Cessna 337, O-2 and Basler Turbo 37/Spectrum SA-5Skymaster Ideas and Inspiration

[The Big Gimper]

Found this cool O-2 conversion over at the FB The Aircraft Resource Group

Single Turboprop and big nose. Next step is to replace the Turboprop with a jet.



And the Sandcrab:



A 2009 Flight International article can be found here.

Source: Facebook The Aircraft Resource Group.

[Weaver]

Interesting!

I've been toying with the idea of twin Allison C-250s driving pusher contraprops and a helicopter-style front end as a super-FAC aircraft.

EDIT: meant independent co-axial props, not geared contraprops.

[elmayerle]

Interesting!

I've been toying with the idea of twin Allison C-250s driving pusher contraprops and a helicopter-style front end as a super-FAC aircraft.

They would have to be driving into a common gear box, much as the two PT6A's on the Learfan did.  It might make more sense to make it a combining gearbox that would allow loiter on one engine to prolong time on station.  Alternatively, use one large turboprop, likely a PT6 or similar (GE's development of the Walther turboprop, for example) since a pusher version of a TPE331 would take some significant engineering work on the part of the engine manufacturer.

[Weaver]

Interesting!

I've been toying with the idea of twin Allison C-250s driving pusher contraprops and a helicopter-style front end as a super-FAC aircraft.

They would have to be driving into a common gear box, much as the two PT6A's on the Learfan did.  It might make more sense to make it a combining gearbox that would allow loiter on one engine to prolong time on station.  Alternatively, use one large turboprop, likely a PT6 or similar (GE's development of the Walther turboprop, for example) since a pusher version of a TPE331 would take some significant engineering work on the part of the engine manufacturer.

Sorry, that's what I meant: each engine driving it's own prop, with the two props co-axial. Like a mini-Gannet setup, basically.

[GTX_Admin]

Another image of the Sandcrab:

[elmayerle]

Interesting!

I've been toying with the idea of twin Allison C-250s driving pusher contraprops and a helicopter-style front end as a super-FAC aircraft.

They would have to be driving into a common gear box, much as the two PT6A's on the Learfan did.  It might make more sense to make it a combining gearbox that would allow loiter on one engine to prolong time on station.  Alternatively, use one large turboprop, likely a PT6 or similar (GE's development of the Walther turboprop, for example) since a pusher version of a TPE331 would take some significant engineering work on the part of the engine manufacturer.

Sorry, that's what I meant: each engine driving it's own prop, with the two props co-axial. Like a mini-Gannet setup, basically.

With where the driveshaft on the Allison is relative to the exhaust, that could make for an interesting installation; especially since the exhaust would not be that far in front of the propeller.  Seriously, I think I'd prefer to go with a 600+ HP single turboprop rather than add all the complexity of a twin-engine installation.

[Weaver]

Interesting!

I've been toying with the idea of twin Allison C-250s driving pusher contraprops and a helicopter-style front end as a super-FAC aircraft.

They would have to be driving into a common gear box, much as the two PT6A's on the Learfan did.  It might make more sense to make it a combining gearbox that would allow loiter on one engine to prolong time on station.  Alternatively, use one large turboprop, likely a PT6 or similar (GE's development of the Walther turboprop, for example) since a pusher version of a TPE331 would take some significant engineering work on the part of the engine manufacturer.

Sorry, that's what I meant: each engine driving it's own prop, with the two props co-axial. Like a mini-Gannet setup, basically.

With where the driveshaft on the Allison is relative to the exhaust, that could make for an interesting installation; especially since the exhaust would not be that far in front of the propeller.  Seriously, I think I'd prefer to go with a 600+ HP single turboprop rather than add all the complexity of a twin-engine installation.

Well the RFB Fantrainer has an Allison C-250 driving a pusher fan, so I don't see why the exhaust position would be a problem.

In any event, let's not get hung up on the specifics of the C-250: I only picked it because it's a common small turboprop in the right power range. My general purpose is having the twin installation was to retain the twin-engine safety and damage tolerance of the normal 337 in a military aircraft that's likely to get shot at.

[jcf]

O-2T & O-2TT


AvWeek April 14, 1969 (page image from the online archive, I have the actual issue, it's in storage at the moment.)


Don't recall where I got the 3-view.

[elmayerle]

Interesting!

I've been toying with the idea of twin Allison C-250s driving pusher contraprops and a helicopter-style front end as a super-FAC aircraft.

They would have to be driving into a common gear box, much as the two PT6A's on the Learfan did.  It might make more sense to make it a combining gearbox that would allow loiter on one engine to prolong time on station.  Alternatively, use one large turboprop, likely a PT6 or similar (GE's development of the Walther turboprop, for example) since a pusher version of a TPE331 would take some significant engineering work on the part of the engine manufacturer.

Sorry, that's what I meant: each engine driving it's own prop, with the two props co-axial. Like a mini-Gannet setup, basically.

With where the driveshaft on the Allison is relative to the exhaust, that could make for an interesting installation; especially since the exhaust would not be that far in front of the propeller.  Seriously, I think I'd prefer to go with a 600+ HP single turboprop rather than add all the complexity of a twin-engine installation.

Well the RFB Fantrainer has an Allison C-250 driving a pusher fan, so I don't see why the exhaust position would be a problem.

In any event, let's not get hung up on the specifics of the C-250: I only picked it because it's a common small turboprop in the right power range. My general purpose is having the twin installation was to retain the twin-engine safety and damage tolerance of the normal 337 in a military aircraft that's likely to get shot at.

Fair enough (I'm just familiar with them from OH-58D and MQ-8C installations).  I can think of several suitable candidates, but you'd need to extend the nose with some significant equipment to maintain weight and balance requirements of the aircraft.  IMHO, I'd rather replace the existing engines with suitable turboprops and locate sensors either under the wings or in pylon-mounted pods (or, for a certain elegance, in forward extensions of the booms).

[Weaver]

Nice one Jon! I had a feeling that something like that had been tried. Any idea why it wasn't adopted? my guess would be that they were focussing more on the larger OV-10 Bronco by that point.

Fair enough (I'm just familiar with them from OH-58D and MQ-8C installations).  I can think of several suitable candidates, but you'd need to extend the nose with some significant equipment to maintain weight and balance requirements of the aircraft.  IMHO, I'd rather replace the existing engines with suitable turboprops and locate sensors either under the wings or in pylon-mounted pods (or, for a certain elegance, in forward extensions of the booms).

Probably the smart option as Jon's post demonstrates. I originally conceived the pusher-FAC as a clean-sheet-of-paper design (a faster, non-ducted fan Edgely Optica, basically) and it only occurred to me later that it could potentially be converted from an O-2. However, as the Basler/Spectrum/Sandcrab designs illustrate, a single rear engine is certainly feasible without too much compensating weight added forwards. If my helicopterish front end included an armoured floor, armoured seats, and possibly a flat sheet of toughened glass inside the rounded outer glazing* that would go a long way to balancing the rear engines.

*Yes I know that might cause problems with internal reflections, condensation and the like, but it's still worth exploring. Alternatively, it could be semi-Fw-189 style, with armoured flat panels on the lower nose and sides and a plastic canopy over the upper half.

[LemonJello]

Another image of the Sandcrab:

Why, oh why must you tempt me to add more kits to the stash?