Thorp Air Command - T18.net

Just purched and flew a T-18. I have previously built an RV and owned a MII for 10 years and 700ish hrs. Getting use to the new bird was exciting as I did taxi testing in a pretty good crosswind. I've read many post and document here and am grateful for all the info available. My first take off was followed by a low pass to get used to things. Upon landing I became very anxious when I found the stick at the aft stops in what was admittedly a slightly nose high attitude. The tailwheel touched first, but not too bad, just a small bounce. I had two notches of flaps and had it about 85 indicated on short final ( I am suspect of the static system). The seats were not preventing aft travel as was my first thought. Still getting use to the 3 point picture but am concerned about the lack of reserve authority. I flew a 800 mile x-country that first day, after a little practice, and made sure I only landed on long wide runways. Time to get out the protractor! I know you guys can help me to rig it right.

Denny

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Denny
N78DW at W-29

The physical aft stop for the pitch control is located between the seats just aft of the walking beam. Make sure there is not something preventing full travel there as well. If rigged correctly you should have no lack of stab control.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

Denny: Sounds like you probably need to check a few things.

1. Is the W & B correct ?
2. You are concerned about the static system? You can test that yourself. You can also test the pitot system yourself. I did it prior to my inital mode C transponder check. I found the procedure to test the system on the Van's site. When I tested my static system a found a leak comming from a fitting on the back of the VSI. Put a litle fuel lube on the fittings.
3. Do you have a set of plans ? There is a drawing that gives the amount of up and down travel of the stab. (can't remember the drawing number off the top of my head) in degrees.
4. There is an aft stop (and foward stop) in the area of the walking beam. When you check the stab travel (using the drawings) it may be possible the aft stop is too long and can be adjusted.


800 mile x-cty first day ! OH MY !

RB

I'll find the stop under the beam, thanks! Definately not enough stick travel aft.
Just got back from some touch n go practice. Did most with single notch flaps to keep aft stick authority.
Weight and balance just done last week. Don't have plans.
Indicated AS doesn't jive at all with GPS. Averaged about 160 on the X-country but the indicated 120 to 125mph most of the flight. During decent it indicated 140 when gps said 178. Felt pretty accurate when in the pattern but, judging from my landings, I'm starting to think my approaches are too fast. The sink rate comes up pretty good at 80 indicated. Pitot w/ static is atop the vertical stab, but not for long.

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Denny
N78DW at W-29

When I had my inital transponder mode C check (static system) the young man also checked my pitot system with his calibration unit. Both systems were well within limits and he charged $125.00 for the system check out. The fact he had to dive from Gillespie Field (KSEE) to Brown Field (KSDM) which is about a 40 mile one way trip, I thought the price was very fair !

RB

The top of the vert tail pitot static is by far the most accurate location. Have a look up there and make sure the ports are clear. Sound like the static side is fine, make sure your pitot side does not have a leak.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

That's sound advice. Already checked the ports but did have the tail off twice last week.

Back to the stabilator travel and the stops. If I allow more travel, the seat will become the stop. Is there any way to adjust at the stabilator?

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Denny
N78DW at W-29

Btw .. Not an expert .. But just to clarify my diagnosis, alt reading ok, roc ok (staitic), as off .. Sounds like either pitot leak or old tired airspeed indicator.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

Yes you can adjust that but beware ... The plane has several hundred hours on it .. Let's make sure it's not operator error (please don't be offended Denny).

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

ROC bounces on occasion on take off and I am climbing a bit when it shows level. When I trim to hold altitude by alt (and gps), roc show a very slight decent. Glad to hear it a good pitot location. These T's are a little different than what I am used to. I will be checking the tubes and connections carefully.
Am I thinking clearly if I consider increasing the length of the stabilator control tube?

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Denny
N78DW at W-29

Hi Denny, and congrats on the T-18!! The push pull tube is a specific length from the pivot bolt centers on each end of the tube. You can check this demention on your tube and make sure it is correct,if it is to print, I would look for some other culprit and leve this tube be. 80'mph over the numbers with one notch and it should tip toe onto the tarmack. All things being to print,a little practice, and it's very friendly going......T pilots chime in here......Dan

Lee, Never offended with advice intended to keep me safe, thanks . I do need mor practice. Been flying Pitts S2-C and very used to the old M II. I think I am a bit spooked by having the stick travel to within 1/4" of the stop during flare and 3 pt.

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Denny
N78DW at W-29

As has been noted before, you need to check your plane with the plans. If your plane came with out them, you can get a set from Eklund Engineering. ROC meters have adjustment screw on the front. Make sure it reads level on the ground. Many T-18s just use cabin air for the static. This causes variations in static with attitude changes many of us just live with that. As for the landings; this ain't a Cub. Try a tail-low wheel landing. You will find it much more comfortable.

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Bob Highley
N711SH
SN 835
KLAL

If the seat was built to plans (you really need a set of plans if the plane did not come with them), then it has a seat fitting with 3 positions to adjust the seat travel...is it at the aft position ? Like Dan said I would stay away from the push pull tube until all other areas have been reviewed and found to be correct. As far as the pitot static system, if you have a Mode C transponder that requires the 24 month inspection I would just have a test box hooked up and have the entire pitot static system checked. It will tell you within minutes if you have a leak. Otherwise you will spend hours trying to track down a possible problem. You can also blow up a party balloon and place it over the pitot tube (attach it with a quick tie). Note the speed on the AS indicator. There is an allowable bleed down rate (I think it is in AC-13 ?). As far as the static system, not sure how you would do the tail installed static. If the static port were on the side of the AC you can attach a suction cup over the port and place modeling clay around the edge of the cup to help seal and hold the cup in place. Then with a large syringe attached to the suction cup with a piece of surgical tubing you pull some vacuum, crimp off the hose and note the altimeter. Again there is a bleed down rate (I think it is in AC-13 ?) for the altimeter and VSI.

Again I would check the stab rigging by making a template from the plans and taping it to the side of the AC. I would start here before tearing the AC apart ! If the rig is off then I would go to the stops by the walking beam and check them. Also while in there where the stops are I would check to see if there is any interference from wires, sheet metal any type of fittings the builder may have installed. If all is good here, then I would look inside the tail to see if the stab. balance beam is hitting anything ?

RB

Thanks Rich, I just downloaded stabilator rigging diagram and instructions from an old newsletter (this site is great!) and will check it first.
The seats do not travel and simply rest on angles. The stick stops just before hitting the seat (very close). When trimmed for 90mph the stick sits neutral, an inch or so from the seat.
I'll be checking the pitot lines carefully. I did have the vert tail off twice last week when replacing the trim Brg. Maybe a tube is loose.
I was skeptical of the pitot location because I was seeing the AS read 40-60 mph while doing taxi tests. I estimated the speed to be around 25. The tail was down.
Thanks Bob, sometimes its hard to do the basics when trying to follow too many variables. My best landings yesterday were just what you suggest. When the wheels touched, in what I thought was a 3 pt attitude, I just relaxed back pressure a bit and held them on. I've been doing mostly 3 pts for many years now. I don't think this thing is finished flying in its 3pt when the sink puts it on. I have the short gear and a fairly big Scott tw. Are there any T18 drivers in the Mid Atlantic?

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Denny
N78DW at W-29