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Rotax in lightweight cub?

KenyaCub

Registered User
Kenya, Africa
OK, here's another idea I would like to get some opinions on.
What about a Rotax 914 in a light cub such as a Sport Cub?
You save about 30-40 lbs on the engine vs. the 0-200 and gain 15hp that will still work at altitude.
What I like about the rotax is the turbo since I'm at 6000 ft.

The disadvantages is that it is complicated (gearbox, turbo, dry sump ...).
The other problem is the fact that you can only use very lightweight propellers because of the gearbox.
That would mean a composite Powerfin or Warp Drive. I spoke to the guys at Warp Drive and they said that they could get about 5.5 to 6 lbs of thrust for every hp (=632-690 lbs). That's hard to believe but would be nice if it were true. They recommend a three blade setup with 68 - 72 inch diameter. The nice things about these props is that they are very cheap and very light.

I'd imagine the airplane would weigh around 880-900 lbs empty once you add the HD gear and big tires. With an airplane of this weight on 35 inch bushwheels, you should be able to run extremely low pressures (1lb?) ... the obstacles you could go over hmmmmm .... :o
I'm wondering what kind of takeoff distance you'd get? I wonder if when light you could get one of these to perform better than a moded PA18?
Anyone with experience with these engines/props? How much thrust can you get out of this combination? Any ideas?
 
For starters it's a water cooled engine. Engine life is relatively short. They are used on the Aircam twins. They probably have lots to say about the engine.
 
Rotax's are good for some applications I guess. There is something about an airplane engine that runs at 4000-5000rpm that doesn't sit well with me personally. I think the Continental C-90,0-200's are hard to beat.
 
The 914 Rotax is 156lb. plus prop weight .I had a Rans S7S witha a 912 100 HP 4.8 gph unleaded car gas I flew it 160 hrs most trouble free airplane engine I have ever owned.TBO is now 1200 hrs complete OH cost Parts and Labor 1800 to 2500 .The 914 is rated at 115HP for five minutes,then 100hp to 16000 ft Matco brakes have a S7S with 914 engine 3.7 gph @ 16000ft 135mph engine boost is controlled by computer,Fuel mixture is by alitude cominsating carbs.I used a sensenich ground adjustable prop on my S7.All new tech engine water cooled high compression,no mixture control,electric ignition,built in alt, no oil cunsumption.Mike O
 
Maybe....

Maybe props for the Rotax are cheap, but the engine isn't. I think I read where the 914 now costs around $24,000. For way less than that, many other engines can be bought. As far as I am concerned, this puts it out of my consideration.

Mike
 
Alec,

I think you are on the right track! I am considering an ultra light SC, no fabric on the fuselage, one wing tank, no cowling other than a pressure cowl, just the bare minimums to fly with only a windshield and some sort of a boot cowl. I want it for a toy in addition to my regular Cub, it would not make a very good Xcountry machine. If I do it I hope to keep the weight under 800 lbs and the Rotax would help me reach this goal.

Doug
 
ksecub said:
Alec,

I think you are on the right track! I am considering an ultra light SC, no fabric on the fuselage, one wing tank, no cowling other than a pressure cowl, just the bare minimums to fly with only a windshield and some sort of a boot cowl. I want it for a toy in addition to my regular Cub, it would not make a very good Xcountry machine. If I do it I hope to keep the weight under 800 lbs and the Rotax would help me reach this goal.

Doug

Might want to save yourself some time and $$ and just buy a J-3 with a C-90-8 on it.

Tim
 
This is the reason I dont like rotax engines...

In a continental or lycoming, all you have to carry aboard is a few spare liters of oil.

With a rotax, you need what you would normally carry in a car... Prestone...Few extra belts and stuff... Hey, who wants to carry prestone in an airplane??

Well, heres the thing. Friend of mine had a bush caddy (dont know if you guys have seen these, kind of looks like a Murphy Rebel) and it was powered by a Rotax 914. Well he was up in northern quebec, on floats, and the gearbox failed in flight... Stuck in the middle of nowhere, and whos gonna carry a spar gearbox??

Anyway, for me, airplanes must stay simple. i dont like opening the hood to something that looks like when I open the hood on my car.

2 mags, starter, alternator 8 plugs, what could break???

just my 2 cents worth!!!

cheers

Fred
 
The Turbo 914 can be a higher maintenance headache than the 912...but nothing minimal preventative maintenance can't handle. Mainly exhaust system problems.

Fortysix12 stated "Engine life is fairly short".....I know of MANY Rotax 912's that have gone 3000 hours + in training aircraft with little other than routine oil changes and oil use to match type of fuel being burned. There were a very few 912's with bad rockers....but any of those in the field should have been addressed by now.

If you cracked the case wide open on your A-65 in the middle of nowhere do you carry a spare? Belts on a 912? Very rarely unless you're running a very high amp load and have installed the optional alternator that is belt driven just like a lycoming. Antifreeze...same as you would for a car on the side of the road...find any water source and fill it. Drain and refill when you get home....although I have never had an issue with coolant on a 912 (and there's always been one or two in the hangar being abused by my f-in-law or wife + 2 regular customers) to the point I have never even needed to top the overflow bottle.
 
Mikeo,

I have actually flown a few rotax powered aircraft to my surprise, and ill tell you why after: I flew a beaver ultralight, I also flew a kitfox, and also a murphy rebel.

The beaver was a two stroke, and altough it never failed, I did get kinda hot on take off when the engine lost power and regained power a few times in a row. Decided to come back down just to find out the oil injection was half blocked and the engine was just about to seize.

I flew a kitfox powered by the 912, and i did have a gear box failure on that one altough I was able to land safely without breaking myself in pieces. A year later, my friend, and owner of the aircraft, lost power on take off, crashed into trees at the end of the runway, and died, as a consequence of the crash. We never found out what was wrong with the 912.

To get my fears away after this crash, i decided to take on of my friends up on his offer: he offered to take his 912 powered murphy rebel up for a spin. I went. Everything went okay... but i still dont like rotaxes and that will always be. I dont mean to deminish anyone who fly rotax powered aircraft, but ive seen too many people have trouble with them. Its almost, 10 hours of maintenance for an hours flight.

Heres the catch... Some one might fly a rotax for many hundred and thousand hours without a glitch. But then someone could have lost of trouble with one. its like a guy that loves chevys, there good trucks, never had any problems and have owned many, and the neigbour just bought one and hes at the dealership with problems very week... I guess its just kind of a fluke!

anyway,

Happy landings and take-offs!

Cheers

Fred
 
Does anyone have direct experience with the 914 and can tell me if there is any more throttle lag than in the non-turboed 912, or how about compared to the lycomings we all know?

I know that the gearbox could be a source of problems. BUT, apparently there is a manufacturer's recommendation as to how much weight the prop can have without shortening the life of the gearbox. I spoke to a rotax engineer who said that most people run props that are too heavy for the gearbox (like the Warp Drives), he said you do get more performance out of them but at the cost of a lower gearbox life. Said if you went with the ultimate performance prop, which is heavier than the recommendation, that the gearbox should be overhauled around 300-400 hours.. That said the overhaul does not cost very much and anyone who is mechanically inclined would be able to do it themselves.
Personnally I do not mind the extra hassle if the added performance is worth it.

Doug, I can't wait to see what you and Greg are going to come up with next. I knew there was someone with crazier ideas than me on this website. It sure will be an ugly machine but it just might be the next best thing. 8)
 
KenyaCub, I'd love to see you do what you're discussing. Yes, you'll beat the pants off an -18 if you are empty. If you take that SuperLIGHTCub and load it like you do your -18, I doubt it'd be likely to continue beating the -18.

I'm sure any reasonable person would agree.

Have you ever flown j-3's or PA-11's with 90 or 100 HP??? They jump off the ground when empty with 1 soul aboard.

Something else:

I am considering an ultra light SC, no fabric on the fuselage, one wing tank, no cowling other than a pressure cowl, just the bare minimums to fly with only a windshield and some sort of a boot cowl. I want it for a toy in addition to my regular Cub, it would not make a very good Xcountry machine. If I do it I hope to keep the weight under 800 lbs and the Rotax would help me reach this goal.

Doug

I guess you have your reasons for no fabric, Doug. What are they?

Thanks. DAVE
 
Some times thinking out load gets me in trouble. I was just thinking about what I use my Cub for. 90% of the time it is used on the weekends flying behind Greg and Loni pushing my own personal envelope. The fun is landing places you have never landed before and that are marginal and challenging. I am almost always by myself, light on gas trying to get every bit of performance out of my machine and myself. I was just thinking that if I had a machine soley dedicated to this mission, I might be able to keep up with my peers.

The goal is to have a Super Cub type aircraft with a 180HP engine, 90" propeller, 35" bushwheels, and long wings with huge flaps that has an empty weight of around 800-850#. I think this would suit my very odd and highly irregular mission very well. It would be an absolute blast to fly. So if you think about getting rid of everything not vitally essential to make the airplane fly you could make it very light and very simple. Here is what I was thinking of for starters:

The new Cub Crafters Sport Cub wings (lengthened) with one fuel tank.

No fabric on the fuselage (no stringers, arches, doors, windows, only a minimal boot cowl and a windshield to keep the bugs out of your teeth.)

Single controls

Straight exhaust (no muffler) only a minimal heat muff for carb heat

No cowling (only some sort of minimal pressure cowling, enough to cool the cylinders and oil)

No electrical (hand prop only) with minimal instruments (just enough to pass the FAA experimental requirements).

Just think how easy it would be to maintain, grated it would be the ugliest Cub in the world, but it might be the best performing Cub in the world.

If you didn't think I was weird before, I am sure I have convinced you now.

Doug
 
The whole point in this approach is to keep things light. So yes, it would be a one person airplane when you wanted the performance out of it. Never said it would be otherwise.
But then again, my PA-18 is also a one person aircraft if you really want to match the takeoff distance to the landing distance. When I am two people, I can get into places I can't get out of.
I'm sure any reasonable person would agree with that too.

No fabric? how about less weight.
 
Last week I did some ski-flying in a buddies Cub with a pod on it. The pod bounces the exhaust blast up to where it comes in the cracks around the door.

When I land on water the spray coming off the tires is pretty strong and goes, like..........everywhere!

2 good reasons to have fabric on your fuselage.

Also, with the extreme stuff like in BigRocks & LongProps, why not learn to work your a/c within what it will do? Most of those LZ's look nuts, unless you HAD TO get in their, and it looks like Lonnie and Greg still have some margin left. Maybe you need to use up a bit of that margin while you 'catch up' to those boys. :D

I should just delete my post and agree with you. You're weird! :D 8) :o

Also, if you're weird, wouldn't you be happy flying an ultralight? Lots of them got no fabric on the fuse and are simply wings and tail and engine, AND will land shorter than Lonnies Cub or Greg's Maule, WITHOUT using the water for touchdown. :D ....all in jest, Doug!@
 
I think when you need to do more you buy a helicopter...

Go fly the j-3 with the 90 in it.

If you could build a j-3 with flaps that weighed 700 lbs with a C-90 on it you would have quite the ticket. For more performance and lower stall you could change the airfoil...and then you could.....and then you could....
 
Kenya, I'm all for a guy "..doing more..", and I'm with you on your idea of the TurboRotax and a light airframe.

On the topic of Dougs stripped Cub: watching the 'Longprops video, and seeing what these guys are doing, it's obvious that Lonnie and Greg are doing something that Doug could do with practice. Why 'cheat'?? I would think someone with aspirations of grandeur would want to master his present a/c, as his 'peers' have done, before doing them "one better" by using a 'cheater' airplane.

Also, I think the 'cheater' airplane would be great! But, what is the whole point? Is there some great fishing hole or gold vein on that gravel bar that Lonnie and Greg can't make but a 'cheater' would? Is there an idiylic camping spot that he simply "must" sleep at without Lonnie and Greg?

If so......go for the 'cheater'!!!. If not, then enjoy the challenges and the knowledge of posessing the ability to skim in, slow down, and roll out on the same bars as Lonnie and Greg.

I'm all for modifying stuff for a mission. But if the purpose is only to beat out some guys who are smoking you with talent and ability you think you'll never posess, GET MORE PRACTICE. :D :oops: :wink: THEN, build something lighter and with more power.

DAVE
 
Dave,

I am not sure how to respond to your posts. I guess a Super Cub is a cheater airplane if I follow your logic. Maybe we should all be flying Wright flyers, I guess that would even up the score. Dave, I am not competing with Greg and Loni, I gave up that fight a long time ago. I do agree with you, practice is really all it takes. Super Cubs are only a part of my life so I can not spend all my resources pursuing the title of the world's best bush pilot, nor is that my goal. I just like to fly Super Cub like airplanes and want to do it the best I can with the best possible equipment. I fly as much as a guy with 4 year old twin daughters and a wife can get away with.

Why are so many people resistant to modifications to Super Cubs? Name one thing in this world that can't be improved upon.
 
Oh boy, we're headed straight for the Rant and Rave now.

Rotax anyone?



PS: TJ, go to India and get an intensive Kamasutra class (don't bring the wife) :anon
 
Ksecub.... I think we ran across the answer to the dilemna a few posts ago. Practice, practice, practice.
Modifying your machine is good, within reason.
But it goes back to the old theory of a well practiced/trained pilot can out perform with a stock cub, the highly modified cub with an unpracticed pilot in it.
As for the Rotax engine, my experience is limited to the '95 Ski-Doo I have that has a 503 in it. I have beat that thing on Spring bear hunts so hard I swear it would never run the next season, it just keeps on going.
 
KenyaCub said:
Oh boy, we're headed straight for the Rant and Rave now.

Rotax anyone?



PS: TJ, go to India and get an intensive Kamasutra class (don't bring the wife) :anon

Kenya-

I like the rotax in my snowmobile.... :lol:

How about one of those normalizer kits they make for the 0-470 on the cessna 182. It would take some engineering, couple that on an 0-320 or C-90.... ?? You can do anything with money and time!

Tim
 
Behindprop,
The other reason for the rotax is lightweight. I already have an "overpowered" cub that has a lot of weight on the front. The idea with the rotax is a completely different approach. I do not want to overpower it, instead I would rather have reasonable power but with an airplane that flies on the wing instead of the prop.
Going with a lightweight cub with an overpowered engine would definetely work too, but would be too similar to what I already have.
 
kseCub, I apologize if you think I am somehow against changing a Cub. I'm not!

I like the idea of the lightest airframe possible with the most horsepower and enough wing area to get the wing loading very, very low.

I thought I was coming across as tongue-in-cheek about the 'cheater'. I had hoped to make the point that practice is worth almost everything. Also, that there's more 'honor' in mastering what one has rather than simply buying the next step higher in performance, then standing back and thumping ones chest with pride......meanwhile, JoeLonnieGregBob is still out there whipping your ass with his same junk....no honor or pride in that.

I'm all for your literally-stripped Cub. Do it up. I was just making a point and I apologize for coming across as an ass! :-? Thanks, DAVE

PS I've seen photos of a stripped-fuselage Cub. UGLY. But.... your money and ideals and ideas are not mine. :D
 
Hi all,

Was just browsing back issues of the Cub Club newsletter. In the May/June 1999 issue (#92), there is an blurb and picture of a Wag Aero Sprot Trainer on floats with a Rotax 914 turbo.

Owner/builder
Martin Lamothe
1897 Provencher
Dolbeau, PQ
G8L 2A8

(418) 276-7889

Rotax 914 turbo (115hp) w/Warp Drive 3 blade ground adjustable prop
Flown on homebuilt floats
1400# gross weight
837 empty weight
T.O. on water @ G.W. 400ft
Rate of climb @ G.W. 800fpm
Cruise @ 70%: 80mph
Fuel Consumption @ 70% 5.1 gph

"a real STOL aircraft with very improved performance compared to J3 with 85hp"

John Scott
 
For better lift, how about using a Selig S1223 airfoil with Gurney flaps?

Jerry, have you tried the Gurney's yet?

JimC
 
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