Engine and Prop Choices

[caleb1]

Hi all,


Have had a deposit on a STi since Oshkosh 2021, and the time has come when I'll have to decide on engines/props/etc. Thought I'd start a discussion on this to see what other's thoughts are regarding the best configuration.


It is likely I'll need to sell the kitfox not long after completing the build. So I'm more focused on what configuration is going to be the most desired for used buyers for the best profit margin, than I am on getting the configuration which best fits my use. I don't have any particular need for extreme performance, I am mainly just doing it for the building experience and enjoying it for a short time.


Short question is, any thoughts as to which engine/prop configuration would be most desired by used buyers?


Long question/where I stand:


When it comes to engines, it's probably between the Rotax 912iS or 915iS, since those are the ones for which a firewall-forward kit is available. (It's my first build so I'm thinking I'll want the most "plug and play" setup). If there's another engine option that's much better, then I might consider it but it seems as if those two are the most popular anyway.
I have read that the 912iS offers a better power to weight ratio... This doesn't quite seem right to me considering that the 915iS is only about 40lbs heavier with an extra 40hp. Can anyone testify to this?
Are there reasons to go NA vs. turbo? Big downsides to turbo? Maintenance?


Props.... I'm somewhat overwhelmed by all the options, discussions, and technical information there are for these. If someone could point me in the general direction of a relatively simplified comparison of common prop options that'd be great... All the discussions I am finding regarding props are somewhat over my head. I'm sure I'll understand it all soon but it'd be nice to find something simple to start with.


Anyways, I'm most likely going to go with a constant speed (variable pitch) unless someone gives me a good reason not to. Kitfox told me they basically have regular hydraulic, single lever, and Airmaster electric.
Unlike the engines, there's really no other components for the props besides the prop itself, so I suppose I wouldn't be limited to what Kitfox sells. Correct me if I'm wrong, but I'd imagine it wouldn't be any harder to install a prop not sourced from kitfox as long as it's compatible with the rest of the setup.


Of course, the best prop depends on the purpose of the aircraft. But once again, I probably won't be able to own it long enough to really care which prop I have, so I'm looking for what's going to be the most desirable to the buyers on the used market.


In your opinions, is the Airmaster worth the extra $12k? Is hydraulic as good as any?


[End elaboration]


All that to say, I'm looking for a place to start on figuring out which engine/prop configuration is ideal for my mission, and I'm having a hard time finding that so far, so I thought I'd make a post.


Any input/thought/opinions appreciated.

[bbs428]

Your post really opens a can of worms... Like what's the best oil? Lol.

Lots of prior discussion on this subject so a search will answer a lot of your questions.

Your mission and where you fly will determine the prop/engine choice imho.

If you're building to sell, calculating profit margins and such, that's really beyond the scope of this forum and I can't offer any insight.

Best of luck!

[ken nougaret]

A couple of things pop out to me. Someone correct me if I'm wrong, but if an in-flight adjustable prop is used, can it be registered lsa? I would think resale would be easier as an lsa. And with the added expense of the 915, you'll have to ask that much more for resale. I would expect that to cut down on your potential customers.

[Jerrytex]

Here's a thought......what about building it mostly generic, so to speak---- rotax 912is, or ULS, ground adjustable prop like a whirlwind, warp, or Luga, use the stock landing gear, stock tailwheel, modest EFIS, etc. which will make it an awesome plane for flying around Florida, which sounds like it would fit your mission, and then when you go to sell it, you can market it as an awesome flying airplane as is, or a blank slate for someone wanting to do all the expensive add ons, of their choosing and you'll be able to price it and market it accordingly? Also, keeping it at 1320lbs is definitely a selling feature that someone could easily change in the future if they wanted.

[jiott]

Ken you are right, in-flight adustable prop cannot be registered LSA, at least right now; who knows what the new FAA mosaic rules will allow in a couple of years.
That being said I would stick with a ground-adjustable 3 blade prop like the Whirlwind. For resale engine choice I would stick with the tried and true 100 hp Rotax 912, probably the iS rather than the carbureted ULS. An airplane like that would be snapped up in a blink if priced fairly and equipped with most of the kit options. Personally I would stick with the Grove gear and some tires like the Desser 6x 8.50, 22" dia. To keep the price reasonable, I would stay away from the Monster shock gear and big bushwheels. Those can be easily added later if the buyer chooses. My 2 bits.

[Kitfox Pilot]

Your sti kit will come with the big gear so you will need some kind of large tires. Engines for resale would be rotax. 915is on a sti would be what most would want but is it worth 16000 more than the 912is for resale?? That's a call you would have to make on your budget. And yes 40ish lbs is the difference between a 912 and 915.
As for the props, I have an airmaster which I like but I doubt it's a good investment for resale purposes with the price difference over a regular prop.
I would guess LSA would be a good selling point but I don't have proof of that. Any Nice kitfox that hits the market right now sells fast and high.
If you are on a tight budget 912 and stiff prop.
If your not the 915 sure is nice and will resale good too........
I've only got 140 hours so I haven't had any Maintenace expenses to speak of yet, I hope it stays that way!
JMO
Harlan

[Danilo]

Here's a thought......what about building it mostly generic, so to speak---- rotax 912is, or ULS, ground adjustable prop like a whirlwind, warp, or Luga, use the stock landing gear, stock tailwheel, modest EFIS, etc. which will make it an awesome plane for flying around Florida, which sounds like it would fit your mission, and then when you go to sell it, you can market it as an awesome flying airplane as is, or a blank slate for someone wanting to do all the expensive add ons, of their choosing and you'll be able to price it and market it accordingly? Also, keeping it at 1320lbs is definitely a selling feature that someone could easily change in the future if they wanted.

Can you change the 1320lbs once its been registered as an LSA? I thought you couldn't do that. Otherwise I fully agree with this statement.

[jiott]

You can change from a 1320# LSA to a non-LSA higher weight limit, but you can never change back down to LSA. This is the law right now; in a year or two things will probably change.

[Danilo]

Cool! This is actually great news for me. Was planning on registering mine as an LSA but will probably end up getting my PPL in the near future so going full gross afterwards would be ideal.


You can change from a 1320# LSA to a non-LSA higher weight limit, but you can never change back down to LSA. This is the law right now; in a year or two things will probably change.

[efwd]

Don't hold your breath though. I have been waiting for the new rules on LSA to come out as well. They gave a pretty good tease this past summer where many stated that they would be posting the rules for public comment at Airventure. Still haven't heard anything.

[Kitfox Pilot]

Don't hold your breath though. I have been waiting for the new rules on LSA to come out as well. They gave a pretty good tease this past summer where many stated that they would be posting the rules for public comment at Airventure. Still haven't heard anything.

I agree with Eddie, I have about given up on any changes that will help us.

[rv9ralph]

During EAA Homebuilders Week in January, there was a webinar on "Advocacy Issues" that addressed the current state of MOSAIC.

Short version... NPRM Summer of 2023. Rules in effect sometime in 2024... I will believe it when I see it.

[caleb1]

Sorry it took so long for me to reply, but thanks for the responses everyone.
This was the type of input I was seeking.




As someone pursuing a PPL, I hadn't considered the benefits of keeping it LSA compliant, but I can see how that could be a big selling point.
Based on this discussion, I'm thinking I'll try to do that. A ground adjustable prop sounds like a good option. And it shouldn't be too hard to upgrade later on if desired.


I can definitely understand the benefits to the simplicity of the "tried and true" 912iS, and the lower price of course. It sounds like most people like that engine.
However, I met with a friend today who has owned multiple experimental (Pipitstrel and Aeroprakt) and he said that 100hp is not nearly enough power for an almost 1300lbs GW aircraft. I'm not extremely concerned about the extra price of the 915iS upfront, but just want to make sure it will be sellable.
Is the added price of the 915 really going to cut down on customers though? They're buying something for $150k-$200k+, will they really be unwilling to pay an extra 10 or 20 grand to get the better performance? I must say I tend to agree with Harlan @Kitfox Pilot that the 915iS would be the "better" engine for the STi.


When it comes to landing gear, it's an STi, so I'm probably going to go with the beefy options. My reasoning is, if someone wants an STi, they'll want it for the STOL capability and hence will want the big gear and tires, (as well as an engine giving the best TO/L distances). If they want small tires and basic gear, then they probably won't want the STi wing. Thoughts?


Thanks again for all the help.


Caleb.

[Eric Page]

@alexM and I did part of a ferry flight back in December in a Kitfox powered with a 912iS and a 3-blade Whirlwind. We started near Montrose, CO and went north into Wyoming before turning east and eventually ending up in Kansas where the weather shut us down. That airplane was about as draggy as a Kitfox can get: Shock Monster gear, big tires and no strut fairings. With two 6-ft 200# guys, two stuffed backpacks and full fuel, we climbed above 12,000' north of Montrose before it ran out of steam. It was my first Kitfox flight experience, so I can't compare it against higher powered airplanes, but it seemed to perform very well to me. I'd say it gave me a sense of comfort with my choice to buy a 912iS for my build.

Of course, as the saying goes, there's never been an airplane built that had enough horsepower.

[caleb1]

Good to know... That's better than I'd expect for that setup.

[Maverick]

FAA's motto: We're not happy until you are not happy! And, they live up to it daily.