a question for Thorp T18 owners

[Stealth Pilot[_2_]]

guys
if you stall your aircraft with power on what does it do?
are there any situations where a T18 will do other than a descending
dive after a stall?
also what aerofoil was used on your aircraft?

nothing sinister about this. we suffered a double fatality the other
day. there is a lot of utter nonsense floating around about this but a
perusal of a video take during the last minutes suggests that the
aircraft flipped over into a loop for some reason,the video then shows
that it rolled inverted during recovery and then made a ballistic
descent to the impact site.

my interpretation is that the aircraft stalled, either with power on
or as a result of recovery efforts, flipped over backwards then fell
out into a stalled loop, one wing unstalled causing the aircraft to
roll inverted, then when inverted stalled again. from there in a
stable inverted stalled condition the aircraft curved down in a
ballistic trajectory until the planetary collision.

I'm reasonably certain that I can explain the flight behaviour in
sound aerodynamic terms but I'm unsure of the initial stall behaviour.
the comment that the T18 can flip over onto it's back comes from two
T18 owners. are their aircraft typical or atypical?

I'd appreciate any first hand comment from T18 pilots.

Stealth Pilot

[Charlie[_2_]]

Stealth Pilot wrote:
> guys
> if you stall your aircraft with power on what does it do?
> are there any situations where a T18 will do other than a descending
> dive after a stall?
> also what aerofoil was used on your aircraft?
>
> nothing sinister about this. we suffered a double fatality the other
> day. there is a lot of utter nonsense floating around about this but a
> perusal of a video take during the last minutes suggests that the
> aircraft flipped over into a loop for some reason,the video then shows
> that it rolled inverted during recovery and then made a ballistic
> descent to the impact site.
>
> my interpretation is that the aircraft stalled, either with power on
> or as a result of recovery efforts, flipped over backwards then fell
> out into a stalled loop, one wing unstalled causing the aircraft to
> roll inverted, then when inverted stalled again. from there in a
> stable inverted stalled condition the aircraft curved down in a
> ballistic trajectory until the planetary collision.
>
> I'm reasonably certain that I can explain the flight behaviour in
> sound aerodynamic terms but I'm unsure of the initial stall behaviour.
> the comment that the T18 can flip over onto it's back comes from two
> T18 owners. are their aircraft typical or atypical?
>
> I'd appreciate any first hand comment from T18 pilots.
>
> Stealth Pilot
I'm a former owner. It's a great flying plane (90% of an RV-6 at 1/2 the
price) but it has a relatively sharp leading edged airfoil & will bite
if provoked. It's not a 'certified' design & it's not required to meet
the nanny level of flight characteristics of a C182 or Cherokee.

I'm building an RV-7 (bigger cockpit, higher gross weight) but I'd own
another Thorp in a heartbeat if one came available.

Charlie

[Billgran]

"Charlie" > wrote in message
...
> Stealth Pilot wrote:


>> are there any situations where a T18 will do other than a descending
>> dive after a stall?
>> also what aerofoil was used on your aircraft?
>>
>> nothing sinister about this. we suffered a double fatality the other
>> day. there is a lot of utter nonsense floating around about this but a
>> perusal of a video take during the last minutes suggests that the
>> aircraft flipped over into a loop for some reason,the video then shows
>> that it rolled inverted during recovery and then made a ballistic
>> descent to the impact site.
>>
>>>>
>> I'm reasonably certain that I can explain the flight behaviour in
>> sound aerodynamic terms but I'm unsure of the initial stall behaviour.
>> the comment that the T18 can flip over onto it's back comes from two
>> T18 owners. are their aircraft typical or atypical?
>>
>> I'd appreciate any first hand comment from T18 pilots.
>>
>>

Here is a comment from a friend who has built a Thorp T-18 and flies one
regularly.

The Thorp T-18 Has had several variants of airfoil and wings, Being a
homebuilt some have stall strips, some do not. So stall characteristics
vary. It is one of the very first "high performance" homebuilts and has a
laminar flow wing. A 'stock' T-18 has an abrupt stall break with ample
aerodynamic buffet as a warning. In a full stall it can easily drop one
wing very quickly. Trying to pick the wing up with aileron only can
aggravate the situation. A secondary stall on attempted recovery can occur
if over-aggressive stick pull is applied. The stall strips applied to the
inboard portions of the wing will increase the early warning buffet and also
soften the stall. Some Thorps pilots experienced a pronounce nose pitch down
or 'bunt' with full (40 degrees) flap. On later Thorps the flap travel was
limited to prevent this.
Accelerated stalls also occur at higher speeds & forces. Wing drops will
then also occur quicker. It is a very aerodynamically clean plane & picks up
speed QUICKLY when nose is pointed down. An excited pull on the stick can
bend things or stall the plane.
I am assuming this is the one that went down in Australia.. As I understand
the owner was fairly new to Thorps. The overall handling of a well built
Thorp is honest , but it is to be considered a high performance plane and
cannot be flown like a 172. Either way, my condolences to friends and
families of all involved.

[Stealth Pilot[_2_]]

On Tue, 2 Dec 2008 06:54:22 -0500, "Billgran" >
wrote:

>
>"Charlie" > wrote in message
...
>> Stealth Pilot wrote:
>
>
>>> are there any situations where a T18 will do other than a descending
>>> dive after a stall?
>>> also what aerofoil was used on your aircraft?
>>>
>>> nothing sinister about this. we suffered a double fatality the other
>>> day. there is a lot of utter nonsense floating around about this but a
>>> perusal of a video take during the last minutes suggests that the
>>> aircraft flipped over into a loop for some reason,the video then shows
>>> that it rolled inverted during recovery and then made a ballistic
>>> descent to the impact site.
>>>
>>>>>
>>> I'm reasonably certain that I can explain the flight behaviour in
>>> sound aerodynamic terms but I'm unsure of the initial stall behaviour.
>>> the comment that the T18 can flip over onto it's back comes from two
>>> T18 owners. are their aircraft typical or atypical?
>>>
>>> I'd appreciate any first hand comment from T18 pilots.
>>>
>>>
>
>Here is a comment from a friend who has built a Thorp T-18 and flies one
>regularly.
>
>The Thorp T-18 Has had several variants of airfoil and wings, Being a
>homebuilt some have stall strips, some do not. So stall characteristics
>vary. It is one of the very first "high performance" homebuilts and has a
>laminar flow wing. A 'stock' T-18 has an abrupt stall break with ample
>aerodynamic buffet as a warning. In a full stall it can easily drop one
>wing very quickly. Trying to pick the wing up with aileron only can
>aggravate the situation. A secondary stall on attempted recovery can occur
>if over-aggressive stick pull is applied. The stall strips applied to the
>inboard portions of the wing will increase the early warning buffet and also
>soften the stall. Some Thorps pilots experienced a pronounce nose pitch down
>or 'bunt' with full (40 degrees) flap. On later Thorps the flap travel was
>limited to prevent this.
>Accelerated stalls also occur at higher speeds & forces. Wing drops will
>then also occur quicker. It is a very aerodynamically clean plane & picks up
>speed QUICKLY when nose is pointed down. An excited pull on the stick can
>bend things or stall the plane.


>I am assuming this is the one that went down in Australia.. As I understand
>the owner was fairly new to Thorps. The overall handling of a well built
>Thorp is honest , but it is to be considered a high performance plane and
>cannot be flown like a 172. Either way, my condolences to friends and
>families of all involved.
>
correct assumptions. owned the aircraft 2 years but low hours on it. a
competent careful pilot though I believe.

the pitch up was the thing that intrigued me. it was observed to loop
which caused some amazing gossip about hot dogging and pilot
behaviour.

I think a mode that might cause this loop involves a stall with high
engine rpm and stick back where the propwash, which would normally be
bent down by wing downwash, suddenly passes over turbulent stalled
flow and impinges directly on the all flying elevator. I can see that
such a situation with up elevator could produce the reported sudden
loop.

I dont believe *any* of the gossip. I think that two responsible
pilots got caught by some high performance aerofoil characteristics.

engine full revs, engine idle, engine full revs, etc was heard on the
way down which indicates to me a frantic effort to reattach airflow.
maybe a good and persistent boot of rudder for its secondary effects
(roll) may have saved them. ...or may save the next guy.

a very sad day.
thanks for the comments.
I also would own a T18 in a flash.
Stealth Pilot