Bifurcated pipe thrust loss
02-02-2012, 03:14 AM
#1
Bifurcated pipe thrust loss
Does any one know how much thrust is lost with a Bifurcated pipe? I fly at 5400 ft and lose about 20% power at 60 deg. I first flew my Avonds F-15 (kit built) yesterday with his pipe and it took the whole 600ft paved runway to get off, than I had to keep it flat tell got some speed. I have a JC P80SE in it, rated at 22# at sea level. The plane is 25# dry. Thanks George
02-02-2012, 04:32 AM
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RE: Bifurcated pipe thrust loss
It has some thrust loss yes, but the main problem is that the F-15 has a lot of drag and needs about 30 lbs of thrust to fly like a fighter should.
I also tried a P80 in my F-15 for a few flights, but even if it is smaller than yours I switched to a P120.
Enrique
I also tried a P80 in my F-15 for a few flights, but even if it is smaller than yours I switched to a P120.
Enrique
02-02-2012, 05:39 AM
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RE: Bifurcated pipe thrust loss
George, I did quite a bit of work w/ Tam back in the 90s determining bi-furcated pipe losses. I used several of his pipes w/ AMT engines (Pegasus and Merc ). The average loss was approximately 4-5%, i.e., about a pound for a 22-pound thrust engine, Standard Day. Of course, these were Tam pipes...the best designed and crafted, IMO. And i knew what the AMT engines were actually putting out. Yours is rated at 22.....(STD, sea level)....wonder if it is.
Re temp and altitude losses: figure 2% for every 10F above a Standard Day and same for every 1000' above sea level. At your 60F, no losses; at 5400', perhaps 12%. So, your total loss w/ a good pipe, your engine, and that altitude, is more like 16%, or 3.5-pounds.
My first jet was an Avonds DF converted to turbine....using he almost 5-pound Pegasus w/ the original 22-pounds thrust (plane weighed 31-pounds at TO). I flew it in and out of 410' good grass, sea level...well barely, as sometimes w/o a headwind I was bending the stick on TO. Over the years, engine was updated to 30-pounds....a real performer in that model. Try full brakes until thrust is full, then release; look for a headwind; also some positive AOA of the wing while rolling makes things easier (i.e. the model sits nose high by a few degrees).
Ray
Re temp and altitude losses: figure 2% for every 10F above a Standard Day and same for every 1000' above sea level. At your 60F, no losses; at 5400', perhaps 12%. So, your total loss w/ a good pipe, your engine, and that altitude, is more like 16%, or 3.5-pounds.
My first jet was an Avonds DF converted to turbine....using he almost 5-pound Pegasus w/ the original 22-pounds thrust (plane weighed 31-pounds at TO). I flew it in and out of 410' good grass, sea level...well barely, as sometimes w/o a headwind I was bending the stick on TO. Over the years, engine was updated to 30-pounds....a real performer in that model. Try full brakes until thrust is full, then release; look for a headwind; also some positive AOA of the wing while rolling makes things easier (i.e. the model sits nose high by a few degrees).
Ray
02-02-2012, 06:19 AM
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RE: Bifurcated pipe thrust loss
ORIGINAL: 67Jag
Re temp and altitude losses: figure 2% for every 10F above a Standard Day and same for every 1000' above sea level. At your 60F, no losses; at 5400', perhaps 12%. So, your total loss w/ a good pipe, your engine, and that altitude, is more like 16%, or 3.5-pounds.
Re temp and altitude losses: figure 2% for every 10F above a Standard Day and same for every 1000' above sea level. At your 60F, no losses; at 5400', perhaps 12%. So, your total loss w/ a good pipe, your engine, and that altitude, is more like 16%, or 3.5-pounds.
Harry
02-02-2012, 10:21 AM
#9
RE: Bifurcated pipe thrust loss
I have often wondered if you could build a bifurcated pipe using the thrust augmenting design of John Wright in the front section of the pipe. Could the gains there cancel out the losses in the bifurcated section.
It would be an expensive experiment to modify (butcher) one of Tam's pipes.
It would be an expensive experiment to modify (butcher) one of Tam's pipes.
02-02-2012, 11:23 AM
#10
RE: Bifurcated pipe thrust loss
Ha,
Sorry guys, but this is crazy-talk!
My P-80SE got my F-15 off the deck in 200' or less, and flew it with authority. Avonds, Air Magic and Yellow F-15's flew on Ram 750's cheerfully before the 1000's came out.
There could be any number of things going on with any one installation. One pipe could be less efficient than another, and the gap between the pipe and bell-mouth matters, too.
These videos may not show a Bandit, but they sure don't show a plane 'asking for trouble', either...
[youtube]http://www.youtube.com/watch?v=LsJyJ8VtVqw[/youtube]
[youtube]http://www.youtube.com/watch?v=DXPmCmUWozo&feature=related[/youtube]
[youtube]http://www.youtube.com/watch?v=AF6AQcpSs2E&feature=related[/youtube]
Sorry guys, but this is crazy-talk!
My P-80SE got my F-15 off the deck in 200' or less, and flew it with authority. Avonds, Air Magic and Yellow F-15's flew on Ram 750's cheerfully before the 1000's came out. There could be any number of things going on with any one installation. One pipe could be less efficient than another, and the gap between the pipe and bell-mouth matters, too.
These videos may not show a Bandit, but they sure don't show a plane 'asking for trouble', either...
[youtube]http://www.youtube.com/watch?v=LsJyJ8VtVqw[/youtube]
[youtube]http://www.youtube.com/watch?v=DXPmCmUWozo&feature=related[/youtube]
[youtube]http://www.youtube.com/watch?v=AF6AQcpSs2E&feature=related[/youtube]
02-02-2012, 11:37 AM
#11
RE: Bifurcated pipe thrust loss
I am sure it would fly fine at sea level. I am going to put the 120 from my Rookie in it. We have tested, on a test stand, Wren, Jet Cat, Kingtech and Jet Central all loose about 20% at this altitude.
I just wanted to know how much thrust a Bifurcated pipe lost.
Shaz I have been nice to you lately.
Thanks George
I just wanted to know how much thrust a Bifurcated pipe lost.
Shaz I have been nice to you lately.
Thanks George
02-02-2012, 11:37 AM
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RE: Bifurcated pipe thrust loss
In an Avonds F-15 in hot or high altitude conditions i would put a 160 or the the new 140 in it. 160 is the same size and it really starts to look like an F-15 with that engine. P-80 really is not enough.
02-02-2012, 12:46 PM
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RE: Bifurcated pipe thrust loss
ORIGINAL: oistein
In an Avonds F-15 in hot or high altitude conditions i would put a 160 or the the new 140 in it. 160 is the same size and it really starts to look like an F-15 with that engine. P-80 really is not enough.
In an Avonds F-15 in hot or high altitude conditions i would put a 160 or the the new 140 in it. 160 is the same size and it really starts to look like an F-15 with that engine. P-80 really is not enough.
Hi,
Does that mean that you think the plane in those videos is underpowered?
[youtube]http://www.youtube.com/watch?v=hLR6dGorVS8&context=C33c7b92ADOEgsToPDskLUK-5H1PSxOfbVdN_q6R2E[/youtube]
02-02-2012, 05:05 PM
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RE: Bifurcated pipe thrust loss
Harry, of course it's a simplification, but the percentages used take many variables into consideration. So, just knowing the temp difference from a Standard Day and the altitude above sea level, makes it an easy calculation and a very good approximation of overall thrust reduction. Certainly for our purposes.
Ray
Ray
02-02-2012, 06:07 PM
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RE: Bifurcated pipe thrust loss
Shaun,
it's unfortunately not as simple as that. I have gotten to know you over time and understand that you are articulate and intellectual. However no amount of prior "knowledge" actually prepares most jet pilots for flying at altitude. Maybe you have flown at altitude, I don't know. But George has nailed it on the head. What most people fail to appreciate is that this isn't just 20% loss of thrust, it's also thinner air....MUCH thinner air up here.
Up here, Jets don't climb out as well, they don't stay up as well, and they like to fall out of the sky. This is why homeruns travel such legendary distances at Coors Field. It is why golfers always marvel at the added distance the ball travels when they swing up here. Thin air = no resistance. Problem is, we WANT resistance, we count on that resistance that nice thick air provides to give our wings something to climb on. Nice thick air down at sea level makes for nice slow landings, nice stable takeoffs, and lots more gliding and predictable approaches. It may limit top speed more too but you get added thrust to combat that.
The last Best in the West that was held in Colorado before being moved to Cali was held at George and my flight site: Chatfield State Park. We have a 650 foot main runway. Bob Violett came out for it and among other jets, he brought one of his p-70/80 powered Mig 15's. The problem he experienced is very common up here:
1. You back off throttle to slow your plane down and set up for landing. You drop gear and set up flaps.
2. Problem is the plane isnt slowing down like you are used to it doing. The air is thin, the flaps aren't really biting into the air, and the wings aren't really floating on that thin air well
3. Your plane starts sinking MUCH faster than you are used to seeing. Trouble.
4. Predictably, you increase throttle to stop the plane from sinking. You realize that the plane has stopped sinking, but is now going 20-25 mph faster than you are used to when landing. Oddly enough however, you notice you are at a much higher throttle setting than you are used to for plain old straight and level "slow flight", that's because you have about 20% less thrust remember?
5. You start realizing that this isn't San Diego or Florida. It is not a municipal airport with a 1.3 mile runway and nice thick air. You are trying to crash land a now seemingly under-powered jet, onto what looks like a postage stamp of a runway, while coming in faster than you have ever landed, and feeling like your control throws are less responsive than ever before.
6. That nauseating feeling in the pit of your stomach is your realization that if you get LUCKY, REALLY REALLY LUCKY, due to your much higher approach speed, and unpredictability as to how your plane is sinking, you MIGHT get to touch down at the mid-point of the runway, and then have about 300 feet to come to a full stop while traveling 80-85 MPH on touch-down.
7. Bob Violett went around 3 times. He landed on the 3rd. He went long. Tore his gear out. Many spectators children still remember the endless stream of holy prophecies that he uttered as he brought his mangled plane back from 75 feet past the runway.
He swore he would never return. He never did. Welcome my friend, to high altitude flying... When we make trips for jet events to sea-level places, it feels like we are flying in jello. Everything slows down and planes actually WANT to stay up in the air...we often wonder how most sea-level people would do at our fields, since it seems so much easier to fly at their fields...but it's not polite to say anything, and we often don't.
So Shaun, buddy, when George says P-80SE is not enough, considering he has been flying and building jets for 20 years - all while living at 5400 feet- he doesnt mean it wouldnt fly your plane down in San Diego, he means it isnt really doing the trick up here. Apples to Oranges.
(P80) 22lb thrust at sea level - 25% thrust (20% for altitude + minimum 5% for bifurcated pipe) = 16.5 lbs
Would you want to fly an F15 with thrust comparable to a P60 or Wren 54 at sea level....? in a place where there is no lift, no glide coefficient, and on a 650' runway? That's what it equates to up here...
Cheers bud,
Shaz
it's unfortunately not as simple as that. I have gotten to know you over time and understand that you are articulate and intellectual. However no amount of prior "knowledge" actually prepares most jet pilots for flying at altitude. Maybe you have flown at altitude, I don't know. But George has nailed it on the head. What most people fail to appreciate is that this isn't just 20% loss of thrust, it's also thinner air....MUCH thinner air up here.
Up here, Jets don't climb out as well, they don't stay up as well, and they like to fall out of the sky. This is why homeruns travel such legendary distances at Coors Field. It is why golfers always marvel at the added distance the ball travels when they swing up here. Thin air = no resistance. Problem is, we WANT resistance, we count on that resistance that nice thick air provides to give our wings something to climb on. Nice thick air down at sea level makes for nice slow landings, nice stable takeoffs, and lots more gliding and predictable approaches. It may limit top speed more too but you get added thrust to combat that.
The last Best in the West that was held in Colorado before being moved to Cali was held at George and my flight site: Chatfield State Park. We have a 650 foot main runway. Bob Violett came out for it and among other jets, he brought one of his p-70/80 powered Mig 15's. The problem he experienced is very common up here:
1. You back off throttle to slow your plane down and set up for landing. You drop gear and set up flaps.
2. Problem is the plane isnt slowing down like you are used to it doing. The air is thin, the flaps aren't really biting into the air, and the wings aren't really floating on that thin air well
3. Your plane starts sinking MUCH faster than you are used to seeing. Trouble.
4. Predictably, you increase throttle to stop the plane from sinking. You realize that the plane has stopped sinking, but is now going 20-25 mph faster than you are used to when landing. Oddly enough however, you notice you are at a much higher throttle setting than you are used to for plain old straight and level "slow flight", that's because you have about 20% less thrust remember?
5. You start realizing that this isn't San Diego or Florida. It is not a municipal airport with a 1.3 mile runway and nice thick air. You are trying to crash land a now seemingly under-powered jet, onto what looks like a postage stamp of a runway, while coming in faster than you have ever landed, and feeling like your control throws are less responsive than ever before.
6. That nauseating feeling in the pit of your stomach is your realization that if you get LUCKY, REALLY REALLY LUCKY, due to your much higher approach speed, and unpredictability as to how your plane is sinking, you MIGHT get to touch down at the mid-point of the runway, and then have about 300 feet to come to a full stop while traveling 80-85 MPH on touch-down.
7. Bob Violett went around 3 times. He landed on the 3rd. He went long. Tore his gear out. Many spectators children still remember the endless stream of holy prophecies that he uttered as he brought his mangled plane back from 75 feet past the runway.
He swore he would never return. He never did. Welcome my friend, to high altitude flying... When we make trips for jet events to sea-level places, it feels like we are flying in jello. Everything slows down and planes actually WANT to stay up in the air...we often wonder how most sea-level people would do at our fields, since it seems so much easier to fly at their fields...but it's not polite to say anything, and we often don't.
So Shaun, buddy, when George says P-80SE is not enough, considering he has been flying and building jets for 20 years - all while living at 5400 feet- he doesnt mean it wouldnt fly your plane down in San Diego, he means it isnt really doing the trick up here. Apples to Oranges.
(P80) 22lb thrust at sea level - 25% thrust (20% for altitude + minimum 5% for bifurcated pipe) = 16.5 lbs
Would you want to fly an F15 with thrust comparable to a P60 or Wren 54 at sea level....? in a place where there is no lift, no glide coefficient, and on a 650' runway? That's what it equates to up here...
Cheers bud,
Shaz
02-02-2012, 06:49 PM
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RE: Bifurcated pipe thrust loss
+1 for Shaz - not bad for a guy used to having to write in "lawyer speak". [X(]
Here's another way to look at it: 65*F day, low humidity, Chatfield State Park (~5400'MSL) = 7100' density altitude........
Even full scale turbine and normally aspirated prop typically struggle up here. That loss of 20% is real.
-Mike
Here's another way to look at it: 65*F day, low humidity, Chatfield State Park (~5400'MSL) = 7100' density altitude........
Even full scale turbine and normally aspirated prop typically struggle up here. That loss of 20% is real.
-Mike
02-02-2012, 07:55 PM
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RE: Bifurcated pipe thrust loss
this isnt about jets but is still thye same thing. my 450 stearman would go near stright up at 38" manold press at sea level but wouldnt make METO power at 7500 feet. and that was a supercharged engine,,,thin air kills power,,,,take a 220 stearman at 8000 feet and 85 degres means you dont fly.
02-02-2012, 09:44 PM
#19
RE: Bifurcated pipe thrust loss
Shaz,
Yeah, I get it. As you know, I'm also a full-size pilot, so I understand about thinner air at altitude. Thing is, not all of the people saying a P-80 is marginal are flying at altitude (or clarified that their assessment of that engine's suitability was specific to George's altitude). Go look at the comments (and where their authors are from) and you'll see how the altitude component didn't seem like the main thrust of the question. If they did, then I withdraw my comments!
Yeah, I get it. As you know, I'm also a full-size pilot, so I understand about thinner air at altitude. Thing is, not all of the people saying a P-80 is marginal are flying at altitude (or clarified that their assessment of that engine's suitability was specific to George's altitude). Go look at the comments (and where their authors are from) and you'll see how the altitude component didn't seem like the main thrust of the question. If they did, then I withdraw my comments!
