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  #11  
Old 06-14-2013, 09:29 AM
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Beer30? Beer30? is offline
 
Join Date: Jul 2006
Location: Longmont, CO
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Default Batteries

For you guys flying with FP (lightweight) props and seeing W&B limits, what do you have for batteries? I'm going with a PC680 and a UPG backup battery, both on the firewall, is this similar to what you have? If so, I'm guessing I'll need the crush plate or engine mount spacers? Does vans have any problems with the spacers?

Good thread!

David
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  #12  
Old 06-14-2013, 09:46 AM
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Quote:
Originally Posted by newtech View Post
I put 5/8" spacers between my engine mount and firewall, added a 20 lb. Saber crush plate and a 12 pound harmonic damper and finally have my RV-7A CG in the "sweet spot." If you have a solid crank I would go with the O-320 engine mount; but, if you have a hollow crank the longer engine mount would mean you couldn't switch to a constant speed prop in the future.

That is a good idea to move the mount, do you have pics of how you did that?
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  #13  
Old 06-14-2013, 09:52 AM
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Quote:
Originally Posted by rockwoodrv9 View Post
I haven't done all the weight and balance, but can you be too light in front? I want a Catto FP prop and I have the small battery. Will I be able to carry any baggage at all? The W&B I have done with sample data, I will be pretty limited unless I add a weight plate to the front. Maybe that is just for the 9, but still something to think about. Spending so much effort to keep the weight down, then adding a plate doesn't sit right! I am sure once I can get the plane on the scales, I will be able to figure things out, but what have others experienced?
I do not have a 7. I do have a 9A however that I built with the ECi IO340, 3-blade Catto and Saber extension. I made reference to this information in this thread concerning the Anti-Splat brace here:
http://www.vansairforce.com/communit...d.php?t=100738

I made this comment in that post:
Quote:
One other point concerning building. I new I would be flying off of grass when I started building. A prime goal of my build was to keep the weight as light as possible on the nose gear. This was the motivation for many decisions I made concerning the firewall forward components. I have a Catto Prop (12 lbs total weight), ECi IO-340 that gave me 360 engine like HP at 320 engine like weights, light weight SkyTech starter, Plane Power alternator, etc. Basically every decision on what to put on the nose of the airplane had a high priority of keeping weight to a minimum. Here are my weights calculated for my Weight & Balance (fully painted, empty fuel, 6 quarts of oil):
Right Wheel 425
Left Wheel 430
Nose Wheel 252
Total 1107
C.G. 78.82
The forward CG limit is 77.95 and the aft CG limit is 84.84 for the 9A.

As you can see with my post, my empty C.G. = 78.82. I have a lot of room to spare before reaching either fore or aft limits. I have multiple CG scenarios in my POH that show where the CG moves at different aircraft loadings. Basically I looked at Empty Weight CG, Most Forward CG and Most Aft CG. In my analysis what I found was there was no real world situation that would bust the forward CG. I didn't even come close with full fuel, zero weight in pilot, passenger and baggage area. Even that criteria had the CG @ 78.48.

I was able to bust the Aft CG with 4 gallons fuel, 255 lb pilot, 240 lb passenger, 80 lbs baggage. There were a lot of other weight scenarios that allowed for busting the aft CG but they were mostly seeing absurd weights for baggage, pilot or passenger that did not represent reality. This one was a realistic real world loading that did not bust the gross weight of the airplane and that I could actually foresee happening. That is, a long cross country with a buddy and our baggage, say on a flight to Oshkosh, and at the end of a leg where we are running low on fuel.

There are some differences with CG between the 'A' models and the tail wheel models that need to be considered. I am sure a tail wheel model builder can chime in with their info. This is a data point that I hope will be useful to you and others though. Hope it helps.

P.S. David, saw your query about what battery is being used after I posted. I am using the Odyssey PC680 mounted on the firewall.
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Last edited by RVbySDI : 06-14-2013 at 09:55 AM.
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  #14  
Old 06-14-2013, 09:56 AM
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I have been mulling over the FP vs. CS issue for a while -- sadly, I won't have to make that choice for a couple of years. However, the idea of a heavy crush plate or harmonic balancer with something like a Catto prop seems reasonable. I mean, the CS prop would add even more weight to the nose, so it isn't like you're adding weight that a lot of planes don't already carry. Then you can keep the normal mount and cowl and have the option (for yourself or a subsequent owner) of going to a CS prop later on.
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  #15  
Old 06-14-2013, 11:14 AM
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Angry Aft CG limit for RV-7

Second time...(see post #5) ...what is the aft C.G. Limit for the RV-7 per Van's design?
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  #16  
Old 06-14-2013, 11:22 AM
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Quote:
Originally Posted by rv7boy View Post
Second time...(see post #5) ...what is the aft C.G. Limit for the RV-7 per Van's design?


86.82" normal

84.5" aerobatic

Recommended W&B numbers for all models available here:

http://www.vansaircraft.com/public/downloads.htm
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Last edited by Brantel : 06-14-2013 at 11:28 AM.
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  #17  
Old 06-14-2013, 12:12 PM
rhill rhill is offline
 
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Default Catto 3B/0-360 on a 7a

The 0-320 engine mount gives you an extra 2" forward. When ordering my finish kit Vans talked me out of the 0-320 mount so I ordered the 0-360 mount for the 0-360 core I'm building.Bob at Aircraft specialties talked me out of removing the inside plug when they yellow tagged the Crankshaft as it would hinder a CS conversion latter, I had the urethane coating applied and the outer plug installed,looks like they used a bead of clear silicone around the bore before installing the outer plug. I'm not there yet but want to acquire a 0-320 mount and will trade new for new or buy outright( whats another G at this point?). Point is 2" won't solve all the problem but is a far better alternative to adding weight. It's tough to argue with Vans or ACS and yes I need to consider any future owner as this project is an asset/liability and may need to go to a new home some day . Has anybody done a 0-360 on a 7a with a 0-320 mount? If so I would like to talk about the numbers,what did it buy you in real world terms.
Bob
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  #18  
Old 06-14-2013, 12:42 PM
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Default More information

In my -7 I started with the 0-360 and the Sensenich metal prop which with the hub weighed approx 42 Lbs. I was not particularly happy with the take off performance as at the time I was at a high altitude airport (Salt Lake #2). I also could not use the full 100 Lbs of baggage on a long cross country due to the CG moving aft of the aft CG point with minimum fuel. To solve the problem I added the landoll ring to the flywheel which put approx 12 Lbs right up front and problem was solved.
I then saw Mel's -6 with the Catto 3 blade and thought it looked very cool plus he told me how it performed so I switched to the Catto which weighs about 18 Lbs and added a sabre 14Lb spacer to compensate for the weight difference with the sensenich. With this setup I can carry 75Lbs of baggage in the baggage compartment and stay in CG until I get down to 10 gals of fuel remaining. Sabre has a heavier spacer that is around 20 Lbs and this would allow me to carry the same 75Lbs until I get down to 5 gals remaining.
I should also note that I carry tools and tiedowns etc in two bags that fit between the seatback and the flap tube which weigh 32.4 Lbs in addition to the baggage 75 Lb limit (114.78 Arm).
The Catto outperforms the Sensenich by quite a bit, has a narrower hub which helps CHT's on climbout, winds down quicker which helps slow down and is very smooth so you will not be disappointed with the choice.
I have a W&B excel spreadsheet with both Solo and Full up configurations which I would be happy to send to you if you want to play with the numbers.

P.S Odessy PC680 battery on the firewall
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Last edited by uk_figs : 06-14-2013 at 12:47 PM. Reason: Update
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  #19  
Old 06-14-2013, 01:53 PM
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Default spreadsheet

Thank you for the offer. I sent you my contact info in a PM.
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  #20  
Old 06-14-2013, 09:00 PM
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Default 7a data

Quote:
Originally Posted by rhill View Post
The 0-320 engine mount gives you an extra 2" forward. When ordering my finish kit Vans talked me out of the 0-320 mount so I ordered the 0-360 mount for the 0-360 core I'm building.Bob at Aircraft specialties talked me out of removing the inside plug when they yellow tagged the Crankshaft as it would hinder a CS conversion latter, I had the urethane coating applied and the outer plug installed,looks like they used a bead of clear silicone around the bore before installing the outer plug. I'm not there yet but want to acquire a 0-320 mount and will trade new for new or buy outright( whats another G at this point?). Point is 2" won't solve all the problem but is a far better alternative to adding weight. It's tough to argue with Vans or ACS and yes I need to consider any future owner as this project is an asset/liability and may need to go to a new home some day . Has anybody done a 0-360 on a 7a with a 0-320 mount? If so I would like to talk about the numbers,what did it buy you in real world terms.
Bob
+1
I would also like to see data on the 7a with io360 and FP and CS prop.
So far I plan CS because she will live at 5+K feet.
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