Thorp Air Command - T18.net

The reason I ask, is because the 40 page POH I got with my current Thorp T-18C, N921JK, had the following in it:

"The glide path may be steepened as required by side slipping with full rudder and opposite aileron with flaps in a extended position (Note: The T18 will "kick back" at the controls and attempt to return to wings level if slipped too steeply.)"

I assume the POH came from Jack Kenton, the son of the builder, John Kenton. There was an extra owner in between me and Jack Kenton. Of course, Jack had over 1000 hrs and 30 years of flying the Thorp. Not sure if Jack is still around.

My experience in doing slips is as follows: I remember as a student pilot in Dec 84, after already trading my C-150 for my first Thorp T-18, N711RF, that I tried to slip on final at Chino, while Bill Warwick was in the right seat checking me out. He gave me the death stare, saying don't do that. I didn't do that. After landing, he said I would be safe. I use to love doing slips in my C-150. I got my private pilots license in 85, by a CFI who was a former F-4 Phantom pilot in Vietnam, who liked to teach massive slips in the school's C-150 for the training. It was fun. Although I have about 200 hrs in Thorps now, at about 100 hrs on my first Thorp, I tried to slip the Thorp again, she kicked back strong. I haven't done a slip since then, figuring the Thorp dropped like a manhole cover anyway.

Decades later, I became a rusty pilot. Since then I've finished up my second BFR last March, I became current again by studying Rod Machado - all private pilot material - esp. How to fly, Jason Miller - The Finer Points, PilotWorkshops - most of everything - including flight simulation, and of course Budd Davisson - using P.A.S.T. for fast landing taildraggers.

Basically, I miss the the control I had with slips. I know, a stabilized approach with flaps is the standard now, but of course, you don't retract flaps on final. I'd like to get into shorter fields, which means a short approach and not hitting the cross at Flabob. Maybe even some grass fields.

Thanks for the help,
Shack
N921JK T-18C Flying
N711RF T-18 Sold

Love this edit option, wish I had seen the button before.
Ryan and Bob, A Big Thanks for saying slipping is ok for you!
Need to go further by asking everyone: Do you slip with no flaps, partial flaps, or full flaps? Maybe throw in the sink rate.
You guys are awesome, just might save my life.

Thanks again,
Shack

If its not OK to slip a Thorp, I didn't know it. I slip mine on final when I need to slip.

Ryan, do you use full or partial flaps while slipping? Full flaps help me out a lot slowing down on the runway.

Thanks,
Shack

I slip mine all the time. My flaps are set at 30 degrees when full down. The original 40 degree setting might yield different results.

_________________
Bob Highley
N711SH
SN 835
KLAL

Bob, my max setting is 30 degrees also, so I take it, you're saying slipping with 30 degrees is ok. If that's so, what type of sink rate are you getting, slipping with full flaps?

Thanks,
Shack

I can’t tell you the sink rate because I’m looking at a face full of dirt, but, yes, I slip with flaps 30. And yes, it comes down like a manhole cover. Just make sure you do not slow down too much. A stall with the controls like that would be quite ugly.
Flaps 40. Don’t ever use them. In a stall, the horizontal is blanked. Zero recovery until flaps are brought up! Ask me how I know.
Cubes

Cubes, that's the answer I was looking for, the best of the best. I will definitely heed your warnings. Of course, what's so great about slips is that you can put'em in or take'em out, usually a no-go on taking flaps out. However, you are Cubes!

Thanks for the awesome answer!
Shack

Practically speaking, I terminate slips no later than 100 feet AGL, whether it be a Thorp or a J3 on floats. Also, slips are not an all or nothing operation. Akin to spoilers on the big boys.

_________________
Bob Highley
N711SH
SN 835
KLAL

Bob, I was thinking the same thing, use what slip is needed, fine tune it as you land. That 100 feet AGL termination sounds like a good rule to go by. I do believe the quote "A Good Pilot is Always Learning".

Thanks for making me better,
Shack

I slip mine when I need to. My flaps go to 40 degrees but I am lighter on the nose than many. I have also stalled mine several times with full flaps without incident before I encountered any info to the contrary. Based on what I have read in the news letters I wouldn’t want to try 40 degrees of flaps if I had a metal or constant speed prop. I don’t think I have stalled it since I moved the battery to the firewall.

_________________
Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

Jeff, I always wondered about the 40 degree flaps, of course N921JK stops at 30. She has a 68x72 Ted Hendrickson wood propeller, 150 hp O-320-A2B Narrow Deck, 944 lb empty weight w/oil, battery behind the baggage, 57 kn stall. Do you find yourself landing in a shorter distance with the 40 degree flaps?

Thanks,
Shack
N921JK T-18C Original Airfoil Flying
N711RF T-18 Sold

Edit - I Changed to word Mine to She

Absolutely! 78WG slips alright, although it is not my default maneuver. Typically she's already coming down like a brick. I do a fair bit of engine out practice in it and I believe it's a critical tool for just such occasions. I use about 1/2 rudder and she'll start talking to you around 3/4 rudder (and I'm not keen on exploring any limits). I'll slip my luscombe and work airplane to the flare, but I usually kick the Thorp straight about 250 feet short of the threshold.

-Andy

My understanding is the warning about flaps 40 is not necessarily stall related. The tail ( on a non-canard aircraft), continuously produces down force. It has an angle of attack to the oncoming air just as the wing does, and it also has a critical angle of attack at which it will stall (and stop producing down force). If the tail stalls, the airplane will rapidly pitch down, as the tail downforce reduces or ceases to exist. It you get a hard pitch over close to the ground, it could be fatal.

Why do 40 flaps potentially cause stabilator stall? When flaps 40 are deployed, it creates more downwash than flaps 30. Imagine curved downward moving air over the stabilator. The stabilator is creating lift towards the ground...if you can call that lift. The leading edge of the stabilator also is very sharp. When you deploy flaps, the aircraft naturally pitches nose down. At a given speed, that will require a bit more “up” stabilator .....that results in more angle of attack that the stabilator sees. If you speed up with 40 flaps, it will create even stronger downwash....and more angle of attack. At some point, the critical angle of attack of the stabilator may be reached, and if so, it will stall. If that happens, and the plane rapidly pitches over, you are now pointed towards the ground with rapidly increasing airspeed and basically no stabilator to save you. The only option is to immediately retract flaps to get the stabilator “unstalled ” so it can stop the houses from getting bigger. Limiting flaps to 30, prevents the stabilator stall from happening....even if you exceed flap extension limit speed. I would imagine that depending on a particular aircraft’s CG (and stabilator leading edge radius), this bunt over may not happen even at flaps 40. But if it does happen, I understand it is quite violent. So seems prudent to stay away from flaps 40, particularly close to the ground.

I may be mistaken on the pilot, but think I remember John Evens having this happen during the test flight phase, at a safe altitude.....and was eye opening!

The only Thorp I have flown is the one I own so I can’t speak to performance comparisons. All I know on the subject is covered in the newsletters and in this forum. I would not modify one built for 30 degrees of flaps to give more because of the potential risk. Every homebuilt is different. Another airplane set up exactly like mine could have a serious issue. My bird had a thousand hours on it when I bought it and has had an O-290, Ford V-6 and an O-320 so I haven’t seen the need to adjust the flight controls from original. The previous owner gave me a pretty thorough briefing on the airplane so I could fly it solo without having ever been in anything like it and survive.

Mine sits too much these days so I expect I will be selling it before long because I don’t like having things around that I don’t use. It’s too hard on them.

_________________
Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

Thank y'all for the help. To be safe, I will keep the Thorp's flaps at 30 degrees. Was thinking 40 might shorten the landing distance, but that appears to be too risky. Of course, will exercise caution while forward slipping or even side slipping the Thorp. As others mentioned, it might be more prudent to end the Thorp's forward slip on final at 100' or 250' AGL.

Shack
N921JK T-18C Orig Airfoil - John Kenton built, son Jack owned 26 years, I own/fly now.
N711RF T-18 - Roy Funk built, I flew about 200 hrs - Sold

Deleted to edit: trying to stay more on the subject.