Speed vs air conditioning scoop

[Jake]

How many knots would you expect to loose with a belly scoop

[Niko182]

14 minutes ago, Jake said:

How many knots would you expect to loose with a belly scoop

I think on the ovations its something like 4 to 6 knots.

[carusoam]

Not enough to worry about...

• If you live in TX or FL.  Advantages far outweigh the added drag
• If you Fly at high altitudes.  Drag is less up there
• If you have Fiki wings.  You already accepted additional small amounts of drag for a different kind of performance...

IOW the drag is real, and it is small, But...if you want AC, you can have an ice cooler system (hassle) or go real AC...

 

It also takes up space... how important is you hat shelf to you?

PP thoughts only... I got to enjoy the AC in an O at the Mooney Summit Last year... it was awesome.   
 

Real men don’t need AC... until their real wives ask for it! 

Taxiing to the active with door open in trail... on a hot day... then reaching across the SIC with two arms to close and lock the door gets a bit Old.... after the second decade of Mooney ownership...

Best regards,

-a-

[TGreen]

My Ovation came with AC. I almost never use it and would rather have the extra few knots and, more importantly, the extra payload.

I have, however, had the privilege of paying to repair it. 

[PMcClure]

I would rather leave someone at home than fly in Alabama summers with the 4 adults and no A/C! With the 3 blade prop and A/C I cruise 180-185 knots at 9k. Never flew my plane without them, so I don't know what I am missing. 

[Jeff_S]

Geez Paul, that's got to be ROP to get those speeds, right?  I generally expect 175 KTAS at cruise altitudes running LOP.  But for pure speed, I've done races with the SARL where I run at 2600 RPM and very ROP (22 GPH) and I can average 192 KTAS.  Could I get to the magical 199 knots promised in the POH without the air scoop? Maybe close, but as has been noted, the benefits far outweigh the drag when you're doing ground ops or coming in to land in Florida on a hot summer day.

[PMcClure]

39 minutes ago, Jeff_S said:

Geez Paul, that's got to be ROP to get those speeds, right?  I generally expect 175 KTAS at cruise altitudes running LOP.  But for pure speed, I've done races with the SARL where I run at 2600 RPM and very ROP (22 GPH) and I can average 192 KTAS.  Could I get to the magical 199 knots promised in the POH without the air scoop? Maybe close, but as has been noted, the benefits far outweigh the drag when you're doing ground ops or coming in to land in Florida on a hot summer day.

No - ROP I can get closer to 190 TAS. I usually run 20 LOP as long as the CHT's look good. 182 TAS is typical.  Before the 3 blade prop, I saw a magazine write up on my plane with 192 TAS (ROP).  I am pretty disappointed if I see a 170 something. True 50 LOP would have me down at 175.

[Niko182]

4 minutes ago, PMcClure said:

No - ROP I can get closer to 190 TAS. I usually run 20 LOP as long as the CHT's look good. 182 TAS is typical.  Before the 3 blade prop, I saw a magazine write up on my plane with 192 TAS (ROP).  I am pretty disappointed if I see a 170 something. True 50 LOP would have me down at 175.

What altitude and fuel flow gets you that 182?

[PMcClure]

1 minute ago, Niko182 said:

What altitude and fuel flow gets you that 182?

8-9k 14-15 gph Usually me an 50-60gal of fuel. 

[TGreen]

172kts, 50 lean of peak.

Wouldn't want to go any faster. The views are just too good.

[Ragsf15e]

7 hours ago, PMcClure said:

8-9k 14-15 gph Usually me an 50-60gal of fuel. 

Different beast, but I find the weight (or lack there of) is a significant factor for cruise speed in my F.  Obviously fuel flow, altitude, temp, etc are important to equalize for a comparison, but I think things like weight, balance, and prop blades make their own significant difference.

[PMcClure]

Not trying to BS here. Thought most ovations are about the same. I just went back and looked at a recent flight to dallas: 182-184 TAS at 8500 with 3c OAT and about 650lbs payload, 2500 rpm 14.7 gph WOT. Realize i may be closer to peak than -20 at that fuel flow but still lop and cht’s were 350 max.  175 for 50 lop with 12.5- 13 gph would yield me about 175 TAS.  

Sorry to hijack thi thread , but i don't think the scoop costs you much. The loss of useful load is a more important consideration.

[Niko182]

Just now, PMcClure said:

Not trying to BS here. Thought most ovations are about the same. I just went back and looked at a recent flight to dallas: 182-184 TAS at 8500 with 3c OAT and about 650lbs payload, 2500 rpm 14.7 gph WOT. Realize i may be closer to peak than -20 at that fuel flow but still lop and cht’s were 350 max.  175 for 50 lop with 12.5- 13 gph would yield me about 175 TAS.  

Sorry to hijack thi thread , but i don't think the scoop costs you much. The loss of useful load is a more important consideration.

AC also helps CG. My cg is 43.21. I need to put stuff in the back if me and my instructor are flying. Granted hes a heavy guy but still. At least ill never fall out of the back of the CG.

[carusoam]

TG,

those are probably videos you tried to share...

It would be helpful if you post the videos in YouTube... then post the link here...

On my screen, it looks like a wrong direction sign... 

 

Not all Os were created equal... some got the ability to crank up the RPM to 2700... and got a fancy TopProp...

So... being stuck at 2500 rpm is going to make a difference...

Best regards,

-a-

[Jeff_S]

16 hours ago, PMcClure said:

No - ROP I can get closer to 190 TAS. I usually run 20 LOP as long as the CHT's look good. 182 TAS is typical.  Before the 3 blade prop, I saw a magazine write up on my plane with 192 TAS (ROP).  I am pretty disappointed if I see a 170 something. True 50 LOP would have me down at 175.

It's amazing how engine set-ups can vary.  If I'm at those cruise altitudes flying WOT, 14-15 GPH would put me probably right at Peak EGT.  If you're able to burn that much more fuel at LOP then that may explain the speed difference.  One has to assume the airframe drag would not differ significantly.  One thing to note about the built-in A/C is that it also adds about 60 pounds (going from memory) of weight in the tail area.  The benefit of this is that you get lower induced drag from the horizontal stabilizer without having to add weight to the cargo area. Still, when I'm racing I make sure to have at least another 20-30 pounds back there for even greater effect.

[buddy]

I’ve got A/C in mine with the 310 conversion and living in FL. I think it’s great. A couple of years ago I was flying at 5500 ft. with 2 people don’t remember the OAT but I was down in FL. and got 197 kts with everything firewalled, only held it there for 1 or 2 minutes . I might have been able to get 1 or 2 more kts. if I held it there longer.  So I don’t think the belly scoop makes that much of a difference. 

[kmyfm20s]

I like having air conditioning! I have been seeing 173 ktas, 12.9 gph @ 2400 rpm, 8500’. I don’t see the ROP numbers other are seeing. 

[M20S Driver]

1 hour ago, kmyfm20s said:

I like having air conditioning! I have been seeing 173 ktas, 12.9 gph @ 2400 rpm, 8500’. I don’t see the ROP numbers other are seeing. 

My numbers are almost exactly the same.   171 Ktas, 12.5 gph @2400 rpm, 7500-8500 feet 30-40 LOP

[FloridaMan]

I'm developing an electric light aircraft air conditioning for ground/taxi use that uses no scoop and is "portable". Even in south Florida, I don't find flying at low altitudes to be all that unpleasant, but the time on the ground is painful. The best investments I've made have been the "cool scoop" that goes in the window and sheepskin seat covers to go on the leather to prevent swamp ass, wet back and duck butter. 

Edited January 31, 2020 by FloridaMan

[philiplane]

Let's say you actually lose 5 knots with a/c. On a max range trip of 800 NM, you're talking 175 versus 180 knots.

To put it in perspective, it's 15 minutes.

Go flying on a hot day without a/c, and your passengers will hate the 15 minutes they spent sweating before takeoff, and the 10 minutes they spend sweating again, taxiing in after landing.

What part of the trip will they remember? The misery, of course.

Want your wife to appreciate the plane and go flying with you? And approve $$$$ upgrades? Having a/c will facilitate all of that.

The best buy for a retrofit is the Arctic Air Real A/C for about $4700. No scoop, no drag either.

Edited January 31, 2020 by philiplane

[mike_elliott]

On 1/29/2020 at 2:45 PM, PMcClure said:

No - ROP I can get closer to 190 TAS. I usually run 20 LOP as long as the CHT's look good. 182 TAS is typical.  Before the 3 blade prop, I saw a magazine write up on my plane with 192 TAS (ROP).  I am pretty disappointed if I see a 170 something. True 50 LOP would have me down at 175.

Wow..here is the best I have done LOP 50 in an Ovation at 8K. No A/C on this one. The Kelly Aerospace AC doesnt have the "scoop" to hinder the airflow and it really works well! DISCLAIMER Kelly Aerospace will be providing the Mooney Summit Reception BBQ this year...Thanks Walter Dodge!

 

[Andy95W]

10 hours ago, FloridaMan said:

to prevent swamp ass, wet back and duck butter. 

Wow, this is pretty graphic for a family-oriented website.  

Also still trying to figure out what "duck butter" is.  I'm really hoping that was a typo.

 

[Atalla]

1 hour ago, Andy95W said:

Wow, this is pretty graphic for a family-oriented website.  

Also still trying to figure out what "duck butter" is.  I'm really hoping that was a typo.

 

Google says it's not a typo and was used in the proper context.

[Andy95W]

1 hour ago, Atalla said:

Google says it's not a typo and was used in the proper context.

If anyone else, like me, had to look this up- do NOT read the Urban Dictionary definition.  I can't not think about it now...

[PMcClure]

10 minutes ago, Andy95W said:

If anyone else, like me, had to look this up- do NOT read the Urban Dictionary definition.  I can't not think about it now...

There is a movie, though!