal of
air loss from tears etc. .
The best thing to help you is the momentum of taking a run at
the hill . I don't know how you drived the 42 degree pitch measurement
but that [assuming it's accurate] is way too steep a pitch. The pitch
should be [from my scat and having played with the pitch settings]
more like 28 - 30 degrees , 32 tops . A very small change in the pitch
can make a world of difference in the effectiveness , especially when
you are using a low power engine . Also a very small turn of the blade
in it's socket makes a huge difference in the actual pitch as well.
Double check your pitch and see to it that it's down around 30
degrees.
Then try the hill with a run at it.
Doug
Kenneth Roberts
>
> Just bought Scat2 with rebuilt 277 rotax and 6 blades multiwing at 45
> degrees pitch, it can't clime even 15 degrees hill, any suggestions?
>
> What if I lower the pitch angel?
> Is changing the skirt will Help?
>
> Thanks in advance.
> --
> HoverRover
> H...@xanta.com
put a rotax 583 on it. it'll climb!
just kidding.
NWCedarDecks
>I am sure some of you have seen the video of the 16hp Sevtec Vanguard climb
>my
>backyard ramp with only 16hp for both lift and thrust. (The video does not
>do
>justice to the steepness of this hill, as it is even hard to mow, due to
>steepness.) The lower hill is only 23 degrees, and the upper hill is only 16
>degrees. The secret is inertia, turning 25mph of kinetic energy into 16 1/2
>feet of potential energy. The biggest problem is that the hull has to make
>the
>transition from level flight to the abrupt steepness of the initial hill.
>
>
>
you mean this hill right? ED
http://members.aol.com/sevtec/sev/hovsev.html
SEVTEC
>From: nwceda...@aol.com (NWCedarDecks)
>Date: 11/13/2000 4:44 PM Pacific Standard Time
>Message-id: <20001113194458...@ng-cq1.aol.com>
No, the ramp you show is that of the late Bill Linkins and is relativly mild.
The hill I am referring to is my backyard ramp. Scout is shown climbing it in
stop action if you follow the video link from the Sevtec main page.
NWCedarDecks
But I would take a running start too.
Val - WhatsTheNumber.com
as Sevtec owners standing waist deep in gas looking for matches to light to
see the light... LOL
I am a Scat owner and proud of it.. The problems with scats is the people
that prepared them and fine tune them were for light weight Asians and not
big men like me... Gee all I did is increase the pitch added a few blades
and small clearance between the blade tip and the cowling and boy.. even
with my 300lb weight has a hard time keeping the front down.
Sorry people that own sevtec... but they are not the only hovers out there
.. and we are don't have to be made feeling stupid because we don't own
one. If Sevtec was the best then there would be no other type of hovers.
I just like meeting people that just enjoying having fun..... ,Don't anyone
just like owning a hover and enjoying the unique experience of the ride and
the thrill...
How about some stories of some adventures and places to see or is this only
a board of men, their machines and gee look at mine it bigger, better and
faster then yours.
To the few that answered my question on this board ... a great thanks... at
least I know that some people willing to help without feeling or treated
like an idiot.
Val
WhatsTheNumber.com
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"SEVTEC" <sev...@aol.com> wrote in message
news:20001113151848...@ng-cr1.aol.com...
> >Subject: Scat2 can't clime!
> >From: "Primus" H...@xanata.com
> >Date: 11/11/2000 9:36 PM Pacific Standard Time
> >Message-id: <RnnP5.32$Am6.7...@news1.pvt.primus.ca>
> >
> >Just bought Scat2 with rebuilt 277 rotax and 6 blades multiwing at 45
> >degrees pitch, it can't clime even 15 degrees hill, any suggestions?
> >
> >What if I lower the pitch angel?
> >Is changing the skirt will Help?
> >
> >Thanks in advance.
> >--
> >HoverRover
> >H...@xanta.com
> >
>
> I am sure some of you have seen the video of the 16hp Sevtec Vanguard
climb my
> backyard ramp with only 16hp for both lift and thrust. (The video does
not do
> justice to the steepness of this hill, as it is even hard to mow, due to
> steepness.) The lower hill is only 23 degrees, and the upper hill is only
16
> degrees. The secret is inertia, turning 25mph of kinetic energy into 16
1/2
> feet of potential energy. The biggest problem is that the hull has to
make the
> transition from level flight to the abrupt steepness of the initial hill.
>
>
SEVTEC
Date: 11/13/2000 7:34:17 PM Pacific Standard Time
From: k...@9ci.com (Kenneth Roberts)
Sender: k...@roberts.9ci.com
Reply-to: ignoret...@9ci.com
To: sev...@aol.com (SEVTEC)
>> Put a bigger engine in the Scat, say a 440cc with the same specific output
as
> the 277, we get 95*(440/277)^2/3 = 129#. Even if the craft does not change
> weight, we still cannot static the 15 deg hill.
>
> I am sure some of you have seen the video of the 16hp Sevtec Vanguard climb
my
> backyard ramp with only 16hp for both lift and thrust. (The video does not
do
> justice to the steepness of this hill, as it is even hard to mow, due to
> steepness.) The lower hill is only 23 degrees, and the upper hill is only 16
> degrees. The secret is inertia, turning 25mph of kinetic energy into 16 1/2
> feet of potential energy. The biggest problem is that the hull has to make
the
>> transition from level flight to the abrupt steepness of the initial hill.
>there must be some inherent design constraint on a scat, or you don't
have your numbers straight. not trying to pick a fight, but my uh-12r
>can climb that slope, from a standstill.
If you would tell me what the UH propeller diameter is and how much power, or
what the engine's are or power split between propeller and fan if single engine
and how much weight you are pushing up the hill, I could comment on this just
by doing the numbers.
Also, what makes you think the numbers aren't straight? They do verify that
the Scat will not pull the grade statically, even when set up properly, if you
have measured the grade correctly and are static thrusting up it. (The test
craft was set at 32.5 degrees, I think.)
(Note, it was indicated here your mailer did not take this message.)
Primus
Thanks for the advises and calculations, now 2 questions:
1- is the finger skirt in scat got any thing to do with the low thrust?
2- how to determine the right pitch for the engine power.
HoverRover
H...@xanta.com
HoverRover
Ken Roberts
>have your numbers straight. not trying to pick a fight, but my uh-12r
>>can climb that slope, from a standstill.
>
>If you would tell me what the UH propeller diameter is and how much power, or
>what the engine's are or power split between propeller and fan if single engine
>and how much weight you are pushing up the hill, I could comment on this just
>by doing the numbers.
my prop i have now is handmade and poorly so, it's too shallow. after my moving
settles down a bit, (i just moved to chicago) i'll make another. i can give you
some numbers of what i've observed and what i guess, and i'll indicate what is
what:
diameter: 48" --measured
pitch: 36" --leading edge too thick, too much glass
hp: 98 --skidoo documentation: probably closer to 80 in this
application. i'll give enough other info to do an
estimate.
static thrust: 200lbs --measured, relatively flat ground, bathroom scale
approximately 1/4 throttle, engine redline.
reduction: 2.5:1
empty weight: 400 lbs --wild guess. haven't had the chance to weigh it.
my weight: 230lbs --measured about 3 months ago.
my next prop, after some discussion with bob windt, will shoot for about 44
inches of pitch, and the same 1x6 construction. my tip speed is something like
550mph, calculated, at redline. my duct is heavily pitted, and needs
work/replacement.
i realize that you can't get any sort of reliable numbers with most of this
being wild guesses. bob says it's reasonable with my duct size and engine size
to get more than 400 lbs of thrust in a real-world situation. he says it would
be possible to at least approach 500lbs in real world, but this is rarely
realized since most people get scared enough with 400 or so. i'll try to tweak
till 450 or so, i guess.
>Also, what makes you think the numbers aren't straight? They do verify that
>the Scat will not pull the grade statically, even when set up properly, if you
>have measured the grade correctly and are static thrusting up it. (The test
>craft was set at 32.5 degrees, I think.)
it seemed to me that your numbers were lower than i expected. i realize what a
gradient is, and i also have a good idea what they look like in real life: i
did work for the soil conservation service a while back, and did some surveying
for a summer.
it may be that i'm not taking into account the size of the duct, and i have to
admit i'm just running numbers in my head. that's prone to error, so your
numbers may be fine.
>(Note, it was indicated here your mailer did not take this message.)
how so? did you try to mail directly to me? i've just moved, and so my mail
service may be jumping around and sporadic for a little while till i get things
straightened out.
SEVTEC
>From: "Primus" H...@xanata.com
>Date: 11/14/2000 10:44 PM Pacific Standard Time
>Message-id: <RFnQ5.5$LV6.28...@news2.pvt.primus.ca>
The finger skirt has nothing to do with thrust. Overall thrust and drag can be
influenced if a finger is caught over an object, but generally at low speeds on
smooth surfaces skirt type should not matter, especially when static climbing a
hill on a reasonably smooth surface.
I await your UH 12r specifications of propeller diameter, propulsion engine
displacement and power, and nature of lift, does it come from the thrust
engine or is there a separate engine. I can guess at the rest if you do not
know.
Ken Roberts
>
>Thanks for the advises and calculations, now 2 questions:
>
>1- is the finger skirt in scat got any thing to do with the low thrust?
probably not. having a worn, torn, or poorly adjusted skirt can make a big
difference on speed, but not thrust.
>2- how to determine the right pitch for the engine power.
you can do lots of math, or you can use a bit of trial and error:
adjust your blades so that your engine comes up to just at or above your power
peak rpm at full throttle, and at top speed. you don't want it to exceed
redline, and getting something close to full power rpm statically will help your
hill climbing abilities but will probably hurt performance in speed, noise, and
economy.
Ken Roberts
barry, i think you may have responded to the wrong message. i sent most of that
via the other thread. my craft is twin-engine, 10hp lift. other than that it's
all in the other thread.
SEVTEC
>Date: 11/14/2000 9:10 PM Pacific Standard Time
>Message-id: <slrn9146...@peesee.at.home>
Of course your UH will pull the hill while the Scat will not. We are comparing
apples with oranges. When comparing machines we should always acknowledge how
much horsepower is used and how much is carried.
If the duct were up to performance and 50% of the rotor diameter long, your
effective open propeller diameter is 68", assuming the duct discharges through
a cylindrical aft section, and your thrust potential is 7.27(68/12*98)^2/3
=491lb, and assuming you have a separate lift engine.
Craft all up weight will be 400 plus 175# for the operator plus 20lb for
fuel=600#.
With a small increase in duct and rotor diameter you should be able to go
straight up, with this much power,
so you would have a Moller air car, not a hovercraft.
Ken Roberts
>>Subject: Re: Scat2 can't clime!
>>From: k...@peesee.at.home (Ken Roberts)
>>Date: 11/14/2000 9:10 PM Pacific Standard Time
>>Message-id: <slrn9146...@peesee.at.home>
>>
>apples with oranges. When comparing machines we should always acknowledge how
>much horsepower is used and how much is carried.
yes, that's probably part of my problem. i've only got experience driving a
couple different universals, webers, and very briefly goog's neoteric. i've
never driven a scat, and so keep thinking it should perform better than the
numbers you provided. there was a post yesterday by a scat owner who says he
just tightened up tolerances and got much better performance. this is
believeable.
>If the duct were up to performance and 50% of the rotor diameter long, your
>effective open propeller diameter is 68", assuming the duct discharges through
>a cylindrical aft section, and your thrust potential is 7.27(68/12*98)^2/3
>=491lb, and assuming you have a separate lift engine.
the duct is only 18" long, just shy of your 50% mark. other than that you're
making proper assumptions, and those numbers sound reasonably close to what bob
windt said.
>Craft all up weight will be 400 plus 175# for the operator plus 20lb for
>fuel=600#.
only 130# for the operator, unless you're talking about safety and cold-weather
gear. the safety gear is always in/on, and the cold weather gear will be on
anytime i get out for the next while!
>With a small increase in duct and rotor diameter you should be able to go
>straight up, with this much power,
>so you would have a Moller air car, not a hovercraft.
well, i've been thinking of replacing the wooden hull with a solid foam
equivalent. bob says it should be lighter and easier to make, and his solid
foam hulls take a huge amount of abuse with almost no degradation of hull
integrity. i go out , land on a rock and i've got a hole in my hull.
anyway, if i do rebuild ill have a bigger diameter thrust duct, more for noise
and efficiency than for the obviously unnecessary increase of thrust potential.
i'd like to turn the prop slower, and have wider blades, in emulation of the
weber crafts--i think that's one main key to their noise performance. the 25hp
kohler is easily more noisy than the prop is. i think they turn it at 1100 rpm
or so. i obviously wouldn't be doing that, but if i could get it down to the
tip speeds considered safe for hovercraft cruising i'd probably drop the noise
an order of magnitude.
thanks for running those numbers.
Hoverjunky
>From: "Val - WhatsTheNumber.com" Val...@WhatsTheNumber.com
>Date: 11/14/00 7:54 AM !!!First Boot!!!
>Message-id: <id6Q5.2183$He2.4...@dfiatx1-snr1.gtei.net>
>
>
>
>
>
>
>
>
Val, I own three Scat myself, including a Scat 2 and I didn't take any offense
to what Barry had to say. They are great for fun hovercraft, but far from being
the best. So don't worry about it, just hover and have fun.