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My next big project since used JT15D's are starting to look "reasonably" priced.

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BoKu

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One quibble about your RFP: You will get virtually no laminar flow with a wing swept that sharply.
 

Swampyankee

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I think you must be mistaking it with a different engine, the SFC is around 0.562 lb/(lbf·h) or a little higher at max depending on model, and a little better at cruise. Thrust isn't that high, 2100lbs-3000lbs or thereabouts, depending on model.

Anyways, little update, I've finished the Request for Proposal requirements, and made the initial concept sizing/weight calculation.



I'm going to have a friend of mine check my numbers just to make sure I didn't do something completely wrong
Est We is 3600lbs
Est Wf is 1600lbs
Max t/o 5600lbs

I just downloaded solidworks 2017 on my home PC and laptop today along with workstation graphics GPUs, so I've been reading up and watching tutorials on it so I can port the initial concept over and begin making the size change requirements.
A design airframe life of 3500 hours is incredibly short; US military aircraft are usually about 6,000 (the one spec I specifically remember is 6,000 hours lifetime, and 360 flight hours/year; to put that into perspective commercial airliners will typically get over 4,000 flight hours per year; one 727 flew over 600 hours in a month). Of course, most GA aircraft haven't been designed for X cycles or Y flight hours; they've been designed to static strength criteria with generous margins of safety.

I don't know what you're design mission is, but a very real concern would be flight cycles not flight hours. Rather obviously, a plane's landing gear doesn't do any more work on a five hour flight than an one hour one, and the same thing is true of fuselage pressurization cycles. These come into the area of low-cycle fatigue. See, for example http://www.am.chalmers.se/~anek/teaching/fatfract/98-7.pdf, http://www.ijeert.org/pdf/v2-i4/2.pdf, and http://academic.uprm.edu/pcaceres/Courses/INME4011/MD-6A.pdf
 
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Kazansky22

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One quibble about your RFP: You will get virtually no laminar flow with a wing swept that sharply.
Ahh thank you, I thought as much as well, but I was under the guidance that leading edge slats would help with smoothing turbulent airflow at lower speeds as long as the alpha isn't too high. Do you have any suggestions as to where I can learn more about that?

A design airframe life of 3500 hours is incredibly short; US military aircraft are usually about 6,000 (the one spec I specifically remember is 6,000 hours lifetime, and 360 flight hours/year; to put that into perspective commercial airliners will typically get over 4,000 flight hours per year; one 727 flew over 600 hours in a month). Of course, most GA aircraft haven't been designed for X cycles or Y flight hours; they've been designed to static strength criteria with generous margins of safety.

I don't know what you're design mission is, but a very real concern would be flight cycles not flight hours. Rather obviously, a plane's landing gear doesn't do any more work on a five hour flight than an one hour one, and the same thing is true of fuselage pressurization cycles. These come into the area of low-cycle fatigue. See, for example http://www.am.chalmers.se/~anek/teaching/fatfract/98-7.pdf, http://www.ijeert.org/pdf/v2-i4/2.pdf, and http://academic.uprm.edu/pcaceres/Courses/INME4011/MD-6A.pdf
Great material for me to go over. So you would recommend having a time limit just based on age, IE Airframe design life of 20 years or something along those lines. I wasn't quite sure what to put in that box when I filled it out, I just knew there had to be some kind of pre-defined goal.

Oh and the design mission is pretty simple, T/O >=4,000 ft, climb to FL280, Cruise 1000nm*, 15 minute loiter, and landing >= 4,000 ft
Unless I did the fuel burn calculation wrong I think 1000nm is doable given the weight goal. But again this is my first time doing anything like this so I'm sure there will be a good bit of iterating.
 

ScaleBirdsScott

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In terms of design....just remember everybody thinks they are a designer, and a good designer is a pirate.....Giving over to a consultant while probably advisable with the scope of this project, he will want to change the design to conform to his prejudices. Good luck.
Truth here. Design is all about stealing the best ideas you can.
 

Lucrum

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I think you must be mistaking it with a different engine, the SFC is around 0.562 lb/(lbf·h) or a little higher at max depending on model, and a little better at cruise. Thrust isn't that high, 2100lbs-3000lbs or thereabouts, depending on model.
They were -5's rated at 2960 lbs thrust
But yeah I may be thinking of another engine's T.O. fuel burns
Even at .56 sfc and 2960 lbs thrust FF would still be 247 gph
 
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Swampyankee

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Ahh thank you, I thought as much as well, but I was under the guidance that leading edge slats would help with smoothing turbulent airflow at lower speeds as long as the alpha isn't too high. Do you have any suggestions as to where I can learn more about that?



Great material for me to go over. So you would recommend having a time limit just based on age, IE Airframe design life of 20 years or something along those lines. I wasn't quite sure what to put in that box when I filled it out, I just knew there had to be some kind of pre-defined goal.

Oh and the design mission is pretty simple, T/O >=4,000 ft, climb to FL280, Cruise 1000nm*, 15 minute loiter, and landing >= 4,000 ft
Unless I did the fuel burn calculation wrong I think 1000nm is doable given the weight goal. But again this is my first time doing anything like this so I'm sure there will be a good bit of iterating.
Depending on how sharp the leading edge is, you may get vortex lift. This is a major factor in the low-speed performance of highly swept aircraft, especially deltas. NASA has a plethora of information, e.g., https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19670003842.pdf and https://ntrs.nasa.gov/search.jsp?R=19810020561. NASA's NTRS (ntrs.nasa.gov), Cranfield's Aerade (http://aerade.cranfield.ac.uk/), and probably DLR (Germany), ONERA (France), AGARD (NATO), and the Von Karman Institute, have searchable on-line resources.

For low-utilization airframes, like many GA aircraft, the lift limit is probably corrosion, not fatigue. I've seen that with some military aircraft.
 

Kazansky22

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Well I have spent a couple weeks going through the rest of the Conceptual design. It's far enough along that I wanted to show it to a couple engineers I know and they confirmed what I was seeing too. Weight/size/complexity were ballooning a bit out of control. So.... yea its a little beyond what I think would be reasonable to pursue.

However with that said I would like to continue the idea of a homebuilt delta winged aircraft with a resemblance to the Mirage, Delta Dart ect... my buddy who works here in the Palmdale CA area in aerospace suggested a ducted fan. Which I always thought was a thing for RC planes due to low efficiency. But like most things (I thought), their is a bit more to it then that.

So I'm going to start the process over with scaled back design objectives. Something more akin to the UL-39 that the gentlemen at CTU in Czech did, as opposed to more akin to a Viperjet.

If any of you guys haven't seen it, heres a link to short video https://www.youtube.com/watch?v=di9IkdY7fvs
 
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Lucrum

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However with that said I would like to continue the idea of a homebuilt delta winged aircraft with a resemblance to the Mirage, Delta Dart ect... my buddy who works here in the Palmdale CA area in aerospace suggested a ducted fan. Which I always thought was a thing for RC planes due to low efficiency. But like most things (I thought), their is a bit more to it then that.
Originally my project revolved around a 450HP Mazda 20B engine driving a ducted fan. Then I stumbled across the T-58 engine. Half the weight, three times the fuel burn. No torsional resonance issues.
 

Kazansky22

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Was the 450hp not enough power for the fan or did the T-58s benefits out weigh the cons of the 20B?

Also how do you calculate the power needed to spin a given fan at certain rpms/altitudes/airspeeds been trying to find the answer to that one for a couple days. Just want to made some baseline calculation to see if a ducted fan is feasible given possible engine combinations and size limitations.
 

Lucrum

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Was the 450hp not enough power for the fan or did the T-58s benefits out weigh the cons of the 20B?
The 450 hp should have been adequate. But I was going to be driving the fan via a relatively long carbon fiber shaft requiring bearing support at the fan end. And I had no way of know what if any torsional resonance issues I might encounter. Once I got it up and running.

Also how do you calculate the power needed to spin a given fan at certain rpms/altitudes/airspeeds been trying to find the answer to that one for a couple days. Just want to made some baseline calculation to see if a ducted fan is feasible given possible engine combinations and size limitations.
Javaprop and a couple of different spreadsheets written by others more knowledgeable than I on the subject.
I had already built one fan which didn't turn out as well as I expected. I was in the process of redoing it in 2024 aluminum when I came across the T-58.
Assuming it all worked as planned the fan should have gotten better fuel economy. But my project is already dragging out for so long. I felt the added operating cost of the turbine outweighed the potential technical problems of the ducted fan.
 

pictsidhe

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Thanks for that link pictsidhe, that is a pretty nifty piece of software, how accurate would you say it is? I suppose the calculations are based off of known data points.
The performance of a ducted fan / shrouded prop is highly dependent on duct/shroud design. javaprop merely has a tickbox. So I'd say ballpark... It's apparently pretty good for propellors. I have a fairly complex spreadsheet evolving for my project, but my laptop or phone won't run java, so it's a while since I've compared it.
 

Swampyankee

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Ahh thank you, I thought as much as well, but I was under the guidance that leading edge slats would help with smoothing turbulent airflow at lower speeds as long as the alpha isn't too high. Do you have any suggestions as to where I can learn more about that?



Great material for me to go over. So you would recommend having a time limit just based on age, IE Airframe design life of 20 years or something along those lines. I wasn't quite sure what to put in that box when I filled it out, I just knew there had to be some kind of pre-defined goal.

Oh and the design mission is pretty simple, T/O >=4,000 ft, climb to FL280, Cruise 1000nm*, 15 minute loiter, and landing >= 4,000 ft
Unless I did the fuel burn calculation wrong I think 1000nm is doable given the weight goal. But again this is my first time doing anything like this so I'm sure there will be a good bit of iterating.

For an aircraft with a low duty cycle -- much less than 100 hours/year -- you may have to change some rubber and elastomeric parts by the calendar, but a very big concern, in general, would be corrosion and possibly delamination, which can be caused by water, especially if there are exposed edges. Since composites tend to have slow crack propagation properties, inspecting for delams, corrosion, and cracks every few months, even if you happen to be storing the airplane in a humidity-controlled, air-conditioned hangar, would not be amiss.

As an aside, I think you mean T/O <= 4,000 ft. >= means greater than or equal to.
 

Kazansky22

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Yea swampy, your correct on the symbol nomenclature, its been a little while :)
But most of the work I did on the initial concept are changing. The costs/size/complexity were ballooning a little out of control so I'm going back to the drawing board so to speak. In the meantime I've just been trying to absorb as much information on ducted fan technology as I can.

Dumb question I think I know the answer to already, are there any ducted fan / shrouded props on the market with adjustable pitch props?
 
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