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grantr
Joined: 12 Sep 2007
Posts: 217
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 Posted: Sat Nov 17, 2007 11:07 am Post subject: Big Twin 4 stroke? |
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What do you guys think of the Big Twin from www.culverprops.com
here is the direct link http://culverprops.com/big-twin.php
Check out the videos of the Kolb MK II.
Its hard to believe that a 38 hp engine turning a max rpm of 3600rpm will fly the plane.
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NeilsenRM(at)comcast.net
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| Posted: Sat Nov 17, 2007 12:17 pm Post subject: Big Twin 4 stroke? |
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This is a smaller version of the same redrive I have on my VW. That is a
fairly light plane with a light pilot and it was cold. This might be a
alternative for a FirestarII.
I had a discussion with Honda Don at Sun N Fun last year about this engine.
His comment was Honda engines are smooth because they have the heaviest
flywheels in the business. The first thing the guys a Valley did was cut the
fly wheel off to reduce the engine weight.
I have never seen it run up close. Maybe the redrive smoothes it out????
Rick Neilsen
Redrive VW powered MKIIIC
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JetPilot
Joined: 10 Jan 2006
Posts: 1246
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| Posted: Sat Nov 17, 2007 2:07 pm Post subject: Re: Big Twin 4 stroke? |
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Given the price of that engine, I would definitely go with the HKS instead. The big twin engine is heavy, low on power, and pretty darned expensive. The HKS has almost twice the power for the weight...
Also, HKS has proven reliability in other planes, there is just nothing that makes bit twin worth the risk. At 5000 dollars, the big twin is very expensive for a anchor of an engine, especially when the HKS does not cost that much more !
JettPilot
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_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!
Kolb MK-III Xtra, 912-S |
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jindoguy(at)gmail.com
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| Posted: Sat Nov 17, 2007 10:02 pm Post subject: Big Twin 4 stroke? |
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At the weight you're quoting for the big twin, which is entirely in
line with the weights listed for the Vanguard and Honda V Twin
industrial engines, the Continental A084 becomes real attractive. They
can still be had for under $1000 and you get the designed in balance
of the flat 4.
Rick
On Nov 17, 2007 4:07 PM, JetPilot <orcabonita(at)hotmail.com> wrote:
| Quote: |
Given the price of that engine, I would definitely go with the HKS instead. The big twin engine is heavy, low on power, and pretty darned expensive. The HKS has almost twice the power for the weight...
Also, HKS has proven reliability in other planes, there is just nothing that makes bit twin worth the risk. At 5000 dollars, the big twin is very expensive for a anchor of an engine, especially when the HKS does not cost that much more !
JettPilot
--------
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!
Kolb MK-III Xtra, 912-S
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=146693#146693
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jindoguy(at)gmail.com
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| Posted: Sat Nov 17, 2007 10:05 pm Post subject: Big Twin 4 stroke? |
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I should add that they have an active following on Yahoo Groups where
you can find a lot of info to make the conversion from generator
powerplant to aircraft engine pretty painless.
Rick
On Nov 18, 2007 12:02 AM, Richard Girard <jindoguy(at)gmail.com> wrote:
| Quote: | At the weight you're quoting for the big twin, which is entirely in
line with the weights listed for the Vanguard and Honda V Twin
industrial engines, the Continental A084 becomes real attractive. They
can still be had for under $1000 and you get the designed in balance
of the flat 4.
Rick
On Nov 17, 2007 4:07 PM, JetPilot <orcabonita(at)hotmail.com> wrote:
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> Given the price of that engine, I would definitely go with the HKS instead. The big twin engine is heavy, low on power, and pretty darned expensive. The HKS has almost twice the power for the weight...
>
> Also, HKS has proven reliability in other planes, there is just nothing that makes bit twin worth the risk. At 5000 dollars, the big twin is very expensive for a anchor of an engine, especially when the HKS does not cost that much more !
>
> JettPilot
>
> --------
> "NO FEAR" - If you have no fear you did not go as fast as you could have !!!
>
> Kolb MK-III Xtra, 912-S
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> Read this topic online here:
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> http://forums.matronics.com/viewtopic.php?p=146693#146693
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grantr
Joined: 12 Sep 2007
Posts: 217
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| Posted: Mon Nov 19, 2007 2:52 pm Post subject: Re: Big Twin 4 stroke? |
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I have been emailing back and forth with a guy regarding the Big Twin 38hp engine and he says this engine is designed to fly a plane up to 1000# gross weight.
Please read the following and make comments.
it kind of sounds reasonable knowing that a heavy piper cub flys well with a 65 hp engine. and a 150 with a 100hp engine.
| Quote: |
General rule of thumb is that static thrust must be 20% of gross
weight. Any more and top speed suffers, any less and climb
performance suffers.
The Big Twin has been optimized for aircraft with a gross weight of
up to 1,000 lbs and and optimum top speed of no more than 85-90mph.
All I am saying that the Big Twin would be a good choice for an
aircraft up to 1,000 lb gross weight with a top level speed of 85-
90mph. The Big Twin is a very efficient engine using the reduction
drive to swing that big ol' 74X58 prop.
A Cessna 150-----
Cessna 150, Continental O-200(100hp), McCauley 68X ?
Aircraft Empty weight= 1,111 lbs
Aircraft Gross weight= 1600 lbs
Thrust at 2332 rpm = 335 lbs
Power to weight Ratio = .0625 hp/lb
Thrust to weight Ratio= .2093 Thrust Lbs/ Aircraft Lbs
Thrust to hp ratio= 3.35 lbs/hp
Wing Area= 160 sq ft
Wing Loading empty = 6.9437 lbs/sq ft
Wing Loading at Gross= 10 lbs/ sq ft
Source: http://www.flycorvair.com/thrustjune.html
Thrust to gross weight ratio : 20.9375%
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A Cessna 120-----------
Cessna 120, C85 (85hp), McCauley 71X46
Aircraft Empty weight= 900 lbs
Aircraft Gross weight= 1450 lbs
Thrust at 2445 rpm = 340 lbs
Power to weight Ratio = .0586 hp/lb
Thrust to weight Ratio= .2344 Thrust Lbs/ Aircraft Lbs
Thrust to hp ratio= 4 lbs/hp
Wing Area= 167 sq ft
Wing Loading empty = 5.3892 lbs/sq ft
Wing Loading at Gross= 8.6826 lbs/ sq ft
Source: http://www.flycorvair.com/thrustjune.html
THRUST TO GROSS WEIGHT RATIO: 23.44827%
------------------------------------------------------------
As you can see the thrust to gross weight ratios are very close to
the 20% rule of thumb I mentioned. The Cessna 120 has a higher
percentage of static thrust (from a smaller HP rated engine) which
explains why it is able to takeoff shorter and climb faster than a
Cessna 150, AND also explains why it won't fly as fast as a 150.
To get the optimum and most efficient use of your powerplant and
for best all around performance... the 20% thrust to gross weight
ratio works pretty well and will get you very close.
Choosing the right propeller is critical in that it must produce
the minimum static thrust... but still propel you to your aircraft's
designed (or desired) max level speed.
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Don G
Joined: 10 Jan 2006
Posts: 156
Location: Central Illinois
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| Posted: Sat Nov 24, 2007 5:27 pm Post subject: Re: Big Twin 4 stroke? |
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Grant,
I think if I were going to use that engine, (which is not 38 hp BTW..but really 32 stock and about 34 with the VW carb on it at 3600rpms)..
I would simply but one from a local engine distributor for about 1200 bucks...(32hp generac) and leave the engine alone other than the buggy Downdraft weber carb, (150 bucks) which is a good thing.
Do not lighten the flywheel, as the Generac vibrates bad enough as it is.
Do not remove engine cooling shrouds.
Install a redrive, but it needs to be a really STRONG redrive..because of very high power pulses from the big V-twin, (read that as a belt eater) and swing as big a prop as I could fit on it at 2200 to 2300 rpms. IT WIll give alot of thrust, and if the plane has enough wing, it should make a very viable aircraft powerplant.
Install on the biggest of Lord mounts as you can find.
Buckeye PPC is now experimenting with this engine on a PPC and having good success, I believe you might get the re-drive from them, at least they plan on offering it last I spoke to them.
In case you didnt see it, They won several awards at OshKosh this year with a V-twin Honda on this set-up, including the inovation award. As Honda does not have a larger engine they are working on the Generac for a better climb rate for heavier pilots. I predict they will be successfull.
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_________________
Don G.
Central Illinois
Kitfox IV Speedster
Luscombe 8A
RV9A |
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