Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: ramzey on August 05, 2005, 04:40:45 AM
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som planes had limited time to fly bottom up due to engine lubrication? (pls do not laug its thats not correct word)
i know about 3 sec for F4u
as far i remember somthing like that was plug in in to old warbirds
any other planes had same ?
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Yes, I remember this was implemented in an old version of either AW or WB (maybe both). Presumably this was based on historical facts but then it makes me wonder why it is never discussed on these boards... a lot of people want all the realism they can think off and no engine in AH dies of oil pressure loss when upside down.
Widewing will probably now.
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Without knowing any facts I think they all destroyed their engines pretty fast if flown inverted without positive G.
3 sec sounds like a very short time in that sense, though, for a radial.
I'd think abt. 10-20 sec to be critical depending on engine type.
-C+
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This has been argued before.
The F4u does have a placard prohibiting prolonged inverted flight of true negative G's. The time frames are never mentioned. Having worked on WW2 aircraft the past 15 or so yrs, I'd have to agree with charge. Maybe closer to 8 secs, maybe more. Radials especially are able coolers. It's all in the realm of "we will never find out" because no one is ever going to turn there f4u upside down and toast a -8w or 18w....
Who knows, maybe Bobby Collings will try it, we all know his track record in the F4u-5 :lol
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Still similar restrictions today.
Lynx heli can do inverted aerobatics i.e. loops and rolls but must keep positive 'g' for as long as possible to avoid engine oil and main rotor gearbox oil starvation.
The positve 'g' time was shortened by fitting baffle plates that slowed down the time it took oil to drain away from the various sumps.
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Originally posted by Kev367th
Lynx heli can do inverted aerobatics i.e. loops and rolls
Wow, can it? Never heard of heli being able to do that kind of stuff. Just out of interest: WHY? And how did they find out?
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Why?
For airshows.
The main probs with inverted flight in a heli is the rotor head.
Can only be done with rigid or semi-rigid heads.
rigid head - no moving parts.
semi-rigid - only moving part is pitch change bearings
fully articulated - uses hinges and bearings for flap,lead/lag and pitch change.
Look at the pic-
Flap is allowed for by the main rotor head flexing up/down (bit in middle)
Lead/lag is allowed for by the area inboard of the blades flexing fwds/backwards. (between yellow bands)
Pitch change is via a bearing (only moving part)
(http://www.b-domke.de/AviationImages/Rotorhead/Images/0789.jpg)
How do I know - Spent 9 years in the British Army working on them. Man, does the pic bring back memories.
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LOL I *thought* I detected an accent from you in Jetb's P38 film in the training forum lol!
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;), accent what accent, everyone else has an accent, not me.
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Originally posted by Kev367th
Why?
For airshows.
The main probs with inverted flight in a heli is the rotor head.
Can only be done with rigid or semi-rigid heads.
rigid head - no moving parts.
semi-rigid - only moving part is pitch change bearings
fully articulated - uses hinges and bearings for flap,lead/lag and pitch change.
Look at the pic-
Flap is allowed for by the main rotor head flexing up/down (bit in middle)
Lead/lag is allowed for by the area inboard of the blades flexing fwds/backwards. (between yellow bands)
Pitch change is via a bearing (only moving part)
(http://www.b-domke.de/AviationImages/Rotorhead/Images/0789.jpg)
How do I know - Spent 9 years in the British Army working on them. Man, does the pic bring back memories.
Only for airshows? Good way of spending tax money :D
How does a rigid rotorhead actually work?
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The picture Kev367th posted shows the rigid head pretty well, entire linkage part rolls with blades.
IIRC the BO 105 was the first full size helicopter able to do inverted flying, nowadays several others (like the Lynx) have same capability. Anyway, that capability is more or less theoretical.
gripen
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Good explanation here of the different types of rotor heads -
http://www.transglobal-aerospace.co.uk/1-504/Ch3.htm
Although I would disagree with what they say is a semi rigid rotor head, I was taught that was a 'Teeter mast' eg the classic Huey.
The Lynx has a semi rigid head and bears no resemblance or shares the traits they say comprise a semi rigid head.
Poss difference in US vs European thinking/definitions?
This is what I was taught -
1st quick explanation - Blades have can have 3 planes of movement-
1) lead/lag - The blade can move fwds and backwards slightly from its central spanwise position.
2) Flap - The blade can rise and fall to allow equalisation of lift.
3) The usual rotation to change the angle of attack (pitch change).
a) Teeter Mast - i.e. the UH-1, all blades pivot around a central point and are in effect one solid mass. i.e. you pull one blade down, the other will rise, but you can have them with 4 blades.
b) Rigid - All movement is allowed for by flexing/twisting areas of the main rotor head. (rare)
c) semi-rigid - i.e. Lynx - Lead/lag and flap are allowed for by areas of the main head to flexing rather than have hinges. Pitch change is allowed for by actaul bearings.
d) fully articulated - Lead/lag and flap use physical hinges, pitch change uses bearings.
One thing I can tell you, the Lynx fitted with the composite main rotor blades (ones with the paddle on the end) was a ***** to do initial tracking on, more unstable than 'normal' blades in the hover but a hell of a lot of fun to fly around in on flight tests.
Grippen - Thats a semi-rigid head.
Inverted as in loops, rolls is not theoretical, Lynx rolls extremely well.
One of my favourite Lynx airshow stunts they do
i) Climb upwards and rearwards increasing speed as it went.
ii) At max rear speed haul the cyclic all the way back and pull max collective.
ii) The aircraft went rearwards over onto its back then into a dive.
Quite spectacular.
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Originally posted by Kev367th
Grippen - Thats a semi-rigid head.
Inverted as in loops, rolls is not theoretical, Lynx rolls extremely well.
One of my favourite Lynx airshow stunts they do
i) Climb upwards and rearwards increasing speed as it went.
ii) At max rear speed haul the cyclic all the way back and pull max collective.
ii) The aircraft went rearwards over onto its back then into a dive.
My mistake, I have been playing mostly with RC-helicopters which can do pretty much everykind of aerobatic stunts (in experienced hands). The head construction is quite bit different in most of these but there is also semi rigid heads in the RC-helicopters.
As an example see here (http://www.helihobby.com/videos/SuperHeadShort.wmv) :)
gripen
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Yeah I used to have one, got too expensive, I kept breaking it :( .
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the rah-68(?) commanche can flip over too and so can an old soviet counterpart to the apache uhh oh the hokum