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-   -   RV-7A - Weight & Balance concerns. Is it the right plane for us? (https://vansairforce.net/community/showthread.php?t=128603)

RVbySDI 08-15-2015 07:50 AM

Don't limit your decision
 
I am somewhat puzzled by your original post when it came to the weights you discussed. I have a 9A and there are, practically speaking, no scenarios that would move my CG out of balance either fore or aft. My 9A all up empty weight is 1117 lbs. In order to exceed the aft CG I would have to load 100 lbs in the baggage area, me in the pilot seat (255 lbs) a 120 lb passenger and less than 2 gallons of fuel. Not a situation I would ever allow. The only possible way I can move the CG too far forward would be if the plane were to somehow take off with full fuel and no humans or cargo on board. Again not going to happen. I can more easily exceed the gross weight than move the CG but still takes some doing. I can load me (255 lbs), a 200 lb passenger, and 100 lbs of baggage with full fuel and bust the gross. Again though, not really planning to do that anytime soon.

You stated you liked the RV9(A) but thought the weight issue would be a problem. The 7(A)s are great planes but so are the 9(A)s. I travel often with friends who fly RV7s. Down low they are faster and they can do aerobatics where I can't. However, for cross country flying I not only keep up with them speedwise but up high I even out perform them when it comes to cruise speed and fuel burn.

Make sure you can honestly analyze all the issues before coming to a conclusion of what you want. Don't let one issue (such as this weight/CG thing) make your decision for you. Evaluate all of the facts honestly then make the call.

Good luck with whatever you decide. Truthfully, you wont go wrong with any RV you choose.

von_flyer 08-15-2015 08:26 AM

I have a -7A. My wife and I with a few bags are not 400lbs.:rolleyes: We fly regularly and are very pleased with RV and its performance. :D. Just saying...

RV7ator 08-15-2015 08:27 AM

Hello, Oliver,

If you build a -7, not a -7A, 100 pounds in the baggage area even with little fuel is do-able. The key is loading dense "stuff" forward of the center section spar in an airplane built with the mindset of keeping empty weight forward and most importantly off the long moment arm of the emp. Avoid gooing up the fuse and emp skins with primer, substitute a lighter-than-Van's tailwheel, and use the original design -8 rudder (1/2 pound lighter then the -9). Hang a 360 or a variant and a CS. Assure your painter understands the importance of minimal coating thickness.

I'm currently operating #5 of the -7s I've built. Even having substituted a Whirlwind for a Hartzell doesn't keep me from loading 100 pounds of bags. Tail draggers don't have the messy, intrusive main gear support structure under your knees; it's a flat floor from fuel selector to sidewall. On either side I can lash tents, water, ammo, etc, and, if it's a carby engine, the floor is flat from the selector to firewall, and here I can also lash down more heavy stuff. It's not so much that the weight is pushed forward on the teeter-totter, it's not in the baggage area behind the empty c.g. (I installed an EFII pump for FI, and designed it so the floor forward of the selector is still quite flat and useful.) Carrying more than 1800 pounds within c.g. is quite easy (Alaska rules!).

I can't answer how otherwise identical nose v. tail wheel airframes balance empty, but the A's gear structure is a deal killer to me in any case. A slider modified to tip up (easy) on a taildragger is the easiest RV to load. If you're considering a -14, consider the contortions of loading stiff, big objects, like an ice chest. To me it's utility is poor and it's a slow, fat -7 with a pricey engine.

I didn't express any opinions here, did I?

John Siebold
Boise, ID

N363RV 08-15-2015 09:08 AM

You have the right idea to make sure that you get the right airplane for your mission. I flew a 182 for many years and carried all that stuff I really didn't need with me. As I grew older my "mission" changed and I was ok with 100 lbs. (most of the time). I do weigh my stuff when I am going to OSH or a similar long camping trip. The last thing you want to do is overload the airplane. You won't... you are obviously thinking about it now. I have 2 small bags for clothing and such that Amanda and I use that automatically keep our weight in the correct range. We usually haul our computers with us too. If you load the plane the same way every time you fly it helps eliminate the worry of being overloaded.

This guy has some really great excel sheets to wb calculations.
I only took a quick look at the 7a sheet and it is missing the wheel weights. They are 0. I'm sure he left it this way because each aircraft can have different weights depending on the engine/prop combo.

http://rv7-a.com/n447rv_documents.htm

So if you are gonna buy, just ask the seller for the wb doc and you can plug in the numbers and "play" with the numbers to figure out if it is gonna work for you.

I have a 6A with a heavy hartzel (7497 blades) 58 lbs prop out front.

So here are my numbers for my bird when it was born.

Nose wheel - 308
Left - 385
Right - 383

I thought this wb issue would be a big deal for me too, but I made the adjustment and really haven't missed the 182. I just flew non stop from dfw to south eastern colorado in 3:05 mins with 10 gallons left in the tanks. I also just came back from OSH camping gear and clothes. I buy heavy stuff (water, food) when I get to my destination.

One last thought. If you and your passenger are in the 250 lbs range, you can simply land every 2 hours and you have enough fuel on board to make your cg a non issue...at least with a heavy prop up front.

The vans community really are a remarkable and special group of people. Just ask Steve and lots of others just like him :-)

Please join us.

Oliver 08-15-2015 10:22 AM

Thank you very much for all your friendly and helpful responses, I now feel a lot more comfortable about a RV-7A again. Very much appreciated. :D
I apologize for the confusion caused by the 9A in my initial statement - the member of the our EAA chapter has a 9A, which we both like. As I am interested in aerobatics, I figured however that a 7A would be the better choice.

With the numbers, including the 1900 lbs gross weight, rwtalbot posted, W&B works out just fine, even in the extreme scenario with 2x 250 lbs guys, 100 lbs in the baggage compartment, only 27 gal. in the tanks and empty tanks when landing. In normal clothes, my wife and I are around 360 - 370 lbs, 400 lbs include stuff like something to drink, survival gear, headsets, etc..

I also looked at the W&B thread again and it appears as whether the CG of the 7 indeed is further aft than that of 7As, particularly if a light fixed pitch propeller is installed. Good for us, since my wife wants a nosedragger... :rolleyes:

I am familiar with the controversial discussion regarding whether the gross weight could / should be increased or not. I took away from it that the plane easily carries 1,900 lbs, as long as the CG stays within the given limits.
Some people were concerned about the landing gear. To define 1,900 lbs as the max. take off weight and 1,800 lbs as the maximum landing weight, as suggested by rwtalbot, would however be a conservative approach which should fix this issue. Frankly, though, 1,900 lbs are just 5.6% more than 1,800 lbs - I would guess that a firm arrival at 1,800 lbs would stress the landing gear significantly more than a normal landing at 1,900 lbs. :cool: And, unless I forgot to lock the car or there is a technical issue, I see no reason to fully load the plane with fuel and gear, only to land right after take off again.

Making the pilot and the passenger lighter is of course also always an option, past efforts showed however no permanent effect. I therefore don't want to count on it... :o

@mlang: I would love to see your project. We are pretty busy the next two weeks, after that we can meet anytime. I'll send you a pm, when our schedule relaxes. :)

Ironflight 08-15-2015 10:48 AM

Quote:

Originally Posted by Oliver (Post 1006211)
And, unless I forgot to lock the car or there is a technical issue, I see no reason to fully load the plane with fuel and gear, only to land right after take off again.

Remember though - staying safer is a matter of building margin. So let's say to have just taken off at your 1900 lb weight, and smell smoke in eh cockpit. You decide that you really REALLY want to be on the ground right away, and pull it into a tight pattern. Tight enough that forget that the stall speed in a steep turn is also dependent on weight - stall/spin on the final turn.

Airplanes that have a lower landing weight than TO weight generally have a fuel dump capability. Thats to provide operational margin. Aircraft design limitations should not be defined by desire to "That looks about right".

Will it work? Sure - if everything goes right. But what if it doesn't? Everyone is free to decide for themselves of course - but everyone should evaluate the risk/trade for themselves as well. SOmeone will search this thread in the future for justification extend their Gross to 1950....

For two large people that want a two-seater to carry luggage and fuel cross-country? That's what the RV-14 is for.

Oliver 08-15-2015 12:08 PM

Quote:

Originally Posted by Ironflight (Post 1006220)
[...] You decide that you really REALLY want to be on the ground right away, and pull it into a tight pattern. Tight enough that forget that the stall speed in a steep turn is also dependent on weight - stall/spin on the final turn.

[...]

Will it work? Sure - if everything goes right. But what if it doesn't? Everyone is free to decide for themselves of course - but everyone should evaluate the risk/trade for themselves as well.

[...]

For two large people that want a two-seater to carry luggage and fuel cross-country? That's what the RV-14 is for.

Admittedly, I am new to experimentals, so please excuse my ignorance. I thought that during Phase I testing, the entire flight envelope, including the stall speed at different bank angles, will be tested and the POH created based on these results!?
Now, 'forgetting' is a different story, which is IMHO however not directly linked to an increased gross weight... ;)

The RV-14 would indeed be a nice two person travelling machine and might indeed be an option if we are able to find a project, as I am concerned that I might not have the patience to work on a kit for around 3 years. :o

Larco 08-15-2015 01:34 PM

Quote:

Originally Posted by Oliver (Post 1006134)
Hello,

This is my first post - I live in Novi, Michigan, close to Detroit. My wife and I own a 0-300 powered 1966 Cessna 172. As we like to travel, we want to upgrade to a faster plane.

Intitially, we thought about getting a 182 or maybe an older Bonanza until another member of our EAA chapter showed us his RV-9A and offered a ride. While we both always liked the looks of RVs, none of us ever even sat in one. OK, now we want one. :o :rolleyes:
Except of that we could not take our bikes with us, a RV-7A would fit our mission perfectly, I could even do some light aerobatics with it. We also thought that a half-finished kit would be a great option, as I always wanted to build, but as I am afraid that I would not have the endurance to work on the project for 3 or 4 years.

Well, the more I investigate RV-7As, the clearer is becomes that we would most likely face W&B issues. My wife and I weigh, including clothes, headsets, a survival kit, something to drink, phones, etc. 400 lbs.. Based on the weight numbers, here in this forum, most finished planes seem to be around the max. empty weight Vans mentions on their website of 1,130 lbs..
This would leave us with an useful load of 670 lbs.. Minus our weight and full tanks (42 * 6 = 252 lbs.) we would have only 18 lbs. left for baggage.

It also appears as whether the CG tends to be very far aft. It actually seems to be so far aft, that reducing weight on the prop, the avionics or the crew and to instead put more baggage in the baggage compartment, would easily cause the CG to get out of the envelope.

I am now wondering, whether my concerns regarding the far aft CG are valid, whether something can be done about it and how much weight we could save with a fixed pitch instead of a CS prop? What else makes the planes heavy, besides of avionics?

Oliver

Google--- paul rosales rv 6A and read the travel stories and you will get good idea of the utility of the RV6-RV7 /A They have pictures of the luggage carried ect. There are many of us that travel across the US on month long vacations every year and think the RV6/7 is more than adequate. :-) All you need to do is go to an RV fly in and see how many different sized people with lots of baggage fly in. or go to HB camping at OSH and look around. It?s a kick

Bavafa 08-15-2015 01:48 PM

Quote:

Originally Posted by Mel (Post 1006171)
with this scenario. Remember you won't be landing with full tanks. Try this loading with minimum fuel and make sure you are still within CG range.

Like a number of others have mentioned, my plane with IO-360-M1B and CS prop came to 1165 and my wife and I weight together a bit over 400lb. We have often taken our dog (55lb) with some bags probably around 20Lb. We have landed with about 12G fuel left with no issues but I try not to push that.

BillL 08-15-2015 02:52 PM

Quote:

Originally Posted by Oliver (Post 1006230)
Admittedly, I am new to experimentals, so please excuse my ignorance. I thought that during Phase I testing, the entire flight envelope, including the stall speed at different bank angles, will be tested and the POH created based on these results!?
Now, 'forgetting' is a different story, which is IMHO however not directly linked to an increased gross weight... ;)

The RV-14 would indeed be a nice two person travelling machine and might indeed be an option if we are able to find a project, as I am concerned that I might not have the patience to work on a kit for around 3 years. :o

Keep an eye, maybe search now, on the classifieds - I think Tom Martin just had his RV14 up for sale. You could not get a better start than that. The RV14 is a literally more than a decade ahead (of the 7 ) in design, and instructions. Don't get me wrong, I will love my 7 but I have seen the 14, and the 10 instructions. They are so much better than the 7. Years of experience at Vans pays off.


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