Thorp Air Command - T18.net

All,
I'm still considering a T-18/S-18 project, but the wing loading and stall speed is causing me a bit of concern. I'm a low-time pilot and all my time is in C-152s. During the time I'm building I'm sure I'll build hours and can probably seek out an opportunity to get comfortable landing something a bit "hotter" (an AA-1, RV-7, or similar). Still, there's no getting around the math of the situation: if an S-18 stalls at 58 MPH, it will be carrying at least 25% more energy in any off-airfield landing than if it could touch down at 50 MPH. The S-18's 58 MPH stall speed is not unreasonable (it's certainly about the same as an RV-7, etc), but I wonder if anyone has explored the tradeoffs of going for a lower stall speed (and probably accepting higher induced drag/lower top end). Lower stall speed can only come from:
1) Lower weight (I don't see much hope for meaningful reductions in empty weight of the T-198/S-18)
2) More wing area
3) Higher ClMax for the wing (maybe more flap area? Or, split flaps can sometimes offer higher ClMax than plain flaps, aren't much harder to build, and they could extend under the fuselage)

I like the aircraft a lot (and will have more "newby" questions), I don't want to double my building time with unwarranted excursions into new areas, but I just wondered if this is something that others have already addressed.

Thanks for your patience.

Mark

Hi Mark, I am a low time pilot, got out of the Skyhawk and into the Thorp. It was very obvious going forward at that point That the designer of the Thorp was in fact One of the best aircraft design engineers of all time. It does as it was designed to do exactly and it does not deviate from the expectations of its designer. It is a pleasure to fly, it is fast, but it is also very docile when the need arrises at least that is my experience with this airplane. I have flow it now for 180 hrs which is not what I would consider to be very high time, and I know for a fact that there are Thorpers out there that are by far better pilots than I will ever be. Have you had a chance to get a little stick time in one by any chance?? I Do believe that you would be pleasantly surprised at how nice this Plane handles and how well you would do transitioning to the Thorp. Ask all the questions you like that's what we are here for there is no such thing as a dumb question(except the ones I ask)....Dan

Mark,

You are fearing something that is not really an issue.

When the first Thorp Flew with the the big Tiger on the side and the plane got the name...Tiger...I was working on my plane in John Thorp's shop in Burbank, CA. My only time was in C-150 and C-172.

John Thorp was Very Irritated that the first Thorp was named Tiger since he said it put in peoples mind the thought that the plane was difficult to fly.

I went on and finished my T-18 and have about 600 hours on it. I have never found it to be difficult to manage in landing or in flight attitude.

And as Dan said, the plane is a delight to fly. I have flown the RV's and the difference is amazing when it comes to control harmony and aircraft stability.

Mark,
It sounds like your primary concern is safety during an off airport landing. I'll address that in a moment but also need to join in with Tom and Dan, the T-18 is not a "Tiger" at all. I'm guilty of continuing the nickname as we all know the name of the current newsletter. Personally I feel the airplane is nearing the 50 year mark and if people haven't realized it's just a name (purely out of convienience as it starts with "T") by now then o-well. The thorp is anything but a tiger, as both Dan and Tom point out, the plane is a dream to fly.

Now on to the off airport issue. I rebuilt a Thorp now owned by Eric Smithhenry up in IL, that airplane was very light (813 lbs), and still stalled at 60. Thats a function of the original airfoil, there's a speed at which it just plain doesn't fly anymore. My point here is that airplane flies like a cub, and due to its low weight it's inertia iis very low, especially on rollout. It is easily landed in 1000 ft (approach in that airplane is flown at 80) and once the power is pulled off the airplane pretty much stops on a dime. Once you get out of 150's, 172's, Cherokees and most other trainer type aircraft you get a lot heavier and thus regardless of stall speed you're still a heavy brick rolling through a field, down a street etc (off airport). I'd much rather be in a lightweight T-18 then spam can weighing nearly twice as much. Once the wheels hit the ground its all to a large degree about weight, the lighter it is the sooner it stops. I'll argue that a 1000 lb T-18 that stalls at 60 and a 1500 lb spam can that stalls at 50 are in the same category once you plant the tires on the ground, heck the Thorp might even stop quicker.

I'd definely seek out a ride in one, you'll see what we mean.

_________________
Lee Walton
Houston, TX
N51863,N118LW
KEFD

Mark,
I believe as long as you get a good check out on a Thorp, you will be fine with your experience. Flying the Thorp is like swimming. You can't read a book or just talk about how it flies and think you will be able to fly this plane well. There are a number of good check pilots in the group that could help you out in this respect.

Jim Mantyla

All,
Thanks for the feedback. I'll find a way to get some time in a T-18, that'll be the best way to get comfortable with the approach/landing qualities.

Mark W.

I think the biggest safety improvements in most light GA airplanes is with secure shoulder harnesses.

Most deaths occur due to head trauma by the person's head hitting the door post or canopy rail etc. So keeping in position and actually wearing a helment would be the two single biggest safety improvements from a crash worthiness perspective a person could do.

I know helicopter pilots always wear helmets. So do fighter pilots. So why not other GA pilots? Don't we all want to be a fighter pilots and what better plane than to look like a sexy fighter pilot than a T-18? Bent wing and sliding canopy just like a F4U Corsair!

Also from a crash perspective getting the fuel out of the fuselage might be a consideration. But you would be trading the off chance of an off field crash situation with the maybe more likely failure of an electric boost pump to get the fuel from the wings to keep the engine running, versus the absolutely reliable mother nature gravity feed. I guess a person has to "pick their posison". A compromise might be a very small header fuselage tank of say 8 to 10 gallongs. That way if the electirc pump failed a warning light or something could indicate the failure and you'd still have an hour of flight time or so to land. And in a crash situation you'd have limited the fuel to 8 to 10 gallons versus 30 or more gallons.

Just thinking out loud.....

Has anyone tried winglets to keep the wing performing longer and perhaps lower the stall speed a tad?

Doug Shinn, please repost the visual!

_________________
Lee Walton
Houston, TX
N51863,N118LW
KEFD

Graham, the Thorp stalls at 55-65 (some heavy ones higher). Both of those speeds will put you into 90% of the runways in this country. I fly a straight John Thorp designed T-18 and have never felt that it's does not go slow enough.

_________________
Lee Walton
Houston, TX
N51863,N118LW
KEFD

Ity is my understanding that winglets won't do much for a low aspect ration wing - It also looks butt ugly


I do $100 hamburger runs with a guy in a 65hp Cub & although he giggles at my angle of attack, I am comfortable & control-able with him in formation. One of the big safety items, in my mind, is that the plane talks to you when it is about to stall. A strong clear buffet.

Find someone who has some time in a T-18 go up high & play around. I think you will find the overall performance / handling (both fast & slow) to be one of the best kept secrets around.

I still don't understand how the market puts RV's well North of $50k & the T-18 in the $20-30's
but it is what it is & makes it a bargain for those smart enough to consider a T-18 .

Crash survivability is a function of airspeed, angle of arrival, and crash worthiness of the aircraft. The Thorp is reasonably close in airspeed to most higher performing aircraft. Angle of arrival is up to you. Where the Thorp excels is in crash survivability. I know of several crashes where our folks have walked away. The airplane was designed by an aeronautical engineer. It is more survivable than most experimental aircraft on the market, even the overly popular ones.
Cubes

My fear is a fear of ending up upside down and not being able to get out. I know there is a roll bar so I'm not too worried about being crushed. But getting out especially if a fire. I realize this is an issue with a LOT of planes.

Has anyone made a side baggage door that for at least certain size smaller people could wiggle thru to get out?

Make sure you have a canopy release handle on the OUTSIDE as well as the inside (Thorp latch) . Have a canopy breaker/harness cutter within reach . I keep mine clipped to my shoulder harness . A fuel valve that you can reach (not one installed on the bottom of the tank) . A small halon fire extinguisher installed in the cockpit . I think you would be hard pressed to get out thru a "baggage door" if it were installed . Having to get around the seats , thru all the crap you have packed for that Fly In you are attending , opening that "door" and trying to crawl out . Hopefully there are folks near by that can lift the tail so you can egress the AC . All the problems encountered are compounded if you have a passenger in the right seat ! Probably best to have him/her jump out at 50ft AGL to improve your chances !

I think the key thing we need to do according to a very wise test pilot (Bob Hoover) is "Fly the aircraft as far into the crash as possible ." I've tried to maximize my chances of a successful egress by incorporating all of the above (not the baggage door !)

RB

The windscreen roll bar is not foolproof. As I read (no pictures) the NTSB report, poor Ken Brock found that out the hard way.

As "Cubes" has pointed out, the T-18 appears to have good crashworthiness. One worry with similar designs is the fuselage tank, which if it ruptures can lead to a nasty fire. In surveying the fatal T-18 crash reports at NTSB, it's remarkable how few involve fire; most severe (that is, fatal) crashes don't lead to a fire. I suspect it's a byproduct of the A frame which ties the engine mount, mains, and fuselage together; this necessitated a strong cowl ahead of the windscreen to carry loads to the top longerons, and the tank is under that structure. By comparison, the much slower Zenith 601 HD has a large number of fatal fires.

However, the same survey of those NTSB reports has one notable trend: stall/spin. This I imagine is due to the airfoil characteristics. The NACA laminars are not noted for good stalls; their wind tunnel data hints at this. The Sunderland modifications may help here --perhaps those who've flown both will comment. The Riblett laminar airfoils are said (I have seen very few comments) to have softer stalls as well. A stall warning vane or other angle of attack gauge might be a wise addition to a T-18 panel.

Ultimately, as I see it, the T-18's wing loading is what gives it a high stall speed. It probably results from the original T-18 being laid out as a 600 lb machine. It proved strong enough to take far more, and most are so built.

Karl