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- convair880mfan
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During a standing takeoff on a water-injected aircraft like the early 707, when does the water start?
Does the water start when the thrust levers are advanced to a certain point or does it start when the aircraft begins rolling. I have been on 707's where standing takeoffs were made with water injection. Sometimes the 707 would wait like 30 seconds before the roll. Is water being used during this time?
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- GalaxyFlyer
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Re: During a standing takeoff on a water-injected aircraft like the early 707, when does the water start?
I think water starts at a certain EPR level and there isn’t enough to be running for 30” before rolling.
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- convair880mfan
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Re: During a standing takeoff on a water-injected aircraft like the early 707, when does the water start?
Did the C-5 Galaxy need water to takeoff or were all of its takeoffs dry? I'm suspecting that it didn't need water since for an aircraft of that size, it didn't need all that much runway to get off the ground. But perhaps I am wrong.
Re: During a standing takeoff on a water-injected aircraft like the early 707, when does the water start?
Right before the shooter kneels and taps the deck and the Harrier launches off the flat end of the ship.
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- GalaxyFlyer
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Re: During a standing takeoff on a water-injected aircraft like the early 707, when does the water start?
convair880mfan wrote:Did the C-5 Galaxy need water to takeoff or were all of its takeoffs dry? I'm suspecting that it didn't need water since for an aircraft of that size, it didn't need all that much runway to get off the ground. But perhaps I am wrong.
No, KC-135As used water got a few rides in them.
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- convair880mfan
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Re: During a standing takeoff on a water-injected aircraft like the early 707, when does the water start?
Did you feel anything when the water ran out, GalaxyFlyer?
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- SteelChair
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Re: During a standing takeoff on a water-injected aircraft like the early 707, when does the water start?
convair880mfan wrote:Did you feel anything when the water ran out, GalaxyFlyer?
I've had flight crew from the KC135A era tell me that there was a noticeable thrust decrease when the water ran out.
Re: During a standing takeoff on a water-injected aircraft like the early 707, when does the water start?
convair880mfan wrote:Does the water start when the thrust levers are advanced to a certain point or does it start when the aircraft begins rolling. I have been on 707's where standing takeoffs were made with water injection. Sometimes the 707 would wait like 30 seconds before the roll. Is water being used during this time?
convair880mfan, there are a couple of different systems.
In one system, as the aircraft aligns with the runway for takeoff, the throttles are set to a pre-determined EPR, known as "Partial EPR." Once this EPR is set, the water injection switch is turned on and the EPR on all engines increases to takeoff rated thrust, known as "wet EPR."
In another system, the water injection switch is actuated prior to beginning the takeoff roll, during the Before Takeoff checklist. This energizes the pump in the water tank. Then when the aircraft is aligned with the runway, the throttles are advance smoothly and symmetrically. At a preset EPR value, the engine driven water pumps activate and the thrust increases to TRT.
Standing takeoffs are not normally accomplished when using water injection; only rolling or static takeoffs.
I cannot address the situation you experienced on the 707, but my guess is that water was not being used prior to beginning the takeoff roll. You need all available water to satisfy climb criteria and meet climb performance. The duration of the water is about two minutes.
Water injection is not used on every takeoff; only when required to achieve runway performance or climb criteria. A water injected takeoff causes additional wear and tear on an engine as compared to a dry thrust takeoff.
e38
Re: During a standing takeoff on a water-injected aircraft like the early 707, when does the water start?
On the HS748 the water is injected when the throttle moves past a microswitch correlating with 14750 RPM (15000 is takeoff power) if the W/M pumps were turned on in the after start checks. If we were to do a standing takeoff it would burn water once the the throttle goes by that position (hence we don't do standing takeoffs).
Re: During a standing takeoff on a water-injected aircraft like the early 707, when does the water start?
Out of curiosity, what’s the difference between a standing takeoff and a static takeoff?
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- GalaxyFlyer
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Re: During a standing takeoff on a water-injected aircraft like the early 707, when does the water start?
To my knowledge, there isn’t any. Some might feel one requires setting full power/thrust prior to brake release while the other only some intermediate setting. Lots of opinions on the efficacy of either versus rolling take-offs. At heavy weights, not a lot of forward movement occurs before full thrust can be set. On the underpowered C-5A, we did lots of standing take-offs as the -1-1 required increasing take-off run by 750’, if rolling take-off. Boeing says, and I’d agree, release brakes and smoothly and positively add thrust, it’s set long before the next 1,000’ marker, maybe 500’ at most. If standing, we also did an accel check at 100 or 110 knots, about 35” into the run. Funny, the few that were close (3 knots below the time to 100 or 110): it was obviously going to close by 80 knots watching the clock.
Re: During a standing takeoff on a water-injected aircraft like the early 707, when does the water start?
Zeke2517 wrote:Out of curiosity, what’s the difference between a standing takeoff and a static takeoff?
Zeke2517, at my operator, the difference is as follows:
Both standing and static takeoffs assume the aircraft is in the takeoff position on the runway ("line up and wait"), brakes set, thrust at idle, awaiting takeoff clearance.
1. Static takeoff: when takeoff clearance is received, brakes are released, then thrust levers are smoothly advanced from idle to takeoff thrust.
2. Standing takeoff: when takeoff clearance is received, while brakes remain set (or PF holding the brakes, i.e., "standing on the brakes,"), thrust is advanced to approximately 70 percent N1 (CFM-56 engine; Airbus A320 series), then release brakes and continue to advance thrust levers to takeoff thrust.
The only time we use a standing takeoff is when engine anti-ice is being used. We are required to conduct the ice shedding procedure prior to takeoff: hold the brakes, set thrust and allow to stabilize at 70 percent N1 for 15 seconds, then release brakes and set takeoff thrust.
e38
Re: During a standing takeoff on a water-injected aircraft like the early 707, when does the water start?
Here's an interesting article on the 707 water system: http://www.adastron.com/707/qantas/bill-fishwick.htm
Re: During a standing takeoff on a water-injected aircraft like the early 707, when does the water start?
All the soviet build aircraft I have flown, they used standing take off. Felt the aircraft was catapulted down the runway after brakes were released. This was common on the Tu-134, Tu-154, Il-86 but also on the props Il-18 and An-24. Was this a soviet design of the engine or just the tradition of takling off?
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- Tristarsteve
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Re: During a standing takeoff on a water-injected aircraft like the early 707, when does the water start?
YQGflyer wrote:On the HS748 the water is injected when the throttle moves past a microswitch correlating with 14750 RPM (15000 is takeoff power) if the W/M pumps were turned on in the after start checks. If we were to do a standing takeoff it would burn water once the the throttle goes by that position (hence we don't do standing takeoffs).
The RR Dart on the HS748 used water/methanol mixture. The tank did not drain after take off and the methanol stopped the water freezing.
After this pure water was used. Anyone know why the methanol was dropped? Probably for weight.
We had water injection on the Spey engine on our BAC 111. In the middle east it was used on most take offs.
It was not tap water. We bought demineralised water from the fuel company, and they had a tank on wheels with a hand wobbly pump to fill up the tank on the BAC111.
Once a week an Air India B747 arrived in Bahrain, and needed 500 gallons of water. Glad I was not the man who hand pumped it in!
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- 747classic
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Re: During a standing takeoff on a water-injected aircraft like the early 707, when does the water start?
Some detailed info about the water injection system/operation of the Pratt & Witney JT9D engines at early 747 classics, see : viewtopic.php?t=764067
Re: During a standing takeoff on a water-injected aircraft like the early 707, when does the water start?
Use of water/methanol was common on RR Dart power planes like the F-27 as well as many TPE-331 turboprops such as the Metro with the -303 series engine as well as the J-31. The point it to enhance takeoff weight carrying performance in hot/high conditions. Water/Meth is heavy and expensive so is rarely used past the second segment of climb. In addition, it is toxic which precludes using engine bleed air for the cabin air during it's use. Bleeds used for air conditioning and pressurization must be off while water/meth is on.
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- DocLightning
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Re: During a standing takeoff on a water-injected aircraft like the early 707, when does the water start?
Somewhere on this forum is a description of the procedure by a retired KLM 747 pilot, probably in this very Tech/Ops forum. If you search, you might be able to find it. And if you do find it, please link it here. I'm not in a place to be doing a deep search at the moment.
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