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I was watching the YouTube video of the interview with Des Barker.
He mentioned that he test flew the turbo dak for the maritime patrol role, which was fitted with an advanced radar in the ventral position.
He could not ok it's release, due to aerodynamic interference in certain flight conditions.
Does anyone have any pictures of that Dakota in that configuration?
What serial number was it?
Any further info?

From memory.

I believe the radar was based on the same hardware as Cheetah C radar, but with processors modernised (I think Cheetah C radar had the equivalent of five 80286 processors, the Dak radar used one or two 80486 processors.) And there must have been major mechanical changes for the 360° horizontal scan.

I believe that it was 6882.

Project Caret used two TP Dakotas - 6834 and 6882. 6882 was the main test platform used for all the flight test clearances etc., but was empty inside other than for all the sensors and recording equipment. 6834 was fully equipped with all the stations and equipment.

6834 was eventually sold to a local client (ZS-OSO) before being resold to a US company(N834TP) and was written off in an accident there. 6882 was stripped of all the bubbles and bulges and sold to a local client (ZS-MAP). Last I have of her she was standing stripped of parts at Lanseria but that is rather old info.

6882 in higher resolution:


6834 in the US:

_________________
MAMBA

Keep your feet on the ground, and reach for the skies!

As an aside I remember being consulted on the design of the radome. Our reccomendation was for the smallest possible hemispherical shape rather than try and make a "streamlined" radome which becomes larger and has more drag in the end. A hemisphere is also best for the radar performance. Of course most people seem to believe that if it looks streamlined it has less drag. This is a fallacy that extends to bicycle wheels and frames today.

Thanks for the interesting replies.
Is that picture of serial 6834 in the US representative of the configuration?

Yes. I with the exception of the ELINT OMNI
Antenna being removed (but visible in the pic of 6882) she is rully representative. I assume you are mainly focussed on the radome...

_________________
MAMBA

Keep your feet on the ground, and reach for the skies!

The tests flown by 6882 at the TFDC determined that when the flaps were selected down, the combination of the deflected airflow as well as the propeller-wash, which impinged on the radome, created a “rudder-type” effect, adversely affecting directional stability of the aircraft. The aircraft would yaw to the left without any rudder application. The resultant yaw (to the left) could not be countered with full opposite aileron and rudder. Single-engine evaluation (emergency situation) tests were also performed to simulate the failure of the critical engine. It was determined that when a go-around was initiated with the left engine inoperable and flaps down, the aircraft became extremely difficult to control safely. It was also determined that the Elta radar was too large and heavy for the aircraft.

The project was scrapped in 1998/1999?

Refering to the above Deltawingman, would the hemispherical radome you proposed theoretically have fared any better in the same situation or was this a case of something not picked up in prior analysis that was only noticed when flight testing started?

_________________
MAMBA

Keep your feet on the ground, and reach for the skies!

That's hard to say and I don't remember details. Suffice to say whoever ran the project wanted something "streamlined" looking. As a rule of thumb nothing is close to being streamlined unless it has at least a 1/5 thickness to chord ratio. And this seems to fail that criterion. Thus I surmise that it's larger size than the minimum hemisphere has had a knock on effect on handling due to its pure volume effect, as well as not being in anyway lower drag than a simple hemisphere.

What is often underestimated in "add ons" to aircraft is the effect of volume. For example drop tanks on a wing have very big effects. The effect on the lift of a wing is similar to taking the volume of the tank and spreading it evenly over the underside of the wing. This as one can imagine the effect is the reduce, or even reverse, the effective camber of the wing. I noticed this in wind tunnel results on the Cheetah, and in my current project, I'm dealing with handling volume effects on steroids.

So same thing adding volume to the underside of a rear fuselage as in this Dak mod, makes an effective suction area and this might have reduced the effect of the flaps. I can also imagine that sidewash effects with single engine operation could be nasty. Again the smaller hemispherical option might have been better, but it's one of those things that need to be tested. Wind tunnels are still useful and I doubt that any wind tunnel tests were done on this configuration.

Hmm. If I'm right and this was basically the same radar as was used on Cheetah C, "too large and heavy" sounds unlikely. The antenna and radome are more plausible obstacles.

I have an idea that we (South Africa) actually bought about 4 of the maritime patrol radars to fit to Dakotas - they were delivered to ??RDI / RDL / whatever the Reunert / Reutech bunch in Midrand was. Now apparently called "Reutech Radar Solutions".