Useful load concerns

[bertschb]

I'm going to be a first time builder soon and recently learned about the ER fuel tanks offered by Sky Designs. I really like the idea of the added range these ER tanks would provide but I'm concerned about the reduction in useful load.

The problem is my passenger and I weight 410lbs combined. I believe this would put me at or near max passenger weight with full fuel with the standard tanks. The extended range tanks would add an additional ~108lbs of fuel and put me over gross weight if I had anything in the baggage compartment.

I don't really need four seats which is why I chose the RV-14 but now I'm thinking the RV-10 might be a better fit because of the higher useful load.

Thoughts?

[dmattmul]

ER tanks make a lot more since in the 10 vs the 14. A 10 uses ~~ 50% more fuel per hour than the 14 yet has only 20% more fuel capacity (60 vs 50) My 14 has over 4 hours fuel taking into consideration min reserves and that's more than enough for my internal reserves. (And my wife's)

Attached is my 14's W&B. At 410 lbs. leaves little for baggage let alone the added weight of ER tanks plus fuel. Granted my 14 is a little piggy.

[David Z]

Just because the tank capacity is there, doesn't mean it needs to be filled. Going solo leaves a lot more room for fuel.

There aren't many planes that can have full fuel and full seats. In fact it's almost unheard-of. (I flew a King Air that could take 120lbs payload with full fuel...that's 0 passengers)

Do the weight and balance before every flight. If that includes taking less than full fuel and adding a stop enroute, then so-be-it.

If 90% of the flying will include 410lbs of people, then maybe the ER tanks are pointless as the ER tank capacity can't be used. However, if there's going to be lots of long range solo flying, then the utilization of the extra tank capacity will be wonderful.

It's nice to have the fuel tank capacity when the load is smaller.

[KatanaPilot]

Hopefully Ken K. will "weigh" in on this question.

Ken produced a very detailed engineering analysis on the RV-10ER tanks, which included a justification for an increase in gross weight roughly equal to the amount of additional fuel added by the ER tanks. There were several caveats along with this included in this report. I have not seen an equivalent report for the RV-14, but I suspect it exists and there may be a similar statement regarding an increase in gross weight.

Not suggesting you do this without additional justification - but you are the manufacturer and you can set the gross weight wherever you choose. That being said, your DAR has final approval.

[Sky Designs]

Hi Brian - as mentioned by Krea, the engineering analysis that went into the design of the RV-14ER tanks has been compiled into a report. Same scope and detail as went into the RV-10ER engineering report that he references.

As mentioned by David Z, you can vary your fuel load according to how much - or how little - your cabin load is. ER tanks give you more flexibility in that respect. Plus our ER tanks incorporate "tabs" for accurately determining partial fuel level.

As mentioned by dmattmul, you can also add weight during the build and end-up with an airplane that, while comfortable & nicely equipped, doesn't have the capability you had hoped for. BTW: our ER tanks will add 4.5 lb to your empty weight. No free lunch.

How much, how far, and how fast? Those are the three questions every aircraft purchaser has to ask. You are off to a good start by making sure you have chosen the best RV to fit your mission. Good job!

[bertschb]

Originally Posted by KatanaPilot

...Not suggesting you do this without additional justification - but you are the manufacturer and you can set the gross weight wherever you choose...

I've read this before and find this interesting. I would think Vans did the engineering to calculate the gross weight at 2,050lbs. My non-engineering mind tells me the RV-14 with it's short take off and excellent climb performance could handle 200lbs over gross during take off but then I'm very risk averse.

I really appreciate the feedback guys! I've never built a plane and I don't know anybody that has so my pee brain is struggling to figure out how I want to build this airplane.

[KatanaPilot]

Brian,

I suspect that a majority of the people on this forum have/had never built a plane before - so don’t let that discourage you from this endeavor.

I know this will sound like a broken record to some here - but the best build assist facility in the country has one of their locations just a few hours west of you in Eugene. I suggest that at the very least - you sign up for one of their Saturday fundamentals classes. It is likely they will have at least one RV-14 under construction there. You will learn a lot and can ask all the questions you want.

I always suggest that folks build their empennage there too, but not everyone can spare the two weeks and additional money to do this. If you can, it is one of the best things you can do (in my opinion) to get your skills well up the learning curve, learn what quality work looks like and to provide you with motivation to continue during the inevitable frustrating times.

I built my RV-7A there and my 10 at the Georgia location. I’m a big fan.

http://synergyair.com/all-oregon-classes/

[Avanza]

Most aircraft's can be flown safely within 10 % over MTOW as long as the CG is respected. This is normal when ferrying an aircraft on long flights.
But, it´s important to understand the implications.
You will be outside of the performance charts in the POH.
Doing this with a passenger and if there is an incident or worse may raise questions.

Good luck

[AlexC]

Originally Posted by bertschb

I'm going to be a first time builder soon and recently learned about the ER fuel tanks offered by Sky Designs. I really like the idea of the added range these ER tanks would provide but I'm concerned about the reduction in useful load.

The problem is my passenger and I weight 410lbs combined. I believe this would put me at or near max passenger weight with full fuel with the standard tanks. The extended range tanks would add an additional ~108lbs of fuel and put me over gross weight if I had anything in the baggage compartment.

I don't really need four seats which is why I chose the RV-14 but now I'm thinking the RV-10 might be a better fit because of the higher useful load.

Thoughts?

I've flown 650nm a couple times and had between 15-18gal remaining in the standard RV-14A tanks. So, if you only fly ~700nm or less routinely, then you really don't need the extra expense and weight of the ER tanks. If you know a substantial number of missions will be >700nm in one shot and are single pilot, then sure, the ER tanks would definitely be worth it. However, with a passenger, it is rare for both you and s/he to have bladders that exceed 4.5hrs or so - a fuel stop with a biological break takes less than 20min.

_Alex

[BobTurner]

Originally Posted by AlexC

However, with a passenger, it is rare for both you and s/he to have bladders that exceed 4.5hrs or so - a fuel stop with a biological break takes less than 20min.

_Alex

Wow, you must visit airports that employ line boys from Indy 500 races! I find that the time spent in the landing pattern, landing, taxiing, figuring out the self-serve fuel credit card reader, bathroom, taxi, checklist, takeoff and climb back to cruise ‘costs’ twice as much time. And if there’s food involved, it’s an hour minimum. I have balanced the injectors (-10) and routinely cruise lean of peak. For trips of a certain length (somewhat longer than 75% best power range) the door to door time is shorter by flying slower - because you can skip the fuel stop. And burn noticeably less gas to boot.
To the earlier poster: many -10’s are the exception to the rule. With full (standard) tanks I can carry 4 180 lb people and be below Vans’ 2700 lb gross.
To the OP: there are many options, many choices, when you build an RV. One thing that surprised me was how many friends and acquaintances wanted to ride with the wife and myself, which made the -10 the right choice for me. No aerobatics, of course, which may be a factor for you. Tim Olson, on this site from time to time, has built and flown both a -10 and a -14. He might offer you some insight.