Foxbat Down Kruger Park- all ok

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Dusty Eagle
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Re: Foxbat Down Kruger Park- all ok

Unread post by Dusty Eagle » Tue Feb 12, 2019 8:50 am

The evidence that led up to the engine failure has probably melted :?
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Re: Foxbat Down Kruger Park- all ok

Unread post by BigglesSA » Tue Feb 12, 2019 9:31 am

Dusty Eagle wrote:
Tue Feb 12, 2019 8:50 am
The evidence that led up to the engine failure has probably melted :?
But I thought Rattletax do not get carb ice due to air being taken from inside the hot engine compartment? Genuine question!
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Re: Foxbat Down Kruger Park- all ok

Unread post by Dobbs » Tue Feb 12, 2019 10:31 am

I have experienced carb ice in my Bushbaby on one occasion - after applying full throttle it continued to run rough for a couple of seconds and then cleared. I think the best we can say is that in a closed cowl environment, the propensity to experience carb ice is typically very low. I wonder how an uncowled pusher config would have faired on that day.....
Another interesting comment was about aero engines not liking to be run at low power settings? When I just want to be up in the air, but have nowhere to go, I throttle back to sometimes less than 50% power and just enjoy the moment, am I inviting trouble doing this?
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Re: Foxbat Down Kruger Park- all ok

Unread post by BigglesSA » Tue Feb 12, 2019 10:42 am

Dobbs wrote:
Tue Feb 12, 2019 10:31 am
I think the best we can say is that in a closed cowl environment, the propensity to experience carb ice is typically very low.
Another interesting comment was about aero engines not liking to be run at low power settings?
Have to agree with Marius on this, exactly my perception as well!
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Re: Foxbat Down Kruger Park- all ok

Unread post by Dobbs » Tue Feb 12, 2019 11:05 am

Well, that is what I am trying to understand, is it just perceptions and opinions, or is it based on fact, and if based on fact, where can I get some more information on this. With the little googling that I have done, I cannot find anything supporting this, specifically Rotax. I am aware of the bedding in requirements of new / rebuilt Lycoming and Conti engines, but nothing on Rotax.
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Re: Foxbat Down Kruger Park- all ok

Unread post by Stephan van Tonder » Tue Feb 12, 2019 1:20 pm

Rotax has the option of fitting a water heated cuff between the head and the carb. Many of them are fitted with this and they will not likely get carb ice.
Also the location of the carb sitting behind the cylinder head causes hot air to flow backwards over the carb so they tend not to get icing.
Not saying it is not possible - but it is very far from a common occurrance in the 91x series engines.
you very rarely see a rotax install that has carb heat ducting.
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Re: Foxbat Down Kruger Park- all ok

Unread post by GERMAN » Tue Feb 12, 2019 5:17 pm

Icing occurs when throttling back and not on full throttle
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Unread post by Micro Aviation » Tue Feb 12, 2019 5:39 pm

Hi Marius I’m inclined to agree with you. Surveillance missions are typically carried out at low speed and these tightly cowled engines as in the A22 Foxbat and Savannah Aircraft tend to overheat when flown at low speed for protracted periods. Fuel vapourisation ? ? Yesterday a Savannah also force landed during a surveillance mission , also with engine failure . The Rotax 912 uls is also used in the Bat Hawks, but in that application it is completely open, no cowlings or covers, and they are working exceptionally well in the surveillance role . There are dozens out there all operating at very low speeds. I could be wrong, but I think the problems are cooling and temperature related. Cowled engines need speed for optimum cooling.
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Marius Schrenk
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Re: Foxbat Down Kruger Park- all ok

Unread post by Marius Schrenk » Wed Feb 13, 2019 8:46 am

I regularly fly in big groups (up to 20 planes) in "lose formation" on holiday's. Unfortunately there is always a plane that does not "keep up" and sometimes (like down the coastline) people intentionally fly slowly to enjoy the scenery and take photos. We have this one very experienced pilot (ha ha a very good friend of mine) that would suggest "one notch flap and 85 kt's". Without exception in the next 20 min the radio clatter would begin about temps/rough running. 8-[ I nowadays prefer to fly right at the back of the formation. Whenever the ""one notch flap" command comes I fall out of formation and go on a side trip. :wink: Only once it caused trouble with ATC close to Couga when he got annoyed with "one plane" that got lost. :wink: :roll:
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Re:

Unread post by priester » Wed Feb 13, 2019 11:31 am

Micro Aviation wrote:
Tue Feb 12, 2019 5:39 pm
Hi Marius I’m inclined to agree with you. Surveillance missions are typically carried out at low speed and these tightly cowled engines as in the A22 Foxbat and Savannah Aircraft tend to overheat when flown at low speed for protracted periods. Fuel vapourisation ? ? Yesterday a Savannah also force landed during a surveillance mission , also with engine failure . The Rotax 912 uls is also used in the Bat Hawks, but in that application it is completely open, no cowlings or covers, and they are working exceptionally well in the surveillance role . There are dozens out there all operating at very low speeds. I could be wrong, but I think the problems are cooling and temperature related. Cowled engines need speed for optimum cooling.
The Savannah is definitely not what one would refer to as "tightly cowled" The engine cylinder heads are water cooled and the bit of barrel between the head and crank case by air. There is also an oil cooler. When one flies slowly it is at reduced power setting, which then also generate less heat. Burning 18 liters/hr at 100 mph cruise compared to 12 l/hr at 45-50 mph
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Re: Foxbat Down Kruger Park- all ok

Unread post by Dobbs » Wed Feb 13, 2019 12:29 pm

Totally agree Priester, also by having one notch of flaps does "bring the nose down" which also assists with cooling. Working for both the Bateleurs and Ezemvelo, my plane spends many hours at temps to to 40 deg at low power settings and I do not experience high engine / oil temps temps.
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Re: Foxbat Down Kruger Park- all ok

Unread post by jasv@acweb.co.za » Wed Feb 13, 2019 6:12 pm

My 3rands worth. flying a Streak with a 912 ul as a pusher at 4100 rpm found that the plugs do foul up due to low revs AND it do not use any oil, 200hrs on the engine, never ever ever had to add oil between services, Rotax 4 stroke do not like to operate at low revs. flown a lot of different Foxbat,s as well and if you do 3000 rpm or lower it is rough, All of them.
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Re: Foxbat Down Kruger Park- all ok

Unread post by priester » Wed Feb 13, 2019 8:19 pm

jasv@acweb.co.za wrote:
Wed Feb 13, 2019 6:12 pm
My 3rands worth. flying a Streak with a 912 ul as a pusher at 4100 rpm found that the plugs do foul up due to low revs AND it do not use any oil, 200hrs on the engine, never ever ever had to add oil between services, Rotax 4 stroke do not like to operate at low revs. flown a lot of different Foxbat,s as well and if you do 3000 rpm or lower it is rough, All of them.
I think if you want to do slow flying it is probably better to have an "in flight" adjustable prop. I have one and is able to adjust manifold pressure/rpm for the smoothest operation. I agree that the Rotax seems to favour higher rpm. I normally cruise at 22/5200
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Re: Foxbat Down Kruger Park- all ok

Unread post by rare bird » Thu Feb 14, 2019 5:00 am

the Rotax was actually a snowmobile engine - so designed for higher revs

can the Foxbat be repaired?
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Re: Foxbat Down Kruger Park- all ok

Unread post by heisan » Thu Feb 14, 2019 9:34 am

rare bird wrote:
Thu Feb 14, 2019 5:00 am
the Rotax was actually a snowmobile engine - so designed for higher revs

can the Foxbat be repaired?
The 912 was designed from the ground up as an aircraft engine.
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