Contemplating an SS-7 - Newbie builder

[jmodguy]

Alan,
Definitely go fot the KF! The 24v electrical system is really not needs on this aircraft unless you just want to spend a lot of $$$..
Batteries cost more, anything electric will cost more. Does Rotax even make an engine with a 24v system? I don't know that's why I ask.
Most EFIS systems today will run on 12 or 28v but the wire size won't change.
VPX is overkill.
Wiring is not complicated but can be intimidating. The one thing you will need is the proper tooling, I.e. wire strippers and crimpers. Do NOT use hardware store strippers and crimpers! These are OK for house or car wiring but they do damage the wire.
Regards
Jeff

[mr bill]

12 volts won't shock you, but you sure will feel 24 volts.

[Danzer1]

Alan,

A few thoughts on the VP-X:

I agree that it could be considered overkill if you are building a simple mostly analogue panel. I to am seriously considering a VP-X for the following reasons:

I am going to be doing full glass dual Dynon panels, each with their own battery backup and lots of other goodies (not in a Kitfox), it integrates very well with Dynon.

I hate fuses! They require some kind of annunciation to determine what is amiss. Pulling fuses to see if burned through while flying an aircraft that has whatever blew, disabling something, is not in my plan.

So the next logical step is breakers. Can see if tripped, but with needing at least 12 to 15 for my config, that takes up more panel space than I'm willing to give up.

So, electronic breakers make perfect sense to me.

Many have reported that the VP-X has been exceedingly fast and simple to wire, setup and diagnose. There have been some niggles mostly with flap/trim wiring & configuration - I believe that has been worked out.

There are many on the Vans Airforce VAF forums that have/are using it, so if you haven't read over there, it may be well worth your while.

Everyone has a different plan, panel idea, mission, so there really is no right or wrong. As a retired engineer though - data (facts), 1st hand knowledge, education, controlled testing, evaluation, real world field results - trumps hearsay every time.

Go with what works for you, your mission, goals and budget.

Greg

[av8rps]

You will really be happy with a Kitfox. And the Kitfox makes an awesome float plane. The biggest thing is to keep it light if you want an amphib as you'll probably be adding 200-250 lbs of weight to the aircraft for the floats.

If I were building a new Kitfox and intended it to be an amphib I would look for a lightweight covering process that still looks good and is easy to work with. (I like Stewarts and Air-tech, polyfiber is too labor intensive and heavy, unless you use only their polytone product).

I would instrument it with modern electronics over steam gauges for weight savings, as well as for all the additional benefits of more information to the pilot (like synthetic vision).

For an engine? I'd go with Rotax as it is proven again and again the best way to end up with a light empty weight Kitfox. And while the UL engines make decent horsepower, they need to turn a shorter prop to use that power as their rpm's are too high for a long prop to work efficiently (once prop tips get close to going supersonic efficiency plummets...). And since seaplanes always use long props turning slower to make them perform better, the gear reduction on the Rotax is premium. A 914 or the new 915 would be awesome, but a 912uls with a big bore Zipper kit might be nearly as good for a lot less money and complexity.

I too would see no need for a 24 volt system. I also would avoid the extra alternator so many*add to their 912 as it is just more added weight and complexity you can avoid by utilizing led lighting and low draw mfd's in the panel.

With all that said, I will admit I don't always follow my own advice. My little 80 hp 912 Kitfox 4-1200 on amphibs is actually a bit "piggy" (heavy) having really heavy paint, steam guages, carpeting, plexi glass for everything. But yet it performs great. I attribute that mostly to the efficiency of that lightweight 912 making the most prop thrust per pound and per horsepower, all while keeping the empty weight on amphibs under 800 lbs. Obviously a Kitfox Super Sport on amphib floats will weigh more than mine, but i believe if you power it with a 912 series Rotax with 100+ hp you will have great performance too.

Paul Seehafer

[Danzer1]

A would agree with Paul and his float plane expertise on everything written except:

the new 915 would be awesome,

A 914 weights 166 lbs plus fluids fully operational.It's rating of 120 hp @ 5800 is only good for 5 minutes. Great for takeoff, but does nothing for cruise. It's rating @ 5500 is 100 hp continuous - might as well be a 912! However it's max torque is at 4900 (torque is the true measure of energy to the prop) and that is 128nm (continuous) or 311nm torque at the prop (minus psru eff. loss) at 91hp. So it's "burst power" capability may have some usefulness for takeoff, but otherwise it's just a more expensive, complicated 912.

For instance, the UL 350is is 173lbs wet (including fluids) and produces over 310nm torque in a band from 1700 rpm all the way up to over 2800 rpm. It beats the 914 in every respect in a real world operating rpm band (not the paper rated 3300/130 or the Rotax "burst power") including cost.

The jury is out though on the 915 as Rotax has not produced any dyno results yet. I can tell you though, they have published the dry weight with PSRU at 185 lbs, if adding everything else to that like all their other engines, that would be another 25lbs or so for 210lbs plus fluids. They also have published that 135 hp to be the max at 5800 rpm good only for a whooping 1 MINUTE! Projected price to be near $35k. Not sure the final price and continuous operating specs will justify the 1 minute "burst" gain to me. I will wait to see the dyno torque curve to further assess.

Bear in mind, I'm not doing floats either.

Greg

[foxbait]

Hi Allan, I'm in Niagara Falls, started my SS7 build last April, been a slow process so far but you are welcome to come and check things out.
Mike

[av8rps]

I also agree with most of what Greg just wrote.

No one at this time really knows what the 915 will really do. So that really is an unknown. But I'm guessing Rotax did their homework before dumping millions into a new engine.
However, if that 915 is too much of an unknown, a zipper kitted 912s is readily available.

And while I really like the concept of the UL brand engines, so I agree with Greg on horsepower and torque ratings vs the 912-914-915, the Rotax PSRU makes for a much more efficient prop on a STOL or seaplane aircraft. It takes whatever torque you have and turns it into a much higher thrust number than an engine without a PSRU would have.

My best example and defense would be to talk about a 130 hp UL powered Highlalnder that the builder (Steve Dentz -who in my opinion is a master builder) struggled a lot with his to get it to the point it was working well. Ultimately I believe Steve got it really dialed in and it gave him a really good performing Highlander. But yet Steve Henry (The dead stick takeoff guy and friend of Dentz) uses highly modified (up to 145 hp) Rotax 912 and 914 engines on all of his new airplanes that he also competes with in Valdez and Oshkosh. So I believe if he knew the UL was better than the Rotax, I'm pretty sure he would have tried one on at least one of his many builds. And I know he is open minded and always looking for something better as he just tried a 4 stroke 140 hp snowmobile engine in his latest Highlander. But he recently took that out and replaced it with a 912, stating there is a lot more to do to make it a viable alternative to the tried and true Rotax.

With all that said, I would'nt want to discourage anyone from using the UL engine as I think it will work well if you just follow what Steve Dentz did with his. And I also think the Ul will work as good or maybe better than the Rotax if it is used on a faster airframe that requires use of a short prop. But for a STOL type aircraft, I still think the Rotax will perform better overall.

Now if someone would just come up with a PSRU for the UL (and the Jabiru) then Rotax would have some serious competition...

[alandbrooks]

Team

Thank you for all comments yes my eyes have been opened even wider..its great to see the difference in opinions

For the engine decision will be a little later - have to decide when I rig the wings...the 1 degree forward rule...etc and by that time (1yr from now) a lot can change and I am sure most issues for both UL and Rotax will be sorted out...

For the electrical I am still pondering. What I plan to do as far as the panel is concerned is go with a single Dynon EFIS, radios, Com etc basic day/night VFR and pre wire everything before hand to accommodate a second EFIS auto-pilot servo's etc. Thats why I like the Vertical Power...simpler - a few bucks more but less pain IMHO.

I am also planning to build as light as possible but not going overboard - as I have access to some real good commercial airplane composite technology and tools...I have some ideas.

I am looking forward to the build process..which I am sure will be a lot of fun.

[Esser]

You don't have to rig the wings forward for heavier engines for the most part. There are some good threads about this if you search. I did a bunch of theoretical C of G calculations and it would be very hard to get enough weight forward to put you outside c of g

[Danzer1]

Alan,

I am sure most issues for both UL and Rotax will be sorted out

For the record:

By all user accounts - the 350is performs as advertised. Those that think it performs poorly either can't read a performance chart/manual and/or have a poorly matched prop. I've heard of neither complaint from ACTUAL USERS.

Steve Dentz built his in 2010 and was an early adopter (kudo's). He has been using a Catto 74" fixed pitch since 2013 and is happy with the current performance. I still don't think it's the best match for the engine.

Sebastian Heintz - owner of Zentith has been using one in his CH 650 since 2011 with a 65" Whirlwind ground adjustable propeller and he's been so pleased, UL engines are their engine of choice for Zeniths. I still don't think that's the best prop match for the 350is either.

Since then there are many more propellers available. Some you won't even find yet on the prop manufacturers sites. Airmaster is working with Whirlwind on a cs prop for the 350is. Whirlwind is also working on a STOL prop too. The recommended normal operating range for the engine (in the UL operating manual) is 2200 to 2800 rpm - well within the parameters of most props. The notion that the operating rpms are somewhat higher than normal is hogwash.

I've been in contact with the manufacturer and they are not aware of any current technical issues to be worked out - zero - none - nada! They are however working on improvements mostly in optimization of the FADEC engine management (I'm still hopefull for a "lean of peak" mode).

There are less single point failure possibilities in the 350is than any Rotax. It has dual plugs and dual iginition. It has available dual ECU's, dual fuel pumps and dual alternators. SO you get to choose your tolerance for risk vs budget.

Contrary to most all Rotax's, it doesn't have or need carb heat, carb issues with floats and balancing, mixture control, fluid cooling system, water pump, psru and it's 500hr inspection, 5 year rubber replacements, etc, etc.

The idea that the 350is has more single failure point possibilities is again - hogwash.

It is my "opinion" that most of the "smoke" regarding these "issues" is more smoke and mirrors than truth. IMHO.

I'm fine and good with those that are happy with their Rotax's, I just don't buy into the religion. I'd rather have the simpler (by far) 350is with it's 310nm of torque (or higher) from 1700 rpm all the way up to over 2800 rpm than a Rotax (912uls as example) that peaks at 310 nm torque (at the prop) at 1934 rpm (also at the prop) and drops swiftly on both sides of that peak.

I, like you have about a year to make a final decision, so anything can happen in that time. And I want to see the the CS Whirlwind and STOL before finalizing.

I am for sure going with the VP-X though - the way avionics change, I want the ability to just change some pin locations and simply reassign and reprogram.

Regards, Greg