Increased takeoff performance downwind on Bell 212's
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But then again.
Does this theory hold water?
Where is the wake from the TR going? Would it get in over the top of the disk? Would this feed the MR to some extent providing some "translational lift" early in the transition? The wake would be fed into the advancing side which is now on the opposite side to forward flight.
Await the response from those that are paid to know this stuff.
Does this theory hold water?
Where is the wake from the TR going? Would it get in over the top of the disk? Would this feed the MR to some extent providing some "translational lift" early in the transition? The wake would be fed into the advancing side which is now on the opposite side to forward flight.
Await the response from those that are paid to know this stuff.
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All our 205's have the strakes on them now and as said I don't find them "crisp" but entirely docile now. You really do need 50% less pedal input (as say's in the suppliment). The 205 is far less twitchy now than before. Apparently you can lift up to 500 lbs more on the hook aswell but we haven't really noticed this sofar but the pedal input amount is remarkably less.
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CyclicRick,
An increase of 500 pounds for tailcone strakes is a bit incredible. The total vertical drag for a typical helo is about 5%, with the bulk of the drag coming from the fat fuselage, and oly a portion coming from the tail cone. 500 pounds on a 205 is 5% of the Gross Weight.
Is that estimate part of the literature for the strakes? Any charts provided with the kit to support it?
The positive effect on pedal margin is quite reasonable, since the side force that fights the tail rotor is virtually eliminated.
An increase of 500 pounds for tailcone strakes is a bit incredible. The total vertical drag for a typical helo is about 5%, with the bulk of the drag coming from the fat fuselage, and oly a portion coming from the tail cone. 500 pounds on a 205 is 5% of the Gross Weight.
Is that estimate part of the literature for the strakes? Any charts provided with the kit to support it?
The positive effect on pedal margin is quite reasonable, since the side force that fights the tail rotor is virtually eliminated.
Thread Starter
Nick,
I am flying 212's with the strakes....and from what I have seen, felt, and heard from other pilots here.....there isn't a lot of noticeable difference. I am sure the manufacturer can support the claims for improved performance....and anything that helps is fine. I would suggest the installation of Sperry Helipilots for increased stability would provide a larger improvement in "lift" than the strakes alone. The more stable the aircraft is....the more it will lift under the same climatic conditions. All I have to do is watch the cyclic banging around the cockpit on takeoffs to realize how much lift is being lost due to the aircraft not having a SAS system installed. This outfit removed the air conditioning system due to the loss of about 400 pounds of useful load but spec'd the aircraft without SAS......I bet we could make up that 400 pounds by stabilizing the aircraft. Handling a Bell 212 without SAS in a 20-25 knot crosswind does require some getting used to.....compound that with the mechanical turbulence obtained from structures upwind of the helipad or helideck and one can understand the improvement in performance that can result from the use of SAS versus un-SAS'ed aircraft. Compound that with flying offshore night in the un-SAS'ed rascals really makes for some interesting times.
I am flying 212's with the strakes....and from what I have seen, felt, and heard from other pilots here.....there isn't a lot of noticeable difference. I am sure the manufacturer can support the claims for improved performance....and anything that helps is fine. I would suggest the installation of Sperry Helipilots for increased stability would provide a larger improvement in "lift" than the strakes alone. The more stable the aircraft is....the more it will lift under the same climatic conditions. All I have to do is watch the cyclic banging around the cockpit on takeoffs to realize how much lift is being lost due to the aircraft not having a SAS system installed. This outfit removed the air conditioning system due to the loss of about 400 pounds of useful load but spec'd the aircraft without SAS......I bet we could make up that 400 pounds by stabilizing the aircraft. Handling a Bell 212 without SAS in a 20-25 knot crosswind does require some getting used to.....compound that with the mechanical turbulence obtained from structures upwind of the helipad or helideck and one can understand the improvement in performance that can result from the use of SAS versus un-SAS'ed aircraft. Compound that with flying offshore night in the un-SAS'ed rascals really makes for some interesting times.
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good answers this time, bit different to the answers i got before:
http://www.pprune.org/forums/showthr...threadid=18787
http://www.pprune.org/forums/showthr...threadid=18787
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SASless, IME the weight of the SAS isn't the main reason operators don't get it, or any other electronic equipment, like flight directors, etc. The big thing seems to be that once you get it, you have to maintain it, so you have to pay for parts, avionics technicians who can fix it, etc, etc. Corporate types in the world only seem to be interested in short-term profits these days. The next quarter is a long way off for them, never mind next year or a couple of years ahead.
After all, you've gotten by without a SAS this long, why would you need it now? :-) And why are you operating in a crosswind? Everyone knows the wind is always favorable offshore, & I simply cannot believe that there could be obstructions around the helideck! :-D Isn't it fun when you only have 2 directions in/out of the deck, & some idiot decides they need more antennas, so they fill one of the approach/departure routes with them, & you find out on short final at 2:00AM?
After all, you've gotten by without a SAS this long, why would you need it now? :-) And why are you operating in a crosswind? Everyone knows the wind is always favorable offshore, & I simply cannot believe that there could be obstructions around the helideck! :-D Isn't it fun when you only have 2 directions in/out of the deck, & some idiot decides they need more antennas, so they fill one of the approach/departure routes with them, & you find out on short final at 2:00AM?
Last edited by GLSNightPilot; 2nd Sep 2002 at 15:38.
CyclicRick,
500 lbs is a huge increase for the 205. Just confirm you are not talking about the A1 with a 212 rotor system? To my knowledge, the Oz Army had no such increase on the UH-1H, even the test and development unit (ARDU) who fully instrumented an aircraft failed to substantiate a significant weight carrying capability.
Why dont the US Army fit strakes? The rumour I will repeat is that NASA first designed the strakes in the late 60s, and they were rejected by Pax river (or US Army equivalent). NASA stopped development following Army rejection. The designer left NASA some time later, and retained design rights to begin selling them by the early 80s. Remember, this is a rumour only - definately in the "alledged" vein.
But, it begs the question - why didn't the US Army adopt them? Why didn't Bell produce helicopters with them? Why dont all helicopter manufacturers use them? Why don't Sikorsky, Nick?
I suspect it is because they do not drastically increase lifting capacity, their main function is to increase pedal margin. Adding to Nick's comments about down force on the tailboom, the strakes actually INCREASE total drag of the tailboom in the way they disturb air on one side, thus producing a non unequal flow (velocity wise) over each side of the boom.
So, if you have heaps of pedal margin - I would think that the strakes would be of negligable benefit. Your thoughts? And note that I think the 212 rotor system provides heaps of pedal margin just as it is.
SASless:
Looks like you are pushing poo uphill trying to convince your company of the benefits of SAS! I believe SAS is appropriate for only limited types of operations. For example, when long lining, slinging, fire fighting, etc, SAS is not up to the job. In fact, we used to turn it off because it is too easy to excite into oscillations when sideslipping, doing precision work, and slinging. Thus I dont agree that you will be able to lift more weight with the SAS fitted.
John Bicker:
Having fun alright! Can you please insert punctuation marks (particularly quotation marks) into your post because I am having difficulty following your discussion? Thanks.
Note that just because you reduce drag, you have not necessarily increased lift at all, and pitching moments do not add significantly to over all lift. In any event, remember that in forward flight, the sych elevator is trying to fly down, not up, and if you are flying backwards you need to consider my earlier question: does an airfoil going backwards reverse the direction of it's lift as you surmise? Again, I would say "nup".
500 lbs is a huge increase for the 205. Just confirm you are not talking about the A1 with a 212 rotor system? To my knowledge, the Oz Army had no such increase on the UH-1H, even the test and development unit (ARDU) who fully instrumented an aircraft failed to substantiate a significant weight carrying capability.
Why dont the US Army fit strakes? The rumour I will repeat is that NASA first designed the strakes in the late 60s, and they were rejected by Pax river (or US Army equivalent). NASA stopped development following Army rejection. The designer left NASA some time later, and retained design rights to begin selling them by the early 80s. Remember, this is a rumour only - definately in the "alledged" vein.
But, it begs the question - why didn't the US Army adopt them? Why didn't Bell produce helicopters with them? Why dont all helicopter manufacturers use them? Why don't Sikorsky, Nick?
I suspect it is because they do not drastically increase lifting capacity, their main function is to increase pedal margin. Adding to Nick's comments about down force on the tailboom, the strakes actually INCREASE total drag of the tailboom in the way they disturb air on one side, thus producing a non unequal flow (velocity wise) over each side of the boom.
So, if you have heaps of pedal margin - I would think that the strakes would be of negligable benefit. Your thoughts? And note that I think the 212 rotor system provides heaps of pedal margin just as it is.
SASless:
Looks like you are pushing poo uphill trying to convince your company of the benefits of SAS! I believe SAS is appropriate for only limited types of operations. For example, when long lining, slinging, fire fighting, etc, SAS is not up to the job. In fact, we used to turn it off because it is too easy to excite into oscillations when sideslipping, doing precision work, and slinging. Thus I dont agree that you will be able to lift more weight with the SAS fitted.
John Bicker:
Having fun alright! Can you please insert punctuation marks (particularly quotation marks) into your post because I am having difficulty following your discussion? Thanks.
Note that just because you reduce drag, you have not necessarily increased lift at all, and pitching moments do not add significantly to over all lift. In any event, remember that in forward flight, the sych elevator is trying to fly down, not up, and if you are flying backwards you need to consider my earlier question: does an airfoil going backwards reverse the direction of it's lift as you surmise? Again, I would say "nup".
SASless, I have done heaps of precision (diamond drills, towers), and production (heli-portable seismic) longline work with the 212, with and without SAS installed. I agree the naked version requires a different touch, but it's not that bad. As we all know, the 212 will not tolerate much in the way of stick-stirring, so one really has to discipline oneself to keep the paws still! One thing to be very conscious of is c/g. She hates being severe aft.
I have to agree, offshore/night I'd be wanting the SAS as a minimum, and would likely be squawking for a Sperry with a flight director
I have to agree, offshore/night I'd be wanting the SAS as a minimum, and would likely be squawking for a Sperry with a flight director
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strakes
With our 205's the max gross weights did not change. They remained 10,200 internal, and 10,500 external (we have the 212 rotor system installed). Where the largest benefit was noticed, was when it's hot and/or high. The strake made an airfoil out of that large tailboom, using that airfoil to create lift in the direction opposite to torque. By unloading the t/r, you reduce the power required to operate the t/r. Thereby giving you a slightly lower power requirement to lift any given load. It may not be much, but I'll take it !! 
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helmetfire et al,
Seems to have gone a bit quiet here as to the conjecture about what is really happening in the back end of the Bell in the manouevre as quoted.
Re your comment about the foil going backwards - from what I recall even a flat board will generate lift just not as efficiently and the stalling A of A is less. I have seen someone fit a set of TR blades on a H300 backwards and it flew OK. Even seen a H500C TR P/Link fitted on one blade of a H500D (one is considerably shorter) and it flew OK although made a funny noise.
It would be interesting to know what is happening to all the wakes in this manouevre. It ain't really as depicted in the basic training manuals wouldn't you say. As I said before where is the wake from the TR going?
A graphic of interest:
Have a look here: http://www.dynamicflight.com/aerodyn...lational_lift/
Imagine what would happen if the aircraft is facing the other way i.e. translating to the rear as was discussed. If this graphic is anywhere close to the truth all of the previous drag and downforces on the tail would be eliminated and/or in a beneficial direction. Going on Nick Lappos' appreciation of the S76 performance losses when they stuck the phone booth on the front of one there may be something in it.
Seems to have gone a bit quiet here as to the conjecture about what is really happening in the back end of the Bell in the manouevre as quoted.
Re your comment about the foil going backwards - from what I recall even a flat board will generate lift just not as efficiently and the stalling A of A is less. I have seen someone fit a set of TR blades on a H300 backwards and it flew OK. Even seen a H500C TR P/Link fitted on one blade of a H500D (one is considerably shorter) and it flew OK although made a funny noise.
It would be interesting to know what is happening to all the wakes in this manouevre. It ain't really as depicted in the basic training manuals wouldn't you say. As I said before where is the wake from the TR going?
A graphic of interest:
Have a look here: http://www.dynamicflight.com/aerodyn...lational_lift/
Imagine what would happen if the aircraft is facing the other way i.e. translating to the rear as was discussed. If this graphic is anywhere close to the truth all of the previous drag and downforces on the tail would be eliminated and/or in a beneficial direction. Going on Nick Lappos' appreciation of the S76 performance losses when they stuck the phone booth on the front of one there may be something in it.
John B,
my comments on the synch elevator related to your earlier statement that:
"When you fly forward in these machines the elevator component is opposite to the lift. When you fly backwards due to the way it is rigged on a Bell 205/212 the sync elevator surface provides lift. This is where the free ride comes from. "
As I have said above: NUP.
An airfoil going backwards does not produce lift in the opposite direction, and an airfoil going at the speeds we are talking about (up to translational) produces no significant lift. Further, a flat board will not produce lift per se, it produces drag, and in particular, parasite drag. Tilting the board may induce a tiny amount of lift before it stalls, but continuing to tilt the board results in increasing parasite drag. If you hold a board out of your car window for this one, you will find that the board appears to be producing lift when you tilt it because it wants to fly up. In fact, your hand is merely overcoming parasite drag by holding it there. This component of "drag reaction" is thought to also contribute to the total lift of an airfoil, but it is not lift per se.
my comments on the synch elevator related to your earlier statement that:
"When you fly forward in these machines the elevator component is opposite to the lift. When you fly backwards due to the way it is rigged on a Bell 205/212 the sync elevator surface provides lift. This is where the free ride comes from. "
As I have said above: NUP.
An airfoil going backwards does not produce lift in the opposite direction, and an airfoil going at the speeds we are talking about (up to translational) produces no significant lift. Further, a flat board will not produce lift per se, it produces drag, and in particular, parasite drag. Tilting the board may induce a tiny amount of lift before it stalls, but continuing to tilt the board results in increasing parasite drag. If you hold a board out of your car window for this one, you will find that the board appears to be producing lift when you tilt it because it wants to fly up. In fact, your hand is merely overcoming parasite drag by holding it there. This component of "drag reaction" is thought to also contribute to the total lift of an airfoil, but it is not lift per se.
