Van's Air Force
Don't miss anything! Register now for full access to the definitive RV support community.
Engine for an RV-9
- Thread starter Russell
- Start date
txaviator
Well Known Member
Van's...
Russell,
If I am not mistaken, when I flew the Van's demo it was equipped with the O-235. And if you haven't been in that plane, it does anything you'd want it to do. It flew great.
I am also currently asking for engine help from the members of this forum right now, and when I did a search for -9 engines within the Traditional Engine section, I noticed a bunch of posts which concerned the O-235's and the guys using O-290's. Check those out. I think both are fine engines, as is the 320. However, the general consensus in the forums was to have as much power as you can get (ie: the 320) as you can always throttle back/lean. Don't get me wrong: I am still undecided myself between the 235/290/320. However, at least from my local friend/supplier, he tells me that he has 320 parts 10:1 over the 235's and 290's. That might help make my decision easier.
Your mileage may vary. It's all purely the choice of the builder, and as I mentioned, Van's demo flew great with the 235.
Take care,
Russell,
If I am not mistaken, when I flew the Van's demo it was equipped with the O-235. And if you haven't been in that plane, it does anything you'd want it to do. It flew great.
I am also currently asking for engine help from the members of this forum right now, and when I did a search for -9 engines within the Traditional Engine section, I noticed a bunch of posts which concerned the O-235's and the guys using O-290's. Check those out. I think both are fine engines, as is the 320. However, the general consensus in the forums was to have as much power as you can get (ie: the 320) as you can always throttle back/lean. Don't get me wrong: I am still undecided myself between the 235/290/320. However, at least from my local friend/supplier, he tells me that he has 320 parts 10:1 over the 235's and 290's. That might help make my decision easier.
Your mileage may vary. It's all purely the choice of the builder, and as I mentioned, Van's demo flew great with the 235.
Take care,
txaviator
Well Known Member
??????????
Russell,
After re-reading your post, now I think I see what you were REALLY asking....does anyone fly a version of the O-235 with 108hp versus 118hp. My bad.......not sure what Van's was running but if I recall from reading the spec's on their site, I believe it was 118. Sorry for the confusion in my previous post.
Russell,
After re-reading your post, now I think I see what you were REALLY asking....does anyone fly a version of the O-235 with 108hp versus 118hp. My bad.......not sure what Van's was running but if I recall from reading the spec's on their site, I believe it was 118. Sorry for the confusion in my previous post.
JimLogajan
Active Member
Russell said:
Just FYI: If you have not already noticed, Van's recommended gross weight (from the specs published in the Information Packet for the RV models) for the RV-9 at 118 HP is 1600 lbs. At 135 HP it is 1675 lbs. At 160 HP it is 1750 lbs. The recommended gross weight increases at about the cube root of the HP. This gross weight increase with HP rule only seems to apply to the RV-9/9A model - none of the other RV models has it. I have no idea why Van's did it that way for only that model. (Maybe the rate of climb at the low HP range was considered too anemic at the higher gross?)
SweetJellyDonut
Active Member
Why yes Virginia, RV-9's do fly with 108hp...
Hey Russ,
There is a guy named Stan Shannon out of Texas and he is flying a 9A with the 108hp O-235. I'm not sure if he is a member of this list but a lot of members know him and could fill in the details.
I think this is his website http://www.kitplaneparts.com/index.htm and it has pictures of his 9A on there.
BTW, this was the route I was planning to go until the first rumors of the RV-12 began to surface.
Hey Russ,
There is a guy named Stan Shannon out of Texas and he is flying a 9A with the 108hp O-235. I'm not sure if he is a member of this list but a lot of members know him and could fill in the details.
I think this is his website http://www.kitplaneparts.com/index.htm and it has pictures of his 9A on there.
BTW, this was the route I was planning to go until the first rumors of the RV-12 began to surface.
N941WR
Legacy Member
There is a 108 HP -9A in Hickory, NC
I've spoken to the owner a few times and he loves it.
The -9A replaced a -6A he also built and his father is now flying.
He flight plans 150 MPH and gets it. Loves the engine and 5 hour flights w/ IFR reserves are the norm for him, OK to NC non-stop.
I've spoken to the owner a few times and he loves it.
The -9A replaced a -6A he also built and his father is now flying.
He flight plans 150 MPH and gets it. Loves the engine and 5 hour flights w/ IFR reserves are the norm for him, OK to NC non-stop.
Robert M
Well Known Member
O-235
I was talking with Bill Repucci the other day and he mentioned another guy that put an O-235 in his -9. Check with him, [email protected]
I was talking with Bill Repucci the other day and he mentioned another guy that put an O-235 in his -9. Check with him, [email protected]
180 HP for the 9A
I am considering putting a 180 HP in a 9A and have read all the recommendations against doing so by Vans. They contend that with more power one could exceed 210 mph TAS which they contend is the speed limit to prevent flutter. they say that the vne line on the airspeed refers to TAS not IAS and that flutter could occur. I asked the support dept for info on whether it is just a coincidence that the red line for structural load limit and the same 210 TAS werethe same. I also asked for any test results they had to show flutter chances at 210TAS. Their response was that they performed ground vibration tests but the info was propriety and would not be released. No mention was made of test flights to check for flutter, which is the way to make a proper determination. I urged release of the info so builders could have all the critical info available to assist them. In fact i suggested that the co had a duty to disclose this info in the name of safety, but so far have been stone walled. I wonder if the 9A with its longer wing and different airfoil has a unique flutter issue that warrented the caution against installing the 180 HP. Vans has not issued such dire warnings with the other RV's, even though they in many cases can excede their vne with TAS reading above the red line. Any comments
I am considering putting a 180 HP in a 9A and have read all the recommendations against doing so by Vans. They contend that with more power one could exceed 210 mph TAS which they contend is the speed limit to prevent flutter. they say that the vne line on the airspeed refers to TAS not IAS and that flutter could occur. I asked the support dept for info on whether it is just a coincidence that the red line for structural load limit and the same 210 TAS werethe same. I also asked for any test results they had to show flutter chances at 210TAS. Their response was that they performed ground vibration tests but the info was propriety and would not be released. No mention was made of test flights to check for flutter, which is the way to make a proper determination. I urged release of the info so builders could have all the critical info available to assist them. In fact i suggested that the co had a duty to disclose this info in the name of safety, but so far have been stone walled. I wonder if the 9A with its longer wing and different airfoil has a unique flutter issue that warrented the caution against installing the 180 HP. Vans has not issued such dire warnings with the other RV's, even though they in many cases can excede their vne with TAS reading above the red line. Any comments
N941WR
Legacy Member
Why?
Karl,
A few questions for you:
1st. Why do you want a larger engine?
If the answer is to go faster, build a -7.
If the answer is for better climb, what's wrong with 2000 solo/1400 GW feet/minute climb?
The -9 is designed with a 1750 GW in mind. Adding the bigger engine detracts from your useful load. Also, the -9 only holds 38 gallons and the O-360 burns more fuel than the O-320. This might have you stopping more frequently.
If you up the GW, that 50 MPH GW stall will go up, probably to match the -7's, or close to it.
2nd. Why do you want to mess with flutter?
- 'nuf said
3rd. Why not build an RV-7?
This sounds like it might be a better aircraft for you, why not build it?
The -9 and -7 are very similar but the tail structure of the -9 is different and uses thinner skins than the -7. Just think of the additional beating those 20 extra HP's will give that tail.
4th. Why stop at 180HP? Why not put in 200HP or make it a super -9 and put in 260 hp?
Just some food for thought
Karl,
A few questions for you:
1st. Why do you want a larger engine?
If the answer is to go faster, build a -7.
If the answer is for better climb, what's wrong with 2000 solo/1400 GW feet/minute climb?
The -9 is designed with a 1750 GW in mind. Adding the bigger engine detracts from your useful load. Also, the -9 only holds 38 gallons and the O-360 burns more fuel than the O-320. This might have you stopping more frequently.
If you up the GW, that 50 MPH GW stall will go up, probably to match the -7's, or close to it.
2nd. Why do you want to mess with flutter?
- 'nuf said
3rd. Why not build an RV-7?
This sounds like it might be a better aircraft for you, why not build it?
The -9 and -7 are very similar but the tail structure of the -9 is different and uses thinner skins than the -7. Just think of the additional beating those 20 extra HP's will give that tail.
4th. Why stop at 180HP? Why not put in 200HP or make it a super -9 and put in 260 hp?
Just some food for thought
RVbySDI
Well Known Member
I cannot answer for Karl but I am considering the same HP issues as he is. I would like to interject my answers to one or two of your questions.
My answer is that the 180 HP engine I am interested in installing is not the O-360. I am looking to install the ECI IO-340 which is reported to put out 180-185 HP and weigh the same as the O-320. If this is all true then your arguments for using this engine do not stand up.N941WR said:
a) As far as going fast is concerned, I am not convinced the -7's are a faster airplane than the -9's. At least not as a general rule. I am sure there are plenty of -7's out there that will be faster than a -9 but my guess is that as more -9's start flying we are going to find they will hold their own against the general population of -7's in the speed department.
b) In my case I have intentions of flying in and out of Rocky Mountain airports with high elevations in the summer months. I am talking about airports in the 8,000 - 12,000 MSL range on days with temperatures in the 90 + degree Fahrenheit range. In this environment having all the climb power I can muster will be important.
c) Running the IO-340 at 55% to 65% should allow for as good or better fuel economy as the O-320 at 75%. It should also allow for a longer life for the engine.
d) If the weight of the engine is not higher than that of an O-320 then there will not be an increase in GW just because you put a "bigger" engine in the airplane. More horsepower does not have to equate to a heavier engine.
e) This will not have any negative effect on the stall speed either because there will not be an increase in GW.
b) In my case I have intentions of flying in and out of Rocky Mountain airports with high elevations in the summer months. I am talking about airports in the 8,000 - 12,000 MSL range on days with temperatures in the 90 + degree Fahrenheit range. In this environment having all the climb power I can muster will be important.
c) Running the IO-340 at 55% to 65% should allow for as good or better fuel economy as the O-320 at 75%. It should also allow for a longer life for the engine.
d) If the weight of the engine is not higher than that of an O-320 then there will not be an increase in GW just because you put a "bigger" engine in the airplane. More horsepower does not have to equate to a heavier engine.
e) This will not have any negative effect on the stall speed either because there will not be an increase in GW.
This is something I have never heard before concerning thinner skins. Can you tell me where you got this information and where I can find out more about it? I am not aware that the skin thickness is any different from one RV model to the next.N941WR said:
Last edited:
N941WR said:
By and large, good questions, and it's always good to consider all angles before changing design parameters.
Having said that.....
Large engines on small airplanes don't cause flutter. Poor pilots cause flutter. You can put 600 hp on -9, and (assuming you can get the CG under control) never approach flutter speed. The issue that comes up is that with over-powered designs, there is no longer a mechanical limitation (HP production) or physical limitation (drag) to prevent speed from building to flutter speeds - you are now relying on the wet noodle processor between your headset earcups, something that is unfortunately lacking in some individuals. PROPER piloting procedure can avoid the overspeed issue regardless of power available, but it requires the operator to pay attention to detail.
High performance sailplanes have to deal with flutter limitations with NO horsepower, and they do it successfully every day. Power is not the issue.
Last edited:
Pilottonny
Well Known Member
Turbo power is what you need to take off "high" and "hot"!
Steve, Karl,
The Wilksch WAM120 Turbo Diesel will put out its initial 120 bhp up to 14.000 ft . I guess even the 180 bhp Lycoming will not do that . If you want to take off "high" and "hot" you need a turbo-intercooler! BTW, Wilksch will be upping their WAM120 to 140 bhp and the WAM160 to 180 bhp when they release it (that may take a while yet, though). Please see other thread on this topic. I sent an extensive email to Wilksch today about the release of the WAM140, because I have to order my finish kit and need to make some decisions real soon. You know, back here in Europe, Avgas prices are insane !! ( Netherlands: EUR 2,40/lt (appr. $ 12,-/gal) , while JetA1 is 1/3 of that!)
The last time I spoke to Ken Krueger, Vans approves the WAM120 and WAM160 for the RV9. With the WAM160 you will certainly have enough power to get out of even the highest airfields.
I do agree that over speeding is a bad thing, but even with very little power and the nose pointed to the earth you will get easily over the Vne and risk flutter to occur. I will certainly install the Dynon with TAS indication in my plane!!
Be careful and live long !
Regards, PilotTonny
Steve, Karl,
The Wilksch WAM120 Turbo Diesel will put out its initial 120 bhp up to 14.000 ft
. I guess even the 180 bhp Lycoming will not do that . If you want to take off "high" and "hot" you need a turbo-intercooler! BTW, Wilksch will be upping their WAM120 to 140 bhp and the WAM160 to 180 bhp when they release it (that may take a while yet, though). Please see other thread on this topic. I sent an extensive email to Wilksch today about the release of the WAM140, because I have to order my finish kit and need to make some decisions real soon. You know, back here in Europe, Avgas prices are insane !! ( Netherlands: EUR 2,40/lt (appr. $ 12,-/gal) , while JetA1 is 1/3 of that!) The last time I spoke to Ken Krueger, Vans approves the WAM120 and WAM160 for the RV9. With the WAM160 you will certainly have enough power to get out of even the highest airfields.
I do agree that over speeding is a bad thing, but even with very little power and the nose pointed to the earth you will get easily over the Vne and risk flutter to occur. I will certainly install the Dynon with TAS indication in my plane!!
Be careful and live long !
Regards, PilotTonny
N941WR
Legacy Member
Steve,RVbySDI said:
There was a thread on this forum a few months back and someone went through the parts on the -7 & -9's tail. They stated the -9 had thinner skins. Now, it might have just been the control surfaces, but I can't remember.
Even if they are the same thickness, the length of the -9's HS will increase the air loads, how much, you will have to talk to an engineer. Maybe George will add a comment or two.
As for flying in CO's high and hot (Leadville?) airports, I couldn't agree with you more but then again, 160 hp C-172's do manage to fly out of those airports and the don't even have 1/2 the climb rate of an O-320 powered -9.
If I lived out there, I might seriously look at turbo normalizing your engine. Only one problem with that solution, weight and complexity.
(Love the Rockies! I spent a week out there a few years back hiking to the top of five 14'ers! Great camping trip!)
jcmcdowell
Well Known Member
O-360/ O-340 for the other reason...
I have a O-320-D2a with 160hp cylinders ready to install in my 9a when its time, but with all the talk about user fees and the added Avgas fuel surcharge- I was thinking it might be nice to get a bigger engine and DERATE the HP to use Mogas. What about getting the low compression cylinders and only have about 170hp but be able to run on Mogas?
I fly a C-172 STC'd for 80 octane and it runs better on Mogas than the Avgas and it costs me $2.15 a gallon (lately) to run around the patch.
Really liked the look of that O-340, but $$$$.
I have a O-320-D2a with 160hp cylinders ready to install in my 9a when its time, but with all the talk about user fees and the added Avgas fuel surcharge- I was thinking it might be nice to get a bigger engine and DERATE the HP to use Mogas. What about getting the low compression cylinders and only have about 170hp but be able to run on Mogas?
I fly a C-172 STC'd for 80 octane and it runs better on Mogas than the Avgas and it costs me $2.15 a gallon (lately) to run around the patch.
Really liked the look of that O-340, but $$$$.
180 HP for the 9A
Bill: thanks for your suggestions. I operate out of an airport a mile high which has much higher density altitudes in the summer. That is the main reason. I figure a Titan 0-360, CS prop, with light wt starter and alt will cost me around 12 #s extra weight over the 160 hp with Cs prop which with an EW of 1100# works for me with the 1750 Gross. I am not aware that the skins in the tail are thinner and will look into that. Your suggestions did not address my more important question of whether Van is correct in saying that the vne of 210 mph should be interpreted as a true airspeed limitation. It is not that hard to get 210 TAS with any of Van's planes at altitude with the nose pushed over, but he says and only for the 9A that one should not exceed 210 TAS because of the possibility of flutter. What does the red line on the airspeed indicator refer to? Indicated speed, of course. So what does anyone know about why he takes this position for the 9A but does not issue any warnings for the other RV's. Perhaps he knows something though testing? Or could it be the long wing and different airfoil. The plane is already rated at lower load limits which would offer some protection if flown correctly. And finally, it is rare to find oneself with too much power in certain situations, but not so rare to wish you had more. And if Van fears one may go to fast and be in the yellow at 75% then I say that the black knob thing on the panel should be pulled back. If anyone has any idea why Van is so afraid of putting the 180 in i would like to hear why>
Bill: thanks for your suggestions. I operate out of an airport a mile high which has much higher density altitudes in the summer. That is the main reason. I figure a Titan 0-360, CS prop, with light wt starter and alt will cost me around 12 #s extra weight over the 160 hp with Cs prop which with an EW of 1100# works for me with the 1750 Gross. I am not aware that the skins in the tail are thinner and will look into that. Your suggestions did not address my more important question of whether Van is correct in saying that the vne of 210 mph should be interpreted as a true airspeed limitation. It is not that hard to get 210 TAS with any of Van's planes at altitude with the nose pushed over, but he says and only for the 9A that one should not exceed 210 TAS because of the possibility of flutter. What does the red line on the airspeed indicator refer to? Indicated speed, of course. So what does anyone know about why he takes this position for the 9A but does not issue any warnings for the other RV's. Perhaps he knows something though testing? Or could it be the long wing and different airfoil. The plane is already rated at lower load limits which would offer some protection if flown correctly. And finally, it is rare to find oneself with too much power in certain situations, but not so rare to wish you had more. And if Van fears one may go to fast and be in the yellow at 75% then I say that the black knob thing on the panel should be pulled back. If anyone has any idea why Van is so afraid of putting the 180 in i would like to hear why>
Geico266
Well Known Member
I like the analolgy about motor gliders, and you don't slam the go peddle of your car to the floor backing out of the driveway.
Power management is everything with an "over powered" airplane. Respect V's, watch the weather for turbulance indications and I'm good to go. I have 323 hours in my 9A with an 0-360. I can cruise around buring 5-6 GPH, or push it to 200 MPH burning 10 GPH to get somewhere. Climbs near 3,0000 FPM if I needed.
No problems so far.
Experimental has it's benifits.
Power management is everything with an "over powered" airplane. Respect V's, watch the weather for turbulance indications and I'm good to go. I have 323 hours in my 9A with an 0-360. I can cruise around buring 5-6 GPH, or push it to 200 MPH burning 10 GPH to get somewhere. Climbs near 3,0000 FPM if I needed.
No problems so far.
Experimental has it's benifits.
LifeofReiley
Well Known Member
235
I know someone that has an overhauled 235 dyna looking for a good home.
I know someone that has an overhauled 235 dyna looking for a good home.
TAS vs IAS limit
Geico: I agree 100%. Still looking for an explanation of why Van says the red line limit on the 9's refers to TAS and not IAS. Check out the spec site on Van's web site for the 9 where it links to an article why 180hp should not be used. very confusing to me. To fly within the 210TAS limit one would have to always be doing a computation unless he had a Dynon or other way of computing TAS. And if that is the case, what does the red line on the airspeed indicator refer to?
Geico: I agree 100%. Still looking for an explanation of why Van says the red line limit on the 9's refers to TAS and not IAS. Check out the spec site on Van's web site for the 9 where it links to an article why 180hp should not be used. very confusing to me. To fly within the 210TAS limit one would have to always be doing a computation unless he had a Dynon or other way of computing TAS. And if that is the case, what does the red line on the airspeed indicator refer to?
Because IAS is affected by the density of the air. As air gets less dense, the airspeed indicator will read lower than the actual speed of the air. TAS is a measure of absolute velocity of the air no matter how dense it is.
Flutter is caused by actual (true) air velocity, not velocity as measured by an instrument affected by density. If that makes sense...
I'm not exactly certain but I'll bet it is placed where IAS and TAS are the same at sea level & standard atmosphere.
Last edited:
az_gila
Well Known Member
Airspeed vs. Alt.
The limits can be in TAS... but for a certified plane they become IAS with altitude ranges.
The Type Certificate for my Mini-Nimbus glider shows this...
I - Model Mini-Nimbus HS-7 (Utility Category), approved September 21, 1984
Airspeed limits (I.A.S.) Maximum Airspeeds In Calm Air
Never Exceed (Vne)
0 - 9800 ft. alt. 135 kts 155 mph 250 km/h
9801 - 19700 ft. alt. 120 kts 139 mph 223 km/h
19701 - 32800 ft. alt. 96 kts 110 mph 177 km/h
If you turn the Experimental Exhibition and Racing certification in for a Standard category (only one in the US did... ...)
...the Airspeed needed to be marked with different redlines corresponding to the altitude ranges above...
In this case, the altitude ranges are essentially 3000 and 6000 meters.
gil in Tucson
karl said:
The limits can be in TAS... but for a certified plane they become IAS with altitude ranges.
The Type Certificate for my Mini-Nimbus glider shows this...
I - Model Mini-Nimbus HS-7 (Utility Category), approved September 21, 1984
Airspeed limits (I.A.S.) Maximum Airspeeds In Calm Air
Never Exceed (Vne)
0 - 9800 ft. alt. 135 kts 155 mph 250 km/h
9801 - 19700 ft. alt. 120 kts 139 mph 223 km/h
19701 - 32800 ft. alt. 96 kts 110 mph 177 km/h
If you turn the Experimental Exhibition and Racing certification in for a Standard category (only one in the US did...
...) ...the Airspeed needed to be marked with different redlines corresponding to the altitude ranges above...
In this case, the altitude ranges are essentially 3000 and 6000 meters.
gil in Tucson
Last edited:
Rick of Austin
Well Known Member
This dead horse is still kicking
Havent flown yet but am very close to flying the RV-9a with a 180hp Superior engine and a Sterba prop. With the 180 hp engine and the wood prop I make less thrust that a 160 hp constant speed right?
It surprises me how many people feel that its a risk when the RV-6 and the RV-9 have exactly the same VNE hence the same resistance to flutter. Of course with a lower stall speed we have a lower manuvering speed which is what the limiting factor is in rough air and that is basically the topic of the correspondence Van wrote describing why he chose 160 as the maximum hp for the 9.
Am I missing something here? Are there other factors or risk exposures I am not aware of.
Thanks in advance.
Havent flown yet but am very close to flying the RV-9a with a 180hp Superior engine and a Sterba prop. With the 180 hp engine and the wood prop I make less thrust that a 160 hp constant speed right?
It surprises me how many people feel that its a risk when the RV-6 and the RV-9 have exactly the same VNE hence the same resistance to flutter. Of course with a lower stall speed we have a lower manuvering speed which is what the limiting factor is in rough air and that is basically the topic of the correspondence Van wrote describing why he chose 160 as the maximum hp for the 9.
Am I missing something here? Are there other factors or risk exposures I am not aware of.
Thanks in advance.
kentb
Well Known Member
Hello Rick
Haven't you already made your decision on this issue? If someone post a good argument to your question, would you change your engine for something smaller? Not trying to pick on you, but it seems a little late to be asking these questions.
VNE: It might be based on structural strength, flutter, or something else. As the builder of your plane you get to decide the VNE of your aircraft as well as all the other specifications. You also get to be responsible for those decisions. As for my plane I decided to use the designers (Vans) recommendation for almost all specification, after all I am not an aero engineer.
I don't think that there is anything wrong with 180hp, other then some weight, but then I went with a CS prop which add weight to my plane. The biggest problem is that the pilot will now have some extra workload to make sure that speeds and loads are not exceeded. Yes with 160hp I also can exceed some of the recommended flight conditions if I am not careful, but not as many as if I had 180hp. I shocked my self the first time I nosed over to head back to the airport (after my fairings were on) and busted VNE before I pulled the power back (I guess that was my flutter test).
The most important aspect of the engine/airplane is the decision making capability of the operator. You can have lots of power or not so much and as long as you understand what it will do for/to you and choose wisely you will be OK. I have flown my C-172 with 160hp out of a 7000 ft density alt. airport at full gross weight. I did this from a 5000ft paved strip and knew my route of flight would allow for a slow climb.
Enjoy your plane, but make sure that you and anyone else that flies your plane knows where its limits are.
Kent
Rick of Austin said:
Haven't you already made your decision on this issue? If someone post a good argument to your question, would you change your engine for something smaller? Not trying to pick on you, but it seems a little late to be asking these questions.
VNE: It might be based on structural strength, flutter, or something else. As the builder of your plane you get to decide the VNE of your aircraft as well as all the other specifications. You also get to be responsible for those decisions. As for my plane I decided to use the designers (Vans) recommendation for almost all specification, after all I am not an aero engineer.
I don't think that there is anything wrong with 180hp, other then some weight, but then I went with a CS prop which add weight to my plane. The biggest problem is that the pilot will now have some extra workload to make sure that speeds and loads are not exceeded. Yes with 160hp I also can exceed some of the recommended flight conditions if I am not careful, but not as many as if I had 180hp. I shocked my self the first time I nosed over to head back to the airport (after my fairings were on) and busted VNE before I pulled the power back (I guess that was my flutter test).
The most important aspect of the engine/airplane is the decision making capability of the operator. You can have lots of power or not so much and as long as you understand what it will do for/to you and choose wisely you will be OK. I have flown my C-172 with 160hp out of a 7000 ft density alt. airport at full gross weight. I did this from a 5000ft paved strip and knew my route of flight would allow for a slow climb.
Enjoy your plane, but make sure that you and anyone else that flies your plane knows where its limits are.
Kent
I have flown my -6 out of Leadville, CO (density alt was 13,500') in the summer back when I had a tired 150hp and a wood prop, climbed over the mountain range to Longmont. I had no problems at all. The 160hp RV-9 has probably twice the performance of most "spam cans." More hp is simply not needed.
Last edited:
vne considerations
Thanks all for your input. Makes sense that since IAS vne goes down as altitude increases that 210 vne TAS would at some point be the limiting factor also. Had a friend talk with someone very important from Van's whose name i will not use because he said that the info he supplied was not the factory's official line. He said that the reason for the 9's lower load limits was because of the longer wing and the company did not want people to fly areobatics with it even though it might well be strong enough. The guy said that they have never had a flutter problem with any of the RV's as might have been the case with the tails on some thin skinned Rockets. He said they never conducted flutter tests, but the factory will not tell you that. All that were done by an outside contractor were ground vibration tests and the factory's load tests on other RV wings. Also he said that the tail on the 9's have same guage as other RV's. He said that there was a guy at his strip who has a 9 with 180 and that it works just fine, and that all that is needed is some speed management. he said that the real concern by Van is that it would be a bit easier to operate in the yellowat 75% and if done so inadvertently, that one might encounter a 50fps gust and then be exceeding the limits Van places on the plane. He said that Van is being very conservative with the speeds to avoid a problem he was worried about but that there have been no actual tests for. This is all second hand info, so take it with a grain of salt. I know the person who received this info and he is generally very reliable, but caveat emptor.
Thanks all for your input. Makes sense that since IAS vne goes down as altitude increases that 210 vne TAS would at some point be the limiting factor also. Had a friend talk with someone very important from Van's whose name i will not use because he said that the info he supplied was not the factory's official line. He said that the reason for the 9's lower load limits was because of the longer wing and the company did not want people to fly areobatics with it even though it might well be strong enough. The guy said that they have never had a flutter problem with any of the RV's as might have been the case with the tails on some thin skinned Rockets. He said they never conducted flutter tests, but the factory will not tell you that. All that were done by an outside contractor were ground vibration tests and the factory's load tests on other RV wings. Also he said that the tail on the 9's have same guage as other RV's. He said that there was a guy at his strip who has a 9 with 180 and that it works just fine, and that all that is needed is some speed management. he said that the real concern by Van is that it would be a bit easier to operate in the yellowat 75% and if done so inadvertently, that one might encounter a 50fps gust and then be exceeding the limits Van places on the plane. He said that Van is being very conservative with the speeds to avoid a problem he was worried about but that there have been no actual tests for. This is all second hand info, so take it with a grain of salt. I know the person who received this info and he is generally very reliable, but caveat emptor.
IMHO, an accurate answer to your q will be hard to find in spite of many opinions. In a perfect world, where the fuel/air mixture is optimized and the same, the burn would be the nearly identical in both engines, because it is directly determined by work done (BTUs burned; HP delivered to the crankshaft).
In the real world however, other variables muddy the waters- things like personal limits regarding heat generation (w/ lean mixtures), FI vs carburation accuracy, and how "well" the mixture needle is set in manual apps (highly subjective and hard to replicate), engine efficiency differences (different ignitions, part condition, tolerences inside the engine, etc), and finally, differences in individual aircraft aerodynamics and prop selection are likely bigger contributors anyway.
In the real world however, other variables muddy the waters- things like personal limits regarding heat generation (w/ lean mixtures), FI vs carburation accuracy, and how "well" the mixture needle is set in manual apps (highly subjective and hard to replicate), engine efficiency differences (different ignitions, part condition, tolerences inside the engine, etc), and finally, differences in individual aircraft aerodynamics and prop selection are likely bigger contributors anyway.
Yukon,
Greatest efficiency was not the question; whether two engines burn about the same amount of fuel to produce the same output was.
My understanding is that IC engines are most efficient at their adbiabatic peak (point of greatest combustion pressure, which generally falls at the engine's torque peak, not the HP peak. Am I wrong?
Greatest efficiency was not the question; whether two engines burn about the same amount of fuel to produce the same output was.
My understanding is that IC engines are most efficient at their adbiabatic peak (point of greatest combustion pressure, which generally falls at the engine's torque peak, not the HP peak. Am I wrong?
RVbySDI
Well Known Member
From my non-expert experience and from my long term research in trying to ferret out the answer to this very question myself I have determined that there may be a difference but only in technical terms. An engineer can probably give you all the numbers to determine exactly what these differences would be. However, in what I have researched, when it comes to the size differences in engines we are talking about in our situations, any measurable differences in fuel burn would be so small they would arguably not even be noticeable, let alone worth worrying over.Daver said:
The issue with our airplanes we are looking at is in the size difference between say an O-235 on the small side and an IO-360 on the large side (ok, maybe some might throw in those IO-390's too but I would definitely not consider that engine on a 9). In fact, the reality is that most of us wrestling with this notion are really looking at the difference between an O(IO)-320 and an O(IO)-360. Between those two engines we are talking about a size difference of 40 cubic inchs. That is a relatively small size difference. It really is not a big enough size difference to see much in the way of change in fuel burn. Yes, I am sure there is some, but in the manner in which we everyday pilots determine our fuel burn, the difference would barely be noticeable.
So the reality is that running a 180 HP engine at 65% is very likely to produce a fuel burn that would be so similar to a 160 HP engine running at 75% that the normal pilot would be hard pressed to be able to notice a difference in fuel burns for the two engines at those two settings.
One other thing to consider also is the longevity factor for the two engines. If one engine spends the majority of its time running at 65% HP and the other spends the majority of its time running at 75% HP I would be inclined to believe that the former is much more likely to outlive the latter.
I know there are many on these threads who do not like the idea of comparing automobile engines to aviation engines but I have a hard time believing there really is that drastic of a difference in the two environments. In that light I would pose this:
- look at the running RPM's on your automobile engine.
- Is it pushed to the limit most of the time?
- Would you think of its longevity as being related to how hard you push its engine?
- Would you anticipate a four banger 100 HP engine in an S-10 pickup that was revved to the high end its entire life by a hot rod racing cement contractor to be in as good shape after 10 years as would be a V-8 350 in a full sized pickup that spent that same time period cruising interstates at 70 mph?
As an example, I have a 2000 GMC 1/2 ton P/U with a fuel injected 350. It has a max RPM of 6000 on the Tachometer. So I can really wrap that engine up if I wanted to. However, it spends more than 95% of its time cruising the highways and city streets where I live. During its most stressed out times it may have a load placed on it that will push the RPM's up to about 2400. That would indicate to me that this engine is purring along well under the 55% of max HP that most aviation engines would be flying at on the slow end of operations (doing the math we are talking about 40% of max RPM at its most abused times). To be more realistic I know that when I have the cruise set at 70 mph that engine is generating about 2000 RPM. Now we are talking about this engine running at 33% of its max RPM (I have not studied the power curve of this engine so I am not sure if max HP is at max RPM. I would expect it is not but I do not know for a fact if that is true). I have all the confidence in the world that my driving this engine at 33% is much more likely to result in a long productive life for this pickup (it is already seven years old with zero indication that anything is going to fall apart anytime soon). There has got to be some merit in choosing an engine that will not be wrapped out like a race car for the majority of its existence.
I would think that even if the fuel savings is a marginal number, the fact I am not pushing the engine as hard should account for something in running a more powerful engine. This is all in addition to the added climb performance the increase HP will provide.
gmcjetpilot
Well Known Member
One O235 in many versions
From the data there are no 108HP O235's. There are:
115 (6.75:1) **
116 (8.10:1)
118 (8.50:1)
125 (9.70:1)
** (I am a little suspicious that the 6.75:1 compression is 115 hp. 1 hp less than the 8.10:1 version, BUT that is what Lycoming publishes.)
The 108 HP comes from a lower RPM rating? It could be probably a 115 or 116 hp engine at 2,700 RPM.
I know 108 hp sounds familiar**:
C152 (110HP)
PA-38 Tomahawk (112hp)
AA-1 Grumman Yankee/Trainer 108 HP)
Could it be a "de-rated" 115hp or 116 hp engine due to prop (lower RPM)? I am not sure.
Usually Lyc advertises "X" HP like 160 HP, and the planes that use that engine also claim 160 HP, say like for a C-172 with a O320, 160HP engine. The Dirty little secret is the C-172 with a "160HP" engine is making may be 135-140HP max, in the airframe with the prop and restrictive exhaust.
This is why the after market power flow exhaust for factory planes like the C172 claim such great HP increase, the original pipes where terrible. The total HP never goes over what Lyc advertised. The Power Flow pipes just gets you back to rated power. Power flow on a RV with good cross over or 4into1 pipes would not see the gain a C172 does, if any.
So why the disconnect between Lyc numbers and the airframe HP numbers for the O235? (I could have bad data but that is what I found.) Does any one know?
There are 125 hp high compression versions (@2800 rpm) of O235 that Lyc came out with but withdrew from the market. It worked great on the test stand but in the hands of pilots, in the field, it had detonation problems.
Strangely there are STCs for high compression pistons (125HP) you can get today for low compression model O235's, which are based on Lycs original design (actual parts). I would recommend NOT using those HC pistons (9.70 to 1). Some do run 125 hp with successes, but an engine monitor and careful operations would be needed.
There are two companies who offer the 125 hp STC upgrades to the low compression O235's, which are typically found in C152, Tomahawk and Grumman Yankee. With an experimental you don't need the STC of course and can just buy the HC pistons and re-jet the carb. I forgot what else was involved in the conversion. I think the STC also had cooling improvements (new baffles & oil cooler). As I say, new pistons will bring the HP up, but I would not go over 8.50 to 1 my self. Forget low octane gas over 8.50:1. You are asking for problems over 8.50 or 8.70 to one. They will fly fine but the detonation margins are less.
Your plane will fly fine with 108 hp. If your prop is pitched for 2800 RPM you will make more than 108 hp in my opinion, like about 115 hp. For each 100 RPM's, it's worth about 5-7 HP. On the other hand if the prop is NOT pitched properly you may not even get 108 hp out of it. One advantage of the metal Sensenich is you can re-pitch it. Of course wheel pants and other drag reductions will be like adding HP. If you lower drag than you also need a new prop. The perfect prop is in a small band and to be ideal must match YOUR airframe. Change the airframe requires a change to the prop to match, to get max performance.
If Van's engine was really making 118 hp, with 108 hp, you would fly about**:
** These are Swags. I am not sure what prop van used or what RPM Van did t/o dist, ceiling, climb, cruise, and top speed at.
Unless the engine is at rated RPM than its not making rated HP (as well as sea level atmo). So the prop (fixed) is key to getting HP. If you have a "108HP" O235 you can get 118 hp out of it with higher RPM. However do you want to cruise at 2800 RPM?
An over pitch cruise prop cause you to suffer loss of t/o and climb performance. A climb prop will give better performance at loss of economy and or speed in cruise. There is a balance with fixed pitch props is between turning enough RPM on TO/Climb (slow speed) and not too much in cruise (high speed).
Yep at 2800 rpm some models of O235 are 118HP.Russell said:
From the data there are no 108HP O235's. There are:
115 (6.75:1) **
116 (8.10:1)
118 (8.50:1)
125 (9.70:1)
** (I am a little suspicious that the 6.75:1 compression is 115 hp. 1 hp less than the 8.10:1 version, BUT that is what Lycoming publishes.)
The 108 HP comes from a lower RPM rating? It could be probably a 115 or 116 hp engine at 2,700 RPM.
I know 108 hp sounds familiar**:
C152 (110HP)
PA-38 Tomahawk (112hp)
AA-1 Grumman Yankee/Trainer 108 HP)
Could it be a "de-rated" 115hp or 116 hp engine due to prop (lower RPM)? I am not sure.
Usually Lyc advertises "X" HP like 160 HP, and the planes that use that engine also claim 160 HP, say like for a C-172 with a O320, 160HP engine. The Dirty little secret is the C-172 with a "160HP" engine is making may be 135-140HP max, in the airframe with the prop and restrictive exhaust.
This is why the after market power flow exhaust for factory planes like the C172 claim such great HP increase, the original pipes where terrible. The total HP never goes over what Lyc advertised. The Power Flow pipes just gets you back to rated power. Power flow on a RV with good cross over or 4into1 pipes would not see the gain a C172 does, if any.
So why the disconnect between Lyc numbers and the airframe HP numbers for the O235? (I could have bad data but that is what I found.) Does any one know?
There are 125 hp high compression versions (@2800 rpm) of O235 that Lyc came out with but withdrew from the market. It worked great on the test stand but in the hands of pilots, in the field, it had detonation problems.
Strangely there are STCs for high compression pistons (125HP) you can get today for low compression model O235's, which are based on Lycs original design (actual parts). I would recommend NOT using those HC pistons (9.70 to 1). Some do run 125 hp with successes, but an engine monitor and careful operations would be needed.
There are two companies who offer the 125 hp STC upgrades to the low compression O235's, which are typically found in C152, Tomahawk and Grumman Yankee. With an experimental you don't need the STC of course and can just buy the HC pistons and re-jet the carb. I forgot what else was involved in the conversion. I think the STC also had cooling improvements (new baffles & oil cooler). As I say, new pistons will bring the HP up, but I would not go over 8.50 to 1 my self. Forget low octane gas over 8.50:1. You are asking for problems over 8.50 or 8.70 to one. They will fly fine but the detonation margins are less.
Your plane will fly fine with 108 hp. If your prop is pitched for 2800 RPM you will make more than 108 hp in my opinion, like about 115 hp. For each 100 RPM's, it's worth about 5-7 HP. On the other hand if the prop is NOT pitched properly you may not even get 108 hp out of it. One advantage of the metal Sensenich is you can re-pitch it. Of course wheel pants and other drag reductions will be like adding HP. If you lower drag than you also need a new prop. The perfect prop is in a small band and to be ideal must match YOUR airframe. Change the airframe requires a change to the prop to match, to get max performance.
If Van's engine was really making 118 hp, with 108 hp, you would fly about**:
100 fpm less climb
20 feet more t/o run
200/300ft lower service celling
5 mph slower top/cruise speed
20 feet more t/o run
200/300ft lower service celling
5 mph slower top/cruise speed
** These are Swags. I am not sure what prop van used or what RPM Van did t/o dist, ceiling, climb, cruise, and top speed at.
Unless the engine is at rated RPM than its not making rated HP (as well as sea level atmo). So the prop (fixed) is key to getting HP. If you have a "108HP" O235 you can get 118 hp out of it with higher RPM. However do you want to cruise at 2800 RPM?
An over pitch cruise prop cause you to suffer loss of t/o and climb performance. A climb prop will give better performance at loss of economy and or speed in cruise. There is a balance with fixed pitch props is between turning enough RPM on TO/Climb (slow speed) and not too much in cruise (high speed).
Last edited:
sparrowhawk
My wife has a 1982 152 with an 0 235 in which we originally put in low compression pistons ( 6.5) which allowed us to use mo gas. But at the mile high airport in Prescott where the plane is now based the plane was a bit under powered, so we got the Sparrowhawk stc and installed 9.75 pistons and the required new baffeling to bring it up to 125 hp at 2800 rpm. We already had the sensenich prop that was part of the stc and no additional oil cooler was required. The plane now has a static rpm of nearly 2400 compared to just over 2200 and has solved our issues. I am not concerned about detonation at our levels and we are able to get about 2750 in flat out if we need to. It was reasonably inexpensive extra hp, especially since we did the work ourselves.
My wife has a 1982 152 with an 0 235 in which we originally put in low compression pistons ( 6.5) which allowed us to use mo gas. But at the mile high airport in Prescott where the plane is now based the plane was a bit under powered, so we got the Sparrowhawk stc and installed 9.75 pistons and the required new baffeling to bring it up to 125 hp at 2800 rpm. We already had the sensenich prop that was part of the stc and no additional oil cooler was required. The plane now has a static rpm of nearly 2400 compared to just over 2200 and has solved our issues. I am not concerned about detonation at our levels and we are able to get about 2750 in flat out if we need to. It was reasonably inexpensive extra hp, especially since we did the work ourselves.
quickieflying
I'm New Here
More HP on the RV9 and structural changes needed
I have the same requirements as Karl and the need for more climb (High DA) is needed. I to don't understand why the RV9 can't be modified with thicker skins (if that's what's needed) along with better balancing to accommodate the additional speed if needed. It would be nice to get some help and understanding from other builders on this so we can make the appropriate changes.
David
I have the same requirements as Karl and the need for more climb (High DA) is needed. I to don't understand why the RV9 can't be modified with thicker skins (if that's what's needed) along with better balancing to accommodate the additional speed if needed. It would be nice to get some help and understanding from other builders on this so we can make the appropriate changes.
David
RVbySDI said:
It's a great airplane! Leave it alone!
If you don't like the flight envelope of the -9, then build a different airplane. There are MANY things that limit an airplane's flight envelope. Span loading, tail span loading, wing loading, etc. The RV-9 will out climb almost any spam can built. Why do you people keep trying to redesign a great airplane. Don't you think that if there was a simple way to improve performance, Van would have done it?
I have flown my -6 in and out of Leadville, CO. (highest public airport in North America) in the summertime with a density altitude of 13,500', with a tired 150 hp engine (over 2500 hrs) and a wood prop. No problem. A -9 should out climb the -6 noticeably at that altitude.
If you don't like the flight envelope of the -9, then build a different airplane. There are MANY things that limit an airplane's flight envelope. Span loading, tail span loading, wing loading, etc. The RV-9 will out climb almost any spam can built. Why do you people keep trying to redesign a great airplane. Don't you think that if there was a simple way to improve performance, Van would have done it?
I have flown my -6 in and out of Leadville, CO. (highest public airport in North America) in the summertime with a density altitude of 13,500', with a tired 150 hp engine (over 2500 hrs) and a wood prop. No problem. A -9 should out climb the -6 noticeably at that altitude.
Last edited:
Bryan Wood
Well Known Member
Here's a picture that might enlighten you on the 9A a bit with an 0-320 under the hood. The reason that I'm posting it is to show the way we pack when we travel and to tell how the plane handles the load. On this particular trip we went over 5,600 miles and crossed the country from the west coast to the east coast at 13,500'. At higher altitudes the plane is right in its element and the fuel burns are down around 6gph. Along with the baggage you see I have a 22 liter oxygen bottle mounted in the baggage compartment. These bags represented enough clothes for two weeks, with the red bags being my wifes and the blue ones being mine. There was also a purse, flight bag, a camera case, a video camera case along with jackets and hats, sunscreen, water bottles, items purchased along the way, etc... The plane climbed effortlessly and flew similar to being at 7,500'! We took off from St. John's Arizona with a density altitude of 9,000' and were airborne in less distance than my Cherokee used at sea level. Again the climbs are strong. I highly recommend you find a ride in a plane equipped the way Van intended and then see if a bigger engine is still for you. I'm back and forth on this still and my plane has been flying 3 years now. The reality is that the plane is very strong with the smaller engine.
Last edited:
David Burke
Member
Here is my take on the subject. The RV-9 was designed for good slow speed handling and to be quite benign. In terms of structure is bigger than a RV-7.
The tailplane is quite a bit larger and of diffrent construction - add to that the extra bay's on the wing. Now put a RV-7 and 9 together in a race and the 7 will beat it - simple as that. Now start adding bigger engines and you add more stress to the airframe and start shaking the tail to bits - fro the engine rearwards you are counter acting the rotational force of the engine.
Going on from this Lycoming engines are very capable of high revs - the noise might be a factor but in reality in an RV you don't have a massive noise footprint. The engine I am using is a Mattituck 0-320 150hp . It was more than capable of dragging a bulky 172 around the sky and now will happily pull a RV-9 at probably half the weight and size.
What people should realise is that Vans designed the RV-9 for good slow speed handling and economy - buy a RV-7 if you cannot handle flying 'RV-9 slow'
The tailplane is quite a bit larger and of diffrent construction - add to that the extra bay's on the wing. Now put a RV-7 and 9 together in a race and the 7 will beat it - simple as that. Now start adding bigger engines and you add more stress to the airframe and start shaking the tail to bits - fro the engine rearwards you are counter acting the rotational force of the engine.
Going on from this Lycoming engines are very capable of high revs - the noise might be a factor but in reality in an RV you don't have a massive noise footprint. The engine I am using is a Mattituck 0-320 150hp . It was more than capable of dragging a bulky 172 around the sky and now will happily pull a RV-9 at probably half the weight and size.
What people should realise is that Vans designed the RV-9 for good slow speed handling and economy - buy a RV-7 if you cannot handle flying 'RV-9 slow'
Mr Burke,
You are partially correct but the 9's were designed to maximize efficiency with smaller engines. If you compare a 7 and 9 with equal power, the outcome will be very close (within 2-3 mph), possibly favoring the 9 at higher altitude.
The 9's advantages are as you mentioned, better slow speed control and improved stability at cruise speeds (an advantage negated by an autopilot in the 7). The 7 is a better choice for top speeds (bigger engine) or aerobatics.
Many consider the 9 to be an improved 7, possibly illustrated by Vans employees preference for the 9 for cross country trips. My biggest gripe involves the smaller fuel tanks in the 9. Both are great designs imho. My biggest problem was not 7 vs 9, but front vs rear wheel and tipup vs slider.
You are partially correct but the 9's were designed to maximize efficiency with smaller engines. If you compare a 7 and 9 with equal power, the outcome will be very close (within 2-3 mph), possibly favoring the 9 at higher altitude.
The 9's advantages are as you mentioned, better slow speed control and improved stability at cruise speeds (an advantage negated by an autopilot in the 7). The 7 is a better choice for top speeds (bigger engine) or aerobatics.
Many consider the 9 to be an improved 7, possibly illustrated by Vans employees preference for the 9 for cross country trips. My biggest gripe involves the smaller fuel tanks in the 9. Both are great designs imho. My biggest problem was not 7 vs 9, but front vs rear wheel and tipup vs slider.
