Sailplane Pilot Design Sickness

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Monty

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I decided to start this thread after Autoreply started to exhibit symptoms in another thread.

Hi, my name is Monty and I'm a recovering SPDS sufferer

symptoms:

1. irrational induced drag phobia

2. complete L over D derangement

3. severe laminar flow dependency

4. fixation on Parsons bodies and interference drag

5. abnormal affinity for pressure distribution plots.

6. Irrational fixation on efficiency numbers.

7. Sufferers may join extreme composite material cults seeking laminar nirvana.

If you suspect someone may be a laminar-haulic some of the warning sings:

Do they own a profilometer?

Do they have a copy of illicit books such as Bruce Carmichael's seditious text?

Do they hoard plots of exotic airfoils?

Do they have a condescending and dismissive attitude towards all "imperfect" aircraft?

If so.....this person may require an intervention.

What to do?

Immediately take this person for an all out-balls to the wall-aerobatic ride in Harmon Rocket. Fly the airplane to the limits of the envelope. :ban:

Let them fly it also.

Then put them back in their perfect aircraft that runs on three horsepower.

Repeat as necessary.

Note: in severe cases long technical discussions may be required.

If discussion fails.....shock therapy may be the only answer!:roll:
 

Monty

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Thank you, Monty, my name is Norman. I recognize several of these symptoms in myself. My fetishes are: wetted aspect ratio and ton-miles per gallon.
Mmmmmmmmmm WET
Welcome brother Norman!

wetted aspect ratio fixation is a definite warning sign. Do you find yourself calculating wetted area drag coefficients and making carpet plots?

The Vulcan bomber!!!!! How is it possible?
 

Aircar

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Add me to the list but at least in remission -- I think that our friend Auto has an allegiance to sailplane technology that might blind him to some of the fundamentals as elucidated so well by his compatriot Henk Tenere (mind just went blank on his surname --I probably would have no hope of pronouncing it and have forgotten the correct spelling as well )

The major difference in comparing sailplane and lightplane 'efficiencies' is the one of wing loading --best reversed to read 'how much skin area do I need to expose to support the neccesary weight" (ie foot squared per pound ) --and the VERY inefficient structure of sailplanes in terms of airframe wing loading (empty weight divided by wing area - a measure of the COST of carrying payload ) belies the otherwise outstanding dimensionless figure of L/D --where a LOT of the "L" is 'dead' lift holding up the heavy cantilver wings the figure becomes misleading --payload per unit of drag comes closer (and being honest about it NONE of our homebuilts is even 1% efficient by definition --there is no "PAY"load or useful work done ,hence zero efficiency strictly speaking.

It does however make for interesting calculation to reduce sailplane tested in flight figures to drag co efficients and then play with the comparable figures from such things as recent CAFE tests or some of the wartime NACA data -- if you for example allow to 'morph' a sailplane so as to optimize the wing area for each flight speed you will be able to shed the excessive drag of excessive wing area (and structurally limiting span) THEN it can get interesting . Legendary soaring pilot AJ Smith built his tractor monoplane racer for the EAA Oshkosh efficiency races (the Byers, ..... something something )and swept the field with it --maybe someone can post a link to it; you might have expected him to have come up with an exotic pusher of sailplane like shape but he didn't --that doesn't prove that the best solution might not indeed be a pusher of some type but it is hard to beat the highly developed conventional tractor for going fast . (nevertheless the Dornier Do 335 showed that the Mustang type layout could be beaten and it was certainly better than the P38'Pond Racer config . The Lear Fan conceded nothing to 'ultimate' performance and used every trick in the sailplane book over 30 years ago --and was carbon to boot --it's flight tested figures should be a good baseline for what is in effect a 'sailplaneized' go fast airplane ( I have a lot of stuff on it -maybe some flight test info somewhere ) - it was the chronological successor to the Douglas mixmaster (in fact Donald Douglas "lent" John Hart Smith to Bill Lear for structural and manufacturing consultancy on it -- I met John by chance in the old airline canteen and showed him my 'related' Opal at the time -we stayed in touch since )

Without some novel innovation it seems unlikely that the level reached by the Learfan could be surpassed --active boundary layer control for example --induced drag is no longer structurally compromised with modern fibres (both for flutter and bending) so we should be able to optimize but when you work out the optimum wing area it is usually so small in cruise that there is not much left be dragging.. (a man's handkerchief is about the amount of wing area devoted to each passenger on a 747 for instance --hard to beat that and also to have it at 40 000ft what's more )
 

autoreply

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Designing a plane that has 2 or 3 times more drag as necessary just doesn't seem a very interesting goal to me. In that case, building an existing design achieves the same thing and we'd still be riding horses, not flying...
Immediately take this person for an all out-balls to the wall-aerobatic ride in Harmon Rocket. Fly the airplane to the limits of the envelope. :ban:

Let them fly it also.
So, where do I go :gig:
 
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Aircar

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Jarno, I think you need to pick up the gaunlet here and defend your thesis (if not your honour!) -- and shouldn't a red blooded moderator object to the 'sickness' inferered in the title ?:devious: For what it is worth, I haven't been in a Harmon Rocket 'balls to the wall' but I did help build a Steen Skybolt (VH -SOD rego ...) many moons ago and foolishly went for an aerobatic ride with the owner --who had a reputation for not being gentle...... I held my lunch down but only just and felt 'green' for hours afterwards --what we describe as aerobatics in gliders is more like ballet while these sort of brutes engage in something like being in a cement mixer (not my cup of tea --less again if I am not doing the flying ..)

Anyway now is your chance to post some reduced drag figures and show your Stemme like 'dreamship' -the gauntlet is down (we need a 'glove across face' icon to go with this )
 

autoreply

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Jarno, I think you need to pick up the gaunlet here and defend your thesis (if not your honour!) -- and shouldn't a red blooded moderator object to the 'sickness' inferered in the title ?
It's hard to argue against opinion, impossible really.

Thanks for bringing up the Learfan, one of the best arguments and astonishing performance for a ship of that size (a third of the drag of competitors, even the Avanti has 50% more drag):

Untitled.jpg
(EFPA in sqft)


Anyway now is your chance to post some reduced drag figures and show your Stemme like 'dreamship' -the gauntlet is down (we need a 'glove across face' icon to go with this )
Nope. I've often argued against unrealistic claims from "revolutionary" designs. I don't put definitive claims out, unless I can put solid evidence (solely flight testing) behind them. The aim for my own design though is RV-performance (all of the parameters) with half the power :)
 

ultralajt

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I dont care about laminar flow or its separation location, as I am pretty modest with my wishes. These are in range of 1:15 glide angle and <1m/s of sinking speed.... quite good for some slope and thermall flying and a homebuild (foldable, footlaunchable) glider. If I wanted more performance and laminar flow, I ve just purchased an old composite glider (Cirrus.. Phoebus...) , but then I will be robbed from daydreaming and figuring out many design features of my homebuild glider. Now, I dont really know, what I am enjoiny more, dreaming and designing or flying.. khmm....? Scratch, scratch on back of my head..

What sickness is that? :)

Mitja
 
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John Newton

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Made me laugh, I suspect I may have some of the symptoms listed! I also suffer from an irrational obsession with lift distributions and adverse yaw although I am well aware I can always stick a fin on it, I like a challenge! :)
 

John Newton

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Vulcan bomber, my favourite plane, hoping to get to see it fly next year, (saw the east kirkby lanc recently) maybe one day I'll get to building an R/C version, it's just having the time, too many projects!
 

Norman

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SPDS. Is that also known as "analysis paralysis?"
Not if there's actual hardware and plans for a follow-on design. OMG there's actual hardware. :cry: and future plans:wail: and the worst part is that I'm getting other people to pay for it:shock: Oh, wait, that's actually not a bad deal:beer: Sadly it isn't my plane though. I'm just working on it for a friend.
 

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Norman

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Add me to the list but at least in remission -- I think that our friend Auto has an allegiance to sailplane technology that might blind him to some of the fundamentals as elucidated so well by his compatriot Henk Tenere (mind just went blank on his surname --I probably would have no hope of pronouncing it and have forgotten the correct spelling as well )
Henk Tennekes, I had one of his books also
 

Jay Kempf

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Henk Tennekes, I had one of his books also
OK, that sounds like a Jeff Foxworthy opener.

If you have any of Alex Strojnick or Bruce Carmichael's books, you might be a laminaholic.

If you think 5 hp is enough to power a cross country airplane, you might be a laminaholic.

If you feel actual pain when you hear a whistling noise, you might be a laminaholic.

If you think a 2" wing tip chord is too much, you might be a laminaholic.


...
 

Hot Wings

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Legendary soaring pilot AJ Smith built his tractor monoplane racer for the EAA Oshkosh efficiency races (the Byers, ..... something something )and swept the field with it --maybe someone can post a link to it; you might have expected him to have come up with an exotic pusher of sailplane like shape but he didn't --that doesn't prove that the best solution might not indeed be a pusher of some type but it is hard to beat the highly developed conventional tractor for going fast .
It was the AJ-2 entered in the Lowers Baker Falck 500. I couldn't find a picture on the internet, but it was a very clean little plane. I was working on my first homebuilt project back then - a BD-5 to be powered by a Polaris snowmobile engine - and had every intention of entering it in the LBF 500 until the project was interrupted by hormonal induced non aviation interests.

Of course a stock BD-5 stood little chance of being competitive but in the best NASCAR tradition of "getting competitive" I had developed a way to maintain total weight for the final weigh thus making it appear that the plane had used far less fuel than it actually did.

If you think a 2" wing tip chord is too much, you might be a laminaholic.
...
Shouldn't that be "If you think the winglet tip chord..........."?
 
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Monty

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Designing a plane that has 2 or 3 times more drag as necessary just doesn't seem a very interesting goal to me. In that case, building an existing design achieves the same thing and we'd still be riding horses, not flying...

So, where do I go :gig:
I'm guessing Toobuilder could hook you up.

I'm making fun of myself as much as anybody. I went through the whole uber-efficiency phase. I have some pretty neat design studies I may post later, if I can stand to sit at my desk later today.

I assure you I'm not just spouting uninformed opinion.

Sailplanes are a special case, near and dear to my heart. I also greatly admire the Lear-fan. One of my favorites. Also the Avanti.

BUT!!!

Twin turbine reliability, and large size allow the designer to accept compromises that would make our smaller aircraft very dangerous.

There are problems with trying to make a high speed cruising aircraft with a high cruise L/D in our flight regime and mission. The wing winds up being impossibly small to meet sane landing speed requirements. If you use a nice laminar airfoil, then you have problems during landing with low Reynolds numbers and laminar separation bubbles. (Probably what killed Lars Giertz). Reynolds number effects are another issue. The faster you go, the less all that viscous drag reduction matters. It eventually becomes irrelevant at supersonic speeds and the flow is for practical purposes inviscid.

With such a small wing, you need complex high lift devices so you can land and take-off. Problem is the wing has too little volume to house everything. If you want laminar flow airfoils, leading edge slats are not allowed. Structure becomes heavy, with no place to put fuel except the fuselage. More heaviness because the spar must carry all that concentrated load. You need very carefully prepared surfaces-composites-rigid polished skins- adding weight, expense, maintenance, and cost. Aircraft wing performance becomes very sensitive to environmental factors like rain and bugs.

There are several aircraft that have attempted to apply all the sailplane tricks to a powered aircraft. The White Lightening is the best example I can think of right now. I have flown in the pattern with one at the LasCruces airport in NM. It was a relatively hot and high day. I was in a team tango with Denny Funemark, and we had no problem getting up and away. The White Lightening took a lot of runway and had a terrible climb rate. The Team Tango was also designed by a sailplane guy and has nice performance. The designer obviously understood the concepts I am talking about.

This is what happens when you go for high L/D at cruise-You get a small wing and engine. Your climb is going to be terrible, and hot day performance down right dangerous.

Well you say...just put a bigger engine on it. Fine, now you will go even faster and be cruising at a lower CL and the wing will be too big, you'll burn too much fuel which you have no room to carry. That's how it works.

So, you need an engine and a wing that is too big for cruise in order to have well rounded design. That's just the way it is. You are going to operate at a CL .1-.2. in cruise. You will have very little induced drag in cruise, and induced drag will be less important than pressure and momentum drag. Just the physics of the situation.

Many of the very low drag airfoils have relatively high pitching moments, and you may find that the trim drag cancels any advantage. You may also find that outside the laminar bucket the drag rises very steeply, so that you actually have MORE drag in climb and maneuvering than a conventional airfoil....no good in a low power aircraft.

It is instructive to compare aircraft like the SX300 and Questair Venture to Glasairs, Lancairs, and the White Lightening.

You will find there really isn't that much of a gain to be had in typically powered GA flight regime.

Now....there is one exception to this. A turbocharged aircraft that flies at high altitude. In the States we are restricted to below 18Kft vfr, and below 25Kft ifr. So there is a limit to how high you can go. A turbo normalized engine, and normal sized wing will operate at a higher L/D in the 25Kft regime.

BUT!!!

Physiological effects are deadly serious and risks go up substantially at those altitudes. I've taken a chamber ride....I know of which I speak.

I still believe in trying to get as much drag reduction as possible out of a design, but I also understand that at some point you are going to reach the point of diminishing returns for a powered aircraft. You will sacrifice performance somewhere else and wind up with a smaller flight envelope and a less fun aircraft to fly.

Don't be so dismissive of the RV. Given what I've just said, look at the trades that have been made.

A short fat wing.-minmum parts count, ease of construction, lots of area, low frontal area, low structural weight, wide CG envelope.

Stone age airfoil-very little pitching moment, insensitive to construction error, insensitive to rain, bugs, dents, relatively low drag. Has a lot of induced drag in climb...so what we have a big engine. During cruise flight low profile drag, low induced drag at low to mid altitude cruise.

I know it looks like there is a lot of interference drag at the wing root, but people have put big expanding fillets and gone....slower.

Let's compare Dave Ander's aircraft to any highly optimized drag reduced aircraft with similar engine.....It' won't be much better if at all. It would be interesting to compare it to the Smith AJ-2. The AJ-2 lands really hot, I'm sure it would not best Dave Ander's plane in the CAFE challenge.

BTHW I don't have rose colored glasses about Dave Ander's plane, I'm sure he is making much more hp than a stock engine...still impressive.

Many of the very remarkable low drag sailplane inspired aircraft (there is a German one that carries 3 people on 40 hp, with very impressive performance, but I can't remember the name just now) all fly relatively small speed ranges, more like a sailplane. The CAFE prize is structured to reward a giant flight envelope-not a tiny specialized one.

It's all about compromises.
 

Toobuilder

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I'm guessing Toobuilder could hook you up...
I'd be happy to. That and show you the flat turns the Hiperbipe can do. It rivals a Formula 1 car - no doubt because the fuselage looks more like a shipping container than an airplane.



Does the above photo make those suffering from SPDS break out in hives?


In all seriousness, I can relate a practical side of the "less than optimal" design like the RV:

I often depart North Las Vegas (KVGT) airport and head due west - right toward a 6,000 foot sheer cliff face 20 miles away. On departure, I stay under the class B airspace shelf for a while and then climb for all the 200HP will give me. Only until the last few moments the cliff face fills my windscreen and I finally squeak across the top. Yes, if I had half the HP on a more optimized airframe I would cruise on less fuel, but if I have to orbit for 10 minutes trying to gain altitude, have I really gained anything? Sometimes it is useful to simply power your way over or through something. Yes, it lacks finesse, but it is the "American way" after all.
 
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