Thorp Air Command - T18.net

I read a couple other build forums for ideas and I see that someone developed a laminar airfoil for the KR2 composite airframe. Has anyone tried this type of developement for the T18? Is the Sunderland Airfoil as good as it gets for this airframe?


Aaron

Harvey Mickelsen modified his nose ribs when he Built Fat Cat. Here's his article in SA. He did a NL write-up, also.

http://www.oshkosh365.org/saarchive/eaa ... _01_02.pdf

I'm not sure how much he increased the Laminar flow, but he felt it improved the overall performance. I don't know if any others made this change. He was kind enough to send me the profile several years ago. When I compared it to the original profile, it looked the same to me. While Lu's nose had a marked difference and also improved overall performance. Fat Cat was purchased recently by someone in Texas and had it for sale, again.
I didn't persue it any further after reading the problems the Q2 had with the GU canard loosing lift in the rain. Now they add VG's to disrupt the laminar flow.

Bob MO

I thought that Fat Cat used the the HB-J-2 profile mentioned in newsletter #50. I tried to draw that profile and it posted on the forum a few weeks back for comparison. To the novice, which I am, there isn't much difference between the 3 profiles and from the reports it sounds like the differences in the air are also subtle.
Someone correct me if I am wrong but from my reading it seems that the S18 profile is the pick, and that there has only ever been the 3 profiles mentioned in the newsletters.
The newsletters mention a detailed report being done on the Lu Sunderland S18 profile I don't have access to it but may provide a useful resource if looking to try a different wing profile

I added some various nose rib pics to my Gallery. Main.....parts&tools.

Here's a pic of both nose ribs. Lu & JT

Given how sharp the leading edge is and the where the maximum thickness of the airfoils sits, it looks like the original airfoil is already pretty close to laminar.

Was the thickest part of the airfoil moved aft from its current location? The way the wing is currently layed out, the thickest part of the airfoil is at the main spar which is at or about the 1/4 chord point. In order to have a laminar flow airfoil, the thickest part of the airfoil has to be moved back to about the 50% chord point. This is done to delay the separation of the boundary layer, which results in a reduction in drag.

The nose rib is the only change that has been done to the Thorp wing. The spar aft stays original with JT's, Lu's & Fat Cat.

I'm not sure about the new airfoil Tom Hunter is using. Lyle Trusty (I think) designed it. Attached is a pic of the tapered nose ribs.

There was an early NL article about a inner wing strake that had 5" added at the fuse. IIRC the rib profile was inverted and this lowered the stall speed, only.

Bob MO

The inner strake you are referring to is the "Trusty Wing" that Lyle Trusty, Tom Hunter and I believe a few other CA guys have or are in the process of implementing. The airfoil on that wing is a completely different profile across the entire chord. The purpose of the inverted rib/leading edge strake is to affectlvely reduce the angle of incidence of the wing which would help out at the top end. Tom Hunter can provide more insight but his airplane has a good 10kts on the rest of us and I'm pretty sure thats not his tail wheel fairing doing that.

In case anyone asks ...

The thought here is that the typical T-18 cruises at speeds well above the original open cockpit designs intent. At these higher speeds the amount of force on the tail required to keep the airplane flying straight and level causes excess drag (ever notice we tend to run out of fwd trim with lw fuel at cruise?). Remember drag from lift is the #1 draggiest thing on an airplane. Reducing the angle of incidence takes load (lift/drag) off the tail and in doing so gives the airplane a little boost in speed.

_________________
Lee Walton
Houston, TX
N51863,N118LW
KEFD

I had forgotten the Trusty fourth wing option untill I ran across the above pic. Wish I had taken more photos. Maybe Tom could update us again sometime. CSA was also building a narrowed single place S18 that I never heard if it was flown or what wing they were going to use. I think they were thinking about a 300hp auto conversion and the Trusty wing.
The NL49.4 had the article about adding the Strake to the orginal T18 wing. Then it kind of disappeared. I guess if it was an improvement there would be strakes on more Thorps.

There are three possible NL topics, Lee.

Bob MO

Someone has not been reading their newsletter(s)!

That's Jim Grahn's Thorp Racer project. Mike Archer has been assisting Cubes with the build design/though. I'm pretty sure Mike is or has built a couple or three Trusty style wings for guys out in CA, or maybe it was just built up a few kits for them. Cubes could probably answer that one.

For those of you who do not subscribe to the NL we have an ongoing series right now "Building the Thorp Racer" in which Cubes has been detailing the build/design of his single place/retractable/auto powered Thorp.

O yeah and the NL 49 blurb was by Bill Johnson. He's the guy who built the conventional/retractable gear Thorp back in the early 70's. I think the reason you don't see the standard wing with a leading edge strake is that the same outcome can be achieved with a stall strip (less complex and lighter too). I know the 4-place Thorp has them too. I talked a guy at Sun n Fun who I believe was the son of the builder of the 4 place. He mentioned some gains from the strakes on that airplane but seeing that was a significantly bigger/different airplane .. who knows if the results apply to standard T-18's.

_________________
Lee Walton
Houston, TX
N51863,N118LW
KEFD

Here I thought I had an epiphany of great ideas for the NL. Even saved it to my T18doc folder and didn't change the title to Tiger Tales 5. Can't wait for #6 so I can steal some more good ideas to suggest.

Bob

The new airfoil ( credited to LT in this thread) is indeed a completely new design. Mike built up a kit which Gus Gorden and Frank Roncelli built up for Bill Cordoza's airplane. It is this only full-up new wing out there. Correct me if I'm wrong Tom, but TommyCat's wing is a hybrid profile. As for the speed, Bill is currently not happy with his new wing. Not sure to what extent, or why. I'm going to try to weasel a ride in it soon. My center section is almost done. It's definitely thicker aft of the spar. It is also mounted at zero degrees angle of incidence as opposed to the normal 1.5 degrees.
Cubes

Fat Cat listed for sale on Barnstormers.com

http://2aw.com/thorp.htm

Bob MO

A good paper on the design of laminar airfoils for low-speed aircraft. In this context, the T-18 is considered low-speed.