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02-23-2011, 09:07 AM
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Join Date: Mar 2007
Location: 45G, Brighton, MI
Posts: 1,867
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Quote:
Originally Posted by DesertFlier
...I can't wait to get started on this. I've got the place to build it and I've got approval from my wife. I need to gather some tools and the plans and then I'll order the empennage kit...
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If you might be interested in a little bit of a head start, shoot me a PM.
http://www.cessna170.org/forums/down...2798&mode=view
__________________
Miles (VAF# 1238, Paid up as of 2018)
RV-7 TU 904KM (reserved)
Wings Fitted and Finish Kit on site
Construction Log
Picasa: Empennage Album, Wings Album, Fuselage Album
1955 Cessna 170B flying since 1982
'To get something you never had, you have to do something you never did.' -Unk.
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02-23-2011, 09:33 AM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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Quote:
Originally Posted by DesertFlier
Thanks for all the greetings, folks!
I can't wait to get started on this. I've got the place to build it and I've got approval from my wife. I need to gather some tools and the plans and then I'll order the empennage kit.
My questions on the turbo...
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Hi,
I'd also STRONGLY recommend you get involved with
http://www.homebuiltairplanes.com/fo...ew-technology/
and ask your questions there. There are some VERY talented aircraft designers there who love to discuss this type of thing. Don't turn your back on VAF, but if you want to start thinking outside the box, the Homebuilt forum is the place to do it. It's like having your own personal aeronautical engineering staff on retainer.
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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02-24-2011, 03:59 PM
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Join Date: Feb 2011
Location: California City, CA
Posts: 18
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Quote:
Originally Posted by Tom Martin
Standard wing rockets are limited by their wings when it comes to higher speeds. As you get above 250 mph added power brings an ever decreasing speed increase. It gets worse the higher you climb. This is the main reason that Mark Fredrick came out with the EVO wing...
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Care to elaborate on that? Where does the standard HR2 wing fall short, and why? How is the EVO wing different?
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02-25-2011, 06:39 AM
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Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,840
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Paul...
,,as the air gets thinner, the lack of wingspan makes the airplane start "mushing", if you will....fly at increasing angles of attack.
Look at a glider's very long wings....most of a wing's lift is produced toward the forward third and RV's just don't have much area there....the exception being the -9 and -10.
Best,
__________________
Pierre Smith
RV-10, 510 TT
RV6A (Sojourner) 180 HP, Catto 3 Bl (502Hrs), gone...and already missed
Air Tractor AT 502B PT 6-15 Sold
Air Tractor 402 PT-6-20 Sold
EAA Flight Advisor/CFI/Tech Counselor
Louisville, Ga
It's never skill or craftsmanship that completes airplanes, it's the will to do so,
Patrick Kenny, EAA 275132
Dues gladly paid!
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02-27-2011, 12:00 AM
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Join Date: Feb 2011
Location: California City, CA
Posts: 18
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Pierre, increased angles of attack are what I'm looking for actually, to a point. I don't have any personal experience with the HR2, but this is how I understand wing operation for airplanes in general:
The wing is at its highest angle of attack at slow speeds during takeoff and landing, when the aircraft is closest to stalling. This isn't the most efficient, but it's creating enough lift to hold the aircraft up, and enough drag to help slow it down.
At the opposite end, when the aircraft is in cruise, the angle of attack is at its lowest. Induced drag is still the same (you're still lifting the same weight), but the wing is at less than its optimum angle of attack (not an optimum lift-to-drag ratio), and form drag predominates.
But, if you climb up higher, you do have to increase alpha to hold up the same weight, because the air is less dense. At some point, you will reach the wing's optimum alpha and thus its maximum lift-to-drag ratio. At this point it will take a minimum amount of thrust to overcome the sum of all the drag forces on the aircraft.
Which brings me back to my original question: At what altitude does the stock HR2 wing reach its optimum angle of attack at gross weight? I realize the HR2 has stubby constant-chord wings, but there's still going to be a point where they are at their best, and my guess is that it's somewhere between 10,000 and 24,000. The turbocharger is there both to get me to that optimum altitude quickly, and to give me enough power to make the most of it.
Last edited by DesertFlier : 02-27-2011 at 12:01 AM.
Reason: grammar
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02-27-2011, 08:45 AM
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Join Date: Mar 2005
Location: Calgary, Canada
Posts: 5,766
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The short HR wing is the not the best design for high altitude but the turbo allows full power to be maintained to say 24,000 feet plus depending on MAP used. This results in higher speeds than an atmo Rocket can attain. Higher speeds mean lower alpha. Due to ATC and oxygen system concerns, it's unlikely you'll be flying much above this altitude and even more likely you'll be below 17,500 most of the time. It would perform just fine here here with 260-300 hp available.
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02-27-2011, 02:11 PM
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Join Date: Feb 2010
Location: SF
Posts: 30
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Quote:
Originally Posted by DesertFlier
Pierre, increased angles of attack are what I'm looking for actually, to a point. I don't have any personal experience with the HR2, but this is how I understand wing operation for airplanes in general:
The wing is at its highest angle of attack at slow speeds during takeoff and landing, when the aircraft is closest to stalling. This isn't the most efficient, but it's creating enough lift to hold the aircraft up, and enough drag to help slow it down.
At the opposite end, when the aircraft is in cruise, the angle of attack is at its lowest. Induced drag is still the same (you're still lifting the same weight), but the wing is at less than its optimum angle of attack (not an optimum lift-to-drag ratio), and form drag predominates.
But, if you climb up higher, you do have to increase alpha to hold up the same weight, because the air is less dense. At some point, you will reach the wing's optimum alpha and thus its maximum lift-to-drag ratio. At this point it will take a minimum amount of thrust to overcome the sum of all the drag forces on the aircraft.
Which brings me back to my original question: At what altitude does the stock HR2 wing reach its optimum angle of attack at gross weight? I realize the HR2 has stubby constant-chord wings, but there's still going to be a point where they are at their best, and my guess is that it's somewhere between 10,000 and 24,000. The turbocharger is there both to get me to that optimum altitude quickly, and to give me enough power to make the most of it.
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Gosh, have you thought about maybe the possibility that maybe John Harmon, the creater of the Harmon Rocket, might be able to give you that information? Who knows, if you ask him nicely, he might even build one for you with the wing specs you require....
http://www.harmonrocket.com/
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02-27-2011, 07:59 PM
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Join Date: Nov 2005
Posts: 358
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An EVO wing is the only choice for a turbo Rocket. It has a higher aspect ratio to take advantage of the alititude, and the CG envelope to accept a turbo....
The best solution for a Turbo would be a top induction -550 powered airplane, that would leave room under the engine for the turbo set up.
Lets use Ole '84 as the baseline.. It currently has a 23/23 critical altitude of 8500 ft... at that altitude it indicates 180 KIAS will true right around 206 KTAS on a summer day burning 13.5 gph on the rich side....
So, lets suppose we put a medium sized turbo on my airplane and boost the critical altitude up to 18,000 ft. The rule of Thumb says that TAS increases by 2%of IAS/1000 ft of altitude when power remains constant, so that means the Turbo Rocket should true about 19% of 180 or 34 kts + 206, or exactly 240 KTAS which is the airframe redline.....
This would be an impressive airplane, but it would require a very disciplined pilot, to keep it in the envelope.......
This would be an airplane that would easily blast through the redline in any descent and sooner or later, there would be problems.....
Tailwinds,
Doug Rozendaal
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02-27-2011, 09:20 PM
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Join Date: Jul 2006
Location: Vul, VA
Posts: 316
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Quote:
Originally Posted by B25Flyer
An EVO wing is the only choice for a turbo Rocket. It has a higher aspect ratio to take advantage of the alititude, and the CG envelope to accept a turbo....
The best solution for a Turbo would be a top induction -550 powered airplane, that would leave room under the engine for the turbo set up.
Lets use Ole '84 as the baseline.. It currently has a 23/23 critical altitude of 8500 ft... at that altitude it indicates 180 KIAS will true right around 206 KTAS on a summer day burning 13.5 gph on the rich side....
So, lets suppose we put a medium sized turbo on my airplane and boost the critical altitude up to 18,000 ft. The rule of Thumb says that TAS increases by 2%of IAS/1000 ft of altitude when power remains constant, so that means the Turbo Rocket should true about 19% of 180 or 34 kts + 206, or exactly 240 KTAS which is the airframe redline.....
This would be an impressive airplane, but it would require a very disciplined pilot, to keep it in the envelope.......
This would be an airplane that would easily blast through the redline in any descent and sooner or later, there would be problems.....
Tailwinds,
Doug Rozendaal
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And you would seriously have to watch the CHT's as they would easily go above redline temps as well.
Is your critical alt. only 8500 ft.? Did I miss something...?
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02-28-2011, 04:37 PM
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Join Date: Feb 2011
Location: California City, CA
Posts: 18
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Quote:
Originally Posted by B25Flyer
This would be an impressive airplane, but it would require a very disciplined pilot, to keep it in the envelope.......
This would be an airplane that would easily blast through the redline in any descent and sooner or later, there would be problems.....
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I don't have a problem flying on the edge of the envelope. Part of it is pilot discipline, but part of it is making sure the aircraft adequately warns the pilot of dangerous situations. I have plans to build a glass panel, and as I understand it at least some EFIS computers can calculate true airspeed and display a barber pole on the airspeed scale, as well as an audible overspeed warning. If possible I'd like to integrate an autothrottle with the EFIS so the computer can adjust the throttle during descent to keep pilot inattention from resulting in an overspeed.
As for the wing design, as I understand it a higher aspect ratio is going to improve wing efficiency regardless of airspeed and altitude. So in that manner the Evo wing would be a step in the right direction. If I wanted to spend more years and dollars, I'd like to throw away the whole Vans/Harmon wing design and start over with something that's better suited to higher speeds. But alas, I don't think that will be happening...
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