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RV-10 Taildragger Study

jeffk

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In 2015, I contracted Ken Krueger, of Sky Designs Engineering, to perform a preliminary feasibility study on a taildragger version of the RV-10. Ken was fantastic to work with and I thoroughly enjoyed the opportunity to speak with him.

To quote Ken: “The idea of a taildragger RV-10 does not seem so far fetched as to be unfeasible but there will be some unknowns.”

Perhaps this may inspire someone, already inclined towards taildraggers, to pursue this project.

Here is the response from Ken discussing the initial layout decisions as well as further thoughts and concerns:


“RV-10 TD Preliminary Configuration Study Results
Prepared by: K. Krueger
Revision: 0 Date: 07-10-15

Customer contacted Sky Designs asking if it would be possible to modify the RV-10 design from a tricycle landing gear configuration to a conventional or “taildragger” landing gear configuration. The taildragger RV-10 shall in this summary be referred to as the “RV-10TD”.

The following decisions were arrived at during the initial telephone discussion with the customer:

The preferred way to mount the main landing gear of the RV-10TD would be to use tapered steel rod legs supported in tubular sockets that are integrated into the engine mount. This is the “typical” main landing gear configuration for most RV aircraft and is a well proven and well understood way of attaching main landing gear. This was chosen for reasons of both the overall look of the aircraft and for simplicity as attaching the main landing gear in this way requires the least amount of new parts to achieve the taildragger configuration compared to the tri-gear configuration.

A preliminary landing gear layout was made and the following preliminary design decisions were made:

6.00-6 tires (17.15 inch diameter) will be used on the RV-10TD instead of the 6.00-6-15 (15.00 inch diameter) tires of the tri-gear RV-10.

7 inch diameter tailwheel. An 8 inch diameter tailwheel was considered but that would have resulted in a shallower angle in the 3 point landing attitude.

The length of the main gear legs and fore/aft location of the wheels was chosen to be the best
compromise between providing a reasonable 3 point landing attitude, adequate prop clearance, and reasonable ground handling characteristics.
The 3 point landing attitude angle chosen was 11 degrees. It would have been nicer to have 12 degrees but that would have resulted in even longer main gear legs and their length is already a concern as rod-type gear legs have a greater tendency to “shimmy” the longer they are.

The main wheel centers were located 1.5 inches forward of the wing leading edge. It would have been preferred to locate the wheels closer to or even with the leading edge but that, again, would have resulted in even longer main gear legs.

Prop ground clearance is quite adequate at 15” (FAR Part 23 requires 9 inches prop clearance)

The biggest structural design concern is the sweepback angle of the legs as the RV-10 has a relatively large distance between the firewall and the wing leading edge. The sweepback is more than both the RV-9 and RV-14 aircraft. This landing configuration may work well but it also may have a greater tendency to shimmy than other rod type leg aircraft.

An aircraft design concern is the adverse effect on directional stability that the main gear leg fairings will have as they are small fixed “wings” but being located forward of the aerodynamic center, they are de-stabilizing. The removal of the nose gear fairing will be helpful but the main leg fairings will more than offset the effect of removing the nose fairing. The RV-10 has reasonable directional stability so it may be acceptable to “give away” a little and still have good flying qualities.

A practical concern is that the taildragger engine mount will occupy a different space forward of the firewall than the space that the nosewheel mount occupies. This difference may require re-configuring of the standard arrangement of firewall forward items. The location of the oil cooler on the firewall will almost certainly be different for a taildragger RV-10 since the sockets for the rod type main landing gear will need to be where the oil cooler is. There will certainly be other changes but the oil cooler is the only one I know of at this time.

The main gear legs can be expected to be about two inches in diameter at their max diameter.

The tail spring can be expected to be about one inch in diameter at its max diameter.

The main wheels and brakes in the standard RV-10 kit can be used.

A new engine mount will need to be developed.

New main landing gear legs will need to be developed. The brake mount flanges in the standard RV-10 kit can be used.

A tail spring mount will need to be developed and integrated into the aft fuselage. The tail spring mount would, ideally, be the same design concept as the well proven WD-409 tail spring mount. Similarly, a new tail spring and tailwheel mount will need to be developed.

Retractable ground handling “handles” will need to be developed and integrated into the aft fuselage.”



Here’s a link to the original documents:
https://drive.google.com/drive/folders/1oHfKM9exJAA4JpyyZBobEDjG0_FsEtdS?usp=sharing
 

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In Other Words

IOW, this is no place for TLAR engineering; in order to make a "10TD", some serious engineering would need to be completed...
 
very interesting thanks!

The 3 point landing attitude angle chosen was 11 degrees. It would have been nicer to have 12 degrees but that would have resulted in even longer main gear legs and their length is already a concern as rod-type gear legs have a greater tendency to “shimmy” the longer they are.

anybody knows what's the landing attitude angle in 14? I would set at least the same number for 10.
 
KK is the real deal

IOW, this is no place for TLAR engineering; in order to make a "10TD", some serious engineering would need to be completed...

Well given that Ken Krueger was the primary design engineer on the RV10 when he worked at Vans and is a close friend as well as his current business is aftermarket RV designs….. I’d say anything he does is far from “TLAR” and more like “TR” (that’s right). And if KK ever did a TLAR it would be spot on.

:)
Smokey
 
I'm surprised there is no mention of fuselage strength for the tailwheel and associated loads.

We discussed this briefly and he didn't feel additional structural modification to the aft fuselage would be necessary. However, this was a preliminary feasibility study and additional consultation with Ken would be encouraged for anyone wishing to go down this path.

As an aside, I was quite taken by the two view drawing of the RV-10TW he created.

I'm also excited to see the number of views on this thread approaching 1000! (975 as I type this).
 
Well given that Ken Krueger was the primary design engineer on the RV10 when he worked at Vans and is a close friend as well as his current business is aftermarket RV designs….. I’d say anything he does is far from “TLAR” and more like “TR” (that’s right). And if KK ever did a TLAR it would be spot on.

:)
Smokey

You are missing the point; Ken listed a bunch of things to be considered when looking to change the -10 to a tail dragger. The issues he listed in summary would need to be engineered to find viable solutions.

It's not that it can't be done but there are substantial structural questions that need to be analyzed for safe and reliable solutions. I'm sure that if you ask Ken, he would say the same...

You can't change one thing on an airplane without affecting many others...
 
Hard to beat perfection.

Let's face it, the RV-10 is indeed a 10.

I have about a thousand hours in taildraggers, from the small 152 converted "Texas Taildragger" to Cessna 180's, L19 Bird dog, Citabria, Pilatus Porter, RV-8 and Beech 18 to name a few.
Would I like to fly an RV-10 taildragger. Meh... not so much.

Could it be done, probably with some great engineering efforts and lots of money.
In what way would it be a better airplane? Can't think of any.
Is it fun to talk about it? Yes!
Would it add value to the RV-10? Don't think so, maybe the opposite.

Somehow I like the high wing taildraggers,
Something like an RV-15 perhaps?

Just food for thought
 
Let's face it, the RV-10 is indeed a 10.

I have about a thousand hours in taildraggers, from the small 152 converted "Texas Taildragger" to Cessna 180's, L19 Bird dog, Citabria, Pilatus Porter, RV-8 and Beech 18 to name a few.
Would I like to fly an RV-10 taildragger. Meh... not so much.

Could it be done, probably with some great engineering efforts and lots of money.
In what way would it be a better airplane? Can't think of any.
Is it fun to talk about it? Yes!
Would it add value to the RV-10? Don't think so, maybe the opposite.

Somehow I like the high wing taildraggers,
Something like an RV-15 perhaps?

Just food for thought

Well said. My 10 is an absolute delight.
It impresses me more and more every flight.
After 10y in a RV7, I was nervous about the 10 being inferior.
I shouldn’t have worried. It’s better in almost every way other than not being able to go upside down. The TD aspect has never entered my mind.

Interesting discussion though!
I speculate that reinforcement in the tailcone is unnecessary because flight loads far exceed ground loads. After all, the rest of the vans fleet have largely identical tailcones whether they are conventional or TD. With the exception of reinforcements for the actual tail wheel leg mount.
 
Well said. My 10 is an absolute delight.
It impresses me more and more every flight.
After 10y in a RV7, I was nervous about the 10 being inferior.
I shouldn’t have worried. It’s better in almost every way other than not being able to go upside down. The TD aspect has never entered my mind.

Interesting discussion though!
I speculate that reinforcement in the tailcone is unnecessary because flight loads far exceed ground loads. After all, the rest of the vans fleet have largely identical tailcones whether they are conventional or TD. With the exception of reinforcements for the actual tail wheel leg mount.

You may be surprised at the loading with a couple of adults and 100 lbs of baggage in the back…but that is what a detailed engineering analysis is for…

Again, no place for TLAR engineering or much speculation…
 
I have no problem with tail draggers.

I have no problem with mustaches.

Every airplane ever flown has been a concoction of design compromises.
Having said that, IMHO, the RV-10 is the best airplane that I have ever flown at meeting its design goals. Near perfection for what it was intended to be, which is a comfortable and efficient cross country cruiser that can carry a very useful load.
It was never intended for sand bars, but it still does an amazing job getting in and out of unimproved strips if the need arises.

Yes it can use different power-plants than originally intended but what was originally intended has proven to be the most successful.
Yes it could be put on floats or fitted with retractable gear, and yes, it would be possible to move the nose wheel aft. All of which are theoretically possible, and perhaps fun to fantasize about, but also IMHO, MAKE NO SENSE! There are other products on the market already designed to scratch those itches, including soon, the RV-15.

Don't mess with a masterpiece. It would be like sketching a mustache on the Mona Lisa.
 
the RV-10 is the best airplane that I have ever flown at meeting its design goals. Near perfection for what it was intended to be, which is a comfortable and efficient cross country cruiser that can carry a very useful load.
It was never intended for sand bars, but it still does an amazing job getting in and out of unimproved strips if the need arises.

I think the same would be true for RV-14A, which when it was announced got all the rave reviews. Then the 14 taildragger appeared and was just as fast with IO-360 engine. That is at least 10HP difference for the same performance.
 
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