I spent some time going over the past few blog posts in a video format for everyone to watch. I'll be updating the blog post with my next post here soon.
In my previous post I covered the costs associated with buying a new certified and used certified aircraft against the SlingTsi. How does the Tsi compare against another Experimental aircraft? Given the 4 seat status of the SlingTsi, there aren’t a lot of other 4-seaters in the same price and performance category. Certainly the Lancair Mako would be a nice airplane to consider, but given the costs associated with the build time, it’s just not in the cards for something I could swing.
After the Lancair there are a number of smaller production experimental aircraft to consider, but the only other one in my opinion would be closest to in cost and performance is the RV10. If you’re new to aviation (and some reading this may be), Vans Aircraft is one of the most popular (if not THE most popular) experimental aircraft supplier in the world. I attended a session at Oshkosh one year around Vans and the speaker stood up on the stage and said “Lets face it, the ‘experiment’ is over on the RV’s” And I don’t think I would disagree with him at all. For those of you who haven’t experienced the RV series of planes, they are very nice and have a fantastic pedigree. The RV10 is their only 4-place aircraft in the lineup. It quite often is mistaken at airports as a Cirrus and it is quite similar in many aspect. But how does it stack up against the SlingTsi?
The RV10 is going to have an obvious advantage over the SlingTsi when it comes to the engine size. With the 260hp Lycoming it’s got 120 extra horsepower over the Tsi’s Rotax 915 at peak power of a 141hp. That’s for the first five minutes - after that the power is pulled back to 135hp. I’ll go more into the horsepower in a few slides as to why this isn’t as big of a factor as it may seem though.
For the rest of the information, the tradeoff is the RV-10 does have a little wider cabin, higher max cruise speed, and overall a bit more performance. What the RV-10 is though, is it is 600lbs heavier. Keep that in mind as that is going to come into play a bit later on in the discussion.
Price and Build Times
My objective in building the airplane isn’t just for something that I can fly long-term, but also how quickly can I get it done?
Price wise, the RV-10 appears to be a bit less expensive over the SlingTsi. The undercarriage line item on my chart is based on the breakout from the SlingTsi kit. There is no undercarriage option as a line item on the RV-10 price list, so I suspect some of those items are incorporated into other areas of the overall prices. Another item to note is the aftermarket items for building an RV-10 is quite extensive. This certainly has to do with the longevity of the airframe. The RV-10 had it’s first flight in 2003 where the SlingTsi had theirs in 2018. So the RV-10 builders have 15 years worth of time for additional aftermarket development. If I were to advise someone on which to choose for building, this is definitely a factor of consideration.
For me though, the build time line item - it is estimated to be 600 hours less to build a Tsi over the RV-10. This primarily has to do with the type of fasters in constructing the airplane. The RV-10 uses buck rivets whereas the Sling uses pulled rivets. This plays a huge factor in the build time. If you aren’t familiar with the differences (I wasn’t other than I drew assumptions based on the name), the buck rivet is where you take a rivet, place it in the rivet hole and use a metal plate on one side and a rivet gun to effectively “pound” the rivet into the hole. This is done through a rivet gun that makes a sound a bit like a machine gun as it molds the rivet into place. It’s actually quite fun to do if you haven’t tried it, but when we’re talking about thousands of rivets the noise can get a little old. I’m sure my neighbors will appreciate the choice of using pulled rivets. As for what a pulled rivet is - the logo for this blog is that of a pulled rivet. You insert the rivet into the hole and then use a rivet puller to extract the center post up and out. When you perform this extraction is pulls the remaining rivet into place. The overall noise generally is a very mild “pop” when the rivet releases.
At the end of the day, as per the chart above the RV-10 is the winner cost-wise, but considering it could add an additional year to my build time I’m not sure I’m that patient.
When you stack up the RV-10 performance wise against the SlingTsi there are some items to consider here. I fly out of KBJC. The standard atmosphere field elevation is 5673 feet MSL. As with most aircraft performance numbers they are all based off of sea level. I’ve often found this interesting as even flying “at sea level” you’re not truly at sea level - you’re some altitude higher than that. A safe bet would be a minimum of 1,000 feet MSL. Sure there are conditions where you’d be lower, but I generally fly with a margin of safety. The RV-10 is generally configured with a naturally aspirated engine, which means by the time the Lycoming engine reaches the field elevation at BJC you’ve already lost 39hp. On a reasonably warm summer day here in Colorado it isn’t unusual for the density altitude to reach 8,000 feet. This means the engine is down another 62hp to 198hp - and the first thing you’re going to do after taking off is add more altitude.
Given this breakdown and that the Rotax 915is is a turbocharged engine, the two engine performance levels start to converge as altitude is gained. The 915is as designed will maintain sea level performance up to 15,000 tp 16,000 feet (depending on the source of the information as the Sling Aircraft site indicates 16,000, the Rotax 915is wiki page indicates 15,000 feet). If we take the reduction in engine performance as the airplane climbs the SlingTsi with the Rotax 915 starts to overtake the airspeed of the RV-10. I recently found a YouTube video of an RV-10 climbing up to FL200 to show off performance running lean of peak showing a True Airspeed of 152kts with a direct 39kt tailwind. It seems to support the numbers as per the chart below.
This is where the conversation about the weight of the aircraft comes into play as well. In doing a breakdown on this by altitude carried to the extremes we see once the airplane is above 16,000 feet the differences tend to start leveling out
This chart goes up to FL240 - which of course the question becomes “what a minute, the ceiling on the SlingTsi is stated to be 18,000 feet?” Well, this is true, the definition of the service ceiling is the height above sea level at which an aircraft with normal-rated load is unable to climb faster than 100 feet per minute under standard air conditions. There are a couple of videos out there of the Sling reaching flight levels of FL240 and up to FL300. Now, in my flying needs I literally have no desire to fly at that level, even if someone demonstrated the aircraft has gone that high. My goals would be in the 14,000 feet to 17,000 feet during long trips. Based on this chart, the SlingTsi will perform exceptionally well in this range
There’s a vast wealth of information online on this topic. Van's Aircraft provides documentation on the loss of horsepower as altitude changes:
Garrett Advancing Motion - while there is no relation to myself and Garrett engines (which would be nice actually), they do have a discussion around turbocharging at elevation when it comes to cars in this article. Oddly enough I don’t live too far from Pikes Peak and can see it on a clear day. This reference is more supporting documentation for the delta differences between a naturally aspirated engine and a turbo engine.
The wiki links for both of the respective engines between the Rotax and the Lycoming power plants:
Rotax Engine Wiki https://en.wikipedia.org/wiki/Rotax_915_iS
Savvy Aviation has a couple of great discussions on the state of engines and turbo engines at https://youtu.be/p22FOawoTCM - Turbocharging Systems in which I grabbed this slide.
The only part of the conversation on this that I am missing is the weight to horsepower expectations. This is where my math skills are failing me. I’ve had a number of conversations and haven’t found anyone that disagrees with these findings so far. If you have more to contribute to the conversation I’m welcome to feedback on this topic.
Overall though, on the surface the RV-10 certainly is a compelling airplane with the heritage of the platform, a bigger cabin and what appears to be a slightly less expensive build, however given the location I’m located, what the mission is and the build times I feel comfortable with the performance the Sling is going to offer when stacked up against the RV-10.
What are your thoughts? Am I missing something? It’s too late for me as I’m committed to building the Sling, but I’m always welcome to feedback to help not just my understanding, but also to share the most accurate information I can with other pilots.