Thorp Air Command - T18.net

I

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http://www.dixiefriedfabrication.com/

Lou,
Do me a favor, put an angle finder on your flaps at 2 notches. If it is over 30 degrees, don't use it. The original design had 40 degrees. That blanks the tail. Trust me, you do not want the horizontal blanked at low altitude. If it is 30 degrees, you are most likely feeling your stall strips nibble the tail - which is ok. What speed does this happen?
Cubes

Lou,
How fast were you going when you got the stick shake? If you're close to 100 mph with 2 notches in you'll get a little wash coming off the flaps on the stab causing the stick to shake, that's not uncommon.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

12 years ago when I first was learning to fly N6CM I experienced the "bunting" that u describe. What we figured out was that it was only occurring with full flaps and being caused by excessive final speeds. If we were 95 mph plus the more u pulled up the more the noise bunted. Very exciting to say the least. Not sure given your airplanes weight and configuration, but our T-18 is 95 mph downwind and 85 to 90 final. With me and a co-pilot I keep my finals in the 85-90 range and my landings are better. Come by my hanger at Corona airport and we can take N6CM around the patch and my brother Chris and I will show u. Our local grapevine told us u had flown and about the bunting issue. We can help u solve it. Also heard your new engine is fast. Good, now we got another T-18 in the area to go beat up on the those pesky RV's.

Happy landings!!!

Brent Schultz
N6CM
KAJO

I have had that little stick shake since day 1. It will happen twice, once just before stall speed is reached and then the second time just before she breaks. Somtimes I can get that little shake if I'm right down close to the Tarmac and I'm just holding it off,just as the wing gives up I get that little growl,or, stick shake. It's kinda like a stall buzzer, if your a couple inches off the tarmack holding it off it will growl just before you make contact. Dan

N18GR has the two flap positions at 20 and 30 degrees. In common with what was described above, I can pull the first notch at 100 MPH, but if I pull the second over 85, it will tend to bunt, and if pulled at 100 MPH it gets real exciting--a definite bunt. So if I want to use the second notch of flaps, I make sure that the airspeed is no more than 85 MPH. I can come in nicely over the fence at 75 and make a great wheel landing with the second notch of flaps. N18GR is a T-18 originally flew in 1978 built to plans.

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Dave M
Sacramento
ex-T-18 owner

I had previously found what might be a related post on the old Thorplist which I have copied here.
It may add something to the discussion.
Cheers
Stuart


--- In thorplist@yahoogroups.com6 "David Prince" <dlprince@a...> wrote:
>
> I saw the photos of N71XP (Jerry Hajek). Jerry6 have you noticed any
> difference with the flap gap seals in place?

David6
Long time ago I got the following kind reply from Mac:
======
>Howdy Mac6
> From your website:
>
>"... and the tips cut and recontoured to reduce the left wing
heaviness
>common to Thorp T-18s when flown solo..."
>
>The LH tip needs to be lowerd at the aileron juncture by about 3/8
inch.
Leave the outboard edge stock. This should line up the ailerons and
tips
when in flight. I would suggest you do not paint them till after you
have
flown with the stock tips6 then adjust them to suit.
Using the flaps to trim the aircraft as many do is a poor solution.
Better to incorporate a bungee type trim. The aircraft will always fly
left
wing low with just the pilot. With 2 up it will fly level.

The -G engine works fine but needs a prop flange stiffener. If you
are
using a wood prop you can use the weight on the crank anyway. The
stiffener
should be between the flange and the engine case and can be copied from
the
T-18 newsletter book. The oil sump can be replaced directly with an
0290-D2
sump and an Ma3 or Ma4 SPA carb. I prefer the MA-4 as the prop should
be
configured to turn up 3000 RPM at sea level. This will produce close
to
150BHP. A book on the conversion was published by EAA back in the
60's.

Seal the gap at the leading edge of the flaps with foam rubber or
with
silicone. Tape saran wrap on the flap leading edge and allow it to
close
against the liquid silicone. When cured you will have a perfect seal.
I
also recommend sealing the aileron gap with a thin bead of silicone
applied
to the underside against plastic tape applied to the top side. The
aileron
effectiveness at low speeds will be much enhanced.

There can be NO play in the elevator anti-servo tab linkage. The
inner
doubler tube must be properly installed6 outboard counterweights
solidly
attached6 and the rivets holding the skin and doulblers to the tubes at
the
inboard end must be solidly set for they will loosen with usage.

You will have a very good flying aircraft when finished.


Mac
=========

After getting some great pointers from Jim at KVIS I decided to do some laps. I

_________________
http://www.dixiefriedfabrication.com/

Try loosening the flap cables before you re-engineer the flap lever. Check your flap deployment rig by putting them down (on the ground) and sighting down the trailing edges.

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Bob Highley
N711SH
SN 835
KLAL

Lou also have you looked any further at installing "flap gap seals" as mentioned in the earlier thorp list. I haven't seen any discussion about it on the forum recently but there might be some value in that modification, i can't comment as to the potential benefit, if any, others may be able to. In any event you will want to adjust the flaps to stop at the recommended 30 degrees
Stuart

Guys,

I have electric flaps and I find that when the stick starts to buzz, I just reduce the flaps enough to eliminate it. I typically limit my flaps to 30 degrees solo and 35 with a passenger. (35 degrees is max for my plane.) I have a sticker on the front edge of the flap that shows 10 degrees and 30 degrees. The only thing is that it's hard to see at night.

Jim Mantyla

I have electric flaps as well and have never experienced the a/m bunt ...

I start flaps at about 90 kts, just a few degrees at a time and slowly bring em down as I decelerate through about 80 kts looking for 75 kts on base/final....70 kts over the fence and 65 or so in the flare

Stug,
The flaps on the T-18 are Fowler flaps. The gap is supposed to be there when they are deployed.

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Bob Highley
N711SH
SN 835
KLAL

Hey Lou,
I wish we had this discussion at KVIS. Before you do anything, take a look and make sure you have a bottom on your wing fillets (if you have them). Air has a way of getting up under those fillets and causing a bunt.
I do recommend max 30 for the flaps, though. I'll tell you why when we meet again.
Cubes

Bob the "gap" mentioned somewhere in past threads i was referring to was the one at the end of the flap where it meets up against the fueslage. I have seen this done on a number of local T18s, usually with some tape. it isn't so much covering up a gap but an infill for the end of the flap which gives the end more of a flush finish which would be aerodynamically cleaner, presumably helping to maintain the airflow going over the tail with less turbulence. Does that make more sense?
Stuart