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External Venturi

D

Dakbuster

Member
Has anybody fitted an external venturi to power instrument gyros?

Is this going to cause excesive drag over the advantage of not fitting vac pumps or going electric

I have searched he archives for earlier posts but found none, if there are please advise

Thanks
 
The big reason that venturis went out of favour is that they are prone to icing up if you are in cloud above the freezing level. If you will never fly in cloud, then they would be a cheap, light, reliable solution. But, if you don't plan to fly in cloud, why have gyros?

How many venturis would you have, and what would the diameters be?
 
I had 3 venturis on my T-Craft and they didn't slow me down a measurable amount. However, that was at 100 mph. At 200 mph, I think you would see a measurable drag. My guess would be about 3-5 kts.
Other than for clouds, gyros are also helpful for night VFR.
 
venturi

I plan on running my AI and DG on a used venture (Sperry Gyroscope) I bought for $20.

It will work thru a vac regulator (recommended).

I just assumed I'd be the laughing stock at the fly-in - "Hey, what's that funny looking thing bolted to the bottom of your airplane?"

No clouds for me but night VFR will be OK.

I thought maybe the carb and my un-heated pitot tube would collect ice before the venturi anyway.

Light weight, cheap, reliable (no moving parts) - what's not to like?

Dave
working on -9a fuselage
 
Venturi

Dakbuster,
If you don't want to install the venturi on the belly, I've seen them mounted on the inside of the lower cowling. You'd have to cut a hole and build a small fiberglass intake but it can be done where it looks clean and smooth.
Charlie
 
Daver said:
I just assumed I'd be the laughing stock at the fly-in - "Hey, what's that funny looking thing bolted to the bottom of your airplane?"

Dave
working on -9a fuselage
Click to expand...

Just tell them the relief tube is hooked to it:rolleyes:
 
Already have the Vac Instruments?

If you don't already have the vacuum instruments would it not be about the same cost to put a Dynon or even one of the "older" GRT EFIS in the panel? Just a thought and not a well researched one at that. I personally like a venturi for the type flying you plan to do. No moving parts! As you said "What's not to like?"
 
Thanks for all the replies. The extra information you have provided has helped me make the decision.
I have a reasonable amount of IFR time, but I have not been current for quite a while
So this is strictly a VFR RV6. The main reason for the AH and DI is my piece of mind. This is why I want to do the cheapest installation I can (bearing in mind our dollar only buys 65-70 cents of yours, then our Government puts another 12.5% GST (goods and service tax)on top (we call it grab snatch and take::D)
From the information I have I would need to install two 4? venturi one to power the AH and the other the DI. (Any further advice on this would be gratefully accepted)
Can these be interconnected and still produce enough power for both instruments?
Yes they would look ugly on the outside (I had thought of installing them on the fuse between the legs) I guess an appropriate place for a relief tube. I never thought of fitting them inside the cowl I have enough room there. The thought of adding another 3-4 knots drag makes this an easy choice
 
BIG venturi

My venturi is the big one - 9" I think.

Its supposed to make enough vacuum for the AI & DG at 100 MPH (I was told).

Dave
 
Well...

gvgoff99 said:
If you don't already have the vacuum instruments would it not be about the same cost to put a Dynon or even one of the "older" GRT EFIS in the panel? Just a thought and not a well researched one at that. I personally like a venturi for the type flying you plan to do. No moving parts! As you said "What's not to like?"
Click to expand...

...not quite. Lots of moving parts in the DG and AI....:D

No moving parts in the electronic EFIS units. Lots more to the system than the venturi...:)

gil A
 
One of the major problems with a venturi is the fact that the gyros will not spool up to speed till after you take off. This makes it real bad for night flying especially. They also cause drag, lots of it.
 
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