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 Ass 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)
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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.
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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
