G

Gerry in Oz

Member
Horizontal or vertical

Hi everybody,

OK, I have settled on the Aero Sport Power IO-375 (low compression 195 hp) for my 8 with a Hartzell prop with Scimitar blades and Vetterman exhaust but am agonizing about the horizontal or vertical induction decision. Philosophically I lean heavily towards the KISS principal (Keep It Simple Stupid) and am wondering about two aspects of this decision.

Is horizontal induction a much bigger engineering issue?

Which produces the greater speed?

I can mentally generate theoretical arguments for both but what is real here? Does the horizontal induction actually generate more manifold pressure and less drag hence more speed? Is the ram effect of the external scoop of the vertical induction system enough to offset the additional parasite drag and make this the faster airplane? How much extra work is there in the horizontal induction installation?
Any ideas and input will be greatly appreciated as Barb at Vans is hanging out for my decision so she can nail the boxes shut.:)
Thanks everybody,
Gerry in Oz
 
I am not an 8 builder but I think there are some parallels between the 8 and the 7. And I have not built a vertical FAB, only seen ones in service. I have horizontal snorkel.

1) Review the cabin heat threads on VAF. Decide what you want to do.
2) Talk to Vetterman about the exhaust system because there are differences in heat muff (or heat muff wrapped mufflers) capability between the two systems that fit vertical and horizontal sumps
3) Think about the engine air intake system. I see a lot of posts about maintenance on the vertical intake FAB. Less posts about maintenance of the horizontal snorkel. The Vans supplied horizontal snorkel may be more tedious to fabricate but I think it and its alternate air are more robust than the vertical FAB.

good luck with your decision
 
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Thanks

Thank you Bill.
That is all very good and gives me several paths to investigate. Decision time is just about upon me so your interest is very timely.
Cheers from downunder,
Gerry.
 
The RV-8 in my avatar has horizontal induction (ECI engine with cold air induction), Vetterman 4-pipe exhaust, and Van's smooth cowl. Also has the Hartzell blended airfoil prop (74" version). Everything assembled about as easily as you can get for this firewall-forward package, and the airplane's performance is an absolute winner. The most difficult part of the firewall-forward assembly and fabrication work on this plane was hand-fabricating a custom-shaped throttle cable bracket for the ECI Titan fuel injection servo.

(Of course fitting the fiberglass cowling is always a pain no matter which way you go :eek: )

The double heat muff that encompases two pipes at once on the Vetterman 4-pipe system makes enough heat, I flew in the back seat across the state of Texas in the wintertime, on a 20 degree F (surface temps) day and my feet didn't freeze too badly... not as bad as the back of my neck :p

After getting to put over 70 hours on this RV-8 myself, if I were in your shoes building an -8 with a big fire-breathing IO-375 on the nose, I'd do it the same way: forward-facing cold air induction, Vetterman's 4-pipe exhaust, 74" Hartzell Blended Airfoil "Scimitar" prop, and the Van's "Smooth" cowl with snorkel induction.
 
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Thanks Neal,

That is great information. Just the sort of thing I need at this time. My thoughts are moving in that direction especially as I am becoming aware of some maintenance issues with the vertical induction FAB as alluded to by Bill Pendergrass. A buddy of mine here is Oz ingested a fastener from his FAB through his IO-540 (his is a 10) with some engine damage. :mad:

Sounds like the combination works very well. I much appreciate your input Neal.

Gerry.
 
Horizontal

I went horizontal...so what if it takes a bit more effort, your building an airplane...it just looks cooler...
 
Hi Gerry,

I would go horizontal, if I was to do it again.

I had to make 3 FAB plates before I got a good fit to my carb. Then I had to mod the lower cowl. This is a real pain in the a$$. Also getting the lower cowl on/off to fit the FAB intake is not much fun either.

What you doing this Sunday ? give me a call, we could go flying if you are free :)
 
Sunday

Thanks for that Jamie,

Yes, it seems there are issues whichever way I go. I am leaning heavily towards horizontal induction now and your comments have pretty much nailed it down for me. David?s experience with FOD damage is scary.

Looks like early to mid Sept delivery for my QB wings, QB fuse and finishing kit. I may include the firewall forward kit too.

Thanks heaps for the offer to go flying Sunday. Sadly, I am away working this weekend. Looking forward to doing it some other time soon however.

Cheers,

Gerry.
 
Horiz...

I have a citabria as well and removing the lower cowl is a pain...getting the airfilter to carb boot back on is always a struggle...by the way, my mum's side of the family is from down under...my uncle was awarded the Brownlow medal in 1939.
 
Cowl removal & reinstall...

Just for an added note.... I can easily remove and re-install both the upper and lower cowl halves on the RV-8, solo, without any help. The lower cowl half pops into place quite easily without having an air intake to deal with.

On my new (to me) RV-6, it is carbureted, with the FAB intake, and I cannot re-install the lower cowl without the help of a second person. It's quite a pain to get the rear piano hinges and intake lined up right at the same time without scratching the paint with the backside of the spinner.
 
In addition to the previously mentioned issues with control cables, exhausts, and the air intake, one other thing to be aware of with the horizontal induction engine is the interrelated nature of the snorkel, air filter, baffles, and cowl opening. The K&N filter is nearly as big as the entire left baffle inlet ramp, so it's easy to paint yourself into a corner if you don't think ahead. I have some photos of the process on my build site that may be helpful to someone traveling the same road.



Ultimately, the choice of horizontal versus vertical induction is probably a lot like the slider versus tip-up debate... both have their advantages and disadvantages, and both are generally equally frustrating to build but in slightly different specific ways. :)

good luck,
mcb
 
New to the forum, first post. I like the look of the cowl with the horizontal induction system. I see there is a Van's snorkle and another ram air system. Is there anyone just running their servo/carb with cowling air? In other words, do you have to provide cold air to your induction or can you run the air inside the cowl.

I know back in the day, it was pretty common on old school Pitts to just run inside cowl air, many without even an air filter.

Thanks in advance.
 
Mufflers

I'm pretty sure that mufflers will not fit inside a cowl made for forward facing induction.

Bevan
 
D.A. said:
New to the forum, first post. I like the look of the cowl with the horizontal induction system. I see there is a Van's snorkle and another ram air system. Is there anyone just running their servo/carb with cowling air? In other words, do you have to provide cold air to your induction or can you run the air inside the cowl.

I know back in the day, it was pretty common on old school Pitts to just run inside cowl air, many without even an air filter.

Thanks in advance.
Click to expand...

You could, but the standard set up also provides for a filter. You would also not have the advantage of ram air that might affect your MP. Injesting the very warm air inside the cowling would also hurt your performance.
 
When I was facing the same decision for my 7A I talked to Mahlon about the choices. It seemed like a toss-up from a performance perspective with a very slight edge to the cold air induction. At the time, the price difference was far too great to justfy an almost immeasurable edge. I don't know current pricing. Bob Axom's race data may give a better sense of real world performance, but I don't know if it is granular enough to show induction types.

As an aside, I have to confess that I always loved the classic RV look of the air scoop. I was willing to give it up if the cold air and smooth cowl was definitively better, but I couldn't see that it was. Maybe your own preference on looks is something you need to include in your decision.

All FWIW
 
jjconstant said:
When I was facing the same decision for my 7A I talked to Mahlon about the choices. It seemed like a toss-up from a performance perspective with a very slight edge to the cold air induction. At the time, the price difference was far too great to justfy an almost immeasurable edge. I don't know current pricing. Bob Axom's race data may give a better sense of real world performance, but I don't know if it is granular enough to show induction types.

As an aside, I have to confess that I always loved the classic RV look of the air scoop. I was willing to give it up if the cold air and smooth cowl was definitively better, but I couldn't see that it was. Maybe your own preference on looks is something you need to include in your decision.

All FWIW
Click to expand...

Exactly what my thought process was. The scoop on the 6 kept the classic look, just like the small tail. I saved over $1,000 on the engine cost too. I was an early adopter so they had not worked out all of the little things that they have now. That cost some time and hassle but it was not a big deal even then.
I had to replace one FAB plate at less than 100 hours. Frankly, it has everything to do with how you make it and install it. My second plate is pushing 500 hours, stock design.
 
Photos?

This is a great thread.....and wondered for the builders like myself that's still learning and gathering info, could someone post a photo of each....horz and vert? I'd love to see the differences to understand the challenges of each. :)
 
Robert,

Here you go, this one shows how little a gap my FAB is to the nose gear leg.

pb082297custom.jpg


Click the "my build log" in my Sig to see more photos.
 
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