Thorp Air Command - T18.net

Thanks, but there are 81 Mark Batchelor accounts on Linkedin and I am not a member anyway.

On a completely unrelated note, what do folks think of the idea of no flaps on a lightweight "mouse motor" T-18?

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Matthew Long, Editor
cluttonfred.info
A site for builders, owners and fans of Eric Clutton's FRED

« Voici ce que j'ai fait...vous pouvez en faire autant! »
"This is what I have done...you can do the same!"
--Henri Mignet (1893-1965)

There use to be one at ZPH airport several years ago,

I may indeed not have heard him correctly. I've been pointed to the builder's blog Stretch created 10 years ago. A T-18 was weighed at 739 lb and it was claimed there was another easy 11 lb which could be removed. However, as I read it, this was his friend's "MMP2," not Stretch's "MMP1." I'll review the blog further this weekend to see if there's more. I'm willing to say 730 lb is a viable lower weight.


It's not as if the T-18 has a low landing speed. If I build a T-18 (I received the plans from Eklund last month), I would do the flaps. An alternative would be to greatly lengthen the mains to get more lift in the 3-point. However, you will certainly be blind over the nose that way, and the firewall angle might have to be changed.

Karl

Pretty sure most T-18's ( I said most not all) have the extended gear on them . If I remember right the extended gear is about 3 inches longer than the "standard gear ?" Not sure what Cubes sells ? Flaps or no flaps ? I like flaps with a side of coleslaw !

RB

Were I set against flaps, I'd consider adding 10-12" to the mains to minimize the increase in touch down speed. That assumes you get the wings right and have a docile stall, and you'd want to try some tail low landings sans flaps to verify the drag isn't so high you have too little time in the flare, or have poor control in roll, or...

Just build the flaps.

What limits the T18 Vso in ground effect? Elevator stall or wing stall?

Recall the early Cessna Cardinals broke nose wheel assemblies and bent firewalls because the all flying horizontal tail stalled before the main wing in ground effect dumping the unsuspecting pilots on their noses. Wouldn't want to repeat that fun.

So if you want to land slower in a Thorp it would be wise to consider the aircrafts aerodynamics at reduced speeds and in ground effect to see what can be achieved.

The more I learn, the more I realize how brilliant of a designer JT was. I do not recommend messing with what he did. The main wing stalls first. I sell the 2 inch longer gear that LS came up with.
Cubes

I'll hazard a guess the flaps were down in those cases.

Since Thorp laid out the plane sans flaps but didn't make the gear any longer than he did, there's all the more reason for caution. Still, some of the aerobatic planes sit very nose high on their gear.

Ah, so the original open-cockpit, open-cowling T-18 had no flaps? That would actually make me think that a no-flaps T-18 ought to be fine with the stock gear. Does anyone know if the gear length was changed between the prototype and the early Tiger models to accommodate the flaps?

The T-18 sounds a bit like the Evans Volksplanes in that sense (not often you'll hear anyone say that!) in that the VPs are intentionally designed with a quite flat three-point attitude so you are actually landing substantially over stall speed. Pilots that try to land a VP as slow as you can go then make very embarrassing tailwheel-first arrivals and slap it down hard on the mains.

I would think that a light T-18 along the lines Mark Batchelor and friend's Motor Mouse Pirate models (under 800 lb empty weight) ought to land without flaps at a speed similar to a heavy T-18 with flaps and do fine with the stock gear.

_________________
Matthew Long, Editor
cluttonfred.info
A site for builders, owners and fans of Eric Clutton's FRED

« Voici ce que j'ai fait...vous pouvez en faire autant! »
"This is what I have done...you can do the same!"
--Henri Mignet (1893-1965)

I agree with Cubes . It is a proven design . We have pretty much reached the upper limit with regard to speed and the lower limit with a couple of notches of flaps . MY S-18 has an MT weight of 1069 , powered by an 0-360 , AD prop and with full fuel on a cool day it gets airborne in a little more than 500 feet . Landing ON SPEED and in the groove it will stop in less than 1500 feet . If slower and lighter is the ultimate goal then a LSA might fit the bill w/o trying to undo 50 years of design .

RB

Matthew, I don't know if the gear changed length early on. It's common to use 2 or 3 inches more today; I recall this is to give the longer props of the bigger engines more clearance.

I wonder if any airplane with out flaps really does a "full stall" landing. At the aspect ratio of the typical sport plane, the stall angle of attack is over 20 degrees in free air, but likely a few degrees less in ground effect. Very few airplanes have a combination of long enough mains and high enough tail to make 20 degrees. To my eye, one hold over in the modern T-18 from the early lay-out is the upward sweep of the tail. It gives over 9 degrees on the ground. Many planes are far less; the Zenith 601 is about 6 degrees.

By the way, in my limited tailwheel experience, touching down the tailwheel first is the way to go. The plane rotates forward reducing lift and killing float.

I'd guess an 800 lb T-18 sans flaps will not land as slowly as a 950 lb plane with flaps. I can make a few basic calculations if you wish. Or you can ask a T-18 owner with GPS to record for you the touch down speed solo with no flaps and dual with flaps. Also, it's not a fair comparison. If you can build an 800 lb T-18 without flaps, you can build one with them at, oh, 820 lb, perhaps?

Karl

All good points, Karl, and while I love to dream and scheme, in reality I'd probably stick very closely to the plans as designed. If you are right about the weight difference between flaps and no flaps, then it would be silly not to have them, I just don't have the numbers. I have heard some folks mention an electric linear actuator for the flaps--is that actually heavier or lighter than the stock manual lever in a plane that already has an electrical system? I'll have to take your word for it on the tailwheel landings as I have only flown a taildragger a handful of times and never as pilot-in-command.

_________________
Matthew Long, Editor
cluttonfred.info
A site for builders, owners and fans of Eric Clutton's FRED

« Voici ce que j'ai fait...vous pouvez en faire autant! »
"This is what I have done...you can do the same!"
--Henri Mignet (1893-1965)

Flaps on a Thorp do two things: Add some drag for a better stabilized approach, and lower the nose so you can see better on final. Only 2-3 MPH difference in the stall flaps 30 or clean. The T-18 stalls in a very nose high attitude (level flight) with the tailwheel about a foot above the mains. Makes for very ugly full stall landings. I use about 10 degrees of flap when flying formation on Cubs and Champs to provide a more stable airplane.

Bottom line: John Thorp knew what he was doing. Get a ride in one; you will be amazed.

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Bob Highley
N711SH
SN 835
KLAL

He's right. Get a ride in one and you'll just want to buy one and fly it. That's what happened to me. Lee Walton was kind enough to give me ride in one. That was it for me. I went out and bought one and haven't regretted a minute of it 6 years later. They are outstanding performers. Not to mention the ridiculously low prices you can get one for.

Hmmm, "very nose high" and "tailwheel about a foot above the mains" doesn't quite jibe geometrically, as I see it.

I second the motion: "Get a ride in one." "Amazed" is a reasonable adjective for the experience; it was the finest flying airplane I've been in (not that I've been in a wide variety of airplanes).

Karl