RV-10 HS engineering question and observations

[BlackRV7]

Yesterday I ran into something on the 10 that was not present on the 7. On the 10, there are two, top and bottom, spar caps nested into the front HS spar. This spar cap is eventually rivet to the spar flange with 3's and the spar web with 4's. It can be seen, for those not building a 10, in the following picture. The spar caps are not part of the aft HS spar. Since I have been away from building for a couple of years, this may be old hat but I couldn't find an answer to my lingering inquisitiveness. Here is the engineering question. Are these added because of the added length of the 10 HS and why on just the front spar. Is it the that the front spar sees more bending than the aft spar?

Now this is just for general comment....by me. I know these obviously do the trick but..seeing these two puppies hold the HS to the tailcone...I'd just a-soon these be made of titanium

And just for grins...dang this is one long HS compared to the 7!!! Any btw, that is my 7 radio controlled in the box under the pool table. Yes, that is the same pool table I took, and posted on VAF, my first picture when I got my 7 emp delivered.

I can say one thing, after having built one, it's much easier to build the second one, a whole lot less head scratching and a whole lot more doing.

Better get back to doing tax returns..only 11 days left. Come on April 18th.

 

[flion]

Only the engineer can tell you for sure but I'd guess your surmise is correct. The -6 had bars on the rear spar for much the same reason. This actually looks like an improvement because the lateral loads are taken up mid-chord by the forward spar caps and the stringers between the spars rather than solely at the rear of the HS.

And I wouldn't worry too much about the HS-1005s. Not only are they much heftier than the similar part on the -6/7/9 but, like those models, they're not the only thing holding the tail on.

As for your third observation, I totally agree. I was measuring my spars against my -6A wings because they reminded me so much of the wing rear spars. That's when it really sunk in that I was building a bigger airplane this time. It's the same, but more so. I even found myself looking at Aluminum Overcast while it was in Flagstaff this week and thinking, "If only that came in a kit..."

 

[rleffler]

Now this is just for general comment....by me. I know these obviously do the trick but..seeing these two puppies hold the HS to the tailcone...I'd just a-soon these be made of titanium

I can't answer your first question, but I suspect your assumption is correct. The HS is also attached to the horizontal attachment bars (F-1011) which are prety substantial in strength. These are instsalled in Chapter 10.

bob

 

[BlackRV7]

I can't answer your first question, but I suspect your assumption is correct. The HS is also attached to the horizontal attachment bars (F-1011) which are prety substantial in strength. These are instsalled in Chapter 10.

bob

Yep Bob, I've already built the bulkhead with the F-1011's....I guess I'm just a woos about HS attachment points...I felt the same way on the 7, yet I ended up yanking and banking it In all seriousness, the HS attachment methods obviously are more than substantial enough it's just sometimes I think.....what I just built is going to be flying. Never, ever say....ah, that's good enough.

As for your third observation, I totally agree. I was measuring my spars against my -6A wings because they reminded me so much of the wing rear spars. That's when it really sunk in that I was building a bigger airplane this time. It's the same, but more so. I even found myself looking at Aluminum Overcast while it was in Flagstaff this week and thinking, "If only that came in a kit..."

Hum, you think we can talk Van's into it.........

 

[Rick S.]

I know it may just be a photo setup thing but it looks like you have the forward attach angles reversed, left on right and right on left.

 

[BlackRV7]

I know it may just be a photo setup thing but it looks like you have the forward attach angles reversed, left on right and right on left.

The pictures does make it kinda look like that now that you mention it. Nah, there on right......which doesn't mean I'm incapable of putting something on back-----erds. If this case, I double/triple checked my right and left.

 

[joedallas]

Section modulus

[QUOTE Are these added because of the added length of the 10 HS and why on just the front spar. Is it the that the front spar sees more bending than the aft spar?

[/QUOTE]

A short Answer

Section modulus

The Spar caps are added to the section to add the amount of material at a distance from the neutral axis.
(Assuming that the I-beam is symmetric, the neutral axis will be situated at the midsection of the beam. The neutral axis is defined as the point in a beam where there is neither tension nor compression forces. So if the beam is loaded uniformly from above, any point above the neutral axis will be in compression, whereas any point below it will be in tension.)

The load applied to the section is a function of its length times the load
And many other things

Good Luck

 

[BlackRV7]

The Spar caps are added to the section to add the amount of material at a distance from the neutral axis.

The load applied to the section is a function of its length times the load
And many other things

Good Luck

Joe, the thing that struck me when I started on the front spar, after finishing the aft spar, was there was not a spar cap added to the aft spar. Nor was a spar cap on the 7 I built. Again, it seemed an obvious answer would have been the mere size of the 10 HS, something close to 12' with the fiberglass tips.

Not that I am questioning the design at all, that would be the furthest thing from what I am thinking, but why wouldn't the caps be on the aft spar with the elevator pivot points and related stresses/loads? I'm certain there are valid aeronautical engineering reasons....they're just beyond my numbers (CPA) brain

 

[joedallas]

Less Aera = Less load transferred

Joe, the thing that struck me when I started on the front spar, after finishing the aft spar, was there was not a spar cap added to the aft spar. Nor was a spar cap on the 7 I built. Again, it seemed an obvious answer would have been the mere size of the 10 HS, something close to 12' with the fiberglass tips.

Not that I am questioning the design at all, that would be the furthest thing from what I am thinking, but why wouldn't the caps be on the aft spar with the elevator pivot points and related stresses/loads? I'm certain there are valid aeronautical engineering reasons....they're just beyond my numbers (CPA) brain

I try to Help
Look at the Skins

Look at the front spar, the load to the area of the skin in front of this spar is transferred to front spar / 50% +or ? of the area in back of the front spar is transferred to front spar

Now look at the back spar
Think it out
Less Aera = Less load transferred

I hope this helps

 

[BlackRV7]

I try to Help
Look at the Skins

Look at the front spar, the load to the area of the skin in front of this spar is transferred to front spar / 50% +or ? of the area in back of the front spar is transferred to front spar

Now look at the back spar
Think it out
Less Aera = Less load transferred

I hope this helps

Got it Joe, actually makes perfect sense. I knew the answer would be something simple when someone pointed it out. Proves you only have to hit me with a 2x4 one time to make it sink in

 

[MTBehnke]

Except that you also have to carry the load from the elevators on the aft spar. I'm working on my HS now and was wondering the same thing about the spar caps on the front spar.

 

[joedallas]

True but not as much as you would think

Except that you also have to carry the load from the elevators on the aft spar. I'm working on my HS now and was wondering the same thing about the spar caps on the front spar.

True but not as much as you would think the moment is through it?s own Spar and back to the stabilizer with help from shorter center spar
Look at the location of the hinges

I knew I should have included this in my last answer

Rest easy vans engineers have it covered.

 

[Guy Prevost]

snip....

Now this is just for general comment....by me. I know these obviously do the trick but..seeing these two puppies hold the HS to the tailcone...I'd just a-soon these be made of titanium

..snip

Just to ease your mind about those brackets. I'm assuming they are of 6061-T6 which has a yield strength of ~40,000psi. I'm guessing they are 1/8" thick by about 1.125" wide after drilling the rivet holes. That means that the two of them together have a cross-sectional area of .282". That also means that if loaded in a nice straight line (which your HS does nearly, but not completely) they would need over 11,000 lbs force to fail. Of course you need to de-rate them for possible builder error and fatigue strength over thousands of hours of vibration, but still--those brackets are surprising robust. Assuming they are 1/8" rivets, the 18 rivets (9 per side) attaching them to the HS have a cross sectional area of .220". A lot of things come in to play when analyzing a triple row of rivets, so I won't do it here. Nonetheless, it is nearly assured that the riveted joint would fail prior to the brackets, but not by a lot. In summary, it appears to be an extremely robust design.

I agree with the comments as to spar load paths made above. (Not that anyone cares )

Best,
Guy

 

[BlackRV7]

snip....

..snip

Just to ease your mind about those brackets. I'm assuming they are of 6061-T6 which has a yield strength of ~40,000psi. I'm guessing they are 1/8" thick by about 1.125" wide after drilling the rivet holes.

I agree with the comments as to spar load paths made above. (Not that anyone cares )

Best,
Guy

Actually Guy, those brackets are made out of AA6-187x2x2-1/2 so the thickness is more like 3/16. They are cut into brackets which are 1x2-3/8x1-1/2.

I was never doubting the integrity of the material it was just the size of the 10 compared to the 7 stab got me to thinking....struts, guide wires.....

Like Patrick said, when I saw these spars my first thought was, these things are longer than my 7 wings!!!

 

[MTBehnke]

True but not as much as you would think the moment is through it?s own Spar and back to the stabilizer with help from shorter center spar
Look at the location of the hinges

I knew I should have included this in my last answer

Rest easy vans engineers have it covered.

Having worked as a structural engineer for about 10 years, I don't see how the elevator spar helps much with the loads on the HS rear spar. The loads from the elevators are applied to the outboard hinge brackets plus some lesser amount to the center bracket. The moment at the center of the rear spar is approximately the same whether the elevator loads are applied at the bracket locations as compared to being applied along the whole length if it was a continuous hinge joint. There is a slight reduction in moment due to some of the load being transferred at the center bracket and thus not contributing to any bending.

That said, I have no doubt Van's engineers have it designed appropriately.

Good discussion.

 

[MTBehnke]

My curiosity was getting the best of me on this question and then I finally figured it out. Just like a wing, the HS is nothing more than an airfoil. The front spar gets more load because of the distribution of the lift across the profile of the airfoil. Here's a picture that represents the pressure along the length of the airfoil:

The majority of the lift is closer to the front of the airfoil, therefore the load at the front spar is higher than at the aft spar. This explains why there's the added spar caps at the front HS spar.

This is also, in part, why the forward wing spar is a very beefy structural element and the trailing edge is much smaller.

 

[joedallas]

The longer anwser

My curiosity was getting the best of me on this question and then I finally figured it out. Just like a wing, the HS is nothing more than an airfoil. The front spar gets more load because of the distribution of the lift across the profile of the airfoil. Here's a picture that represents the pressure along the length of the airfoil:

The majority of the lift is closer to the front of the airfoil, therefore the load at the front spar is higher than at the aft spar. This explains why there's the added spar caps at the front HS spar.

This is also, in part, why the forward wing spar is a very beefy structural element and the trailing edge is much smaller.

You are Right

This may not be a RV 10 ?
I added it to show angle of attack
From www.dynamicflight.com/aerodynamics/pres_patterns/
Thans Mike

Note:RV 10 Wing Loading 18.6 lb/sq ft
Wing Area 148 sq ft

The center of lift
now look at my anawer
So much for a short answer

I try to Help
Look at the Skins

Look at the front spar, the load to the area of the skin in front of this spar is transferred to front spar / 50% +or – of the area in back of the front spar is transferred to front spar

Now look at the back spar
Think it out
Less Aera = Less load transferred

One more note the elevator increases or decrees the lift and the load.
In general the loads are uniform and point loads as in the hinges, there are many other forces that are applied and this could go on for days

Disclaimer I have a structural engineering background not in airfoil design, I am learning to

 

[joedallas]

Confused

Having worked as a structural engineer for about 10 years, I don't see how the elevator spar helps much with the loads on the HS rear spar. The loads from the elevators are applied to the outboard hinge brackets plus some lesser amount to the center bracket. The moment at the center of the rear spar is approximately the same whether the elevator loads are applied at the bracket locations as compared to being applied along the whole length if it was a continuous hinge joint. There is a slight reduction in moment due to some of the load being transferred at the center bracket and thus not contributing to any bending.

That said, I have no doubt Van's engineers have it designed appropriately.

Good discussion.

Mike I held off responding to this post, as I am trying to see it in your view
My statement the moment is through its own Spar and back to the stabilizer with help from shorter center spar

The way I see it the elevator moment is at each side of the four hinges with point loads at the hinges and the cantilever at the out board hinge is only multiple by less the 12”
The Stabilizer center Spar supports the cantilever rib that supports the rear spar at the inboard hinges

Your statement ( The loads from the elevators are applied to the outboard hinge brackets plus some lesser amount to the center bracket. )

You may be right but in my view I think the loads are higher at the inboard hinges
The inboard hinges are 56 ½ apart and 28” to the outboard hinge = 56.5/2 +28/2 = 42.25” of elevator point load on the inboard hinge and 14 +12 = 26 of elevator on the out board hinge this is based on simple span which this may not be

It has been a long time since school
Clear this up if you can
Thanks