Re: SEA OH-6 help

Here is a page with a picture of the system on a IAF MD500 Defender. >
That system is the later Hughes-designed "black hole" IR suppression,
which was also sold under the name "Ocarina".
The Vietnam OH-6s had field mods instead - there were several
different designs done as field expedients. They all basically
consisted of a metal cone to fit over the hind end of the engine
compartment, and the exhausts were vented out through cuts in each
side, above the engine clamshell doors. The design of the cover over
the exhausts differed - I've seen photos of round ones, photos of
squarish one, etc. Some appeared to be made of fiberglass or light
metal, with some sort of sealant applied to the fuselage join. I've
examined several OH-6As that had the field mods and then were
de-modded back in the US, and all of the side-holes were different
shapes, angles, etc. indicating no standardization.
At the same time that field units were making mods Hughes was also
experimenting with an early IR suppression kit for the OH-6. There
are small photos of it in a 1972 AWST article. It consisted of a tail
cone and two largish "toilet bowls" which redirected the exhaust
plumes upwards, not towards the back like the later "black hole"
system. The standard black hole system as used on the IAF MD500s
mixes ambient air with the exhaust plume. I don't know that Hughes
ever fielded a standard kit in Vietnam - I've never seen photos of
anything which is like the later standard "black hole" system.
I did see the black hole system fitted to an OH-6B in 1989/90.
Several OH-6As of varying National Guard units were upgraded by the
NGB in an effort to get the OH-6A in as a contender for the AHIP
program. These few airframes were known as "OH-6Bs" and they had the
black hole mod. The tail cone was held on by two metal struts which
were welded to the interior of the upper engine area.
As far as photos of the Vietnam-era field mods, they are as rare as
hen's teeth.
Two Hughes 500Cs (369HS) flown by Air America in 1972/3 also had side
John Hairell (

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John Hairell
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Maybe Hugh Mills will drop in and comment on this. He did have a "little bit" of flight time on Vietnam-area OH-6s. 8-)
Don McIntyre Clarksville, TN
John Hairell wrote:
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Don McIntyre
John ..
Thanks for the info, it does help quite a bit and know that I know what I am looking at is a field mod I will be able to replicate it a bit easier ...
I have also seen one poor pic of one of the AA 500C's and can't really make out the exaust area ... I wish there was a better pic showing them ... I have seen some decent pics of the two other 500's they operated ...
Thanks again ..
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