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shortfielder
12-02-2009, 02:33 PM
Some have recommended that the best plane for my mission would be the Model 4 classic, long wing, 100 hp.

All of the Model 4's that I have seen sofar have been 80 hp.

How big of a deal to swap out a 80 for a 100.

Seems the 80's have 2 blades and the 100's 3 blade so ya have to change the prop also.

Would a used, low time 100 be readily available, and what would you expect price wise.

What could you get for a low time 80?

What could I expect to gain in cruise speed w/m4-100hp-long wing?

Thanks again Gary

DesertFox4
12-02-2009, 03:26 PM
Not too many used 100 hp. Rotax engines out there yet. You might find one but likely it has been salvaged off a damaged aircraft which doesn't mean it is not a possible good purchase. You just have to do your homework. Saw a couple in the $12,500.00 range with 400 hours.
You find most model 4's equipped with a 912 80 hp because when most of the model 4's were sold back in the 90's the 912S 100 hp Rotax was not available.
Either a model 4 that has a 912S now was retrofitted with a 912S or it was built/finished since the 912S became available from Rotax.
A couple of our members have swapped out the 912 for the 912S for more performance. They could address the ease of the conversion.

What could I expect to gain in cruise speed w/m4-100hp-long wing? I'm thinking 8- 10 mph but again our members that have converted can nail this question for you. My model 4 with 100hp. cruises easily at 115mph and can criuse at 125mph.

shortfielder
12-02-2009, 05:43 PM
Good evening Steve
And thanks for all your thoughts. I just noticed that you are in Phx. Any chance we could meet somewhere between Durango, and Phx. so I could check out your plane, and you could tell me about it, and how it, practially, compares to the model 5

Gary

Av8r3400
12-02-2009, 06:20 PM
(Both of my 80hp Model IVs have 3-blade props, warp on my yellow 1050 and an IVO Ultra Light in flight adjustable on my 1200.)

I can easily red-line the airspeed in both of my planes in straight and level with 80 hp. With this in mind, 100 hp would not gain much of a speed advantage in my opinion, it will help takeoff performance.

DesertFox4
12-02-2009, 06:43 PM
Gary , I think you'll find the majority of Rotax 912/912S equipped model 4's have 3 blade props. Check out the Photo album directory under model 4's and you probably will discover that very quickly. Ivo props and Warp props probably make up the vast majority. GSC (wooden) props are still used but less and less.

jrthomas
12-02-2009, 07:44 PM
Hey Gary, The model 4 with the 80horse 912 still has an abundance of power. If you get a chance to fly one, you may feel you really don't need more power. Look at the Jimmy Franklin videos on u-tube and see what he did with 80hp. Horsepower is like money, we never have enough.

Av8r3400
12-02-2009, 08:00 PM
Do they have the short wings?
Gary

Both of my planes are the long wing versions. Cruising at 100-110 is very easy at ~5000 rpm.

Paul Seehafer (KTOM for November (http://www.teamkitfox.com/Forums/showthread.php?t=931)) has no problem getting 120 mph out of his amphib with only an 80 hp 912UL & IVO.

DesertFox4
12-02-2009, 08:10 PM
Photo Album Directory (http://www.teamkitfox.com/Forums/showthread.php?t=118)

Above is a link to the main page. Scroll down to find the model 4 category.

shortfielder
12-02-2009, 10:12 PM
Av8r
Those are good numbers. I would be happy with that. Must be a prop,or riggin issue with this one????
Thanks Gary

shortfielder
12-02-2009, 10:17 PM
Steve
Thanks for the link. I had looked through that the other day. Again this evening after you gave me the link. Some cool planes in there. My interest is purely backcountry/off strip. I am assuming the Grove gear would be preferred for that. And some larger tires. I'm guessing 21-26"??

Generous offer to come to Phx. I will stay in touch w/you on that.
Gary

Av8r3400
12-03-2009, 06:26 AM
The grove system is nice, but, it is heavy and, believe it or not, shorter than the bungee gear. This makes the bungee gear actually better in the bush. Weight is the enemy in STOL performance.

Remember, your example was 80 kts. That equates to 92 mph. This is not far from the mark I gave for my plane. Depending on rigging, farings and prop I see nothing outrageously out of line about this speed.

90 mph is a real easy cruise at ~4000-4500 rpm with my yellow plane.

shortfielder
12-03-2009, 06:36 AM
I understand the concerns for wt. Which means, I would be doing myself a favor to lose 20#'s, on so many levels.:)
I would think if you wanted taller gear, you could just call Grove and have them build you an extended gear, but if it isn't as good, then it doesn't matter anyways.
Also talked with a fella the other day that builds an extended,bungie/spring type gear for the Kitfox.

In regards to the speed issue. I think the fella told me he was getting 80kts.@5400 rpm. And I forgot to mention, w/o whel pants.

Gary

Av8r3400
12-03-2009, 06:50 AM
I understand the concerns for wt. Which means, I would be doing myself a favor to lose 20#'s, on so many levels.:)

My plane would be a rocket ship if I did the same thing... :o



In regards to the speed issue. I think the fella told me he was getting 80kts.@5400 rpm. And I forgot to mention, w/o whel pants.

Was that a model IV? I ask this because the older 1-3 models this would sound more accurate. The under-cambered, earlier, wing is very draggy and therefore much slower. I fly without pants, too. :D

shortfielder
12-03-2009, 06:55 AM
No,it was a newer mod 4 long wing classic

Slyfox
12-03-2009, 08:35 AM
If you want to get the most out of your 80 rotax on your model 4, put the prop that I have for sale on it and you will get up to that 110mph. I know, I had it on my 80 model 4 and it did move right along. I have the IVO patriot ultra light prop in excellant condition for 700 dollars, it's yours if you want it. You pay the shipping.

I did switch to the rotax 100 and I might have gained 3mph on the top end, the biggest change is the take off. I ended up putting on the medium IVO that's why the old one is for sale. It's is a straight across switch out, no suprises. Same engine, just more juice.

shortfielder
12-03-2009, 12:32 PM
Hi Steve
And thanks for the info on the engine swap. And the prop. The plane I have been talking about, has the long wing, so I woud expect it to be a little slower than your Speedster.
And I would think that the prop may be considered a cruise prop, so you pay a penalty on t/o performance.
Usuall everything is some kind of trade off.

Gary

Slyfox
12-03-2009, 01:43 PM
Hi Steve
And thanks for the info on the engine swap. And the prop. The plane I have been talking about, has the long wing, so I woud expect it to be a little slower than your Speedster.
And I would think that the prop may be considered a cruise prop, so you pay a penalty on t/o performance.
Usuall everything is some kind of trade off.

Gary

THe prop is an inflight adjustable, so it is both cruise and take off prop. I originally had the long wing on my aircraft and when I shortened the wings I didn't notice too much gain on cruise with the short wing. I've had the plane for 5 years and about 1300 hrs now.

jdmcbean
12-04-2009, 08:24 AM
I understand the concerns for wt. Which means, I would be doing myself a favor to lose 20#'s, on so many levels.:)
I would think if you wanted taller gear, you could just call Grove and have them build you an extended gear, but if it isn't as good, then it doesn't matter anyways.
Also talked with a fella the other day that builds an extended,bungie/spring type gear for the Kitfox.

In regards to the speed issue. I think the fella told me he was getting 80kts.@5400 rpm. And I forgot to mention, w/o whel pants.

Gary

Gary,
We have a Bush Gear for the IV and earlier models that is taller and has been available for some time. Built to use either .750 axles or the larger 1.25 axles. Although the 80 hp is a great engine and performs very well on the IV's, being in Durango, CO the 100 hp is going to be much better choice for you with the density altitudes you deal with on a regular basis.

shortfielder
12-04-2009, 12:41 PM
Good Afternoon John
Sofar, most that I have talked to feel that the Grove gear is better gear for the off strip landings. Paying a penalty for weight, but more stable on irregular ground, and tougher.
What have you found,or youur thoughts on which gear would work best for my application. Mountain pastres, beaches, gravelbars, etc. Hoping not to encounter anything much bigger than a grapefruit.
And how much is our extended gear?
Thanks Gary

Les Evarts
12-21-2009, 08:32 PM
Gary,

I’ve swapped an 80 for 100 hp Rotax in my Model IV 1200. While it’s not a “big deal”, it was much bigger deal than I had turned up in my investigation. So hear are the potential issues (in order of certainty);
1) The bigger starter will require you to modify the starter (cut off tabs) and/or modifying your firewall (i.e. its longer). For me it was both, but I’ve heard others get away with just the starter mod.
2) New radiator. The bigger engine requires a larger radiator than was typically sold with most Model IV/912 setups. No problem, but likely (as in my case) the holes won’t line up, hence requiring shifting the position of radiator (and so on…).
3) Oil cooler. This was new to me, and while not such a big deal when building, to modify and accommodate an oil cooler is not the same dealing with it during building. “Back in the day” when I bought my 912ul, I never heard of the need for oil cooler (nor in my opinion does a 912ul need it in Montana) , but they are highly recommend of the 912uls.
4) Related to oil; at some point, the oil tank changed size. I don’t know, but I assume the current oil tank dimensions are the same for the ul and uls. Anyhow earlier 912ul engines came with a shorter and fatter oil tank that I received with my new 912uls. Well these minor changes in dimension can be a big problem. This was perhaps my most perplexing problem to solve and I know at least another converter whom encountered the same issue. There was not enough room under the cowling for the height of the new tank. The other person I talked with solved this by keeping the short/fat tank and selling the taller version with the used 80hp engine. Rotax (R.O.A.N.) advised me that the inlet and outlet fixtures of the tank were also changed and were larger in diameter than the older tanks. They suggested this redesign was not without reason. I’ve taken a class from these folks and one of the first things they do is impress you with how highly engineered (exacting) these engines are. My solution was to re-route some engine wiring and modify the tank by eliminating the quick drain plug on the bottom (requires some high-tech welding) to gain space. It barely fits, but works, the tank essentially rests on the engine. I’ve put anti-chaff on the bottom of the tank and check it regularly. This may or may not be an issue with other cowling installations that might provide more room.
5) This is the final issue and perhaps the most unusual. At some point Rotax changed the distance between the two bolt holes used by the mounting system provided by Skystar and Kitfox Aircraft LLC for the 912. This affects only the top holes on the mounting brackets that go back to the “donut” (one hole is on the gear box, the other on the engine case). I was surprised to fine that the distance between the two holes for each bracket were not the same as my old brackets. This seemed to surprise Kitfox as well. The solution is simple; welding or purchase new brackets. I mention it here because it’s just another potential issue, hence cost and time. I talked to one other converter whom dealt with this as well.

Again, I don’t know when they made these changes (oil tank, bolt hole distances) so these last two issues may or may not be applicable. My ul was a 92-93 version (i.e. very early) and my uls is a 2008 version. My reasons (personal rational) for the upgrade are complicated and would take too much ink to explain, but I agree with many of the other posts here: A 912ul is a great match for a Model VI and is likely sufficient for most purposes, however, I’ll fly circles around you with these extra ponies.

As for your performance question (expected gain): This science and data are not exacting because of a number of different inputs (temp. & alt.). I’m in Montana and generally flying at 4000 and up. I’d guess I gained an average of 200-300 fpm climb and can get 1100 fpm out of my home base of 3500ft. The difference seems more noticeable at higher altitudes. As for cruise; I was formally a 100mph plane; now 110-115mph is pretty easy. I’ve started to worry about my duct tape. Mine is a pure to design Model IV-1200 (long wing) with 8” wheels and ATV tires (627 lbs empty). These numbers are difficult because of the biggest variable; a new prop, which goes to your second question; props.

I’ve always run three blade props and was a fan of the GSC wood prop on my 912ul. I generally only adjusted it for long x-country trips for better speed. While GSC makes a prop for the 912uls, the one I had on my 912ul was inappropriate and I had to change. I now run a IVO Medium in-flight adjustable prop. Lets just say that I definitely adjust it to fit my needs and this accounts for some of the gain I mention above.

As for your questions about engine values: One of my many reasons for the conversion was the high cost of rebuilding these engines and their high re-sale value as used engines. Verifiably good used engines (mid-life or lower) command good prices (ul or uls). My ul was over the hump, and I had other good reasons so I made the conversion. If your going to buy a new engine, it makes sense to go 100hp, even in a Model VI were it might be considered excessive. But I was happy with both engines. I just grin a little more with the new one.

I didn’t intend to write a detailed novel or "how-to" but perhaps this will be useful to others who might research this conversion now or in the future. This may become more common as older 912ul engines run their time out. I wish had more information to draw on when I made the jump.

Les

shortfielder
12-21-2009, 09:09 PM
Mr. Evarts
Thankyou so much for taking the time to give me, and others, that great response.
I am still in the hunt for a plane. Sofar, I think the setup you have will do the best for what I want also. Higher alt., off strip flying(landing and t/o). I am looking for a -4 long wing Classic, hopefully with the 912s already in it. Just not sure it has enough room in it, so I am also considering the -5.
I will be going to Phx. in a couple weeks and get to see a variety of models. Hopefully after that, I will know exactly which model will work best for me.
Thanks again have a Merry Christmas and enjoy the holidays with your family, friends, and Kitfox
Gary

shortfielder
12-22-2009, 08:13 AM
To Anyone

I think I have read where they have a kit to make 95hp out of the 80 hp engine. Would this be a better/more affordable option, or do you pay a penalty in reliabiliy/TBO? Trying to get more power out of an engine than it was specfiically designed for.

Thanks Gary

Slyfox
12-22-2009, 08:39 AM
Thanks Les for the input. Yes everything you stated is true. I to have the vintage kitfox from 1995 with said motor. What I did was this. I had breakage of the motor mount with the 912ul engine, so It was a no brainer to purchase the newer engine mount for the 912uls. I had to change over the intakes and where the brain box sits, no big deal, I just copied what was set up on the old engine. I also put in new engine insolators and bolts. This allowed me to get 90percent of the engine change over done in a nice warm shop. You see I did this in the dead of winter, outside temps were around 10degrees. I originally used my old tank because the new one was not going to fit. I ended up cutting the tabs off the starter and than just beat in the firewall with a hammer and an object and that worked out just fine. Than the big day, I took my cherrypicker out to the hanger and in one day removed the engine and mount and put the new engine on. Only took a couple hours if that and that's with running into the pickup and warming up, got to remember it's 10degrees out. No heat in the hangar.

Now with that said there was also an issue with the water hoses, when you change around the brain box the water tank needs to change location also, so you will end up moving some hoses on top and changing at least one with regular heater hose, I don't remember anymore. The cover for the water pump is wrong, so at first I removed the one off the old engine, cleaned it up and installed it on the new motor. I originally put on the ultralight IVO prop and it worked, but I didn't like the fact that it cavitated on to much power. So I purchased the medium IVO which is a perfect match for the engine. I have an elevation of 2000ft and I get over 1500fpm on take off and in the winter can be as much as 2000fpm on take off. Cruise is around 120mph.

Now I had an opertunity to purchase the motor for about 1500less from an outfit in canada. Why didn't I do this? It's hard to trust across boarder businesses and I wanted things to work for the kitfox. Where did I purchase it, from John at Kitfox. Very wise move, because not only did I get the latest motor, I got the mods necessary to make the engine work. I got the engine mount, new and improved. I sent the cover for the water pump and John fixed that to work on the model 4 with a new gasket. I returned the new tank and John cut that down to fit. All this was free to me and they all fit great. The way I put the engine on, it was running in two days and flying on the third. What a joy. I had already purchased a new radiator, it was just sitting in my hangar. The new radiator was an aluminum one. So when I did get the water pump housing and things warmed up a bit. I emptied everything and put both the radiator and the water pump cover on.

A little suprise to me was that fact that the new engine comes with sensors that are one wire. The sensors on the old engine were two wire. What happened was all the sensors read to high. Now with my little wisdom I didn't want to trust the oil pressure sensor and moved the one from the old engine to the new, good thing, at least that one was right. The other sensors were wrong and to rectify, I had to move those over also. If I had a dynon, they would have been just fine, but since I had guages of a different type it didn't work out.

All in all I think things went just fine. Here is a list of some of things I had to do.

Replace the motor mount, I felt the tubing was just too thin, it wouldn't hold up, was nice for getting things ready to install.

Needed to get the water pump cover set up for the model4.

needed to modify the starter and firewall for clearance.

needed to move the intakes so the carbs set on the outside along with moving the water tank and hoses and the brain.

needed to send the tank to John for cutting down the size for clearance.

I installed filters behind the carbs.

I put straight hoses to the carbs from the fuel pump, haven't needed the return system, didn't have it before so I went with the simple.

I reinstalled the oil cooler I had

reinstalled the oil thermostate.

I really thought the kitfox was great with the 912ul, but after installing the 912uls, wow, what an airplane.

Les Evarts
12-22-2009, 08:01 PM
Steve,

Ahh yes, I forgot about the issue with the water hoses. I should have made this #1 on my list of most likely issues to deal with in this conversion; it’s a given because of the engine mount. It’s also the easiest to fix. I solved it the same way you did, by changing the parts out of the old engine. If you can’t do that, you would need to buy a new elbow and replace/redirect these hose attach points. Or as you suggest, John at Kitfox provides excellent support on these type issues and its and the best place to go for information and support.

Interesting you mentioned the motor mount failure. This too happened to me and as part of my conversion, like you I ordered the new one from Kitfox. It’s improved as per the Skystar SB-54A. This is another missed detail on my account of issues related to this conversion. It should be item #2 (if not already done; actually, its mandatory as of April 2001, see SB-54A) on the list, so shift my 1-5 to 3-7 and add your observations to the top. However, when I did this, I did not re-order the arms that I mentioned in my earlier post (because they were thought to be the same); hence I had to modify them as per item # 5 in my earlier post. I’m comfortable, but watch this stuff like a hawk.

You’re close, if you ever drift east with the prevailing wind and get close to Polson… let me know, we’ll line up these Model IV’s and compare notes to see if those “speedster mods” count for much.

Les

Slyfox
12-23-2009, 08:30 AM
Doesn't look like you are too far away, either you come over here or I'll try and make it your way. Heck with trying to compare on the ground, lets do it in the air.