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helno
Jun 19, 2003

hmm now were did I leave that plane
It looks clean on the outside. It got a paintjob last year to sell it. Has just over 9700 hours on the airframe and 2500 on the motor.

Back when it was towing banners the paint looked pretty rough. It is at the municipal airport so it gets flown off tarmac. No grass fields are open around here this time of year. There are a few guys with ski's but the winters have been pretty hit or miss lately.

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CodfishCartographer
Feb 23, 2010

Gadus Maprocephalus

Pillbug
Whops, nevermind.

CodfishCartographer fucked around with this message at 10:33 on Mar 18, 2013

Colonel K
Jun 29, 2009
Some good questions there,

you have plenty of options for travel / camping. If you want to land off field I'd suggest something with a decent set of balloon type tyres. I'm not sure what the US regulations are, but there seem to be a lot of places where you can land anywhere.

When you're thinking about aircraft you really need to think about mission profile. Do you want to go really long distances? is short take offs and landings more important? and then there is cost.

Sounds like a supercub type aircraft might fit your bill, or a light sport equivalent. Although there's also the cessna 170 in all metal format which would allow you to fly in more types of weather.

It's a great hobby and I understand in the states there are plenty great airfields where you can camp. Jhonson creek has a great repuation. http://www.youtube.com/watch?v=ZnaXor86Ep0

helno
Jun 19, 2003

hmm now were did I leave that plane

helno posted:

Getting the gopro camera has officially paid for itself. I entered a pretty dull video in a contest but apparently the competition isnt that great because I got the most votes.

http://www.urthecast.com/urtheview/vote


Digging this back up because I just won $1000 from that contest.

Edit: http://www.urthecast.com/blog/updates/urtheview-competition-announces-its-first-grand-prize-winner-video/

I have a feeling they wanted to forget it even happened due to the lack of submissions. I emailed them a few weeks ago asking who won the grand prizes and they replied yesterday that it was me.

Hopefully with the weather improving i'll be able to get the Lazair back together. The 172 is missing a turn coordinator right now so I haven't started on the night rating yet.

helno fucked around with this message at 02:02 on Apr 11, 2013

Slung Blade
Jul 11, 2002

IN STEEL WE TRUST

helno posted:

Digging this back up because I just won $1000 from that contest.

I have a feeling they wanted to forget it even happened due to the lack of submissions. I emailed them a few weeks ago asking who won the grand prizes and they replied yesterday that it was me.

Hopefully with the weather improving i'll be able to get the Lazair back together. The 172 is missing a turn coordinator right now so I haven't started on the night rating yet.



Hot drat, congrats Helno!

charliemonster42
Sep 14, 2005

So Nerobro found this thread for me again. I've been thinking I would love to build an ultralight lately for a variety of reasons, mostly that it's much cheaper in all aspects than building an experimental plane.

I've narrowed it down to the Legal Eagle as my prime choice, mostly because it is a conventional style plane with a four stroke motor. For some reason, four stroke is my main decision factor. I just can't seem to get past the oil and noise and finickiness of a two stroke. As much as I love two stroke motorcycles, planes and two strokes just don't push the right buttons.

If I do decide that I can get past the two stroke thing, I do like the look of the minimaxes and also the airdrome eindecker replica.

Can anyone chime in with suggestions or experience? I don't even really know where to begin.

Nerobro
Nov 4, 2005

Rider now with 100% more titanium!
First off, since you're getting your license, why limit yourself to a ultralight? There are a lot of small, easy to build airplanes out there. Which opens your options to all sorts of "normal" engines.

Is the engine the only thing that is really keeping you on the legal eagle?

My only "problem" with the legal eagle, is that you need to learn to weld, as well as woodwork. A texas parasol is a very similar rig, but is all wood, simplifying life quite a bit.

helno
Jun 19, 2003

hmm now were did I leave that plane
I would say that if you are getting licensed anyways build one of the larger planes that can use a 4 stroke engine.

You just give up way to much airframe to get a 4 stroke engine under FAR 103. Hell you can get an Ercoupe for <$20000 and that can fit in as an LSA and has a GENUINE AIRCRAFT ENGINE. I'm hoping in 5-10 years i'll be able to split an RV-6 for a decent price.

charliemonster42
Sep 14, 2005

My biggest concerns with doing a full scale airplane is time and money. I don't know how readily I'd be able to commit 3 years to a project like that. I've looked at a few full size kits, like Sonexes and RVs and the like, and would love to do one, but the level of involvement with a kit like that is orders of magnitude bigger.

The Legal Eagle is stuck in my head because it's the first one I've really looked into is all. I'm comfortable with welding and need an excuse to improve my skills. I suppose the 4 stroke aspect of it made it stick more than the others because it sounds more enjoyable. The weight penalty of the 4 stroke really is a pain in the rear end though.

What are the odds of getting caught with an overweight ultralight? How would they even know? Ramp check you?

Nerobro
Nov 4, 2005

Rider now with 100% more titanium!

charliemonster42 posted:

My biggest concerns with doing a full scale airplane is time and money. I don't know how readily I'd be able to commit 3 years to a project like that. I've looked at a few full size kits, like Sonexes and RVs and the like, and would love to do one, but the level of involvement with a kit like that is orders of magnitude bigger.

The Legal Eagle is stuck in my head because it's the first one I've really looked into is all. I'm comfortable with welding and need an excuse to improve my skills. I suppose the 4 stroke aspect of it made it stick more than the others because it sounds more enjoyable. The weight penalty of the 4 stroke really is a pain in the rear end though.

What are the odds of getting caught with an overweight ultralight? How would they even know? Ramp check you?

Ultralights, and "full scale" airplanes are very close in size. In fact, for single seaters, ultralights tend to be much, much bigger than "full scale" airplanes.

For example, a KR-1
Length 12' 9"
Wing Span 17' 0"
Total Wing Area 62 sq. ft.
Cruise 180mph

Lets compare that to a Lazair:
Length: 13 ft (3.96 m)
Wingspan: 36 ft 4 in (11.1 m)
Wing area: 143 sq ft (13.3 mē)
Cruise 40mph

The lazair is almost twice as big!

Lets try another. The Legal Eagle:
Length: 13 ft 0 in (3.96 m)
Wingspan: 23 ft 6 in (7.16 m)
Wing area: 107 sq ft (9.9 m2)
Cruise speed: 50mph

Lets get back to "conventional" aircraft. Those that don't have the ultralight tag. I'm going to stick wtih single seaters to keep things even.

Rutan Q1 "Quickie"
Wingspan 17 ft 9 in
Length 17 ft 5 in
Cruise 120mph

FRED
Wing span: 22 ft 6 in (6.86 m)
Wing area: 111 sq ft (10.32 sq m)
Length: 16 ft (4.88 m)
Cruise: 71mph

RV3
Length: 19 ft 0 in (5.85 m)
Wingspan: 19 ft 11in (6.12 m)
Cruise 170-190mph

So, why a "legal" plane versus an ultralight? Ultralights live in a very narrow range of airspeeds. And in a very narrow range of weight loading. Ultralights can't fly around populated areas. Ultralights aren't really welcome in controlled airspace. Ultralights have quite short durations.

Building a plane that fits into the narrow little corner of the law that is "ultralight" is just that. A plane that exists in a narrow little corner of the law. If you don't need to live in that little corner, don't.

Building an ultralight means leaving a lot of the fun stuff at home. A decent guage cluster. Comforts, and even some safety systems. You don't see carb heat on ultralights, nor cabin heat. You also almost never see flaps, and things that you should want to use to keep your skills up.

"Real" airplanes give you more room to fudge. You can leave things a little heavier and you will still get a decent plane. "Real" planes also are smaller, which means there's less material to buy, and usually cheaper materials to buy. They also tend to use normal covering techniques, and normal materials, so you can get normal advice from normal airplane people.

Not that I'd personally use normal materials or covering... I'm just saying.. you can. :-)

Now, you asked about the plane getting checked. As far as I know, nobody gets checked. But, if you crash, and there are legal proceedings, your rig WILL get checked, and then you could be up the creek. Operating an unregistered aircraft, that sort of thing. And no insurance will want to touch you ever again.

Why do you think an airplane will take you three years to build? why do you think a Legal Eagle will take much less time than say.. a Cub clone? (they are of about equal complexity.)

Something like a FRED assembles very quickly. So can a KR-1.

I went through the same thing. I didn't think I could afford to actually get a pilots license. when I discovered that it was going to be a reality, I did a careful check of myself and what my desires were. Building a ultralight just didn't make any sense once I knew a real license was in reach.

Recently I read through all of bob hoovers blog. I picked up all the really choice stuff on building an airplane on the cheap. http://realtinker.blogspot.com/2013/04/cheap-aircraft-building-techniques.html

Helo: no offence eh? :-)

Ninja Edit: And somehow i got through a post without mentioning a DA-2 or a Hummelbird. Amazing.

Colonel K
Jun 29, 2009
Perhaps I might chime in on this one.

The thing I'd say most of all is try to work out what your mission profile is and what you want to get out of it.

Microlights and ultralights are fantastic for bimbling around at low cost when the weather is excellent. They give you a lot of feeling for the air and are cheap to run. I think Helno posted a video of him flying later on in the evening and it just looked like a brilliant way to relax and unwind.

I'm no expert on the actual building of kits, but the people I speak to who've done it say that the quality of the kit and how much comes asembled makes the biggest difference to construction time rather than the size of it. That being said there is an rv9 in our hangar which is now ready for test flying which has taken their group 8 years to build.

The four stroke little engine of choice at the moment seems to be the 80 or 100hp rotax, it seems to be put on nearly all that category of planes at the moment. It also has the advantage of running on mogas and using very little.

If you do want to go places though, a little bit extra size and weight helps a lot.

I learned to fly on fixed wing microlights, which are fantastic little flying machines, but I have found that group A stuff deals with turbulence a whole lot better.

helno
Jun 19, 2003

hmm now were did I leave that plane
As far as ultralights and homebuilts go Canada has some pretty kick rear end laws.

Our ultralights do not have the same ridiculous weight limit but in exchange we need to get a basic license. Oh and we can fly into the states and the only restriction is no passengers and you have to have an ultralight instructor rating or a rec/PPl.

On the homebiult side of things I recently learned that we are not as restricted as you guys are. When someone builds a plane in the states they can do any maintenance needed. Once that plane is sold the new owner does not get this same privilege. In Canada this is not the case. You do not need to be the original builder to sign off the maintenance release.

The more I keep looking the more I am leaning towards a used homebuilt over an inexpensive certified plane. The Lazair is great for what I currently use it for (ultracheap flying but only in great weather and very little cross country) but I really would like a second seat and the ability to go places faster than driving.

Used certified planes are quite cheap but the cost of the annual maintenance kills the hourly rate with a single owner. An Ercoupe or a C150 can both be had for less than $20k but unless I fly 75+ hours a year it is cheaper to rent. An RV-6 costs more up front but split 2-3 ways cuts this down quite a bit and you get far more plane for the money with a lower hourly cost without needing to fly 75+ per year.

isnoop
Jan 9, 2001

I used to be an admin,
but then I took an arrow
to the knee.

charliemonster42 posted:

My biggest concerns with doing a full scale airplane is time and money. I don't know how readily I'd be able to commit 3 years to a project like that. I've looked at a few full size kits, like Sonexes and RVs and the like, and would love to do one, but the level of involvement with a kit like that is orders of magnitude bigger.

The Legal Eagle is stuck in my head because it's the first one I've really looked into is all. I'm comfortable with welding and need an excuse to improve my skills. I suppose the 4 stroke aspect of it made it stick more than the others because it sounds more enjoyable. The weight penalty of the 4 stroke really is a pain in the rear end though.

What are the odds of getting caught with an overweight ultralight? How would they even know? Ramp check you?

Consider the STOL CH-750
http://www.zenithair.com/stolch750/

It's a relatively inexpensive kit that is estimated to snap together in about 350 hours, but don't take my word for it.

isnoop fucked around with this message at 10:27 on Apr 16, 2013

helno
Jun 19, 2003

hmm now were did I leave that plane
Got the Lazair mostly together last night. Everything is on but the engines. No video this time my gopro was dead.

I have started flying with an instructor in the 172 to get my night rating but it looks like a buyer might have turned up so it is hard to say if I will finish that rating this season.

helno
Jun 19, 2003

hmm now were did I leave that plane
Finally got the first flight of the year in the Lazair tonight. A 5 mph direct crosswind is the best weather I am going to see for a while.

I did a few circuits and lost the display on my airspeed/altimeter. Didn't really miss it but was probably climbing out way faster than best rate because of it.

Colonel K
Jun 29, 2009
Glad to hear you've got it ready for the year again. Did you do much maintenance over winter or just reassemble?

babyeatingpsychopath
Oct 28, 2000
Forum Veteran

I'm going to be falling into a big pile of money soon, and figured I might as well build an airplane now that I've got ASEL. Old issues of EAA have planes in them, and I've got a parts list going for a fully skinned fuselage and wings for about $1500 for a two-seat low-wing aircraft. Engine and avionics are obviously a big extra cost on top of that.

I guess I'm asking for a sanity check. Is building this thing really just as easy as meticulously following the prints to the limits of precision and not accepting any shortcuts?

The alternative is renting, and that makes phone sex addiction seem cheap in comparison.

helno
Jun 19, 2003

hmm now were did I leave that plane

Colonel K posted:

Glad to hear you've got it ready for the year again. Did you do much maintenance over winter or just reassemble?

I fixed up a few things. I installed a new fuel tank and got better lines, the old ones were hard as a rock after one season. New tubes and tires not much else other than chasing the threads on the odd nut/bolt.

As for building $1500 for a two seater seems crazy cheap even without an engine/avionics. With the market the way it is currently you can buy for cheaper than building in alot of cases.

Find a partner if you can and the cost will go way down.

MrYenko
Jun 18, 2012

#2 isn't ALWAYS bad...

babyeatingpsychopath posted:

I'm going to be falling into a big pile of money soon, and figured I might as well build an airplane now that I've got ASEL. Old issues of EAA have planes in them, and I've got a parts list going for a fully skinned fuselage and wings for about $1500 for a two-seat low-wing aircraft. Engine and avionics are obviously a big extra cost on top of that.

I guess I'm asking for a sanity check. Is building this thing really just as easy as meticulously following the prints to the limits of precision and not accepting any shortcuts?

The alternative is renting, and that makes phone sex addiction seem cheap in comparison.

What is your fabrication experience? Building an airplane from prints isn't exactly like snapping together a model...

helno
Jun 19, 2003

hmm now were did I leave that plane
Did some work with Sandy and Addie on Sandy's Challenger.

Finished up a few electrical things and found/fixed all the leaks in the fuel system.




This storm put a bit of a damper on things.

Colonel K
Jun 29, 2009
Do you worry about timber frame hangars during the bad weather? When we had some heavy snow a few years ago there were one or two steel framed hangars that collapsed, it wasn't a pretty sight.

I managed to get out for a flight yesterday that was the first for a nearly two months which was great.

I'm also trying to put together an organised toolkit for the aircraft and maintenance on it. I'm going to help the a&p doing my annual in a few weeks and will attempt to get an idea of what I should be getting together.

Blistex
Oct 30, 2003

Macho Business
Donkey Wrestler

Colonel K posted:

Do you worry about timber frame hangars during the bad weather? When we had some heavy snow a few years ago there were one or two steel framed hangars that collapsed, it wasn't a pretty sight.

A properly built timber framed building will kick the crap out of a prefab steel building 9 time out of 10.


helno posted:

Did some work with Sandy and Addie on Sandy's Challenger.

Finished up a few electrical things and found/fixed all the leaks in the fuel system.


So why the reduction gear? Is it using a Mazda rotary engine? I know part of it is clearance for the pusher prop above the fuselage, but I figured it would still be 1:1.

Gisnep
Mar 29, 2010

Blistex posted:

So why the reduction gear? Is it using a Mazda rotary engine?
It looks like a Rotax 582 two-stroke. They operate around 6000rpm, hence the need for the gear reduction.

helno
Jun 19, 2003

hmm now were did I leave that plane

Blistex posted:

So why the reduction gear? Is it using a Mazda rotary engine?

As was previously stated it is a Rotax 582 that wants to turn very fast. Pretty common engine.

I honestly have never seen a Rotary powered plane. I remember reading articles about them but they seem to have fallen out of favour.

Did my first night solo last night.

Colonel K
Jun 29, 2009
I found this and thought it would fit in well here. http://vimeo.com/32121344 . an 80's short on microlights.

helno
Jun 19, 2003

hmm now were did I leave that plane
That was pretty awesome. That guy was flying the poo poo out of that little plane. Doing a touch and go off the top of the airliner was pretty ballsy.

Edit: Here is a bit of footage shot this year. https://www.youtube.com/watch?v=asUmW8XKcWE

helno fucked around with this message at 22:52 on Jun 11, 2013

sleepy gary
Jan 11, 2006

I want a cri-cri very badly. Someone make me one. Thanks in advance.

helno
Jun 19, 2003

hmm now were did I leave that plane
I'll take a Subsonex if anyone is taking requests.

Oshkosh tickets are purchased. If all goes to plan I am trailering the Lazair down and camping at the private campground adjacent to the ultralight area.

Giblet Plus!
Sep 14, 2004

Nerobro posted:

The motors from motorcycles that most easily convert to airplane use are the bmw boxer twins, the honda flat fours and sixes, and harleys. All of those motors are separate crank and gearbox engines. And most of them run conventional car speeds. So you're not really finding more power.

I was reading this post and got really curious about the bmw boxer twins. Here's something I found:

quote:

Hi,
The use of the BMW motorcycle engines is well documented, and well proven. Although not common in the US, these engines fly in many aircraft in Europe and have a devoted following.

Of the available engines, the new generation (ie R1200 series) engines are far superior to earlier incarnations. Most importantly, the R1200 series have balanced chrank shafts, which almost entirely does away with the typical rocking vibration common to opposed twins. These new engines run from low to high revs with barely discernable vibration. Ideal for aircraft.

Secondly, one should go for the "S" variant of the R1200 if possible since these engines in stock form produce 122hp. Earlier engines produced far less, and were heavier, to boot.

I would also strongly recommend using as much of the original BMW parts as possible. For example, don't mess with anything unless absolutely vital. Keep the engine stock. Don't fiddle with the engine. If you want 122hp, then essentially you need to transplant the engine from the bike to your plane and go fly. There is no need to adjust anything, add anything or replace anything. If you can buy a relatively new engine, then that is (almost) all you need to do. IE There is little or no "conversion" to do.

One of the major reasons new "aircraft conversions" give so much trouble is that builders INSIST on trying to do things to the engines. The R1200 has fuel injection and dual plugs. Leave as-is.

There are four things you WILL have to do before you can go flying behind your BMW, however...

You will need to fit a new exhaust. The BMW engine is mounted back-to-front in the plane (ie gearbox side forward. In the bike it is the other way round). This will require a new exhaust. However, a word of caution. Don't go fiddling with the exhaust trying to improve it. Keep the header pipes the same length. Lead the two pipes into a single pipe (just like on the bike). Keep the catalytic converter. Lead the exhaust into the stock muffler. You will end up with a quiet, efficient, manageable and above all, reliable exhaust system. So you lose a few HP because of the catalytic converter. Get over it. 122hp is plenty. So the exhaust is quite long, and relatively heavy. Big deal. There is no particular reason why the exhausts of aircraft need to be 6 inches long, poke out of the bottom of the cowling and roar loud enough to wake up every conservationist in the tri-county region. In my installation, I'll keep as much of the original exhaust as possible, and have the silencer also. It will exit the plane behind the cockpit.
You will need to create your own air intake box. The one on the bike is custom designed to fit in the bike frame. Keep the same volume, but make your own.
You will need to fit a PSRU. Here you have a number of choices. Because the BMW offers such a clean surface on which to mount the redrive, it is a relatively simple operation by anyone who knows what they are doing. The older BMW1100 engines accepted the Rotax C box, I believe. I prefer to go with one of Neil Hintz' Autoflight gearboxes. These are used world-wide in everything from trikes, to gyros to fixed wing. He has a universal mount drive which can easily be matched to the R1200. It is reliable, has an excellent reputation (no reported failures - ever - I believe) and is competitively priced.
The above three "conversion" items are pretty easy, and should present minimal problems, since you are basically keeping sizes and lengths identical to the bike. The PSRU is a bolt-on option. But the fourth "modification" is more problematic. The R1200 is computer controlled. Problem is, the ECU expects a zillion inputs which are specific to the bike. They are out of place (or non-existant) on an aircraft. The only way round this is to fit an aftermarket ECU. Having said this, the task is far from being as daunting as it sounds. I am using a Link ECU. This is a Kiwi-designed unit, and widely used on aircraft here and in Australia. These units are (almost) self-tuning. But for the final tweaks and adjustments, any competent tuning shop can oblige. I intend to make my ECU map available for other users, so that even this part of getting your aircraft flying behind the R1200 will be a "bolt on" option.
Regards,
Duncan
http://www.homebuiltairplanes.com/forums/general-auto-conversion-discussion/4438-bmw-motorcycle-engine-plane.html#post36353

helno
Jun 19, 2003

hmm now were did I leave that plane
That is an engine family I had not even thought of.

One part of that thread that really stood out to me is that BMW makes 250 of those motors per DAY. Seems like a pretty good option in the 100-115 hp range.

Weight is listed at 75-85 kg installed weight which is right about the mass of a 912/914 once you fill up the radiator.

sleepy gary
Jan 11, 2006

helno posted:

I'll take a Subsonex if anyone is taking requests.

Oshkosh tickets are purchased. If all goes to plan I am trailering the Lazair down and camping at the private campground adjacent to the ultralight area.

Will you be able to fly it at all?

helno
Jun 19, 2003

hmm now were did I leave that plane
Technically the Lazair fits in under Far 103 but I will be using an SFOC that allows Canadian ultralights to fly into the states.

http://www.faa.gov/aircraft/gen_av/ultralights/sfa/media/ultra.pdf

sleepy gary
Jan 11, 2006

helno posted:

Technically the Lazair fits in under Far 103 but I will be using an SFOC that allows Canadian ultralights to fly into the states.

http://www.faa.gov/aircraft/gen_av/ultralights/sfa/media/ultra.pdf

I was asking in terms of being able to fly during oshkosh... is there any capacity to just go for a quick flight? It seems like it would be way too busy to do much flying.

helno
Jun 19, 2003

hmm now were did I leave that plane
There is a separate runway for ultralights in the southwest corner of the field and they have designated times for the various types of ultralights.

helno
Jun 19, 2003

hmm now were did I leave that plane
Did something a little different last night.

A buddy of mine who is restoring a Thorp T18 also owns a homebuilt glider.

He hasn't flown the glider in a few years and is thinking of selling it so we did a little photo op last night.

https://www.youtube.com/watch?v=crifjztsi24

Nice looking plane with incredible craftsmanship.

http://s1175.photobucket.com/user/Helno/library/Flying/Gliders

Sagebrush
Feb 26, 2012

helno posted:

I honestly have never seen a Rotary powered plane. I remember reading articles about them but they seem to have fallen out of favour.

My understanding of why rotary engines seemed to be a good idea in planes is that it came down to two things: (1) the inherent smoothness of the design, and (2) with iron rotors in an aluminum housing (vs. aluminum pistons in an aluminum or iron housing) they can't seize from overheating. You can also run a rotary engine with pre-mixed oil like a two-stroke, which saves you from having the oiling system as a point of failure.

Not sure why they fell out of favor, though. Just too strange a design for people to get used to?

helno
Jun 19, 2003

hmm now were did I leave that plane
Perhaps it is more to do with a dwindling supply of donor cars.

That BMW conversion looks like a much better option than the VW conversions but it is quite a bit heavier.
There is a guy up here with a 1/4 scale hurcules and it is powered by 4 VW engines.

IOwnCalculus
Apr 2, 2003





Sagebrush posted:

You can also run a rotary engine with pre-mixed oil like a two-stroke, which saves you from having the oiling system as a point of failure.

I know people run them premix to treat the seals better, but would this actually protect the bearings on the eccentric shaft too? It seems like they would still need oil pressure.

Sagebrush
Feb 26, 2012

I actually was wondering that after I posted. I think what they take out is the oil metering pump, which continuously feeds a small amount of oil into the combustion chamber, and just premix the gas instead. I remember now that the 12As (at least) have oil coolers, though, so there must be a larger supply of it somewhere for maintaining the e-shaft and things. And oil cooling may be very important to the engine's running, since there's such a huge temperature differential.

Well, scratch that as an advantage. They're still extremely smooth though and only have like three moving parts (that's definitely fewer points of failure) and the power-to-weight and power-to-volume ratio is quite high. Plus you can negate the low torque by running them at their optimum RPM all the time and just gearing down to the propeller.

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Nerobro
Nov 4, 2005

Rider now with 100% more titanium!

Sagebrush posted:

My understanding of why rotary engines seemed to be a good idea in planes is that it came down to two things: (1) the inherent smoothness of the design, and (2) with iron rotors in an aluminum housing (vs. aluminum pistons in an aluminum or iron housing) they can't seize from overheating. You can also run a rotary engine with pre-mixed oil like a two-stroke, which saves you from having the oiling system as a point of failure.

Not sure why they fell out of favor, though. Just too strange a design for people to get used to?

That's because nobody "really" seems to understand wankels. (I avoid the term rotary because that can mean a different kind of engine. See: Gnome rotary)

Wankels really don't seize. (Modern cylinders and piston rings don't either..) But they do start detonating. Instead of seizing, the hot cylinder walls start to bulge, and you lose compression. And you lose apex seals. Or, if you manage to keep the seals around, then they start detonating, and really bad things happen. Like busted center section bearings, and more, blown out seals.

The big advantage with a wankel, is it's size. They're downright tiny. However, they aren't a light as people seem to think they are.

The need to have oil in the fuel is a sign of a design FAULT, not a design advantage. You can run a little oil in normal piston engines and it helps with ring life. Much as it helps with apex seal lift.

The fundamental problem with Wankels is cooling. Piston engines have several methods for cooling pistons. There's the incoming air charge, there's air under the piston, there's contact with the cylinder walls, there's heat conduction through the rings, there's oil squirters to cool the bottoms of the pistons...

There's NOTHING to cool apex seals, other than contact with the cylinder wall. And then they don't get any oil.

The only way to carry significant heat from the rotor, is through oil. (or, in the case of the Hercules motorcycle, intake air... It ran the intake air through the rotor.) Oil management within the rotor isn't easy.

There's also no easy way to increase the displacement of a Wankel. Rebuilding one is not far removed from building a new engine, because you can't refinish the cases.

And, from what I've seen of installed weights, the weight of a Wankel is comparable to whatever horsepower engine you intended to run in the first place.

... I am a fan of these motors.... I've got several books on their history, and the math involved in them is inspiring. So is the story of making them survive. And the different engine case arrangements. (thing spinning block, with a straight crankshaft...)

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