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T-18 vs. S-18
http://thorp18.com/thorpforum/viewtopic.php?f=34&t=7916		 Page 1 of 2
Author:  cluttonfred [ Sun Mar 27, 2016 1:58 pm ]
Post subject:  T-18 vs. S-18
This may end up being one of these never ending Chevy vs. Ford conversations, but here goes. I am interested in scratch building a relatively simple plane with good performance on modest power. VFR only, fixed pitch prop, and likely a 115 hp O-235. Are there any strong arguments in my case for choosing the S-18 over the T-18?
Author:  Hagle347 [ Sun Mar 27, 2016 4:20 pm ]
Post subject:  Re: T-18 vs. S-18
Hi Fred , I'm not sure that you are starting this with the correct premise. If you read the design specs, the original T-18 was designed around the 0-290 because of its availability. There are lots of good performing "mouse motor" T-18's out there. I'm not sure why one would want "less" power than what John Thorp originally specified. To my knowledge - there are no S-18's flying with O-290's. What you desire may not be practical under the Thorp umbrella.
Author:  leewwalton [ Sun Mar 27, 2016 4:35 pm ]
Post subject:  Re: T-18 vs. S-18
Not to disagree with my fello dedicated Thorp builder/flyer/SOB but a lightly built Thorp would run just fine with an 0-235. That being said those motors are not cost effective to even consider in a new plane and quite frankly not that efficient. In my opinion the 0-320 or 0-360 are the only options in 2016. 0-290 and 0-235 parts are $$$ and not as readily available as the other two.
Author:  James Grahn [ Sun Mar 27, 2016 5:14 pm ]
Post subject:  Re: T-18 vs. S-18
Good luck getting T parts.
Cubes
Author:  KWK [ Mon Mar 28, 2016 8:37 am ]
Post subject:  Re: T-18 vs. S-18
cluttonfred wrote:
Are there any strong arguments in my case for choosing the S-18 over the T-18?

I can think of only one small point in favor of the T-18: It weighs slightly less. Thorp mentioned the O-235 as a possible engine, but that was back when the plane was lighter and simpler (no flaps, etc.).

As I recall, using the drag numbers from the CAFE report on the T-18, I estimated 145 mph for the O-235, or was it 140 mph? The engine though will be working hard. At that speed, an O-320 will be loafing and will likely be quieter and not using much if any more fuel. There's a lot of competition in the -320 parts market and pretty much none in the -235. If you're keeping it super simple and leaving out the electrical system, the -235 does flip over by hand much easier. One of Lycoming's competitors mentions a lighter weight -320, erasing much of the weight difference.

The Tailwind can be built lighter than the T-18 and has more wing area. It would be a good choice for your criteria. Both the W-8 and W-10 versions have flown with an O-200.

For an aluminum airplane, the Zenith 601-HD is about as simple as it gets. It does not, though, have "good performance."

Karl
Author:  James Grahn [ Mon Mar 28, 2016 9:38 am ]
Post subject:  Re: T-18 vs. S-18
The T also has bigger ailerons if you are into using them.
Cubes
Author:  cluttonfred [ Mon Mar 28, 2016 10:39 am ]
Post subject:  Re: T-18 vs. S-18
Thanks, all. I thought that an O-235 would be both lighter and cheaper than an O-320 or O-360 since the latter are much more popular in the kit plane world. If that is not the case, then I'll have to rethink my approach.
Author:  cluttonfred [ Tue Mar 29, 2016 1:03 pm ]
Post subject:  Re: T-18 vs. S-18
Well, FWIW, I have settled this first of many, many more decisions to make on the road to a new Thorp project by ordering the T-18 plans set from Richard Eklund. The journey of 1,000 miles begins with a single step.
Author:  KWK [ Tue Mar 29, 2016 6:52 pm ]
Post subject:  Re: T-18 vs. S-18
I received my cubic foot (or so) of plans from Eklund recently. There are over 200 sheets. It seems daunting until you find some sheets have a single small part on it. Thorp's goal was an "irreducibly simple" airplane. Chris Heintz bested him in that regard, but in the air the Thorp is a Cadillac in comparison. The T-18 has a surprising number of parts machined from aluminum plate and bar. If you tire of making aluminum chips, the parts from the S-18 shop should work, but you'll have to do all the wing bits yourself. I remain on the fence. I find the 601 plans easier to follow, but both are clear enough. My teenage son really wants to build a T-18, but I was hoping for something more sedate and simpler. We'll see.
Author:  Ryan Allen [ Tue Mar 29, 2016 7:03 pm ]
Post subject:  Re: T-18 vs. S-18
Once you get used to the WL, STA, and BL system, it will be very simple. I began with the same thoughts as you. I didn't build my Thorp, but when I first began reviewing the plans, I was a little behind the curve, but it comes quickly.
Author:  fytrplt [ Tue Mar 29, 2016 8:07 pm ]
Post subject:  Re: T-18 vs. S-18
Comparing the 601 to the Thorp is like comparing a Yugo to a Corvette. Not even in the same sky. If you want to compare; the RV series has 1/3 more parts count than the Thorp with lesser flying qualities. I know, I've built and flown both. You will spend considerable time on any homebuilt. Choose one that you will be happy with even as your pilot skills improve.
Author:  KWK [ Tue Mar 29, 2016 8:56 pm ]
Post subject:  Re: T-18 vs. S-18
fytrplt wrote:
Comparing the 601 to the Thorp is like comparing a Yugo to a Corvette.

;D Having flown in both a Zodiac and a T-18, and I can second your analogy.

It's been over 30 years since I took my drafting classes in engineering, but I've had no trouble with either set of plans. As a design, the 601 needs work, but I've pretty much decided on a number of fixes for the squirrelly handling and other issues. I'm still going over both sets of plans, but so far I have the impression the 601 could be built in less than 3/4 the time, when scratch-building. At this point in my life, a docile, low-and-slow flivver is all I need. My son has a different perspective, of course. No decisions so far. Of late, I've been favoring the T-18, but a month ago it was the other way. Time will tell.

Karl
Author:  cluttonfred [ Tue Apr 12, 2016 3:33 am ]
Post subject:  Re: T-18 vs. S-18
Cubes and anyone else...a quick question...will all of the major firewall-forward S-18 parts also fit an original T-18? Engine mount (regular or dynafocal)? Cowling? Landing gear? Fuel tank? And if the landing gear fits, is it the stock length or extended or are both available? Cheers, Matthew
Author:  Hagle347 [ Tue Apr 12, 2016 6:40 am ]
Post subject:  Re: T-18 vs. S-18
To answer your question simply would be easy. I'm reminded of what my Dad would say when I would ask similar questions." I could tell you the answer, but you will more likely remember and retain the information if I tell you where to find it". Here's the same advice for you. Matthew, if you go to the home page of this forum...on the right column down half way you will see ' Newsletter archive.'
Lee Walton has scanned all the newsletters that were ever written regarding the Thorp. These are an excellent resource and will more than likely answer all the Questions you pose. From that you alone can make the best decision on which aircraft and engine would be best for the outcome you desire .
As the design has been available for more than 50 years- there's a lot of great information in the newsletters. Happy reading
Terry
Author:  dickwolff [ Tue Apr 12, 2016 7:18 am ]
Post subject:  Re: T-18 vs. S-18
Mathew -

Two other underutilized resources:
1) The old (retired) forum, accessible by clicking on the "T18 dot net" logo above and choosing the "forum" tab
2) The old Thorplist Archive, 1998-2009, accessible through the old forum.

All of the forums, current and retired, are searchable.

D
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