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mustang II vs s-18 thorpe

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keefer66

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Joined
Feb 20, 2009
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14
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myerstown pa US of A
just curious both these planes are similar but the take off and landing runs are at opposite ends of the spectrum ? is it the airfoils or just the way that the designers listed or tested the planes .
 

N2T18S

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Sep 7, 2003
Messages
69
Location
Evansville,IN
Keefer,

I don't know where you got your numbers, but the two planes are almost idenitcal. The T18 and the MMII have the same fuse width. The S18 is a couple inches wider and five inches longer. Both designers worked together and apparently shared ideas. I've seen Bernie Fried wheel land his award winning Thorp T18 in 1000 feet.

The biggest difference I know of is in the wings. The MMII has a tapered wing, which is much harder to construct, and the THORP has a Hershey Bar. Everything on the Thorp wings is laid out to use four foot wide sheets of Aluminum. (JT wrote an article on the Sports Aviation Archive on EAA.org like: Birds have tapered wings) The Horizonital Stabilator (like on the Raptor) is unique.

The Folding wings are almost identical. I don't know who copied. But, it is the best system ever designed for one person.

The THORP T18 is usually about 100lbs lighter than an RV7, thus the better performance at half the price. A light Thorp weighs 850lbs. One was built at 701lbs, but it was pretty Spartan. Canvas seats, 1/2 Carbon fiber panel, .025 skins, etc.

As you can see I'm a little perjudice. John Thorp was ahead of his time. Designed the first Homebuilt Aluminum Airplane. Came up with "Matched Hole Construction". All flying Stabilator and a great, timeless Airplane. No jigs, everything is laid out to fit standard size supplies. Wings and controls are removeable for transport. Then you have Lu Sunderland's folding wing!! Still the best after forty years. Classic Sport Aviation has the S18 kits. The T18 plans can still be purchased from Richard Eklund for "plans built". Richard has John Thorps house and shop where he constructs parts on JT's original equipment.

Thanks,
N2t18s
 
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lr27

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Nov 3, 2007
Messages
3,822
I spoke to a guy who'd built a Mustang II. At least I think that's what he said it was. He said it scared him. I don't think because anything was awful about it, just that things happened pretty fast when flying it and by the time he finished it, he was old enough to be slowing down. Kind of sad, really.
 

Wrongway John

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Joined
Dec 8, 2005
Messages
230
Location
Wichita Falls, TX
The Mustang wing also has a laminar flow wing, which is supposed to be more difficult to build, and I hear this has some meeting performance specs with those high cruise speeds mentioned, while others are falling somewhat short of what they were expecting, due to not getting this aspect right.

I like the fact I can use smaller engines on the Thorp if one wants to go this route, and JT’s reputation as an aero engineer is legendary, so I feel comfortable with his design. How do others like the Thorp plans? I’ve started researching Thorp’s T-18’again, and it’s difficult to know what I’m getting into just yet. I prefer not to build as a kit, but materials mostly. I understand the plans are $300.00 and are quite comprehensive. I was told there is also a supplemental part for an extra $50.00. Not sure if this is needed or not. Then there was shipping, so I’m guess I’m looking at close to $400.00 for plans. I talked to the guy at Eckland Engineering that says his is the T-18 plans which don’t cover the folding wing, and not sure what else it doesn’t include, so I guess there would be even more additional supplements to buy, I dunno.

IIRC, the Thorp S-18 plans that offer the folding wing, wider cockpit, longer fuselage and also supposed to be an improved wing airfoil that lowers stall without affecting cruise and top end, but their plans have to be purchased with a kit. What are most building these days?

Does anybody have some used plans for sale? I would like to look things over to see if it is doable, before I took the nearly $400.00 plunge on these plans.

I’ve notice virtually every site I’ve looked at doesn’t mention take off or landing specs on the Thorp; just know it takes up quite a bit of runway. Not sure if the Thorp can actually out perform the RV-7 or not. On Van’s site the RV-7 lists 199 mph at gross weight for their cruise on 180 HP. Van’s forum seems to have many confirming these numbers. What few numbers I seen others share for their Thorps seem to be around 180 mph for the 180 HP, but again, haven't heard from that many Thorp builders. Not much data is given with altitude, temp, etc for me to really know and make a comparison. It seems the Thorp has the potential to make for a faster plane due to generally being 100 lbs lighter, and the wingspan is quite shorter as well, but haven’t read from anybody cruising around 200 mph with the 180 HP engine. Van’s aircraft certainly have way shorter take offs and landings. But gosh, their prices have been through the roof for some time now since their kits have gotten so comprehensive, and is why I think building a Thorp with materials and not a kit form is probably best for me. You’ll have a similar aircraft for about half in it of what the RV’s have in theirs.
 

N2T18S

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Sep 7, 2003
Messages
69
Location
Evansville,IN
T18 plans are now perfect, but a little overwhelming at first. The $50 supplement is a basic instruction manual. There are about 150 Newsletters available detailing construction and the Yahoothorplist.

Every nut, bushing, bracket, etc has a drawing. (JT had a drawing of a wingnut) The original T18 was totally plans built. Now, Richard Ecklund sells many of the hard to build parts and Classic Sport sells the complete S18 kits. Some of the original T18 builders did not build the wing perfect. So, there were some T18's that had a very abrupt stall with no warning. Now most T18's have Stall Strips on the leading edge of the wing to give a buffet warning.

Lu Sunderland came up with the S18, the more forgiving wing profile and the folding wing.. Many of the T18's have the Sunderland wing profile and/or the folding wing mechanism. I've added Pics of prints and a Bellcrank at:

http://www.angelfire.com/pro2/gsa/tools/

Bob
 
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Puggo1

Member
Joined
May 19, 2020
Messages
6
Hi,
anyone got a set of Sunderland S-18 plans with the folding wing?
thanks
Graham
 

rv7charlie

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Nov 17, 2014
Messages
1,153
Location
Jackson
I've owned an original (very well built) T-18 and two RV4s. I currently own an RV6. All were purchased as flying aircraft. I've flown several Mustang IIs, and had a M-II project for a while, many years years ago. Only thing I actually built was the flap.

I consider Thorps to be great a/c for the money, but are typically a bit slower than the typical RV at the same HP. Standard construction is with pulled rivets, so that alone will cost a bit of speed. Cooling drag is likely to be a bit higher, if the original cowl design is used. The really short wingspan costs a bit of cruise speed at altitude, and causes a higher sink rate in approach (induced drag, both cases). Not that the RVs are immune; just that it seems to affect T-18s a bit more. Actual stall speed is similar, but the T18 tends to bleed off speed quicker.

Mustang IIs (also a great value) can be quite a bit faster than RVs, and can have stall speeds fairly close (but higher) than RVs, but it's highly dependent on build quality. The wing's airfoil has a relatively sharp leading edge that can be hard to home-fabricate accurately, so stall speed and stall behavior can be highly variable among the scratch built examples.

Flying qualities of well built examples of either one are no worse than an RV, but they are...different. Anyone coming straight from a Cessna or Piper will likely find them (and RVs) to be quite a handful, and if there are build quality issues, it'll be worse. On the other hand, I learned to fly in a Luscombe 8A, transitioned directly to the T-18 with about 80 hrs total time, and found it a joy to fly; easier handling in many circumstances than the Luscombe.

All the 'somewhat', 'a bit', etc are unquantified because there is so much variation among examples of both the T/S-18 and the Mustang II. To be clear, I'd be grateful to own a well built example of either one, and either would likely cost quite a bit less than an RV-6 with the same build quality (in some cases, as little as 1/2 the price).

I lost the T18 to a tornado that hit Westheimer Field back in 1992.

I sold the M-II project in favor of starting an RV7 to get a bit more cockpit room, easier build ('everything's in the box'), more widespread support, greater payload, and greater likelihood of meeting performance specs. The -7 remains a work in progress while I've owned/flown the other RVs.

My choice has been the RV family, but based on my experience, I can totally understand someone picking either a T-18 or a M-II as their project or purchase.

Charlie
 

fixnflyr

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Joined
Mar 7, 2009
Messages
59
Location
Springfield, Ga. USA (2ga2) Swaids Field
I have owned a T-18, several M-II's, and a couple of RV-6A's. (I wish they were taildraggers). BTW all were flown out of my grass airstrip.
I think the M-II is the best airplane for the money in my experience with the examples I owned/flown. It was faster that all the rest and had good low speed manners. I would wheel land it most of the time as I do on all taildragger aircraft. The stall characteristics were spirited but not as exciting as the T-18. The T-18 I had would make you stomach drop hard when you stalled it and it would always drop one wing and start a spin entry. It could be controlled with rudder but you had to get busy pretty quick or you could lose a lot of altitude. Now, with that said, you have to take in account that these are all hand built airplanes and not two wings are exactly the same. I liked the T-18 but they don't hold the value of the other two, especially the RV's.
The RV's have better ergonomics in the cockpit, visibility is better. The T-18 I had was narrow and deep, the controls were really quick and took a little practice for the light inputs it required on the stick. The M-II was somewhere in the middle.
There is a very good magazine article comparing the RV to the M-II one should read.
One airplane is not clearly better than the others they are just different. They all have their good and bad points. I would suggest go fly them all.
T-18's and M-II are great performance for the dollar and there are good deals that pop up every week/month on Barnstormers. (Too many airplanes, not enough time!)
If you wind up with a plane that doesn't fly right there are "fixes" you can do the tune and trim the flying characteristics. Stall strips, VG's, wedges on the flight controls, tape a pencil on the trailing edge, fixed tabs on controls, even bump the LE of wings with a rubber mallet to bring airfoils into equal contours.
One will get a lot of advice on which is best, especially from people who have never flown or owned the plane they are critiquing. If you find a good deal on one, buy and fly it! Hours flown on a homebuilt increases its value. (proven aircraft).
If you don't like it you can always sell it and get you money back.
 

cluttonfred

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Feb 13, 2010
Messages
7,984
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Fort Walton Beach, Florida, USA
I have never flown a T-18 but I was on a kick about them a few years ago, bought a set of plans, eventually decided I just wasn’t enthusiastic about the idea of a scratch-built metal plane, and sold the plans on. One thing that I did discover was a small sub-community of T-18 builders with planes as light as possible and power on the low end, still enclosed but closer the the intent of the original open cockpit prototype. Personally, that’s what interests me, not the overweight plane with the most power but the spartan and light one slipping through the air on the smallest possible engine. The T-18 seems well-suited to that approach.
 

Blueberry

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Sep 13, 2020
Messages
20
Location
NC
From a $/lb perspective you can't beat the MII's kit price. I know this is a very simplistic way to look at it but if you divide the kit price by the gross weight (less engine weight and maybe 30 lbs for electronics) you can compare what you are paying for pound to pound. @ $15,910 (price listed for basic kit on the website) and a gross weight of around 1300lbs less engine, you come out at around $9.75 per pound. If you look at aluminum prices on Aircraft spruce you see the prices run from $9 - $10/lbs depending on gauge. So the cost of the Kit, with fully formed parts is barely more than you would pay for the raw materials. The T/S18 comes in at around $12.60 and the RV7a at $15.25/lb.
 

rv7charlie

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Nov 17, 2014
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I haven't followed the current M-II kit company in many years, but about 20 years ago when I was getting ready to pull the trigger on a kit, the M-II kit price was quite a bit lower than an RV-7 kit. BUT....the stuff *not included* in the M-II kit drove the price to quite a bit above the price of an RV-7 kit. And the pre-fabrication level was a lot less than the RV kit, as well. I haven't looked at either T/S-18 offering either, but I'd bet that the prefab level is far lower than the RV kits, also. Buyer's choice on the level of work they want to do, but more prefab obviously is worth more in terms of kit cost.

Not sure where you're getting weight figures. At 1300 lbs, less engine, none of the planes we're discussing would be flyable when completed. (Even at 1300 lbs including the engine they'd probably not be flyable; adding fuel would come so close to gross that there's no capacity left for the pilot.

I'm not sure that 'simplistic' accurately describes measuring value in dollars per pound. It's really kinda backward. In a/c, it's typically the case that the *more* it costs per lb, the better it will be. Costs are more frequently judged on the cost to *lose* a pound, rather than the cost to buy a pound. Witness the current fad of replacing a $40 SLA battery with a $300 lithium battery, to save 10 lbs of weight.

Charlie
 

Blueberry

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Sep 13, 2020
Messages
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Location
NC
Thanks Charlie. I miss typed that. 1300 is after engine weight is removed. Gross weight for MII is recommended at 1600. 1600 - 300 (rough wet weight of a O-360) = 1300. And before everyone jumps on this 300 pounds I know that it all depends.... Lycoming lists dry weight at 254lbs. And I probably should have gone with Empty weight (930 - 1100 depending...) for my comparison.

I am sure you are correct in your assessment of what is and what is not included in the RV kit vs others. I'm not going to get into that debate.

For those that are debating the "Scratch build to save $" vs "Build from Kit", it is a valid view. Strip away the engine, prop and the electronics, most of what's left is aluminum. Take out what it is going to cost you for the aluminum ($9-$10/lbs) and that is all you are saving. You also need to add in 15%-20% scrap if scratch building into the cost of the aluminum, more if its your first.
 

rv7charlie

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Nov 17, 2014
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Jackson
If that's the value yardstick you want to use, you still need to get airframe weight correct. Gross weight is empty weight (including engine) + max fuel + payload (people/cargo).

Empty weight of a typical RV6/7 is between 1000 & 1150 lbs, depending on engine, prop, and builder's attention to weight gain. The FWF propulsion package (not included in the kit) will weigh, real world, between 350 & 450 lbs, depending on engine choice and prop choice. It's unlikely you'll find *any* Lyc 360 at 254 lbs; virtually all will be at least 285-335 lbs without exhaust system or oil cooler/hoses, and often without starter/alternator. You'd also need to subtract the weight of any avionics and interior (seat cushions, insulation, upholstery, etc).

You're still left with the issue that less (weight) is actually worth more money. Driving airframe weight *down* while maintaining strength allows greater useful load, which carries greater value to most of us (more fuel, more people, more baggage). "Everything's a compromise"; we have to pick our tradeoffs, within technically and financially available options.

Charlie
 
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