Longer engine mounts

[hohocc]

Gidday,
I notice a common thread among 6 (and 4) builders seems to be lack of weight carrying ability in the baggage compartment (or rear seat) if the aeroplane is built nose light ie small engine light accesories wood prop etc.
Has anybody ever built and flown an rv with a slightly extended engine mount to shift the CofG forward slightly?
Thanks....

 

[todehnal]

Excellent Idea

I agree with the longer engine mount, when reducing firewall forward weight. In fact, my dream is an RV-4 with an IO-233, weighing in at about 75 lbs less than an O-320. My quick calculations call for about a 9" extension to the engine mount, to put the CG right where you need it. I think that if you were to go directly to the folks who build the mounts for Van, you could get the mount made that you need. Now, your biggest challenge would be with the cowling.

If anyone can think of other pitfalls, please chime in.

Tom

 

[hohocc]

Other issues

Good point on the cowlings.
I'm also interested in any structural considerations, particularly at g loadings that aerobatic RVs routinely experience. Any thoughts on this?
Thanks.

 

[L.Adamson]

Contrary to some claims, unless you've already got a smaller displacement engine; then throw an 0360 on it. The takeoff performance and ability to get somewhere faster, is much of the fun! And the CG problem is taken care of!

L.Adamson --- RV6A /0360/ Hartzell C/S
(and I know that Rockets and Citation X's are even faster..)

 

[hohocc]

Thought I'd bump this back to the top as it's come up in discussion recently with another nearby builder.
Any more thoughts on it?
Thanks.

 

[N941WR]

Van's makes a 2" longer engine mount. I had a full 12" mount on my -9 with the O-290. The replacement mount that I'll use with the O-360 is only 10" long. Granted, the -9 mount won't work with a -6 (different gear leg angle) but I'm sure you can get Van's to make you one.

 

[ronschreck]

Gidday,
I notice a common thread among 6 (and 4) builders seems to be lack of weight carrying ability in the baggage compartment (or rear seat) if the aeroplane is built nose light ie small engine light accesories wood prop etc.
Has anybody ever built and flown an rv with a slightly extended engine mount to shift the CofG forward slightly?
Thanks....

DETLEF HEUN and his wife are flying around the world in a RV-7 they built. They extended the engine mount in order to allow them to carry lots of baggage for the trip. Here's their web site with contact information:

http://www.flight-around-the-world.org/aircraft.html

 

[Kiwi]

RV-9 Engine Mount.

Van's makes a 2" longer engine mount. I had a full 12" mount on my -9 with the O-290. The replacement mount that I'll use with the O-360 is only 10" long. Granted, the -9 mount won't work with a -6 (different gear leg angle) but I'm sure you can get Van's to make you one.

My friend?s RV6 has an RV7 firewall. His is a very late kit for the RV6. Given that the RV7 and RV9 fuselages are pretty much the same, this establishes some compatibility for the RV7/9 firewall on the RV6. So, why won?t the ?long? RV9 mount ?work? on the RV6? How different is the gear mount angle, and in which direction (does it point more aft, more forward, more inboard or more outboard), and would it matter? Who knows, it might be better?..

Cheers,
Andrew.

 

[JonJay]

Vans Mount Supplier....

...lurks on this site. He just might chime in. If not, and you are serious about it, I can get you in touch with him.

 

[N941WR]

My friend?s RV6 has an RV7 firewall. His is a very late kit for the RV6. Given that the RV7 and RV9 fuselages are pretty much the same, this establishes some compatibility for the RV7/9 firewall on the RV6. So, why won?t the ?long? RV9 mount ?work? on the RV6? How different is the gear mount angle, and in which direction (does it point more aft, more forward, more inboard or more outboard), and would it matter? Who knows, it might be better?..

Cheers,
Andrew.

Andrew, actually the 7 & 9 used the RV-6 firewall. You can tell the linage of the part by the first number. My firewall started with a "6" and the aileron bell cranks with "4", while the tail cone parts all start with "7". Very few parts on the -9 (other than the wing, HS & elevators) start with a "9".

To answer your question, I don't really know the exact angle at which the legs exit but my gear legs are about 2" longer than a -7 based on the trim mark included in the template for cutting the gear leg fairings. Van's had to get the nose up higher to get the wing on the -9 full stalled in the three point attitude.

So, part of this equation is to put the wheel in the correct location relative to the center of lift (I'm guessing here, maybe some Aero Engineer can correct me.) Either way, when you look at the -9 next to a -7, the wheels look like they are in the same location.

Your best bet is to contact Van's and ask them for the name and number of the guy who makes their engine mounts. I'm sure he will be happy to make you a custom mount.

 

[hohocc]

In the last couple of days there was a post in general discussion called "engine mount factory" with the link to the business concerned.
And thanks Ron, for the link to the round the world RV7, have had some contact with them already as a result of your link.
I'm probably 2 years off ordering the finish kit/mount but just wanted to investigate possible solutions to what is apparently a common issue. Another idea that's been put forward is solid aluminium spacers at the firewall to move the standard mount forward.
Thanks for all the responses.

 

[ronschreck]

In the last couple of days there was a post in general discussion called "engine mount factory" with the link to the business concerned.
And thanks Ron, for the link to the round the world RV7, have had some contact with them already as a result of your link.
I'm probably 2 years off ordering the finish kit/mount but just wanted to investigate possible solutions to what is apparently a common issue. Another idea that's been put forward is solid aluminium spacers at the firewall to move the standard mount forward.
Thanks for all the responses.

Please use care when useing spacers only. If you use more than a couple of washers the shear forces on the mounting bolts will increase dramatically and you may be inviting structural failure. Think about what forces are put on the engine/gear mount by the landing gear on a hard landing. I would consult an engineer if you do anything dramatic to change the stock configuration here.

 

[hohocc]

Thanks for that, I did wonder if spacers would be a problem, and if there was a point where a washer or two for shimming became something that changed the loading on the mounting point significantly.
Bill/Andrew, the 9 mount, possibly with 9 undercarriage legs sounds very good to me, not least as it uses bits from off the shelf, meaning the guy who makes the mount doesn't have to do something dirrerent as a one off exercise. I guess then the whole firewall forward package may as well become 9 as well, including cowls.
Since the aeroplane will be a mix of 6 and 9 I'll lay claim to being the builder of the prototype RV 7.5!
Thanks.

 

[Kiwi]

Firewall.

Andrew, actually the 7 & 9 used the RV-6 firewall. You can tell the linage of the part by the first number. My firewall started with a "6" and the aileron bell cranks with "4", while the tail cone parts all start with "7". Very few parts on the -9 (other than the wing, HS & elevators) start with a "9".

Yes Bill, you are quite correct, the RV-9 uses an F-601 firewall, the "6" being for RV-6. I have the RV-9 drawing and RV-6 drawing for both and the detail differences however are significant. My friend was building his RV-6 after the RV-9 came out, and maybe the fuse after the RV-7 came out, hence he called it an RV-7 firewall.

Since the RV-9 has longer legs, the gear sockets will be angled forward a bit to keep the wheels in the same place, otherwise the nosing over tendency would be stronger. I do wonder how those long legs will go on an RV-6.

Cheers,
Andrew.

 

[sibriggs]

W&B help

I'm building an RV9 with a IO320 and an 18 lbs composite prop. In order to keep the CG in the empty weight design range, I ordered a 2" longer engine mount. I put together some calculations based on the data provided in the RV9 plans to determine a target CG.

I guest-a-mated the datum locations for the engine and prop based on the drawings and a note from Ken Scott that the prop on the demo RV9 was located 54 " forward of the wing leading edge. I can't confirm the actual locations because my RV is not that far along yet.

If anyone has the time I'd really appreciate another set of eyes looking over my work for errors. I sent a note to Vans, but find they're quite busy and don't have time to look the info over.

Here's the email with the info I sent to Vans:

Ken Scott to Me
10:30 AM (19 minutes ago)
Ok? look for a shipping call tag in your email soon. I?m afraid our engineers are pretty tied up and aren?t able to do individual consulting, so we?ll have to trust your numbers.

From: Stephen Briggs [mailto:[email protected]]
Sent: Tuesday, February 16, 2016 8:12 PM
To: Ken Scott
Subject: Engine Mount

Hi Ken,

I have the Sensenich composite prop I bought through Vans, not the metal prop. I think based on the weight difference I'll stay with the longer mount.

These are my numbers, they are based on my engine weight at 291 lbs, moving it forward from location 28" to 26", using the numbers shown for the demo RV9 in the plans document (pg 14.4)

Removing the Sensenich Metal Prop off the demo RV9 at datum location 16" at 31 lbs and adding my Ground Adj FP (I bought from Vans) at location 14" at 18 lbs.

Below at my calculations based on the numbers in the plans (pg 14.4);
Weight Location Moment
Aircraft 1057 77,68 82107
Engine -291 28 -8120
Engine +291 26 +7540
Prop -31 16 -496
Prop +18 14 +252
Totals 1044 77.8 (cg) 81281

These calculations didn't include additional cowling length or the added weigh of metal in the engine mount.

Would it be possible for one of the engineers to look these over and see if I have made any bad assumptions or calculations?

If it checks out OK then perhaps you can email me a shipping label I'll round up a box and wooden base for to return it for honing

Thanks for checking into this for me and the help you've provided.