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  #31  
Old 11-13-2005, 08:44 PM
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Quote:
Originally Posted by w1curtis
Uh, Continental. The Continental has a dry weight of 305 pounds, the IO-540 dry weight is 381 pounds. The dry weight of the IO-390 will probably be in the area of about 300 pounds.

I'm guessing that even though you work in the prototype shop at Van's, you are not an engineer. No engineer would recommend adding weight via heavier components or state that 80 extra pounds on the nose won't make much of a difference in performance or efficiency.

If you ARE an engineer then refresh our memories on the cube root of power. Tell us all how much speed difference we should see between 210 and 260HP (19%HP difference, 11 mph?). Then assume we throttle back our 540 to 210 HP for efficiency; tell us how the additional 80 pounds on the nose that have to be counteracted by additional lift on the wing and additional negative lift on the elevators contribute to drag. Then convince us that the heavier engine operating at the same power, producing more drag is just as efficient as a lighter engine.
Whoa William
Don't get so frazzled.

You put what ever engine in your RV-10 that you want,

but I really don't like it when people speak for me and say things I never said.

Where did I say anything about efficiency comparisons between a smaller engine and the IO-540?

Where did I recommend to add weight? Re read the post. I did just the opposite. I said you "could" do that to counter the W & B issues but that the last thing you want to do is add weight to an airplane that you are using a smaller HP engine in.

Where did I state that 80 extra lbs on the nose would not have an effect on efficiency?

I also never mentioned anything about what the speed difference would be between the largest recommended and the smallest recommended engines.

And finally... I never said that a bigger engine throttled back to the same power will be as efficient as a smaller one.

Once again to make it clear...What I did say was that the airplane was designed around an engine the weight of the 6 cyl Lyc.

A Cont. IO-360 was also tried, but that it does have a reduced usable C.G. range and a service ceiling reduced to 13 to 14 K ft.
A standard RG 25 battery is mounted on the fwd side of the firewall instead of in the fwd tailcone area to help counter the reduced weight of the engine.

This proved that the IO-360 Cont is a viable option if you so choose, but Van's has decided not to support it with kit parts because there was very little interest in it from RV-10 builders.

I think it would be a big mistake for any RV-10 builder to assume that since Cont, claims that there engine weighs 305 lbs that you could use any enigne that is close to that weight. I know for a fact it weighs more than 305...yea sometimes they fib a bit.

As for your guess... your right I am not an engineer but I don't see how that matters.

What does seem to matter to you is if someone presents a view that is contrary to the one you have chosen. I apologize for making you feel that way.

The only reason I occasionaly even view posts in these forums is to help builders out; or in this case maybe prevent someone from making a decision based only on what other experts on an internet discussion group have to say about a particular subject.

Scott

These opinions are my own and may not represent the views or opinions of my employer.
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  #32  
Old 11-13-2005, 09:24 PM
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Quote:
Originally Posted by rvbuilder2002
Whoa William
Don't get so frazzled.
Nope, not frazzled and we were not talking about the Continental IO-360. I made reference to the weight since the Lycoming IO-390 is about the same weight. I think most folks have given up on the Continental IO-360. You were deterring folks from looking at the LIGHTER Lycoming IO-390 because it was TOO LIGHT and that is what I find objection to. If someone wants to give up a little climb performance, cruise speed and ceiling for a 20% less fuel burn and a lot less expensive engine then why are you so opposed to it.
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  #33  
Old 11-13-2005, 10:58 PM
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Quote:
Originally Posted by w1curtis
Nope, not frazzled and we were not talking about the Continental IO-360. I made reference to the weight since the Lycoming IO-390 is about the same weight. I think most folks have given up on the Continental IO-360. You were deterring folks from looking at the LIGHTER Lycoming IO-390 because it was TOO LIGHT and that is what I find objection to. If someone wants to give up a little climb performance, cruise speed and ceiling for a 20% less fuel burn and a lot less expensive engine then why are you so opposed to it.
I am opposed to using engines that require major modifications to make the weight and balance work. Because most builders have no idea what they would be getting themselves into if modifications ended up being required.

I believe it is a mistake to assume the IO-390 will work just because you read on a web site that the weight is about the same as the Cont. With all accessories installed the Cont. is not that light. If you asked Van tomorrow (he's the one that is an engineer ... can I use a Lycoming IO-360 angle valve engine if I am willing to except the performance of only having 200 HP? I know that his answer would be "no". "It is too light".

The Lyc. IO-360 angle valve engine weighs about 340 lbs.

If you decide to use a IO-390, I will be interested to see how the W&B works out. It's always posible that I am wrong, but I think you are going to have to either move the engine or use ballast, which to me seems to kind of defeat the purpose.

Scott
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  #34  
Old 11-14-2005, 01:09 AM
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gmcjetpilot gmcjetpilot is offline
 
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Talking Wow numbers please

I did not mean to start a s-storm; Thanks for those who supported my opinion that the IO-390X would be a good 210 HP engine from a technical standpoint, which I still do.

Scott?s contention is the market demand is not there, is no doubt a fact. To be clear I do think the 540 is a better (best) engine for the dash 10. It is hard to argue with more HP and weight that keeps the empty CG in a desirable location without ballast. Pilots want more HP, No really they do.

Who knows what Van will do, but Van bases his moves on business and market demand, ok. That does not make the IO390X a poor theoretical match or fit to the RV-10. The 540 is granted just a better fit.

I am guessing that it's likely the only engine Van will support for sometime. People want 250/260 HP, so the argument about whether an IO390X is a good choice is academic at this point. Just for fun and grins I?ll make some SWAG's (Scientific Wild *** Guesses).

Looking at the cost of an IO-390X and an IO-540, the difference is $6K to $7K, so the incentive to use an IO-390X may not be as great. After you factor in all the other items the 540 may cost $8K-$9K more?

For fun running some rough numbers, I think the CG/weight issue is not hard to solve, as I try to show below

(Super Secret calculations, Don't tell any one)
--------------------------------------------------------------------------------------

My numbers may be off, but an IO390X with a 20lb heaver 3-blade prop will keep the CG about the same as a 540 with a light 2-blade prop. Not having exact dimensions I made some SWAGS.

We will look at equivalent moments at the firewall, which is the arbitrary datum.

A 3-blade Hartzell (cool scimitar style) is 75lbs; a 2-bladed is 55lbs and a MT is 43 lb. Assume the prop CG is about 45 inches forward of the firewall. The total moment increase with the heavy prop:

45" x (75-55)lb = 900 in-lbs

(The exact arm is not critical and is used throughout, so it somewhat washes out. Again this is not rocket science for a moon shot but just an example).

Now the engine: Assume the IO-390X is *310 lbs and a (I)O540 about 374 lbs.
(Ref. Lycoming 540 weights from Lycoming)

The difference is 44 lbs. Because the IO-390X CG will be forward of the 540's CG, say 2", we can calculate a difference in moment at the firewall:

540: 45"/2 x 374 lb = 8415 in-lb
390: (45"/2 + 2") x 310 lb = 7595 in-lb

(Note: the 2" fwd CG shift of the IO390X is a SWAG, but it should be at least this far forward of the 540, if not more. The 390X is cantilevered further out from the firewall by the engine mount, accounting for a shorter engine length. In the end the engine crank/prop flange is at the same station.)

So the IO360X has 820 in-lb less moment, BUT our heavy prop gave us 900 in-lb more moment. Therefore we have forward CG with the heavy prop and IO-390X combo!!! The total weight of the IO390X is 385 lbs, the (I)O540 is 429 lbs, so we are 44 lbs lighter with the IO390X. All good except the prop cost $2K more.

May be instead of an expensive prop we could use 20lbs of lead? We might get away with a heavy starter and alternator and keep a 2-bladed prop with a little ballast? From these rough numbers 20 lbs mass / ballast on the nose if the engine (under the case behind the flywheel) is all that is needed. Even if it was, 23 lbs or 30 lbs lead ballast, the IO390X combo is lighter.

The true engineering solution would be move the IO390 prop crank flange further forward than the 540 and make a longer cowl. Than you could use the less expensive and lighter 2-blade prop with no ballast. However this would no doubt be unacceptable to Van, due to the need to make and stock a different (longer) cowl. Van would not do it unless the demand was there, which I don't think will happen as long as 540's can be found for cheap. Cheap in aviation terms at least.

--------------------------------------------------------------------------------------


If Van did make this option it would Open the whole world of 200hp, 180hp, 160hp engines up. Shoot, what about a Grumman Traveler, Cheata and Tiger, C-172, Piper Cherokee all have HP ranging from 140 HP to 180. Well the numbers are lame for these planes. Well than look at the Hi-Perf 4-place retracts with 180-260hp engines (Bonanza, Mooney, Piper Comanche). Look at the specs of 4-place retracts with like gross/hp as a RV-10 the RV-10 compaires very well. Of course many of these factory planes are very old or very expensive. Maintenance and fun to fly are factors in favor of the RV-10 even with a 210 HP engine. With 210 HP the RV-10 matches or bests most retracts with like or even greater HP in almost every catagory: range, payload and speed.

Lets be real, you don't need 260hp to slipped the surly bonds of earth. May be Van should look into little engines? Naw, it is too fun passing Mooney's and Bonanza's with the gear hanging out.[/u]

Van "The man" himself designed the RV-10 for 210 HP, so why not. Well you answered that, people don't want it. It is not a surprise pilots want more HP. However from a pure technical standpoint the IO360X is a reasonable consideration and do-able, market demand not withstanding.

Your post states the design is to match RV 2-seat models. What 2-seat RV are we talking about? A 150 HP RV-6 with a fixed wood cruise prop *OR* a 200HP RV-8 with c/s prop? Even with a 260 HP engine, the RV-10 does not match a high end RV 2-hole'ers, even close.

Scott: "If you choose to use a smaller engine you will be limited as far as the utility and payload capabilities of the airplane go."

Even the RV-7 with an light O320 and wood prop cannot carry the full 100 lbs in the baggage compartment due to aft CG. In fact with a passenger you can't even carry 20 lbs. I understand your point, but compromise is a fact in any plane.

If Van or the market deems the RV-10 shall have 2-seat RV like performance, than a 260 HP IO540 is the only engine. Less HP of course is less performance at similar weights. Doha! Physics bite ya in the butt again.

Thanks
George

Last edited by gmcjetpilot : 11-14-2005 at 03:18 PM.
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  #35  
Old 11-14-2005, 08:39 PM
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You also should consider the continued maintence costs of the 6-cylinder vs. the 4 banger. The Sixes have a nasty tendancy to eat up rear cylinders and shock cooling is a much bigger issue with them. The Lycoming 4-banger is probably 2/3's the cost of the six to maintain (which kinda makes sense).
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  #36  
Old 11-15-2005, 12:01 AM
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Quote:
Originally Posted by gmcjetpilot

Looking at the cost of an IO-390X and an IO-540, the difference is $6K to $7K, so the incentive to use an IO-390X may not be as great. After you factor in all the other items the 540 may cost $8K-$9K more?

May be instead of an expensive prop we could use 20lbs of lead? We might get away with a heavy starter and alternator and keep a 2-bladed prop with a little ballast? From these rough numbers 20 lbs mass / ballast on the nose if the engine (under the case behind the flywheel) is all that is needed. Even if it was, 23 lbs or 30 lbs lead ballast, the IO390X combo is lighter.

The true engineering solution would be move the IO390 prop crank flange further forward than the 540 and make a longer cowl. Than you could use the less expensive and lighter 2-blade prop with no ballast. However this would no doubt be unacceptable to Van, due to the need to make and stock a different (longer) cowl. Van would not do it unless the demand was there, which I don't think will happen as long as 540's can be found for cheap. Cheap in aviation terms at least.

Even the RV-7 with an light O320 and wood prop cannot carry the full 100 lbs in the baggage compartment due to aft CG. In fact with a passenger you can't even carry 20 lbs. I understand your point, but compromise is a fact in any plane.

Less HP of course is less performance at similar weights. Doha! Physics bite ya in the butt again.

Thanks
George
[quote=gmcjetpilot]

Further looking at the cost of an IO-390X and an IO-540, the difference is $6K to $7K, so the incentive to use an IO-390X may not be as great.
- - - - - - - - -
It looks even less geat after you figure in a more expensive prop. to try and get the C.G. where it should be.
- - - - - - - - -
(Note: the 2" fwd CG shift of the IO390X is a SWAG, but it should be at least this far forward of the 540, if not more. The 390X is cantilevered further out from the firewall by the engine mount to account for the shorter engine length. In the end the engine crank prop flange is at the same station.)

So the IO360X has 820 in-lb less moment. Well our heavy prop gave us 900 in-lb more moment. Therefore we have forward CG with the heavy prop and IO-390X combo!!! The total weight of the IO390X is 385 lbs and the (I)O540 is 429 lbs, so we are 44 lbs lighter with the IO390X. All good.

May be instead of an expensive prop we could use 20lbs of lead? We might get away with a heavy starter and alternator and keep a 2-bladed prop with a little ballast? From these rough numbers 20 lbs mass / ballast on the nose if the engine (just under the case behind the flywheel) is all that is needed. Even if it was, 23 lbs or 30 lbs lead ballast, the IO390X would still be lighter.

No disrespect to you Scott but the way you wrote it seemed to imply performance with the IO380X would be sub par. To paraphrase you, "less HP is not a good thing".
- - - - - - - - -
Since par stands for a benchmark standard, what I said was true in the context that you are using. The performance would be sub par compared to an O-540 powered RV-10.
- - - - - - - - - - - -
Scott, you talk about limited. What limitation, besides the obvious reduction in cruise and climb. I think we see the CG issue is not really that big of a deal. Do you have some numbers? The biggest limit I think you imply is the aft CG and useful baggage with 4 folks, right? OK, well many 4-place planes cannot filler-up, load 4 butts with full bags and blast off.
- - - - - - - - - - - -
So why compromise and have your RV-10 be like other airplanes???
This is the weakest excuse I have heard for putting a smaller engine in an RV-10.

- - - - - - - - -

Even the RV-7 with an light O320 and wood prop cannot carry the full 100 lbs in the baggage compartment due to aft CG. In fact with a passenger you can't even carry 20 lbs. I understand your point, but compromise is a fact in any plane.
- - - - - - - - - - - - -
How about staying with apples/ apple comparisons...is anyone likely to build an RV-10 with a wood prop.?
- - - - - - - - - - - - - -
Less HP of course is less performance at similar weights. Doha! Physics bite ya in the butt again.
- - - - - - - - - - - - - -
That statement seems to say the same thing I have already said...maybe you agree with me after all.


This final statement is for anyone else following this thread, that is truely interested in the realitys of using engines outside of what is recommended...

The whole story is much bigger than just getting an exceptable empty C.G. location. There are other issues to consider, moment of "inertia" being one of them.
Using your logic and suggested use of a heavier prop. or even adding Lead, we could install a 250 lb. engine on the front and just use a heavier prop and some lead. This would have an effect on the moment of inertia on the front of the airplane. Messing with this can effect yaw and pitch stability and have a major impact on spin and spin recovery caracteristics.
Moving the engine even farther fwd and extending the cowl as you suggest would at first seem better because you don't need to add lead, but it is probably even a worse choice because it would probably increase the moment of inertia even more.

Anyone considering moving heavy components (or adding lead!) toward the extream fwd or aft end of an airplane, to get an exceptable C.G. location should read up on what moment of inertia effects can have on an aircrafts flying qualities. And you should consider youself a true blue test pilot when you begin your flight testing, because much of the flight qualities and spin recovery testing done by the kit mfr. will not apply.
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  #37  
Old 11-15-2005, 09:09 AM
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Quote:
Originally Posted by rvbuilder2002

Moving the engine even farther fwd and extending the cowl as you suggest would at first seem better because you don't need to add lead, but it is probably even a worse choice because it would probably increase the moment of inertia even more.

Anyone considering moving heavy components (or adding lead!) toward the extream fwd or aft end of an airplane, to get an exceptable C.G. location should read up on what moment of inertia effects can have on an aircrafts flying qualities. And you should consider youself a true blue test pilot when you begin your flight testing, because much of the flight qualities and spin recovery testing done by the kit mfr. will not apply.
It would affect the moment interia a small amount, but the angle valve 4 cylinder vs. the parallel valve 6 isn't as big a difference in weight as people are making it out to be. I think were past the idea of putting lead in the nose as it just wouldn't be necessary (as demonstrated earlier). Quite a few people have used 3-blade props metal props on RV's without a problem (there was a turbonormalized -7 with a McCauley 3-blade in Sport Aviation a year or so ago). I think the IO-390X is an excellent alternative to the 540 (and can produce as much HP as some versions of it) and should be seriously considered as an firewall forward kit from Van's. The reality is, with a little bit of work, it will put out more HP than the O-540 235's and be more fuel efficient. I also doubt that putting a 2-blade Hartzell BA would be out of the question if someone really ran the W&B numbers.
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  #38  
Old 11-21-2005, 05:49 PM
bhughes bhughes is offline
 
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Default the only way you could make this engine less attractive to is to put a gearbox on it,

Quote:
Originally Posted by Rotary10-RV
Ok William I got it,
Strange as I didn't get the questionare on the engine choices. Perhaps you need to have ordered the fuselage or finishing kits to have been included? I'm one of the first kits paid for at #41, (they saved a block of numbers for the expected orders from Oshkosh and #44 was the first kit actually shipped). I have only bought the empecone and wing kits so far however. I let my Rvator sub lapse, I need to restart that.
Bill Jepson
Bill,

What's a gearbox?

Bobby Hughes
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  #39  
Old 11-21-2005, 06:29 PM
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Default Moment of inertia lol

The previous writer is correct; I would look into stability and all that wonderful stuff. My guess is the difference is so small that it's not a big deal. Again good points all around, including maintenance.

If I had a 210hp 4 banger laying around and wanted to make a RV-10 I would consider it, despite the gear box comment. What would I really want. A IO540, **** ya. This is just academic for me (but fun). The real issue is from the first post of this thread, "Where do you get an Engine mount" (for a IO390X). G
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  #40  
Old 11-22-2005, 02:37 PM
Rotary10-RV Rotary10-RV is offline
 
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Quote:
Originally Posted by bhughes
Bill,

What's a gearbox?

Bobby Hughes
AKA...PSRU
Bill
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