Page 5 of 42 FirstFirst 123456789101115 ... LastLast
Results 61 to 75 of 627

Thread: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

  1. #61
    Registered User fly2kads's Avatar
    Join Date
    Jan 2010
    Location
    Justin, TX
    Posts
    1,040
    Likes (Given)
    557
    Likes (Received)
    305

    Re: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

    Just like you've suggested, getting back out of an airport is often more demanding than getting in. I usually want enough runway for my expected takeoff length +50%. I fly for fun. I don't mind pushing my limits here and there, but I can do without pucker factor if I can avoid it.

  2. Likes Topaz liked this post
  3. #62
    Registered User
    Join Date
    Jan 2013
    Location
    USA.
    Posts
    4,210
    Likes (Given)
    2008
    Likes (Received)
    3483

    Re: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

    Angle of climb is sometimes Very, Very important . Friend of mine built a new 900' grass runway with a 30 deg bend in the middle, at his new cabin. I came in low and didn't look as close as I should have, made a low pass looking at the surface. There is an entrance of a blind box canyon at the end of the runway. After making the first turn after entering the canyon, I saw the canyon end right in front of me with a steep wall . Had to use every foot of my angle of climb. At the top on my left side there was a low gap in the tops of the trees that I was able to go through to get out. Few days latter I call another friend and mentioned that I landed at the 900' runway and the first thing he said was "you didn't enter the box canyon like I did , did you? ". Dan
    Pops

  4. Likes BBerson liked this post
  5. #63
    Registered User
    Join Date
    Sep 2009
    Location
    Northern California
    Posts
    174
    Likes (Given)
    136
    Likes (Received)
    115

    Re: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

    Quote Originally Posted by BBerson View Post
    I never look at the POH. It is for a new aircraft tuned to perfection and a bit of exaggeration.
    The real aircraft performance is learned from experience and takeoff needs has to be " guessed at" from experience in similar conditions.
    Just too many variables, density altitude, wind, slope, grass, etc
    I agree with BBerson. It really depends on knowing what kind of performance you can expect, and what kind of conditions you will encounter. Most of my powered flying is behind 0-235 engines; in other words, not much performance, and typically well below what 'the book' promises. Living in the Sierra CA foothills, I have no problem flying 10 minutes west to Sacramento Valley airports and comfortably fly in and out of airports with less than twice the book numbers (ie around 1500' to 2000' depending on DA.) Most of these airports are at sea level, though, and there's not a tree or hill for miles off the departure end. On the other hand, 10 minutes to the east of me, there are runways I won't fly in or out of in an O-235-powered plane even with four times the book numbers. It's not the 5000' elevation and the real 50' pine trees encircling the runway that 'the book' says I should clear with plenty of room that deters me; it's the typical 500'/min downdraft blowing into the canyon off the departure end that scares me away. Like Pops wrote, in some cases Angle of Climb is as important as runway length. In other cases, it's Rate of Climb that you need.

    Your Catalina Island example is another good one: you really only need a few hundred feet of runway for takeoff, as you can always build flying speed rapidly by following the cliff face down. It depends on your personal pucker factor

    For your design exercise, I'm not sure a 'safety factor' is of any use. It's your plane--use the numbers the calculations produce, and then verify them during test flight. Once you know the numbers for your plane, it then becomes a judgement call about other factors. On my plane, with numbers I've proven, at an airport low, flat, and with wheat fields for miles around, I'd be comfortable with very little safety factor. Give me that same plane and an airport in the mountains, in the middle of a forest (or city), that I've never flown at before, and I'm probably going to be looking for at least enough runway to get to 50' and then back down and stopped if things don't feel right. As a low-time pilot, that's what I like. Give me more hours, a mountain checkout, and a Maule Super Rocket, and my answer will change.

  6. Likes BBerson, Topaz liked this post
  7. #64
    Moderator Topaz's Avatar
    Join Date
    Jul 2005
    Location
    Orange County, California
    Posts
    12,426
    Likes (Given)
    6980
    Likes (Received)
    3964

    Re: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

    Quote Originally Posted by rdj View Post
    I agree with BBerson. It really depends on knowing what kind of performance you can expect, and what kind of conditions you will encounter. ... For your design exercise, I'm not sure a 'safety factor' is of any use. It's your plane--use the numbers the calculations produce, and then verify them during test flight. Once you know the numbers for your plane, it then becomes a judgement call about other factors. ...
    Thanks, everyone for your input. I think I've got pretty clear idea what I want to do, based on my original thoughts and your comments. Unless someone really feels I'm being foolish, I'm going to stick with my 60%/40% rule for the design of the aircraft, and then I can do exactly as you all are saying once it's built, tested, and I gain experience with it (assuming that ever happens). I absolutely agree about the "conditional" nature of any given airport - obstructions, oddities like box canyons, etc. I'm going to account for bad-case density altitude in my calculations, and a review of the "obstructions" column regarding the airports I chose to look at for this design study shows nothing that's really a factor. Small stuff, mostly.

    I'll absolutely be addressing both rate and angle of climb a little further on. Right now I'm finishing up cruising range, altitude in the Build Log thread, and speed, and climb rate/angle is next on my to-do list.
    "If you have built castles in the air, your work need not be lost; that is where they should be. Now put the foundations under them." - Henry David Thoreau

    Design Project: Conceptual Design of an "Inexpensive" Single-Seat Motorglider
    Discussion Thread for the Project: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

  8. #65
    Registered User BBerson's Avatar
    Join Date
    Dec 2007
    Location
    Port Townsend WA
    Posts
    7,375
    Likes (Given)
    1259
    Likes (Received)
    1109

    Re: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

    I think your speed will be much less than 110 mph.
    The single seat Song has a cruise around 60. And it is very slick with carbon fiber molded smooth skin.
    Of course, I don't know what is meant by "inexpensive" at this stage. Or what your engine is.

  9. #66
    Moderator autoreply's Avatar
    Join Date
    Jul 2009
    Location
    Rotterdam, Netherlands
    Posts
    10,723
    Likes (Given)
    245
    Likes (Received)
    2301

    Re: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

    Quote Originally Posted by Topaz View Post
    Just a quick note. This question has been vexing me, so I took another look in JAR 22, the rules set I'm generally using at a guideline for requirements. JAR 22.51(a) specifies that the takeoff run should be less than or equal to 500 meters to an altitude of 15 meters. That's 1,640 feet to an altitude of 49 feet. JAR 22.51(b) specifies particular speed conditions that apply.

    That's shorter than the full runway length for both of my "critcal case" runways, so I'll use that as a threshold "absolute" value for takeoff length, and then try for better in matching the 60% runway lengths I've already listed.
    That's ISA+0 right?

    Very different from your real-world much higher DA's. 500 meters at ISA is already borderline pathetic.

    Just a thought, but you might want to study some OLC-traces from tow's in the mountains, like Sisteron or Gap or equivalent places in the US for some real-world performance data and correlate that to text-book performance.
    Kennis vermenigvuldig je door het te delen.
    (You multiply knowledge by dividing it)

  10. #67
    Moderator autoreply's Avatar
    Join Date
    Jul 2009
    Location
    Rotterdam, Netherlands
    Posts
    10,723
    Likes (Given)
    245
    Likes (Received)
    2301

    Re: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

    Quote Originally Posted by BBerson View Post
    I think your speed will be much less than 110 mph.
    The single seat Song has a cruise around 60. And it is very slick with carbon fiber molded smooth skin.
    Detached flow+climb prop. Not necessarily representative.
    Kennis vermenigvuldig je door het te delen.
    (You multiply knowledge by dividing it)

  11. #68
    Moderator Topaz's Avatar
    Join Date
    Jul 2005
    Location
    Orange County, California
    Posts
    12,426
    Likes (Given)
    6980
    Likes (Received)
    3964

    Re: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

    Quote Originally Posted by autoreply View Post
    That's ISA+0 right?
    Very oddly, they don't specify, anywhere that I could find. It has to be demonstrated by flight test, so I suppose one could go to the Dead Sea on a cold morning, but that really doesn't accomplish much for the real-world pilot.

    Quote Originally Posted by autoreply View Post
    Very different from your real-world much higher DA's. 500 meters at ISA is already borderline pathetic.
    Agreed.

    Quote Originally Posted by autoreply View Post
    Just a thought, but you might want to study some OLC-traces from tow's in the mountains, like Sisteron or Gap or equivalent places in the US for some real-world performance data and correlate that to text-book performance.
    Agreed completely. The current "threshold" value for takeoff on my requirements sheet is to at minimum meet the specification (500m and 15m AGL) for whichever is worst of the two cases in post #11 of my Build Log thread. These cases include a rather substantial density altitude penalty. My actual goal (60% of the runway length of whichever case is worse, to 50' AGL, also with the density altitude penalty) is somewhat more difficult still.

    If these both place an undue burden on the sizing of the aircraft, I'll revisit it, but I'd like to make these happen, for exactly the reason you're talking about.
    "If you have built castles in the air, your work need not be lost; that is where they should be. Now put the foundations under them." - Henry David Thoreau

    Design Project: Conceptual Design of an "Inexpensive" Single-Seat Motorglider
    Discussion Thread for the Project: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

  12. #69
    Moderator Topaz's Avatar
    Join Date
    Jul 2005
    Location
    Orange County, California
    Posts
    12,426
    Likes (Given)
    6980
    Likes (Received)
    3964

    Re: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

    Quote Originally Posted by BBerson View Post
    I think your speed will be much less than 110 mph.
    We'll see. This is what I'm asking for. Whether or not I can get it is part of the design process.

    Quote Originally Posted by BBerson View Post
    Of course, I don't know what is meant by "inexpensive" at this stage. Or what your engine is.
    Neither do I.
    "If you have built castles in the air, your work need not be lost; that is where they should be. Now put the foundations under them." - Henry David Thoreau

    Design Project: Conceptual Design of an "Inexpensive" Single-Seat Motorglider
    Discussion Thread for the Project: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

  13. #70
    Registered User something-awful's Avatar
    Join Date
    Sep 2014
    Location
    Over the hills and far away
    Posts
    55
    Likes (Given)
    3
    Likes (Received)
    20

    Re: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

    Late to the party, but a couple of notes/my thoughts.

    Chances are you'll never get your real flight tests at ISA so if I remember right EASA/FAR specs have correction methods somewhere in the appendices or AMCs, so that way all the aircraft tested are given a standard datum to compare from.

    Also, not sure what motor gliders you use in the US but Slingsby Ventures and Grob 109s are pretty much the motor glider 'workhorses' here at the moment, a vast amount of clubs that own or operate TMGs use a Venture and the rich ones a 109, maybe have a look at the selling price of a used one of them. We use them for much like you'd intend to, cross country experience/nav training, stick and rudder experience when the sky isn't working and general putt-putting around. Their price won't be indicative of the price of a one-off though...

    Incidentally, referencing your note about future use as a trainer. When working on a training glider project a year or two ago we found that in the UK at least, the fleets of trainers/two seaters were actually appreciating rather than depreciating because of the demand they're in. Not quite the same on the TMG front but a good, spacious and well thought out trainer couldn't go amiss. The Ventures work but they only take off because the earth is round...

    Either that or if there's enough excess power and your field performance is good enough you could double a future iterative design as a tug. That would probably increase the cost effectiveness of it.

  14. #71
    Registered User
    Join Date
    Apr 2007
    Posts
    173
    Likes (Given)
    1
    Likes (Received)
    30

    Re: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

    Quote Originally Posted by Topaz View Post

    So far, this airplane is falling well inside the definition of an LSA under 14 CFR Part 1.1, so I think that's a good place from which to grab my threshold stall speed requirement. That's not more than 45 knots CAS (52 mph) with high-lift devices retracted. Again, no altitude is specified, so I'm going to use my worst-case density altitude airport and day of 90°F at Crystal (46CN), which puts density altitude above 6,400 feet MSL. I'm not thinking about flaps for this airplane anyway, but the requirement to show the stall speed without them in the LSA definition is an interesting wrinkle.
    Density altitude will not matter as the regulation for stall speed is based on CAS.

  15. #72
    Registered User
    Join Date
    Sep 2014
    Location
    Canada
    Posts
    662
    Likes (Given)
    3
    Likes (Received)
    166

    Re: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

    Quote Originally Posted by Hot Wings View Post
    I may have not been clear when used the word assumption, or I'm still misunderstanding the distinction between concept and preliminary stages.

    Lets presume that your concept involved using an off the shelf aluminum tube for the tail boom. Lets further presume that this is based on the fact that similar planes have done so successfully making this a reasonable "assumption". Unless you stop at this point and actually calculate if the tube is sufficient, based on the concept sizing and loads, you won't know until you get to the next step if there is in fact an off the shelf tube that can take both the torsion and bending loads. At this point you then have the choice to have a custom tube extruded that will take the loads (busting the budget) or go back to the conceptual stage and either reduce the tail loads or plan on using a different method to attach the tail.
    .................................................. .................

    May I suggest a third option: rivetting on stiffeners to handle localized stress?
    Last edited by Riggerrob; September 30th, 2014 at 12:49 PM. Reason: Spelling

  16. #73
    Registered User BJC's Avatar
    Join Date
    Oct 2013
    Location
    97FL, Florida, USA
    Posts
    5,186
    Likes (Given)
    2711
    Likes (Received)
    3241

    Re: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

    Posted by Topaz Just a quick note. This question has been vexing me, so I took another look in JAR 22, the rules set I'm generally using at a guideline for requirements. JAR 22.51(a) specifies that the takeoff run should be less than or equal to 500 meters to an altitude of 15 meters. That's 1,640 feet to an altitude of 49 feet.
    To put that T/O and climb performance in perspective, it just about matches the performance of a Cessna 152.

  17. Likes Topaz liked this post
  18. #74
    Moderator autoreply's Avatar
    Join Date
    Jul 2009
    Location
    Rotterdam, Netherlands
    Posts
    10,723
    Likes (Given)
    245
    Likes (Received)
    2301

    Re: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

    Where it concerns the regulations; over the last decade EASA CS23 and FAR23 have been brought really close together and are now essentially identical save your silly units.

    The only major change in CS22 over the last years is the crash load on the nose. From memory that's 10G's, acting backwards and upwards 45 degrees. Nasty to design for, but a realistic load case no powered plane in existence I'm aware off would survive. (That's 10 tonnes or so...)
    Kennis vermenigvuldig je door het te delen.
    (You multiply knowledge by dividing it)

  19. #75
    Registered User Hot Wings's Avatar
    Join Date
    Nov 2009
    Location
    Rocky Mountains
    Posts
    4,400
    Likes (Given)
    142
    Likes (Received)
    1334

    Re: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

    I do believe that you may be totally delusional!

    "The smaller of my two vehicles is my '73 Porsche 914, which I want to store indoors anyway (they tend to rust)."

    Tend to rust!? They are addicted to that activity and aggressively seeks the next fix of Fe2O3

    Your workplace restrictions would seem to prove to be as great a problem to solve as the design of the plane. It really makes me appreciate what I have available for build space and the next time I find myself grumbling about not enough room - I'll go clean the shop!
    Conventional wisdom and practices yield conventional results. If that is good enough for you:
    Problem solved.

    "--and pompous fools drive me up the wall. Ordinary fools are all right; you can talk to them, and try to help them out."
    Richard P. Feynman

    “Without deviation from the norm, progress is not possible.”
    Frank Zappa

  20. Likes Topaz, akwrencher liked this post

Similar Threads

  1. Replies: 68
    Last Post: November 29th, 2016, 02:32 PM
  2. Another "napkin sketch" - single seat composite microlight/LSA - AirFlo v1.0
    By Floydr92 in forum Aircraft Design / Aerodynamics / New Technology
    Replies: 69
    Last Post: August 24th, 2014, 11:14 AM
  3. "New Design Concepts" and "Project underway" sections
    By flyvulcan in forum Feedback and Suggestions
    Replies: 31
    Last Post: May 17th, 2012, 07:35 PM
  4. Converting two-seat glider into single-seat motorglider
    By cluttonfred in forum General Experimental Aviation Questions
    Replies: 4
    Last Post: August 5th, 2010, 09:26 PM
  5. Replies: 7
    Last Post: November 21st, 2008, 01:18 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •