ACRO E-mail Archive Thread: [Acro] Pitts S-1S questions - Here are the REP ...
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Thread: [Acro] Pitts S-1S questions - Here are the REP ...
Message: [Acro] Pitts S-1S questions - Here are the REPLIES!
Follow-Up To: ACRO Email list (for List Members only)
From: Klusmanp at aol.com
Date: Wed, 17 Oct 2001 02:22:13 UTC
As I have received no less than six requests from other members of the Acro list to fwd replies to my Pitts S-1S questions, I have condensed the many replies I have received and now offer them to all on the mailing list. My apologies to anyone who replied to me in private and did not intend for their comments to be made public on the list. In the spirit of privacy I will not include names with the comments. My thanks again for the almost overwhelming response to my questions! I receive mailings from another aircraft list and an automotive list. This acro list is by far the most friendly and responsive list of the three. Below are my original questions and responses from one or more people. 1) A sport aviation article mentions that "Sparcraft" wings don't fly quite as well as true "Pitts" wings. How significant is this? Is there an appreciable weight or strength difference? <<As far as Sparcraft wings I have not heard mention them flying differently but there is a factor of strength. Sparcraft wings have a routed plywood rib as opposed to truss style built ribs in the pitts wings. There have been some problems with the Sparcraft ribs breaking. A good source of information for this would be the IAC technical tips manuals available through EAA. How hard the aircraft has been flown and how hard you plan on flying will play a factor in this also.>> <<<<All I do is aerobatic aircraft maintenance... <snip> ...sparcraft wings are o.k. , the spars are built the same as the factory , but the ribs are 1/4 " routed out plywood instead of build up ribs , roll rate is a little slower on a sparcraft wing due to the freese ailerons and the large gaps in the aileron wells>> <<Although many folks fly the Spartcraft wings they haven't always been as stout as the Pitts style wings. Although all of them have pull block problems from time to time. >> <<Same airfoil as the Pitts S-1 but heavier because the ribs are solid. Weight is bad but if this is your first Pitts, not the end of the world.>> <<Unless you buy a factor Pitts, you have a slim chance you will be getting Pitts wings. Most are sparcraft. They are good wings, but however, are slightly heavier (so I am told. At out levels, it will not be noticable. Later on you can build you own set.>> <<Sparcraft wings are OK, not as light, but not many floks will know the difference.>> 2) Many planes have a flat pitched prop for good climb. These props have the potential to over-rev the engine at full throttle. What is a good conservative TBO for an engine that has seen a lot of 3,000+ rpm operation? <<With a fixed pitch prop you will over rev the engine. I have a 74-56 so it runs about 3500 RPM max in the box. You may get varying responses on this but the bottom line is that the RPM isnt as bad for the motor as high EGT or CHT temps. You can burn a cylinder very quick at 2000 RPM if the CHT is too high. My motor has over 700 hrs of Advanced acro and the compressions are all over 78 and the oil analysis is better than my Aeronca. If you fly often enough the high RPMs shouldnt affect it too much but obviously bearings and some other rotating parts will wear out sooner than the 2000 hr TBO. I would think my motor will go 1000-1100 hrs but Sportsman type acro would yield 1400-1500 hrs. Its a different story if the airplane sits for a long time between flights as the corrosion that builds up acts like sandpaper. If you fly once a week or more often that would be ideal>> <<<<All I do is aerobatic aircraft maintenance... <snip> ...as for the prop a 60" pitch works the best with a 180hp and your rpm's will still be 2900 straight and level. all aerobatic engines should make it 1200hr.s even with high compression pistions.>> <<800 hours is a common time to do a major overhaul on an over -revved engine.>> <<You cant have it all. If you want climb performance, you have to have a climb prop and the engine will be operated above red line at times. My Pitts, at full power in level flight will indicate 3300 rpm. >> <<Many people wind the Lycomings up to 3500 RPM without any apparent damage to the engines or significant loss between overhauls. That 800 or so RPM represents almost a 30% boost in horsepower which is nice to carry into a vertical. High pitch, hi revving props are noisy and slow crosscounty but they do help while doing figures.>> <> <<3000 rpm will not hurt a TBO is the engine is/has been taken care of properly.>> 3) Do high-compression pistons reduce TBO? <<The high compression pistons will do a lot more to reduce TBO than high RPM. The increase in CHT and Oil Temps will reduce TBO due to cylinder wear. I dont run them in my airplane but I wouldnt hesitate to throw them in. Just understand the TBO may go down a couple of hundred hours as a result>> << Reaching TBO, you will probably get allot of different replies on this one. I have seen both sides of the story here. I know San Burges had a engine with countless overspeeds that went to TBO, but have also heard not to expect an acro engine to get past halfway to TBO. The two large variables here how hard the aircraft has been flown and how well it has been maintained. I would suggest contacting some of the better known acro engine builders,Lycon, Barret, Demars and get there opinion. They should also be able to give you some insight into the question of high compression pistons.>> <<High compression pistons make if extremely difficult to hand prop a hot engine!>> << (Do high-compression pistons reduce TBO?) Not that I know of. Some certified engines (Lyc 0-320-D2A) are high compression engines and the TBO is 2000 hours. Heavy aerobatics will reduce TBO.>> <<(Do high-compression pistons reduce TBO?) Quite simply, yes.>> <<The higher compression the engine is, usually the lower the TBO is.>> 4) Any items of airframe stress and wear I should look for? <<The weakest part of my airplane is the fabric. Due to the propwash and g forces the tapes on the inside portions of the wings tend to come loose. Many people never glued down their tapes and just doped them on. This is bad. After mine came loose I reglued them and switched to 3" from 2" wide and no more problems. There is nothing worse than having to do fabric repair on a shiny new Pitts If you plan to only fly Sportsman or rec acro I wouldnt worry too much about anything else. Once you start flying Advanced engine mounts, tapes, and drag wires will start to go. They are generally very strong airplanes>> << Be sure to check wing attach brackets for cracks and any signs of the bolt hole being enlarged by movement. If the aircraft has spring type gear inspect the longerons around the gear attach VERY WELL. As I am sure you are discovering most S1S's being home builts there are endless variables to deal with. I would suggest getting some with pitts knowledge to inspect the aircraft.>> <<There are some stress points on the S-1S you should be aware of. The lower wing, rear attach fitting and the upper longeron just forward of the instrument panel are 2 areas. Check the AD's or factory support. >> <<Some of the things that are likely to bite you and cost money are: Fabric and paint. If the fabric and paint are not in good shape walk away because it costs more to recover and paint than it does to put a new motor on AND it takes 6 months. Motor. Obviously you want to check the heck out of it, I'd want to get an oil sample, have a look at the oil screen, compression test etc. etc. nothing out of the ordinary for a good mechanic. Tubes etc. make sure there is close to zero rust. Once it starts to rust its hard to control it. Note that rust on some of the fittings is no big deal, just change them but if the tubes in the back start to go its gonna be expensive. There are rear spar attach AD's that require inspection every 50 hours but I've never heard of an S1 with a cracked rear spar attachment. It happened on an S-2B and the entire line got the AD. The fuel tank in the S-1's is subject to cracking. Check the front and rear of the tank to make sure there are no cracks. If it is cracked and has been putty repaired it will cost many thousands of dollars to repair properly. (I found this in my pre-purchase). The S-1s were modified early on to stiffen up the tail feathers. In particular they added under stab diagonal cross braces. Make sure your plane has these as it's a rather important mod. The S-1's were also prone to tail wheel breakage. The tab at the bottom of the rudder post would come unwelded and let the tail wheel leaf springs go left or right for a run ride. The SB calls for a small triangular tang to be welded behind the tab. Mine broke on my 5th landing. No problem but a pain to get fixed and on a narrow runway it could have been costly. Check the dates on all the rubber parts in the plane. All the hoses etc. and especially the flop tube in the gas tank. If its more than say 8 years old that rubber is getting hard and probably needs changing. A complete hose change in a Pitts is many thousands of dollars because of the inverted oil system which adds a bunch more hoses to the system.>> <<First, check out the service bulletins. One major one you will hear alot about is the rear attach point. Also, go to www.musclebiplane.org and then to the maintainence area. Excellent photographs and suggestions for stuff to look at. If you are going to get into tailslides later on, you will be advised to get the rear tail struts. Ckeck the motor mounts. Also, find out if has EVER been ground looped or even just "dragged a wing (common)". Even though it may be just cosmetic dammage, there is a signifigat moment out there and it puts alot of stress on the wind atach points AND the upper cabine attach points. Check carefully.Also, check the cut out area around the bungees. Sometimes they will start to wear the protction around the bungees and will lead to an earily replacement.>> <<Check the longerons, especially by the landing gear. If you are able to, check the H-tube (by the horizontal stab).>> 5) I've encountered many different engine types: Ellison pressure carb, fuel injected, and some carburated engines converted by adding a Bendix fuel injection system. Is there a big operational difference between pressure carb. and fuel injected? <<Stay away from the Ellisson TBI lke the plague. I have it on my airplane and its the worst. Already been overhauled twice in 500 hrs at a total cost of $1500. Do whatever you can to find a fuel injected airplane but if not the pressure carb is good>> <<All I do is aerobatic aircraft maintenance... <snip> ...Ellision throttle bodies suck , allways a probelm , as the same for pressure carbs . Fuel injection is the only way to go>> <<Bendix or AirPower fuel injection systems are now the most popular. Pressure carbs are expensive, difficult to keep repaired and designed for much larger engines so they give problems. Some folks have had no problems with the throttle body Ellisons. Others have had trouble. It may do with cleanliness. I don't know. The only throttle body that has ever had any success in aerobatic circles is the Ellison. Overall it is hard to beat the Bendix or its successor fuel injection.>> <<The Bendix pressure carb is excellent if it is well cared for. If you find a Pitts with one, make sure it has been recently overhauled and the NEW gaskets installed. If you have the replace the OLD gaskets the bill is $1400 dollars. The overhaul of a PS-5C with the NEW gaskets already installed in about $150. Experience talking>> <> <<On the carb vs FI, the only pressure carb is the PS5C. It performs OK, but is quite expensive to have OH'd. I have one on a O320 pitts. Not many know how to work on that carb so its important to find a shop that can work on them. Bendix FI is probably best, but it is not cheap to OH either. The Ellison TBI is the lowest cost to buy and to OH, but it can be very frustrating to get it working properly as it is VERY sensitive to the air box and airflow into the TBI.>> <<A fuel injected engine is better overall, whether it is from the factory or from Airflow Performance.>> 6) Do I need to look for a specific aerobatic crankshaft on the engine? <<As far as the crank that depends on what kind of acro you will be doing. With a metal prop regardless of wether you have an acro crank or regular you will break a crank when you do a lot of snaps. I run a composite prop on my std crank and no problems and I do 20-30 snaps a flight. My buddy cracked a crank on his S-2B after 300 hrs with a metal prop>> <<Be certain you have the aerobatic crankshaft or else don't ever do snap rolls, tail-slides, flat spins and gyroscopics. You might "toss your prop".>> <<If possible, make sure it has the solid flange crankshaft.If not you will be doing frequent inspections and will always have the worries accompaning it. If you can get an wooden OR composit prop, it will be less wear on the flange.>> <<On the crank, best is to have the aerobatic crank. These don't have holes in the flange. If you have a CS with holes in the flange, then you must inspect it each 25 hours per AD and/or Lyc SB if you are flying any acro.>> 7) What inspection interval does the prop need? <<A fixed pitch prop is good for only 800 hours or so according to Sensenich. Don't get one that has been re-pitched or damaged -ever.>> 8) How much is a composite prop and where do I get one? <<A commposite prop is nominally an advantage if you plan to do a lot of gyroscopic maneuvers such as tumbles, agressive snaps etc. It reduces the precession forces on the crankshaft. Otherwise it may not be worth the considerable extra price over a fixed pitch. One advantage of a fixed pitch is that you can wind up the engine considerably over the 2700 rpm that is imposed by a controlled pitch prop.>> <<Composite - Performance Propeller Wood - Sensenich>> 9) Other comments: <<What made you decide on an S rather than a T? While the S is a good aircraft the T will outperform the S. Now that I've said that you will understand my bias when I tell you I have a S1t that I'm selling. Its a factory built aircraft with the AEIO 360. About 600hrs on the engine and 930 TTAF. Was built in 1986 and and recovered about 94. With out the log books in front of me not real sure of exact numbers.>> <<You do want to get a good pre buy from someone that knows Pitts though as many builder problems will cause headaches later on>> <<Hi Paul and welcome to the world of aerobatics. As a former owner of a Pitts S1S I can recommend a very reliable source for all of your questions. Call Mike Mays at So. Aerobatics in West Palm Beach. He has been working on aerobatic airplanes (especially Pitts) for many many years. Mike likes to talk and he can answer all of your question. He seems to be tapped into a network of the Pitts market as well and can help you locate just the right airplane for your needs. Yes, he will make a buck on the transaction, but in the end, you will thank him for taking your money and steering you onto the right (safe) airplane. By the way, every one of us thought when we started that we only wanted to do recreational aerobatics. I am sure that some people do stick to that level of the game, but most who I have known have gotten totally involved. It is a real head rush to compete.>> <<Don't look at anything. Find the best Pitts machanic in the area and pay him to find you a good Pitts. Then plan on spending $3000 to $5000 more to do what needs to be done. You haven't got a clue on what to look for and you might get hurt if you try. I have owned a few aerobatic airplanes and worked on many more. I have seen things flying that you would say could not fly. Most Pitts ' with sparcraft wings are not S1Ss. Thye are S1Cs made to look like S1Ss but there is much more to it then that. Just don't buy one. That is why they are so cheap. $30,000 to $35,000 is a good price for an S1S. You won't get 1000 hours out of any aerobatic airplane. Find a good machanic.>> <<Paul, I do not claim to be an expert but hopefully I can give you some information that will be helpful. First of all how much tail wheel time do you have. I you do not have allot I would strongly suggest getting tail wheel proficient in a another type of aircraft, cub,champ,citabria ect. Then practice flying a citabria or decathlon from the back set. When comfortable with this the transitioning to a pitts is not a big deal. Another good source for information is the Muscle Biplane web site, I think the address is <musclebiplane.org>. >> <> <<All I do is aerobatic aircraft maintenance , and the best advise I can give you is get a good prepurchase from someone who knows the wear points on an aerobatic plane . Whatever area you are looking at one , there should be someone around who can check it out for you. <snip> MAKE sure you are buying a S-1-S and not an S-1-C , the S has a longer fuselage and more inside room. <snip> get one with 180hp or better.>> <<Get some complete spin training before you start fooling around in your Pitts. there are many places you can get this training. Since I don't know where you live I will give you a few names of reliable sources. I may overlook a few. That doesn't mean I don't approve, just forgot or am ignorant. Bill Finagin (Annapolis MD) H-R Aviation (LaPorte, TX) John Walkup (Chandler, AZ) Michael Church (Sunrise Aviation at Orange Co. Airport) Don Hart (Hart-Aire at Long Beach, CA) Ken Erickson (Sean Tucker's School at Salinas, CA.) Dick Rihn (Attitude Aviation at Livermore, CA.) The Pitts is a pussycat when you know how to fly it. It is a tiger until then. Get trained by experts. It will be money well spent.>> <<Find an A&P with Pitts experience and have him/her go over the plane IN GREAT DETAIL. Dont get overly concerned about HP. At your stage there is little to be gained by having an 0-360 instead of an 0-320>> <<My mechanic has been Ray Williams near Nashville TN. He is w/o a doubt the best Pitts mechanic anywhere. Ask some of the aerobatic people and they will know of his rep.>> <<Paul, I sent a similar email out to this group a couple of years ago and the advice I got was invaluable. I purchased a Pitts S-1T about 2 years ago in Florida and my use of a very good knowledgeable Pitts mechanic saved me 10's of thousands of dollars.>> <> <>